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Thread: Lightweight construction method advice

  1. #36
    Join Date
    Oct 2000
    Padanaram, MA USA

    Default Re: Lightweight construction method advice

    Particularly if built with soft plywood like okoume, Ive found glued lapstrake boats got chewed up at the laps.

    Strip composite construction can get to about the same weight as glued lap, but will take knocks better. If painted, you can beef up the outer glass where you expect bangs.
    For your use, Id start with a weight target and do a VERY detailed weight budget. Do a few test panels to estimate weight. Try to be parsimonious with epoxy. THicker coatings do not add strength.

  2. #37
    Join Date
    May 2015
    Guerilla Bay, NSW, Australia

    Default Re: Lightweight construction method advice

    Quote Originally Posted by pandelume View Post
    So I just reread the chapter in Building Classic Small Craft on the Herreshoff rowboat and the McInnis bateau. These are both boats that seem close to what I'm looking for - particularly the McInnis boat. Gardner's version has a 3/8" ply plank bottom, six 3/16" ply strakes per side, and laminated frames every 6 inches or so. Instructions call for epoxy gluing and clench nailing through the laps and frames.

    From what I understand of glued ply lapstrake construction, this is overkill. Gardner estimates ~90lbs for the finished boat, which seems on the high side.

    The original version drawn by McInnis was a multichine with 1/4" ply bottom, 3/16" sides and seam battens on the inside of the chines. According to Gardner it weighed ~60lbs. This is closer to the weight I'm looking for, although I believe Gardner's version will make a prettier boat.

    What do those with lightweight boatbuilding experience think of these methods of construction? I'm wondering whether it might work well to build Gardner's version with laminated frames and stringers - perhaps three or four - instead of the ply planking, and then skin each side with 8oz polyester. This would give a solid bottom for beaching, and seems like it should be lighter - lighter still if I use 1/4" ply instead of 3/8". I'm sure this has been done before - I recall a previous thread where someone had a SOF pram with a solid plank bottom - but I'm not sure how successful it has proven to be. Thoughts?

    Here's a photo of this boat that I found on the internet:

    Attachment 65158

    I have just built an Oughtred designed Gannet (14' 6" sailing dinghy) - it has no ribs or stringers. I can lift it at the stern with one hand. She is made from 6mm Okoume Brunyzeel plywood. Her stiffness comes from the floors, knees, breasthook, inwale and thwarts. I have gone for a narrow (100mm wide) sidedeck with a carlin which also adds stiffness but mainly this was added as I didn't want to sit on the gunwale when trying to stop capsize :-) FYI Iain Oughtred also designs several rowing boats which I'd suggest you take a look at. Good luck in your search.
    Regards Neil

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