How does a chine work?

[Polux]

Originally Posted by Dockhead

You keep misreading what I write. I said -- the effect of form stability becomes negative, not that the sum of form and ballast stability becomes negative. That -- as I said -- depends on the boat. As I wrote, a deep keel with a heavy bulb will compensate any such effect, which is exactly what is done on all of these boats.

To see how form stability works without any compensating ballast stability, all you have to do is look at dinghies without ballasted keels and their AVS. nearly all of their stability is form stability.

You were talking about the boat being dangerous after 20º of heel. Even if we consider only the hull without the keel of ballast (meaning a hull without keel or ballast), negative stability on hull form stability will be achieved only when the boat passes the AVS point on that condition. Surely you agree that such a beamy boat heeled at 25º degree will not capsize but will return to the right up position, the same at much bigger angles of heel (45º,50º) that means that only after that heel angle (at some point) the hull form stability will become negative.

I understood what you wanted to say and it is true that these boats rely more on form stability then other types of boats but what you said was just not correct. Sorry for being such nit picking about this but I like to have this kind of technical stuff well clear.

[Suijin]

Originally Posted by Polux

It depends on the boat. It is true that on the Oceanis 38 for instance there will be s sudden heel after one takes enough efforts to pass that chine, as we can see on the video I posted but it is not dangerous only stupid since the boat will lose a lot of performance.

You imply that the the Max righting moment of the boat (the heel angle where the boat makes a bigger effort to right itself up) is near the angle the chine enter s the water. It is not the case, the max RM on that type of boats is normally somewhere between 50 and 60º while the heel angle where that chine gets immersed is about 20º. Even much more heeled then 60º the boat is making a superior RM than the one that is making at 20º. The average AVS of that that type of boat is not different from the Average AVS of more narrow, different typed main market cruisers and it will be around 120º.

It's pretty clear that the hard chine that we see, while perhaps contributiing to some degree to stalling leeway, is largely a function of coupling a flatter, surfing, or at least larger RM bottom with the aesthetics of the times. I have yet to see any NA argue strongly that the hardness of the chine helps with leeway...in every case their remarks are focused on getting the flattest bottom possible, and the widest aft beam, with an acceptable boat beam.

It's not rocket science to state that after the chine is immersed, the RM of the boat is going to fall off dramatically. It may still be great, depending on the width of the hull before the chine, but the chine itself does nothing to contribute to RM...and in fact detracts from it, at least versus the hull extending out further along the arc of the curve. It's pretty simple physics. So it comes down to the width of the hull beneath the chine, and its extent outwards. The chine shape is itself pretty much irrelevant to the whole equation, as far as I can tell.

If you sail in these types of boat, the chine is going to get immersed. But that's not really relevant. What is relevant is the overall width of the that displacement hull, and overall shape, hard chine or not. The chine is nothing more than a means of getting the maximum RM for a given beam by making a hard turn up to the gunwale.

[Polux]

Originally Posted by Suijin

...The chine is nothing more than a means of getting the maximum RM for a given beam by making a hard turn up to the gunwale.

Well and that's not what we all want: the more powerful and stable boat for a given beam?

[UNCIVILIZED]

Originally Posted by Dockhead

The problem with "just reducing sail" is that once you even barely start reefing a roller furling headsail, the shape goes to hell and you lose tons of performance. So you have a choice of losing performance because you are heeled too far over (and your rudder is acting like a brake) or losing performance because your headsail is reefed. Not an attractive choice.

The only way out is to change down the headsail to another size, but why have roller furling gear in the first place if you're going to have a sail inventory? How many cruisers can manage sail changes under way?

And this is exactly why large SA/D ratios, great for racers, or maybe racer/cruisers, are wrong for cruising boats, except perhaps in latitudes where you rarely experience good breezes.

Up here with our good wind, the typical racer cruiser with SA/D of 20 or even more, which will fly with a full crew and sail inventory, with a short-handed family crew, on the other hand, struggles all the time.

