Here's yet another question about properly seating screws in laminate
fibreglass.

Transom: fibreglass over wood. I have three 1/8" holes for the
transducer mount screws. Should I widen those holes, fill them with
West 105/205, let it harden, and then redrill the 1/8' holes to put
the screws into solid fibreglass with 4200?

If so, then what filler should I harden the epxoy with -- silica?

Thanks,

Jim

Are the holes deep enough to go into the plywood? If so I would drill the
holes larger and do the epoxy bit. I am not sure the 4200 is necessary if
the area is totally sealed in epoxy by virtue of the larger screw hole.

David
"Jim Thompson" wrote in message
...
Here's yet another question about properly seating screws in laminate
fibreglass.

Transom: fibreglass over wood. I have three 1/8" holes for the
transducer mount screws. Should I widen those holes, fill them with
West 105/205, let it harden, and then redrill the 1/8' holes to put
the screws into solid fibreglass with 4200?

If so, then what filler should I harden the epxoy with -- silica?

Thanks,

Jim

On Fri, 23 Apr 2004 19:11:18 GMT, Jim Thompson
wrote:

Here's yet another question about properly seating screws in laminate
fibreglass.

Transom: fibreglass over wood. I have three 1/8" holes for the
transducer mount screws. Should I widen those holes, fill them with
West 105/205, let it harden, and then redrill the 1/8' holes to put
the screws into solid fibreglass with 4200?

If so, then what filler should I harden the epxoy with -- silica?

Your techique is good, but why not through-bolt? A transducer is
light, sure, but through-bolting, fender washers and 4200 or 231 or
similar would give you a mount that will evenly compress, won't EVER
leak if bedded correctly, and most importantly (to me) if a trailing
line or whatever yanks on the transducer, IT will snap off rather than
the secured base. Screws, even properly bedded and isolated as your
technique indicates (which is good, by the way) might rip out if
something hooks on the transducer. This could leave a nasty hole in
the transom. Me, I would rather just lose the transducer in that case.

R.

"Jim Thompson" writes:

Here's yet another question about properly seating screws in laminate
fibreglass.

Transom: fibreglass over wood. I have three 1/8" holes for the
transducer mount screws.
snip

I'm doing something very similar as far as penetrating a plywood core
covered with glass.

This is what I'm doing:

1) Drill out those 1/8" holes to 1/2".

If that means the holes break out into each other, then drill out say a
1-1/4" hole with a hole saw to clean out the entire area.

2) Close off one end of the holes with some duct tape.

3) Mix some epoxy with micro-balloons to a rather stiff mix and stuff some
in each hole. Don't try to fill the entire hole, you'll be wasting your
time.

4) Allow 24 hours, the remove tape and back fill holes from both sides, if
necessary, with more epoxy/micro-balloon putty.

5) Allow to cure at least 48-72 hours, sand off excess putty, then drill
1/8" holes as req'd.

6) Seal all "raw" edges of putty with epoxy using a pipe cleaner to coat
holes. Allow to cure 24-48 hours.

7) If you need to gasket the transducer to the transom, use the old "tube
gasket" technique to build a gasket using something like SikaFlex 291 and
finishing nails as spacers.

8) If you don't need a gasket, install transducer and you are good to go.

What I have just described is a total PITA process, BUT, it insures that the
plywood core remains totally protected and will not rot.

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures

Thanks all. What is the best filler? Here are the options from West
System's User Manual, in descending order of hardness/strength:

403 Microfibers (strongest adhesive filler).
404 High-density filler (the manual recommends this for hardware
applications).
405 Filleting bond.
406 Colloidal silica (this is their less preferred filler for hardware
applications).
407 Low-density filler (microballoon, not recommended for this
application).
410 Microlight (not recommended for this application).

The optimum would be a filler that I could squeeze into the hole using
a syringe after mixing, but when it cures will be hard enough to hold
the screws and prevent water penetration.

My transducer model is a breakaway type, by the way. It is designed
to fail before the screws if the transducer hangs up on an obstruction
in the water.

Jim

On Sat, 24 Apr 2004 00:53:03 GMT, "Lew Hodgett"
wrote:

3) Mix some epoxy with micro-balloons to a rather stiff mix and stuff some
in each hole. Don't try to fill the entire hole, you'll be wasting your
time.