Bit of Advice on Props Please

[Pash 1]

Just got back from testing a 25P chopper and managed to get 67.7 MPH on GPS as about 5200 rmp which im happy with to be honest it scared the cr.p out of me when she finally started to fly ,,,

The question I have is, getting from low speed to anything approaching 15-20mph there is a tonne of prop slip and it takes about 30 seconds at full throttle to get her moving, I must be doing something wrong! I know with cleavers and choppers there is some prop slip then they bite but this seems excessive.

Any advise would be greatfully accepted

[roofer]

Just curious why you're using a chopper prop which is a bow lifting prop, I think you may find a cat's got plenty of bow lift by its design. You need a cleaver which will pick the arse end up and make it fly. I reckon your cat with a 300 promax, a good prop and good setup should be good for 80 plus mph.

By the way if you insist on using the chopper try feathering the throttle untill you get on the plane.

[Pash 1]

Originally Posted by roofer

Just curious why you're using a chopper prop which is a bow lifting prop, I think you may find a cat's got plenty of bow lift by its design. You need a cleaver which will pick the arse end up and make it fly. I reckon your cat with a 300 promax, a good prop and good setup should be good for 80 plus mph.

By the way if you insist on using the chopper try feathering the throttle untill you get on the plane.

Thanks Roofer, The reason I went for a Chopper was that Steve H said it used to run well with a chopper and I borrowed on from him on approval. Your right with regards to Cleavers Geoff Purves recons cleavers would be best and Ive got a Pair of 28's a 26 and a 24 so going to give them a try

Will I get the same prop slip with a cleaver??
Cheers
M

[steve h]

Originally Posted by roofer

Just curious why you're using a chopper prop which is a bow lifting prop, I think you may find a cat's got plenty of bow lift by its design. You need a cleaver which will pick the arse end up and make it fly. I reckon your cat with a 300 promax, a good prop and good setup should be good for 80 plus mph.

By the way if you insist on using the chopper try feathering the throttle untill you get on the plane.

just curious how much cat experiance you have,

[Techteam]

Theoretically

Don't know what ratio box you have but a 1.62/1 at 5200 on a 25 should give 76mph.

A 1.75/1 at 5200 on a 25 would give 70mph.

So if you achieved 67.7 on GPS that gives a theoretical slip of 9% at 1.67/1 or only 3% at 1.75/1

So many factors have an effect so TEST TEST TEST.

[cfun]

As regards set up and the scary bit...might be worth thinking about paying Neil Holmes for a bit of tuition and know doubt he would impart useful information regards the set up, he always made cat dancing seem eezy pizzzy

[Pash 1]

Actually ive got a lesson booked with Neil so hoping to pick up some good advice

[Pash 1]

Originally Posted by Techteam

Theoretically

Don't know what ratio box you have but a 1.62/1 at 5200 on a 25 should give 76mph.

A 1.75/1 at 5200 on a 25 would give 70mph.

So if you achieved 67.7 on GPS that gives a theoretical slip of 9% at 1.67/1 or only 3% at 1.75/1

So many factors have an effect so TEST TEST TEST.

It's the prop slip when going from 5mph to 20mph thats the problem the prop just spins like an egg wisk

[Cookee]

Originally Posted by Pash 1

It's the prop slip when going from 5mph to 20mph thats the problem the prop just spins like an egg wisk

I can't speak for your setup as I don't do cats, but the Phantom 18,19 and our 24' Rib are all the same with 200+hp on, they have the engine high and will rev the nuts off the engine if you floor it. The reason for this is the little holes in the prop combined with the amount of power. The holes are there to stop the engine bogging down at slow speeds by allowing exhaust out of them to aerate the prop, once the water is going past at a reasonable speed the exhaust exits the rear of the prop - you will see surface drives often have the exhaust pointing directly onto the prop for the same reason.

I'm sure someone will point out an error or two in the above, but it is my understanding of the way things work.

Listen to roofer - you have to play with the throttle to get it to bite, the same as your rally car!

[cfun]

Neil booked sounds like a smart move...I used to find the same thing with prop slip, again I used to feather the throttle to get it to bite but another thing I found worked well for me on a mono, although I don't think it's going to work on a cat is turning the boat one way then the other ie... bouncing it from one chine to another that often got it to bite much quicker especially when loaded with people and fuel