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ContinuousWave: Whaler Performance
Hole palcement on 1975 Evinrude on 1967 Sakonnet
|Author||Topic: Hole palcement on 1975 Evinrude on 1967 Sakonnet|
posted 09-28-2002 07:05 PM ET (US)
I'm new to the forum so please excuse me if this topic has already been discussed. I have a 1967 Sakonnet with a 1975 70 HP Evinrude. I've owned it for the past 15 years and have 3 different motors on it during this time. I put the Evinrude on the Whaler myself without knowing too much about it. I placed the motor as far down on the transom as it would go (the top hole). Is there a better placement for the motor? The motor seems to extend down pretty far below the bottom of the the boat. Can I raise it up and what effect will this have on the performance? I don't know the shaft length of the motor. I know they come in 20 and 25 inch lengths but where do I measure from to determine the length?
posted 09-28-2002 08:54 PM ET (US)
The anti vent plate, [ cavitation plate ] should be about 1/2 inch above the bottom.
While the boat is on plane, either you or someone else needs to look at where that plate is, if it's above the water, your fine, if your below the water, the engine needs to be raised.
You measure from the inside of the bracket. [ the part that sits on the transom ] down to the anti vent plate.
Just for your own info, the shafts come in , 15", 20", 25" & 30"
Yours should be 20", but the bigger outboards are mostly 25".
It depends on the type of prop your running, to determine how high the engine can be raised, a standard omc aluminum prop will blow out, [ vent, or cavitate ] if the engine is raised very much, where a prop with more cup, will hang on far better at higher hieghts.
By raising the engine a couple holes, it will give you about 200 more rpms, & if the boat porpiouses [ sp ], raising the engine should cure it.
Less of the shaft coweling [ engine leg ] in the water, means more speed.
posted 09-30-2002 09:36 AM ET (US)
1975....they did not make 25".
posted 09-30-2002 08:24 PM ET (US)
Thanks for the info. I measured the cavitation plate and found that it is about a half inch below the bottom of the hull. I haven't had the boat in the water to see where it is when it planes but judging from the the height below the hull, it should be raised up. As I mentioned, it's in the top hole on the top monting bolt, however the bottom mounting bolt goes through a single hole, not the adjusable slot further down. Does this mean that in order to raise it up I'll need to drill anther hole in the transom so that the bolt goes in the adjustment slot? I don't like the idea of drilling additional holes in the boat. Any advise?
posted 09-30-2002 11:12 PM ET (US)
That engine should have 4 holes for the top bolts & a slot to slide up or down, for the bottom bolts.
If your plate is 1/2" below the bottom, my guess is, your going to have to raise it 2 holes, thats the 3rd hole down.
If your running an omc prop, it possibly will blow out or vent.
My suggestion is, get a s/s Stiletto for $249.00 from Aftermarket, it will not blow out as the omc will, because of no cup in their props.
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