My boat is made for these conditions, with very light displacement for her size (under 190 D/L), and modest sail plan (16.5), so is hard to beat in our typical 20 - 25 knot breezes. But even so, the sail area is still too much for many days, which is why I decided to bite the bullet and have a high aspect blade jib made for my boat, out of carbon laminate, which should push up the useful wind range 4 or 5 knots, I hope.

The big question is whether to put it on a separate Solent stay or hoist it in the main furler, a PITA with sails this size and not realistic short-handed at sea.

This question about the "unreasonability" of changing headsails on a boat your size has already been discussed & answered, (at the time, mutually it seemed) when you were looking for advice on what sails to purchase for your boat.

It is EXACTLY why the concept of a Solent stay was invented, & unless one's advanced in age, it's completely reasonable to use such a setup. Particularly if one goes with a detachable Spectra/Dyneema Solent stay as I recommended.
A hanked on 80%-90% jib on a 50'er is far from uncontrollable (to hoist or douse).

And to reiterate, going to a standard 120%'ish jib on the primary (outer) headstay furler, & a Solent Jib, on a furler in said location, in conjunction with a hanked on staysail (in the standard staysail location), you're covered for pretty much every windspeed, when going to windward. Plus, with that kind of setup, there's even less reason to leave the cockpit.
- See posts #96 - #105 http://www.cruisersforum.com/forums/...ml#post1668258
Sail sizes, efficiencies, & rig design are covered there.

In said thread I also provided the example, where, with an ankle sprained to the point which I couldn't walk, I changed down from a #2 jib, to the #3, solo. On a 68' Swan. Which has jibs larger than your entire combined sail plan (and such sails weigh in excess of double that of most men). So IMO, rolling up say a 120% jib, & hoisting a Solent (on a 50'er) is a no brainer.
And I'm happy to provide more info on Solent setups, including detachable ones, & those made of Spectra/Dyneema (much like those used on some generations of the Volvo boats, amongst others).

In point of fact, at times, on one of the 50'ers which I used to race on regularly, I was the only one who could handle (understood the procedures) to act as bowman. So I would routinely sleep at the base of the mast on distance races, waking up to changing out headsails, often sans help, all the time, as needed.
And plenty of my sailing mates can, have, & do the same kinds of things routinely (and on far larger vessels as well).

As to chines, Polux, thank you for straightening out some of the misconceptions about them!
Although one which still seems prevalent, is that once you heel over until you begin to immerse a chine, then that's all of the form stability which you get from it.
This is incorrect. With a chine, the further you attempt to immerse it, the more resistance (form stability) you meet. If you spend any amount of time in a properly (for purpose) designed dory, this will become VERY apparent.

In my 9' dory type dingy, the initial stability was only average for a dinghy of her size, but as you leaned her over she began to stiffen up. And at #230, I could stand on the gunwale, in a 2' seaway, & only ship a few cups of water into her over the side. Plus she was comfortable to handle, & row for distance, in 50kt winds & the sea state which goes with such.

Such is definitely NOT the case in a slab sided, or more traditionally designed dingy. They'd have capsized with 1/2 - 2/3 that amount of weight on the gunwale, if that. Nor do they progressively stiffen up in a manner akin to a dory as you heel them over.
- Many, to all, of these principles apply to sailing vessels with chines, when properly designed. In fact, it's a good part of the reason why they're designed into the hull shapes (SIC).

Sadly, there's only the abridged (dumbed down) explanation about chines in the article link which I previously posted (on chines). taking it on the chin(e) | Sailing Anarchy

[UNCIVILIZED]

Originally Posted by Suijin

It's pretty clear that the hard chine that we see, while perhaps contributiing to some degree to stalling leeway, is largely a function of coupling a flatter, surfing, or at least larger RM bottom with the aesthetics of the times.
If a vessel has less leeway, & a larger RM then can it not go faster, as well as making better VMG? It seems from my perspective, that your statement here is in fact a self contradictory one.
I have yet to see any NA argue strongly that the hardness of the chine helps with leeway...in every case their remarks are focused on getting the flattest bottom possible, and the widest aft beam, with an acceptable boat beam.

