Cavitation problems

[dabood]

I just bought a 24' Stamas, it used to be a single engine boat, the other owner had it repowered with twin 150 OptiMax. Motors are great "but"
I didn't notice at the time but the motors sit about 3" to high from bottom of hull, I have major cavitation problems in rough water and whole shots. If I put a jack plate the steering and trim/tilt won't work, the plate will be in the way, same as spacer set backs.
I have been told to cut the tramsom down. That concerens me.
I don't know if I can get an extention for the lower unit, even if I can that's going to cost alot for the drive/shifting shaft & ext.
Should I cut the transom?
I don't know what to do, I don't want to just try things that cost and won't work. Any help or advice would be nice.
Thanks, David.

 

[hwsiii]

Re: Cavitation problems

David, if you would like us to Help we need to actually see what your problems are. If you will take about 10 pictures of the antivent plates and the bottom of the boat as well as the cables going to the motors, it is very hard to do this long distance, but pictures should make it where we can see what needs to be done.

Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a straight edge under the keel and sticking out to the anti ventilation plate for a reference
Motor Transom Height

H

 

[bob johnson]

Re: Cavitation problems

I wonder why the steering AND the tilt trim wont work with a jack plate...is it because the motor would then lean ONTO the transom instead of inside the boat???

if you are 3" off, i wonder if you have long shaft motors on a boat that needs extra long shaft motors!!

there should be a good 2" of hieght difference on the motor brackets mounting holes top to bottom...

have you checked to see what holes you are on???

got a photo from cavplate height angle???

bob

 

[dabood]

Re: Cavitation problems

THE MOTORS ARE SITTING DOWN AS FAR AS THEY CAN GO.
I've looked at it over and over. I had two people look at it and they said the same thing about the steering and trim.
I don't know what to do...my old lady is not happy with me, I need to fix this problem. $11,000.00 and its a lake boat, I need off shore.

 

[dabood]

Re: Cavitation problems

How do I send pics on this? I never used it before, you guys are great and I thank you. Please help.

 

[QC]

Re: Cavitation problems

dabood,

Take a look at the three stickies at the top of this section.

 

[steelespike]

Re: Cavitation problems

What props are you running?Size?(usually on the barrel or under the prop nut.brand?model? number of blades?Are they in good shape.
Is there room to place the motors slightly farther apart?

 

[dabood]

I know there Mirage S.S. don't know what pitch could go look...

I'm going to look at props pitch, there in great shape.

They are Mirage Mercury Marine Plus 48-13702, 21P great shape.
Thanks for the help, I can catch Dolphin and Wahoo but I don't rig boats...

The motor bolts are about 6" from tramsom side, maybe could move them a couple inches at most.

3 blade. Sorry.

Edit: I merged those single line posts to clean it up a little. Not a big deal, just a little housekeeping. I know the thoughts were just coming as you pondered and read - QC

 

[hwsiii]

Re: Cavitation problems

These are David's pictures.

I will be back shortly to discuss this with you.

David, I need to know the manufacturer and models of the props you have on the boat right now.




H

 

[QC]

Re: Cavitation problems

The motor bolts are about 6" from tramsom side, maybe could move them a couple inches at most.

Depending on how bad the issue is that could make the difference. Looks like 20+ degrees so the hull to AV plate dimension changes pretty significantly as you go out . . .

 

[dabood]

Re: Cavitation problems

Yes it does change, the right plate is about 1" low, the left side of the plate is about 3" low, if I move the motors out 2" that might help, it will give me me a couple inches, is that enough? The thing is I'm tring not to experiment with the solultions but get it right' one time. That very well could work but are we sure? I spent alot of my savings on this boat assuming it would work and last me. I need to get it right the first time. I'm tore up over this. I only fish off shore and it need to be right. I fish 40 out of the Cape of Fl. That's why I went with twins.

David.

 

[Fl_Richard]

Re: Cavitation problems

Can you extend the motors with longer cases or shafts? If so how much longer are they? You may be safer to pony up for the XL long shafts. You did say the motors can be moved up if the XL shafts are too long. It may give you more adjustment for fine tuning.

BTW I know nothing about Merc's execpt their black!

 

[hwsiii]

Re: Cavitation problems

David, The motors are OK where they are,you just need the right props. Will the place you bought them from take them back in trade for different props.



H

 

[dabood]

Re: Cavitation problems

Sure, rasing the motors is easy, however the cost for the lower units is expensive, I know nothing is cheep with boats but I "need" the cheepest best fix known. Most say cut the transom, but I rather not do that.

 

[dabood]

Re: Cavitation problems

I bought this boat a week ago, don't even know where they bought them.
What props would you suggest? These Mirage are top of the line, that doen't mean the pitch is correct. Would you go buy big $ props and assume that would fix the problem?
I don't mean that to be a.. but Is that the answer?????
I don't hate to throw money at a problem and than trow more.

 

[hwsiii]

Re: Cavitation problems

David, you need a pair Revolution 4 props, I will send you an email where you need to buy them.



H

 

[Dhadley]

Re: Cavitation problems

There are a couple of things to consider. Check the toe in and make sure it's right. Very important with multiple motors. Then try swapping the lower units.

While the Mirage props are pretty good they wouldn't be my first choice for your rig. At this point I'm thinking that your issues can be corrected with set up and probably 4 blade props made for your type of boating. The last thing I'd do is any cutting on the transom. A shorter transom in open waters just throws up a red flag to me.

 

[dabood]

Re: Cavitation problems

hwsiii just suggest the same thing, I totaly agree about cutting the tramsom when fishing off shore. If it was you and money was tight is that what you would do? Throw the money at the props? not saying that's not the problem, but do I know that it???

 

[dabood]

Re: Cavitation problems

I know I'm asking for alot of answers but I don't know whats the best chose of the money...

 

[Dhadley]

Re: Cavitation problems

No, at this point I would not throw money at props. I would work with what's already there and get it as good as possible. Yes, I believe you'll end up with different props but you need to review the 2 things I mentioned first. If the toe in is off now it's going to be off with other props. That alone could be adding to your venting issues. And if so correcting the toe could clear up some of those issues. If reversing the prop rotation helps then that improvement is basically free. And easy to change back if need be.