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Special precautions when drilling into Fiberglass?

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I want to swap out my boats Fortrex for a Terrova. I may have to drill 4 new holes. Is there anything special about drilling into fiberglass?

I read some things like, you need to champher the hole, drill backwards first, drill with a uni-bit, use masking tape over the hole before you drill it, and such things to avoid cracking the fiberglass. 

 

Are these true? Do you need to take such special precautions when drilling into fiberglass to install a TM?

 

I've watched a few videos on installing TMs and the guys appeared to just be using regular drill bits and not doing anything special. No one brought up the fiberglass potentially cracking or chipping. 

 

 

What kind of drill bit, wood, metal, other?

 
 

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Since the holes are going to be covered by the motor, you don't have to worry about having some chipping around the edge of the holes.  Putting masking tape over the spot you want to drill helps minimize the chipping and a good, sharp bit does also.   Usually, 1/2 and smaller holes don't tend to chip bad anyway.  If you are drilling from the back side into the finished side is where you get you usually get your worse chipping.

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I use masking tape and drill backwards until I'm through the gel coat. I just use a standard drill bit, and have had to use a hole saw as well. I haven't had any issues with cracking or chipping. With a tm you shouldn't have to worry about champher the hole because the only part of the bolt going through it is the straight shank so there's nothing exerting a spreading force on it. 

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Sharp bit, go slow don't push, and masking tape can help with dust/chipping and helps the bit get an initial 'grab'

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Make sure you know what is on the other side of the fiberglass, i.e. wiring, hull, etc. 

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I work in a fiberglass shop I drill and cut fiberglass for a living. If worried about chipping start small and work way up or use a uni bit. Other wise just drill the hole 

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Don't drill into the bottom of the hull.  That might be bad.  :P

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20 minutes ago, Redlinerobert said:

Don't drill into the bottom of the hull.  That might be bad.  :P

I've done that, lol.  It's not as bad as you'd imagine.  I think my gf's line was the best: "Why is the floor always sopping wet?"

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Thx guys. I went with a Brad bit and started out in reverse. Once I was through the gelcoat I went forward. Worked great. 

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As has been said.  Put a piece of masking tape on the gel coat where you want to drill the hole. 

Then, drill a small hole.  Use a countersink to enlarge the hole at the surface.  Make the surface hole just a bit larger than the finished hole will be.  Then drill your hole.  You will have a slight bevel at the top of the hole, but that is better than chips.

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