Fitted 07 115hp 2 stroke motor to my 16ft Dancraft ski boat recently. Previously had old Evinrude 235 which was ported, polished and had god knows what done to it (aparrently 260Hp tested @ flywheel) and got 55mph @ 5900rpm. It had poor compression on 2 cylinders...so I reckon about 150-175hp with 83kg extra weight over the new yammy (approx 183lb for the non-metrics). The 115 yammy had 24hrs @ time of purchase, 25hrs upon delivery and in the first day of running on my boat racked up to 28hrs. Ran beautifully and my boat handles & rides much better. The original speedo was fluctuating around 48-52mph at WOT on new motor...so not too much drop in speed but much better holeshot - even with much less power. However, reccomended WOT on the yammy is 4500-5500rpm. I was still pulling 6000 @ WOT on 17" factory s/s prop and hit the limiter (which is set at 6050 on these motors). Need to change to higher pitch to get WOT down to or slightly under 5500rpm. Will get better top end speed in the process. Holeshot is not a major concern because the boat is very light. My theory is for every extra 1" pich increase would drop WOT by 200rpm. I estimate 19" would be 57-5800rpm or 21" 54-5600 rpm (factoring in increasing rpm drop with extra prop
itch load). Speeds recorded in this boat were done on same part of river @ sea level with 1-4 passengers on board and approx 100ltr (20gal) of fuel on board, with negligible difference in performance. Desired top speed is the 60mph mark, but my main concern is getting WOT to the top end of recommended range, as I do like to do WOT runs from time to time. Any advice would be appreciated.
itch load). Speeds recorded in this boat were done on same part of river @ sea level with 1-4 passengers on board and approx 100ltr (20gal) of fuel on board, with negligible difference in performance. Desired top speed is the 60mph mark, but my main concern is getting WOT to the top end of recommended range, as I do like to do WOT runs from time to time. Any advice would be appreciated.