23' twin engine blowout problem
 

I have a 1986 SeaCraft walkaround cuddy, with twin 1988 mercury 135's. I have a problem with the props blowing out around 2000 to 2300 and I have to slow down or pick up speed till they bit.
I was told the engines sit to high on the transom. The engine have 25" shafts and are mount all the way down. Can anybody HELP.

Re: 23' twin engine blowout problem
 

Tony,

I am no expert by any stretch but I run a 25" shaft on my 23' CC. I have a single outboard, a Mariner, and it gives me no trouble, I am thinking, with twins, they would sit more outboard from the keel thus the hull bottom should be drawing less water than at the keel right? Strange problem...but, I think that somewhere in this site, someone will have a suggestion for you. I bet someone has had that problem before and can correct it. Sorry I cant help you more....Gordon

Re: 23' twin engine blowout problem
 

Hooper, Thank you for your reply. I forgot to say that my center line on the transom is 31"s, I think the boat built in the 80's had deeper center line then the early ones. Your boat may be more of a classic then the one I have. But I LOVE MY BOAT.

Re: 23' twin engine blowout problem
 

Tony and Hooper welcome to the site!

Tony like Hooper says I'm no expert but your not getting clean water for some reason....I would however be inclined to think that if you have a 30" transom with twin motors with 25" shafts your good. There’s a lot of stuff you could look at.

Thru hull / Transducers causing turbulence in front of the props?
I would guess that you've made sure the cavitation plates are on the same plane with the bottom of the boat?
What about the props are they the right ones for the motors.... pitch??
Have you messed around with the trim while running?

The only time I've experienced this has been when air has gotten under the boat and the props got caught in the wash.

Not alot of help but some things to consider if you havent already..
Scott

Re: 23' twin engine blowout problem
 

Scott Thank you, I tried everything you said. I think the one thing I did not try, is a new setup. The engine cavitation plates are 1" above the transom. Do you know the proper setup. (spacing and transom hight).

Re: 23' twin engine blowout problem
 

Tony

My engine is about even (a single) with the bottom. You wouldn’t want to go higher than that(the 1" even though I don’t think that’s too high) but if you could lower the engines a little it wouldn’t hurt......just more drag. Doesn’t sound like that can be done though [img]images/icons/confused.gif[/img]

Trayder ... where's the cavitation plates on the Contender??? or anyone else???

Has the boat always done this.....and does it do it when on plane??

Re: 23' twin engine blowout problem
 

Trayder, I had the boat for 3 yrs. it has been doing it since I got her. I thought it was going to be an easy fix !!! Once she is on plane she will run fine. My props are mirage 15x15.5 and my max RPMs. are 5200. (The engine max are 5000 to 5500), so its in the range. I was hoping it was a prop problem..

Re: 23' twin engine blowout problem
 

Tony,
What is the engine center to center measurement?You can find by measuring from left mounting bolt center on one motor to left bolt center on other motor.
d.h. [img]images/icons/smile.gif[/img]

Re: 23' twin engine blowout problem
 

Hello guys-

DH would be the authority on this one. I have not checked the measurements on The Contender yet but regardless D.H. would know the best [img]images/icons/wink.gif[/img]

Re: 23' twin engine blowout problem
 

The measurement from the tiller of one engine to the other is 24.5". I was told it should be 26" and my transom height should be 30". ???? My transom center line is 30.5" I was told to cut my transom down to 30" and move engines to 26" centers. I do it in a heart beat if I was sure it was the cure...

Re: 23' twin engine blowout problem
 

Tony,
I need the engine centers! Not from the tiller,from the mounting bolts,as the motors probably have some toe in if they were installed correctly.
d.h.

