Switching to a raker, should I let it vent?

[NWolf]

It will spin higher. When the jack plat is fully down I was getting 5400 at 55 mph and not ventelating at all. All of this is with the wrong jetting though. I haven't ran it yet with the new jets. But I do think that a 22 is probably the right prop, couldnt find one in my area. I went ahead and got the 24 because I think it will be right when I upgrade my intake.

[phillnjack]

first of all whats the "full trim" ? why would you want the trim all the way out ?
only trim to get the best speed and rpm, if you want a big rooster tail then buy a chicken.. rooster tails lose thrust if too high.
maximum rooster you want is about as high as the bottom of the motor hood, that way its all forward thrust= max speed.


for testing this is what I would do....
with boat on trailer put the jack plate so the centre line of the propeller shaft is 1 to 2 inch inch below the bottom of the transom.
use a long straight piece of wood and have cavitation plate level with bottom of boat too. now leave everything in this position and go test the boat.
do not trim up or down and DO NOT raise or lower the jack plate from this setting. get the boat of full throttle and take note of the speed and the rpm.
do a few runs like this and if i use the power trim make sure it dont lose speed and raise the revs, you need max speed at the lowest revs ,say 58 mph at 5500 rpm.
then mark the plate with pen or some sort of marker and this time get up to speed then drop it down just 1/2 inch and se the speed and the rpm, then put it back to same as before and raise it half inch and take note of what that done etc etc until it gives max speed at whatever rpm... just dont over trim.
ideal is with cav plate level with water surface to get best speed.

by the way what is the boat ? is it a performance boat or heavy weight ski boat ?

[NWolf]

You shouldnt make blanket statements about how high to set a jackplate. At 2 inches below the pad I loose water pressure and it ventalates at all trim angles. Not trying to be rude but if you were talking to someone who didnt know better you could have cost them a motor.

[phillnjack]

if you loose water pressure with the centreline of the prop at 2 inches below the pad you have serious problems or not measuring correctly.. would like to know how your water pressure gauge is fitted to the motor... bet your a T-fitting guy.

[Skip 7750]

A good safe to start is with the prop shaft 3" below the bottom of the boat. Should not loose water pressure and prop will still give some bow lift. You can go up or down a 1/4" at a time until you get it dialed in. At the speeds you are running, it usually offers no advantage by raising the motor super high. If you were going 80 mph or faster, raising it might help. The higher you raise the motor, the less leverage you have to raise the bow. Rakers are a good fast prop!

[rochelle howell]

Raker good! Within 1.5 mph. of top speed with 23 srx without holeshot headaches. My piece of crap.....6 inch setback jackplate, all the way up, clamp bracket on highest hole, no loss of water pressure, lucky, I guess. Running 55 GPS. Old Glastron Jetflite no pad, with prop rated 70 omc. 23 srx very fun and dramatic. Best mid range acceleration punch. Probably not running high enough to benefit enough fromm it. Fun though! Hope its worth somethin' to ya!