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Author Topic:   Proper engine height
TrackerDave posted 07-29-2004 10:39 PM ET (US)   Profile for TrackerDave   Send Email to TrackerDave  
I'm mounting a 1980 Johnson 85 hp. outboard on a 17 foot
1967 Whaler. I have to raise the motor 2 inches so I can
bolt above the splash well. My question is if I do this,
will the motor be low enough to work properly. My only
other option is to lower the motor all the way and use
lag bolts which I really don't want to do. I've already
consulted the reference page on this site. Thanks for any
information you can provide.
Chuck Tribolet posted 07-29-2004 10:42 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Where will that put the anti-ventilation plate relative to
the bottom of the hull?


Chuck

JamesB posted 07-29-2004 11:00 PM ET (US)     Profile for JamesB  Send Email to JamesB     
I just went through this a month ago. I have a 1963 16' whaler. It had a tired old 1980 100hp Evinrude on it. I just repowered to a 2004 115hp 2-stroke Yamaha.
What I found is that the old 100hp had an additional set of holes designed for shallower transoms. Interestingly, these two holes (the lower) where threaded in the engine bracket and didn't extend all the way through the engine bracket. You'd insert the 1/2 coarse thread bolts from the splashwell side, through the transom, then they'd screw into the engine bracket.
Of course the new Yamaha didn't allow that option. What I wound up doing is buying a 2 1/2 inch setback plate (actually a two piece unit) from Cook Manufacturing. I drilled two new holes in the set-back plate to match the existing holes in the transom, then mounted the engine to the set-back plate. Worked like a charm.
Since it was only a 2.5" setback, the lip on the engine bracket prevents the engine from being mounted as low as would be possible if it were resting on the transom. What I found though is that I still had way to much engine in the water. Now my engine is on the 3rd hole up, and sits about 2" up on the transom. The A/V plate is still just below the waterline when on step. I gained about 4mph raising it up. If I were doing it over again, I might just go to a Cook's 4" or even 5.5" manual jack plate. That way I could fine tune the engine height without unbolting anything. The cooks units are 1/2 thick aluminum, pretty stout stuff.
I was concerned about the extra torque on the transom with the engine set back, so I bolted a big hunk 1/2" thick aluminum plate on the transom inside the splashwell. Works great, but a little heavy.
kingfish posted 07-30-2004 09:35 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Give strong heed to Chuck's question - when all is said and done, the correct mounting height is determined by the relationship Chuck asked about. Best performance nominally puts the AV plate at or slightly above the lowest point of the hull (1' to 1-1/2" above, sometimes a little more) if the motor is on the transom and not on a bracket.
Bigshot posted 07-30-2004 01:37 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Dave do what you are suggesting....it will be perfect. Setting it on the transom is TOO low, up 2 or 3 bolt holes will be optimum. You can even go all the way up but making tight turns may suffer. You WANT the AC plate about 1.5" or so above the keel, mounting it up 2 holes should make it about 1-1.5" which is fine.

If holes do not line up then get a manual jackplate for about $150 and drill through that to fit holes in hull. Your engine will then boltto bracket. My engine is up about 4-5" ABOVE the keel and runs great and I draw 4-5" less water...Whooo hoo.

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