[ May 02, 2002, 10:25 AM: Message edited by: HermCo ]

Re: 23' twin engine blowout problem
 

HermCo, I'll check that this weekend. Thanks

Re: 23' twin engine blowout problem
 

HA TONYS
I HAD A SIMILAR PROBLEM ON A SINGLE ENGINE OMC ONCE AT CERTAIN RPM I GOT CAVITATIONS. I TALKED TO THE PROP GUYS AT OMC AT THE MIAMI BOAT SHOW THEY TOLD ME TO GO WITH A 4 BLADED PROP I TOOK THEIR ADVICE AND NEVER HAD THAT PROBLEM AGAIN. I KNOW BUYING 2 PROPS TO TEST THIS OUT COULD BE $1,000 BUCKS BUT SOME PROP GUYS WILL LET YOU TEST OUT THE PROPS AND IF IT DOESN’T WORK WILL TAKE THEM BACK. THE OMC GUYS SAID THAT I COULD EVEN RUN MY ENGINE UP 1 OR 2 MORE INCHES HIGHER OFF THE TRANSOM NOW WITH THE 4 BLADED PROP.
FELLOW-SHIP [img]images/icons/wink.gif[/img]

Re: 23' twin engine blowout problem
 

Good suggestion on the 4 bladed props. That should solve your problem. Another suggestion is to Contact Bob's Machine Shop in Ruskin, FL. They are world fameous for setting up shallow water flats boats. I think they could sell you a pare of aluminum plates that would bolt onto your existing cavitation plates. That may be a cheep alternative to help reduce blowout. Cutting your transom down seems scary and expensive. Moving your motors 1 1/2 inch further apart could be done with a cherry picker and a drill in about 3 hours. Then again, how often do you drive at 2000 to 2300 rpm's? You could just live with it.

Re: 23' twin engine blowout problem
 

Hello Briguy, thank for the info. I have been living with the problem since I got the boat and I don't mind, but when people say what up with that! It bugs me, because I love this boat and I would like to have it right. I know everyone who has a SeaCraft feels the same. Thank

Re: 23' twin engine blowout problem
 

Tony,

When your guests ask you what the noise is when your prop's blow out, TELL 'EM THAT'S YOUR TURBO KICKING IN!

Re: 23' twin engine blowout problem
 

Briguy, THATS GREAT! Thanks

Re: 23' twin engine blowout problem
 

HermCo, The measurement from the center of left to left bolt is 24.5". I hope this helps.
Thanks

Re: 23' twin engine blowout problem
 

Should be at least 26" and the transom should be no more than 30" high at center.What kind of steering does the boat have? Cable or hydraulic?
[img]images/icons/confused.gif[/img]

Re: 23' twin engine blowout problem
 

D.H. I have hydraulic steering front mount. Also you are right the starboard engine runs hotter at trolling speed, it never overheats and the alarm does not sound but the gauge shows it just below the red line. once on plane she cools down. this year I installed a high speed pick up on her but have not tried it yet.

Re: 23' twin engine blowout problem
 

Tony,
If it was me I would try props first since you have high speed pickup allready and the motors are mounted high. The setup you have will give you the fastest WOT speed when you get the props dialed in. [img]images/icons/grin.gif[/img]

Re: 23' twin engine blowout problem
 

I have a 75 Model 23'CC with twin 150 hp Mercs with 25" shafts on a bracket. The only props I could get to work were 17" and 19" Mirages. I ended up with the 19" because I turned them 5400 to 5600 and wanted the extra speed. They have never cavitated under any circumstance. I did try a pair of 4 bladed props which ran great as long as I didn't turn the wheel. The second I turned the engines, the outboard engine to the turn would blow out. If the mirages don't work you must have something throwing dirty water in front of your engines or they are indeed mounted too high.

Re: 23' twin engine blowout problem
 

Thank you REPETE, are your props mirage 2 or the older mirage, because I was told the new mirage are better. The bottom of the hull is clean, no sea chocks or transducers. I had it sandblasted and barrier coated and painted with epoxy paint.

Re: 23' twin engine blowout problem
 

They are the new Mirages with the plastic inserts. The inserts are supposed to take the place of the pressure installed rubber hubs. The diameter of the Mirage is such that it will not cavitate if its got relatively clean water. Most of my friends with Yamaha's run the Mirages also.

Re: 23' twin engine blowout problem
 

Toni, what is barrier coated.RS.

Re: 23' twin engine blowout problem
 

RS, barrier coat system is a two part epoxy sealer used to seal water out of the gel coat. Its more waterproof then Gel coat and prevents water blisters. ( so it claims)