Suitable material as a filler under fibreglass

[Wotname]

Matt, I really don't want to get you to change your mind but……

Filling up that void with epoxy fillers, or ping pong balls or whatever seems awfully permanent to me. Once filled, you are never going to get the space back - at least not without a shipload of effort in removing whatever you finally put in.

Perhaps good low down space is readily available on a 42'er but I am used to smaller boats (~30') where all space is highly valuable. I can't help thinking that one day you (or even the NP) might want to use that space.

I understand your concerns about a big air gap but what about thinking of ways to mitigate these concerns rather than just filling up the space.

I am thinking that first re-seal the bottom and sides of the space with epoxy resin then putting a sealed cover over the space (as if you were making a tank in the space). Put a big sealed inspection plate in the top cover. Done well, it will be airtight and thus water tight. Nothing should ever get in there and if it somehow does, you have the big inspection hatch to deal with it.

As suggested earlier, you could fit a permanent pickup pipe (say 25mm) in it to pump out the stuff that will never get in there and really, that should only be water .

This is the lightest and probably cheapest solution and covers all you requirements except your fear of fluid penetration. It is no different than building a water or fuel tank except we want the inside to be empty rather than full.

Just my 2 cents

[GILow]

Originally Posted by Scout 30

What about the stuff that you pour into transoms after the rotten core has been removed? I haven't priced it but it looks like it would work well. Here's one brand: https://www.transomrepair.net/

I just priced it....

About five minutes ago...

I have crawled back on to my chair now.

Eeek!

Still, good to know it exists.

[GILow]

Originally Posted by Wotname

Matt, I really don't want to get you to change your mind but……
...
Just my 2 cents

All very, very valid points.

I am not (quite) silly enough to think that I won't ever want more space on a 42 footer, even a broad old truck like the Swanson 42, so I heed that point. (After all, I am now trying to figure out where to fit the micro brewery)

But the whole slimy keel tank thing really rocked me, and it has made me absolutely paranoid about creating another void.

And even if I put 100 litres of fill in this particular spot, I am only knocking out a small useable volume because of how lumpy the current keel top surface is. In practice, I am probably only limiting potential tank volume by half that amount. Any tank fitted in there now would have huge gaps underneath it.

I could turn the space into quite a good inbuilt fuel tank I suppose... but I have read a lot on that process and it seems a lot of work when I can just buy some prefabbed poly tanks and drop them in the keel. Much less efficient use of space I know, but still more volume than I can imagine every needing for fuel.

I concede that I may no longer be completely rational about this process, but if you'd spent the days I spent in that slimy hell-hole you'd probably understand my fears.

Matt

[Wotname]

Originally Posted by GILow

……...

I concede that I may no longer be completely rational about this process, but if you'd spent the days I spent in that slimy hell-hole you'd probably understand my fears.

Matt

Matey, ya got a boat and ya not sailing so ya rationality is already shot…
And I'm in the same boat