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View Full Version : replacing planks on a dry boat need help



JLM
03-24-2002, 06:12 PM
i'm going to be replacing a couple of planks on the bottom of my boat thats been out of the water for 6 to 7 years. she is lapstrake mahog on oak frames my ? is if i seal the new boards with 3m 5200 (acually the whole bottom )will she pull apart when she swells.i'v done 1 already but am concerned. thanks for the info.

windfall
03-24-2002, 06:33 PM
Most boats are built with lumber at 12%, which then gets wet when launched. Don't worry too much abou the swelling especiaslly on a lapstrake

nedL
03-25-2002, 08:29 AM
JML, Who built her, when was she built & how long is she? Some lapstake boats were originally built with the laps pretty much glued together. Chris Craft sea skiffs were built with the laps sealed with (I believe) thiocol(sp). Chris Crafts however were all plywood planked. I suspect that your boat (being solid lumber planks) never had the seams glued, and would recommend following suite. Plywood is much more stable dimensionally as it dries out & then swells so there isn't much seam movement through the cycles. Solid planking will want to be able to move as it dries & then swells. If your boat was built on the New Jersey shore (where most of the lapstrake boats on the east coast were built), the seams were never meant to be glued.

Alan D. Hyde
03-25-2002, 01:07 PM
The Chris-Craft Sea Skiffs were built in Salisbury, Maryland out of fir marine plywood strakes, screwed to the white oak ribs and riveted to each other. Thiokol (3M 5200) was used as a sealant and adhesive between strakes. It makes their hulls incredibly strong.

As to whether or not this approach would work well with solid wood strakes, I don't know. Here is a question where the results of an experiment might be informative.

Has anyone here ever tried 5200 on natural wood strakes?

Alan

Noah
03-25-2002, 04:09 PM
As you all know, I have a lapstrake Folkboat with very temperamental planks. IE they dry and swell at a remarkable rate.
In observing what is going on, I would have to say that glue between the planks wouldn't be a bad thing. I say this because in general with a well clenched riveted lapstrake hull, the plank to plank seam is stronger than the wood. On my larch planked boat, all the planks split in the middle because they were fastened on either edge. I don't think that glue in the seam would change the way the wood moved, and it would give it more strenght to boot.

On a more healthy boat, I'm not sure how this would affect it. I have seen some movement in the planking on my Whitehall (lapstrake) and the joint overlap changes with moisture content. It takes about 4 hours of constant wet for the boat to swell up in the spring. The difference is that this boat is very lightly built.

I think that part of each persons profile should include the boat that they own or are asking questions about. This would cut down on the amount of cunfusion on this board.

What type of boat is it, when was it built, and what condition is it in apart from being out of the water for 5-6 years?

Noah

JLM
03-26-2002, 05:58 PM
NOAH & NedL the boat is a 1970 34' pembroke built in suncook NH By pembroke inc. a total of about 1500 boats were built. it is built using solid mahogany bolted with bronze nut& boltsno rivits and it does have some kind of sealer but i did not know if it was the previous owner who put it there.as for the condition the hull for the most part looks in good shape no wide gaps no rot (except by the transom above the waterline)i just have about 3 or 4 split planks.thanks JLM
noah take a look www.imagestation.com (http://www.imagestation.com/album/?id=4291958749)

nedL
03-27-2002, 08:17 AM
JML, I saw your pictures on your other post a couple of days ago, quite a project. it looks like you are making good headway. I am guessing that all your new planking will be back by the new transom (mostly in the obvious spots ;) ). I see no problem in going either way here, put the new planks in dry or with a bedding compound if you wish. I do think I would stay away from 3M5200 though (it is such a tenacious adhesive that it me make additional future work more difficult). I would comment that when you get to planking you should work in a nice butt schedule & keep all the new planks long enough so that when finished it doesn't look like a repair job.(No one will ever know then).

[ 03-27-2002, 08:24 AM: Message edited by: nedL ]