It's not rocket science to state that after the chine is immersed, the RM of the boat is going to fall off dramatically.
On a keelboat, it's RM does not fall off until it reaches it's AVS, at least the last time I checked.
It may still be great, depending on the width of the hull before the chine, but the chine itself does nothing to contribute to RM...and in fact detracts from it, at least versus the hull extending out further along the arc of the curve.
As to chines contributing to RM, see my above post, where I use a dory dingy as an example. Because the shape of a chine is THE reason which it contributes to stability. Such is why they're so prevalent on the high HP to Weight ratio, current generation racing boats. And as much is stated in the link in several of my other posts in this thread, to an article which explains the why, & the popularity of chines.
It's pretty simple physics. So it comes down to the width of the hull beneath the chine, and its extent outwards. The chine shape is itself pretty much irrelevant to the whole equation, as far as I can tell.

If you sail in these types of boat, the chine is going to get immersed. But that's not really relevant. What is relevant is the overall width of the that displacement hull, and overall shape, hard chine or not. The chine is nothing more than a means of getting the maximum RM for a given beam by making a hard turn up to the gunwale.

As also stated by Polux, isn't getting the maximum RM for a given beam the whole idea? So then if by your own admission, chines work, & work well (in addition to the same statements by experts) where is the logic in what you're trying to say? AKA chines don't work, but they do?

[Dockhead]

Originally Posted by Polux

A sail can be furled to a point without a being loss on performance. I agree that over that point the sail will have a bad performance. The ones that have fast boats will change sails (on the furler) according with the place or season where they are sailing. For instance on Italy on the summer I sail with a 140% genoa on the furler, but already after being in Greece and before going to the Cyclades or Dodecanese islands, where normally it blows from F4 to f8, I change the the big genoa on the furler by a jib.

I can sail with full jib till F7 (upwind). With more I furl the jib.

Many boats have also two stays with two furlers with different sized frontal sails. I have a furler and a removable stay but I am in the process of installing two furlers.

You can sail without reefing to F7? Over 30 knots of true wind, so 37 or 38 knots of apparent wind? Upwind? Without reefing? You have some wonder boat with a 6 meter deep tungsten keel, or else SA/D of less than 8. Or maybe both would be necessary. That doesn't exist in nature to my knowledge, but if you say so . . .


The usual double furler is used to avoid having a normal genoa at all, at least around here. Discovery yachts come with this setup from new. On one furler you have a 90% blade, and on the other a light Code 0 or extra large light wind genoa. I think it makes a great deal of sense, and I've thought about it for my boat. But there are drawbacks -- windage, for one -- a very serious problem, since sails on furlers have far more windage than bare stays. This causes drag and extra heeling moment, hurting upwind performance. The second problem is balancing tension between the two forestays. Some superyachts designed by Bill Dixon with this setup have hydraulic tensioners under the deck with strain gauges, to solve this problem.

[Dockhead]

Originally Posted by UNCIVILIZED

As also stated by Polux, isn't getting the maximum RM for a given beam the whole idea? So then if by your own admission, chines work, & work well (in addition to the same statements by experts) where is the logic in what you're trying to say? AKA chines don't work, but they do?

Well, there are two different things going on here.

Righting motion from form stability comes from buoyancy, not from any hydrodynamic effect (that would be a different kind of stability). We figured out in the course of this thread where that comes from -- flatter bottom. Chines allow the bottom to have a larger curve radius, giving more form stability. That form stability falls off rapidly when you reach the chine, which however, can be compensated for with ballast stability to give you a not bad overall stability curve. So as far as that's concerned, it's all about the shape of the bottom -- the chine itself doesn't do anything with regard to righting moment.

The other interesting question is whether the chine has any hydrodynamic effect. It certainly does on seaplane pontoons and power boats -- as the chine can redirect the water jet downward producing lift which helps with planing. But those are chines of a different shape, and full planing does't occur with normal keelboats.

Does an immersed chine act as a runner or a another keel, if it is immersed? That would be a different hydrodynamic effect, and I can't say whether it exists or not. I have not found anything written by a naval architect which indicates that this is a significant consideration, but my mind is open. I rather doubt it, myself, as the chines on cruising boats are too shallow to make a significant projection into the water like a keel, but I am not a naval architect (and would like to remind all of you who are not naval architects also not to pretend that you are and fantasize that you have technical knowledge which you don't) so can't say for sure.

