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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Exceeding maximum designed hull speed

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Steve Milby
Past Commodore

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USA
5895 Posts

Initially Posted - 12/02/2009 : 10:17:55

For those who still wonder whether a sailboat can exceed it's theoretical maximum hull speed, check out this link to a video of a C-22 doing 8 knots.

You can only reach such speeds by surfing. Some people say that you can only surf if you have big waves, and some say that you can only surf for very brief spurts, while running down the face of a big wave, and some say a C25 can't do it at all. This video refutes all but the last assertion.

The video was made on an inland lake with no big waves, the speeds at or near 8 knots were maintained throughout the entire video, and you can see that the speed was not a brief spurt, but was holding steady at about 8 knots.

Two years ago, my C&C 35 surfed at about 9 knots, without letup, for over an hour on the Chesapeake Bay.

I know a C25 could have also surfed in the same conditions.

Enjoy!

http://www.youtube.com/watch?v=YEsiw9UmnzM

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

Edited by - on

Renzo
Admiral

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USA
621 Posts

Response Posted - 12/02/2009 : 10:49:48

I'm a believer! Many years ago, on a lake, flying a spinnaker on a friend's C&C-26 in 30+kt winds, we pegged his analog knot meter at 12kts and held it there for at least a half hour.

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Even Chance
Captain

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USA
393 Posts

Response Posted - 12/02/2009 : 11:56:29

As St. Francis said, "Only God can say always and never." The hull speed calculation is "theoretical hull speed." With big dinghies like ours, I suspect there are certain conditions when the boat gets up on top of the wave and surfs.

On the other hand, I'm surprised at that turn of speed dead downwind (wing and wing). I've exceeded theoretical hull speed on a broad reach, but I suspect tide had something to do with that.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/02/2009 : 13:29:30

I'd call that planing--the act of climbing over its bow wave by lifting the hull. Surfing is a special case of planing, where gravity on the front side of a big wave adds some power. The C-22 is more of a planing hull than the C-25--flatter and broader relative to its length. However, a C-25 can sort of do it--I've hit about 7.5 knots on a reach, probably with a little "surfing" help. For a boat that really planes, take a ride on a Flying Scot in a nice breeze. (...or an Open 60 if you can find one!) Check the video at http://www.flyingscot.com/ .

Dead downwind, you need stronger wind to plane because (a) the apparent wind drops as your speed increases, and (b) you aren't getting the full aerodynamic effects of the sloop rig--you're more like a square rig at that point.

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tbosch
Navigator

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163 Posts

Response Posted - 12/02/2009 : 14:03:05

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 ... and some say a C25 can't do it at all.
<hr height="1" noshade id="quote"></blockquote id="quote">

I hit 10 mph several times one terrifying day on Lake Superior. We were running in 25-30 mph winds and 8 foot following seas. We definitely did some surfing down the waves. The waves were faster so they would eventually travel under us and we would hang on for the next one. Steering was a big challenge. I was NOT going to let myself get turned sideways to the waves. It was a little more adventure than I wanted!

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 12/02/2009 : 14:28:12

I had long surfs in the 8 knot range and hit 8.8 on the GPS on a long reach back from Islas de los Todos Santos under spinnaker in strong winds 15 knots or higher and 6 foot waves from astern. They took a video of us at the finish and I wish I could get ahold of that. A strong finish and a perfect douse.

Nothing like the ride in a sport boat, they stay on the waves and surf for miles in conditions like that with boat speeds in the teens.

But a ton of fun, none the less!

Edited by - on

DaveR
Master Marine Consultant

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USA
2015 Posts

Response Posted - 12/02/2009 : 14:37:38

I think in any case it's a matter of current with a displacement hull. Whether you're surfing a wave or riding a current it's all the same, the water under your boat is not still, but moving in the same direction as you are and so increases your speed over land.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/02/2009 : 15:09:00

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by DaveR
 I think in any case it's a matter of current with a displacement hull. Whether you're surfing a wave or riding a current it's all the same, the water under your boat is not still, but moving in the same direction as you are and so increases your speed over land.<hr height="1" noshade id="quote"></blockquote id="quote">I just hate to be disagreeable,

but no. As waves move through water, the water pretty much stays where it is (although it oscillates as the wave passes). Many sailboats are definitely able to get up on top of the water and beat their "theoretical hull speeds".

