Transom setback

[mdwillis]

I have a stern bracket providing a six inch setback. The outboard is six inches behind the transom. I have read that, in a normal application, outboard mounted directly to transom, the cavitation plate should be even with or 3/4 inch above the bottom of boat. Shouldnt I be able to increase this distance by at least an inch or two considering that the lower unit and cavitation plate is farther back? While running, the water flow comes from under the boat rising to reach the higher unit. I am in the process of testing and no considerable cavitation taking place. I want it as high as possible for use in shallow water. I would like to know if there is a rule of thumb or even a formula for converting this distance.

 

[Philster]

Re: Transom setback

It depends on so many factors... the best thing to do is line it up as you would if it were at the transom and test it. Then make adjustments and test it again. This is why it helps immensely to have a quick adjust bracket that lets you raise/lower with a few turns of a wrench while in the boat. You might be able to set it a little higher, but the only way you'll know if that is best is if you set it lower and run it to compare.

So, in short, the only way to handle this matter is multiple test positions, runs and a reliable tach and speedo.

 

[SparkieBoat]

Re: Transom setback

philster is correct..I would add that you basically want the motor as high as you can get it with out cavitation. I think the rule of thumb is you can raise your motor 1" per 12" of setback, but again the move and test is the way to go, I would also install a anti cavitation plate on my motor if you dont already have one, it may help you get higher without cavitation.

 

[Philster]

Re: Transom setback

It's imperative to know if your water pickups are up to the task, too. Some motors can't be run higher because they lose the ability to pick up water at speed. There's probably a safe, modest range for engine height that you don't need to get too concerned about, but if you are trying to really optimize speed and want the highest setting for speed and draft, then the effectiveness of the water pickups becomes a factor that you have to account for.

 

[SparkieBoat]

Re: Transom setback

good point. but I have found that in most cases I will start getting cavitation specially in the turns if your motor is too high. but the water pick ups definitely need to be checked for sure. I am always checking that pee stream and check/test my over heat alarm yearly