Trade In Fantasy Ch. 4: Modes Of Transport, Pt 2
Rivers provide a natural alternative to roads and overland travel, if the river happens to go where you want it to. That’s more likely than it might initially seem, because rivers provide natural resources and defenses that make them natural locations for settlements, with transportation of cargo a bonus on top of those advantages.

While it fits the general subject matter of travel, this doesn’t really fit the subject of today’s post – but it was too good to leave out, and the relevant images that I did find were not as evocative. So here it resides. Image by Sean Wareing from Pixabay
Table Of Contents: In part one of this chapter:
Chapter 4: Modes Of Transport
4.0 A Word about Routes
4.0.1 Baseline Model
4.0.2 Relative Sizes
4.0.3 Competitors
4.0.4 Terrain I
4.0.5 Terrain II
4.0.6 Multi-paths and Choke Points
4.0.6.1 Sidebar: Projection Of Military Force
4.0.7 Mode Of Transport
4.1 Backpack / Litters / Shanks Pony
4.1.1 Capacity
4.1.2 Personalities / Roleplay4.2 Horseback
4.2.1 Capacity
4.2.2 Requirements
4.2.3 Personalities / Roleplay4.3 Mule Train
4.3.1 Capacity
4.3.2 Requirements
4.3.3 Personalities / Roleplay4.4 Wagons
4.4.1 Capacity
4.4.2 Requirements
4.4.3 Other Exceptions – Animal Size
4.4.3.1 Sidebar: Road Trains
4.4.4 Fodder / Food & Water Needs
4.4.4.1 People
4.4.4.2 Horses
4.4.4.3 Mules
4.4.4.4 Oxen / Cattle
4.4.4.5 Elephants
4.4.4.6 Other4.4.5 Personalities / Roleplay
In today’s post:
4.5 River Boats & Barges
4.5.0 A Splice Of Maritime History
4.5.0.1 Dugouts & Canoes
4.5.0.2 Rafts
4.5.0.3 Boats
4.5.0.4 Poled Rafts & Barges
4.5.0.5 Oars
4.5.0.6 Land-based motive power
4.5.0.7 Sail
4.5.0.8 Better Sails
4.5.0.9 Trading Ships
4.5.0.10 Warships & Pirates
4.5.0.11 Beyond the age of sail
4.5.0.12 Riverboats
4.5.0.13 Sources4.5.1 Riverboat Capacity
4.5.2 Favorable Winds
4.5.2.1 The Beafort Wind Scale
4.5.3 Favorable Currents
4.5.4 Unfavorable Winds / Currents – Oarsmen Requirements
4.5.5 Unfavorable Winds / Currents – Sail Solutions
4.5.6 Extreme Weather Events
4.5.7 The Tempest Scale
4.5.8 Vessel Rating
4.5.9 Weather CataclysmsAnd, in future installments:
4.6 Seagoing Vessels
4.6.1 Capacity
4.6.2 Favorable Winds
4.6.3 Favorable Currents
4.6.4 Unfavorable Winds / Currents – Oarsmen Requirements
4.6.5 Unfavorable Winds / Currents – Sail Solutions
4.6.6 Extreme Weather Events
4.6.7 Vessel Rating
4.6.8 Weather Cataclysms4.7 Exotic Modes Of Transport
4.7.1 Flight
4.7.2 Teleport
4.7.3 Magic Gates & Portals
4.7.4 Capacities.8 Loading & Unloading
In future chapters:
- Land Transport
- Waterborne Transport
- Spoilage
- Key Personnel
- The Journey
- Arrival
- Journey’s End
- Adventures En Route
4.5 River Boats & Barges
If I were to use the term “River boat”, depending on where you are from, one of two images probably come to mind; Either a paddle-wheel steamer, like this one:

Image by Christiane from Pixabay
…or, perhaps, one of the canal-going houseboats of Europe, which could house whole families but are these days more synonymous with a mobile retirement lifestyle:

Image by Siggy Nowak from Pixabay
…which are often open-sided these days and used for tourism. But there are other classes of river-going vessel and some are explicitly devoted to trade and cargo-carrying, and those are easily overlooked. Perhaps a little historical context to start…
4.5.0 A Splice Of Maritime History
Boats pre-date writing and were actually built by Homo Erectus about 800,000 years ago, or so it is believed. Their simple vessels then enabled them to spread out to other parts of the world.
The earliest known depiction of a maritime vessel of any kind is on a rock carving in Azerbaijan dating to 10,000 BC and showed a boat carrying about 20 men.
The Pesse Canoe is the oldest known and confirmed vessel. Discovered in the Netherlands, it dates back to 8200-7600 BC. It’s three feet long and made from the hollowed out trunk of a single Pinus Sylverstris tree.

Image from Drents Museum, CC BY 3.0, via Wikimedia Commons
In time, people learned how to construct a wooden frame and stretch animal hides (or later, canvas) over it, which were coated in sap or fat to seal any gaps. Better materials for that job soon followed.
The first method of using multiple pieces of timber in the one vessel was almost certainly a raft;

A simple raft – in this case, with an unexpected passenger. Image by Ronald Plett from Pixabay
A 7,000 year-old raft made of reeds has been found in Kuwait and is the earliest known example. However, the workmanship displayed is such that this was clearly not the first – it’s just the one that happened to have survived. Some have even suggested that the raft predates the dugout canoe, but what archaeological evidence there is argues otherwise.
There were any number of solutions to the problem of keeping the water out of vessels made of cut timbers, none of them completely adequate on their own, but eventually they were combined to create what we would recognize as a true boat.
Of course, metal tools were needed to create the planks in the first place, so we’re talking after 3000 BC here. This also made possible the construction of masts, and therefore, of sails. So I’ll have to backtrack a little to talk about motivating power.

This example is relatively simple and shows the construction more clearly than most. Image by PublicDomainPictures from Pixabay

A more sophisticated boat that is – to my eye – slightly reminiscent of the Dragon Longboats of the vikings. Image by Uwe Jelting from Pixabay
Early boats had a limit of about 400 tons, fully laden. Trips that took just days when winds were favorable become sagas of weeks and months when they weren’t. This had two effects that have persisted for centuries: First, sailors became very superstitious, adopting a ‘take no chances’ approach to the subject; and second, they became acutely interested in meteorology, because winds are an aspect of weather, and there are patterns both daily, periodic, seasonal, and annual – and they spelt the difference between a successful voyage and one where the crew arrived destitute and starving.
