Make a wood centerboard

[David S.]

I love wooden boats. At age 14 my Dad and I built Frolic from plans in Mechanics Illustrated or one of those small mags about 1950. It was a 12 ft v bottom plywood sailboat with a metal centerboard, it was a good boat and stood up to a good trade wind on the intercoastal south of Lake Worth Fla., to the Boynton Beach Inlet.
Since then I have built, to my own designs, 2 wood frame canvas covered kayaks. and a plywood 2 part nesting 16 ft schooner with 2 dagger boards hung one on each side over the 'gun'al', Phil Bolger style and each one of the 2 hulls can be sailed separate, my grandson and me have a good time with it either way, and repaired a Phil Bolger 16 ft Windsprint, its fast with 113 sq ft of lug sail.
Now to making a wood center board, I have to sheepishly admit it is for a 22 ft O'day keel/ctrbrd sailboat, yea, its fiberglass, but I got the thing free with only a few minor repairs by me and my grandson. The original ctrbrd got broke when the lifting cable let go, the board hung strait down and broke off an inch or two below the keel, not enough left to rebuild it.
It needs to be 12"x 48"x1.25" thick. The slot in the keel is 1.75 wide at the opening on the bottom of the keel and tapers slightly upwards. Is there some rule of thumb on how much clearance is needed between ctrbdr and trunk opening.
I have thought of making it out of 2 or 3 pieces of 2by with drift pins and bolts. Also you may have read lately in Woodenboat mag, the builder used 2 sheets of 3/4 plywood for his 28/29 ft cat boat. Both of those methods require a lead insert. What do you think about a full size say 3/16 thick sheet of aluminum or s.steel and wood combo together?
Looking forward to you guys comments.

David S.

[StevenBauer]

On my John Gardner skiff the centerboard is made from a layer of 1/2" plywood with a layer of 1/4" ply glued to each side. For the lead weight you cut a square hole about 10" x 10" in the 1/2" layer and just lay some squares of lead roofing flashing in the hole when you glue the sides on. Very easy, no melting lead.

Steven

[David S.]

Thanks John, good idea, what kind of glue did you use? My Dad and I used a weldwood powder mix with water, I know Glen-L sells it.
And did it have a lifting cable, if so how was it attached?

David S.

[Killick]

Here's a different method that was specified in a couple sets of plans I have. It's a bit labor intensive by makes for a pretty accurate NACA section foil.

Get a printout of a series appropriate NACA foil sections each slightly smaller than the other. With your dimensions that should work out to a 10% section I think. In my case, these came full size with the plans, but you should be able to find software to draw these for you or print one and make different sized photocopies to achieve the same result.

The aim here is to cut out these paper templates, glue them to some appropriate stock, then accurately cut them out. When you stack them, you have a stair-step representation of a tapered centerboard. Plane/sand such that one blends smoothly into the smaller one below it, lay a strip of carbon fiber down each side for strength and wrap the whole kaboodle in glass.

It's fairly laborious, but you can get a nice finished result. I did the board for my Delta V this way using some carefully chosen straight-grained WRC 2 x 4 s that I found in the deck materials section at the local big box building supply store.

[Thorne]

Sounds like you have it a bit backwards here, as the centerboard is often the least 'trad' part of many otherwise all-wooden boats -- either metal or glassed marine ply. The centerboard in my dory is the only piece of ply in the boat, and the only glass cloth used is over the lead weight and around the CB slot.

;0 )

Why not pull the exisiting piece and get the exact measurements -- that gives you the critical dimensions. You REALLY REALLY don't want the CB to swell up and stick either up or down -- don't ask me how I know this, OK? And putting wood in where glass used to be will require more space for swelling -- and CB's get dinged up so a thin layer of glass often won't protect the inner wood.

My San Juan 21 had a 'swing keel' -- a 600lb weighted centerboard -- and used a small trailer cable winch to raise and lower it. It also had a big SS pin to hold the swing keel in one of three positions -- fully up, 45 degrees down, and fully down. This was very handy for trailering and hoisting as you didn't have to rely on on the trailer winch's little locking brake.

I'd ask other O'Day 22 owners for the specs, as the weight will really impact the desired materials used in the swing keel / centerboard. If it is much lighter, just glassed marine ply will work well. But if it needs to be heavy, you may want to use a metal core with shaped and glassed ply to give it the correct NACA foil shape.

[Steve Lansdowne]

Duckworksmagazine.com has a recent article on building centerboards just as Killick described. http://www.duckworksmagazine.com/06/howto/foils/index.htm