I have a 22ft 79' Starcraft Islander.
Weighs about 2,200# with fuel and me.
Mercruiser 470 with 1.84 MC-1 outdrive.
My recommended WOT is 4,200-4,600.
New tach (set for 4cyl)
Iphone GPS
I'm currently using a 3 blade 13 3/4 X 21 and can only achieve 4,300 at 35MPH(30 knots). According to the Mercury prop calculator, I'm getting about a 25% slip. The other day I had a load of 4 adults, 4 kids and 2 medium dogs and could only get 3,900 RPM and it was a dog out of the hole. I know I'm over propped and the diameter is too small.
I purchased a 4 blade 15 X 17 and had the same results. 4,300 at 35 MPH (30 Knots) The prop calculator shows a 7% slip.
Today I'm going back to the prop shop and get a 4 blade 15 X 15.
Am I on the right track?
I'd like a cruising speed of 30MPH (26 Knots). It looks like the 15' prop will put my top speed about there. (30/26)
I can currently cruise about 28MPH (24 Knots) at 3,600.
I guess I'm rambling and don't seem to have a real question. This is my 1st 4 cyl motor. I am accustomed to SBC performance. The 470 seems very fuel efficient though.
I'm not sure weather to go with a 3 or 4 blade either. The prop shop owner recommended the 4 blade because of my slippage. Thanks for any ideas.
Weighs about 2,200# with fuel and me.
Mercruiser 470 with 1.84 MC-1 outdrive.
My recommended WOT is 4,200-4,600.
New tach (set for 4cyl)
Iphone GPS
I'm currently using a 3 blade 13 3/4 X 21 and can only achieve 4,300 at 35MPH(30 knots). According to the Mercury prop calculator, I'm getting about a 25% slip. The other day I had a load of 4 adults, 4 kids and 2 medium dogs and could only get 3,900 RPM and it was a dog out of the hole. I know I'm over propped and the diameter is too small.
I purchased a 4 blade 15 X 17 and had the same results. 4,300 at 35 MPH (30 Knots) The prop calculator shows a 7% slip.
Today I'm going back to the prop shop and get a 4 blade 15 X 15.
Am I on the right track?
I'd like a cruising speed of 30MPH (26 Knots). It looks like the 15' prop will put my top speed about there. (30/26)
I can currently cruise about 28MPH (24 Knots) at 3,600.
I guess I'm rambling and don't seem to have a real question. This is my 1st 4 cyl motor. I am accustomed to SBC performance. The 470 seems very fuel efficient though.
I'm not sure weather to go with a 3 or 4 blade either. The prop shop owner recommended the 4 blade because of my slippage. Thanks for any ideas.