Adding fuel to the first was the spread of disease – even back then, people knew that not being around other people who were sick made it less likely that you would get sick – but on a boat for weeks on end, there was no place to hide. On top of which, there were some maladies to which boatmen seemed especially vulnerable like Rickets and Scurvy. It was not until the causes of these diseases were understood that they ceased being a source of ongoing fear aboard. And if the only defense you have is rooted in superstition, then you had better be superstitious!
Rafts with some sidewalls created a barge, but they needed some form of locomotion to get them where they were going. In place of paddles (which probably came along not long after the original canoes), a long stick was used to push the floating assemble of vessel and cargo along – a technique still in use today in some parts of the world.

Image by DEGAN Gabin, CC BY-SA 4.0, via Wikimedia Commons
Barges rarely have their own source of motive power. They are pulled by another vessel, or (if used as a ferry) by ropes or chains attached to the shore, or by land-based motive power (see below). It is only in the industrial age when power sources improved massively that this has ceased to be the universal case – and even now, the old definition still holds true in most locations.
What has changed is that the barges used to be towed by tug boats and are now more frequently pushed by “pusher boats” (not a terribly imaginative name).
However, some river barges did have sails, especially when ship’s sails were not as well developed. Most river merchant barges in England in the 18th century had a mast, for example. They could carry 20-40 tons of cargo – an important reference value for us, going forward.
Oars meant that the work of moving the vessel could be spread amongst many, enabling greater speed and more reliable performance. This led, in time, from the humble rowboat to the Syracusia, the floating palace of Hieron, King of Syracuse, designed by Archimedes and alleged to have been the largest transport ship in history in ancient times. These days we have only estimates as to its dimensions, but it had a garden, a palace, and a temple, all on the main deck. It housed 200 soldiers as well as the court and the slaves to make it go, and everything those imply. The Syracusia could carry a cargo of some 1600 to 1800 tons and a capacity of 1,942 passengers, according to one Historian. She was reportedly too big for any port in Sicily, and thus only sailed once from Syracuse in Sicily to Alexandria in the Ptolemaic Kingdom of Egypt, whereupon she was given as a present to Ptolemy III Euergetes.

This image is an exaggerated depiction of the vessel, a hand-colored copperplate engraving from Robert von Spalart’s “Historical Picture of the Costumes of the Principal People of Antiquity and of the Middle Ages,” Metz, 1810. Copyright on this image has expired, so it is in the public domain. Image courtesy of Wikimedia Commons.
If you look closely, the author has added masts and furled sails to his depiction of the Syracusia, but those were actually not thought to exist on the real vessel.
Where the terrain was amenable, it was possible to have one or more teams of horses pulling a barge along the river. Coordination of multiple teams was always a problem with this approach. The advantage was that the river was carrying the cargo, so it actually took relatively little motive power to get the vessel moving, regardless of the load it happened to carry.
Some places and cultures even went so far as to make roads along the river bank (carefully removing any trees between the two) in order to facilitate this mode of transport.
Sails, when they appeared, were something of a game-changer. Early sails could only go with the wind, at best quartering it; if the wind wasn’t blowing in anything approximating the right direction, the sails had to be furled and the oars broken out.
There is ample evidence to show that the Ancient Egyptians had sailing boats used for river travel – there are relief carvings showing the transport of obelisks for Temple Entrances along the Nile. These had (and needed) oars as well as a single square sail, and were about 100m long (328 feet).
After about 500 years of using them for River travel, Egyptian boats were good enough to venture out into the Mediterranean and Red Seas.
No maritime history is complete without at least mentioning the Phoenicians. From 1550 to about 300 BC, Phoenicians from the Canaan civilization (yes, the one referenced in the “Settlers Of” board-games) were making boats known as Galleys. The primary motive power was oars; most had multiple sails for gaining added speed, arranged in rows. They were used for trade, warfare, exploration, and piracy, and remained in use until the 19th century, though they were at their height in 16th-18th centuries.
A Monoreme has one group of rowers; a Bireme, two; and triremes have three banks of oarsmen. Most galleys are Biremes, though the Greeks and Romans had a few triremes.
In 1571, during the Lepanto war, hundreds of rowing ships and about 400 galleys were used, marking it as the largest naval war recorded in history.
Almost 600 years earlier, from 1000 AD, Vikings used Long Boats for raiding, trade, war, and migration. These were rowed by 60-70 men and also carried a large Mainsail for when the winds were favorable. This made them quicker and larger but narrower than the Galleons and other ships of the time. It made them especially suitable for river travel as they did not have a huge draft.
And, about 100 years later, the Chinese started to build boats that we would now recognize as Junks, as warships and cargo vessels. They were much advanced over the European ships that – like these Junks – added rudders and watertight compartments to their designs, even though the Chinese were hundreds of years earlier in adding these innovations. The largest of these Junks measured 150m in length (nearly 500 feet) and had 9 masts.
People can be extremely clever, and eventually a way was found to configure sails so that vessels could sail directly into the wind.
That meant no more need for oars, and smaller crews, and more space for cargo. Thus began the Age Of Sail.

Image by Michelle Raponi from Pixabay
This example seems to be using its extra capacity to carry more people, though – and that was a legitimate purpose. Whole armies could travel under sail – all you needed was enough vessels.
Ships could grow bigger, faster, and stronger, and trading ships took to the open seas. More on that sort of thing in the next post of the series!
The largest vessels of the age of sail (16th-18th centuries) were, perhaps, the Galleons of Spain and Portugal. It’s when you start reading up on them that a term crops up that I have avoided using thus far: displacement. In essence, this is the weight of the vessel and cargo, which equals the amount of water that has to be pushed out of the way for the vessel to float; every vessel has a maximum displacement, and there is usually a lower figure that constitutes a maximum safe displacement.
Load enough cargo onto a vessel and the sides will sink so much that water starts coming in over the sides. At that point, the vessel starts sinking. Adding to that are waves, which are generally fairly gentle on rivers, moderate on lakes (even in the stormiest of seas), but can be truly epic out at sea. And making this problem worse is the fact that most ships that don’t have flat bottoms tend to sail at an inclined angle because of the wind, so the water is a lot closer on one side than the other – and so are the waves. The amount of sail you raise increases both your speed and this angle, relative to the force of the wind – so it’s not a simple thing at all.
