Prop help please

[DAN M VAGOS]

Hi all I purchased a 1999 Key largo 160cc and it has a 99 Johnson 70 hp on it the prop that's on it is a 13 3/4x15 the rpms at wot are 6000 and the boat is only going 28mph. I have a prop that my prop guy made me witch is a 13 1/4x17 and it's no better. The boat is not a heavy boat and it's super quick out of the hole but I want more speed and less rpm. What should I try.

 

[Sea Rider]

Re: Prop help please

Check to see if you have a flooded hull ? If so, drain water, rpm will rise with same prop. Is 6 K the max wot factory stated for that engine ? Just 28 mph with a 70 is slow. Check best engine/transom height and trim for best performance.

Happy Boating

 

[DAN M VAGOS]

Re: Prop help please

The hull is dry. Just seems like it should be faster then 27

 

[steelespike]

Re: Prop help please

From your description a 17" pitch should take off about 400 rpm. Don't know why your 17 doesn't work but it may not be a 17
or not very efficient. At 5600 rpm and 13% slip, speed could be about 32 mph still, have a good hole shot.
Perhaps your 15 is actually a 17.
Is the anti vent plate just above the prop about even with the bottom of the transom?

 

[DAN M VAGOS]

Re: Prop help please

The cavitation plate seems to be level with the transom or just above the bottom. The prop on it now is a 15 the prop I had made is a 17 but I just changed out the tac and have not tryed it yet but I know the speed was not a lot more then the 28-30.