suzukis seatrialed!

[Island Fish Lifter]

I just got back, spent the night at menzies. The new power ran great. I cruise at 3200-3400 rpm and maintain 27- 29 mph. Top speed 50 mph at 5500rpm- a little low. I have 23 pitch props on now and can either pay to prop them down to 21, or find a set of 19's on ebay. Id rather have 19's so Ill see what I can find....

 

[nedarb2]

5500 rpm is right around where it should be isnt it?

 

[Island Fish Lifter]

a little low, 6000 would be ideal. Its better to have too much than not enough. I would live with 5800.

 

[bananas]

21s would for sure take you to 5800 but i agree 6000 is best.

 

[mlaag]

Every 1 inch of pitch will equal 300 rpm

 

[Island Fish Lifter]

Every 1 inch of pitch will equal 300 rpm

wrong

 

[Island Fish Lifter]

actually 1 inch equals about 150 rpm difference. Prop pitch is graduated in sizes by 2" increments. So, if I go from a 23p to a 21p, I can realistically expect to get 300 more rpm. These are stainless props. Aluminum props actually flex. An example of this is lets say I had a 19" aluminum prop. It will actually become a 17- 17.5 under full load, loses efficiency!

 

[Gypseas]

So IFL if I get it right if I have a 17pitch aluminum prop and want to change to ss should I get a 15 pitch?
Or keeping the same 17pitch, speed will increase and wot decrease? And probably the motor will also labour. Slower plane?
What do you suggest?

cheers
vic

 

[Island Fish Lifter]

vic, I definately dont want to sound like Im trying to be a propping expert, however: If you have a 17 pitch aluminum prop that you want to convert to stainless, and your current performance is optimal, you will have to choose a sst prop size that will compensate for the aluminum blade flex experienced by your 17p alum. I think it is 1 prop size (2" of pitch), I would call a prop shop to verify the correct conversion factor.
So, you asked me what I suggest. Fair enough, but I need to know what your application is, also what your current performance is (max rpm). Its also important do know how much extra weight is in your boat at the time of WOT test.

 

[Island Fish Lifter]

Every 1 inch of pitch will equal 300 rpm

wrong

It appears I may have been talking out of my butt. I spoke to the prop shop today and he figures I may get as much as 500 rpm by propping down 1 size. That would definately cheaper than buying new props!