Drilling through GRP - Advice please

[Athene V30]

I need to replace a section of rubbing strake.

The teak is through bolted onto the GRP hull so mostly I intend to use the same holes. However I will need to drill a couple of new holes at each end of the new section. The GRP is about 3/4 inch thick as this is the join in the hull / deck

My last experience of drilling into GRP ended up with a snapped off drill bit embedded in the (fortunately out of site) boat. I used a battery powered drill.

What type of drill bit should I use? Is it better to use a hand drill or electric / battery? I don't want to end up with a drill bit sticking out of the rubbing stake!!

Thank you

 

[BarryH]

Drill the hole in stages starting with a small bit, then work up to the desired size in a couple of stages. Make sure the swarf is cleared from the hole to stop the bit jamming. A tip to stop the back of the grp splitting out is to use a piece of scrap wood on the back held in by an assistant. Make it large enough so you dont drill their hands though. Seal up the raw glass edges with resin or gel coat to stop water getting into the layup of the hull.

 

[Buck]

Use a "flat" wood drill bit.

Buck

The thing about men and fish is one is always trying to eat the other.

 

[Ecartar]

What size holes?

 

[oldharry]

I have just replaced the entire rubbing strake on my boat - it looks great! Drilling through GRP is not difficult, but you should use the highest available drill speed - which means using a mains drill.

As with drilling in hard or resiny timber, you must 'relieve' the drill frequently, by withdrawing it from the hole to allow the residue to clear the channels on the bit. Using high speed means it should clear itself automatically as it goes, but this is not an ideal world! Always withdraw the bit if there is the slightest sign of it binding in the hole, clear the fluted channels in the bit shank, and continue drilling.

If the material clogs the channels in the bit, it rapidly becomes so compacted that everything jams up: - then, as you discovered, the bit breaks.

Drilling pilots holes is rarely necessary in GRP up to around 10mm dia, provided the bit channels are kept clear and you are using a sharp, good quality HSS bit. Larger sizes need lower speeds, and a pilot hole serves to keep the drill aligned in the material.

 

[Athene V30]

Thanks all for the advice.

If the air turns blue in Brightlingsea next weekend you know I've got it wrong!

 

[graham]

GRP blunts drill bits quickly so buy a few top quality drill bits from a tool supplier not a DIY shop. The extra expense will save you a lot of frustration.