need advice on prop

[skinnyrunner]

Hi guys, I'm having a problem getting the mid-range rpm from my engine, I will give details. I have a 1860 center console aluma-craft all welded tunnel hull with a 90 etec. My overall weight is 2100 lbs. I was having trouble with cavitation when making turns. My motor is mounted to a CMC hydraulic lift with tilt and trim, I was having this problem when I had the motor raised. I talked with a guy at Dan's Prop Shop and he advised a cupped prop. He said I needed a power tech SWW4R15POM140. I installed it on the motor, tested it out and sure enough that prop would bite like nothing i had ever seen, with the motor raised to its max position it will bite in a 90 degree turn...i warn anyone who is riding to hold on tight. The only problem is i only get 4500 rpm out of my motor, the range is 5-5500 per etec specs. I talked to the guys at Dan's Prop Shop and they tell me I have to give up somthing to get what i want. I assume they are telling me in order to run a high-lift cupped prop that i have to live with low rpm's which equals poor performance from my 90 etec. I would be appreciative to any advice on this situation.

 

[WesNewell]

I think what he's telling you is you need a lower pitch prop of the same style, assuming you mean you only get 4500 rpm on a straight wot run.

 

[skinnyrunner]

WesNewell I appreciate your response, he said that the power tech SWW series cupped prop only goes down to a 14 pitch, and that would not be enough to make a considerable difference. I guess my question now is can i get the prop i have now cut down and machined to what i need or is there another manufacturer that makes a cupped 4 blade prop for high lift and cavitation problems.

 

[Sea Rider]

Is motor having cavitation or ventilation (aeration) problems ? Can you post a pic of lower leg shot sideways to see both lower plates.

Happy Boating

 

[skinnyrunner]

Sea Rider, My motor is mounted on a hydraulic jack plate so I can adjust the position of my motor in the tunnel while running in shallow water. My original problem was my prop was loosing bite when I made sharp turns. I mostly run in the river and their are obstacles everywhere, so having control of my boat while making quick turns around logs and rocks is very important. I would loose bite before I went to this cupped prop. Now with the cupped prop it steers where I tell it to no matter how high my motor is raised, but it lowered my rpms from 5500 to 4500.

 

[jimmbo]

Almost all props these days are cupped, even BRPs Aluminium props. As I have never seen or even heard of a 'Power Tech' prop I don't know how their blades are different.
But as mentioned above, if your rpms are low, a lower pitch is needed, grinding off the blade to reduce diameter will not affect RPMs as much, and will probably create more issues.
Since you run mainly in Rivers, perhaps you should consider a Jet Drive for the outboard

 

[Sea Rider]

Which pitch is your current SWW4R15POM140 prop, is it a 15 pitch ? With it the motor is revving 500 less rpm from min and 1,000 less rprm from max wot revs factory stated. Send the current prop to a prop shop and have it repitched by 2 less sizes which is the max any pro prop shop will dare to go for. The motor will perform much better with a higher rpm range than with current prop.

At close tight turns is called ventilation, aeration, cavitation is more of a cosmetic issue. We had same issue with an ETEC 150 HP on a large boat, After a test on flat calm, no wind water run found the motor was sitting high, the motor was bolted much lower and the problem was canceled, afterwords the prop was maximized to a lower pitch for motor to run to its full wot revs with 4 up which is the fixed load the combo will usually carry.

Will try to post a pic over the weekend to show at which lower leg height those motors works fine. It's a matter of matching that precise lower leg height while playing with the hydraulic jack plate, once dialed will need to mark that position on the jack plate, control, lever, whichever to know you're there and not make a wild guess playing with such controls.

Happy Boating

 

[Faztbullet]

This what he has Sea except a Erude....and no the motors not too high.

 

[Sea Rider]

Quote : Hi guys, I'm having a problem getting the mid-range rpm from my engine, I will give details. I have a 1860 center console aluma-craft all welded tunnel hull with a 90 etec.. Faz, don't read any Yam motor posted nowhere.

Skinnyrunner, can you post a neat pic of your current ETEC 90 HP motor shot sideways ?

Doesn't matter much which motor brand or model they are, all have upper and lower plates, some of them with shorter plate distance between them, other way larger. It's a matter to find the right lower leg height for best prop thrust in most water conditions. The issue is that nobody visually looks what's going on at front of lower leg which is the fastest way to dial the opt transom/lower leg height,

Playing excessively with trim settings, ear sound transom height optimization as to determine if having prop aeration or water splash issues while wild guessing with motor heights is the correct procedure to going nowhere and losing precious neat boating time.

Happy Boating

 

[Faztbullet]

That is the type of boat he has and that how high motor sets on these......and a Yam and Etec lower unitsare also copys of each other.