2 x 300 hp on a 5.5mtr rib. OH YES !!!!!

[Bigmuz7]

Originally Posted by Sonar

Very interesting So I guess the answer is not to over power.
I am hoping the rib will be quite heavy when loaded .

So would it be better to make another hull with out a planing pad .????

There are other posts on here that suggest ifs and buts or more likely just views of how people found them, but no .. I'd go for it with what youve got and let us know how you get on .. Its gonna be fine, but like Chuck Yaeger breaking the sound barrier .. You'll never really know till the last minute how it performs .. but like I said .. you just add ballast and shift some weight around to prevent it if all else fails .. or dont go into the danger zone with the throttle, if youve put a lot of hp on the back.

Some hull manufactures might offer some comment here, but my concern with a pad of that shape is that if the boat is too light, it will drag to one side very quickly, causing a sharp loss of steerage, which could be a bit nasty and even more violent than just the usual slap onto one side .. I dunno ? just my VHO

[chewy]

I'll take it out for the first time for you if you want, sounds like fun!

Ultimately with chine walking you'll get thrown out of the boat, although throttling back or trimming in a bit can reduce it.

[captnjack]

I have never seen a planing section that large. I am guessing that it will actually help with the high speed performance and moderate the chine walking (depending on load). There's not that much flopping from chine to chine (hence the name) it can do. But that pad will also probably degrade the rough water performance a little bit and create some "slam". This will again depend on weight and the lift you are getting "over" the waves from the tubes vs. how much deadrise you have forward etc.

I would keep it as is for now and plan on powering with a ~115-125hp

[Sonar]

Thinking i will have to complete it and weight it then consult the forum.
But I do know at the stage it is in now it's quite heavy.

Thanks everybody and Chewy looks like he will be the test pilot.

[pvm]

You say you need an 'extra long shaft outboard' but that planing pad has removed lots of rear hull height, and also your transom seems to have an engine cut-out in it.

Surely the prop will be way too low in the water if it is an extra long shaft?

I think you are being very brave designing a hull from scratch with such a radical planing pad. Manufacturers have CAD/CAM, experience and ££££ yet they still get it wrong.

good luck.

pvm

[Sonar]

Originally Posted by pvm

You say you need an 'extra long shaft outboard' but that planing pad has removed lots of rear hull height, and also your transom seems to have an engine cut-out in it.

Surely the prop will be way too low in the water if it is an extra long shaft?

I think you are being very brave designing a hull from scratch with such a radical planing pad. Manufacturers have CAD/CAM, experience and ££££ yet they still get it wrong.

good luck.

pvm

No this is a fletcher converted hull.

Reading through the forum ( transom height ) thread seems that the long shaft is required.

says from the bottom of the keel to the top of the transom 26" to 28"
so I made it 27" high from the bottom of the keel.

I dont know if the pad makes any deliverance on the length of the outboard.Or not.

[r mcdonald]

Originally Posted by Sonar

Very interesting So I guess the answer is not to over power.
I am hoping the rib will be quite heavy when loaded .

So would it be better to make another hull with out a planing pad .????

Sonar
I would see how it goes before I started another hull. You could always add to the hull if you wanted to reduce the planing pad latter on.Looks like a nice finish on the hull.
Good luck with the sea trials.
rpm

[chewy]

Originally Posted by Sonar

Thanks everybody and Chewy looks like he will be the test pilot.

Happy Days!

[Sonar]

Originally Posted by chewy

Happy Days!

What's your insurance like .????

[chewy]

Originally Posted by Sonar

What's your insurance like .????

I don't mind swimming back if it sinks...... whats yours like?

[Sonar]

Originally Posted by chewy

I don't mind swimming back if it sinks...... whats yours like?

Thinking now a 2 hp.!!!

[Jimboat]

Originally Posted by Sonar

What are the symptoms of chine walk ?? what happens when chine walk ??

Originally Posted by Sonar

...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

[Sonar]

Originally Posted by Jimboat

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

[Zubenelgenubi]

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?

[Jimboat]

Originally Posted by Zubenelgenubi

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.

[Zubenelgenubi]

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?

[Jimboat]

Originally Posted by Zubenelgenubi

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.

[Cookee]

Originally Posted by Jimboat

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 ...........

[Bigmuz7]

Originally Posted by Cookee

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'

Originally Posted by Cookee

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

[Sonar]

Originally Posted by Bigmuz7

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.