Chopper Prop

[YELLOWSS]

when i run my 30" and start to trim a little the boat starts turning left/
no trim tab straight skeg. it runs fine on the 26 and the 28.
boat is a allison 2000 ss
thanks,
roy

[pyro]

For starters, you SHOULD have a torque tab. Not just for taming the steering torque, but to prevent crabbing at higher heights, which is probably what's happening here.

as for the 30, read here:
http://abiossa.gearhost.net/adamsdock/chopper.html

If your 26 and 28 are big-ear choppers, the 30p is a much different prop. Less diameter, more rake, skinny blades. At the heights you're running, the 1/4" of blade diameter difference means less blade in the water. On top of that, higher-pitched props have more trouble with the "paddlewheeling" effect that causes motor crabbing at higher settings, since the blade tends to try to push the water sideways with the tall blade pitch. The extra blade rake angle and the positive trim makes it worse.

I know absolutely NOTHING about Allisons in particular, but here's a few questions:

Why are you running a chopper? Seems that the ET's and custom "cut" round-ears are the popular choice with Ally's. Are these props you're running "stock" choppers? Check the chopper page against their part numbers.

How much trim are you giving it? What height are you running at? (propshaft centerline, in relation to the pad bottom)

Speed? (GPS) RPM?

Good luck with getting your problem figured out. :)

-Chad

[YELLOWSS]

jack plate is hydro but all the props run well about 1/2 below the pad.
26" big ear chopper II
28" allison cut big ear chopper II
30" small ear chopper
allisons don't like a lot of trim but i can't trim the 30 much at all with out it pulling to the left.
it did the same thing on my norris craft bass boat.
i was running a 2.4 175 turning 6400 with a 1.87 ratio lu with the 28
same set up with the 30 but 3/4 throtle she starts to hook left.
i have a 2.5 260 with a sportmaster coming. i just wondering if the bigger the prop pitch could the prop torque cause this ? or is it setup? trim tab?
thanks,
roy

[pyro]

The Sportmaster and CLE cases have a much larger skeg than the 200 style case. This helps to keep the case in-line when turning higher-pitched props. A torque tab is still a good idea.

The "bastard" 30p chopper only runs well on a handful of certain hull and motor combinations. If you need more pitch than the 28, I would suggest looking for a more suitable prop in that pitch range. Once again, I'm not an Allison guy, so hang tight and wait for a reply from someone who knows the answer for sure...
-Chad

[David]

Mark Smiley was into the high 90s with a lightly modified 150 pro max and a 30" small ear chopper on an SS2000. I think the idea is that the smaller blades work on a boat that has limited power and doesn't need bow lift.

You probably should try a torque tab before giving up on the prop.

If you want to give up on the prop, let me know.

David
SS2000/XR4

[BJACKBLADES]

I have a 2001D, That I run a 30 small blade chopper, the boat weights 530lbs and i don't need any bow lift. I had a 2000ss w/a drag motor, my best prop was a 28 chopper. I't was thinned & diameter cut a little, Tillman's propeller did work for me. You need a allison torque tab.

[r.c.]

rwr, i'll have to go with pyro on this one. i don't think the boat is turning left, the rear end is walking to the right. drop the motor.
ron

[pyro]

...And GET a TORQUE TAB for that lower unit.

The torque tab will help push the tail of the skeg to the left as the prop is attempting to crab the stern to the right.

Your attempts to counter-steer the crabbing will result in the gearcase and skeg travelling though the water on an angle, a dangerous situation that can easily lead to a blow-out condition. Nobody wants to see you get thrown out of your boat.

You got a lifeline vest, right? Got the kill tether hooked up?

[YELLOWSS]

guys i'm runing a 2.4 vertical reed motor turning a 28" chopper II 6400.
i havent run the 30 because of the way it was acting.
changing motors to the 260 with the sportmaster.
i will get a torqe tab. i have a 14 1/2 x 32 chopper coming.
just wanted to make sure i can run these big props with the allison
thanks guys
roy

[sandbagger]

I have a grandsport with M280 don"t worry about that 30" prop the engine will not spin it to rev control.The chopper II prop works great on this boat 26 or 27 is all the prop that motor will spin.The lightning ET I have 28 will let the bow drop above 95 the chopper won't 26.Check skeg for cracks mod. lower unit so boat will settle down above 95

[sandbagger]

Sorry I missed it was a 2000ss I have no idea what you need