bottom boards and lapstrake adhesive/sealant?

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  • tim in providence
    Junior Member
    • Jun 2008
    • 6

    bottom boards and lapstrake adhesive/sealant?

    so i'm building this swampscott dory from gardiner's book. it's my first real boat to be built using what i think is traditional techniques and wood. i've built two kayaks last year, but they were stitch and glue which i followed from another book. i'm basically self taught in all this, so i'm very blessed and grateful to have found this forum.

    i'm using eastern white pine for both the bottom and strakes; everyting else is white oak. i've been very fortunate to have found a supplier which carries a lot of different species of wood at a moderate price.

    i have three boards for the bottom and after joining them i place them side by side and attach the oak cleats. do i use any sort of adhesive or sealant at the seams to prevent leaking? i know the joint needs to be tight and all that but it seems that there should be something else.

    the same goes for when i start applying the strake boards, which is also eastern white pine. i'm using the lapstrake method, but it seems that there sould be something at the seams when they lap over each other.
  • Captain Blight
    Banned
    • May 2008
    • 7648

    #2
    Re: bottom boards and lapstrake adhesive/sealant?

    I hear a lot of people discussing 3M 4200 or 5200 in applications like this. Maybe rout out a groove down the mating edge of each plank so you can get a little more of the sticky goo in there to act as a spline. When i built a dory a few years ago, that's what I did with 5200. The boat mostly lives on davits at dockside in Wisconsin, and (besides being way too heavy and leaking a bit on the second strake hood end on the port side) has been leak-free on the bottom for... what... holy cats, 9 years now.

    I've been that long without a boat? Jeezums crow.

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    • Thorne
      Like my hat?
      • Aug 2005
      • 16414

      #3
      Re: bottom boards and lapstrake adhesive/sealant?

      This has been discussed here before, worth trying searching the Forum.

      Will you be putting a false bottom on the dory, or rubbing strips? Will it be stored in the water or dry-sailed?

      Personally I'd be tempted to coat all the faying surfaces with red lead primer, then glom a thin bead of Vulkem116 or 3M 4200 in the gaps in the bottom planks, ditto for the laps in the strakes.

      But trad solutions may be best, so let's see what the more experienced folks say...
      "The enemies of reason have a certain blind look."
      Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

      Comment

      • Daniel Noyes
        Banned
        • Jan 2007
        • 8532

        #4
        Re: bottom boards and lapstrake adhesive/sealant?

        congratulations on picking a dory and welcome to the forum!!

        On the North Shore of Massachusetts we put a traditional dory together with tight bottom seams and a 5 degree bevel on one side of each board just enough of an opening to calk with a single threat of cotton. a single thread of cotton set in wet primer runs around the perimeter of the bottom and up the stem as the garboard is nailed on and the laps go together dry, no caulk. red lead is fine if you want to use it. I would stay away from 5200 and other rubbery sealers as they have the ability to trap and hold water against the wood resulting in rot, you want the wood to be able to dryout/breathe
        Dan
        Last edited by Daniel Noyes; 07-09-2008, 01:18 PM. Reason: more info

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        • dmede
          Member #6948
          • Jun 2003
          • 2426

          #5
          Re: bottom boards and lapstrake adhesive/sealant?

          If I recall correctly, Gardner himself advises gluing the bottom boards together (The Dory Book).

          The gains in the planks can be bedded with sika, or 5200 (or similar), but you will want a dry fit on the rest of the lap faces. After completion what you can do to beef-up the seal is go back and score a grove along the outer lap joint (use a screwdriver and get just 1/16" grove in there) then caulk that groove and wipe smooth. It will keep your boat dry and be tons easier to reef out if you need to as opposed to the nightmare of trying to pull apart the lap if fully bedded with sika or 5200.

          Comment

          • Bob Smalser
            Member
            • Jun 2003
            • 9716

            #6
            Re: bottom boards and lapstrake adhesive/sealant?

            I'll repeat Daniel but more firmly.

            Under no circumstances glue the boards together or to the cleats with anything adhesive...especially 3M 5200. They'll be prone to cracking if you do and you'll have to destroy the boat to repair it.



            Do it exactly like The Dory Book tells you to only add caulking seams. Plane in seams that look like the picture, clamp the bottom planks together tightly with door clamps as you screw them to the cleats. Then caulk with cotton as one of the last steps before painting. Red lead alone in the faying surfaces and laps is more than sufficient. Goo in the laps is unnecessary, difficult to make neat and often becomes a mess that lasts the life of the boat.

            This way you have cotton gaskets that take up with seasonal movement and you can replace a damaged plank without unnecessary damage.

            Gardner and other traditional builders often didn't caulk dory bottoms at all, relying on the door clamps and wetting alone to swell the planks tight. I have work boats done that way but they stay submerged in the water year round, are pumped out for use, and are perpetually slimy. A trailer boat needs caulking seams or it will soon and forever will be a weeper and seeper, disconcerting your rookie passengers.
            Last edited by Bob Smalser; 07-09-2008, 09:04 PM.
            Bob

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            • dmede
              Member #6948
              • Jun 2003
              • 2426

              #7
              Re: bottom boards and lapstrake adhesive/sealant?

              I went back looked at The Dory book and Bob's right (of course) I can't find it in there. I may have been thinking of Atkin? I Know I have read one of the old masters allowing for the use of glue in laying up a trad bottom for dories. The compromise would be to use a greater number of boards I believe.

              My Harry Bryan designed Fiddlehead canoe (which is essentially a very small sit on bottom dory) uses three planks of POC for the bottom edge glued together per the designers instructions. Tight as new 2 years after completion, but she's much smaller than your dory.
              Last edited by dmede; 07-09-2008, 09:17 PM.