Inevitably – and possibly even before trading vessels – boats were used for battle. These days, it’s considered normal for there to be specialized designs for our warships, but in the age of sail, vessels were far more multi-function. Ships routinely carried cannon and men; the major difference between a warship and a trading vessel was how many of these were traded away for cargo capacity.
Once you have armed ships, and other vessels carrying valuable cargoes, the rise of piracy seems all but inevitable. These days, that adds to the romance of the era, but in the day, piracy was a scourge – especially once politics entered the picture.
We’re now entering waters that are less relevant to the subject at hand, so I’ll make this fairly brief. Steam power and then diesel power signaled the end of the age of sail, liberating vessels from dependence on the wind. Steel hulls made vessels stronger, and the combination plus better designs made them faster. Modern cargo ships can be awesome sights to behold and their capacities are stupendous. The current designs sacrifice gains is speed from the technological improvements of the modern age for size and capacity. Of course, this only makes for a bigger problem when something goes wrong – remember the ship stuck in the Suez Canal, or the problems caused by the Exxon Valdez?
With the historical context sorted, it becomes clear that there are three primary factors that determine how much a vessel can carry, and how fast it can travel when at its maximum safe loading:
1. Motive power & sophistication
2. Hull material and construction technique
3. Size and shape
Each advance in one of these areas increases the capacity, and/or speed, of the vessel. Quite often, an advance pushes the boundaries to the point where one of the other areas becomes the limiting factor.
Riverboats are usually less sturdy than ships built for the open seas, as they don not have to withstand the high winds or large waves. There is also a perception that they tend to be slower, but this is only true when sea-going vessels are operating at their best possible speed, or in the modern era, where capacity is the number one design criterion.
Critically, the design of a riverboat is restricted by the width and depth of the river they are designed to travel, as well as by the height above the water of any bridges that span the river. Mississippi Paddle-wheelers could operate in water less than 2 meters deep (6.56 feet).
A riverboat can be considered a narrow barge for the purposes of defining cargo capacity. If a barge can carry 20-40 tons and a riverboat is the same length but only 1/5th the width, a rough rule of thumb would be that the riverboat could carry 4-8 tons of cargo.
The reality is not so encouraging because riverboats don’t have a square shape. They are more going to approximate one of the shapes below:
The diagram above looks very complicated, but it isn’t really. Let’s take them one silhouette at a time.
The top one has a distance from bow to widest point of the vessel of a and a length down the middle to a line connecting both widest points of b. Half the width is obviously e. It equates the size of the craft with an area formed by four triangles, a-b-e. This is exactly 1/2 of the area of a rectangle 2e-2b, by definition – and that rectangle is what we used earlier to get an estimate of 4-8 tons of cargo, earlier
The reality is overlaid and shaded – the hull curves outside the a line. And the stern is closer to the mid-line than the simple method given above, by a distance, d. I have seen suggestions that the two stern triangles should be (b- 1/2 d) by e as a means of correcting the estimate. I’m not having it – I contend that the extra area at the stern closely balances the lost area at the sides, close enough for gaming purposes, anyway.
The second diagram shows an even more complicated approach. It only takes one glance to say that the shape more accurately reflects that of a real boat.
It divides the length of the boat into three pieces – b, c, and f. Instead of measuring to the broadest point, it measures to a point some undetermined distance forwards of that, at which point, the boat has a width of 2g. It then extends two lines parallel to the mid-line of the boat from those points until they again intersect with the hull, giving the width of g; this defines the length of c. While I’ve shown it to be roughly the same as b, the reality is that it could be more, or it could be less. Anyway, this defines a square, c-by-2g. On each side there are a couple of triangles (h=e-g)-by-(1/2 c), 4 of them in total, two each side of the boat. And then we are left with the stern – you could use the total length and subtract b and c to get f, or you could pretend that f is b again as I did in the first diagram. The problem is that the compensatory mechanism isn’t there any more. So now we really do need to shorten the length by some fraction of d – but what fraction? There are too many variables. This model looks more accurate, but it actually has a boat-load more fudge factors built into it. As a means of estimating the cargo capacity, it is worthless.
I should also fess up to having made a deliberate error in the diagrams – the mid-point of the port side (the bottom side as you view these diagrams) is just a little closer to the bow than the one on the other side. As a result, this boat would have a tendency to turn – my instinct says to the right, but I’m not sure of that. This sort of manufacturing defect is all too common when you’re talking about manual labor and craftsmen without modern conveniences.
I cherry-picked a lot of different sources in compiling the above, extremely abbreviated though it is.
▪ Google
□ especially extracts from When Were Boats Invented | Marine Insight.com, and
□ the entry for “Ship” | Encyclopedia Brittanica
▪ The Complete History Of Boats | Newswires
▪ Rioverboats | Wikipedia
▪ Early History | Everything About Boats.org*
▪ The History Of The Barge and Why It’s Still A Crucial Part Of The Supply Chain | OpenTug
▪ The History Of Barges | Archway Marine Lighting
▪ Barge | Wikipedia
▪ An Insider’s Guide to the History of Barges | European Waterways
▪ Asian maritime & trade chronology to 1700 CE | Maritime Asia
▪ Maritime History Of Ancient China | China Underground, and, finally,
▪ Naval History Of China | Wikipedia
* NB: one of the security certificates at Everything About Boats.org expired 40-odd days ago, so my Antivirus and browser both chucked a fit over visiting this web-page. Hopefully the issue gets resolved soon.
4.5.1 Riverboat Capacity
If you have defined a trade unit as the cumulative carrying capacity of X people of a specific average strength – which we have – then it’s easy to get a total weight for one. Divide the capacity of the vessel – determined above to be 2-4 tons – by this to get an exact number of trade units.
But we don’t care about exact numbers very much – we want something sloppy and simple.
What’s more, if river transport is the key to the operation set up by the PCs (or by an NPC), then that approach is putting the cart before the horse – it’s very much simpler to define the boat as having a particular cargo capacity in Trade Units and worry about the manpower situation and loading / unloading later on.
Abstracting vessels in this way makes everything a lot simpler.
My suggested values:
Rafts: Sm 0.25, Me 0.333, Lg 0.5 TU.
