4 blade for 90hp rude

[cougar1985]

hey guys i got a 1982 90 hp rude that im currently running a new 17p vortex prop on. it performs well for the boat ,maxs out 5600 rpm.i want a spare prop or even a nicer main prop. i want to order a solas amita 4 blade in 12 3/4 x 17p.my question is will or should i keep same pitch when going to a 4 blade? as i cant afford to run wide open all the time i thought a 4 blade would be better at the 1/2 to 3/4 throttle range,correct,false?

 

[walleyehed]

Re: 4 blade for 90hp rude

To get the efficiency out of a 4-blade, you about have to be mounted on a jackplate to get the engine up....other-wise, you're wasting technology you can't use, and it will actually be slower.

 

[cougar1985]

Re: 4 blade for 90hp rude

thanks a lot i wasant sure

 

[Crownie2]

Re: 4 blade for 90hp rude

Kenny's right. The only exception might be if you were pushing a heavy load...

Bob

 

[cougar1985]

Re: 4 blade for 90hp rude

what do concider a heavy load? the boat alone weights 1250.thats before motor or anything else.

 

[Crownie2]

Re: 4 blade for 90hp rude

Probably over 3500 lbs. as a guesstimate.

 

[cougar1985]

Re: 4 blade for 90hp rude

thanks for the input guys,i had allready ordered a solas amita 4 blade and was looking for the input you guys graciousley gave and will get it this week and will certianly let you know how it works out whether good or bad.im not concerd with top speed performance or id have bought a gass guzzling speed boat(id still like to have one but id only be able to go out once a year with the cost of gas)lol. again thanks alot.

 

[Crownie2]

Re: 4 blade for 90hp rude

I would suggest you compare speeds at say, 3,000 and 4,000 RPM's with each prop (as well as WOT speed) to see if you have a gain with the 4 blade. If you do, then you know you are ahead, given your desire for a good cruising prop.

Good Luck! d

Bob

 

[cougar1985]

Re: 4 blade for 90hp rude

thanks it came in today. odd though ,when i picked it up at the depot there was no bill or catalog.its a good thing canada customs was in a good mood cause i didnt fell like going back to the u.s. to see if the depot had the billing and pillfured the catalog or if iboats just forgot to put in.so either tomorrow or sat. i will go play.

 

[cougar1985]

Re: 4 blade for 90hp rude

just got back from fishing and playing with the prop. for what ever reason this prop runs far superior to the same pitch 3 blade vortex that was on it. top speed is 3mph faster ,cruising speed is also better.go figure,but you cant beat facts! why i dont know but im very pleased with this prop.engine was in the exact same position and trim,and the lake was exactly the same as the other day of testing with the 3 blade.so the 4 blade solas moves to number 1 prop for my boat.

 

[walleyehed]

Re: 4 blade for 90hp rude

That would be an exception to the rule....and also proves not all react the same, although in the same pitch, it may be the same speed. We usually drop 1" in pitch to keep the same RPM with a 4-bld.
Just a shot in the dark here, but your RPM should have dropped about 200...Are we still at the upper end of the range?

 

[cougar1985]

Re: 4 blade for 90hp rude

yes for my motor before 4 blade it was 5600 ,after 5600.its been suggested that maybe the 4 blade is giving more lift thus the better numbers.im certianly not complaining as i was prepared for slightly less performance.

 

[cougar1985]

Re: 4 blade for 90hp rude

yes for my motor before 4 blade it was 5600 ,after 5600.its been suggested that maybe the 4 blade is giving more lift thus the better numbers.im certianly not complaining as i was prepared for slightly less performance.

 

[cougar1985]

Re: 4 blade for 90hp rude

yes for my motor before 4 blade it was 5600 ,after 5600.its been suggested that maybe the 4 blade is giving more lift thus the better numbers.im certianly not complaining as i was prepared for slightly less performance.

this is the design of the boat ,i dont really know if it had anything to do with it.