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Old 02 June 2009, 15:31   #1
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Trevor G's Avatar
Country: UK - England
Town: Crowthorne
Boat name: Black Adder+BabyBlue
Make: Shearwater + Avon
Length: 8m +
Engine: TDi Diesel + Merc 60
MMSI: 235026679
Join Date: Jun 2008
Posts: 881
Advice on Drilling holes in my Transom

Not sure if this should be in this section or Engines....?
I want to fit an auxiliary engine bracket to my transom - as much as a way of carrying the engine when wanting to use it on a SIB as for use as an auxiliary, but before I drill holes in my transom thought I'd ask for any relevant advice before starting the surgery.....
1. Is there a limit to how close I can drill the holes for the M8 bolts to the top lip of the transom? (the lip is on the outside of the transom)?
2. When (if) I do drill the holes, should I try and run any sealant into the holes or around the bolts to seal them?
3. The boat is a 6.5m ballistic - does anyone know if the transom is solid or does it have a plywood centre, and if it does have a ply centre will drilling the holes risk letting water into the ply and it getting soggy over time? (This is linked to Q2 of course!)

The pictures show how/where I intend to mount the bracket (the main engine is on full lock), and the transom with the intended M8 hole locations marked with a blue spot.

Thanks for any advice - unless I panic due to warning reply's I'm hoping to get the bracket mounted before this weekend. Trevor
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Old 02 June 2009, 17:28   #2
Country: UK - England
Town: Winchester
Boat name: H2O
Make: Avon
Length: 4m +
Engine: 50hp Honda
Join Date: Oct 2005
Posts: 78
Trevor I can't help with the holes location but can you not clamp the outboard on? If not ALWAYS use a good quality silcone sealant everywhere including in around and on and under the bolts to seal the holes; use good quality A4 penny washers and A4 bolts and nuts and you should be fine. It is the power of the outboard the affects what it does and with an auxillary such as this I would be happy to go ahead and fix the mounting bracket. Others may me able to advise you about how this will affect the balance of the RIB and the performance of the main outboard if bits of the auxillary get in the way of the RIB under power. With mine I work on common sense and then learn from experience, good luck, Steve W

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Old 02 June 2009, 18:41   #3
spartacus's Avatar
Country: UK - Scotland
Town: Aberdeenshire
Boat name: Sula
Make: Ribcraft 4.8m
Length: 4m +
Engine: Tohatsu 60hp + aux
MMSI: 235087213
Join Date: Jun 2007
Posts: 3,547
It should probably be under the engines thread.

1/ You don't want to go too near the lip of the transom for obvious reasons. Allow a couple of inches depth.

2/ Use Sikaflex sealant after you've drilled the holes and run the stainless steel bolts through them to coat the inside of the transom. Tighten the bolts before the sikaflex cures - but don't over-torque them. I used stainless steel washers inside - as there wasn't space outside.

3/ No idea.

Although my boat is a smaller set-up, the principle is the same. I used a Plastimo adjustable bracket which I had to customise in order to fit on my Zodiac 7-man Pro. This meant cutting the stainless-steel bracket flange slightly so it's held in place with 3 bolts (due to the slight sloping angle of the Pro transom). I also had to cut the injection moulded mounting pad (so the main engine doesn't touch it on full lock). The Tohatsu long-shaft engine is completely clear of the water in the raised position.

Lastly - consider using a ratchet strap to secure the auxilliary engine in the raised position while towing or underway. There's a lot of vibration when negotiating a heavy swell, and the auxilliary transom clamps or tilt mechanism support pin simply aren't up to the job.
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