Height Stern Drive

Fellows,

Does anyone have experience with the height of the anti-ventilation plate of sterndrives in regard to hull bottom?

The installation manual says that the anti-ventilation plate should be at leas 6mm (1/4") above bottom of the hull, for boats with a top speed over 25 mph.

Our Boat is predicted to top at 50 mph and the manual says that we can install the sterndrive higher than recommended, for performance. They just don´t tell us how much more, so I´m relaying on the forums expertise to try to install it at the correct position.

Any hints (besides going out and test, since the installation of the sterndrive is more difficult to shift up and down)?

Thanks

 

It also depends on the deadrise of the hull and if it has a flat pad.

 

No flat pad, deadrise 20 degrees

 

Trial and error.

Since no two boat are really the same, but "generally" the same. So do as one does in tank testing, try various heights under the same conditions and see what the effect is on speed, trim fuel consumption etc.

Far better to try it yourself, then just bolt it on at one height and hope for the best.

 

Is there a trick to changing the sterndrive height without rebuilding the transom over and over and over? Can a transom retain enough strength if you "slot" the cutout to allow vertical movement?

 

Paul

All depends how the structure of your transom is arranged and what load paths exist. Can't say without seeing it.

 

Also depends on the drive
You can get extension adapers for Merc II, III, IV, V and VI drives
and bravo from the aftermarket.
You can also get aftermarket bravo lower units that are shorter than stock raising the propshaft.
The weight of the boat is the critical issue...
If it will do 50mph with a 4 cylinder drive the drive can be very high as you dont need so much thrust to get it on the plane.
If on the other hand you have 500hp and the boats going to do 50mph its heavy.....
Some after market standoff boxes can also raise or lower the X dimension without altering the transom cut out.
What is the package you are installing?

 

Dear all,

I got the (paper) drawings from Yamaha for their Hydra Drive and, since the Sterling Legend 28 is a new boat, we will stick with the standard "X" dimension suggested by them and hope it will perform. After this, I guess we will have data to "tweak" out the "X" dimension...

 

For those who want to see it

I attached a picture of the transom and the insert, while the lamination was under way...

 

To me, the hole seems to be a bit low. For the stern drive it doesn't matter much, but the engine needs space for the oil pan and the stringer below the engine's front end must not be too high.
I once installed two units, using the carton they came in. There were drawings on it for single and twins, but my boat's bottom was thicker that Mercruiser expected, so I had to cut part of the bell housings.

 

how much horspower?

 

Sl28

Standard engine is a 270HP Volvo Gas engine. This particular boat will have a Yamaha 275HP Diesel engine. Maximum HP is 2 x 270HP Volvos. I added full specs...