How does a chine work?

[Cadence]

Originally Posted by Jim Cate

We are seeing lots of new designs with fairly hard chines in their aft sections. There are claims of improved hydrodynamics, primarily in increased stiffness. I find this to be non-intuitive, and would appreciate knowledgeable input on the actual means by which this design feature works (or not).

Thanks for any informed input!

Jim

Jim,

I read many of the posts. There seems to be confusion as to cruising single chine or racing boats with a double chine. That a case of apples and oranges. I still maintain a single chine stiffens a boat. Looking at the posts of the double chines, it would appear the intention is to reduce wetted surface.

[Dockhead]

Originally Posted by Polux

Bob Perry has no experience working with this type of chines and he does not even use CFD to perfect the performance of his boats. I am not talking about the old chines that were used on the 60/70s near the waterline, kind of motorboat chines.

The evidence is simple and its given by all contemporary top Nas: All solo racers have chines the type that are used on the Oceanis 38. The same NA don't use that type of chines on top racing crewed designs. Do you mean they are all wrong and don't know what they are doing? Hardly belivable besides racing results speak by themselves.

You are not addressing any of the questions.

No one doubts that boats with chines have certain performance qualities. The questions are (a) how does it work; and (b) is it the chines themselves, or other qualities associated with chines, such as large radius of the curve of the bottom, which cause the effect?

Can you address the questions?

[neilpride]

Well, chine hulls are not really a new stuff today, Steel chine hulls are sailing since years and years, i visit the other day a f456 Bene by frers, it have something like a chine in the bow área oposite as what we see today in the aft sections, it work like if the boat heel, it sail faster, kind of a wide flat section below the waterline crossing from the bow to amidship and later turning rounded to the stern.

Anyway, i just see the chine hulls in terms of perfomance in boats doing supersonic speeds, for dad and mom cruising boat i dont see any real benefit apart from the initial stiifness when heeling and the internal volumen in that flat wide beamy aft , keep in mind that those decks are lovely in a capsize scenario, flat, wide, and with low deck coachroofs.

[Cadence]

Originally Posted by Dockhead

You are not addressing any of the questions.

No one doubts that boats with chines have certain performance qualities. The questions are (a) how does it work; and (b) is it the chines themselves, or other qualities associated with chines, such as large radius of the curve of the bottom, which cause the effect?

Can you address the questions?

In order to answer the above would basically be providing a course in naval architecture. Each little variance in the hull design and rigging would require numerous calculations. Probably a program for a PC today. Although doing it manually would answer the questions. I primer in calculating the GM might provide a short answer.

[Suijin]

Originally Posted by Dockhead

You are not addressing any of the questions.

No one doubts that boats with chines have certain performance qualities. The questions are (a) how does it work; and (b) is it the chines themselves, or other qualities associated with chines, such as large radius of the curve of the bottom, which cause the effect?

Can you address the questions?

I was talking not long ago with a friend of mine who had Bob Perry design a +45' cruising sled for him. It had chines, and according to Perry, they reduced wetted surface. His comments on their impact of stability, and the fact that it's not a simple "yes or no" answer, have already been referenced.

I find it counterintuitive that a hard turn reduces wetted surface, given that the "perfect" cross sectional shape for a hull is a circle, in terms of wetted surface to displacement, but I ain't no NA. As a disclaimer, it is possible that my friend did not accurately pass on Perry's conversation with him.

Despite Polux's dismissal, I do put a certain amount of credence into what Perry has to say about boat design.

[Polux]

Originally Posted by Dockhead

You are not addressing any of the questions.

No one doubts that boats with chines have certain performance qualities. The questions are (a) how does it work; and (b) is it the chines themselves, or other qualities associated with chines, such as large radius of the curve of the bottom, which cause the effect?

Can you address the questions?

How they work is obvious. The scientific explanation why a chined hull creates more stiffness at the point it is immersed regarding a completely rounded hull does not interests me, neither I thing most NA. I don't know and I don't care, except in what regards how it works in a practical way. It is intuitive anyway, at least for me.

No, that's two separated things, chines and large radius curves. Before using chines all the Na designed already all solo ocean racers with those large radius curves. Some years back the NAs continued to us the same type of large radius curves they used before plus chines to increase stability and make the boat control easier.

