hydro shield?

[Bushwacker]

Originally Posted by badhabit

. . . I will try to get better pictures this weekend starting with the motor all the way down . . . l

Here are a few tips on the kind of pictures you want. Motor height is important for best performance and good handling . . . you want the Anti-Ventilation plate up on top of solid water when you're up on plane at cruise, with motor trimmed up/out as far as you can normally trim it without porpoising or ventilating during a sudden hard turn.

Best way to measure AV plate height is to place a straight edge up against bottom of boat, extending back along side of motor AV plate. (I used a section of aluminum angle, held against hull with a bottle jack.) Then trim motor so AV plate is parallel to the straightedge. My motor is parallel to keel when the I-Command gage reads about 45% trim, where 0% is trimmed all the way down. Once motor is parallel to keel, stick a scale on it and measure distance from straight edge to bottom of AV plate, as in first pic below.

Second pic is what my motor looks like when looking over the transom. (You may need to put some black electrical tape on top edge of AV plate, because it's very hard so see that white plate in white water!) I added the SE sport fin on AV plate because I have a very aft CG due to 30" setback bracket and a motor that's ~ 130 lbs heavier than the boat was designed for; the fin, along with the 4B prop provides much needed stern lift that lets me plane at about 12 mph and helps keep running angle flat.

3rd pic is what motor looks like when it's too low. (Most dealers mount the motors too low because they either don't know any better, or just don't want customer complaints from blowouts/cavitation and don't care that the extra drag costs speed and wastes fuel!)

4th pic shows AV plate at correct height. Because the water flows up after it comes off the transom, motors need to be much higher when mounted aft on a bracket. I had to add a 3" setback jackplate and raise my motor/AV plate up to about about 6" above keel as shown in last picture, to get the AV plate above water. A motor hanging on the transom will typically want to run somewhere around 1-2" above keel. Depends on prop because some props can run higher than others depending on design and amount/location of blade cupping. In my case, getting the motor height correct allowed me to run a better, more highly cupped prop that increased top speed by 2-3 mph and reduced cruise fuel burn by about 10-15%, all while maintaining great handling and good low speed planing performance, so I think it was well worth the effort!

BTW, I think you're losing some lift on those trim tabs that slope up at the sides. I spent my engineering career studying fluid flow in jet engines, and water will tend to run off the sloping sides of those tabs! A vertical turned down "fence" on the outer edges like on the Bennett Sport tabs would stop that and increase the pressure on the bottom sides of the tabs. Some swept wing aircraft use similar wing "fences" to prevent transverse flow along the wings that reduces lift. Might be worth riveting some aluminum angles to the outer edge of the tabs to see if it improves tab performance!