Ethan wrote:
I have an aluminum Jon Boat that has some holes in it. I was wondering
if I could repair it with a strip of fiberglass. I have some left over
fiber glass and resin that I was hoping to utilize for these repairs.

Ethan

Ethan here's a paste of an answer from long ago, it's certainly a good
fix for otherwise sad alloy boats.



Paste of previous answer:

Robin,

You don't mention how old the hull is so I'm obviously guessing,
but these "long cracks" usually start appearing as the hull bottom in
general starts to lose it's integrity from corrosion. Small cracks can
usually be welded, but long runs such as you describe are caused by too
much flexing so the crack is only the symptom of a wider problem.

Obviously welding in new bottom plates, despite the extreme expense
related to an old hull can help, but doing only one side can sometimes
just aggravate the rest of the corroded bottom, so the whole thing will
need re-plating anyway.

This might not suit your situation, but even so it might still be
of general interest to resuscitate old aluminium hulls. It may (probably
will) be criticised but is regularly done here on commercially used salt
water tinnies, which can have their service life (at least until a
complete bottom re-plate) significantly extended.

(i) Have the bottom grit blasted to provide a good "keying" surface
(you'll be amased at the corrosion that was not previously apparent)

(ii) Without delay, have any sharp corners (around keel, spray guards
etc.) filled & smoothed with fibreglass filler (Q cells in polyester
resin are fine)

(iii) Then apply two layers of chopped strand mat over the entire
bottom. (again; cheap easy polyester resin works fine but if your
supplier can supply one of the slightly more "flexible" polyester resins
all the better but not absolutely necessary)

(iv) The glass covering usually finishes at the chine & if done
immediately after the grit blast & the al./glass junction is finished
over with filler it will have a good (no delamination) service life.

(v) The bottom can then be surfaced finished to the desired level,
(although in hard commercial use not too much) anti fouling, whatever..

(vi) Yes the boat is a bit heavier (but don't forget fibreglass below
the waterline, displaces half its weight) & it's not as abrasion
resistent below the water line, but it's cheap, the boat's strength is
back & no leaks.

(vii) The boat can always be re-plated further down the line, or the
glass if damaged can be repaired in the normal manner.


K