Advice on Rabbet in Marine Plywood... - Router Forums
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post #1 of 16 (permalink) Old 05-10-2014, 06:37 AM Thread Starter
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Default Advice on Rabbet in Marine Plywood...

We are replacing some of the bottom on a flat-bottom wooden boat at our yacht club. It was suggested that I rabbet the ends of the existing 3/4" marine ply to join the new section. The new section, 42" long, will be 2 pieces of 3/8" marine ply as it needs to bend around the bow (tough to bend a 3/4" section). The intent being one of the 3/8" would butt against one part of the 3/4 and the second top piece of 3/8" would overlap to the inner part of the rabbet.

I'm thinking I will rabbet about 1 1/2", 13/32's deep, into the 3/4" to allow for screws and glue/silicon. My approach would be to rabbet about 1/4" at a time by moving the clamped guide till I get to 1 1/2".

The two 3/8's will be glued together by laying the first piece and then bending the second 1 1/2" longer piece over that and the rabbet. I'm thinking Titebond III for the two 3/8's and caulking for the rabbet'ed section. Router is the Rigid handheld and am thinking 1/2" straight bit nice and slow...

...and yes, the end of the 3/4 to be rabbeted is a slightly delaminated (maybe about 1/4" into the board).

Have I learned anything from you guys or shall I modify my approach...?

Thanks in advance...Nick

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Last edited by Nickp; 05-10-2014 at 06:40 AM.
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post #2 of 16 (permalink) Old 05-10-2014, 07:30 AM
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I would never use a water resistant glue on a boat, I would use a water proof glue approved for use below the water line like an epoxy or fiberglass resin or possibly a polyurethane. Another member who was more versed in boats than I suggested a sulfonyl caulk. It too is approved for use below the water line. Can't remember the full name of it now but a boat supplies shop would know it. I wouldn't use silicon.
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post #3 of 16 (permalink) Old 05-10-2014, 09:14 AM
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Interesting. Personally, I would not rabbet the plywood, instead I would use 1/2" X 1/2" glue strips - which would basically accomplish the same results.

IF the boat was taken out of the water after every use - lives on a trailer perhaps - then I would quite possibly use water resistant glue. HOWEVER, if the boat lives in the water, water resistant is unlikely to cut it - unless covered with fiberglass sheathing, and epoxy.

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post #4 of 16 (permalink) Old 05-10-2014, 04:12 PM Thread Starter
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Originally Posted by Cherryville Chuck View Post
I would never use a water resistant glue on a boat, I would use a water proof glue approved for use below the water line like an epoxy or fiberglass resin or possibly a polyurethane. Another member who was more versed in boats than I suggested a sulfonyl caulk. It too is approved for use below the water line. Can't remember the full name of it now but a boat supplies shop would know it. I wouldn't use silicon.
Good point, Charles. Intending to use 3M 4200 sealant at the seams but not between the 3/8's...guess I should re-think that. Reason behind the Titebond was to keep the cost down...I suspect, in the long run, we should use something better. Thanks for the nudge...

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post #5 of 16 (permalink) Old 05-10-2014, 04:16 PM Thread Starter
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Interesting. Personally, I would not rabbet the plywood, instead I would use 1/2" X 1/2" glue strips - which would basically accomplish the same results.

IF the boat was taken out of the water after every use - lives on a trailer perhaps - then I would quite possibly use water resistant glue. HOWEVER, if the boat lives in the water, water resistant is unlikely to cut it - unless covered with fiberglass sheathing, and epoxy.
Thanks, Theo...boat is staying in the water. I guess so far the Titebond is out...

On your other point...I don't understand the application of 1/2 x 1/2 glue strips. Can you elaborate ? Thanks

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post #6 of 16 (permalink) Old 05-10-2014, 06:33 PM
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I would use WEST Epoxy..

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post #7 of 16 (permalink) Old 05-10-2014, 06:35 PM
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I would use WEST Epoxy..
anther vote for West Systems...

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post #8 of 16 (permalink) Old 05-10-2014, 07:00 PM
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On your other point...I don't understand the application of 1/2 x 1/2 glue strips. Can you elaborate ? Thanks
What they are is reinforcing strips. I've been using them for so long pretty much forgot how to explain them. This will probably be a better example then I could give. Sometimes I use short blocks, sometimes long strips. They really increase strength in a joint, and I seldom, if ever, use nails.
http://www.diynetwork.com/how-to/how...int/index.html

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post #9 of 16 (permalink) Old 05-10-2014, 07:56 PM
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The standard against which all others are compared, for waterproofness, is resorcinal.
Whether you can find it is another story.
Resorcinol Marine Glue
If you're concerned about toxicity, keep in mind that epoxy is highly carcinogenic as well. Whatever you use just be sensible about protecting yourself from both skin contact and vapours. We don't want to lose members that way...
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post #10 of 16 (permalink) Old 05-10-2014, 10:28 PM
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Living on the Sunshine Coast, you probably have a much better handle on that sort of thing than I do Dan. I will say that I have used autobody fiberglass resin as glue on an occasion or two and it has excellent holding power as well as unsurpassed gap filling capability but I wasn't using it for anything that would be submerged.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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