That oscillation can be very unsettling (and cause broaches)... A following wave causes water to move bow-to-stern you as the wave builds under you, and then the water reverses, moving stern to bow as the wave passes under you. This momentarily reverses the effect of your rudder on the back-side of the wave so that if you try to steer to port, for example, the bow slews to starboard (as if you were backing up)! This is often why, in large following seas, a boat seems so "squirrelly"--it can even end up abeam to the next wave, which can cause a broach.

Surfing is a gravity thing--as on a surfboard... When you're doing it, water is spraying off the bow. That's because you're moving and the water under you basically isn't--actually, on the front side of the wave, it's moving against you.

Edited by - Dave Bristle on 12/02/2009 15:26:18

Rich P
1st Mate

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USA
77 Posts

Response Posted - 12/02/2009 : 16:45:04

According to the caption on the right, they are doing 8.1 MPH or about 7 Knots

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Even Chance
Captain

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USA
393 Posts

Response Posted - 12/02/2009 : 18:05:42

Thanks, Dave, I really meant planing. My first boat was a 17' Mobjack, which planed pretty easily.

But if he was sailing dead downwind, maybe he was surfing. It's pretty cool either way.

Edited by - Even Chance on 12/02/2009 18:07:55

DaveR
Master Marine Consultant

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USA
2015 Posts

Response Posted - 12/03/2009 : 07:02:09

Dave B, When a wave passes, a given area of water will move a certain distance, that given area of water MAY basically stay associated. Or it may not. It depends on conditions, boundaries, currents, etc. Nevertheless either there's movement in the water or forces moving through the water. Either will propel or impede your boat. Without that a displacement hull won't go appreciably faster than hull speed. Wind also moves water, in a big way, this is why tides vary so much depending on the velocity and direction. So you may experience faster speeds on a downwind run. So many things are a factor but the logic and mathematical principal of the displacement hull holds true.

Edited by - DaveR on 12/03/2009 07:31:23

PCP777
Master Marine Consultant

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USA
1225 Posts

Response Posted - 12/03/2009 : 07:56:03

I hit 6.9 on a reach in a lake, non GPS on my ray marine knot meter. I know this reading can be inaccurate but on another day, comparing it with a GPS, they were almost dead on. We had too much sail up and some large people on board which I took full advantage of in 20 to 25 knt wind. If not for the extra weight we would have been completely over powered.

Whatever it was, we were hauling ass.

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Ed Cassidy
Captain

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USA
365 Posts

Response Posted - 12/03/2009 : 09:05:17

Hull speed is actually the maximum efficient speed the boat can reach. It can go faster but it takes an excessive amount of energy. Wiki has a small article on 'Hull Speed' and it has a picture of a steam boat going three times it's hull speed. It actually gets lower in the water.

Edited by - on

andypavo
1st Mate

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USA
51 Posts

Response Posted - 12/03/2009 : 11:32:18

If I was in a hurry I wouldn't have bought a sailboat.

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PCP777
Master Marine Consultant

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USA
1225 Posts

Response Posted - 12/03/2009 : 13:15:29

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by andypavo
 If I was in a hurry I wouldn't have bought a sailboat.
<hr height="1" noshade id="quote"></blockquote id="quote">

I get that, but it's fun to get her going as fast as you can.

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Voyager
Master Marine Consultant

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USA
5352 Posts

Response Posted - 12/04/2009 : 20:19:34

With current, I made 8 knots returning on the incoming tide from Mystic to Stratford in 10 hours. Distance is 70 miles (as the crow flies), and I had two twisty rivers to traverse on either end.

I was very happy to have been able to make it back home in one day, for what would normally take 1.5 to 2 days.

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