Optimum outboard mounting position on ST PB w/ NV logs

[wrd1972]

Trying to determine if my outboard is mounted at the optimum height for best overall performance. Boat is 2008 Sun Tracker 21 footer with NV logs and a Merc 90HP four stroke. Currently with the boat sitting still, there is 7" of distance between the cav plate and the water surface.

There are 5 mounting positions available, 1=lowest and 5= highest. Mine is currently mounted in the #2 position so there is room to raise it if needed. How to I determine if the outboard is mounted in the optimum position?

[jimrs]

Your cavitation plate should be about even with the bottom of the poontoon.

[wrd1972]

Your cavitation plate should be about even with the bottom of the poontoon.

Hmmm...
All I have right now to look at is this pic. It appears that the cav plate is much higher than the bottom of the toon.

[GregF]

You really need to know how deep the boat sits in the water and where it rides up on the step.
That is when you want the cavitation plate right below the water. Some go fast boats even exploit the bump of water that comes up behind the transom and put the motor out behind the boat on a bracket to get it as high as they can.

If the motor pod is designed correctly the skid plate will be just smoothing the water flow feeding into the engine (not "plowing water") and the motor has the cavitation plate about even with the bottom of the skid plate. The down side of being too high is it can blow out on a tight turn.

[brumbyvet.1044]

Yours is mounted just like mine. The service manager that rigged my boat said that was where Sun Tracker recommends it to be. You want your cavitation plate even with the bottom of the motor pod not the pontoons.

[Bryden24shp]

Actually, to have it at the best performing position, you want the cavitation plate to ride just on top of the waters surface.
Here is a video that shows it real good. Have someone run the boat WOT, look over the transom to see where it is. If its under the surface, raise her up. Mine was down 3", water was splashing from in front of it onto the transom. I raised it up to where it should be and gained speed, RPM's and by my Smart Gauges, about 1 mpg. Best was 2.7 at 3200 RPM's now its 3.8 @ 3400. Nice improvement, there is alot of drag that can be reduced by raising it up.

http://www.youtube.com/watch?v=4TavDjfe0Ng

http://www.youtube.com/watch?v=zQAU3BynTeo
Hope these work....
Bryan

[Bryden24shp]

Here are some pics of where mine is at now. It runs like a different boat.

[wrd1972]

Please check my outboard height position.



I can easily raise it f bolt positions.
Comments?

[Bamaman]

You already have the fastest running 90 hp pontoon on earth @ 36 mph.

If you're not having any cavitation problems in turns (after trimming the engine down slightly) and if you're capable of pulling the redline, you are at the optimum height. Speed tells.

It's just too bad Tracker chose to do away with the NV toon option.

[Liquid Asset]

I don't think there is one set up that works for every boat even the same model. Just the difference of how you load two of the same boats will change the set up. It won't hurt to raise it up a hole and see how it performs. Keep going up until you start slipping to much. Trial and error is how I have always done my height settings. It sounds like you are doing well right now with the way it's set up. I would think you stand to gain more by cleaning the logs ,transom , and lower unit . From that pic it looks like you might have a fair amount of drag there.
I always liked the n.v. logs and how well they seemed to work. I remember seeing a video with 2 matching boats, one with the strakes and one with out. They were only running 60h.p. motors and what a difference it was. It sure blew the theory of a 100+h.p. need to get a boat up on strakes !!!

[brumbyvet.1044]

From your last pic, it appears that your motor is about 2" lower then mine. I also noticed from your waterline mark on your toons that your boat sits quite a bit lower in the water then mine. Do you have any extra weight in the stern? Also I agree with above post regarding the neeed to clean all the scum. That could easily cost you 1 mph or more.

[wrd1972]

The boat is going to get a good cleaning and with the new dry dock storage, growth will never be a problem again.

Brumbyvet,
I dont have any significant weight in the rear, but I think I am going to raise it a hole and see. Maybe I should lose some weight. LOL