Prop Slip 30%??????

[PatinIdaho]

Boat is a 1984 Bayliner 24.5 Ciera. AQ225D/280
Original prop was tore up kinda bad and it is a 15X17 Michigan. Don't know how its performance was to well as it was a test ride and i could not see any sense in running it hard with a prop in bad shape.
So today me and the wife had it out at the lake. Get home and checked performance numbers.
I had put a new Solas Amita 3 that i had on hand on it. 15-1/4X19 cup and it seems to thoroughly suck!!!!
3200 RPM, 25 MPH(gps)
3800 RPM, 30 MPH(gps). WOT could not get anymore out of it.

IF im reading the prop calc right it is giving me 30% slip at 25mph and 29%slip at 30mph.
IBoats lists the weight at 4550. Had 2 adults #350 and some gear maybe #35, about 40gal fuel.

What would you suggest i switch to given the above numbers?

Also originally bought this prop for a 18F TriHull with a AQ225D/280. I remember how bad it sucked on that also.

 

[steelespike]

We are mostly lost with the Volvo numbers so you will need to get us as much info as possible about your numbers.
I learned a AQ140A is 125 hp .You'll have to help us with the AQ225D.(5.0?) Do you know your gear ratio? wot rated rpm? I used 1.66.ratio
3800 at 30 mph calculated at 16% slip Acceptable for 4500 lbs at 3800 rpm.Your 19" cup would usually calculate at 20" so that would raise your slip
more than I figured but still in the ball park at only 3800 rpm. A 20" prop may be too much for your setup.
Looks like you need at least 600 rpm At 100-200rpm per inch. puts you at 16" prop.
The original 17" prop may be a clue. I do think you need a lot of diameter. I6" seems to turn up with a 16" pitch.
Usually the Solas props do well and are predictable.

 

[PatinIdaho]

Hi. Thanks for helping here.
It has 225hp with a gr of 1.61:1.
Looking at the props side by side the new one has WAY more pitch. Could be marked wrong maybe?
I am getting a 15x17 and will try it this weekend.

Oh also it is wot rated at 4400 rpm

 

[steelespike]

I'll be interested to see your results.

 

[PatinIdaho]

Ill be sure to post results Saturday or Sunday.

 

[PatinIdaho]

Here is the numbers.
Prop Michigan 15X17
RPM 4100
Speed 32MPH(gps)
Engine is a 350SB

 

[steelespike]

I think the a 15" might be a good choice. I think your wot rpm range is about 4400 to 4800.
You need to be at or about 4400 at least.
I like the 16 X 16 but I don't think it will get you there.