Cutting Holes in Fiberglass

[goboatingnow]

Originally Posted by Capt. lulz

reading this thread has brought to my curiosity how could you make these holes air-tight? For instance, if you're running a pipe or whatever it is you sailors might want to run through the hole, what could be used to keep water from coming in through the sides of the hole?

You don't , you use bulkhead fittings for that
Dave

[Capt. lulz]

Originally Posted by goboatingnow

You don't , you use bulkhead fittings for that

That makes too much sense.
thanks

[sdowney717]

it also costs too much money. I sealed a rubber hose thru a bulkhead with polyurethane caulk adhesive.

[Ian Streten]

Obviously it really depends the type of component that you are fitting into the hole,& weather it is above or below the waterline. Personally I would treat any fixture as if it was below the waterline & use the appropriate bonding agent to prevent any water ingress. Sikaflex offer quite an expansive range of bonding solutions.

[capttman]

Originally Posted by goboatingnow

You don't , you use bulkhead fittings for that
Dave

all you do is make two holes and label each one, Water in and the other water out.. easy

That may have gotten me a demerit

[minaret]

Use carbide abrasive hole saws for fiberglass. Better even than the forstner. A forstner will dull and start to stutter if cutting in thick glass. But it certainly has it's uses, especially bottoming holes and counterboring for large bolt bungs.

Tungsten Carbide Grit Hole Saw

[Capt. lulz]

in a magical land, i want to pretend my boat is as leaky as a submarine

[Blue Stocking]

I am surprised that some here support the idea of using a Forstner bit in a resin/glass laminate.
My woodwork teacher would be doing flips in his grave if he heard that said.
Forstner bit has a raised peripheral cutting edge to sever, and prevent wood fibre from tearing as it penetrates the wood fibres.
If the cutting edge of a Forstner bit grabs a layer of the laminate, when installed in a drilling machine with healthy torque, it can, and likely will, cause delamination in a surrounding lay-up.
Wrong tool for the job. Fire away

[Capt. lulz]

Originally Posted by sdowney717

it also costs too much money. I sealed a rubber hose thru a bulkhead with polyurethane caulk adhesive.

I googled it, and it seems these things are about 10 bucks or less on average.

[minaret]

Originally Posted by Blue Stocking

I am surprised that some here support the idea of using a Forstner bit in a resin/glass laminate.
My woodwork teacher would be doing flips in his grave if he heard that said.
Forstner bit has a raised peripheral cutting edge to sever, and prevent wood fibre from tearing as it penetrates the wood fibres.
If the cutting edge of a Forstner bit grabs a layer of the laminate, when installed in a drilling machine with healthy torque, it can, and likely will, cause delamination in a surrounding lay-up.
Wrong tool for the job. Fire away

I've used a forstner in glass quite a bit. As long as you keep it sharp and cut slowly and carefully it works out fine. But it's really only for special applications. Carbide holesaw works much better for most cuts in glass. You gotta try pretty hard to delam most laminates thick enough for it to be a concern. Anything up to 1/4" or so a forstner will pop right through without even heating up. After that it usually only makes sense if you have to bore a pocket hole in G-10 or something or counterbore for a bolt head.

[osirissail]

Everything on a boat moves when the boat flexes as you sail. So any bulkhead or hull holes that need to be watertight have a through hull or other fittings installed permanently and then hoses or pipes are hooked to each side or one side of the fitting.
- - In areas where watertight is not needed then caulking like marine silicon or an adhesive like T5200 can be used along with a long list of marine adhesives specific to the material that is passing through the hole or the material through which the hole is cut.
- - There are long lists of the various caulks and adhesives in the marine supply catalogs and you locate the one best suited to your application.

[sdowney717]

I googled it, and it seems these things are about 10 bucks or less on average.

wow, I must be real cheap then.

I have used Pl premium polyurethane black roof flashing caulk for this.
The stuff stays very rubbery. It is similar to 5200 but dries quicker and I dont think it is as strong of a bond but still pretty strong stuff.

For example, passed a fuel line to the generator thru a plywood bulkhead, no way I would cut that.
I passed a rubber engine exhaust hose thru the 3/4 inch plywood, just sealed it by smearing the goo on each side. I suppose they make a large flanged bronze pipe for several hundreds, about a 5 or 6 inch width hole, I would have needed 2 and then more clamps to fail. These openings are going 2 -3 feet above the bottom of the hull

[Capt. lulz]

Originally Posted by sdowney717

wow, I must be real cheap then.

I'm not concluding that. I am trying to understand your reasoning.

Maybe you are cheap, maybe I'm looking at the wrong item, maybe you prioritize your purchases differently. I wont know if you don't tell me. I'm not here to suggest my financial superiority, I am simply trying to understand the reasoning behind what you are doing so that if in the future I am to cut holes, i am making a more informed decision.

[osirissail]

Just as an example of a fitting that is water and air tight - propane lines need to be sealed where they pass from the propane locker into the interior of your boat. Here is a fitting that is mounted into the bulkhead hole and the rubber gas hose is passed through it.
- - Other such fittings are available for different kinds of wires, cables and pipes and hoses that need to pass through watertight bulkheads.