[Dockhead]

Originally Posted by UNCIVILIZED

This question about the "unreasonability" of changing headsails on a boat your size has already been discussed & answered, (at the time, mutually it seemed) when you were looking for advice on what sails to purchase for your boat.

It is EXACTLY why the concept of a Solent stay was invented, & unless one's advanced in age, it's completely reasonable to use such a setup. Particularly if one goes with a detachable Spectra/Dyneema Solent stay as I recommended.
A hanked on 80%-90% jib on a 50'er is far from uncontrollable (to hoist or douse).

And to reiterate, going to a standard 120%'ish jib on the primary (outer) headstay furler, & a Solent Jib, on a furler in said location, in conjunction with a hanked on staysail (in the standard staysail location), you're covered for pretty much every windspeed, when going to windward. Plus, with that kind of setup, there's even less reason to leave the cockpit.
- See posts #96 - #105 http://www.cruisersforum.com/forums/...ml#post1668258
Sail sizes, efficiencies, & rig design are covered there.

In said thread I also provided the example, where, with an ankle sprained to the point which I couldn't walk, I changed down from a #2 jib, to the #3, solo. On a 68' Swan. Which has jibs larger than your entire combined sail plan (and such sails weigh in excess of double that of most men). So IMO, rolling up say a 120% jib, & hoisting a Solent (on a 50'er) is a no brainer.
And I'm happy to provide more info on Solent setups, including detachable ones, & those made of Spectra/Dyneema (much like those used on some generations of the Volvo boats, amongst others).

In point of fact, at times, on one of the 50'ers which I used to race on regularly, I was the only one who could handle (understood the procedures) to act as bowman. So I would routinely sleep at the base of the mast on distance races, waking up to changing out headsails, often sans help, all the time, as needed.
And plenty of my sailing mates can, have, & do the same kinds of things routinely (and on far larger vessels as well).

Yes, thank you, I gratefully took on board all of this good advice and still think about it. I'm weighing the drawbacks (windage, stay tension) against the huge advantage of having both sails in furlers ready to go.

Originally Posted by UNCIVILIZED

As to chines, Polux, thank you for straightening out some of the misconceptions about them!
Although one which still seems prevalent, is that once you heel over until you begin to immerse a chine, then that's all of the form stability which you get from it.
This is incorrect. With a chine, the further you attempt to immerse it, the more resistance (form stability) you meet. If you spend any amount of time in a properly (for purpose) designed dory, this will become VERY apparent.

I don't think Polux said that, nor did the SA article say that, and I daresay it's clearly not true. Could you draw it and explain how the buoyancy of a chined hull works with the chine immersed? After the chine, there is no more bottom to provide buoyancy. Form stability comes only from buoyancy, by definition. Polux understood and acknowleged that in about Post 5 of this thread.

[malbert73]

Great discussion- very informative.

I think there is no doubt that the wider and flatter aft hulls that are being developed allow more power and less heeling, and higher top speeds when reaching and running in heavy stuff. Also faster speeds under power due to more "powerboat like" aft sections. I think for them to steer well in all conditions they have to have twin rudders. The only problem is all that wetted surface aft requires more sail area to get the boat moving, especially in light air. This means higher loads, requiring more gear like electric winches to handle. If these go down, can be a handful in heavy air.

I think for sake of balance it's worth presenting the counterpoint - narrower beamed boat with more moderate aft sections. Advantages are that such hulls are much more easily driven, especially in light air. These boats require less sail area so handling sails, etc may be more manageable and safer especially in the heavy stuff for shorthanded crew. They generally track more easily and are easier to steer when heeled over by waves, wind, etc. Downsides are more initial heel, less interior space, and older designs with slack bilges roll especially when going downwind.

