Association Forum - 2-3 Knots with Keel Up

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

Catalina 25 Specific Forum

2-3 Knots with Keel Up

New Topic

Topic Locked

Printer Friendly

Author

Topic

sethp001
Mainsheet C-25 Tech Editor

Member Avatar

814 Posts

Initially Posted - 07/26/2012 : 11:46:08

A couple of weekends ago, we were on a run in light winds, and I tried lifting the keel to see if there was any difference. I was surprised when we got an extra 2-3 knots.

Unfortunately, I haven't install the keel spacers yet and the keel banged back and forth so loudly that I put it back down.

Do any of you regularly raise your swing keels on runs and find this type of speed improvement?

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

Edited by - on

Chris Z
Captain

Members Avatar

452 Posts

Response Posted - 07/26/2012 : 12:10:36

I am not sure I would want to raise my keel unless I ran into shallow water or launching. The issue is that unplanned things happen when sailing and if you were forced to turn up wind quickly you would be in quite a spot without the keel down.

I don't think they ever intended for the swing keel to be up when sailing.

Edited by - on

Steve Milby
Past Commodore

Members Avatar

USA
5909 Posts

Response Posted - 07/26/2012 : 13:18:26

The only way raising the keel could have made a difference of 2-3 kts in boatspeed would be if some weeds or a crab pot had been caught on the keel, and they fell off when you raised it.

Edited by - on

pastmember
Master Marine Consultant

Members Avatar

2402 Posts

Response Posted - 07/26/2012 : 14:07:20

What Steve said. Another problem with the goal to increase speed down wind by raising the keel is down wind is when you get quartering waves and raising the keel would exacerbate the "roll" that can accompany a quartering wave. You can help yourself a lot more by fairing the keel and leaving it down.

Edited by - on

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9089 Posts

Response Posted - 07/26/2012 : 15:24:24

The wetted surface may not be less, but the area of the forward-facing surface of the keel, which creates the most drag, will be some fraction of that of the lowered keel--possibly decreased further by the release of a big blob of seaweed.

In any case, I suspect the boat was designed to have the keel down whenever the sails are up, just as the C-250 WB must have the ballast tank full when the sails are up. Doing otherwise creates the possibility of a situation like that of the Silverton on the 4th of July. That skipper can attest to the difficulty of explaining things after the tragedy. ("Your Honor, I was just seeing if I could get another knot out of her...")

Edited by - Stinkpotter on 07/26/2012 15:26:34

PCP777
Master Marine Consultant

Members Avatar

USA
1225 Posts

Response Posted - 07/26/2012 : 15:48:09

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 The only way raising the keel could have made a difference of 2-3 kts in boatspeed would be if some weeds or a crab pot had been caught on the keel, and they fell off when you raised it.

I suspect you caught a wind puff at the same time you raised the keel. When sailing downwind, you might not have felt the presence of the puff.

We have discussed this before, and, while some think raising the keel increases speed, even the "believers" only claim a fraction of a kt increase.

IMO, nobody has ever made out a very good case for why it makes a difference. Raising the keel on a C25 doesn't reduce wetted surface. The keel doesn't retract into a keel well, or lift out of the water like a daggerboard. It just rotates up against the bottom of the boat, so that you are dragging the same amount of surface area through the water as when it is down. Instead of presenting the foil-shaped edge of the keel to the water flow, you are presenting the blunt end of the keel to the water flow. Raising the keel moves the center of gravity aft somewhat, but I don't see how sailing stern-down makes the boat faster. You'll get both sides of the argument here, but you're not likely to get a definitive answer. There is disagreement here, with some of the best sailors on both sides of the issue.
<hr height="1" noshade id="quote"></blockquote id="quote">

This was interesting. I crewed on a S2 7.9 and we always hauled up the dagger board down wind when flying the spin but alas, as you've pointed out, it is a dagger board. (And a true PIA to winch up!) Small boats with a centerboard complete with centerboard trunk so that the centerboard goes all the way up into the hull also can take advantage of this.

What you have said about the swing keel makes sense.

I really don't know how much more speed we got out of lifting the dagger board on the S2 either. Not 2 to 3 knots for sure.

Edited by - on

Dave5041
Former Mainsheet Editor

Members Avatar

USA
3758 Posts

Response Posted - 07/26/2012 : 19:40:24

I gave this some thought but never got around to testing it since I think it adds significant risk as noted. Most of what I balanced has already been mentioned. Positive effects: slight reduction of keel surface in the water stream since some is shrouded in the slot, major reduction of frontal area, shifting the CG aft would help get on a plane (joke, please) Negative effect: turbulent flow caused by the slot runs the full length of the keel and causes a major increase in surface drag. I could see it adding a very small advantage in light winds and speeds below the threshold of turbulence, but who knows. Potentially a lot to lose and very little to gain.

Edited by - on

Derek Crawford
Master Marine Consultant

Members Avatar

USA
3323 Posts

Response Posted - 07/27/2012 : 08:32:03

On our old C22 we raised the keel about 2/3rds of the way and the speed actually increased by 1/2 a knot. I can't explain it, just know it worked.

Edited by - on

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9089 Posts

Response Posted - 07/27/2012 : 09:42:00

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Derek Crawford
 On our old C22 we raised the keel about 2/3rds of the way and the speed actually increased by 1/2 a knot. I can't explain it, just know it worked.<hr height="1" noshade id="quote"></blockquote id="quote">Downwind, up, or both? Maybe she liked the weight shifted aft. Maybe it's like sweeping an airplane's wings back. (The speed is lower, but the fluid is thicker.)

Edited by - on

jerlim
Master Marine Consultant

Members Avatar

USA
1484 Posts

Response Posted - 07/30/2012 : 16:42:38

FWIW...I'm w/ Chris 110%...

Edited by - on

GaryB
Master Marine Consultant

Members Avatar

USA
4316 Posts

Response Posted - 07/30/2012 : 20:54:48

Maybe the keel closing up some of the keel slot reduces some of the turbulence and drag created by the opening?

Edited by - on

Derek Crawford
Master Marine Consultant

Members Avatar

USA
3323 Posts

Response Posted - 07/31/2012 : 08:52:10

Dave - we only raised it going downwind. I'd hate to go to weather with it down!

Edited by - on

Stinkpotter
Master Marine Consultant

Members Avatar

Djibouti
9089 Posts

Response Posted - 08/01/2012 : 08:26:24

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I'd hate to go to weather with it down!<hr height="1" noshade id="quote"></blockquote id="quote">
Maybe that's why you mixed up the "Side UP" on that boat... ?

(Inside joke.)

Edited by - Stinkpotter on 08/01/2012 08:29:41

Derek Crawford
Master Marine Consultant

Members Avatar

USA
3323 Posts

Response Posted - 08/01/2012 : 08:58:23

That was an "oops"...

Edited by - on

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.