Ship Speeds

[Kid Charlemagne]

The SRD lists a sailing vessel as having a speed of 2 mph, for a total of 48 miles per day (thus assuming a 24 hour sailing day). I know this is meant to be an average, and that there are various books out there that go into further detail on speeds, wind conditions, etc. However, I've recently been re-reading the Baroque Cycle by Neal Stephenson (Quicksilver, The Confusion, and System of the World), and sailing is a major component of these books - especially the second. Time frame is 1690-1710.

In these books, Stephenson often remarks about it taking the better part of a day just to get out of a major harbor (London, Amsterdam, Manila), and having to travel very slowly in coastal waters, taking depth soundings all the way to make sure you don't run aground, etc. In one case, a ship spends the better part of a month on the Boston coast in winter waiting for a suitable wind to sail to London.

(Carlzog, help me, you're my only hope!)

So I'm interested in knowing what elements are most often missed in seafaring rules systems. I want something fairly simple but I want to understand the challenges of sailing in coastal areas better, so that I can explain how long it takes to go anywhere. Simply knowing the average speed isn't enough...

 

[Doug Sundseth]

Two miles per hour is a really low average speed. The top speed of a good first rate ship of the line (the biggest sorts of ships during the Napoleonic period) was about 10 knots (11.5 mph). Clipper ships are recorded as having gone up to 20 knots over long distances. Without considering other issues, and assuming relatively favorable winds, I'd WAG an average sustained speed somewhere around 5-8 mph.

Complications:

Type of sails - a sloop-rigged vessel can travel closer to the wind than a ship-rigged vessel, so is less slowed down by unfavorable winds.

Barnacles, etc. - Poorly maintained ships have higher coefficients of friction, so are slower than well-maintained ships.

Currents - Ocean currents can move as fast as 2.5 m/s (about 10 mph). 1-1.5 m/s currents are pretty common. Depending on direction, this can dramatically speed up or slow down a voyage.

Weather - Rough seas slow ships, though rough seas are often coincident with strong winds, which may mask this. Really strong winds, though, will require a vessel to shorten sail to prevent rigging damage. And, of course, a true calm can mostly stop a sailing ship.

Shoaling water - Something of a problem in unknown seas, this is usually not a consideration for voyage speeds. Shoals can usually be seen from a distance by the difference in the way the waves move over them, and shoals are mostly well-known when they occur on or near a regular shipping route.

ps. The long times necessary to leave or enter some harbors have little to do with the speed of the ship in general and much to do with maneuverability, crowded or constrained waters, tides, currents, and winds. And in the case of some ports (like London), there's the issue that the port is a long distance from the sea.

 

[S'mon]

I generally double the 1e-3e ship speeds, ca 100 miles/day for a typical merchantman. BECMI uses those kinds of figures.