Need prop size for Evinrude Lark 40

[crystgryph]

Hi! Newbie boater here. Haven't done any boating since I was a kid (25 years ago!). I just got a 1957 Cadillac Coronado 14' Runabout (Aluminum ~ 625 lbs.) with a 1960 Evinrude Lark 40hp (Model #35520). Have no info on motor/RPM/gear ratio, etc. Prop on boat in bad shape, gouged, chipped and spins on shaft by hand while in gear, it is a three blade alum. 10-3/8x15 according to a guy my neighbor took it to, but he didn't think he could fix it without cracking the hub. He has one that is used, ~10 dia. with 14 pitch for $40, don't know if this prop would be right for the boat. Plan to use the boat for tubing my kids around, cruising and fishing (not trolling) on a small lake. I figure 1000 lbs. min and 1400 lbs. max loaded. No tach, don't know if speedometer even works yet. How would I be able to check RPM's? Would appreciate any information or direction.

 

[crystgryph]

Re: Need prop size for Evinrude Lark 40

^

 

[Paul Moir]

Re: Need prop size for Evinrude Lark 40

A 14" prop is probably exactly what you need - don't worry about the diameter, that's the prop designer's problem. The only ways to check RPMS right now is with a Tiny Tach (from tinytach.com) or find an old 60s OMC tach. WOT RPM is 4000-5000, with 40hp @ 4500RPM. Lower unit gear ratio is 12:21 (1:1.75). Try out the 14" and see what you think. Might want a 13" though if it doesn't have enough grunt for tubing.

 

[crystgryph]

Re: Need prop size for Evinrude Lark 40

Thanks! Got the 14" and I'll give it a try.

 

[123afro]

Re: Need prop size for Evinrude Lark 40

Well i am in the same boat..lol.. 40 hp same motor but on a 16 ft fiber glass with two seats when tubing and 4 when touring.should i try a 14" as well? is the pitch standard?is stainless steel worth it...i was told under torque othe pitch on an aluminum prop will flex causing loss of "get up and go"..
thanks afro...

 

[steelespike]

Re: Need prop size for Evinrude Lark 40

Welcome,You should start your own thread ,can get very confusing especially as Qs and As accumulate.No need for stainless in your application
a good AL will perform fine.No such thing as a standard pitch; pitch selection
is based on the application. What size is on your motor?If its good enough to test get a tinytach and try it.Both of you should not make a prop change without a tach.the wrong selection could cause premature mechanical problems with the motor as well as poor performance ,mileage etc.
A gps for speed to compare to rpm is helpful as well.