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Questionable Performance

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Jjam52

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Just bought a Bennington 24' SSRX in the Spring of this year. Upgraded to a 115 horse Yamaha motor with a stock propeller (13.75 X 15). Since driving all summer I have noticed some inconsistent performance issues with the boat that I was hoping to get some advice on. First question is the boat maxes out at 5200 RPMs and will do about 24mph WOT. (With no more than 2 adults) This seems a little slow to me and low on where it tops out with regard to RPMs but our dealer assures us it is well within the appropriate range for Yamaha. Any thoughts?

Secondly we occasionally experience ventilation issues with the engine depending on the water conditions and the number of people on the boat. It ventilated more often with more people. The motor is fastened to the boat allowing the motor to be deepest in the water. We have twin elliptical pontoons with lifting strakes.

Any insight to these questions would be very appreciated!! We love our boat but I don't feel as though I am getting all the performance we should. Thanks in advance. John
 
Welcome from a former New Jersian. The motor should be spinning at 6000 rpm at Wot with just 2 of you on board. You might want to try a smaller prop (less pitch).
 
See my info under props and power. Had a similar problem. All good now.
 
JSM, I read your post but not sure I have a "Ken". What size motor did you have?
 
Ken is the guy at prop gods. He is in Florida, but will ship anywhere. I believe it is $35 plus shipping. He shipped to me in Wisconsin. He carries mercury props and others. He does not have yamaha props. Many have recommended him. Just google prop gods.
 
What trim position were you in when you ran only 5200?  Proper trimming can get you several hundred more RPM's.  Is the prop SS or aluminum?  In general 5200 is near the bottom of the motors RPM range and is good if you were really looking for the highest top end.
 
Thanks for your input. I had the trim all the way down. I have trimmed it up a little in the past to see how that would effect the engine but it has never helped that much. I have seen about 5500 RPMs with WOT on a calm day in the bay with just me and my son on the boat after I have played with the trim a little. Raising the trim does not consistently help increase RPMs when I'm out running. As far as the prop it is aluminum.
 
Jjam52 said:
JSM, I read your post but not sure I have a "Ken". What size motor did you have?
Click to expand...
I have the F70 on a 2275 GCW. Ken does have props for Yamaha, Mercury and others. I ended up with a SS 14x9 that he had the center softened  to eliminate a low speed vibration that I did not have using the stock aluminum 13 5/8x13, nor on the Talon 13x10.5. He sent me a 14x10 SS originally but it did not move the rpms but by more than 100 and had a vibration at near idle speed. I sent it back ($35.00 charge) and he sent me the 14x9 softened hub. Boat feels great, strong hole shot, strong climb and now maxing out at about 6200 rpm. 
 
Another thought toy ventilation issue because it is very sporadic..... Could seaweed from the bay cause the engine to ventilate?? Any thoughts? We thought it could be related to the weight in the boat but went out with a full boat today and had no issues. Any thoughts on this new theory?

Thanks in advance for any feedback
 
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