engine height with bracket

[johndezman]

after much anguish i finally have my engines running fine and can concentrate on setup.

first the boat is a chris craft 313 scorpion with twin 200 suzukis. with current props and engines as low as they can be on the bracket i'm getting 42 mph. (prop is 15" pitch and rpm is 5500)

i know if i raise the engine one set of holes on the bracket, the prop tips get close to the surface and you can hear a difference but they don't unload - just getting close too.

if i return to that setup height (up about an inch or so) i'll have to go up in pitch. short of making this a career, what kind of rule of thumb is there for a increase in speed ie do i go up 2" in pitch or 4? just want to do it once only.

thanks to all that help

 

[hitace]

Re: engine height with bracket

heres a rough rule of thumb every time you go up a hole it will give you close to 100 more rpm if you are running 5500 rpm right now you shouldit have to change your prop.also you should get a little bit more top end due to the re dues of drag when lifting the outboards a hole.theres no rule of thumb for speed increase/decrease fore changing pitch that i know of.it seems your props are just right your getting 5500 rpm which is perfect for that outboard you never want to stray to far away from the recommended rpm or you could be looking at some serious damage and loss of speed