Prop Depth

[ljc1957]

Is there any rule about how far below the bottom of the transom the prop should run in the water? I'm replacing the transom in my 14' runabout and I have the opportunity to increase the top side of my transom by 3". Of course, this raises the engine/prop 3". Would that have an impact on performance? I'm doing this because it lessens the opportunity for waves to wash over the transom into the splashwell. The prop originally sets 7" below the bottom of the transom, with my adjustment, it would sit 4" below the bottom. thanks

 

[steelespike]

Re: Prop Depth

You didn't mention what motor you are running.
Basic height measurements are based on the antivent(cavitation) plate
just above the prop.Even with the bottom is considered a starting point.
Most end up a little higher.A good prop will allow the best height.
You may want to rig your transom so you can adjust the height or
add a jack plate.
Most motors without height adjustment holes you can raise an inch or so
just by adding sticks to the transom usually 1/4" at a time.Sticks are just to hold the height while you set the clamps.Raise it to a point just before venting becomes a problem.Be sure it pumps water.Let us know the motor type we can suggest a starting point.

 

[ljc1957]

Re: Prop Depth

Steelespike, I have a 1966 Seaking/Chrysler, 50hp. short shaft. Currently, the cavitation plate rides well below the transom. With my new adjustment, it will be riding 1/2 above the bottom of the transom. This isn't the original motor for the boat, so that explains why it was so low.

 

[steelespike]

Re: Prop Depth

It would be great if you could run that high but::
I don't think you should build it so it is locked in at 1/2 inch above I think even with the bottom is as high as I would go with a permanent setup.
You could probably add up to an inch if you wanted to go higher after a test.
A jack plate would allow much more adjustment and would give you a setback getting the prop in less disturbed water.
It appears your water pickup is on the bottom of the antivent plate.(can't really tell from the manual).Also you could have venting problems.While you could combat problems with a good prop don't know whats available for that motor. If you can maintain that height you might gain 2 or 3 mph. with an improvement in the hole shot and mileage.
Depending on the boat and motor the final height could vary an inch or more up or down from the starting point I mentioned.