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Old 14-06-2006, 06:09 PM   #1
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Stern lifting props

Ive been out on my cat today for the first time and had a few problems with handling, started off with a 29 et and did 60, tried a 29 hydromotive quad iv and ran 84 then tried a 28 cleaver which also ran 60, all the speeds at 6500rpm on the limiter, and before any wise comments they are gps speeds.

Trouble is steering is nigh on impossible to control and it porpoises like a bastard, plus its running bow high and only dropped with the quad iv.

What are the best stern lifting props ? looks like it will need to be a 4 blade.

Will probably end up fitting a tunnel tab to compress the air a bit more and hope it helps.

Any comments and ideas are welcome.
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Old 14-06-2006, 07:09 PM   #2
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whats a tunnel tab and how does compressing the air more help?
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Old 14-06-2006, 07:13 PM   #3
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Quote:
Originally posted by PuppiesBalls
whats a tunnel tab and how does compressing the air more help?
Its like a trapdoor in the tunnel, the more compressed the air the more lift it generates.
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Old 14-06-2006, 07:13 PM   #4
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Talking

Its what it says! A tab that mounts in the tunnel.
it acts similar to flaps on a airplane putting it down will give more stern lift
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Old 14-06-2006, 07:14 PM   #5
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I would guess its a tab that directs the air downwards thus compressing it which intern helps lift the boat. Thats all guess work though so feel free to correct me!!!
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Old 14-06-2006, 07:15 PM   #6
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cool cheers dudes!
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Old 14-06-2006, 07:17 PM   #7
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Quote:
Originally posted by Me
I would guess its a tab that directs the air downwards thus compressing it which intern helps lift the boat. Thats all guess work though so feel free to correct me!!!

When I posted that no one had answered!!! so it seems I was pretty much on the money
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Old 14-06-2006, 07:17 PM   #8
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Roofer, check out these puppies http://stores.ebay.com/Ron-Hill-Propellers
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Old 14-06-2006, 07:20 PM   #9
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Quote:
Originally posted by PuppiesBalls
Roofer, check out these puppies http://stores.ebay.com/Ron-Hill-Propellers
There's a thread on scream + fly about ron hill props, to put it nicely they aint what they used to be.
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Old 14-06-2006, 07:35 PM   #10
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interesting..... whats changed has he changed his methods or is there just better props on the market now ?
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Old 14-06-2006, 07:37 PM   #11
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Quote:
Originally posted by PuppiesBalls
interesting..... whats changed has he changed his methods or is there just better props on the market now ?
I believe its something to do with a family fallout.
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Old 14-06-2006, 07:39 PM   #12
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i see!
Dude how much did that ddt set you back in the end?
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Old 14-06-2006, 07:58 PM   #13
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Quote:
Originally posted by PuppiesBalls
i see!
Dude how much did that ddt set you back in the end?
This is what I got, You wanna buy it ?
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Old 14-06-2006, 08:45 PM   #14
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Errrrr a side effect of a flap will also move the Ctr of lift aft, dont just compress the air. Thats why the nose drops when used.
Propwise I'd think a look at an RE4 from Mazco or an older DR4 from Spenilli about the 30-32 inch range will really help on the handling, but you might get hold of a 4 blade clever somewhere. Higher speed prop will I suspect be a 3 blade Clever in the 32-34 range but that might make it a bit of a handful. Whats the gear ratio ? & boat weight, off web if you like.
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Old 14-06-2006, 08:53 PM   #15
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John gear ratio is 1.62 and weighs about 1100kg all up, going to try a mach 4 blade cleaver, a worked bravo 1, a 30 winrace cleaver and 30,32 and 34 cleavers tomorrow.
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Old 14-06-2006, 09:13 PM   #16
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Try as many as you can get ya mitts on. It will feel pretty flighty compared to the Phantom anyway, loads of lateral stability but quite vage on the steering till you get a feel for it. You will notice crosswind effect a lot more also. Try and make ya runs at the same trim setting with different props, eggs with eggs en all that. Trim angle of about 4 deg as a start. Will stick me thinking head on it a bit off for a scoff
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Old 14-06-2006, 09:23 PM   #17
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Steerings not vague, its almost impossible to turn with the 4 blade quad iv and it doesn't like trim. Must admit its a lovely ride compared to my phantom though.
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Old 14-06-2006, 09:45 PM   #18
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Quote:
Originally posted by roofer
Steerings not vague, its almost impossible to turn with the 4 blade quad iv and it doesn't like trim. Must admit its a lovely ride compared to my phantom though.
thats because ur phantom was designed to have 150 to 200 hp on it max not 300+ lol
p.med ya about the ddt
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Old 14-06-2006, 11:22 PM   #19
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I raced with Mike Spinks in 2002 in his 27 foot Cat. That had a hydraulic tunnel flap. We tried it a few times in testing but as mentioned before, it not only pressurises the tunnel but moves the centre of lift back. This starts to create bowsteer which is obviously extremely dodgy, particularly in a cat. I don't know if Mike has experimented with it since, but I don't think we ever used it in a race.


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Old 14-06-2006, 11:46 PM   #20
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Weight distribution, possibly obviously a heavier motor any other changes from when it run before, Adam would be the best to advise. You can end up with so little of the boat in the water it can seem that way when you try a turn. I suspect if you can get a little quicker you might loose the porpoise a lot of cats suffer with it within their own model specific band. Possibilty of increasing motor height ?
What shaft size 19 spline? prop options available
Try & get sombody to Vid you while running then review it, that can give a lot of clues.
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