Fiberglassing Lapstrake - reinforcing the hull

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Wesley2022
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Fiberglassing Lapstrake - reinforcing the hull

Post by Wesley2022 »

Hi all,

I 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

Any suggestions or feedback is appreciated!
Attachments
stem and hull 1.jpg
transom and plank thickness.JPG

Fuzz
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Re: Fiberglassing Lapstrake - reinforcing the hull

Post by Fuzz »

If you fillet the laps you can get light cloth to go over the laps...................BUT you might lose the lap look doing it. And getting the glass on smooth might be a challenge even for an experienced glass guy. You could glass one plank at a time on the outside and then glue them in place. I say that but I have never done it so take it for what it is worth :D

OneWayTraffic
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Re: Fiberglassing Lapstrake - reinforcing the hull

Post by OneWayTraffic »

An option would be to fillet and glass the inside only. Or light glass on both sides, just go over the overlaps and then cut out the bubbles on the joins. Fair and paint. But if appearances matter and you want it bright, I'd just leave it epoxy coated.

fallguy1000
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Re: Fiberglassing Lapstrake - reinforcing the hull

Post by fallguy1000 »

4mm is too weak. For sure!

What is the goal of lapstrake below the waterline?

Glassing one side results in adding some strength, but under impact, the glass will expand, the ply will crack.

I'd probably add another piece of 4mm plywood...how, nearly impossible even with vac, but that is how my 1960 Carver was built.

I'd probably lose the lapstrake where the 4mm is, fillet for glass and put some 1708 down there and paint it.

if you want to keep the look, you'll want to piece in two layers of 6 oz glass over each of the 4mm laps
My boat build is here -------->

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