Proper Engine Height Question

[drodkey]

I've been doing some online research about props and have seen numerous post about making sure your engine is mounted high enough before taking on the question to get that perfect prop... I don't find anything really explaining how make sure the engine is mounted properly. My boat is a 1990 Larson International 204 center console. The engine is a 1990 Johnson 150. The distance from the bottom of the boat to the center of the prop shaft is 7 inches. I've attached a couple pictures (hopefully) and apologize for the photo quality. Any and all suggestions, comments or advise is greatly appreciated.

Thanks,
Dave

 

[fishndirk]

Re: Proper Engine Height Question

The thing you really want to be focussing on is not the distance from your transom to the center of the prop shaft but the height difference between your anti ventilation plate and the bottom of your transom. As your boat speeds up and water begins to pass under your stern faster, the back of the boat will lift up higher causing the waterline behind the transom to come closer to where the prop is rotating. The AV plate helps prevent air from being sucked into the spinning prop which severly reduces blade pressure and lowers speed while causing rpms to surge. With the AV plate and boat level to the horizon, the AV plate should sit as close to flush with the bottom of the transom as possible, usually within 1 inch works for most applications. Hard to tell from the picture but it looks like yours is about right.

 

[steelespike]

Re: Proper Engine Height Question

Yours seems fine to me.
If you don't experience any venting turning or in various sea conditions its possible you could raise it some more.
Some more sophisticated props allow more height than others.
Usually the the best results come when fine tuning a setup with a motor that is not right.
I have seen setups with a 1/4" change in height certainly not likely to make a measurable improvement unless in the beginning of solving a bad setup.
The idea is to get the highest setup with the least venting.
there isn't an exact measurement for every boat.
Even the same boats might have different maximum height.

 

[drodkey]

Re: Proper Engine Height Question

Thank you for the responses!
Dave