im prop dumb

[county436]

i am trying to find a new prop for my 1983 Johnson V4 outboard. The one that i have found with same pitch and diameter is 13 X 21 cupped. Can anyone tell me if a OMC Cobra 400 prop will work with my outboard or is it for an inboard motor? Thanks for any help.

 

[Dhadley]

Re: im prop dumb

There is an OMC 400 series drive and a Cobra drive which may or may not use the same props. However, if the prop you want to buy is a 13 1/4 diameter, the hub should be the same. Just for piece of mind you can count your splines and the prop splines. <br /><br />Are you sure you need a 21" pitch? How much do they want for the prop you are looking at? What brand is it?<br /><br />Good luck!

 

[county436]

Re: im prop dumb

THE PROP IS NEW AND THEY WANT 125.00 DOLLARS. IT IS A OMC BRAND AND I HAVE BEEN TOLD THE ONE THAT IS ON MY BOAT NOW IS 123/4 X 21 CUPPED BUT IM NOT SURE HOW TO SIZE IT AND HAVE NO MARINE DEALERS AROUND ME THAT CAN TELL ME.

 

[Spidybot]

Re: im prop dumb

Your prop is too important to be a 'best guess'.<br /><br />Get a proper ID of your motor or take the prop to a dealer. There are several brands, makes and materials (and prices) and good guidance on size & pitch based on test runs, is needed.<br /><br />If you have the figures on speed and pitch of your existing prop, thumb rule says motor rpm change by 200 per inch pitch. Higher pitch=less rpm and vice versa. This way you might calculate the pitch you need to get motor rpms at WOT right. Next comes the question about your use, boat hull design, motor mount hight etc. which will help in choosing number of blades, material and prop type.<br /><br />For many uses you'd choose a pitch slightly lower than the best for WOT to gain better accelleration and performance with load - hence reducing the rpm when on plane to prevent over-revving.<br /><br />Check www.boat-props.com <br /><br />Many here will share experiences and give good advice if you state your details about the above - especially exisiting prop specs. and rpm.