TOPIC: Cuping props

I think I understant what it means but still not sure how the prop is cuped. Does anybody have a good digram of how it is done?
I know this has been asked before some were on here. But it may help a few other out on what it means
Mike aka pathfinderz1

Not getting much response on this question yet, huh Mike. I think on aluminum props it would have to be cast into the prop, if you tried to add it afterward it would crack the blades? I assume it's possible for an experienced prop mechanic to "hammer" or press some into the steel or bronze props, but it seems like it would take an experienced craftsman to do it without screwing up the prop.

(I've heard of it being done, but it sounds scarey!)

Check this tutorial out:

www.iboats.com/basics/propeller_basics.html

Cupping refers to a lip, or dish, found at the trailing edge of the prop blades. They add "grip", in a way, to props that are on motors that are raised on the transom high enough that they may be exposed to air, such as when the cavitation plate is above the keel. Some prop shops can mildly cup an aluminum prop, but mostly done on bronze and stainless, since the material is stronger, and are more likely to be used at elevated transom heights.

Oops- Frank beat me to it- I'm a slow typer.

this is my disclaimer....Firstly I do not know how to cup a prop, I do not own any appropriate tools to cup a prop, I do not advise anyone to cup their props, take it to a prop shop, that being said I do know how to make my props run faster, right or wrong I do not care, it makes me faster and that makes me happy

cupping an aluminium prop you can increase the pitch by one
bronze & SS props can be increased the pitch to about 2

aluminum is very difficult and should certainly only be done by the experienced, or prop damage is likely

its not quite the black magic its made out to be, the trailing edge of the blade is curled to add the additional bite & pitch
see the photo of the SS blade I pounded over my trailer hitch to make some changes because this prop wasnt getting the job done, this pounding did make a considerable improvement so I have begun to sand out the hammer marks to polish it back up again
I experimented on a cheap broken prop my first time , then a second cheapo prop to see the affects, I was happy and occasionally employ this tactic
I wouldnt do this to a really expensive prop because I dont know what Im doing but I cant help myself, I just want to go faster

oh crap Im really slow I see others replied, oh well confirmation

Decode props
www.savvyboater.com/s-49-understanding-the-language-of-boat-props.aspx

www.boattest.com/Resources/view_news.aspx?NewsID=3726

Back in the 1960s, a friend had a 3 blade cupped bronze prop for his 40 hp. Johnson. I can recall borrowing the prop to make a timed speed run with my boat ( and 40 hp. Evinrude) , and the bronze prop added about 2 mph to my top speed. I don't recall making any other adjustments to the motor, such as height on the transom or angle. The engine rpm seemed to be about the same with both props.
I normally ran a 13 inch pitch aluminum prop in place of the 12 inch stock prop.

Mike,

Not sure if the links given say this or not - but the trailing edge of the blades is carefully curled upward at a very gradual rate. As the water is slipping over the top surface of each blade, it hits this little raised area and aditional friction is created. This makes the prop "bite" into the water a little better, almost always lowering the rate of slippage. this causes the rpms of the motor to decrease because it takes more power to spin the prop for any given speed. It makes the propeller more efficient, and is impoerant for many reasons. They hold better in tight turns, suffer less "blow our" or cavitation unter full throttle, can increase speed and economy if done right. Can be done for any motor, regardless of ride height or tilt angle.

Cupped props cost more because they are harder to make and repair. If a boat performs well without a cupped prop, then it can be left alone.