i need help please

[electroman]

i can see i am at the right place. i am no where in the same class of preformance , as this form is. i hope you can share your understanding of "hydrodynamics" , to help me solve an setup issue.

here are the specs 16' aluminum runabout with 60" beam ,45 mariner with 2:1 gear ratio 5400rpm @ 25mph (gps) package weight 1300# (with driver) current slip .6 prop 11"dia 15" pitch 3 blade 8 13# batteries are located in the ski hole , to provide 9 gallon of gas in the fantail.

the reason for this post . i installed a sting ray hydrofoil . my mininum plane speed went from 17mph to 14 mph (trimed in) i had to trim out for max speed with some slight porposing .the boat did not wake a deep trough, but i had alot of engine spray . the splash line on the hull went to 6' to 1' . i feel the motor is set to deep . the dealer says 20"transom needs the 20" shaft .the hull has a set of strakes on the deep vee (does not look that deep but it is a dry boat on lake erie) the area below the cavitation plate seem elongated. the water pickups start 2" below the cavitation plate , i have enough clerance to mount a 16"dia prop. please take a look at the picture. the strakes are located outside the bunks

i would think that the top of the prop being even with the keel would set the cavitation plate even with the strakes. would be more hydronamic

[vector mike]

Welcome to the board. What we do on our boats is get the lower unit out of the water as far as possible to create as little drag as possible. If you lift your motor up and still get good water pressure that would be the first thing that you could try. From the look of your picture you could go up a bit and still have your water pickup holes in the water.

[electroman]

thank you vector mike , for your response . i have one other tech question . do the strakes try to create a hypothetical "pad" at a relationship to the keel? :o one more, do i have 2 set of strakes or 1 with a hard chime?

[electroman]

a hard chime?

[VectorPat]

That Hydrofoil is causing some BIG time drag!!!! It may help on lowspeed but it will kill your top end speed,especially being that deep in the water..

[Rickracer]

...water pressure and bite permitting. You'll probably need a higher pitch prop then. Go stainless if the budget permits. :cool:

[vector mike]

The strakes create lift. They help the boat get out of the water. That sharp edge is your chine.

[electroman]

you guys are great in defining gray matter to a thinner line . my last question , how do setbacks work ? are they a mechanical advantage , or a positioning convenance ?

[Rickracer]

...as well as using the weight of the motor as leverage to lift the bow. The less of your available power is used to lift the bow, the more can be used to propel you forward. They also allow you to fine tune the motor height to get the least amount of drag, while maintaining water pressure and prop bite. :cool: