Porposing / Engine Height

[Bucketmouth King]

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Hi everyone. I bought my first boat (1986 - 18' winner bass boat) that was repowered with a 2000 Yamaha vmax 150. after doing some reading and measuring, it looks like my cavitation plate is 2" above the very bottom  of my hull V, and I can only lower it by one bolt hole, which I believe is only going to gain me 3/4" . I read that the plate needs to be in line or within 1 inch of the bottom of the hull V.  Is this boat going to be a porposing nightmare? At all speeds ? Just low speed? High speed ? Any suggestions ?
thanks for any help !!!!

[Way2slow]

Cavitation plate has nothing to do with porpoising.  That's controlled by the setback and how much trim angle you have on the motor.  If you have too much set back, mid speed porpoising can be a problem and it you have it trimmed out too much at it's going to porpoise

[Bucketmouth King]

I had it trimmed all the way down and never really go to plane due to a fuel problem which is now fixed. But i noticed some bounce of the bow which lead me to investigate and now we are here. 

My prop is stamped 17-M. Not sure what that means or matters?

[Kevin22]

Is it a 4 blade? 4 blades are generally mounted higher on the transom than 3 blade.   

You need to test the boat before anyone can help. You need to take it to the water the way it is and give her some juice. See what the RPM top out at when trimmed. Trim up until it porpoises and then trim down until it runs smooth. Take note of your speed (use gps speed) and your RPM. Keep an eye on the water pressure gauge as well. 

[Further North]

I had a 1998 Tracker Super Guide V-14:

...with a Merc 40 on it...the only way that boat didn't porpoise at speed was with the trim all the way down.  I didn't know diddly about raising or lowering it on the transom, don't know if it would have helped or not.

[Bucketmouth King]

Its a 3 blade prop stamped 17-M

[Kevin22]

1 hour ago, Further North said:

I had a 1998 Tracker Super Guide V-14:

...with a Merc 40 on it...the only way that boat didn't porpoise at speed was with the trim all the way down.  I didn't know diddly about raising or lowering it on the transom, don't know if it would have helped or not.

Yeah that motor is way too high. Looks like 3/4 of the prop is above the bottom of your transom! Probably had one heck of a quick bow rise on hole shot huh? 

[Further North]

14 minutes ago, Kevin22 said:

Probably had one heck of a quick bow rise on hole shot huh? 

It was a 14 ft. boat with a 40 on it...it came out of the water like an ICBM...

[Kevin22]

1 minute ago, Further North said:

It was a 14 ft. boat with a 40 on it...it came out of the water like a ICBM...

I just spit out my drink. I imagine it did! 

[Further North]

Here's a couple pictures from when I bought it:

If I'd known then what I know now, I probably could have fixed the problem.  Woulda been some work, but I could have done it.

There are days when I wish I would have kept it, converted it to a jet motor and used it in the rivers.

[Kevin22]

You darn near had a jet motor with it mounted so high! Looks like your mounting plate has another setting (lower).. that would have helped some. That is a very cool set up, would make for a NICE one man river runner. 

[Further North]

Yeah, it would have...but there was no room in it for rods, tackle...much of anything.  It was a good starter boat, learned some good things with it.

[Way2slow]

A friend of mine had a 17.5' Tracker with a 115 Merc and once it got to 42 mph, you couldn't ride in it, the sucker would jar your eyeballs loose.  It was steadily beating the water about like taking your hand and slapping the water as fast as you could, but at 40, it rode fine.   I've seen a number of aluminum boats that would start doing that because the water pressure on the hull starts it to flexing once they get to a certain speed.

If a boat has a rocker in the hull, that will cause them porpoise.  It's also very common for boats to porpoise when slowing down to come off plane.