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Author Topic:   E-tec cavitating
Harv posted 06-12-2006 12:05 PM ET (US)   Profile for Harv   Send Email to Harv  
I have a 2006 50 hp E-tec installed on a 18ft Smoker craft pontoon boat. I am experiencing what I suspect is cavitating prop surge at avarious RPMs . The boat comes up on step at about 3500 and tops out at about 5000 .

Surge / hesitation is experienced periodically at all speeds above 3500 but most pronounced at about 4200.

There is considerable frothing at the engine and water actually works its way over the transom at 3500

How can I determine if this is really prop surge and can the problem be resolved with a different pitch prop?

Thanks

Harv

fourdfish posted 06-12-2006 02:42 PM ET (US)     Profile for fourdfish  Send Email to fourdfish     
I would think going back to your dealer would be the first step! It could be several different things. Some of the great people here could offer suggestions but without actually seeing it, they would be just guesses!
The Judge posted 06-12-2006 03:26 PM ET (US)     Profile for The Judge  Send Email to The Judge     
ALL pontoons I have driven will cavitate if not equipped with what we call a "pontoon cup" on the prop. This is basically a double or triple cupping that keeps her from cavitating.
seahorse posted 06-13-2006 07:36 AM ET (US)     Profile for seahorse  Send Email to seahorse     
BRP makes a line of props for pontoons called Hydrus and also a couple of low pitch SST "triple-cupped" props that work well in the aerated water.
seahorse posted 06-13-2006 07:40 AM ET (US)     Profile for seahorse  Send Email to seahorse     
I forgot in the previous post to add this pontoon boat test report with an E-TEC 50.

http://www.e-tecinfonet.org/sitebuildercontent/sitebuilderfiles/e-tec50-sunset_bay260.pdf

Denny posted 06-13-2006 10:25 AM ET (US)     Profile for Denny  Send Email to Denny     
A friend of mine had a problem like this and it turned out the dealer had not mounted the motor correctly on the pontoon boat. As the boat speed would come up the motor rose out of the correct position in the water and cavatate. The motor would not get enough water for cooling at high speed as a result, the water pump was replaced twice. A dealer up in Iron River Wisc noticed what was going on when he walked forward on the boat and someone on the dock noticed the water tell was not sending out water at idle. This was a subtle problem and the first time he had seen it. Hope this helps.

Denny

swist posted 06-14-2006 07:33 AM ET (US)     Profile for swist  Send Email to swist     
I believe the correct term for what you are experiencing (prop too near the surface) is ventilation - a quick jump in engine speed when the prop grabs air instead of water.

Cavitation is a more subtle phenomenon where the wrong combination of high speed, warm water, and other factors cause the water to actually boil on the surface of the prop - when the resultant vapor bubbles collapse, they can corrode the surface of the prop.

Ventilation can wreck your engine. Cavitation can wreck your prop.

kingfish posted 06-14-2006 08:08 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Exactly right, swist...and related to that, the part of the lower unit often called the "cavitation" plate, is correctly called the "anti-ventilation" plate.

John

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