Repowered 115 2stroke

[mjasin]

Recently aquired a '99 115hp 2 stroke yami and it came with a 13x19 solas prop. New Saturn i think. Boat is a key west 17'6" flats (~1000lb without motor). Took it out for the first time yesterday and found it to run about 4800-4900 at WOT with 2 people...close to max load. I have no complaints about the performance (the boat flies . I read that operating range for WOT for my motor (s115TLRX) is 4500-5500rpm. I heard from some guys at the parts shop that my motor likes the upper end of the range better (?). I feel happy with the performance but want to do what will help the motor run its best with the least wear/tear at WOT and at cruise speed. Should I think about changing the prop to get a higher WOT rpm or is this setup just fine?

Thanks!!

 

[jestor68]

Re: Repowered 115 2stroke

It sounds like your prop is right as well as your rpm. Your motor develops it's peak power at 5000 rpm.

Given that the boat is listed as having a 20" transom height, I would experiment with motor height to achieve optimum performance. Depending upon how you have the motor height on the transom now, it may be possible to raise it a hole to achieve more performance by reducing drag. This should raise your WOT rpm by a couple hundred rpm and gain more speed.

I believe the suggested mounting height for the motor on that boat is hole #2.

Your motor will last longer running at a lower rpm, as long as it is within the recommended WOT rpm range; which you are.

 

[steelespike]

Re: Repowered 115 2stroke

Do you have a gps speed to go with your rpm? What year is the Key West?
While your rpm range seems reasonable It does seem that a 1000 lb boat with a 115 and a 19" prop would turn closer to 5500.
Your gps speed would help tell better where we are at.

 

[jestor68]

Re: Repowered 115 2stroke

Have you performed a compression test on your 13 year old motor?

The 1000 lbs is just the dry weight of the hull.

The prop you have is a "general purpose" prop, and not really the ideal design for your flats boat. A high rake "bass boat" type prop might be better to squeeze all the performance from your flats boat.

 

[steelespike]

Re: Repowered 115 2stroke

The tests I've observed were 1200 -1600 dry weight.running about 5500 with a 19" prop.
granted probably faster hulls and possibly more sophisticated props but does seem the rpm should be there.

 

[mjasin]

Re: Repowered 115 2stroke

Wow. Thanks for all the input. I'll get more info after the holidays. The seas were a little rough so it was difficult to play much at WOT. I'll get gps info after the next trip. My old motor was a '94 suzuki dt100 with a 13 1/4 x 18 prop and it ran at about 5400rpm WOT...it felt slower though. Boat is a '94 Key West Stealth. Same hull design as the current model i believe. I have it at the second hole as it was with the old motor. I need to test compression...

I spoke with the key west people and without hesitation they said 13.25x 18 was the prop for me. I didnt shell out the $$ for a new one cuz the one i have seems close. Would there be much difference between the two?

Thanks and more data to come

 

[steelespike]

Re: Repowered 115 2stroke

Your 19" seems to be doing fine, based on your comments.The 18 would add a couple of hundred rpm
for no constructive purpose. If your rpm is with your typical load I think the 19 is probably faster and the motor appears to be within
its rpm range.