Mercury 80HP Mounting on transom

[Lassodew]

I have a 1980 80 HP Merc that I am putting on an old fiberglass boat. The transom is solid. This is replacing a 1971 Johnson 50HP.

I have patched the mounting holes for the Johnson.

My problem is that there are only 2 mounting holes on each bracket, for a total of 4 holes. There are not multiple holes so you can adjust the height which I have read about in these forums. The upper 2 holes will end up in the shelf (not sure of the right term), not below it or above it. To bring the motor high enough for those holes to clear and be on the inside, my cavitation plate would be 1.5" - 2" above the keel. I hope this picture helps




Is it safe to drill holes into these mounting brackets? The only other way to get this done may be a jack plate.

Any guidance you could provide is greatly appreciated.

 

[racerone]

You only need to drill the slots at the bottom ( total of 2 ) holes.------That and the 2 clamps keeps the motor from going for a swim.

 

[Chris1956]

You need two 3/8" bolts in the base of the transom clamp slots.

There are 2 holes each on the power trim brackets. it is very important that the PTT brackets be bolted, as the power of the motor is pushing against those brackets.

Not sure how to answer your question. Perhaps the PTT bracket slots can be utilized, as mounting the motor 2" above the hull may be too much.

 

[racerone]

Remove that wood shim.------Drill the transom ( 2 holes total ) through the slots at bottom of brackets.----Done.

 

[Chris1956]

Depending on the boat (high performance or not), the shim may be a good idea. On high performance boats, they can lessen drag, w/o inducing ventilation. No way to tell w/o a water test.

 

[Lassodew]

Thanks for the tips. I should have pointed out that the picture showing the wood shim was taken when I had lifted the motor off center to patch the previous holes. So, the wood shim is not intended to be there.

I think I can get the PTT holes to fall below the fiberglass shelf so I would have 4 bolts holding. I will not be cranking this motor up much as it is more for puttering around a lake when the boat traffic is not out. I will give that a try in a few days.

 

[Chris1956]

As long as you have 2 bolts in the PTT brackets, you should be OK.