Any ideas why my 27 hp kohler is wanting to push the prop out of the water? The cavitation plate is even and level with the bottom of the boat in the running position, also it is very awkward to try to steer (possibly due to the problem with the prop wanting to come out of the water?). I have it on a old fiberglass go devil skiff, if anybody knows anything about this boat or the problems with the prop coming out of the water please let me know. Oh yeah, the engine is a homemade design but very similar to a original go-devil longtail.

Take a large crescent wrench and bend the trailing edge of the cavitation plate up 1/4" at a time till you get it dialed in. With mine I can sit down and drive it like an outboard and the plate runs just below the surface.

Not a good idea to run 2 threads with the same title !

viewtopic.php?f=2&t=8534

Also not a good idea not to answer base questions when folks try to help.

Picture might be worth a thousand words !

Transom height / cavitaion plate angle / prop condition are the most
likely issues.... In the other thread it sounded as if you got max speeds
with the prop "surfacing" which means the cavitation plate was up and
completely out of the water - right ?

If - YES - and when you slowly add throttle it pops up on its own - then
there is an issue with the cavitation plate or possibly prop....

Show us a picture of that cav plate parallel to the hull bottom...

Then measure your prop and post a picture of it too....

Sorry about the multiple threads guys !! Here are a couple of pics of the tail on my mud motor that i'm having issues with. In one of the pics you can see that there are small plates that are even with the prop shaft these plates are not currently adjustable but they could be modified anybody knows what these plates are used for?

OK - picture helps a lot....

Prop looks a bit rough but it is fine....

That lower "rock guard" and big ugly bolt look like they are
the biggest part of your problem....

Try to remove them - they are at a different angle than your
cavitation plate and are likely the source of the unwanted lift
and drag....

Your cavitation plate is thicker and shorter than the GDLT and other
longtail designs - a 2 to 3 inch adjustable trailing edge could be added
if removing the rock guard does not solve your problems..... Also the
trailing edge of the skeg has a slight bend on the GDLT to eliminate the
side to side torque.... At 2/3rds power it should track effortlessly and
you should be able to steer by shifting your body weight from side to side...

Ok I'll remove the secondary rock guard and try to go run it soon, I"ll let ya'll know what the results are once I know!!