Take a guess at what size prop I need....

[jimmypal]

Hi boaters,
I have a 1961 14' Lonestar fiberglass boat. I just put a 1985 70 hp Evinrude on it. The motor has a 4 blade prop on it which is pretty beat up. Would anyone like to take a stab at what size prop might work best? My marina will let me try out some used ones he's got laying around, but I don't know where to start.
Whaddaya think?

Thanks, Jim

 

[steelespike]

Re: Take a guess at what size prop I need....

You need a working tach to be sure the rpm is right.A gps for speed will help tell if the setup is working right. The antivent plate(just above the prop) should be visable at speed.There should be a size on your prop (on the barrel or under the prop nut.Wouldn't hurt to run the 4 blade, if it isn't destroyed, just keep in mind the 4 will usually knock 2 or 300 off the max rpm. compared to same pitch 3 blade.On that little boat I would start with a 19.The problem with testing used props is condition and changing brands can cause confusion due to different pertformance features.Stick with aluminum.The motor needs to operate near the top of its rpm rating.My info says 6,000.

 

[jimmypal]

Re: Take a guess at what size prop I need....

Thanks for the advice! My buddy had a 17 laying around that he wanted me to try and it ran pretty good, but it looks like a 19 would be perfect. Good guess!

Thanks a lot,
Jim