Need Prop Recommendation for 90HP Yamaha - More questions

[hwsiii]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

We need to move the motor up one noth and buy the Solas Amita 4 blade 15" prop, it will bring the RPM up very lose to maximum and I don't think we will lose more than 1 MPH. But the performane differene you will see with hole shot and aeleration as well as the smoothness will make you very happy B.


H

 

[bc2009]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Changed to the 15" pitch 4 blade Solas Amita and now have 5300 max RPM with roughly 36mph. Comparison to the 17" pitch 3 blade Michigan Match:

RPM 15" 17"
3000 14.5 mph 19.6 mph
3500 18.0 24.7
4000 24.3 28.3
4500 27.6 30.9
4900 36.0
5000 30.0
5300 36.0

My wife noticed that the boat seemed to get up on plane quicker and it appears I used less gas today than the trip on the 28th (distance, amount of fuel, passengers all the same). I have not yet raised the motor up a notch - will that possibly raise the RPM to 5400-5450? I have noticed that the motor seems to require quite a bit of trim up to get the max RPM - I am assuming raising it up a notch would also lessen the trim needed?

Thank you, again hwsiii!

Bc

 

[bc2009]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Just got done moving the motor to the next notch higher mounting holes. The ventilation plate is now just above the bottom of the boat. Something I forgot to ask about with my questions last night - the boat had been pulling slightly to the right with the 3 blade 17" pitch prop, now it pulls to the left with the 4 blade 15" pitch prop...I'm assuming that means I need to move the trim tab to the left some. Might the adjustment in height help some too?

Thanks,
bc

 

[hwsiii]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Yes it will bc and move it to the left.


H

 

[bc2009]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

hwsiii,

Just got back from a run with the motor mounted 1 notch higher - 5300 rpm with 36 mph for speed (two adults 19 gallons gas) (same as with the motor mounted in the original position - 2 adults/2 small children/19 gallons). I could get 5400 rpm by trimming higher, but I also got a roostertail and a lot of water splashing into the boat.

Let me know if I should try adjusting anything or ?

Thank you!
Mark

 

[hwsiii]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

It sounds like we are not going to be able to trim the motor up as much with the motor raised up another notch, so we will not be able to get any more than the 5,300 RPM we are getting now. I would appreciate it if you would take a few pictures of the motor anti ventilation plate and the stern so I can see what we have.


H

 

[bc2009]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Let me know if you need any other angles...hopefully they show up (first time posting pictures). The antiventilation plate had been lined up with the keel, now is slightly above.

Thank you, again hwsiii - I appreciate all the help. In the past the boats I have used were well broken in and everything was pretty much set - this boat had almost no use before I bought it (kind of assumed it would need some tweaking, but wouldn't have known where to begin without your help!). Let me know if I need to adjust the motor height or if everything should be good.
bc

 

[bc2009]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Another update - with a change in passengers (one adult and one small child) I was able to get up to 5400 and a top speed of 38 mph). Added pictures in the previous post of the motor/stern from the back and side - let me know if it is most likely in the best position or if it would be best to move it...

Thank you!
bc

 

[hwsiii]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Bc, from the pictures it looks like you only have one notch that the motor can be moved up anyway, and we should be able to gain another 100 to 150 RPM moving it up the last notch, and that is my recommendation.


H

 

[bc2009]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Numbers for my last trip with the motor in the highest setting available, 2 adults, 1 small child, and 17 gallons of gas. The boat reached 37.5mph @ 5500 and 38.6 @ 5600 - when the motor was about 3/4 trimmed up to max it did splash water into the back of the boat but settled down once trimmed to max RPM. Also, it was an extremely windy day and the roughest water I have been on in years...I would imagine it could do a bit better on speed, but I likely won't find out until Spring. Let me know if this is where it likely should be or if I should watch for anything the next time out (ie. do I need to lower the motor because of the 5600RPM or just keep it away from WOT?).

Thank you again!
bc

 

[hwsiii]

Re: Need Prop Recommendation for 90HP Yamaha - More questions

Bc, I believe we have done everything we can, you are at maximum RPM and we picked up a little speed. Running it at 5,600 RPM every once in a while won't hurt anything. And you are very welcome.


H

 

[wellsc1]

Re: Need Prop Recommendation for 90HP Yamaha - Dhadley

Re: Need Prop Recommendation for 90HP Yamaha - Dhadley

HWS and Carl - thank you for the info. Carl, I am interested in finding out how the Yamaha prop worked on your boat...and any other prop recommendations.

bc

The semi-cleaver Yamaha painted ss prop, 17-pitch caused the motor to dog like the full-bladed, cupped one I returned. My mechanic recommended I check the fuel filters. I didn't realize there was a filter under the cowling in addition to the spin-on aftermarket one. That's my next step to do. If that doesn't work, he recommended to suspect partially clogged carbs. I'll keep ya'll posted.