Drilling hole through cored hole - how do I seal it?

ZZ13

ZZ13

Well-Known Member
Nov 25, 2009
5,325
Lady's Island, SC
Boat Info
2001 400 Sedan Bridge
Engines
Cummins 450 Diamond
Soon I'll be drilling a 1 1/2" diameter hole through the side of the hull to install a direct drain from the galley sink. It's a cored section of the hull and I want to seal the coring off from the outside world after I drill the hole. What is the technique for this? Should I gouge out a certain depth of it to make space for the epoxy? Should I use a flowing epoxy or can I use something like Water Weld? If flowing, how do I get it to flow "uphill" for the top of the hole? Questions like that are running through my mind.
 
Drill the hole to1 3/4 to 2 inches. . Cut the coring out by bending a headless nail 90* roughly 1/4-1/2 inch out at the bend. Use that 1/4-1/2 inch to remove the core. Fill the void between the inner and outer skins with SikaFlex or a glas/resin mix. Make a new hull wall. Drill a new hole to proper size. Install the through hull (bronze or stainless) with lots of 3000. Tighten. Double clamp. Go boat. Yes it's overkill. Yes it works for a long time.
 
7168E57D-EA72-47E8-BABD-5FE0AFD22DB1.jpeg
I installed led lights below the waterline/swim platform and wonder if I should reseal the holes with the epoxy method.

For each light I drilled (2) 3/32 holes, filled them with 4200, then coated the screws with 4200 and mounted the lights. On the inside of the hull since I drilled in a thinner part of the transom for two of the hoes I see the 4200 has come through to the bilge.

Above the waterline Ill use a waterproof clamp for the wires which will have to be a larger hole. Not done yet.
 
dpmulvey said:
Drill the hole to1 3/4 to 2 inches. . Cut the coring out by bending a headless nail 90* roughly 1/4-1/2 inch out at the bend. Use that 1/4-1/2 inch to remove the core. Fill the void between the inner and outer skins with SikaFlex or a glas/resin mix. Make a new hull wall. Drill a new hole to proper size. Install the through hull (bronze or stainless) with lots of 3000. Tighten. Double clamp. Go boat. Yes it's overkill. Yes it works for a long time.
Click to expand...

Same as above, but.... Instead of sikaflex or glass/resin, buy the larger cans of marine epoxy resin and also cabosil (Cab O Sil) powder thickening agent. Then you would first mix a small amount of epoxy without cabosil and paint the open exposed core with epoxy and let it kick off and semi harden. Then mix a batch and add cabosil powder until it is thick enough to spread like peanut butter or a bit thicker, and fill in the hole sides so its full and as smooth as you want it to be. Clean off excess and let it harden. that will never leak and will be more solid than using sikaflex. also easier to handle and mix than chopped glass/resin
 
This video is the correct method and what I use for all thru-hull penetrations that have coring.
The only thing I do differently is apply masking tape over the surfaces around the hole then temporarily install the thru-hole fitting assembly. Then, cut the tape around the perimeter of the thru-hole fitting, remove the thru-hole assembly then remove the tape which is under the fitting. This will make the cleanup of the 5200 or 4200 (whatever you use) much easier.
 
I don’t mind doing the work, but it’s for a 3/16 screw, not coring.
 
The transom on a 310DA is cored with plywood. Which will rot if the screws leak. Repairing a rotted transom will require removing both engines, both transom assemblies, removing the exterior transom skin, then replacing the wood which runs all the way across the transom, re-glassing the exterior skin, re-gelcoating and fairing the transom where the exterior skin was cut and bottom painting....all in all, a very expensive repair.

I would think twice about installing lights below the waterline, but if you must, then think twice about not bothering to seal the core before running screws into it from the outside.
 
You must log in or register to reply here.

Forum statistics

Threads
113,117
Messages
1,426,460
Members
61,033
Latest member
SeaMonster8
Back
Top