Canoes: Sm 0.125, Me 0.25, Lg 0.333 TU.
Small Boats: VSm 0.333, Typ 0.5, Lg 0.75 TU.
Medium Boats: VSm 0.5, Typ 0.75-1.25, Lg 1.25-2 TU
Large Boats: VSm 0.75-1, Typ 1-1.75, Lg 1.75-2.5 TU
Barges: Sm 2, Me 4, Lg 6-8, VLg 8-12 TU
You can also multiply those numbers by any of the following factors to get a smaller unit of measurement if that’s more convenient: 3, 4, 6, 10, 12, 20, or 24.
Those last couple are pretty extreme. I think 6 or 12 would be the most useful.
Factor of 6:
Rafts: Sm 1.5, Me 2, Lg 3 TU.
Canoes: Sm 0.75, Me 1.5, Lg 2 TU.
Small Boats: VSm 2, Typ 3, Lg 4.5 TU.
Medium Boats: VSm 3, Typ 4.5-7.5, Lg 7.5-12 TU
Large Boats: VSm 4.5-6, Typ 6-10.5, Lg 10.5-15 TU
Barges: Sm 12, Me 24, Lg 36-42, VLg 42-72 TU
Factor of 12:
Rafts: Sm 3, Me 4, Lg 6 TU.
Canoes: Sm 1.5, Me 3, Lg 4 TU.
Small Boats: VSm 4, Typ 6, Lg 9 TU.
Medium Boats: VSm 6, Typ 9-15, Lg 15-24 TU
Large Boats: VSm 9-12, Typ 12-21, Lg 21-30 TU
Barges: Sm 24, Me 48, Lg 72-84, VLg 84-144 TU
Remember: You control the design and parameters of the vessel. You can define its capacity as whatever is convenient to you, and the definition of a Trade Unit that you are going to use derives from that. Try to stick to simple fractions, though!
Complicating everything is the fact that our measurements are in tons (presumably short tons) while everything else in this work is measured in kg, except when it’s in lb..
1 short ton = 2000 lb = 907.2 kg.
So, 2-4 tons = 1814.4 – 3624.8 kg.
If the higher number is 24 trade units (factor of 12, Medium Boat, upper end of the scale), each TU would weigh 151.03333333 kg – close enough that I would call it 150 kg.
Or, using lb, it’s 8000 lb total = 24 TU, then 1 TU = 333.333 lb. Which is highly inconvenient – I would round it to 325 lb.
Double to get lift equivalent, look up the highest capacity in the maximum encumbrance bracket on the STR table, and this defines a TU as 1 character of STR 23.5. Or 2 of STR 18.5. or 3 of STR 15.5. Or 4 of STR 13.5. Or 5 of STR 12, which is by far the most reasonable average STR that’s been mentioned, assuming that loading and unloading freight is a job that attracts somewhat stronger-than-average types.
You can see how everything starts to fall into place very quickly – in the space of a couple of paragraphs, we’ve defined a large vessel, a Cargo Unit / Trade Unit (by weight), and a Labor Unit (5 men of STR 12).
4.5.2 Favorable Winds
How fast can a riverboat powered by wind, go? Well, ignoring currents for the moment, and looking only at how good favorable winds are, let’s stick a top value of 30 knots (empty) – simply because that’s the speed of a strong wind.
1 knot is 1.15 mph
(actually, it’s slightly more, but that’s close enough).
So 30 knots is 34.5 mph, or 55.56 kph.
If the wind isn’t strong enough, the vessel goes nowhere. The wind needed to get a vessel underway and sustain it despite friction / resistance from the ocean is the area of sail divided by the mass of the vessel, including cargo.
Too complicated!!
Let’s instead define a standard size of sail that’s equivalent to the size of the boat, which is defined as a certain number of trade units.
Maximum Speed at full sail = 34.5 mph (or one of the other units as is convenient) × Weight of boat / (Weight of boat + Cargo).
So, we need to know how much a boat weighs. Or whatever sort of vessel we’re using.
This sort of information is incredibly hard to track down, I know from past experience. So let’s cheat and simply assign some numbers.
A large riverboat weighs as much as two large pick-up trucks. There, done. Call it about 5 tons, or 10,000 pounds.
So, our formula now becomes:
Maximum Speed at full sail = Base Speed × 10,000 / (10,000 + Cargo).
Still not the most useful of formulas. Let’s rearrange it a little to see if that helps:
Maximum Speed at full sail × (10,000 + cargo in lb) = 34.5 mph (or one of the other units as is convenient) × 10,000 = 345,000.
But wait, it gets even more convenient: Simply divide both the 10,000 and 345,000 by the weight assigned to one Trade Unit (650 lb in the example), and round appropriately to get a bespoke formula specific to your choices:
Maximum Speed at full sail × (15.25 + cargo in TU) = 530.
This is starting to get somewhere. Now, that’s at a full 24 “Sails” – so multiplying the speed by the actual amount of sail available and dividing by 24 takes another factor into account. That “530” is an idealized situation, after all. The reality might be that this vessel can only provide 20 sails out of an ideal 24.
Maximum Speed at full sail × (15.25 + cargo in TU) = 530 × Sails / 24.
530 × 20 / 24 = 441.67. Less convenient than I would have hoped, but you can’t have everything.
Next, let’s consider how “perfectly ideal” the wind direction is. Consider a compass, as shown to the right:
As you can see, it’s a simple trigonometry calculation to derive the effective wind speed from the actual wind speed and direction.
Too Complicated!
So let’s simplify: we know that any wind direction other than perfect is going to reduce the effective wind speed to something less than the actual wind speed, yes? So let’s define Effective wind speed as a fraction – in tenths, maybe – of Ideal wind speed.
100% (perfect) drops off to 90%, then 80%, 70%, 60% and so on, all the way down past 10% to 0% at 90° to perfect wind direction.
All we have to do is incorporate that into our personalized formula:
Maximum Speed at full sail × (15.25 + cargo in TU) = 5.3 × %Wind × Sails / 24.
What’s good about this formula is that it lets you trade off one factor for another. You can see how much faster the vessel will be if you drop 50% of the cargo – or add an extra 50% onto the top.
Or you can set a desired speed, make a reasonable assumption about the wind, and determine how much cargo you can carry.