Finally, it seems to me that the hard chine is really a style thing now. I personally don't love the look. Naval architects have known for a while that a firm turn at or above the waterline achieves the flatter section aft that benefits downwind speed and nterior space. Sure, the chine may give you a few inches more, but I think that is significant only for race boats. Cruisers, if it werent for marketing, could easily have a radiused chine (sharp curve) which isn't so apparent aesthetically. I think NA's have been doing this for a while. These days, though, chines are a fad. I wonder if the extra fiberglass needed to reinforce a sharp edge outweighs the advantage in cruisers.


In summary, long and narrow is always more easily driven for given horsepower (look at rowing shells, canoes, kayaks, etc). There may be a downside in sailboats that have beamy hull shapes in terms of price and loads imposed by the larger rigs needed to make them move in lighter or moderate air. Clearly some advantages, which I think are mostly in places where wind is heavier. I pass a lot of chined cruising boats on the Chesapeake in the light to moderate stuff. They seem to be stuck there when the wind isnt up.




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[Polux]

Originally Posted by UNCIVILIZED

[COLOR=#000080]...
As to chines, Polux, thank you for straightening out some of the misconceptions about them!
Although one which still seems prevalent, is that once you heel over until you begin to immerse a chine, then that's all of the form stability which you get from it.
This is incorrect. With a chine, the further you attempt to immerse it, the more resistance (form stability) you meet. If you spend any amount of time in a properly (for purpose) designed dory, this will become VERY apparent.
....

I don't know, maybe. You are certainly right regarding the type of chines on a Dory or on the several very successful cruiser racers Vand de Stadt designed on the 50's and 60's but those chines were different, sharper and designed to provide stability when immersed. In fact they were not designed for that they were a product of the building techniques using mostly plywood and the discovery that those chines could have a positive enhancement on stability was an agreeable discovery.

Regarding modern chines one thing is for sure: they are not designed as the old ones to be sailed immersed. Drag will increase and will make the boat slower. As I said those learning wheels on a bicycle are a good comparison: they are very helpful but when they touch the ground they create drag and diminish speed.

As i said on the fastest racing boats to be controlled by a huge top crew the tendency on new designs is or not using chines or using them much higher on the hull allowing for much more heel downwind taking advantage of the big B/D ratio and the weight of the crew on the rail. Anyway in what regards top crewed races the chines and the way they should be designed (or no chines at all) is not settled and each top designer plays differently even when they have a lot of experience with them and use them on other designs.

Look for instance to these two recent boats designed by two top racing NAs, Beau Geste (Botin) and Alegre (Mills):





You can see that even on Beau Geste those chines are a lot higher on a more rounded hull (allowing more heel) then the ones that are used on the top solo racing boats, for instance the fastest of them, Banque Populaire (Verdier):





Regarding solo racers the question regarding using chines or not and the type of chines is settled. Solo sailors need a lot more help to control a hugely powerful boat and on this case being an easier boat to sail makes it a faster boat, even if at the cost of some extra drag.
Anyway, interesting stuff

[Dockhead]

Originally Posted by malbert73

Great discussion- very informative.

I think there is no doubt that the wider and flatter aft hulls that are being developed allow more power and less heeling, and higher top speeds when reaching and running in heavy stuff. Also faster speeds under power due to more "powerboat like" aft sections. I think for them to steer well in all conditions they have to have twin rudders. The only problem is all that wetted surface aft requires more sail area to get the boat moving, especially in light air. This means higher loads, requiring more gear like electric winches to handle. If these go down, can be a handful in heavy air.

I think for sake of balance it's worth presenting the counterpoint - narrower beamed boat with more moderate aft sections. Advantages are that such hulls are much more easily driven, especially in light air. These boats require less sail area so handling sails, etc may be more manageable and safer especially in the heavy stuff for shorthanded crew. They generally track more easily and are easier to steer when heeled over by waves, wind, etc. Downsides are more initial heel, less interior space, and older designs with slack bilges roll especially when going downwind.

