Prop cupping

[danfrompgh]

Do props need to be purchased cupped or is this something you have your local prop guru do? Also, what effect does cupping have on rpm versus a non cupped prop? I would think a cupped prop will raise the rpm,correct?

 

[12vMan]

Re: Prop cupping

You can purchase a prop that is already cupped, or take it to a reputable prop shop to have done.

Many of today's propellers incorporate a cup at the trailing edge of the propeller blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases. A cupped propeller also works very well where the motor can be trimmed so that the propeller is near the surface of the water. The cup will typically result in higher top end speed on one of these applications.

Switching from an un-cupped to a cupped propeller will reduce your RPM. The actual amount of RPM decrease is dependent on where, how much, and the quality of the cupping. Typically, a cupped propeller of the same pitch and diameter will reduce your RPM by approximately 200

 

[Dhadley]

Re: Prop cupping

There's all kinds of "cup". There's different styles, different amounts and it can be put in different places to do different things. Basically , very basically, cup grabs more water. Where the cup is determins what that extra "bite" does. The amount of cup, angle of cup and style of cup all plays a role in how the cup affects what the prop does.

Cup can affect bow lift or stern lift or overall lift. Since cup adds "bite" or decreases slip percentage it, at first glance, would seem that it should decrease rpm. In most cases that's true. However it is very possible to go from an uncupped prop (pretty rare these days) or one with minimal cup to a prop more suited to your given hull design and actually gain rpm. That will happen if the new prop adds lift therefore reducing drag which increases rpm & speed.