New Prop Help? 1994 EVENRUDE 90HP, 1660 LUND PRO-V

[SDbowhunter]

I am trying to size a new prop for my boat. Can anybody with some boat expertise help me out. My current prop is out for repairs and I could not find anything stamped on it before I sent it off.

This prop ran at about 5500 RPM (I cant remember RPM exactly) at 34-35 MPH. I wouldn't mind squeezing a few more MPH out but this is not necessary.

Any recommendations?

How about brands of props?

[Loon]

Your motor has a wide open throttle range of 4500-5500rpm.

Since you're already at the top of that range, I'd say you've got the right prop for your payload.

Dropping the pitch will raise your RPM above the recommended range and risk powerhead failure.

Raising the pitch will drop your RPM...and your MPH.

I agree, though...35 mph doesn't seem right...but honor thy tach!

[solbes]

I agree that your RPM's seem right, but your speed does not. Weren't the 1660 Pro V's in the 79" beam range? If so, I would guess a 90 horse would push it above 40 mph. Even if the later models were in the 80"+ range, you should see speeds closer to 40 mph than 35. I had an '84 Evinrude 90 on a 16' Forester boat with a less efficient hull than your Pro-V. It ran 38 GPS with a 17" pitch prop (5400 RPM's).

My current 1625 Lund Rebel (84" beam) with an F75 runs 39 GPS right at max 6000 rpms.

Possibly your numbers include some significant slip if your prop was damaged? I think you should try a new prop if the repair does not improve your numbers. Try buying one from a company that will let you try them out for free. Your tach accuracy and/or motor running condition might also be in play.

[SDbowhunter]

I should have stated more clearly... Whats starting point of pitch should I be looking for?

The beam width is something like 78 or 79"

Again, It was not stamped on the old prop so I am shooting in the dark. I am getting close to a fishing trip and I may need to order one if I can't get my old one back in time. I would also like to have a spare even if the pitch isn't perfect so that I can limp home.

As far as the old prop it was pretty nicked up and I had worked it over with a file many times. It had a tough life already when I finally took a chip out of it and sent it in.

[hydro]

Your numbers back calculate to a prop pitch of about 16", assuming 15% nominal slip, 2:1 gears, 5500 RPM at the powerhead, and 35 MPH actual speed. Probably very close to the best combo for your rig.

Is your current prop aluminum? If so, I would look at a 17" stainless three blade prop to test out. Watch the hole shot and WOT RPM with a typical load. If it struggles out of the hole or your WOT RPM drops below 5200, try the next lower pitch. Good luck!

[SDbowhunter]

I found out today that my prop should be in by thursday next week. I'll pay attention to all the tips everyone pointed out and also take note of the pitch.

I was not sure of the gear ratio's or normal slip ratings so that is why I was at a loss for where to start.

Thanks again.

[toddb]

Motor may be mounted too low. If you cant see the top of your ventilation plate when trimmed out normally at cruise or WOT your motor may be mounted too low. You may be able to raise motor and go up in prop pitch and gain MPH. Lots of drag when lower unit is too low, ventilation plate should be at least in line or somewhat above the bottommost portion of the hull. You should be going at least 40 with a 90 on a 16.5' I would think. check these out, this guy is pretty spot on when it comes to prop advice

Too low. http://i201.photobucket.com/albums/aa105/kenuwf/toolow1.jpg

correct. http://i201.photobucket.com/albums/aa105/kenuwf/correctheight21-1.jpg