screwing into (fibreglass) transom and how to do it right...

[comfortably numb]

Ok I need some advice and I know I will get the right answer here...

I have got my hands on a set of trim tabs and am going to fit them up to my new rig.

There are about 8 screws each side that need to go in to the timber, and 3 more for each actuator that go through just fibreglass, along with a hole for the hydraulic line about 12mm.

Was thinking I would predrill all the holes and dip the screws in flowcoat before screwing into place? And for the actuators drill, seal the holes with flowcoat and bolt, then sikaflex around the hydraulic lines.

Or should I predrill, fill the holes with flowcoat and screw into that?

Or would marine grade sikaflex be better for the job?

Will flowcoat work better than gelcoat?

So many questions, just dont want to stuff it up and have to do a transom in a few years...

[kokomo]

pre drill with an over size drill.. fill with epoxy use tape to hold epoxy in.. add micro balloons to help with texture..

then drill holes to suit

[welder]

Drill the hole you want then champher the edge of the hole with a much larger drill bit , this keeps the gellcoat from cracking in the future.
Most will drill then install the screw, Remove screw[ this makes threads] then fill hole with 5200 or the like and reinstall screw .

If your not hitting timber with the screws I would go with through bolts and sealer.

Just remember to leave NO sharp edges on the glass .

Measure twice and drill once, good luck.

[comfortably numb]

Thanks for the advice.
the oversize holes with epoxy idea sounds a bit more complicated but i see how it would work.

welder im guessing 5200 is sikaflex or similar?

[northernblue]

Thanks for the advice.
the oversize holes with epoxy idea sounds a bit more complicated but i see how it would work.

welder im guessing 5200 is sikaflex or similar?

I think Grand_marlins advice is oversize drill, fill with flowcoat and re-drill correct size hole. I think he might frown on epoxy.

Try a search or a pm

[Far side]

Drill the holes fill with sica screw the screws into the sica cover the plate return with sica and the tab actuator plates with sica and your done leave no gaps between the boat and the accessory otherwise it will rust. Clean off with KERO
If you have to go right through and use bolts then panic because there is no wood in the transom behind the glass and there is no strength to support the actuator

[Grand_Marlin]

G'day Guys,

Pre drill the holes.

Use a bigger drill (say 10mm) to schamfer the holes - do this with the drill in reverse and it stops the drill bit biting in ... as Welder says - stops it from cracking the surrounding gelcoat.

For screws going through glass and into timber - fill the hole with Sika 291 and cover the back of the fitting in Sika so as it squashes out when tightened.
You are better having too much Sika than not enough.
When screws are tightened, wipe off excess Sika with a dry cloth.
Clean the rest off with metho.

For fastenings going only through fibreglass and with no timber - use bolts, 1" diameter washers and nyloc nuts.
Again use Sika on back of the fitting, do the nuts up and wipe off excess.

This is how I do it and I don't have any problems.
I have to be extremely fussy when doing thru hull fittings like skin fittings and transducers on permanently moored boats.

I don't drill an oversize hole and fill it with anything for two reasons.
1) you have the chance of cracking out the epoxy or flowcoat you have put in wheen you drive the screw into it - then water gets in.

2) The strength for the screws to hold is in the fibreglass and timber ... the oversize hole filled with epoxy is a weaker place to fasten to.

The only time I will do this is if I am forced to ... i.e. existing holes have been flogged out , or new fitting doesnt line up properly.

Cheers

Pete

[trueblue]

I use a 45 degree countersinking bit in the drill instead of a bigger drill bit in reverse. same outcome, but a better angle with a better tool in my view. go slow with the countersink so it does not chatter. if it chatters, put a little (1" x 1")piece of rag on the end of the countersink bit and change each hole

[comfortably numb]

Thanks for the replies all.

Grand_Marlin I have been told you are the guru.

trueblue I didnt know you could get countersink bits, im always up for a new tool.

Guess im off to get my drill...

[Grand_Marlin]

trueblue I didnt know you could get countersink bits, im always up for a new tool.

Guess im off to get my drill...

Thats what I like to see ... any excuse to get to the Hardware

Cheers

Pete

[welder]

3M 5200 is used when you are making a permanent addition , check the link it shows the product.

http://www.shipstore.com/SS/HTML/MMM/MMM5200.html

[Ringoscar]

Bennett Tabs recommends standard-sized (not oversized) holes in f/g/timber transoms with the screws dipped in marine epoxy before fastening. For a bit of extra hardness in the epoxy and less run, you could add a little Cabosil (colloidal silica) if you have some. Screwing in will force the epoxy right into the timber pores; if you want to remove the screw down the track, wipe the thread with a little oil before fastening. If not, you'll need the Easy Outs...