Adding cup to a prop

[omcstratos]

I know Mr. Ron would love to have another prop customer, but I am wanting to work with what I have before buying a new prop. I have a johnboat I run around in for fishing and hunting and what not. Its got a 2000 Johnson 2cyl 50 and I am running a 17pitch stiletto. I am losing bite in turns and sometime in the holeshot, which it is running fully submerged at all times. I am wondering how simple it is to add some cup to the blades and if I can use this prop in the future running a little bit higher up on the transom. I know that a lot of people don't like solas props but do stiletto's have much potential for a little better speed setup. Its a semi-v with like an ice-runner type keel running down the middle of the hull. Boat runs a solid 37mph wot at 4800 rpms. I am just wanting to raise it a little more to get to the proper wot revs.

[omcstratos]

I guess nobody has any experience adding cup to props?

[Bill Van Steenwyk]

I guess nobody has any experience adding cup to props?


It can be done several ways, depending on the type equipment you have to do it with.

Example of a very simple way is a ball peen hammer and a trailer hitch ball., to specialized pitch blocks with cup added to the blocks in small increments to act as a "master" to shape the prop over, and use of heat if required to soften the material if too thick and hard while cold. Of course the use of heat can ruin the temper of the material and cause further problems if you stress or crack the material while adding or removing cup. The harder the material the prop is made from and the thicker it is in the area you are trying to cup, the more difficult it is to do using the trailer ball/no heat method, but many props have been cupped on the trailer ball on the bank at the race course this way.

If you do not know what you are doing, and do not want to ruin a good prop, you might be better off to send it to someone who does know what they are about. If you do send it to a prop person, be sure and tell them what you are trying to accomplish, speed and RPM of the motor/boat now, and how high on the transom you are running it.

If not a valuable prop, and does not run that well now, and if a soft material like aluminum, bang on it yourself, starting small, and taking steps, and if you accomplish something you saved money and learned something besides.

Props are one of the big mysteries of boats and making them perform better. If you accomplish that on your own, within the parameters mentioned, more power to you, and more dollars saved to spend on more props.

Good Luck

[Fastjeff57]

One caution on doing this: I DID mess up a bronze prop (thru hub exhaust type) by doing this. It didn't want to cup for me, the stubborn thing, so I added some heat, which created some really ugly pitting. (I assume that, since this was a CAST prop, not forged, that was the problem.)

I'd leave this to an expert, as Bill said, if it's a bronze prop.

Jeff the wiser (now)