Which brings in another factor to consider (this one’s helpful): Statistics. We don’t want to have to waste time as GMs rolling for weather when the PCs aren’t even going to be there to experience it. Instead, define climate as typical averages, and assume that no matter what happens, over time, the average experience will trend toward that typical average.
The typical average for summer is 70% favorable winds, and only a 10% chance of zero favorability? The average wind speed is 20 knots? We want to carry 5 TUs of cargo? Our vessel only carries 18 sails out of a possible 24? What is our average speed?
Let’s plug those numbers into our formula:
Average Speed at full sail × (15.25 + 5) = 5.3 × 70 × 18 / 24
= S × (20.25) = 278.25
S = 13.74 mph. In an 8-hour day, that’s about 110 miles.
What about that 10% chance? That simply means that there’s a 90% chance of some progress, with the minimum defined as being 10% of whatever speed we can usually expect.
10% of an 8-hour day is 48 minutes. On a typical day, we’ll make average speed for 7 hrs 12 minutes. At worst, we might have to slowly limp along and wait for the wind to change for 2×48 minutes = 1 hr 36 minutes. But if our normal speed is 13.74 @ 70%, then our speed at 10% is 1.96 mph – so even in this worst case, we will make 3.1 miles progress in that 1 hr 36 minutes, and about 88 miles in the rest of the day – so even in the worst case, we get 91 miles traveled.
Things aren’t quite as rosy if we look at a bigger picture. 10% of a 3-month season is about 12.2 days. So, conceivably, we might experience those worst-case conditions for up to 12.2 days.
The average is going to be less – a lot less. There are 6 × 6 × 6 possible results on a 3d6 roll; define each season as that many rolls of 3d6. The results will range from 3 to 18, a range of 16. The bottom 10% is 1.6 – so we want only 3-4.6. Everything else is fine and covered by the 70% average.
It’s really hard to get a 4.6 on dice that only roll integers. But, using a 3d6 graph, like the one below, we can get estimate it.
The above shows a quick graph showing “at least” results for 3d6. I’ve drawn a red bar at more-or-less where 4.6 is and noted where it crossed the curve. A Horizontal line from that point shows the % chance, or in this case, of time that the average event duration is going to be. Eight of those adds up to about 25%, so 25/8 = 3.125. But that’s an average – while there might be an event up to twice this long, there would need to be multiple much shorter events to get the average back down.
If there are 9 other events:
9 × X + 6.25 = 10 × 3.125 = 31.25
X = (31.25 – 6.25) / 9 = 25 / 9 = 2.78 days.
If there are 19 other events:
19 × X + 6.25 = 20 × 3.125 = 62.5
X = (62.5 – 6.25) / 19 = 56.25 / 19 = 2.96 days.
If there are 121 other events, i.e. the double-length happens once a season, but at least part of every day in that season is worst possible conditions:
121 × X + 6.25 = 122 × 3.125 = 381.25
X = (381.25 – 6.25) / 121 = 375 / 121 = 3.1 days.
Here’s the trend: the smaller the incidence of double-length periods, the closer to the 3.125 days the rest of the time has to be to get the average to work out. The deviation from that average just gets smaller and smaller.
So, if your market is 100 miles away, once a season it might take you a week; most of the time, it will take 1-4 days. And, with the 10% figure still in mind, 9 times out of 10 it will be the one-day number.
The practical upshot: Use the 1-day time with a 10% chance of it taking longer. Use 3d6-3 to determine how much longer, dividing the result by 4 to get the number of additional days.
Of course, if your chance of worst-case results is 1 in 122, or 1 in 365, or 1 in 3650 – or 1 in 5 – you will get different answers. This shows how I derived that simple statement, to be used only when it matters, so that you can make your own settings and determine the results.
I was going to link to the US National Weather Service’s page on the subject, but given recent events there, I don’t think I can rely on it. Nor was the Australian equivalent much more helpful. So, instead, here’s a link to the Royal Meteorological Society‘s page on the subject of Wind Scale.
In a nutshell:
0 Calm = <1 km/h = <1 mph = <1 knots.
Probable wave ht = 0 even at sea.
1 Light Air = 1-5 km/h = 1-3 mph = 1-3 knots;
Probable wave ht = 0.1 m at sea.
2 Light Breeze = 6-11 km/h = 4-7 mph = 4-6 knots;
Probable wave ht 0.2 m, max 0.3m.
3 Gentle Breeze = 12-19 km/h = 8-12 mph = 7-10 knots;
Wave ht 0.6m, max 1.0m.
4 Moderate Breeze = 20-28 km/h = 13-18 mph = 11-16 knots;
Wave ht 1 m, max 1.5 m.
5 Fresh Breeze = 29-38 km/h = 19-24 mph = 17-21 knots;
Wave ht 2m to 2.5 m. Crested wavelets on inland waters.
6 Strong Breeze = 38-49 km/h = 25-31 mph = 22-27 knots;
Wave Ht 3m to 4m. Incidence of large waves increasing.
7 Near Gale = 50-61 km/h = 32-38 mph = 28-33 knots;
Wave ht 4m to 5.5m. Foam blown in streaks across the sea.
Vessels should seek shelter.
8 Gale = 62-74 km/h = 39-46 mph = 34-40 knots;
Wave ht 5.5m to 7.5m. Wave crests begin to break apart into Spindrifts.
Be prepared to cut sails loose if they cannot be lowered quickly enough.
9 Strong Gale = 75-88 km/h = 47-54 mph = 41-47 knots.
Wave ht 7m to 10m. Wave crests topple over, spray affects visibility.
Risk of masts being torn free if ship is under sail.
Do not attempt to quarter or sail against the wind.
10 Storm = 89-102 km/h = 55-63 mph = 48-55 knots.
Wave ht 9m to 12.5m. Sea surface is largely white.
Uproots trees, may blow down masts & rigging even if sails are furled.
Structural damage is likely and extensive.
Seldom experienced inland.
11 Violent Storm = 103-117 km/h = 64-72 mph = 56-63 knots.
Wave ht 11.5m to 16m. Rarely experienced even at sea.
Accompanied by widespread damage.
Medium-sized ships become completely lost to view behind waves.
Seas are covered in white foam and visibility is seriously impaired.
Masts and rigging almost certain to be lost.
Decks likely to buckle. Keels may break. Ships may be torn apart.
12 Hurricane = 118+ km/h = 73+ mph = 64+ knots.
Wave hts 14m+. May generate tsunami-like waves.
