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fosterjohn
12-18-2000, 06:11 PM
I'm a non-marine architect (but amature builder), I'm curious if anyone has used a vertical lifting centerboard on a large scale. I'm playing around with a 32'LOD Sharpie design that winches a 800lb centerboard into a interior wall. Don't worry I won't try building it without consulting a marine architect.
Thanks

Thad
12-18-2000, 06:43 PM
There is an extensive recent forum discussion "the bones of the scow Rahini" that is now on page two of the Miscellaneous pages. Therein you will find drawings and pictures of N.Z. scow schooners which apparently had just the boards of which you speak. There are books mentioned and there may still be one of these scows around so how they work the board might be accessible information. Good luck.

Ian McColgin
12-18-2000, 07:48 PM
Just don't put it in a tight CB box. You need room for it to move when you run aground at speed. Some put a bit of extra space at the forward end of the box and fill it with foam to make a sacrificial crush cushion. You'll want the CB structure to extend a bit fore and aft somewhere, either just above where it pierces the keel or just at it's top at deck level, to allow this heavey object to spread it's weight off the lifting tackle.

If you're really slick, you can design a bolt-on end plate (bolt-on since the only way to install is from above) to keep silt out of the trunk when your grounded, not to mention teasing your aerodynamical firends about tip vorticies.

G'luck

TomRobb
12-19-2000, 08:07 AM
I think I'd want the lifting mechanism to be idiot/bullet proof. The consequences of dropping an 800lb board could be unfortunate.

Tom Lathrop
12-19-2000, 09:58 AM
My largest sailboat has a 600lb centerboard. Well, it's really called a daggerboard. Works just great for its purpose but I would never design one into a strictly cruising boat. I think the structure would withstand a full drop of the keel but I'm not about to try it. It has taken the shock of a dead stop from 6kts without any major damage. The slot is fairly tight and I recommend that, rather than a loose arrangement which would allow the thing to constantly bounce around. And yes, I do occasionally worry about the lifting tackle.

For cruising, I would opt for the compromise of a keel/centerboard.

The Chinese use large daggerboards on their junks, some of them very large.

kpenokie
12-19-2000, 02:17 PM
In the plastic world a Melges 24 has a verticle lifting daggar board with 650 lbs. of keel bulb attached.

Dale Harvey
12-19-2000, 07:35 PM
All the ones I've seen have been nothing but needless trouble. Centerboards and leeboards have been around for a long time because they work.

Zane Lewis
07-30-2002, 03:53 AM
Was searching through the forum and I found this. I am working on a simalar type of design and was wondering how you are getting on. What have you decided to do for your lifting tackle?
Who's design are you working on and do you have any Pics any where.

Zane

JJoohhnn
07-30-2002, 09:53 AM
Hi;
I had a Matilda 20 sailboat for almost 20 years
and it was equipped with a 300 pound steel and lead daggerboard .
I never had any problems with it . Once a year I would grease the pullies
and the groove the daggerboard slid up and down in.
I never had to replace the cable in all those years.

The way the tackle worked was , at both top edges fo the board there was a
pulley attached. The cable was attached at the top of the case,
went down through the first pulley on the board, up through a pulley at the top of the case, down through
the second pulley in the board , then up to a pulley at the top of the case, then to a
winch with winch handle to do the pulling.
You had to hold a "deadman sort of switch while
cranking the keel up or down that would stop the winch incase you lost your grip on the handle.