[neilpride]

This is writed by David de Premorel, from Finot Conq.

The chine is a feature that developed out of an IMOCA safety ruling that asks for a very

high capsizing angle (angle of vanishing stability or AVS ), which is hardly compatible with

a wide beam at deck level. The chine has lately spread to fast cruisers, both for aesthetic

and technical reasons, as it provides more power and/or more interior volume for a given

beam. Since we still want as much power as we can get, we design a very wide hull and

then reduce the upper part by introducing the chines, positioned so they don’t reduce

too much of the power at the useful heel angles. Since it also reduces the hull and deck

area, the boat is lighter and thus faster. Being fast and powerful also means high loads on

the structure, so we required very high build quality from the boatyard, which has been

verified by extensive non-destructive testing.

Hope this help ...

[Cadence]

Originally Posted by Suijin

I was talking not long ago with a friend of mine who had Bob Perry design a +45' cruising sled for him. It had chines, and according to Perry, they reduced wetted surface. His comments on their impact of stability, and the fact that it's not a simple "yes or no" answer, have already been referenced.

I find it counterintuitive that a hard turn reduces wetted surface, given that the "perfect" cross sectional shape for a hull is a circle, in terms of wetted surface to displacement, but I ain't no NA. As a disclaimer, it is possible that my friend did not accurately pass on Perry's conversation with him.

Despite Polux's dismissal, I do put a certain amount of credence into what Perry has to say about boat design.

I'm old school or not interest in racing. Take a look at the double chine hulls heeled. Their wetted surface appears to be the area between the chines. Some pics of single chinned hulls with the chine well above the WL may be for no more than interior space?

It would be nice to have a naval architect chime in. Then again I had one say he wouldn't hold it against me that I had met another certain one.

[Dockhead]

Originally Posted by Polux

How they work is obvious.

It's not obvious to me. And it's not obvious to the OP. If it's obvious to you, please enlighten us all.

[Dockhead]

Originally Posted by neilpride

This is writed by David de Premorel, from Finot Conq.

The chine is a feature that developed out of an IMOCA safety ruling that asks for a very

high capsizing angle (angle of vanishing stability or AVS ), which is hardly compatible with

a wide beam at deck level. The chine has lately spread to fast cruisers, both for aesthetic

and technical reasons, as it provides more power and/or more interior volume for a given

beam. Since we still want as much power as we can get, we design a very wide hull and

then reduce the upper part by introducing the chines, positioned so they don’t reduce

too much of the power at the useful heel angles. Since it also reduces the hull and deck

area, the boat is lighter and thus faster. Being fast and powerful also means high loads on

the structure, so we required very high build quality from the boatyard, which has been

verified by extensive non-destructive testing.

Hope this help ...

That sounds very reasonable to me

What it boils down to is this: introducing a chine allows you to make the bottom flatter without increasing the beam. That is, the radius of the curve of the bottom can be greater, which provides greater resistance to rolling/heeling without increasing wetted area. In other words: the greater the radius of the curve of the bottom, the more the buoyancy of the boat is distributed to resist rolling/heeling -- the very definition of form stability.

But as you increase the bottom curve radius, the beam of the boat gets wider and wider, which has a negative effect on stability (cf "capsize screening ratio"). So you introduce the chine to allow the topsides to go straight up from the heeled waterline (or thereabouts) and limit the beam, so that you aren't hurting the stability of the boat with your increased bottom curve radius. It gives you the possibility of greater bottom curve radius without a proportional increase in beam.

So the chine itself does nothing except get you around an unacceptable increase in beam. You can radius the chine without reducing this effect -- as Bob Perry mentions.

It would be nice to have a real naval architect weigh in, but that sounds right.

And if this interpretation is correct, then the chine in a sailboat performs a completely different function than the chine in a planing powerboat hull.

[Polux]

Originally Posted by Suijin

I was talking not long ago with a friend of mine who had Bob Perry design a +45' cruising sled for him. It had chines, and according to Perry, they reduced wetted surface. His comments on their impact of stability, and the fact that it's not a simple "yes or no" answer, have already been referenced.

I find it counterintuitive that a hard turn reduces wetted surface, given that the "perfect" cross sectional shape for a hull is a circle, in terms of wetted surface to displacement, but I ain't no NA. As a disclaimer, it is possible that my friend did not accurately pass on Perry's conversation with him.

