advantages of a cupped prop vs non cupped

[crazy charlie]

I am running 15x16 4 blade alum props on twin 5.0lx alphas. Big 28ft boat 10ft beam.I didnt realize my props were not cupped and boatyard offered to have them cupped for about $25 each.What should I expect to be different if I cup them.Charlie

 

[Jilly - 5]

Re: advantages of a cupped prop vs non cupped

Cupping will add the equivalent of about one to two inches of pitch on the wheels, depending on how aggressive the cupping is, giving you effectively 15 X 17 or 15 X 18 wheels. Do you feel you need more pitch? Any current performance deficiencies? Generally, an inch of pitch (increase)knocks off 200 rpm (you gain in the other direction with pitch reduction). Incidently, $25 each for a four blade wheel sounds too cheap. Are they sending them out, or putting a sledge and anvil to them in the shed?

 

[crazy charlie]

Re: advantages of a cupped prop vs non cupped

The props perform well except when I need to trim up while in a chop.they will allow me to trim up a bit but then they begin to cavitate before I get it trimmed to where I would like it to be.By the way I know I am not overtrimming because it happens so soon when trimming up.The outfit that quoted me 25-30 bucks each to add cupping, reconditions props and custom makes props.They are the outfit that most marine stores and marinas in our area take their props to for recond.

 

[sundog]

Re: advantages of a cupped prop vs non cupped

I had my 3 blade 13x17 cupped and noticed that it handled better slightly better in turns (I am having problems with cavitation at speed in turns). other than that, I didnt really notice a difference, speed or otherwise. boat still cavitates, but can turn slightly sharper.

 

[crazy charlie]

Re: advantages of a cupped prop vs non cupped

Sundog,Is your cavitation on turns only???? I am not concerned with turns as much as I am having trouble when trimming up,loosing my bite.Charlie

 

[ThomWV]

Re: advantages of a cupped prop vs non cupped

Cupping alone will not add the equievelent of 2" of pitch, or even an inch in most cases, but it will have a slight effect similar to moving up in pitch.<br /><br />The main advantage of having a cupped prop is that it will hang on better than a non-cupped prop, so in your case with premature ventilation (its not cavitation, that is an entirely different thing that we almost never see in small boats) when cranking in trim it will likely have a pretty noticable and desirable effect. You'll be able to trim it up a bit more. I'd pay the money if I were you.<br /><br />Thom

 

[crazy charlie]

Re: advantages of a cupped prop vs non cupped

Thanks Thom,sounds like thats what I am looking for.Charlie