Virtually zero visibility, there’s too much water in the air.
Almost everyone knows what Hurricanes are capable of.
Tornadoes: The enhanced Fujita Scale lists the following:
65-85 mph = EF0 (light damage)
86-110 mph = EF1 (moderate damage)
111-135 mph = EF2 (considerable damage)
136-165 mph = EF3 (severe damage)
166-200 mph = EF 4 (devastating damage)
>200 mph = EF5 (incredible damage)
It’s worth comparing those speeds with the Beafort Scale for wind speeds – EF0 essentially starts part-way through B11.
This Wikipedia Page also describes the sort of damage that accompanies each level on the EF scale. The information has limited relevance to vessels, however, given that buildings are essentially attached as solidly to the ground as possible, and therefore are liable to be torn apart; that’s not true of a boat, which is likely to be lifted into the air (perhaps to some considerable height). Note that the damage to “large vehicles” described assumes vehicles constructed of steel; for wooden vessels, such damage would occur one category sooner.
4.5.3 Favorable Currents
Wind isn’t the only thing that moves boats – there are also currents in the water. These are typically a fairly languid pace, because unless they are specifically designed for it (and not for carrying cargo), boats and barges can’t cope with raging river currents.
The average speed of a river current, Google informs me, is 3-4 mph (5-6 kph). The actual value depends on the river’s size, gradient, water volume, and conditions. In a flood situation, a fast-running river can achieve speeds of 15 mph.
The fastest water flow in a river is typically in the middle of the channel and around the outside of bends.
Unless you’re talking about some sort of river ferry, the situation is simple: the current is either for or against you, because you want to head either upstream or down. So it either adds to the effective windspeed (going downstream) or subtracts from it (going upstream).
In comparison to the wind speed, it’s a relatively minor variable, but something to be aware of, nevertheless.
One important thing to remember is that what helps you coming, hinders you going – if currents were all the same speed, all the time, it would be, overall, a non-factor across a round trip.
But that’s not the case. Tides raise water levels, and that changes river size and (effectively) deepens channels, and those factors make currents run faster if the tide is going out and slower when it is coming in. Get your timing right, and the river gives you a little added boost to your efficiency; get it wrong, and it will fight you.
As a very rough rule of thumb, tides occur 1 day + 50 minutes apart. Over a 7-day period, that 50-minute ‘drift’ totals almost 6 hours; over a 30-day period, it’s 25 hours. Over a year, about 12.674 days – or 12 days, 16 hours, and some minutes. But there are variations according to time of year and local geography and many other factors. In fact, calculating tides used to be so difficult that a calculating machine was developed exclusively for the purpose. You can get a lot more information on the subject at this Wikipedia Page..
4.5.4 Unfavorable Winds / Currents – Oarsmen Requirements
The one thing you can be sure of about the weather is that there will be times when it seems dead-set against you.
When that happens, you have two choices: drop anchors and (effectively) moor yourself to the bottom, or fight back – with oars.
The right place to start is obviously by thinking about the use of oars in a completely becalmed situation, and then to extend that to cover situations where one or both of these natural forces is opposing you.
So I’m going to do it the other way around, because I can.
Whatever speed the oarsmen can generate under ideal conditions has to be enough to counter the effective wind speed (allowing for the current) that is trying to push you in some other direction.
Obviously, if the sails are up, that gets a lot harder – multiply the wind speed by the square root of the Sail Number +1 before applying the effects of the current.
If you have 15 “sails” up, that’s 4 × the wind speed for the purposes of determining rowing speed.
Clearly, if the effective wind speed is more than your oarsmen can generate, you’ll go backwards. This is so unnatural in any sort of marine vessel that helmsmen have been known to turn their tillers and rudders the wrong way – go hunting for footage of someone trying unsuccessfully to reverse with a trailer and you’ll get some idea of how confused they can get. You can literally tell someone to turn left and they will turn right. Either comedy or disaster soon follows.
The problem with currents is that they flow whether the sails are up or not. On a river, that’s not too bad, because they are (generally) predictable to at least some extent; at sea it can be disastrous.
So, to get the rowing speed of the vessel, total it’s weight and that of any cargo on board, and divide by the total carrying capacity of the oarsmen, then multiply by 84%, and multiply all that by the typical rowing speed over distance of 14 km/h.
If the oar design is more primitive than the best modern oars, reduce that 84%. Even the most primitive oars can manage 25-30% efficiency, though. For simplicity, I would use 24%, because that gives a nice, round 60% loss of efficiency – so all I have to do is estimate where on that 60% scale the current state of the art is.
Another factor that has to be taken into account is vessel size, because that impacts oar size and therefore the difficulty of manhandling the oar. Large vessels may have three or four people manning each oar, they are so long and heavy. If you have only 3 people when you should have 4, that’s going to reduce your efficiency to 75% of what it otherwise would be.
Let’s take the vessel we described earlier – 15.25 Trade Units, plus 5 TUs in cargo, for a total of 20.25, with one TU being defined as 650 lb.
If the average STR of the oarsmen is 12, that’s a lift value each of 130 lb, or a carry capacity of 65lb. So 10 oarsmen is enough to get 1 TU up to full speed. Which means we need 10 × 20.25 = 202.5 oarsmen.
We have only 60 oarsmen, let’s say. That’s 60 / 202.5 × 84% (at best) × 14 = 3.484 km/h = 2.165 mph = 1.88 knots.
With the sails furled, any current faster than this can’t be overcome. If the current is assisting, on the other hand, it adds to this speed, and the oarsmen are as much assisting in steering the vessel as they are propelling it.
And that’s with the full 84% efficiency (reduced for the shortage of crew). If it was only 64%, the speeds would be 60 / 202.5 × 64% × 14 = 2.655 km/h = 1.65 mph = 1.4336 knots.
The long and the short of it is that 60 oarsmen aren’t really enough for a vessel of this size.
4.5.5 Unfavorable Winds / Currents – Sail Solutions
The invention of the lateen or latin-rig sail – a triangular sail mounted at an angle and in a fore-and-after direction – permits a vessel to tack or zig-zag around an overall direction upwind.
In practice, the closest you can sail toward the wind source is 45 degrees.
This creates the zig-zag with 90 degree turns (approximately), each of which requires the lateen to be reset.
