CAVITATION issue on a 2008 25 CONTENDER OPEN ? HELP !!

[madinina]

Hi , a freind of mine a brand new 25 CONTENDER OPEN , he installed twin 250 HP OPTIMAX on it . The problem is that at lower speed (when getting out of the hole) , the propellers seems to suck air and they cavitate .
So, when you re offshore in rough sea, and that you cannot maintain high speed, it is impossible to get on plane and stay at a medium speed .
Is there anyone that can help us solve this problem . I also would like to know what should be the better distance between the two engines. We thought that maybe the engines were installed to close from each other ?
If there is somebody that can give us the corect set up it will be nice !

thanks

[MakoMyDay]

Likely a prop issue, or they are mounted too high. Engines at 26" centers I believe. I'd bet 21p Rev4 props would be the ticket for that hull. PM Back in Black---he has a 25 Contender with 250 optis

[Tom W Clark]

I think you are confusing CAVITATION with VENTILATION.

It comes down to props. What is on there now? Are they Mercury props with the PVS vent hole system? If so, are there open plugs in there? Is it some other vented prop?

The first thing to do would be to plug the vent holes, if any. Very few offshore capable boats need vent holes in the prop(s).

The second thing to do would be to determine if the right props are being used and it sounds as if they may not be.

I am sure the engine spacing is not the problem.

[Booker]

Bring it back to whoever sold it or rigged it?

[madinina]

Yes it is VENTILATION rather than CAVITATION .
I will check with my freind what type of propellers he has tested. But they are MERCURY for sure.
I will also ask him for the plugs .
As I said the problem for him is in rough seas when you cannot ride at high speed unless if you want to break the boat (or your ******... !!!
Anyway the boat is EXCELLENT !!!

J-C

[madinina]

When you tell 26 " center , you mean that the distance between the two engines "center to center" is 26 " ?
Is that correct ?

J-C

[madinina]

the props are BRAVO ONE 22 P 4 BLADES.

[sundancekid]

Check to see there isn't a thru-hull or transducer in front of one of the engines, I've never heard of Bravos ventilating like that, they always hook up. A small amount of ventilation is OK as it helps to get the boat moving, excessive would be if the boat cannot maintain plane at 15-20 mph without the props slipping. I have rigged a 25 Contender with 225 Optis with the engines mounted on the bottom hole (high as possible) and the 22 Bravos do not slip a bit, boat has awesome hole shot, and runs over 60 at WOT.

[madinina]

BUT !
What was the distance between the 2 engines ?
I understand that it should be 26 " center to center ?
Is it correct ?

J-C

[madinina]

WHAT WAS THE SHAFT LENGHT ? WITH THE TWIN OPTI 225 . (XL or XXL)

[Back-in-Black]

madinina - 6/6/2008 9:25 AM

Hi , a freind of mine a brand new 25 CONTENDER OPEN , he installed twin 250 HP OPTIMAX on it . The problem is that at lower speed (when getting out of the hole) , the propellers seems to suck air and they cavitate .
So, when you re offshore in rough sea, and that you cannot maintain high speed, it is impossible to get on plane and stay at a medium speed .
Is there anyone that can help us solve this problem . I also would like to know what should be the better distance between the two engines. We thought that maybe the engines were installed to close from each other ?
If there is somebody that can give us the corect set up it will be nice !

thanks

What props are you running? Had similar problems with mine when I first installed my 250's. I was running 23" Mirage Plus'. My props would blow out coming up on plane as the boat "laid over onto plane" and I always had to back off the throttles to keep from red-lining the motors. While running offshore, a lot of times one prop would blow out and I'd have to back off the throttles and wiggle the steering wheel to get it to bite again.

Posted the problem and Sundance Kid suggested a different set of props. 24" Bravos. Went with those and they absolutely cured the problem. I have my motors currently mounted on the second to highest position. I need to raise them all the way up to highest position because we were riding around a few months ago and i walked back to the back of the boat and peaked over the transom at the cavitaion plates. My cav plates were still about 1" underwater at 47 mph.

[Back-in-Black]

madinina - 6/6/2008 4:27 PM

BUT !
What was the distance between the 2 engines ?
I understand that it should be 26 " center to center ?
Is it correct ?

J-C

If I remember correctly, that's what mine are... 26"

[Back-in-Black]

Ummm, stupid question. I see now that you ARE running Bravos and just like Sundance, I find it hard to believe they are cavitating.

Now for the stupid question: Are they counter rotating motors and is the right prop on the right motor? Don't know how or if it would work at all with wrong direction props, but can't hardly think of what else it could be.

[spearnreel]

Back-in-Black - 6/6/2008 5:42 PM

Ummm, stupid question. I see now that you ARE running Bravos and just like Sundance, I find it hard to believe they are cavitating.

Now for the stupid question: Are they counter rotating motors and is the right prop on the right motor? Don't know how or if it would work at all with wrong direction props, but can't hardly think of what else it could be.

You are right, that is a stupid question.

[Back-in-Black]

spearnreel - 6/6/2008 8:04 PM

You are right, that is a stupid question.

Got any ideas yourself? I have the same boat with the same motors and the same props and mine performs awesome. So what's wrong with his boat that it does so poorly? It ain't the motors, or prop selection and mine runs well with the motors mounted as high or low as they will go. So what's the problem? Something unconventional would be my guess. How about 2 RH or 2 LH props?


Proper shaft length is XL (25")

I can also tell you this. I rigged my motors myself (changed out from Yamaha). The instructions for the Merc Binnacle shift cable hookup for the port (CR) motor is more than a little confusing and I got it backwards the first time around. And I'm not alone on that one, have since talked to several others who made the same mistake. Anyway, I realized my mistake right off because there was always a question in my mind when I originally hooked them up and I went back a re-read the instructions several times and still got it backwards.

[propbender24]

Just grasping at straws, being back -in- black has almost the same setup, could one of the boats be set up with inboard rotation (counter on starboard and standard on port) and one being set up conventional. The other question are they the same year model, did contender change the trim tab pockets on the 2008 from previous years, I have heard that some tab pockets cause a vaccum.

[epanzella]

I had a problem with my starboard engine ventilating on my Maycraft 2450 Pilothouse and it turned out to be a thruhull tansducer mounted almost 4 ft in front of the motor. Switched to a transducer that mounts flush with the hull and problem solved.

[Tom W Clark]

OK, so the props are Bravo Is, but are the vent holes plugged? If not, plug them.

[ShortCircuit]

Didn't Contender change the location of the trim tabs on the newer boat? I know one person that had to modify his trim tabs to keep from interfering with the motors.

[baitkiller]

Check the toe setting. Had a 2660 sailfish with 225's last week blowing out at hole shot. Re-set the toe and solved 90% of the problem.

Run the boat a cruise speed and take off the tie bar to see where the engine wants to run.