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Old 11 May 2010, 07:48   #31
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I don't mind swimming back if it sinks...... whats yours like?
Thinking now a 2 hp.!!!
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Old 11 May 2010, 14:57   #32
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What are the symptoms of chine walk ?? what happens when chine walk ??
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...just seen something about chine walking that's bothering me a little now as I fitted a large planing pad...I was hoping porpoising and the walking would be out of the equation.
sonar - chine walk is pretty common on performance hulls, particularly vee hulls. As the hull accelerates, lift increases and the wetted running surfaces that are required to support the hull are reduced (more Speed = more Lift = less Surface). As the speed increases, the hull often gets to a point where the lifting surfaces become very much reduced and the hull is now "balancing" on a small area of the vee-portion or the "vee-pad" of the hull. When that surface becomes sufficiently small, it becomes very tricky to "balance" the hull on its vee or pad. The result is a dynamic unbalance and a rocking of the hull from side-to-side. This rocking can tend to get a little more extreme with each motion, and so the "balancing" must then be provided by additional driver input (steering/throttle/trim) in order to maintain the hull in a balanced state.

check this thread for more on chine walk.

and check out this magazine article on chine walk.

Porpoising is pretty common...any vee hull (or tunnel hull) can be susceptible to porpoising, depending on design and setup. Flatter bottom vees are more prone to porpoising than steeper deadrise vee hulls, but there are several contributors to the occurance and any vee hull can find the problem caused by dynamic instability. Adding a pad can often make a hull more suseptible to porpoising.

here is a reference for more info on porpoising

Also, have a look at this article on "Hump Zone/Why does my Boat Porpoise?

and check here for how to consider whether your hull will be susceptible to porpoising
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Old 11 May 2010, 15:38   #33
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sonar - chine walk is pretty common on performance hulls, particularly vee hulls. As the hull accelerates, lift increases and the wetted running surfaces that are required to support the hull are reduced (more Speed = more Lift = less Surface). As the speed increases, the hull often gets to a point where the lifting surfaces become very much reduced and the hull is now "balancing" on a small area of the vee-portion or the "vee-pad" of the hull. When that surface becomes sufficiently small, it becomes very tricky to "balance" the hull on its vee or pad. The result is a dynamic unbalance and a rocking of the hull from side-to-side. This rocking can tend to get a little more extreme with each motion, and so the "balancing" must then be provided by additional driver input (steering/throttle/trim) in order to maintain the hull in a balanced state.

check this thread for more on chine walk.

and check out this magazine article on chine walk.

Porpoising is pretty common...any vee hull (or tunnel hull) can be susceptible to porpoising, depending on design and setup. Flatter bottom vees are more prone to porpoising than steeper deadrise vee hulls, but there are several contributors to the occurance and any vee hull can find the problem caused by dynamic instability. Adding a pad can often make a hull more suseptible to porpoising.

here is a reference for more info on porpoising

Also, have a look at this article on "Hump Zone/Why does my Boat Porpoise?

and check here for how to consider whether your hull will be susceptible to porpoising
Many thanks i will have to read as much as I can again thanks for the links.

Robert
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Old 11 May 2010, 17:12   #34
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chine walking

Will a twin outboard set up on a deep vee rib be any less inclined to chine walk than one with a single engine set up?
Would a twin engine set up provide any more lateral stability given that there is more of a grip on the water either side of the boats centreline?
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Old 11 May 2010, 18:26   #35
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Will a twin outboard set up on a deep vee rib be any less inclined to chine walk than one with a single engine set up?
Would a twin engine set up provide any more lateral stability given that there is more of a grip on the water either side of the boats centreline?
Zubenelgenubi - one of the influencing factors for initiation of chine walking is the location of dynamic (longitudinal) center of gravity. The added weight of a twin engine setup (compared to a single engine setup of similar hp) would move the CofG aftward, changing the balance of a hull design. This is more likely to require a "higher" trim angle, and so might then make the hull more susceptible to chine walk. More hp itself, however, is likely to aid the performance of the hull, and allow for a "lesser" trim angle, and so the additional hp would be an asset to chine walk prevention. Analysis of the hull is the best way to settle the "balance" of the influencing factors.
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Old 11 May 2010, 18:34   #36
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Lets assume that the combined weight of two smaller twins was the same or very similar to that of a large single outboard, then the LCG in both cases is the same or similar.
Would the twin setup then be less inclined to chine walk v's a single engine set up & to what if any degree is the distance between the engines a factor, again assuming that there is some flexibility in the spacing of the engines on the transom? ie the further apart the engines are the more stable the boat may be?
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Old 11 May 2010, 19:32   #37
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Lets assume that the combined weight of two smaller twins was the same or very similar to that of a large single outboard, then the LCG in both cases is the same or similar.
Would the twin setup then be less inclined to chine walk v's a single engine set up & to what if any degree is the distance between the engines a factor, again assuming that there is some flexibility in the spacing of the engines on the transom? ie the further apart the engines are the more stable the boat may be?
I don't think that the "distribution" of the 2 engines would delay the onset of chinewalking. There isn't really any additional stability gained by separating the weights of the engines to the outboard of the hull. The longitudinal dynamic instability is what initiates the chinewalk. The side-to-side "balance" is an important setup feature to ensure, but with 1 or 2 engines, this issue is still the same.
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Old 12 May 2010, 04:35   #38
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I don't think that the "distribution" of the 2 engines would delay the onset of chinewalking. There isn't really any additional stability gained by separating the weights of the engines to the outboard of the hull. The longitudinal dynamic instability is what initiates the chinewalk. The side-to-side "balance" is an important setup feature to ensure, but with 1 or 2 engines, this issue is still the same.
Are you taking into account counter rotating props?

That large V planing pad is so big it may actually produce more drag than anything and the keel doesn't need to be as round as that either! just a couple of thoughts ...........
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Old 12 May 2010, 13:38   #39
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That large V planing pad is so big
I had one that was bigger but had a rectangular profile, with a small swept leading edge to blend it with the 'V'

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it may actually produce more drag than anything
This is my thinking, and the leading edge may haul the boat to one side, if its sitting on top of it at high speed.. however because its effectively an angle being presented to the direction of travel it may not count as much, particularly if there is enough weight forward ... looking forward to see how it goes whatever Sonar keep us updated
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Old 12 May 2010, 13:57   #40
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I had one that was bigger but had a rectangular profile, with a small swept leading edge to blend it with the 'V'

This is my thinking, and the leading edge may haul the boat to one side, if its sitting on top of it at high speed.. however because its effectively an angle being presented to the direction of travel it may not count as much, particularly if there is enough weight forward ... looking forward to see how it goes whatever Sonar keep us updated
Sure will but it's going to be some time away from completion.
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