Predrilling Quesiton

[Jeff T]

I'm getting ready to install the last deck speaker. The hole has been cut and the speaker is ready to go in. I do know that I need to pre-drill the holes that are used for the screws. I aslo know that fiberglass isn't like wood...

So my question is, how big (relative to the screw size) should I drill the holes to avoid cracking in the fiberglass.

[philwsailz]

I'm getting ready to install the last deck speaker. The hole has been cut and the speaker is ready to go in. I do know that I need to pre-drill the holes that are used for the screws. I aslo know that fiberglass isn't like wood...

So my question is, how big (relative to the screw size) should I drill the holes to avoid cracking in the fiberglass.

Drill it so that your screw threads have a little bite; not too tight, not too loose.

Another thing that I learned recently. Prior to putting the screws in, take the phillips head bit in your screw gun and "counter-sink" all of the speaker screw holes a little. This will let the screw bite the fiberglass matt and resin behing the gel-coat, and NOT grab the gel-coat. This will prevent a lot, if not all cracking issues.

[spharis]

Or get a bit a little larger and spin it in reverse by hand to countersink.

[philwsailz]

Or get a bit a little larger and spin it in reverse by hand to countersink.

Perfect!

Regardless, youy don't want the screw engaging gel-coat

[Moki]

I have found that you will want to drill a little larger hole than you would with wood.

[Jeff T]

Here is another question. We have seen a lot of discussion around how to prevent the gelcoat from chipping when drilling. If the gelcoat does chip a little, is more prone to chip further over time? I'm just curious to know why, other than cosmetic reasons of course, it is a big deal to keep the gelcoat from chipping.

A perfect example is the holes required for these stereo installs. Speaker holes, speaker wire hole under tower mount, etc. None of these can be seen one the equipment is installed.

[Moki]

You can either try putting tape over the hole or drilling backwards initially to get through the Gel coat.

[da.bell]

Didn't someone say something about using a fine grit sandpaper to the edges of the hole after the cut???? Was that one here on this website or WW.... Can't remember....

[philwsailz]

Here is another question. We have seen a lot of discussion around how to prevent the gelcoat from chipping when drilling. If the gelcoat does chip a little, is more prone to chip further over time? I'm just curious to know why, other than cosmetic reasons of course, it is a big deal to keep the gelcoat from chipping.

A perfect example is the holes required for these stereo installs. Speaker holes, speaker wire hole under tower mount, etc. None of these can be seen one the equipment is installed.

From my perspective, we all have a possibility of spreading cracks once they are started. If you have ever removed your rubrail for any reason you will see that the manufacturer grinds a groove all the way around the two halves of the hull to prevent the spreading of any cracks caused by the screws they use when gluing the two halves of the boat together. This groove is hidden by the rubrail when it is installed.

I do not know this for sure, but have to believe that if we get a crack that is even hidden under something else, eventually it will spread outwards to a point it is visible.

Don't take that statement as fact, but rather an opinion, based on the fact that there is so much care taken not to crack the gel-coat.

My

[Jeff T]

I'm going to drill backwards and use masking tape. I will also use 2K grit sandpaper afterwards. I was just wondering if the reason everyone is concerned about chipping when drilling a hole is just because there will be a chip or because that chip will eventually grow/spread into something serious.

[philwsailz]

I'm going to drill backwards and use masking tape. I will also use 2K grit sandpaper afterwards. I was just wondering if the reason everyone is concerned about chipping when drilling a hole is just because there will be a chip or because that chip will eventually grow/spread into something serious.

I should call and ask my gel-coat guru..
BTW, did you get my voice msg?

[Jeff T]

I did. Thanks a ton. I was at the eye doctor when you called.

[philwsailz]

I did. Thanks a ton. I was at the eye doctor when you called.

Still looking for the black and white answer, but we will see...

'Got a message in to my custom builder buddy on the gel-coat. We ought to use all the care that we can when doing this kind of work, (I am doing an Ebbtide install tonight) but it would be nice to get an explanation from someone who hand-builds boats for a living.

I'll post up when I hear.

[spharis]

The concern when drilling is the chipping while drilling. The concern for countering is the chipping after install.

[Jeff T]

Yea, I know. I was just curious what the real reason for the fear of chipping. Just cosmetic or that the chips will continue to grow or cause cracking.