Drilling into Fiberglass

M

mastersp

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Joined
Jun 19, 2002
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9057
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56
Hi All - I need to drill two small holes into my transom to install a new transducer bracket- no existing transducer so can't use old holes.

Any tips to prevent the drill bit from binding (previous experience on other boat) or the gelcoat from chipping?

I also plan on using 5200 in the holes.
 
Very sharp bit. Very tiny pilot hole and work up. Tape over the area. Drill larger than necessary then fill with 5200 then drill proper size to preclude any water intrusion.
 
Everything David said above. +1
For larger holes that require a hole saw after drilling the pilot hole run the hole saw in reverse until you are through the Gel Coat then run in the normal direction to finish off.
Bill
 
He said its just a transom mount transducer, but I guess I would ask if 5200 is so strong and permanent, why do you have to drill at all?
Could you just 5200 to the boat?
 
Davids method is best, but you might be able to get away with just putting excess 5200 on the screw threads.
Cored areas needs to be done as above or perhaps even using epoxy instead then drilling that and filling with 5200, not cored you can probably get away with using 5200 on the threads of the screws.
My question is where is the wire entering the boat at the transducer or above the waterline? I assume above the water?
 
There are drill bits made to drill plastic. If you saw one, you could easily modify a standard bit. I'll try to explain...a standard bit has a chisel cutting edge that digs into and cuts the material. A plastic bits 'cutting edge is cut back so the edge scrapes instead of cuts into the material. You can find them at Tap Plastics.
 
Run the drill backwards for a time then forward and drill the hole. That is basic.
 
quote:
Originally posted by JimPend

Run the drill backwards for a time then forward and drill the hole. That is basic.

Click to expand...


YEP
 
Bobalong, I'm glad someone else knows what they are doing.
 
To prevent the possibility of a core problem in the future I've attached a block of plastic, starboard, or plexiglass and attached to that. If you clean the surfaces properly a 3x3 square of surface attached with 5200 will hold about a thousand pounds. This way you never penetrate the hull integrity. I've done it with a transducer and it worked even at 50 knots.
 
mdoherty, I don't know what you're talking about and I believe you don't either. You have to be on the wrong forum.
 
quote:
Originally posted by JimPend

mdoherty, I don't know what you're talking about and I believe you don't either. You have to be on the wrong forum.

Click to expand...

I'm offering an alternative to drilling into the transom. By attaching the transducer to a 3 in by 3 in backing plate you now have 9 sq inches if surface area. If you then attach this to the transom skin with a reasonable adhesive, since everybody knows 5200 I used that but there are better adhesives. With the properties of 5200 (shear strength of a fully cured bond) you get a shear strength of about 1000 lb. which is the lowest failure mode. The actual force would be a peel strength which is about 3 times greater but I would have to know what materials he used.

I have done this on several boats and the transducer held on to 50 knots without failure.

I will agree with the first part of you comment, you don't know what I'm talking about but I assure you I do.
 
quote:
Originally posted by JimPend

Run the drill backwards for a time then forward and drill the hole. That is basic.

Click to expand...


I bet you could mount a bracket in your cockpit for a smart phone.
 
quote:
Originally posted by JimPend

mdoherty, I don't know what you're talking about and I believe you don't either. You have to be on the wrong forum.

Click to expand...
Very productive comments Jim, many people expressed good ways of accomplishing this task.
Bill
 
Jim P. - not sure what you meant by running the drill backwards then forward? I would run it backwards to extract it from the hole.
 
mdoherty, I'm liking your idea!! I really don't like to drill holes in a boat, especially below the water line.
 
I don't appreciate Jims style, but since starboard and 5200 were mentioned, I have had personal experience with that combination not working. Starboard, at least when I used it some time ago, did not bond well with 5200. Maybe something has changed, but I'm skeptical. I strongly suspect a plastic other than starboard was used by mdoherty. That or something else is going on here as its a well known limitation of those two materials.

I'm also not at all a fan of using 5200 in general, and especially for non permanent I installations of items that should periodically come apart. In this example, I'd follow the general process already well outlined here, but would fill the oversized hole with epoxy, then re drill to the correct size. That's a permanent solution, and then you can use any good quality sealant, while preserving your ability to change it out quickly with a normal level of aggravation.

The only other thing I can add to the otherwise great advice by others is to ensure you use a good quality sharp drill bit. It won't be sharp when you get done!
 
quote:
Originally posted by mdoherty

quote:
Originally posted by JimPend

mdoherty, I don't know what you're talking about and I believe you don't either. You have to be on the wrong forum.

Click to expand...

I'm offering an alternative to drilling into the transom. By attaching the transducer to a 3 in by 3 in backing plate you now have 9 sq inches if surface area. If you then attach this to the transom skin with a reasonable adhesive, since everybody knows 5200 I used that but there are better adhesives. With the properties of 5200 (shear strength of a fully cured bond) you get a shear strength of about 1000 lb. which is the lowest failure mode. The actual force would be a peel strength which is about 3 times greater but I would have to know what materials he used.

I have done this on several boats and the transducer held on to 50 knots without failure.

I will agree with the first part of you comment, you don't know what I'm talking about but I assure you I do.

Click to expand...


That is a perfectly good idea. As is running the drill backwards first.

But I bet you've never glue Starboard to anything for long with 5200.

:-)
 
Starboard is a real PIA to use any adhesive with, at least that's been my experience. However I see nothing wrong with using 4200 or 5200 behind the Starboard and using a screw in each corner of the Starboard that protrudes into the fiberglass transom then use shorter screws to mount the transducer into the Starboard. This method spreads the forces of the water resistance encountered when backing down or accelerating on the transom and secures the transducer.
Bill
 
If not 5200 or a better adhesive and starboard, then a piece of treated or very hard lumber. IIRC, GeeBee made a new BGE holder/work table from some wood that ate several drill bits in the process. I too like the idea of a backer board vice drilling into the hull. It's not so much the drilling as the water intrusion.
 
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