sel1 wrote:
Hi all,

I want to put on backing plates for all the stuff attached to the transom
(exhaust ports, swim platform, steering arms etc). Through continually
snugging them, the previous owner has burried a couple of nuts through the
glass! I am really new to all this but the first thing that comes to mind is
reaction between two metals. If I use stainless bolts, could I use aluminum
for backing plates or maybe I should use something else, or maybe I
shouldn't do this at all?

Still asking and not able to answer much yet.

Thanks, Steve




To do it properly takes a little time but doesn't cost a single cent
more as in;

(i) Aluminium is OK say;
(a) 1/4"
(b) Size/shape of the backing is up to you, usually the available space
will dictate the shape size etc, the rule is; if it looks right it
probably is:-)
(b) it's not under water as such so dissimilar metals shouldn't be an
issue (even with stainless you'd still need to ensure the same stainless
as the bolts say 316 vs 3xx or it corrodes anyway:-)
(c) aluminium is much easier to work & you can even drill it in situ
from the outside if you have a tricky nook or cranny.

(ii) Chamfer just the outer perimeter of the plates away from where
they'll pull against the hull, if you leave a sharp edge it can cut into
the outer glass under load & leave a crack in the flow or gelcoat for
water to get in.

(iii) You should try to seal inside all the through hull holes:
(a) particularly if it's the cored transom
(b) Coat the holes right through with any of the good epoxy fillers, then
(c) push the bolts back in while it's wet, having given the bolt a good
coat of grease first (dipped in candle wax works too).
(d) Once epoxy has gelled you should be able to get your bolts back out
with a spanner, leaving a good protection for the transom core (usually
plywood) & a good fit for the bolt.

(iv) When ready to put it all together again;
(a) use plenty of any of the good sealants, sadly price is a good
indicator so any marine recommended 3M or marine sikaflex (German?? not
sure) is OK.
(b) Clean the hull, parts, holes, bolts etc with solvent so the sealant
can adhere.
(c) Put all the bolts in & tighten the nuts (don't turn the bolts if
you can avoid it, it messes up the sealant) just tight enough to get all
the parts mated & snug, don't over tighten at this stage,
(d) get rid of excess squeezed out sealant with whatever solvent.
(e) Let the whole thing set for a while at least a day but longer is
OK, so the sealant can fully cure.
(f) Now you can tighten it all up, but again make sure someone holds
the bolts so they can't turn & you just tighten the nuts.

It'll be ticketyboo:-)


K