Newbie Notes- Working w/G4 (Long post)

[LouK]

Started out reasonably enough, after close inspection & finding out my thru hulls probably should have been replaced 10 years ago, I decided to replace them with new. Several hours of grinding later I found thru hulls that had been shut off w/o piping attached & I decided to fill a couple. BTW, in hindsight it’s much cheaper to simply cap them w/ a new stopcock than to seal, but very bad stewardship.

Went to Utube U, saw some ideas I liked, did a search, read the West Systems brochure, etc, etc, etc. Rather than trying to source a 4’x8’ sheet of 3/8” marine ply for a 2” dia circular plug, i went out & bought a 12” sq of G4, thinking I could use the remainer for backing plates at some point. How hard could it be?

I read you could cut it on a table saw, but all I have are expensive blades & from what I saw was that once a G4 blade, always a G4 blade. I tried to rough it out on my bandsaw and a 8tpi blade cut out a 2-1/2in square pretty easily. The stuff is tough though. Next I tried a bi-metallic hole saw in a drill press and all it did was score the surface maybe 1/64”. Strong as steel? I dunno but it is easy though to drill small dia holes.Ok, second try was to put it on my wood lathe thinking I could cut it out with a parting knife or a small gouge. Forget about that.

Note: before tackling G$ you need to gear up with NIOSH Mask & eye protection! A gouge on the lathe at 1,000 rpm could barely scratch it, it then tried to grind it with a bastard file while it was spinning- might have worked if I had a week. Next came the bench grinder & since the G4 , still mostly square was already on a mandrel, I put on a crappy old wheel and voila, this worked. In 15 min I had an almost round 2” dia disk. Back on the lathe & sanded w/40 grit to a nearly round 2” disk. At this point, I decided that 1/16” oversized was probably ok. Rather than have it be too small, I knew it would be easier to enlarge the hole than to start afresh.

Now I’ve got the plug, will abrade the face & start the infill tomorrow. FYI, for those of us who have delayed replacing old thru hulls, I did find one that had deteriorated core around it, probably explains slight leak in the engine compartment & am hoping this means my shaft seal is not the issue. Youch! Rather than trying to machine another round hole you can bet this will be a square plug. Final note: if you think a boat is a hole in the water where you throw $, just think about where you’d be if one of these suckers gave up the ghost- there is no marine bilge pump that would keep up. Praying for good patches, good sealant & no leaks!

Live & learn.