Want to gain a little

[jenla]

I've got a 2009 tracker flat bottom 16.5 foot boat with a 2009 60hp Yamaha 4 stroke tiller. I have a 14pitch prop. I am revving 5300 rpm and getting 38mph. I would like to know if I was to use a 12 pitch stainless steel, would I be closer to revving 6000rpm and would I gain speed to 40mph? Reply to Private Message Forward .

 

[John_S]

Re: Want to gain a little

I've got a 2009 tracker flat bottom 16.5 foot boat with a 2009 60hp Yamaha 4 stroke tiller. I have a 14pitch prop. I am revving 5300 rpm and getting 38mph. I would like to know if I was to use a 12 pitch stainless steel, would I be closer to revving 6000rpm and would I gain speed to 40mph? Reply to Private Message Forward .

Welcome to iBoats.

It would rev higher, and have a better hole shot. I'd say you probably wouldn't hit 40mph, but there is a slight chance.

While SS may help get 1-2mph, it comes at a price. Guessing wrong on the prop choice can be very expensive. Might be better working with a prop shop that will let you try different props.

Are you at your highest speed trim position?

Is the cav plate on top of the water at planning speeds?

 

[steelespike]

Re: Want to gain a little

If my figures are right,assuming a 1.85 gear ratio,your figures are optimistic.
I have you for 34 mph at 10% slip. Is your speed by gps?
correction,My following calculations were way off::
Again if my figures are right a 12" prop @ 6000 rpm at 10% slip would be about 33 mph.corrected
But I doubt the prop change would make up 700 rpm.
At 5700 a 12 would make about 31 corrected. Of course all these figure are approximate.
You might check the height of your motor usually the antivent plate(just above the prop)
should be about an inch above the bottom.
This could net a couple of mph under ideal conditions.
Prop change from al to ss is unpredictable I have seen poorer performance initially at rare times
so more than one selection may be necessary. Some dealers will do exchanges with the agreement you will buy the correct prop.Usually requires a hefty deposit.

 

[Silvertip]

Re: Want to gain a little

Just because you make the engine rev faster by lowering pitch, that merely means the prop is taking less of a bite on the water so it takes more PROP revs to move the boat the same distance as before the swap. If the engine was severely over propped (way too much pitch) then there would likely be a noticeable increase in speed.