Drilling Composite

[Fleetwalker]

I just snagged a Jensen C1W on Craigslist (that's a 16' 6" downriver solo racer). It's a 1991, but it looks new. It's the heavier gel-coat layup, which is still only 45 pounds (that's spec; it feels quite a bit lighter).

It does lack a few items that are preferable for downriver racing: bow deck, spray rails, grab loops, flotation bag lacing, hip pads, and a foot brace. I went through this with a Royalex boat, so I'm not quite so edgy about drilling through the hull as I was once.

I'm wondering if there is anything special I should know about drilling through a composite hull (in this case Kevlar with a gel-coat). Is it better to drill from the inside out? Are certain types of drill bits better. The foot brace will be below the water line, so I am feeling a little nervous about that one.

[pblanc]

I have seen people recommend forstner drill bits for composite boats, but I have drilled plenty of holes in composites using nothing but standard high speed bits and I have had no problems doing so. For larger holes I would start with a smaller bit and progressively enlarge the hole.

To my recollection I have always drilled from the outside in. My guess is that going the other way could result in the gel coat chipping. If you had to go inside out, I would again start with a small bit and go progressively bigger and put a piece of tape over the gel coat where the bit is going to come through, which reduces the tendency for chipping.

[Bob P]

To avoid chipping the gel-coat, drill from the gel-coat side. Start with a small pilot hole. Hold the drill firmly, but press very gently. Control is the key, because if the drill catches, it will chip the gel-coat.
If I am going to drill many holes, I'll reduce the drill bit's draft angle to near 90 degrees so that it has less of a tendency to catch.

[JFC]

Applying blue masking tape first helps keep wood from tearing out. Has anyone tried it for gelcoat?

[JimW]

Yes masking tape can help avoid gelcoat chipping, but the tip I learned when building composite canal boats is to use a reversible drill (most battery ones are) and set it in reverse to drill through the gel coat (kind of grinds it down) and then switch to forward when you get into the fibre reinforced part. Tape and starting in reverse is a good combination. I think it is obvious that this means drilling from the gel coat side....

Ordinary jobber bits work fine, but I guess you could try bits for ceramic tiles if you wanted - jigsaw bits for ceramics work well for cutting (although any fine hacksaw blade can be used).

Word of warning, you probably won't cut the kevlar reinforcement cleanly with the bit - expect the hole to remain a bit furry and feel tighter than you expect. Glass and Carbon will be cut cleanly.

[Sir Adam]

I'm confused...

Why not just glass in what you need rather the drill and bolt? That is one of the nice things about composite boats after all:)

That said, for lacing above bags drilling as other folks have mentioned is the way to go.

[hazardharry]

i drilled and rivited some jam cleats onto a glass boat this past weekend. i used a titanium nitrite coated high speed steel bit.

[clt_capt]

Applying blue masking tape first helps keep wood from tearing out. Has anyone tried it for gelcoat?

Yes, Using blue tape works well. You can also use a countersink bit - simply reverse your drill and use the countersink bit to go through the gel coat. then switch to your drill bit.

Remember to let the drill cut - it is a drill, not a nail. if you apply lots of pressure, it will push through on the back side with less than desireable results.

[kaz]

Drill baby, drill. You guys are wacky.