Fiberglassing Lapstrake - Advice needed

Discussion in 'Fiberglass and Composite Boat Building' started by Wesley2022, Jun 13, 2022.

  1. Wesley2022
    Joined: Jun 2022
    Posts: 3
    Likes: 1, Points: 3
    Location: Quebec

    Wesley2022 New Member

    Hi all,

    Started an 18 foot pulling boat (Ken Basset’s LIZ) a few years ago, but had to shelve it for a spell. Finally in a place where I can get back to her, but had some questions about hull reinforcement I wouldn’t mind some feedback on.

    The construction is glued lapstrake with Sapele marine plywood. Originally, I planned to use 6mm ply, but another builder recommended 4mm ply due to the extreme curves where the keel meets the transom. I chose to use 4mm ply for the first 4 planks and 6mm for the last 3. A little strange I know, but the thinner ply managed to (barely!) handle the curves near the transom, and the thicker adds a touch of much needed rigidity near the gunnels. I will be adding ribs to the inside of the hull to stiffen it up once it’s off the hardback, but even with that I’m worried the 4mm ply will be too delicate. Instead of an actual keel, I plan to glass the keelson and first plank of the boat in order to keep the weight down.

    Now I have a few ideas about how to further reinforce the hull, but I’ve never applied glass before, so I am not sure how feasible they are.

    1. Would glassing all the 4mm planks be an option? I’ve heard that the cloth would have trouble following the sharp angles of the laps. If so, would fileting the laps first ‘dull’ them sufficiently to take the cloth? What radius of epoxy filet would you recommend? Could ‘dulling’ the laps in this way negatively affect the performance of the boat in the water in some way I'm not anticipating?

    2. If filleting the edges wouldn’t work, could the cloth be applied plank by plank? Again, new to fiberglass cloth so not sure if this would be a colossal pain in the neck or even possible.

    3. Would glassing the inside of the boat instead be a better option? The inside would not have the sharp edges of the laps to deal with.

    4. Is there any issue with just glassing one side of the boat?

    I’ll try to attach photos to clarify things a bit along with a shot of the end result I am looking for (not my build!)

    Any suggestions or feedback is appreciated!

    stem and hull.JPG final3.jpg transom and plank thickness.JPG
     
  2. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    How do you plan to use the boat?

    For normal use of an elegant pulling boat the combination of 4mm and 6mm planks with the internal ribs should be more than sufficient. Remember that the laps add a lot of stiffness.

    Glassing the bottom and garboards (lowest planks) would help with abrasion resistance. Otherwise I wouldn't do any glassing.

    Attempting to glass a lapstrake boat is likely to ruin a nice boat.
     
  3. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    I agree with every word of this,but if the owner is a large and heavy fellow it might be necessary to distribute the loads from his feet.Are bottom boards a part of the plan?
     
  4. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    Bottom boards / sole boards would be a good idea in general.
     
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Just glass two layers 6 oz to each of the 4 mm panels with epoxy, no fillets, weave fill like 2-3 times..invisible protection
     
  6. Wesley2022
    Joined: Jun 2022
    Posts: 3
    Likes: 1, Points: 3
    Location: Quebec

    Wesley2022 New Member

    Thanks David, the initial plan was to use it as an elegant pulling boat, and I was assuming that 4mm would be enough, but the amount of flex in the hull had me second guessing when I moved the hull to the new workspace. I'm thinking I'll stick to the original plan and just glass the garboards and bottom, put the ribs in, then re-evaluate. the bottom boards are good suggestion that I hadn't thought of (though I'm not a large or heavy fellow - part of the reason I thought I could get away with 4mm). Thanks again for the feedback, this is a little more delicate than most of my projects!
     

  7. Wesley2022
    Joined: Jun 2022
    Posts: 3
    Likes: 1, Points: 3
    Location: Quebec

    Wesley2022 New Member

    I might go this way if it still feels flimsy after the ribs go in, thanks!
     
    fallguy likes this.
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