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 Heloboarder 01-09-2009 02:51 PM

Average Speed of a Sailboat

What are the average cruising speeds for a 30-40' displacement and semi displacement hull sailboat?

 CharlieCobra 01-09-2009 03:06 PM

6-9 knots depending on conditions and the boat.

 CBinRI 01-09-2009 03:18 PM

Quote:
 Originally Posted by CharlieCobra (Post 429631) 6-9 knots depending on conditions and the boat.
If you are talking about averages over the course of a long sail, I think that is a bit high.

 JohnRPollard 01-09-2009 03:21 PM

This is a tricky question -- so many variables. Length, displacement , rig, crew, windspeed, upwind, downwind, etc.

There's a fairly large speed difference between a typical 30 footer and the typical 40 footer. I would say Charlie's estimate is pretty high for a 30 footer, but in the ballpark for a well-crewed performance oriented 40 footer.

I'm wondering what you plan to use this average speed figure for? Is it for planning a passage? IF for that purpose, I would use a figure closer to 4.5 knots for the 30 footer and maybe 5.5 knots for the 40 footer.

If you are trying to compare the speeds of displacement vs. semi-planing hulls, that's another conversation. A bit more info, perhaps?

P.S. Welcome to Sailnet!:)

 btrayfors 01-09-2009 03:34 PM

As was said, this is a tricky question.

But, for consideration, a well-sailed cruising boat on passage will make about 75-80% of her hull-speed potential over a 24-hour period.

Example:

Waterline length: 34'
Hull speed: 5.8*1.4 = 8.2 knots
80% of hull speed: 6.56 knots
24-hour run: 157.4 nm

Mine does a bit better, averaging 6.7 knots or 160 nm per day on offshore passages on a 34.2' waterline (27K lbs displacement, 42' LOA).

Obviously, there are many variables. But, the "80% rule" often comes close, I've found.

Bill

 nolatom 01-09-2009 03:38 PM

I'd agree with what our esteemed moderator has said.

Low, about 4 knots. High, about 6 knots. Subject of course to weather being higher or lower than usual. With GPS, you'll know your speed over the bottom. With a wood or stryofoam chip, timed from bow to stern, you'll know what your speed through the water is. They you'll know if you're sailing in current.

But our estimates on the web don't mean much to you on the water, you'll have to take both an over-ground and a through-water speed, then compare to see if you are in a current and if so what its direction is.

 Faster 01-09-2009 03:44 PM

All these guestimates also need to take into account the point of sail and the wind speeds vs the different designs. I suspect there's little difference between "displacement" and "semi-displacement" designs. However a boat that can outright plane in certain conditions will have a much higher potential threshold with the right wind speed, course and sea state.

JRP's estimates for overall average speed look good.

 chucklesR 01-09-2009 04:14 PM

To figure out how long it will take to get somewhere, figure 5kts as a average. When bragging at the local sailing bar, figure the hull speed plus 10%.

Unless you are in the trade winds, then figure on 75% of hull speed depending on the skipper, condition of sails, the load of the boat multiple times a random number derived from adding up the letters of the words "silly question".

 rayncyn51 01-09-2009 04:22 PM

I measure average speed in quarts of rum per hour. Is that incorrect?!?

 N0NJY 01-09-2009 04:25 PM

What are the average cruising speeds for a 30-40' displacement and semi displacement hull sailboat?

I think you have to add up all the displacement hull boats at 30', then all the semi's at 30', then all the 31s, 32's etc and divide by the actual number of boats for this problem.

:)

That ought to give you some good, round, averages. hehe

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