Pontoon boat cavitation & Vibration

[Pessemist]

I just bought an old 1989 24 foot Party Barge Paontoon boat. When acquired it had a blown engine which I had replaced by a 1984 rebuilt V4 Evenrude 115hp.<br /><br />We seem to have some vibration from the lower end of the unit and at about 40% throttle it cavitates very badly.<br /><br />The old engine had a sliding plate attached to the pontoon boat that allowed a lower mount into the water of the outboard. The guy that installed the Evenrude took it off and installed it directly to the transom.<br /><br />Could the vibration of the motor be asscociated with the cavitation or do I have a serious motor problem?<br /><br />Is there some guide to measure to assure the motor is deep enough in the water to wrk. It really looks about the same as other toons around the marina.<br /><br />thanks in advance for any help in this matter.<br /><br />pesse

 

[Steve135]

Re: Pontoon boat cavitation & Vibration

Pessemist - first off most boater confuse Cavitation with Ventilation this is very common. They are not interchangeable terms.First off as the propeller roates thru the water a high pressure area is created on one side of the blade and a low pressure on the other side of the blade. The propeller moves toward the low-pressure area carring the boat with it.Cavitatation is the boiling of water around the blades so to speak. Ventilation is air entering from obove or thru the exhaust. thats the simple short vertion. Now if you check your prob out you should be able to tell which is acurring by the dammage to the prop if any. The anti vetilation plate on your motor should be even with the bottom of the boat. Or you will nee to add another over the counter one to stop the problem.<br />steve

 

[BillP]

Re: Pontoon boat cavitation & Vibration

Whatever you want to call it the prop is getting air. At 40% power your pontoon boat is starting to get hard to push and the prop is pitched too much for the speed so it churns air. I'm sure there is a more politically correct way to say that but you get the picture, right?<br /><br />On my pontoon boat the cavitation is stopped by trimming the engine down or reducing speed. Lower pitch props help too. The jack plate your mechanic took off is the very best way to eliminate the problem. The answer is to make sure the engine is deep enough to grab solid water. If that doesn't work find a lower pitch prop.<br /><br />Either way, the engine cavitation plate (universally correct part name)needs to be down<br />at water level when the engine is at high speed. Check it when running and see where it is. Lower the engine if the plate is more than about 1/4" above the water. <br /><br />Yes, cavitation may be causing the vibration.

 

[steelespike]

Re: Pontoon boat cavitation & Vibration

Pess, In the process of getting your motor to not cavitate be sure your prop lets it run in its proper rpm range. If it doesnt it could cause premature engine failure.<br /> Your motor will need less pitch than if it was on a typical 18 foot runabout.

 

[Pessemist]

Re: Pontoon boat cavitation & Vibration

Thanks for all the help guys.<br /><br />Can anyone suggest what pitch prop I should be looking at for a 1989 24 foot Suntracker Party Barge with a 115hp 84' Evinrude V4?<br /><br />Or at least give me a starting point to compare against the prop on there?<br /><br />Thanks in advance for any help in this matter.<br /><br />Pesse

 

[ob]

Re: Pontoon boat cavitation & Vibration

What prop are you running? What is your rpms at WOT?

 

[rickdb1boat]

Re: Pontoon boat cavitation & Vibration

A 14"X13" usually will get you close. May need a 13X15 if loaded light. Check RPM'S as suggested. Also you may call a Prop shop and they can usually recommend the correct Prop, that would be close.

 

[Pessemist]

Re: Pontoon boat cavitation & Vibration

It is currently using a 14x13 cupped prop. I just got done talking with the guy that installed it and he wants to try a 14x15 prop.<br /><br />Interesting to see what that does.<br /><br />pesse

 

[sloopy]

Re: Pontoon boat cavitation & Vibration

try a15 by 12 that will get ya going, I would use a composite prop. were you can replace the blades..they worl greatfor pontoon boats

 

[rickdb1boat]

Re: Pontoon boat cavitation & Vibration

Yeah, I have a 13 3/4" dia. x 15 pitch which I now use as a spare. I also wanted to see what it would do! It really did'nt seem to make that much difference in top speed, but it did slow down hole shot alot. Seems like it took forever to get going, so I switched back to the 14X13. For some reason, it just seems like the 14X13 is the Ideal Prop to use! The Parts dealer that I got mine at said they recommend it for any pontoon from a 70 HP on up to about 120 HP. You would think a more powerful Motor would use a higher Pitch to gain more speed, but pontoons are funny that way! Unless your Prop is damaged now, I doubt that it is your cause of vibration. I have hit some pretty hard objects and darn near tore off one blade and It still did'nt vibrate at low speed!(Had to get back to the dock). Good luck and let us know what happens!

 

[rickdb1boat]

Re: Pontoon boat cavitation & Vibration

No such thing as a 15X12 for that Motor. Can't replace blades on a composite Prop!! Ignore post above!!!!

 

[Dhadley]

Re: Pontoon boat cavitation & Vibration

Rick, I think most folks already ignore those posts!

 

[sloopy]

Re: Pontoon boat cavitation & Vibration

yes you can I have seen them.. You can actualy buy buckets of used/demo blades from the company. stop yelling at me! this compositprop company evin has a comercial that I see on OLN and PBC all the time. THERE IS SUCH THING!@

 

[rickdb1boat]

Re: Pontoon boat cavitation & Vibration

Comprop 4-BLADE PERFORMANCE COMPOSITE PROPELLERS -- Four-blade Comprops are used as original equipment by many boat manufacturers such as Regal, Wellcraft, and Four Winns. Comprops run fast and smooth, while providing excellent cornering characteristics. You'll also find outstanding acceleration and quick on-plane times with these new props. Comprops are made of a high-tech composite that resists leading edge dings common to aluminum propellers. If you have a high speed prop strike, the Comprop blades are designed to break and absorb much of the shock, reducing costly drive train repairs. (It costs much less to replace a Comprop than a lower unit.) At prices up to 40% lower than aluminum props and up to 80% less than stainless steel, Comprop simply can't be beat for low cost and high performance. Boats and applications vary widely. When replacing a propeller use one of similar size and pitch to achieve similar performance. IMPORTANT NOTICE: If application is more than 225 shaft hp or boat is more than 21' long or 3,000 lbs. in weight, then a Comprop is recom-mended at reduced power only. 13 tooth, 4" hub

 

[rickdb1boat]

Re: Pontoon boat cavitation & Vibration

OK Sloopy, I'll give you this one!! There is a company that DOES offer replacment Blades for composite Props! Link is Below!! <br /><br />PIRANHA