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Old 05-10-2005, 06:35 PM   #1
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please advise(one for bob??)

shouldnt my boat be out of the water more,photo was taken doing about 60mph,my thoughts are that it should be,it has a cleaver prop maybe thats why,any ideas,perhaps one for bob?
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Old 05-10-2005, 06:36 PM   #2
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whoops forgot photo!!
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Old 06-10-2005, 05:33 AM   #3
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your engine looks very trimmed in.try trimming out more to lift the bow.
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Old 06-10-2005, 08:48 AM   #4
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What pitch & Dia is the clever?, try a approx same sized bow lifting prop. does the back walk when it breaks the surface?
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Old 06-10-2005, 08:56 AM   #5
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I would be more concerned about the performance - is it flat out at that point - what revs / speed are you pulling - remember they are very different hulls and don't behave the same as regular monos - especially cornering!
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Old 06-10-2005, 12:07 PM   #6
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It looks nice and flat to me. You could hardly get that motor more square to the water. But I know fekk all about fast boats....
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Old 06-10-2005, 12:08 PM   #7
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Yes it is running very level but about what you would expect at 60ish.

Mine used to run best on a small hub laser & fastest on a Yamaha High performance (semi cleaver) !! as already suggested what RPM are you doing ,
When running properly into the high seventies it will literally be flying .
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Old 06-10-2005, 01:14 PM   #8
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Quote:
Originally posted by BluFin
What pitch & Dia is the clever?, try a approx same sized bow lifting prop. does the back walk when it breaks the surface?
What does it mean when the back walks when it brakes the surface?
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Old 06-10-2005, 01:26 PM   #9
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I beleive they are refering to Prop Blowout which happens at a point where the prop loses drive for a variety of reasons usually down to setup ie engine too high, over trimming, poor boat balance etc.etc. it is caused by the gearcase tracking at an angle allowing high pressure on one side & low pressure on the other which at a certain point allows air to take the place of water around the prop resulting in loss of drive. Now because you are effectively holding against engine torque under normal running (hence the crab effect ) when that torque dissapears the back of the boat will walk sideways , if this happens over about 70-75 MPH you will probably need a change of underwear the first time but you do get used to it.
I may not have explained very clearly but i tried !!
There are a number of tricks to cure this one of which is the smaller hub props as they produce less torque I wont go into the others at the moment but if anyone wants to they cann ask.
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Old 06-10-2005, 01:31 PM   #10
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My tandem p21 does this at W.O.T but you cant feel it when youre driving , only when youre in the back when you land off a wave you can feel it kick back over to the right very slightly when it re-enters the water! strange feeling but the boat feels stable ?
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Old 06-10-2005, 03:07 PM   #11
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Thats different , Thats merely the paddle wheel effect of the prop biting.
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Old 06-10-2005, 05:48 PM   #12
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Blowout is caused by the water being unable to follow the contours of the gear case at high speed, either because the gearcase is way too blunt (Honda 225), or just because the speed is too high fora convensional profile case, and a gearcase with a more streamlined profile is needed, or a nose cone fitting to give the same effect.

Most stock gearcases (except the Honda item) are pretty good tho', so you shouldn't be experiencing this at the speed you're going. Looks to me like you just need a bit more bow lift, assuming you're going quick (ish) in that pic.

When it happens, it's as if at a certain speed (very high), the prop appears to start slipping, almost as if the bush has gone, but as your speed falls off, all returns to normal, until the critical speed is again reached.
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Old 06-10-2005, 06:05 PM   #13
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No it is'nt but i won't argue about it !!
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Old 06-10-2005, 06:22 PM   #14
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Quote:
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No it is'nt but i won't argue about it !!
Blimey Bob, your going for it here mate ain't ya?
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Old 06-10-2005, 06:44 PM   #15
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No it is'nt but i won't argue about it !!
Could it be that on a big heavy hull blowout meerly cause's a loss of drive and steering where as on a small light hull it also cause's the back end to walk round a bit? I've read that on very light hulls it can cause a hard right turn. Back in the day I remember seeing an F1 cat in Bristol docks do a 90 degree turn straight into a wall whilst traveling at speed down a straight. I was only about 10 at the time and so had no idea of the cause but in more recent years I have often wondered if it could have been blowout?
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Old 06-10-2005, 06:47 PM   #16
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thanks for all your replies,not really sure on revs as the counters a bit shagged,as for how much throttle left i would say about just over half way at that speed,boat feels very stable and no signs of walking,bob,not sure i like the idea of it flying but me plums are slowly getting bigger!!!would like to try the lazer prop as you suggested last time.
thanks for help again,
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Old 06-10-2005, 06:52 PM   #17
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On the big heavy boat, what you describe is more likely to be Cavitation rather than Blow Out . The F1 Cat you refer to more than likely just Hooked or suffered steering failure . I was also not very old at the time but do remember.
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Old 06-10-2005, 06:55 PM   #18
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bob if your ever down brighton way let me know please
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Old 06-10-2005, 06:56 PM   #19
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Quote:
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The F1 Cat you refer to more than likely just Hooked or suffered steering failure . I was also not very old at the time but do remember.
Ok thanks!!!!
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Old 06-10-2005, 06:57 PM   #20
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Likewise if you find yourself in Devon !!
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