What does prop cupping do for performance?

Mike Cork · January 02, 2016, 03:33:30 PM

I hear it all the time. "I've added some cup to my prop"

So what are the advantages?

When talking with people that know props, I've been told a variety of things from "the cup will help hold the bow of the boat up" to cupping will "give the prop more bite and help in cornering" and "because of extra bite, the cupping will bring down your RPMs"

What does cupping truly do for a prop?
How much cup can be put into a prop?

Pferox · January 03, 2016, 10:15:02 AM

Good question Mike, I never understood the physics involved with cupping, and would like it to be explained a little more in depth.

hughesjasonk · January 03, 2016, 11:33:54 AM

Cupping adds surface area. A boat prop works almost exactly as a airplane prop except for with an airplane prop the air goes front to back where a boat prop water goes from inside to the outside. I don't know if it follows Bernoulli's principle to the T but it comes pretty close from my understanding.

HOLESHOTPROPELLER · January 03, 2016, 04:50:36 PM

It does pretty much everything you said Mike , cup help's the prop GRAB the water and lower your slip numbers which helps in all aspects of a bassboat running , and it does not always affect rpm's it depends on where you put the cup and how much....i adjust cup based on how the customers boat is running with reference to speed and rpm's and pysically looking at the prop when i get it , also heavier boats usually need a little more than lighter boats to help them get up out the water...

Mike Cork · January 03, 2016, 05:01:00 PM

Thanks everyone!

HOLESHOTPROPELLER · January 03, 2016, 05:52:40 PM

Adding or fixing cup is one of the most fequent fixes i do on bassboat props

Mike Cork · January 03, 2016, 08:57:01 PM

So according to Merc's site I'm running about 11% slip on a 25 pitch. It didn't ask but it's a fury prop. Will adding cup increase speed. I'm exstactic about my handling. Again it's a Legend and a heavy boat that likes to ride flat. Interesting to me, I have the exact same numbers on a 26 fury, give or take 50 RPMs

5750 PRMs at 69 mph full tournament load. (Light and perfect conditions 71)
250 Pro XS
1.75:1

coldfront · January 03, 2016, 09:45:34 PM

this won't help, but it sounds awful similar to experience when I went to a 4 blade prop vs a 3-blade.

on my little semi-v with a flat area at the transom, it'd slide on corners with the 3-blade.
not so with the 4-blade.

merc1997 · January 04, 2016, 08:41:27 AM

getting the right prop for a boat is not an exact science. hardly ever will two same boats run right with the same prop. getting the right wheel on the boat is the first thing. then, you can tweak that wheel by adding cup to the right areas of the blade. sometimes cup needs to be added to the top edge of the blade all the way around the tip. others might only need cup added to the tip.

the cup can add boat lift, not just nose lift, and the ability to not let loosed in corners. 4 blades always do a better job of cornering. they, most of the time will not have the straight away speed of a 3 blade, but often when constantly running boat traffic and rough water will get you there before a 3 blade. 4 blades will just not run well on some hulls because they are not offered with a blade length that is long enough to run some hulls.

some hulls can run a shorter blade and less rake because of the hulls natural lift. this most often relates to a fast hull. then one can most often run a prop with more pitch and can run faster at the same rpm provided you are not just slipping.

at the 11% prop slipage you mentioned, you need to get that down to 10 or less at wot. if you can get down to 8%, you have done a good job.

mazco is known for their ability to blueprint a prop that will get every bit of speed out of your particular hull. expensive way to go, but there are many that go that route.

there are other prop people that know their stuff and can help you get the right wheel on your rig, and then tweak it to get it to the most efficient point.

so, bottom line, you might need to try some other types of wheels on your hull, and then start tweaking the one that did best right out of the box. believe it or not, but a yamaha wheel might be the best fit for your rig. i believe the fury is similar to a yamaha, but still not the same.

remember the longer the blade and the more rake a prop has, it will most often take longer to come out of the hole. shorter blades less rake will most often come out quicker. so, longer blades more rake, you will not be able to have as much pitch in the blade as a shorter blade with less rake.

hope this will make sense.

bo

Mike Cork · January 04, 2016, 10:05:52 AM

Yep it does Bo, I pretty good with determining all this. I'm just stuck here. I've run the Legend for several years with little to no hull change. Weight has changed though. My fastest one was a 76 mph boat. The last two won't touch 72 unless I'm about to run out of gas.

Out of all of this, even with the three blade prop, the boat is like it's on rails in the corners. My hole shot is very satisfactory, except when heavy and I might have to feather it as it wants to blow out as the nose comes down. Tried lowering the motor and of course it fixes that but I loose RPM obviously. Well my RPMs are not where I want them. I reckon at 5750 (BTW is what I got with the 76 mph boat) my motor will last longer

HOLESHOTPROPELLER · January 04, 2016, 10:34:18 AM

Send me that prop Mike then you will be able to raise the engine higher and see the improvement

Mike Cork · January 04, 2016, 11:05:08 AM

Quote from: HOLESHOTPROPELLER on January 04, 2016, 10:34:18 AM
Send me that prop Mike then you will be able to raise the engine higher and see the improvement

I got your PM and will answer here in just a bit.

merc1997 · January 04, 2016, 11:46:40 AM

Quote from: Mike Cork on January 03, 2016, 08:57:01 PM
So according to Merc's site I'm running about 11% slip on a 25 pitch. It didn't ask but it's a fury prop. Will adding cup increase speed. I'm exstactic about my handling. Again it's a Legend and a heavy boat that likes to ride flat. Interesting to me, I have the exact same numbers on a 26 fury, give or take 50 RPMs

5750 PRMs at 69 mph full tournament load. (Light and perfect conditions 71)
250 Pro XS
1.75:1

mike the math for those numbers is 70.08 mph, and that will be + or - 2mph of actual speed, and this is using a factor of 10% slippage. funny how math never lies. you might be able to tweak your numbers a bit by adding some cup in the right areas of your blades.

bo

Mike Cork · January 04, 2016, 11:53:15 AM

Quote from: merc1997 on January 04, 2016, 11:46:40 AM
mike the math for those numbers is 70.08 mph, and that will be + or - 2mph of actual speed, and this is using a factor of 10% slippage. funny how math never lies. you might be able to tweak your numbers a bit by adding some cup in the right areas of your blades.

bo

Yep, math is a constant.

I'm going to play with one of them.

merc1997 · January 04, 2016, 02:58:44 PM

i don't know if you ever scaled any of your other hulls. but, even 100 lbs. more can make a big difference. but, you did mention that this one even almost out of gas still does not run. that somewhat points back to the hull itself. the first few out a new mold will always be the fastest, even with the better technology of building hulls we have today.

you can probably tweak another couple mph out of this one, but might have to wait for the next new one to get more

.

bo

caddyjoe77 · January 09, 2016, 10:57:50 PM

Once again, so much good info here.

Thanks guys.

I am in a similar "boat"--pardon the pun--as Mike. I feel like my Z119 should run faster and have dropped it .25. seems a little better but I need to run her on a long lake to see how it really runs.

running a 25 tempest on a 225 Opti Pro XS. Fastest I have ever had her is 72. Feel like I ought to be able to get 75.