The technicalities of how the Lateen achieves this motion aren’t all that important. What matters is this: if you don’t have a lateen sail, you aren’t sailing closer then broad-side to the wind; your vessel simply isn’t configured to do it.
Obviously, if you have such a sail, things become possible that weren’t before.
The most efficient lateen is effectively only 2 or 3 sails worth; most are only 1 “sail”. So speed is obviously going to be compromised.
Let’s look at the example from earlier – 20 sails out of 24 possible, 15.25 TU in vessel weight and 5 TU in cargo. Let’s say that the remaining “4 sails” are dedicated Lateen sails – so, when the wind is in slightly the wrong direction (up to 45 degrees from perfect), they can make for at least some of the losses. 4/24 or 1/6th of the total, in fact.
But, when there’s nothing else for it, let’s drop those mainsails and see how these 4 Lateen sails manage.
Average Speed at full sail × (15.25 + 5) = 5.3 × 70 × 4 / 24
= S × (20.25) = 61.83
S = 3.0535 mph.
To that, let’s add 1.65 mph for 60 oarsmen, or a total of 4.7 mph. This is at a 45-degree angle to the direction we want to travel, so we need to multiply by sin (45) to get the actual amount of travel in the direction we really want to go – this is × 0.7071. So, all told, progress without a current is 3.32337 mph.
If the current is in our favor (3-4 mph) then that’s 3.5 × 0.7071 = another 2.47485 to our speed at the 45-degree headings, for a total of 7.175 mph – which translates to 5.07 mph in our desired direction of travel despite the winds.
If the current is not in our favor, then that 2.47485 difference gets taken off our speed, slowing it to 2.22515 mph in a straight line – or 1.57 mph in the direction we want to travel.
Rivers seldom run in a straight line. We turn one way and the wind becomes our enemy, we turn the other and we’re best buddies.
Here’s a realistic river that I threw together. Our vessel starts off getting 94% of the benefit of its mainsails, which rises briefly to 100% as we curve to the left before dropping back to 94%. As we start to curve to the right, it again goes up to 100% before dropping back, first again to 94%, and then to just 64%. As the river continues to curve to the right in the loop, the mainsails continue to drop in efficiency until, just past the half-way mark, they drop to 0%. I’ve changed the river from white to yellow at that point.
Furl the mainsails and raise the Lateen; unship the oars, and pay close attention to the currents. While the river is yellow, we can continue directly down it’s course, but it isn’t long before we exceed the 135° mark and the river goes from orange to red. From that point until we enter the bend left, we’re fighting the wind.
Once into that bend, we can again sail directly using the Lateen, until finally, we can raise our Mainsails once again.
The overall measure of the wind angle is shown as 79°R – so, effectively, our Mainsails work at an average of 19% or not at all.
Do we have to subject every journey to this kind of detailed analysis? Of course not. What matters is the vector sum – so long as it’s within 135° of the wind direction, we’re traveling in the right direction. For 1/3 of that, we’re using the lateen and sailing direct – slower, but still progress.
So, what’s the shortcut? Draw a line between start point and end point. Measure the greatest distance in the direction of the wind to that line. 2/3 of that we’re zigzagging, which increases the length 1 / 0.7071 = about 40%. The rest of it, we’re at our slower speed. Combine those and you get 1.4 × 2/3 + 1/3 = 126% of the distance at lateen speed plus oars plus current. The rest of it, we’re under mainsail – for roughly the same distance. So, if our mainsail speed is X and our Lateen speed is Y, we get a combined speed of 1/2 X + (1/2 Y / 1.26). If you know the ratios of sail to lateen – 20/24 and 4/24 in relative terms in our example – then we have 20 / 2 + (1/2 × 4 / 1.26) out of 24 = 10 + 0.79 = 10.79 out of 24.
Add to that the current, always in our favor, and the oars contribution × 1/2 / 1.26, and we get our net speed. And it will work out to 19% of our mainsail speed.
The overall direction of travel relative to the wind and the actual length of the journey are all we actually need.
But we don’t even need that – because we have already determined that 70% of the trip will have favorable winds. It’s right there at the start of the definition of the journey. So 30% of it is at lateen speeds plus oars and current, and 70% is at mainsail plus current.
And if that doesn’t match up to what you have on the map, you have to remember that geographic features get distorted by speed. In effect, slower sections are larger and longer than fast sections by the ratio of the two – 20/4 = x5 in the case of our example. So the upwind slog is effectively 5 × the size shown in length.
4.5.6 Extreme Weather Events
If the weather seems out to get you when it’s just fighting you, what do you call it when it goes to war with you? This makes simply fighting the wind seem like playing with an aggressive kitten in comparison.
I’ve already discussed the Beafort and Fajita scales and what the wind can do. Some areas are more prone to this sort of event than others, as Florida residents know all too well. But it’s not just the equatorial regions, as the story of the Edmund Fitzgerald makes clear (the Gordon Lightfoot song doesn’t get everything right but it’s close enough to make the point).
Extreme weather events can happen anywhere, any time – they are just more predictably likely at some places and times.
So, what are the odds?
A once-in-five years event will happen once in 1825 times. Such an event with no warning is probable twice as rare – once in 3650 times.
That’s 0.0274%. Or, to phrase it more usefully – you need to make a daily d% check and get an 01 to have a 2.74% chance of it happening.
Maybe there’s 5 such events, all different. Then you would expect one of the five to happen, on average, every year. But some (bad) years, there will be two of them, and some years, there will be none.
And some years, the event will be (comparatively) mild, while others, it will be relatively severe.
Sounds like we’re in need of a statistical approach.
So a 1 in 5-years event means that you expect one every 5 years, i.e. that there’s a 20% chance each year. If there is a 1 in 4 chance of greater severity and a 1/4 chance of an extremely mild version of the event, that means that there’s a 5% of a weak event, a 10% chance of a typical event, and a 5% chance of a severe event, each year. Call these outcomes A-, A, and A+ and a 0 for no event.
If there’s a second 1-in-5 event that can occur completely independently of the first one (and those are comparatively rare), then no matter what the outcome of the A check, we get the same chances of a B event.
5%: A-.
▪ 5% × 5% = 0.25% A- and B- in the one year.
▪ 5% × 10% = 0.5% A- and B in the one year.
▪ 5% × 5% = 0.25% A- and B+ in the one year.
▪ 5% – 0.25% -0.25% -0.5% = 4%: A-, no B.
