Measuring old style prop

[royal0014]

I have a Johnson Super Seahorse 40hp, RK-28B (1966) The original prop is spun. I can turn the inner hub by hand. I have another prop from ebay, have not had it in the water yet. The leading edges are pretty dinged up. I intend to call a couple prop shops about repairing the spun one.

However, I have located new props online for $84.00. My question is, how do I measure the old props so that I get the correct or same size new? What are the odds of the repair being cheaper than this price for new?

Thanks to all

 

[basspirate]

Re: Measuring old style prop

somewhere on the prop should be a stamped number it should be something like 12x15. that is the diameter and the pitch. in my example 12 would be the diameter and 15 the pitch. diameter is easy to measure. lay the prop flat on a piece of cardboard, try to draw a circle around the outside of the blades, then measure across the circle. that is your diameter. or you could just measure from the tip of one blade to approxitmatley where the blade should spin. the pitch on the other hand is probably quite complicated to measure. pitch is a measure of how far fowards you would move with one rotation of the prop. so in my example with the pitch being 15, if the prop rotated once you would move 15 inches fowards. i'm sure prop shops have special gauges or instruments to measure the pitch.
just be aware that the diameters of diffrent props can change slightly even though their for the same engine.

 

[steelespike]

Re: Measuring old style prop

As suggested look for numbers on the prop.It came with a 10 1/2 X 12 but the final size would depend on the application.A prop shop can measure the pitch for you.
I would get the spun hub replaced and the blades repaired if necessary.
Then if you get us the present max rpm and speed and the prop size we can help decide if you need a prop change for best performance.If a prop change is in order you can get one of those new ones use the other for a spare.

 

[royal0014]

Re: Measuring old style prop

Well, on the original prop I can't find any markings or stamps at all....

The ebay prop is marked 10 3/8 x 11 1/2. Sound about right? It is mounted, so just holding one up to the other, they appear to be the same size.

I'll try to call about repairing the first one tomorrow.

Thanks

 

[steelespike]

Re: Measuring old style prop

If you read the stickies at the top of the page and the helps on the prop satore page it will help you understand prop selection.
as far as the right prop that depends heavily on the type and size boat.
also the present performance,typical load and activities.