Fiberglass rope laid into the fillets will be much stronger than powder or even wood. You can get it from surfboard supplies places, and probably boat building suppliers like Glen-L. A boating hardware store may not carry it, but a real boat building supplier should.

While it is stronger, it may not be necessary. That will be a judgement call.

Since there is already a pair of matched up flanges, have you considered bolting it together with stainless steel fasteners? It may some day come in handy to be able to take it apart for hull repairs or some other reason. It's worth giving it some thought, although in the end, I think I'd be inclined to go with a fiberglass rope fillet.

> Fillet is how I usually see it spelled, but Fill It seems to
> be a good term, too. this is just some resin (epoxy in this case,
> please) with a thickening agent added to give it the consistency of
> putty, and keep it from ronning all over the place before it sets.
> Fine sawdust is cheap, and I have read the common household flour
> (like you bake cakes and bread with) works fine, too. Any place that
> sells fiberglass materials and resins wil have a variety to chose
> from. Since you are using a thickend resin as a bonding glue, in addition
> to a strip of fiberglass cloth on the outside, and inside, you do
> not need to worry about stuffing the voids with any other materials.
> The thickend epoxy should be fine. Of course, for a gap of 1/4 inch
> or more I'd put in som scrap wood shims, just to fill some of the
> space. The wood is a lot cheaper than the resin. Paul Jacobson