Association Forum - Why a sailboat can go 22 knts

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Why a sailboat can go 22 knts

New Topic

Topic Locked

Printer Friendly

Author

Topic

djn
Master Marine Consultant

Member Avatar

USA
1561 Posts

Initially Posted - 03/06/2006 : 13:50:34

Hi All, I've been watching clips of the Volvo race and have seen there speed readouts. Those boats, with a freash wind, are doing 22+ knots. So why can't our C25 go that fast? Is it perportionate to size? I don't know sailboat design therory, but think it would be fun to go 22 knots in my C25. Cheers.

Dennis
No Boat
S.E. Michigan

Edited by - on

tinob
Master Marine Consultant

Members Avatar

USA
1883 Posts

Response Posted - 03/06/2006 : 14:23:50

There is a formula for displacement hulls that limits the theoretical speed relative to the length of your boat's waterline..something like 1.34 times the square root of your waterline...our boats are capable of approximately 6.2 knots, unless there are forces at work that are raising the hull out of the water at which point the hull waves are not holding the boat back and greater speed are posible.

The boats that you refer to are not displacement hulls and are capable of planing ergo the 22kts per. I saw some tests of multihull boats that, at the time I saw them, set a world record of 52knts. they employed hydrofoils and were totally wind driven.

I can't think on the water at that speed

Val on the hard DAGNABIT # 3936 Patchogue, N.Y.

Edited by - on

At Ease
Admiral

Members Avatar

672 Posts

Response Posted - 03/06/2006 : 14:24:12

This will get your C25 up to 22 knots...forget all that square root stuff, what we need is horse power!

http://www.bath.ac.uk/~ccsshb/12cyl/

Edited by - At Ease on 03/06/2006 14:25:24

Frank Hopper
Past Commodore

Members Avatar

Pitcairn Island
6776 Posts

Response Posted - 03/06/2006 : 14:25:16

Google, sailboat theoretical speed limit
you will read about bow waves, the theoretical hull speed for a displacement hull (like most sail boats). It is a function of the length of the wave created by the boat as it moves through the water. Wave speed is a function of wavelength, longer wavelength is faster. Longer boats make longer waves. Since longer waves are faster boats that make longer waves are faster [Garrett]. The hull speed may not be as precise a figure as the formula leads you to believe (1.34 sounds pretty precise doesn't it?). LWL is not static. As the boat heels it can increase. Older racing boats with long overhangs used this to get some extra un-measured LWL to beat the rating rules of the day. As the boat goes faster the bow and stern are immersed deeper in the wave made by the boat. This also increases waterline. In the 19th century sailing ship speeds were often expressed with a hull speed factor. A ship might have a speed factor of 1.17, meaning it can make a speed of 1.17 x sqrt(lwl) [Chapelle]. There are conditions where you can exceed the theoretical hull speed. Surfing down a wave for example. I have had my boat (LWL=21.6 feet, HSPD=6.25) surfing at 10 knots on waves. When surfing or planing the hull is not in a displacement mode. So hull speed may be a bit of a moving target.

Edited by - on

Dave Bristle
Master Marine Consultant

Members Avatar

Djibouti
10005 Posts

Response Posted - 03/06/2006 : 14:28:46

Size matters... (There are many discussions here and on the Web about theoretical hull speed as a function of the length of the waterline). Another factor, especially with the Volvo boats, is the hull shape--theirs are designed to plane, while ours are not (although they can do it for a few seconds on the face of a wave). For a boat to exceed it's "hull speed" (ours is about 6.3 knots), it has to be able to climb over it's bow wave and get up on the surface (planing). Until then, the bow wave pushes back with as much force as the boat is pushing forward with, and the boat can't go any faster. I believe the simplistic formula for maximum hull speed is 1.3 x sqrt(LWL). Other factors (shape, multi-hulls, etc.) can affect that. (This from the Department of Redundancy Dept.)

Edited by - Dave Bristle on 03/06/2006 14:32:53

John V.
Admiral

Members Avatar

USA
559 Posts

Response Posted - 03/06/2006 : 19:37:17

Val, I didn't know the 50 kt barrier had been broken. could you let me know where I could read about it. The last record I knew of was a sailboard at 48+ kts. I was in a car wreck on Christmas eve and I havn't been alltogether here so perhaps I missed the news.

Edited by - on

jwilliams
Captain

Members Avatar

USA
357 Posts

Response Posted - 03/06/2006 : 20:02:30

Forget all that technical stuff about 1.34xSRxWL, etc.

The real answer is how much water is in contact with the hull...less water faster boat. That's why a lot of people sail their boat onto a trailer from place to place...no water at all=fast boat. Sometimes 55mph!

Jim Williams
Hey Jude C25fk 2958 (6.5kts on a good day)
SF Bay

Edited by - on

takokichi
Captain

Members Avatar

USA
321 Posts

Response Posted - 03/06/2006 : 20:58:26

I agree - 50kt barrier not yet broken. I'd settle for 15, though...

Edited by - on

Champipple
Master Marine Consultant

Members Avatar

USA
6855 Posts

Response Posted - 03/06/2006 : 22:06:24

Without going into details - Dennis Connors book Sail Like a Champion discusses this in Depth, yet understandible to us non physicists. Page 18-25 or so.

Also, for guys new to racing, this book touches a lot of the basics and is fairly easy to understand.

thats my buck and a quarter (inflation, rising interest rates, the cost of opinions went up )

Edited by - on

dlucier
Master Marine Consultant

Members Avatar

Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 03/07/2006 : 08:16:52

A DN boat went 68mph over water...very hard water.

Edited by - on

OJ
Master Marine Consultant

Members Avatar

USA
4382 Posts

Response Posted - 03/08/2006 : 20:42:49

This reminds me of a guest we had at one of our local, annual sailing club meetings. She had crewed on one of the all women crew whitbread boats.
On one leg they were sailing out of a channel towards open seas. A large cat with an all male crew passed them going the opposite direction. Boys being boys, they came about and thinking they would appoach and overtake this monohull craft filled with an all women crew.
Even I enjoyed the look in her eye as she explained how they left the hopeful boys in their wake when they changed to a close reach.

Edited by - OJ on 03/08/2006 20:43:35

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.