Out board mounting

M

mmeric8802

New member
I was changing my oil on 4 stoke Yamaha , I noticed motor is mounted 1.5 inches higher from top of transom , I have extra mounting hole on top of the mounting bolts and bottom holes are adjustable so I can lower the engine down on transom before I do it I like some input from u guys thanks in advance :)
 
More importantly is where does the anti cavitation plate run in the water while on plane. Roughly it should 1 inch below the water surface to even with the water surface. My motor was mounted to low from the dealer and I have since raise it.
 
Again, we need more information--what is the speed and RPM at WOT? Does the boat handle well; does it "blow out" on turns or ventillate the prop? It is not unusual for a motor to be mounted a bit higher than the top of the transom to get the most effecient running.
 
Most rigging guides say run a straight edge from the bottom of the hull to the bottom edge of the cavitation plate .Most transoms are not exavtly 20" or 25" [hence the adjustment holes] .If a bracket is involved , 1/2 inch up for every foot behind the hull . I.E a 36" bracket would mean 1.5" above the hull . That inch below the transom creates a lot of drag.........
Different props behave differently as well , as far as "blowout" and cavitation are concerned.
Marc
 
mmeric - Marc is correct, it is important to have the cavitation plate in line with the hull. If you look at the lower leg of an outboard you will notice that below the cavitation plate the leading edge is sharp to cut the water. Above the plate it is flat. If the motor is mounted too low - when underway the water flowing under the boat will hit this flat section and splash water(a lot) up the back of the boat. It will very quickly fill the splash well - its drain will not handle the volume. And of course it will also slow you down.

Don't ask me how I know these things! :oops:

Regards, Rob
 
Back
Top