A25 electric bilge pump discharge location

[Desertboater]

Another way to make a backing plate is to use GPO-3 polyester/fiberglass or G-10 epoxy/fiberglass sheet as described in the Compass Marine tutorial on thru hull replacement.

https://pbase.com/mainecruising/replacing_thruhulls
https://pbase.com/mainecruising/backing_blocks

The following is a quote from his tutorial:

Quote

I bought a pre-made fiberglass/epoxy sheet from McMaster-Carr. If you go to their website and search for GPO3 (that's the letter O, not zero) you'll find in in various sheet thickness and sizes. A 12 X 12 X 3/4 sheet was around 30 bucks. Shipping was cheap, around $7. Don't bother with next-day shipping, they have warehouses around the country, so standard shipping only takes 2 days in most cases.

You will need at least a 5.5 to 6.5 inch hole saw and a very large and powerful drill.
The friction of the six inch hole saw, on the fiberglass hole, is tremendous and can and will kill a wimpy drill. I use my drill press for this but a large and powerful 1/2 inch drill from the likes of Milwaukee, Porter Cable or DeWalt is a must. Home Depot will rent you large drills and I advise this if you don't have a drill that is up to the task.
Trust me you will kill a Black and Decker or Ryobi before you even make it half way through your first hole!
One word of advice on drilling these backing plates is "CLAMPS". By this I mean always clamp your work down before you begin drilling or you'll have a giant spinning fiberglass saw on your hands..!
Circular fiberglass backing plates are certainly the best looking but tough on the hole saws and too much for cheap drill motors.

Later comment: I then had a local granite countertop shop use their waterjet machine to cut an assortment of backing plates to match my new seacocks and struts, as well as an irregularly-shaped backing plate for my underwater exhaust. Hiring the cutting means no fiberglass dust, dull saw blades, or burned fiberglass.

Unquote

We followed this method in making backing plates when replacing all the thru hulls on the boat. They were all replaced due to lack of faith in the thru hulls due to the presence of galvanized iron fittings on several thru hulls, such as the capped toilet discharge under the deck of the head.

[nebulatech]

Nice work Desertboater!

Thank you for the articles. I didn't know about GPO3, and when I checked McMaster-Carr for G10, it was pricey, so I made my own block. Rereading the article prompted me to rethink my rectangular backing block, and I'm glad I did. I didn't realize why round backing blocks are preferred on fiberglass, nor did I realize the edges should be tapered. I still have time to modify my block as I'm waiting for some new colloidal silica. Thank you again!

I did install the thru hull for my forward bilge pump. Tested and working well. Pictures promised soon.

[tribologist]

I was amazed at how easily my drain plug came out. Take your time to remove the 84 layers of bottom paint. I long lamented that I didn’t have a bilge plug, only a slight bump in the bottom paint. When I stripped the bottom to gel coat while prepping for paint a couple years back, lo and behold! Faith and begorrah!

Clean the screwdriver slot to full depth. Get a bigazz screwdriver to fit. Squirt your preferred corrosion buster on it and let it work. You may be pleasantly surprised

And, Stephan at Albinmotor still has replacement plugs. I use pipe dope on the threads and have no issues removing it every year.

No exaggerations please... At most there should be about 50 coats...

[WillieC]

Well, excu-u-u-use me! (Credit Steve Martin) HA!