Screw right into the fiberglass/getcoat?!?

[imported_JLowe]

Being new to boating, boat body material is a new media for me to play with. I'm preparing myself to install the mounting hardware for a bimini top and just wanted to make sure it is as straight fwd as it sounds/looks.

So when I get ready to mount these on the boat, I simply drill the appropriate size hole into the outer shell/coating? There is no wood or solid material underneath to screw into, right? Then screw in with the correct type of screw (sheet metal?). That's it? No getting screws long enough to reach some thicker, more solid underlying material? The fiberglass hull material is strong enough to hold? No back bracing, reinforcing, or anything like that?

I'd hate to punch little holes in the top of the boat if there is something I'm missing. Thanks!

 

[tommays]

Re: Screw right into the fiberglass/getcoat?!?

In general its a good idea to be sure what your drilling into there are cables and wires that are secured under most boats in that area

you need to use stainless screws or it will become a mess

The glass has a good amount of holding power IF you use the right size pilot drill for the screw size


Other things like a cleat that would put a lot more stress than a bimini top would require through bolts and backing plates to make it strong enough

Tommays

 

[KaGee]

Re: Screw right into the fiberglass/getcoat?!?

It's also wise to slightly countersink the holes slightly before screwing to prevent chipping and cracking of the gelcoat.

Also wise to dip the screws in a silicone or 3M 42/5200 to illiminate the possibility of water weepage.

 

[lakelivin]

Re: Screw right into the fiberglass/getcoat?!?

...
The glass has a good amount of holding power IF you use the right size pilot drill for the screw size

Tommays

Any guidelines you could post as to the correct size bit for pilot holes in gelcoat (e.g., screw size minus X)?

Does X change as screws get bigger? If so, would it be possible to post a little table?

e.g. For screw sizes a to b, use drill bit size same as screw size minus X. For screw sizes c to d, use drill bit size same as screw size minus Y, etc.?

 

[tommays]

Re: Screw right into the fiberglass/getcoat?!?

http://www.boltdepot.com/fastener-information/Wood-Screw-Pilot-Hole-Size.aspx


I would test it first but it is a chart


Tommays

 

[studlymandingo]

Re: Screw right into the fiberglass/getcoat?!?

Whenever I am going into fiberglass with stainless I use 3M 4000, it is the only formulation recommended for joining metal to fiberglass.

 

[Drrockter]

Re: Screw right into the fiberglass/getcoat?!?

Isn't it a good idea to put masking tape over the spot to drill to reduce the likelyhood of cracking? I've heard this but unsure if it's true or not.

 

[tashasdaddy]

Re: Screw right into the fiberglass/getcoat?!?

masking tape helps keep drill point from wandering.

 

[Reel Poor]

Re: Screw right into the fiberglass/getcoat?!?

Chamfering/countersinking hole will reduce chances of cracking gelcoat if you chamfer wide enough (but not to deep) that the screw threads don't make contact with the gelcoat. Do not chamfer with a large drill bit, a large bit will grab and crack gelcoat, use a chamfering bit. I use 1/4-5/16 highspeed ball tipped dremel grinding bits (depending on hole size). Bonding with 3-M 4200 or 5200 is a must.

BTW do not over tighten the screws, once they strip, well.........

 

[JRJ]

Re: Screw right into the fiberglass/getcoat?!?

5200 is for permanent bonds. 4200 and 4000 aren't so hard to undo if needed. Masking tape is a good tip. Start smaller on drill size and give it a try. You can always go larger. Keep asking questions until you feel comfortable enough to start drilling.

 

[phatmanmike]

Re: Screw right into the fiberglass/getcoat?!?

all very good advice

 

[imported_JLowe]

Re: Screw right into the fiberglass/getcoat?!?

Thanks for all the advise guys!! Y'all are making me feel comfortable enough to give this a go. I'll use the masking tape, a pilot hole, and 3M 4000 or 4200 as mentioned.
8)