Prop Problem ?????

[JGra]

Hello, I picked up a 1996 Sundird Spirit 170 with a 1996 Evinrude 88 SPL at a good price. The boat was in good condition and did not need to much. Got the boat running and did some basic maintance to it. Took it out and it did really well, gts up on plane fairly easy. Question, I could only get about 4200 RPM's all trimmed out and was running about 34 MPH. Motor runs great with no problems. I am tols I should be getting about 5500 out of her and that the prop may be the problem. The boat is a 17 ft and I am not sure the weight. I have looked and looked and cannot find a pitch on the prop anwhere. The prop is a little chewed up but I dont know where to start with what to replace it with. Thanks

 

[steelespike]

Re: Prop Problem ?????

did you look for a number under the prop nut?
Is the speed by gps?
To get to 34 at 4200 you would probably need a 19" pitch
Hopefully you can find the pitch under the nut.
It's fairly common for a tach to not be accurate

 

[JGra]

Re: Prop Problem ?????

OK, So I pulled the prop nut off this morning. The only numbers under the prop nut/washer says 5 2 1 CUP, what that means I have no idea. The boat weighs about 2000 lbs accordind to what I can find on the net. It is 17 ft long and I am running a Evinrude 88 SPL. Like I said the best I could tell was it was around 4100-4200 RPM's at around 33-34 MPH. Mostly the highest RPM's stayed around 4000 with 29-31 MPH. This is all through the speedo on the boat. I need to check it with GPS. Like I said I am satisified with the way the boat runs, I just want to make sure I am running the engine where it is supposed. The prop is chewed up some and I want to replace it but I donk know what I have now.

 

[steelespike]

Re: Prop Problem ?????

A prop shop can measure it for you. I'm leaning more to a 17.
If it turns out too light you can still use it by watching the rpm.

 

[JGra]

Re: Prop Problem ?????

I could not find anywhere local that would lend out a prop so I found a 13 1/4 x 17 on E-bay for about 50 bucks. The one I have on the boat now measures about 13". Will that extra 1/4" make a differance? I have the clearance for it.