Center board adjustment

Moderator: GreenLake

Center board adjustment

Postby GleamB » Mon Aug 24, 2020 9:58 am

I am new to sailing, and try to learn as much as I can.
I have seen instruction regarding raising the centerboard as you change direction from close haul, downwind to a broad reach.
Basically, the instruction is to lift the centerboard different amounts as you head downwind.
My question is....do Daysailer ll operate in the same manner?
How could I possibly tell the position of the CB?
Do you just leave the CB down all the time?
Thanks for any help with this.
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Re: Center board adjustment

Postby GreenLake » Mon Aug 24, 2020 5:39 pm

@GleamB

There are several reasons for adjusting the CB.

If you raise it fully (as recommended for downwind), you eliminate drag. Going downwind, there should be no large forces pushing the boat sideways and therefore a device, like a CB, that resists those sideways forces isn't needed. Therefore, any drag isn't offset by some useful contribution and the CB should be raised out of the way. There are situations while sailing downwind, such as during a gybe, where the boat may experience momentary sideways forces that can be quite strong. In those cases, having the CB raised allows the boat to slip sideways a bit in response. With the CB down, on the other hand, the boat could "trip" over the CB, turning the sideways force into heeling and possibly a capsize.

For a broad or beam reach, you would raise the CB part ways. For motoring, you might raise it almost all the way, but leaving just enough to help the boat track.

If you were sailing without the jib, you would adjust the CB for a different reason: by taking down the jib, the center of effort of the sail plan is now further back, as only the main contributes. To balance the boat (and to prevent excessive weather helm) you would want to move the CB aft as well. That's not directly possible, but if you raise it slightly, the CB starts by swinging aft, therefore giving you what you want with only a small reduction in usable area.

On a boat with a CB handle, like the DS1, these adjustments are straightforward and intuitive. On a boat that uses lines to control the CB, like the DSII, you may have try different adjustments at the dock and mark the positions on your CB line.
~ green ~ lake ~ ~
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Re: Center board adjustment

Postby tomodda » Mon Aug 24, 2020 6:47 pm

Hi Gleam!

GreenLake explained it very well. For what it's worth, I'll add that the centerboard acts very much like an airplane wing, it provides "lift" at the cost of drag. In this case, lift is upwind force, counteracting the downwind force of the sails. If you look at the entire planaform shape (side view) of the hull under water, you'll see that it looks very much like one half of an airplane - CB is the "wing", rudder is the "tail." Incredible that a little 3-foot by 1-foot "wing" is counterbalancing the entire sail rig, but it does because water is so much thicker than air. Likewise, though, the drag is so much more. Therefore, you'll want to manage the trade-off, by swinging (raising) the CB, as GreenLake outlined. Likewise you may have to swing the keel (just like a swing-wing) to counterbalance any change in forces to your sailplan, like sailing without the jib. And then, of course, sometimes you need to raise the CB because you're in skinny water! If you do it while sailing upwind, watch how much you skid off to the lee (downwind).

Overall, you don't need to adjust the CB constantly or very finely... in my typical sailing sessions (upwind as far as I can go then run downwind back home), I adjust it only 3-4 times. To one of three positions "All the Way Down", "Half Way", and "Almost all the way up (leave 6" of fin sticking out for tracking)". And let's not forget "Dammit, I ran aground and popped the CB.. push it back down, please!" With few exceptions (as outlined by GL), there's no horrible penalty for having the CB in the wrong position.. you'll go slower and probably sideways, but no big deal. You'll soon learn to "feel it".. Damn this boat is acting weird! Oh, the CB is up (or down or whatever). Life is easier with a CB handle (DS1), I can instantly see how it's set. As Gl wrote, you'll have to mark your CB line, I recommend doing it in shallow (3.5 feet) water. Hop over the side and feel where the CB is (with your foot) while someone in the boat raises/lowers is and marks the line. Again, you'll be fine with a mark for "All the way up (minus 6 inches or so for tracking)" "All the Way down" and "Middle" (I recommend different colored marker pens or waterproof tape).

Best,

Tom
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Re: Center board adjustment

Postby GleamB » Mon Aug 24, 2020 6:51 pm

Thanks for the help.
So, the CB would be fully extended when tacking upwind, and adjusted up, as you described.
So much to learn.
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Re: Center board adjustment

Postby tomodda » Mon Aug 24, 2020 7:39 pm

Yes. But don't sweat it too much while you're learning. Check out Green Lake's Sailing Basics thread.

Tom
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Re: Center board adjustment

Postby IslandFarmer » Mon Aug 31, 2020 11:17 am

Should I be able to pull the centerboard all the way up so it is flush with the hull? My boat is on a mooring and I'm learning as I clean the boat each week (swimming) that the bottom of the CB is down about 5" despite having cleated it as high as I can pull it. I'm wondering if I need to make some sort of adjustment to the pulley system in the off season. (1983 DSII is new to me as of end June.)

P.S. It's hard to find posts about controlling the centerboard because centerboard by itself isn't searchable (too common) and I was using words like "all the way up" and "control*" and "draw" not "adjustment". Fortunately I found GL's posts in the Seamanship and Boat handling section. Very cool stuff there. I will return. TY!!
1983 DSII 12250
Stonington CT
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Re: Center board adjustment

Postby GreenLake » Mon Aug 31, 2020 11:36 am

The "too common" is an annoying feature of the forum software (and one that misfires) - use google to search instead, by adding "site:forum.daysailer.org" in your search expression (without the quotes, of course and no space after the ":"). You will be pleased to see how much better the search results are --- only that you cannot search by topic title that way.
~ green ~ lake ~ ~
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Re: Center board adjustment

Postby GreenLake » Mon Aug 31, 2020 11:39 am

You should be able to do better than 5".
~ green ~ lake ~ ~
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Re: Center board adjustment

Postby IslandFarmer » Mon Aug 31, 2020 12:19 pm

Thanks, I'll try again once the boat is out of the water and I can make sure the trunk is clean. (I removed lots of marine growth in early August and have been cleaning weekly since, but only at arms reach while swimming so doing by feel - not able to see.)

Thanks also for the google search tip. It's one I use elsewhere -- hadn't thought of it for DS forum.
1983 DSII 12250
Stonington CT
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Re: Center board adjustment

Postby GreenLake » Mon Aug 31, 2020 12:33 pm

If you leave your boat in the water, you may want to paint it with anti-fouling paint below the waterline. Be sure you use the kind that tolerates periods on the trailer.
~ green ~ lake ~ ~
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Re: Center board adjustment

Postby jalmeida51 » Tue Sep 01, 2020 10:49 am

If you go the route of painting the bottom you should use multi season bottom paint also called ablative. Ablative paint wears as you use the boat so you don't have paint buildup. I try to get 2 years between bottom jobs. My boat sits on the trailer 3 to 4 months during the summer due to the heat, storms, and not much wind here in S.W. Florida. Other than that it's at a dock. About 3 or 4 months I pull the boat and wash off the slime.

Talk to other sailors in your area and ask them on what bottom paint they use because a paint that gives good protection in warm waters might not do a good job in cold waters. Bottom paint has a wide range of prices. The major manufactures are Pettit, Interlux, Sea Hawk, West Marine.
Happy Sailing, John
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