10%: A
▪ 10% × 5% = 0.5% A and B- in the one year.
▪ 10% × 10% = 1% A and B in the one year.
▪ 10% × 5% = 0.5% A and B+ in the one year.
▪ 10% – 0.5% -0.5% – 1% = 8%: A, no B.
5%: A+.
▪ 5% × 5% = 0.25% A+ and B- in the one year.
▪ 5% × 10% = 0.5% A+ and B in the one year.
▪ 5% × 5% = 0.25% A+ and B+ in the one year.
565% – 0.25% -0.25% -0.5% = 4%: A+, no B.
80%: No A.
▪ 80% × 5% = 4%: B-.
▪ 80% × 10% = 8%: B
▪ 80% × 5% = 4% B+.
▪ 80% -4% -4% -8% = 64% neither A nor B.
But if I generate 5 random d400 numbers, and divide by 4, each time there is a 64% chance of nothing happening – that might be only 10.73741824%, but it’s a non-trivial chance.
Generate a sixth. 6.87% chance of nothing.
Generate a seventh. 4.4% chance of nothing.
Generate an eight. 2.8% chance of nothing.
Generate a ninth. 1.8% chance of nothing.
In fact, we have to extend the run to 14 years before there’s a less than 0.25% chance of nothing happening. That makes it near-certainty that something will happen in that time-period.
We can use the same principle to add a third event to the possibilities, and then a fourth and fifth. But each time, we make the smallest chance only 5% of the previous smallest chance – so we have to increase the size of the roll 20-fold. From d400 to d8,000 to d160,000 to d3,200,000. And the number of entries in the resulting table would be 16 × 4^3 = 1024 entries.
The last one – of nothing happening – will remain by far the biggest. We used 16% out of 80% for the cases with just two events; with a third event, the chance will drop to 80% of 64% = 51.2%; with a fourth, 80% × 51.2 = 40.96%; and with a fifth, 80% × 40.96% = 32.768%.
There’s 100 × 0.32^5 = 0.37779% chance of nothing happening in a given 5-year time-span.
Every time there’s an A event, be it A-, A, or A+, there is a 4% chance that it’s a once-in-25-years event instead (100/25=4). And a 0.8% chance of a one-in-125 event. And a 0.16% chance of a 1-in-625-years event.
Having tossed all these numbers around like confetti, it’s time to bottom-line it: Events like this will happen at the speed of plot. If it suits the GM’s plans for something to happen, it will – and unless that’s the case, it won’t.
4.5.7 The Tempest Scale
Let’s say something does happen. How severe is it going to be?
Divide the B scale number from 1 to 11 by 2.5. Add 1 for each F number. Then square each number
B0 = 0^2 = 0.
B1 = 0.4^2 = 0.16.
B2 = 0.8^2 = 0.64.
B3 = 1.2^2 = 1.44.
B4 = 1.6^2 = 2.56.
B5 = 2^2 = 4.
B6 = 2.4^2 = 5.76.
B7 = 2.8^2 = 7.84.
B8 = 3.2^2 = 10.24.
B9 = 3.6^2 = 12.96.
B10 = 4^2 = 16.
B11 = 4.4^2 = 19.36.
F1 = 5.4^2 = 29.16.
F2 = 6.4^2 = 40.96.
F3 = 7.4^2 = 54.76.
F4 = 8.4^2 = 70.56
F5 = 9.4^2 = 88.36.
4.5.8 Vessel Rating
Every vessel receives a rating for their capacity to withstand storm and wind damage. The rating depends on the vessels (1) resilience, (2) construction methods, (3) materials, (4) magic, (5) captaincy, (6) Maintenance history, and (7) karma, which can add to or subtract from the other factors. When confronting a potential disaster, the GM rates each factor except karma out of 5, and Karma out of plus-or-minus five.
The highest score (or one of them if there’s a tie) and the lowest score (or one of them, again) then get reduced by 1, representing age and wear-and-tear since the last time the vessel was checked.
For every score of 2 or better after the first, he adds +1 to the total.
For every score of 3 or better after the first, he adds +2 to the total.
For every score of 4 or better after the first, he adds +3 to the total.
For every score of 5 after the first, he adds +4 to the total.
That’s six opportunities to record a 5, so 4 opportunities for +4, giving a maximum of (5×5) + (4×4) +4 = 25+16+4=45.
The total score is divided by 2 and rounded down.
Karma is then applied, so the maximum score is 27.
This is subtracted from the Tempest scale to get the % chance of the worst outcome associated with that weather phenomenon taking place (a total of <0 = no chance of that happening and the vessel will survive the event just fine).
If it doesn’t, this is also 10 more than the % chance of the next worst happening, and so on, until you get to B7 unless condition or maintenance history are 3 or less. If one of those is the case, go to B6; if both, to B5.
And at this point, I should remind readers of one of the earliest notes made with reference to riverboats and barges: “Riverboats are usually less sturdy than ships built for the open seas”.
4.5.9 Weather Cataclysms
How much damage will experiencing a weather cataclysm cause?
The answer is the damage chance + the total of the basic six ratings + a d20 roll. The bonuses for multiple high scores remain.
Half of this total, or 20 points maximum, is minor incidental damage – 1 point for each item. Ropes, rigging, hatch covers, etc.
Half of what’s left, or 20 points maximum, is more significant damage – 2 points for each item. Anchor chains snapped, cannon lost overboard, fires on board, crew lost, etc.
Half of what remains, or 24 points maximum, is non-fatal structural damage. Missing prows, broken decks, lost masts, and such are worth 3 points per item.
Whatever remains is potentially fatal structural damage. Holes in the sides, fires in the powder magazine (if there is one), cracks in the keel (2 cracks = 1 actual break), missing officers, etc are worth 5 points each – partial damage mean that an officer isn’t lost overboard, but is badly injured. Two breaks in the keel and it’s lost and the ship will break in two. It’s likely to be taking on water and may even have overturned if it isn’t a barge.
Of course, wind isn’t the only potential disaster to befall a vessel – but, with the possible exception of river pirates and the odd pleiosaur, everything else is more likely to afflict a seagoing vessel.
And that brings this part of this chapter to a close. It’s covered quite a lot of territory, and that means that the next post should be relatively small, as I turn my attention to the deep waters… But first, it’s time for another Time Out!