Despite Polux's dismissal, I do put a certain amount of credence into what Perry has to say about boat design.

I would appreciate that you don't put me sayng things that I did not said. What i said it was that Bob Perry had no experience in what regards designs with top racing boats with chines (modern chines like they are used on the solo racers or on the Oceanis 38) and that he does not use them on his ocean performance cruisers, that are rather few on the last decades, and are not top racing boats anyway.

The only one that could fit your description is Icon, a 65ft, but it is a fast performance cruiser or a cruiser racer and not a "sled" nor a top racing boat and most of all it has no chines.



Maybe you can tell me of what boat you are talking about regarding a Bob Perry designed over 45ft performance cruiser with chines? I don't know that boat and I know pretty well Bob Perry's work.

[Polux]

Originally Posted by Dockhead

It's not obvious to me. And it's not obvious to the OP. If it's obvious to you, please enlighten us all.

Some have already explained that:

Originally Posted by noelex 77

Intuitively I would expect the chine to increase stability.

If you look at the possible underwater shape of a rounded hull section and a similar section with a hard chine the added buoyancy of the boat with the chine would produce more of a righting moment and increase form stability.

You can see how the chinned hull section (the lower blue line on the diagram) has more buoyancy and a wider effective beam at most angles of heel.

....

and...

Originally Posted by UNCIVILIZED

...
Look at a round bilged boat from dead aft, & compare it to say, a tire. Now, look at a chined bilged boat from dead aft & compare it to a hexagonal or octagonal "tire". Which one's harder to get to roll, side to side?
And stability means speed, due to the ability to control more sail for a given boat size.
..

These two points put together sums it up in what regards being obvious in an intuitive way to me.

[Dockhead]

Originally Posted by Polux

Some have already explained that:



and...



These two points put together sums it up in what regards being obvious in an intuitive way to me.

OK, but that's entirely consistent with the post above, the only one on point by a real naval architect, which says that:

"

Since we still want as much power as we can get, we design a very wide hull and

then reduce the upper part by introducing the chines, positioned so they don’t reduce

too much of the power at the useful heel angles.

"

The flatter bottom in the drawing obviously has more resistance to heeling because -- it's flatter. It would have the same resistance to heeling if it had no chine and the flat curve just continue on and on.

So if that is what is obvious to everyone, then we all agree with David de Premorel above that the chine is merely a way to get the effect of a much flatter section -- a larger curve radius -- without a corresponding increase in beam?

If so, then we agree that the chine does nothing by itself; there is no magic effect of the chine hitting the water.

[Polux]

Originally Posted by Dockhead

...
And if this interpretation is correct, then the chine in a sailboat performs a completely different function than the chine in a planing powerboat hull.

It seems you did not read well what Neil had posted from one of the collaborators of the ones that designed the Oceanis 38 and many top solo racing boats:

Originally Posted by neilpride

This is writed by David de Premorel, from Finot Conq.
The chine has lately spread to fast cruisers, both for aesthetic and technical reasons, as it provides more power and/or more interior volume for a given beam.

Since we still want as much power as we can get, we design a very wide hull and then reduce the upper part by introducing the chines, positioned so they don’t reduce too much of the power at the useful heel angles. Since it also reduces the hull and deck area, the boat is lighter and thus faster...

It seems to me that he is talking about cruising boats but even if not, all he is saying applies to cruising boats. How can you say that "the chine in a sailboat performs a completely different function than the chine in a planing powerboat hull"?.

[Dockhead]

Originally Posted by Polux

It seems you did not read well what Neil had posted from one of the collaborators of the ones that designed the Oceanis 38 and many top solo racing boats:



It seems to me that he is talking about cruising boats but even if not, all he is saying applies to cruising boats. How can you say that "the chine in a sailboat performs a completely different function than the chine in a planing powerboat hull"?.

Because the chine in a planing powerboat (or a seaplane hull -- lots of stuff about this) directs spray downward, increasing lift. The spray resulting from the water jet at the interface with the water. This effect might work with a really fast racing boat capable of full planing, but not a cruising boat. What is interesting about this is that the form of the chine itself is important here, unlike the case with sailboats.

To the extent that the chine is being used in powerboats to allow a flatter bottom, then of course I agree -- same principle. But that's a different function.