Hole in boat.

I built a 12 foot vee bottom skiff last year out of 1/4 inch luan plywood and 2x4s and she's been wonderful on local lakes. But then I started fishing in the local bayous and I found a lot of fish, and a lot of cypress knees. One of them finally holed my boat and she's been in the garage all winter. I want to repair my bottom in a way that will defeat these underwater daggers. A friend suggested sheet aluminum epoxied onto the flat sections of my bottom where the knees usually hit. Will this hold? I suppose after preparing the bottom I would slap some epoxy mixed with sawdust (pancake batter consistency) where I want to put on the aluminum sheet. Then I will put some on the aluminum and put it on the boat. Since aluminum is non-porous I ama worried it won't adhere well. Will I need to use a physical connection as well, like pop rivets, and then epoxy over those? Has anybody ever tried this, I mean adding alumnium sheet as a final ply on the bottom of a plywood stitch and glue boat?

 

Penetration resistance will not be increased with a thin sheet of aluminum on the bottom of the boat. You'd have to burden the boat with a pretty thick sheet of metal to gain any real penetration protection.

A 'glass sheath on the inside of the hull will offer much more protection for the needs you desire. 1/4" lauan is pretty weak stuff, so you're working around the limitations of the material, but an inner skin will (depending on thickness) dramatically increase the penetration resistance of the bottom.

 

original plan

Yeah that was my original plan. I have some red oak 1x4 scrap that would make a nice floor where the thin part is.

 

I'd suggest a good, solid and air-bubble-free fibreglass layup on the inside of the hull. Use a good epoxy and don't skimp on the glass. Luan/lauan/however-you-spell-it is said to form a good bond with epoxy.
I doubt a sheet-metal solution would last long- you'd get corrosion, rot and it would tend to just tear on impact, letting the boat break anyway.

 

Unless the sheet aluminum was 12 gauge or 1/8" plate, you'd not see much improvement in penetration resistance. The cost of this amount and gauge aluminum should keep you for considering it, but it needs to be on the inside to increase the puncture qualities of lauan. Matt, I don't know how to spell it either.

 

I can do this

I have very good quality epoxy and I learned during the building process how to put it down without bubbles. I had to get it from U.S. Composites because nobody in Monroe Louisiana sells epoxy or fiberglass. Question: How many layers of glass should I put down? Should I do two layers of glass in one action. Is that the right thing to do? Here's my plan: 1. Remove the paint and rough up the lauan to allow good penetration by the resin. 2. Make sure I have two sheet of glass the correct size ready to go. 3. Mix a batch of epoxy and slap down a coat of it. 4. Mix some sawdust powder in the batch and lay in some fillets in the corners. 5. Roll the glass onto the wet area. 6. Wet out the glass with epoxy. 7. Squeegee like mad to make sure there are no air bubbles. 8. Hit the cerveza.

Another question: I noticed U.S. Composites sell graphite fiber cloth in addition to glass fiber (fiberglass). Is that a lot stronger for punctures?

 

Why not use a cloth, but I do not recommend Kevlar

 

My experience with carbon-based composites is that they are very stiff and strong, but under an impact load will tend to shatter rather than give. An E-glass cloth is both stiff and strong (although not nearly as good as carbon), but will tend to flex more rather than fail suddenly. Kevlar is extremely good in tensile loading (like on the inside of the boat in an impact) and it gives and recovers very well on impact, but is not very stiff and cannot handle compression well. I would suggest you lay up both layers in one session; that way you have a good chemical bond- not just a physical bond- between the layers.

 

If anybody dropby Borneo...... Try stocking up cheap Damar..........:d

 

Interesting that nobody suggested epoxy-ing a piece of tortured 1/2" marine plywood over the bottom.

 

An extra skin of ply would add some abrasion and penetration resistance at the cost of increasing the bottom weight by + 200%.