Fish box thru hull ?
 

Just noticed the fish box thru hull (brass tube)on my 1975 18 SF is loose. There was mention in a thread a while back that there is a wooden block between the liner and the hull and I'm assuming the wood is wet . Has anyone dealt with this issue ? If the wood is indeed rotten how is it replaced ? Can expandable spray foam be substituted ? The present thru hull is a straight brass tube that is flanged on both sides, should it be replaced with a threaded thru hull fitting for a better seal ?

Not a single nibble ! come on folks help me out with this.

You talking about the box on the foredeck in front of the console?

I guess that's it, the box in the bow with the big lid that drains through a thru hull on the starboard side.

when I bought my boat the past owner told me it had sunk at the dock and suspected this throughull was the reason. so I changed it looked ok to me but when I had it out it didn't seem there was any block of wood between the hull and the well they were tight against each other

This past winter while rehabbing my 1975 18SF I replaced that brass tube with some pre-fab 1" ID FRP tubing from mcmaster-carr.
I was re-doing my transom and bought the tubing to replace the brass scupper drains.
Figured since I was already making dust I might as well replace the fish box drain as well.
Drilled out the old brass tube with a hole saw (hole-saw inside a hole-saw trick) and a forstner bit, and with a little grinding, some epoxy and some glass scraps I now have a nice watertight drain for the fish box.
Was pretty easy.
Pre-fab glass tubing - 5ft stick (way more than you'll ever need) less than $20.: http://www.mcmaster.com/#8535K26

They went to Plastic threaded around '77. A lot of stress between the outer hull & the inner liner, The brass would not give & the flare would split on you, just like the floor scuppers, yet the plastic grows weak over time and also cracks which allowed water speepage between the hulls.

I yanked my plastic one out in '05 and replaced with a SS threaded Gem thru hull with the nut in the fish box sealed with 4200

I keep a semi-yearly eye on it to ensure NO Water intrusion! Still good to go.

Inside & Outside pictures

BTW: Measure first, then cut the tube to fit. It would be difficult to trim it once in place. It will take two people. One to hold the flange outside in place while person 2 tightens the nut inside the fish box.

The depth or lenght of the brass tube thru hull on my 18 SF is 2 1/4" so I doubt the hull and the liner are thick enough to be tight against each other.

Thanks Chuck I was thinking the exact same thing with the Gem 3/4" x 6 1/4" threaded thru hul BUT was wondering if I need to re-enforce between the hull and the liner to create a solid base for screwing it tight withuot flexing the skins too much.

Thanks erebus, that would be my prefered choice IF I were redoing the hull but I would much rather not disturb or compromize the existing gellcoat on the hull.