              Comment

              • Bob Smalser
                Member
                • Jun 2003
                • 9716

                #8
                Re: bottom boards and lapstrake adhesive/sealant?

                Originally posted by dmede
                .... I have read one of the old masters allowing for the use of glue in laying up a bottom for dories.

                ....uses three planks of POC for the bottom edge glued together per the designers instructions. Tight as new 2 years after completion.
                Dunno about your examples, but there are no shortage of professionals now and in the past who don't build with repairability and ease of maintenance in mind. It's faster and cheaper that way. But those of yesteryear weren't the designs that survived. Copy them if you like, but copy them with your eyes wide open. POC is one of the worst possible planking wood choices to glue in place.

                Again Tim....good choice and good luck. If you are concerned about your joinery not being perfect and the joints weeping, instead of goo add a length of cotton wicking on the water side of the fasteners in the joint you're concerned about. This is a typical method to apply a waterproof gasket between planks and sides in crossplanked boats, and in dories you can use wicking in the bottom-side joint and even between the laps, holding it in place with a dab of goo until it's fastened in tight. Effective and no mess.

                Spun cotton, cotton wicking and seam compounds to protect the caulking are available at Jamestown Distributors near you.





                Order of Stability in Wood Species
                Percent Shrinkage Green to Oven Dry as an Indicator of Relative Stability


                Radial Tangential (R+T)/2
                Northern White Cedar 2.2 4.9 3.5
                Honduras Mahogany 3.0 4.1 3.5
                Khaya 2.5 4.5 3.5
                Redwood, 2d Growth 2.2 4.9 3.5
                Western Red Cedar 2.4 5.0 3.7
                Eastern Red Cedar 3.1 4.7 3.9
                Atlantic White Cedar 2.9 5.4 4.1
                Eastern White Pine 2.1 6.1 4.1
                Teak 2.5 5.8 4.15
                Incense Cedar 3.3 5.2 4.25
                Alaska Yellow Cedar 2.8 6.0 4.4
                Purpleheart 3.2 6.1 4.65
                South American Cedar 4.0 6.0 5.0
                Iroko 4.0 6.0 5.0
                Sassafras 4.0 6.2 5.1
                Okoume 4.1 6.1 5.1
                Spanish Cedar 4.2 6.3 5.25
                Black Cherry 3.7 7.1 5.4
                Black Spruce 4.1 6.8 5.45
                Tamarack 3.7 7.4 5.55
                Baldcypress 3.8 6.2 5.6
                Port Orford Cedar 4.6 6.9 5.75
                Dark Red Meranti 3.8 7.9 5.85
                Black Locust 4.6 7.2 5.9
                Sitka Spruce 4.3 7.5 5.9
                Sapele 4.6 7.4 6.0
                Douglas Fir 4.8 7.6 6.2
                Longleaf Pine 5.1 7.5 6.3
                White Ash 4.9 7.8 6.35
                Black Ash 5.0 7.8 6.4
                Yellow Poplar 4.6 8.2 6.4
                Rock Elm 4.8 8.1 6.45
                Slash Pine 5.4 7.6 6.5
                Apitong 4.6 8.2 6.5
                Light Red Meranti 4.6 8.5 6.55
                Black Walnut 5.5 7.8 6.65
                Tangile 4.3 9.1 6.7
                Western Larch 4.5 9.1 6.8
                Angelique 4.6 8.2 7.0
                Ipe 6.6 8.0 7.3
                White Oak 5.3 9.1 8.0
                Live Oak 6.6 9.5 8.0
                Greenheart 8.8 9.6 9.2
                Last edited by Bob Smalser; 07-09-2008, 09:48 PM.
                Bob

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                • dmede
                  Member #6948
                  • Jun 2003
                  • 2426

                  #9
                  Re: bottom boards and lapstrake adhesive/sealant?

                  Originally posted by Bob Smalser
                  Dunno about your examples, but there are no shortage of professionals now and in the past who don't build with repairability and ease of maintenance in mind. It's faster and cheaper that way. But those of yesteryear weren't the designs that survived. Copy them if you like, but copy them with your eyes wide open. POC is one of the worst possible planking wood choices to glue in place.
                  No, I think I made the whole thing up. Can't find it in either of Gardner's books. I really thought I read him say that. I would never have put any stock in it if it were just some designer, but Gardner, Atkin, Chapelle etc get my attention. For that matter so does Harry Bryan, and he does mix methods with what I see as some success.

                  Comment

                  • Bob Smalser
                    Member
                    • Jun 2003
                    • 9716

                    #10
                    Re: bottom boards and lapstrake adhesive/sealant?

                    If anyone absolutely, positively, can't live without a solid bottom on an otherwise traditionally-built boat, then use strips.

                    Plane your pine to the specified bottom thickness then rip into square strips. Orient the strips so the qsawn sides are up and edgejoin using epoxy. Attach the cleats and saw out the bottom profile and bevels. Remove the cleats then glass both sides and the edges using 2 layers of fabric and epoxy before completing the build traditionally.

                    The more boards are in the bottom, the less uniform the grain and the less likely the bottom will crack in use. For stability in a caulked bottom, 4 boards are more stable than three, and for gluing strips are best of because you can orient the most stable grain outward to halve the seasonal movement. In turn, gluing three flatsawn boards together is a recipe for problems.

                    Plywood edges don't take screws well and even the best plywood without glass used for the bottom will have a shorter life than the rest of a traditional dory.
                    Last edited by Bob Smalser; 07-09-2008, 10:40 PM.
                    Bob

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