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Marc Donnelly
10-18-2016, 06:59 PM
Hello I will be replacing pretty long planks on my 13ft Lyman. Lapstrake Plywood hull.

My question is...
is it common to use 3M 5200 between the planks, I mean sealing the 2 beveled joints? Or simply sealing up the exterior seam? How about both?

Thanks for your feedback,

Marc

nedL
10-18-2016, 09:56 PM
Maybe 4200 or sometjing else, but I wouldn't use 5200.

skaraborgcraft
10-19-2016, 04:03 AM
Im sure some people have used it, but a polysulphide or mastic will guarentee you can take stuff apart at a future date without damage.......some say there should not be anything in the lap at all....

nedL
10-19-2016, 06:19 AM
.......some say there should not be anything in the lap at all....

correct, and in a Lyman there was nothing used when she was built.

David G
10-19-2016, 08:53 AM
For a fellow that's made a career out of doing just what you suggest, read Danenberg on restoring runabouts.

Bob Cleek
10-19-2016, 02:05 PM
Planks gotta move. If the laps are rigidly glued, the "weakest link" elsewhere is where the problems are going to occur.

Tom Lathrop
10-19-2016, 05:53 PM
Bob,

I will guess that you are having a bad day.

Bob Cleek
10-20-2016, 01:44 PM
Bob,

I will guess that you are having a bad day.

Who, me? Naw, just succinct. The mania for slathering everything with poly-goop and epoxy "to keep the water out" is really the antithesis of wooden boat construction. A properly fitted lapstrake plank needs nothing beyond a good fit. Not bedding compound. Not goop in the "outside seam." It may open up if dried out, but it will close up when wet. That's the whole point of lapstrake construction, isn't it?

nedL
10-20-2016, 03:12 PM
Who, me? Naw, just succinct. The mania for slathering everything with poly-goop and epoxy "to keep the water out" is really the antithesis of wooden boat construction. A properly fitted lapstrake plank needs nothing beyond a good fit. Not bedding compound. Not goop in the "outside seam." It may open up if dried out, but it will close up when wet. That's the whole point of lapstrake construction, isn't it?

Yep! Amen!

Eric Hvalsoe
10-20-2016, 03:28 PM
Hello I will be replacing pretty long planks on my 13ft Lyman. Lapstrake Plywood hull.

My question is...
is it common to use 3M 5200 between the planks, I mean sealing the 2 beveled joints? Or simply sealing up the exterior seam? How about both?

Thanks for your feedback,

Marc

You may find some instances, but I don't think 5200 in this application is common. Dannenburg is famous, or infamous, for seating outer skin over inner skin runabout bottom planking in 5200. His second volume touches on lapstrake and is not easy to find - maybe he also beds laps with 5200.

I don't. With cedar I will use a less aggressive product like Boatlife LifeCaulk. For new planking a modest bead down the center of the lap. More liberal in the gains and hood ends. One of the Sikas or 4200 would be a similar idea.

Many years ago I used nothing the length of the lap. Well fit traditional lapstrake plank 'taking up' is not onerous. Then again, for a little more trouble you can have a dry bilge, always. Occasionally you find an old lapstrake hull with a strand of cotton down the lap.

I've rehabbed old hulls with careful prep and a bead of Sika along the outboard seams.

You know of course, 5200 is forever.

Both planks may be beveled at the ends, but for the length of the lap, only the underside plank is beveled.

JohnPlatou
10-29-2016, 09:38 PM
I first used 3M 5200 in 2004 when redoing a complete lapstrake 1960 Cruiser Inc 16'. I removed every lapstrake, stripped and sanded, applied CPES and varnished the inside of each lapstrake. I do not understand why so my people are against 5200. The boat has been used, not a garage queen in any respect for 12 years and over 200 hours in less than ideal water. Absolutely no leaks! It has also been trailered about 10,000 miles. 5200 was applied between plants during reassembly. Did not use it as a caulk. Cruisers and Thomsons are bolted together, very easy to take apart. the old oil based sealant was weak and leaking beyond belief. Your Lyman is clinched nailed, harder to take apart, but similar.

I read before I started the rebuild, Lyman used 5200 in the mid 60's before they stopped building? No idea if it is true.

I was told it would never come apart, I took that as a good thing, if I ever have to replace a plank, I will cut it out, but so far 12 years not a issue.

I have also built 8 small 8' boats 3 Minmost 8' an hydroplane and 5 rowing prams, since 2014. Not one issue with leaks. One of them has been kept year round on my dock upside down, and used.

I am having trouble with understanding why not to use 5200?

I have also built 2 to 3 8' prams a year since 2006, as a project with ACBS in Houston, building boats with kids. The program is called KID BULLD A BOAT, we work with about 60 to 80 kids a day, each putting several screws in the boat, the project is part of the Houston Boat Show and Keels-Wheels. We use PL with building and find it is both cheap and easy to use. Messy is the only question, but with kids 15 months to 12 years old not an issue. Just keep alcohol around for clean up.

The 2M 5200 seem to go one a little easier.

Please share with me you negatives, been off the forum for a long time.

Marc, if I can help you in any way, please PM me and we can talk. John

signalcharlie
11-01-2016, 08:49 PM
https://youtu.be/GYq25xU0Gfs

Andrew2
11-02-2016, 06:38 AM
Are people missing the PLYWOOD bit in the discription? Quite different from real wood, so gluing or sealing might be OK. The edges would certainly need a couple of coats of poxy to avoid rot.
A2

nedL
11-02-2016, 06:51 AM
Are people missing the PLYWOOD bit in the discription? Quite different from real wood, so gluing or sealing might be OK. The edges would certainly need a couple of coats of poxy to avoid rot.
A2

Yes, there were builders of plywood lapstrake who used similar compounds in the laps (Chris Craft built with Thiokol in the laps), and there were those who didn't.
The edge grain doesn't necessarily need to be covered with epoxy.

Wood boats don't reLly need to be sealed with, and covered in goop to float and last.

Tom Lathrop
11-02-2016, 01:23 PM
Who, me? Naw, just succinct. The mania for slathering everything with poly-goop and epoxy "to keep the water out" is really the antithesis of wooden boat construction. A properly fitted lapstrake plank needs nothing beyond a good fit. Not bedding compound. Not goop in the "outside seam." It may open up if dried out, but it will close up when wet. That's the whole point of lapstrake construction, isn't it?

My lapstrake sailboat is EPOXY glued plywood and I do not ever expect it to need "taking up", leaking in any way or act like other than the unitized piece of structure that it is. As erster says, rivets and screws are really inviting places for rot and unsealed plywood edges are much worse. I can appreciate a finely built boat built with lumber strakes that are precisely fitted so leaking is absent or at least kept to a minimum, but for actual use in a small open sailboat with the stresses that want to twist it apart, I don't want one. I also appreciate the time and effort that the owners of such craft take to make and keep them afloat.

My first car was a 1936 ford that bought in San Francisco in 1949 and truly loved but if I had it now, it would only be driven on special occasions while I enjoy the comfortable air conditioned automatic with windshield wipers that, along with the other reliable systems actually work and that can go more than 1,000 miles between oil changes with some more oil added along the way.

Of course, Herreshoff called them "frozen snot" but being the natural engineer that he was, I expect he would see the long lived value of such boats if he were still around today. We can build and love wooden boats without being such snots about them.

BBSebens
11-02-2016, 05:10 PM
How is the rest of the boat? Your best plan is to emulate the original construction, rather than introduce a new variable.

Your Lyman is how old? 40+ years seems a safe assumption. That seems like pretty good longevity for the original method.