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-   -   What does the Centerboard Do...? (http://www.sailnet.com/forums/general-discussion-sailing-related/92255-what-does-centerboard-do.html)

Squidd 09-19-2012 03:34 PM

What does the Centerboard Do...?
 
I have an AMF era Paceship, PY26 with an iron shoal keel and swingdown centerboard...

2200# of Iron Keel with a 2'7" min draft and swing down board for 5'7" draft...

I've only been sailing it for this summer, but always made sure the CB was down before the sails went up, thinking it kept me from blowing over in strong wind...not heeling, but an unexpected knockdown...

The other day I was in the islands, lunching at a dock second space in, so I had the CB up as I was sitting in less than 4' of water...when we left there was no wind, so we motored out for a bit till the wind picked up...(CB up)

When we got out in the open and there was a breeze, we put the sails up, heeled over and took off sailing...wasn't a strong wind, maybe 5-8 knots, but I noticed the boat seemed a bit faster (per gps) in said wind speed and that's when I noticed the CB was still up...

We were comfortable heeling, out in middle of lake so I didn't notice any "side drifting", and decided to continue the run with CB up to see what difference it made...

Wind never got crazy maybe a few puffs to 10k and we never felt "tippy", and seemed to do OK on most all points of sail...

So the question is...is CB only neccessary in higher winds/gusts, do I gain any actual speed (less drag) with it up, and am I giving up any/some control by sailing with it up...?

Is it neccessary all the time or is there any advantage to keeping it up...?

Irunbird 09-19-2012 03:42 PM

Re: What does the Centerboard Do...?
 
You may have been going faster, but not probably not in the direction you wanted (due to side-slipping). With board down, you'll point better (especially in progressively stiffer breeze). I would think your boat would be plenty stable with board up when you dropped her in the water, giving you time to finish rigging and raising sails, then you could drop the board when you head out. You would probably want to raise the board (at least part way) when heading down wind, especially ddw. If you ever raced, you'd definitely want board all the way down sailing to weather.

Chadfunk48 09-19-2012 03:55 PM

Re: What does the Centerboard Do...?
 
Irunburd is totally right. The centerboard doesn't do so much to keep the boat upright as it does to keep you sailing the direction intended. The board itself probably doesn't weigh all that much as compared to your ballast. If you are trying to get the most out of your centerboard design you should be changing the postion of your board evertime you chane your point of sail (see below). Of course you can just always leave it up or down if you're not really concerned with performance and just out to have fun!

•Close-hauled: board fully down
•Beam reach: board halfway to three-quarters down
•Broad reach: board one-quarter down
•Run: board fully raised

peterchech 09-19-2012 03:57 PM

Re: What does the Centerboard Do...?
 
Ditto what irunbird says. You start crabbing with the board up. Running downwind it's not an issue, and the extra drag can be safely lost by lifting the cb. Dinghy sailing 101 :) It should be progressively lower the closer you get to the wind, to fight the side slip and turn the power of the sails into velocity made good (vmg).

Most of your ballast is in your shallow keel, but I'm pretty sure that your cb has significant weight to it and keeping it down low can't hurt, esp upwind. Might want to see if there's a way to lock it down, if you are concerned about broaching/knockdowns, but unlike a catalina 22 or something, your boat doesn't seem to rely on the cb for ballast.

True dinghy or c-22 racers will post here soon I'm sure and explain how raising/loweing the cb effects the center of lateral resistance (clr) since I don't understand that as well as they probably do...

kwaltersmi 09-19-2012 04:01 PM

Re: What does the Centerboard Do...?
 
We use to sail a 25' swingkeel boat and found her relatively stable/stiff without the board down, but that boat (Helms 25) did have a very shallow (~6") keel running the length of the hull.

As mentioned above, dropping the board will allow you to sail to weather more easily without moving excessively to leeward. We put the board all the way down when sailing close hauled, about half down on a beam reach, and fully up when we were broad reaching or running downwind. Our centerboard (swingkeel) was heavy, so it also provided a good amount of ballast and therefore changed the boat's center of gravity depending on the amount it was lowered or raised. You'll just have to experiment with your board and see what she likes.

NateCP16 09-19-2012 04:06 PM

Re: What does the Centerboard Do...?
 
Some people with keel/CB designs end up removing the CB due to maintenance issues. My ComPac 23 only has a 2' keel (no CB), and it sails just fine (though it would make less leeway if it did have a CB or deeper keel).

CapnBilll 09-19-2012 04:18 PM

Re: What does the Centerboard Do...?
 
My Aquarius has lead keel in addition to Centerboard. I would like a way to lock it down. It is so light compaired to ballast it mostly just keeps boat from sideslipping on a beam or close reach.

SchockT 09-19-2012 04:55 PM

Re: What does the Centerboard Do...?
 
As others have stated, your lead keel is what provides most of your righting moment. The centerboard's primary function is to generate the lift required to sail upwind. It will certainly reduce leeway when reaching, but the big benefit is allowing you to point much higher when beating. I would not advise removing it! You don't NEED it but without it your upwind performance will suffer. Off the wind it is nothing but drag, so go ahead and retract it and you will sail faster.

CalebD 09-19-2012 05:34 PM

Re: What does the Centerboard Do...?
 
Squid,
Trust your GPS. You were going faster although not necessarily in the exact direction you were pointing. Hopefully your GPS can also show you your bearing (actual course) as this can help you know your VMG (vector made good?).
My Tartan 27 sounds very similar to your PY 26 in hull design. We have been racing her against other fin keel boats (Tartan 30, Catalina 30 etc).
For one light wind race our CB was stuck up in the slot and would not come down. We ended up winning anyway. No CB deployed = less underwater drag + a little extra leeway. In higher winds I'd speculate that with no CB you would end up with more leeway that trumped the lack of drag. In other words, there is a point of diminishing returns on keeping the CB up as the wind speed increases.
The cut in stone recommendations for deploying the CB given above are more for dinghy sailboats that only have a CB and no keel. Our boats have a keel and track well even without the CB deployed. I'd recommend that you play with different settings of the CB on different points of sail in different wind strengths.
For instance, in high winds (10 - 18) to reduce weather helm on a beat (close hauled) we can raise the CB to 1/2 way, which moves the center of lateral resistance aft. Counterintuitive perhaps but true. This website explains the sci-fi details better than I can: Helm Balance – Center of Effort, Lateral Resistance, Centerboard, Mast Rake - Waves Jordan Yacht Brokerage

PACESHIP PY26 sailboat specifications and details on sailboatdata.com

flo617 09-19-2012 05:56 PM

Re: What does the Centerboard Do...?
 
Actually the centerboard down could make broaching worse, during an accidental jibe for example. At least that's the case on a dinghy.

When broaching with the centerboard down, the centerboard prevents the boat from slipping and makes heeling even worse (that's sometimes referred to as tripping over the centerboard).

However, at the same time, the centerboard can add stability when running (downwind) as it can dampen the lateral oscillation due to the sail and the waves.

Now I'm not expert nor am I a racer but this is my experience.

On a bigger boat, with a ballast and a higher drag, I'm not sure how much the centerboard will affect the behavior but it should be along the same trends.


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