Cavitation plate height vs wot rpm

[reiddo1]

I have a 2000 oceanpro 150 hp and at wot the maximum revs are 4,800. I noticed recently that the cavitation plate is at least one inch lower than the hull. Can anyone relate cavitation plate height to maximum rpm's ? The propellor is one recommended for the motor and according to Piranha propellers web site, I should try to raise the rpm to 4830. I am wondering whether I will pick up the additional rpm by raising the engine on the transom by one inch. All replies are appreciated.

 

[V153]

Re: Cavitation plate height vs wot rpm

I would start 3/4" above the keel'n go from there. 'Less'n it's some weird hull. What kinda boat's it on?

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

I would start 3/4" above the keel'n go from there. 'Less'n it's some weird hull. What kinda boat's it on?

The boat is a Glastron Sea Fury V216.

 

[V153]

Re: Cavitation plate height vs wot rpm

Imagine that. I'm kinda fond of Glastrons. Cool boat! I know of two in the area.

Glastron is a fast hull. Hell yeah raise that motor a hole or two!

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

I guess I am somewhat biased, but this hull is extremely good in rough water and behaves well in cross lop, down wind and up wind operation. I acquired it last January with a 1979 200 Evinrude which was quite tired and gave up the ghost in October. The current 150 hp Oceanpro is a 2000 model year with very low hours judging by its appearance, compression etc. I have only used it for about one hour in a very short trial on the boat and am making plans for substantial boating when it gets warmer here in April-May. The lower RPM at wot is something I am hoping can be cured by raising the engine on the transom. Thanks for your help.................Don

 

[boobie]

Re: Cavitation plate height vs wot rpm

Is your tach accurate..................Maybe it should be checked.

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

Is your tach accurate..................Maybe it should be checked.

The tach is a new Faria and at 4800 rpm, according to my gps, the boat is moving at 59 km per hour. That speed seems about right for the rpm's to me, but after I raise the engine on the transom, I'll take a closer look at the tach if my rpm's don't increase to where they are supposed to be.

 

[bwkre]

Re: Cavitation plate height vs wot rpm

4800 to 4830 rpm. That is only 30 rpm more. About 1/2 a revolution per second. I think it would make no detectable change in boat speed Correct me if I'm wrong, leave it be.

 

[Silvertip]

Re: Cavitation plate height vs wot rpm

Where did you come up with the 4830 number????

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

4800 to 4830 rpm. That is only 30 rpm more. About 1/2 a revolution per second. I think it would make no detectable change in boat speed Correct me if I'm wrong, leave it be.

That number comes from a Piranha propellers web site program for propeller sizing. I am not suggesting that 4830 is all I need. I am merely stating that 4830 is the lower level offered by the Piranha program. I would like to get around 5200 rpm.

 

[Chris1956]

Re: Cavitation plate height vs wot rpm

I have a similar motor and boat. What is the pich of the prop?

When I first got my boat, I raised the motor all the way up on the transom. I slowly lowered until it was all the way down again. Made no difference in performance, no matter where it was.

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

I have a similar motor and boat. What is the pich of the prop?

When I first got my boat, I raised the motor all the way up on the transom. I slowly lowered until it was all the way down again. Made no difference in performance, no matter where it was.

14.25 dia. X 19 pitch

 

[emdsapmgr]

Re: Cavitation plate height vs wot rpm

You want the water flowing past the keel to flow just under the anti-ventilation plate. If it's flowing over the plate you probably have a lot of spray/drag due to that setup. Hard to tell about the engine height unless you run the boat at full trim at WOT in the water. If you run a stainless high rake cupped prop, you could move the engine up (higher,) on the transom so that the water flows under the plate- maybe 3/4". You might pick up a couple hundred rpm's and some fuel efficiency. I think you'll find that your current engine is rated to run between 4500-5500 rpm's. Best to prop it to run at the upper range of the normal rpm's, or 5500.

 

[bwkre]

Re: Cavitation plate height vs wot rpm

That number comes from a Piranha propellers web site program for propeller sizing. I am not suggesting that 4830 is all I need. I am merely stating that 4830 is the lower level offered by the Piranha program. I would like to get around 5200 rpm.

Sorry, I misunderstood the original post. It said " I should try to raise the rpm to 4830" . To me that meant 4800 at wot and trying to reach 4830.So sorry.

 

[Outsider]

Re: Cavitation plate height vs wot rpm

Forget about cavitation plate v. hull and web sites. Conventional wisdom says your cav plate should be at (meaning just above) the water flow at WOT, and I wouldn't make any motor adjustments until you know where you are. I don't know if raising the motor will achieve what you want in RPM, but I'm betting you're gonna have to have it 2 or 3 holes from the bottom. Once you're there, then you can play with props, cups, and web sites to get the RPM where you want it. Conventional wisdom says the upper half of the max range, and I'd shoot for the upper quarter ...

 

[Chris1956]

Re: Cavitation plate height vs wot rpm

I found a 19" pitch prop was a bit tall for my 21' DC and '98 150HPV6. Unfortunately, the 17" pitch prop lost a bit of top speed, but improved low end power.

 

[bob johnson]

Re: Cavitation plate height vs wot rpm

id turn that rpm up to at least 5800 rpm......id also move the motor up at least 2 holes.... there should be at least four rows of holes on that bracket....the 60 degree loopers like to turn fast......6000 rpm is common...just run temperature gauges in each head and you can monitor your motor.....

bob

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

id turn that rpm up to at least 5800 rpm......id also move the motor up at least 2 holes.... there should be at least four rows of holes on that bracket....the 60 degree loopers like to turn fast......6000 rpm is common...just run temperature gauges in each head and you can monitor your motor.....

bob

I have raised the motor up two holes from the bottom and on a short trial yesterday, I gained 300 rpm at wot. I expect better than that since the motor has not been run enough for the effects of engine fogging last fall to disappear. I have since the short trial added Seafoam to approximately 60 litres of gas and expect that by the time that fuel is burned, my rpm's should rise a little more. Hole shot performance seems better but on sharp turns at high speed I do experience some increased revving and I have to trim in the motor somewhat. While my speed is higher according to the speedometer, I did not have my handheld GPS with me and therefore cannot give an acurate speed increase. Also I did not view the anti ventilation plate height after planing since i was the only person on board.

 

[emdsapmgr]

Re: Cavitation plate height vs wot rpm

You have made some excellent progress on your setup. It takes slow, incremental steps to really get it dialed in. That low-port engine will make good hp up to 5800. Above that, the engine runs out of breathing capability and you are twisting it for little real gain. If you gain any more rpm's by add'l tinkering, I'd consider a higher pitch prop. It will put the rpm's in a higher torque band.

 

[reiddo1]

Re: Cavitation plate height vs wot rpm

You have made some excellent progress on your setup. It takes slow, incremental steps to really get it dialed in. That low-port engine will make good hp up to 5800. Above that, the engine runs out of breathing capability and you are twisting it for little real gain. If you gain any more rpm's by add'l tinkering, I'd consider a higher pitch prop. It will put the rpm's in a higher torque band.

When I see how much additional rpm's I get after running the Seafoam through her then i will evaluate. This engine was used on a 24' Cape Island hull which certainly is not a planing one. Consequently the PO ran it around 3000 rpm for best boat handling and economy. I would suggest this engine has substantial carbon buildup by now. I expect the Seafoam will clean up the carbs and combustion area carbon nicely. It certainly worked wonders on a carboned up Honda Gold Wing motorcycle that I own. Thanks for all your comments.......Don