Finally, it seems to me that the hard chine is really a style thing now. I personally don't love the look. Naval architects have known for a while that a firm turn at or above the waterline achieves the flatter section aft that benefits downwind speed and nterior space. Sure, the chine may give you a few inches more, but I think that is significant only for race boats. Cruisers, if it werent for marketing, could easily have a radiused chine (sharp curve) which isn't so apparent aesthetically. I think NA's have been doing this for a while. These days, though, chines are a fad. I wonder if the extra fiberglass needed to reinforce a sharp edge outweighs the advantage in cruisers.


In summary, long and narrow is always more easily driven for given horsepower (look at rowing shells, canoes, kayaks, etc). There may be a downside in sailboats that have beamy hull shapes in terms of price and loads imposed by the larger rigs needed to make them move in lighter or moderate air. Clearly some advantages, which I think are mostly in places where wind is heavier. I pass a lot of chined cruising boats on the Chesapeake in the light to moderate stuff. They seem to be stuck there when the wind isnt up.

A very valuable additional perspective.

For racing and ultimate speed, the more power you can get into the boat the better, and at any cost. You don't mind the extra drag from the wide stern because you can more than make up for it by carrying more canvas.

But carrying a lot of canvas has a lot of cost. It demands more strength of everything, and demands more of the crew. It is hard to sustain for long passages or short handed and especially both. It gives you a narrower useful wind range which forces you to reef earlier or change sails more often.

It's ideal for racing, and it's fine for high performance day sailing, or sailing like Polux does where 4 to 10 hours is considered a passage, from one restaurant to the next. All of those are perfectly valid ways to sail, and I get them all.

But for long distance cruising, many sailors won't find this model attractive. They might very well want speed (I do!), but they don't want the stress of carrying huge amounts of canvas.

So what you are talking about is exactly Dashew's model -- an ingenious one. With his Sundeers and some of his other designs. Here he takes the interior space of a 45 footer, but stretches the boat out to 65 feet, with a 65 foot waterline, without increasing the beam. He puts on a modest, low rig, a modest, relatively shallow keel. He builds the boat light, but super strong with a full SCRIMP process infused balsa core.

And what you get is a boat which is the opposite of these sleds with chines -- a boat which is easily driven up to an 11 knot hull speed, and easily held there for days on end without stress by a short handed crew, even a couple, working with the modest rig.

So don't get me wrong -- I like both types of boats, both the sled-like boats with chines and wide sterns, and the Sundeers. But for the kind of sailing I do at this stage in my life -- long passages often short handed or even single handed, sometimes lots of people on board and always lots of spares and supplies on board, etc., or for ocean crossing -- the Sundeer model of speed, with the narrow, easily driven hull and modest rig, would be my personal preference.

[Polux]

Originally Posted by Dockhead

You can sail without reefing to F7? Over 30 knots of true wind, so 37 or 38 knots of apparent wind? Upwind? Without reefing? You have some wonder boat with a 6 meter deep tungsten keel, or else SA/D of less than 8. Or maybe both would be necessary. That doesn't exist in nature to my knowledge, but if you say so . . .

Yes, I have a powerful boat and yes I said that I can go on a F7 without a reefed jib. The rest you are assuming. I never said that I sailed with jib and main or with a full main. If I said that I can sail with a not reefed jib in a F7 it is because I have experience of doing that on my boat while you obviously not.

You talk about 37/38K apparent. It is you that are talking about that, not me and i don't understand why.

F7 is from 28K to 33K. 28k is already F7. I have sailed several times upwind on the med with a F7 and very nasty sea with 2/3m short period steep waves, normally I do on those conditions about 5.5K at an apparent wind angle of about 35º and with and apparent wind of 33k. That corresponds to about 29K true wind, F7 as I said. That's the point where I roll the jib a bit. With those conditions I sail normally only with a full jib, no main.

I can have the main on a 3rd reef, point a little better and go slightly faster but that is a very sportive way to sail the boats on those conditions, it demands a crew and not a solo sailor, or at least, not my wife aboard It is also harder to reef the boat if the wind increases (with only one sailor).

Originally Posted by Dockhead

The usual double furler is used to avoid having a normal genoa at all, at least around here. Discovery yachts come with this setup from new. On one furler you have a 90% blade, and on the other a light Code 0 or extra large light wind genoa. I think it makes a great deal of sense, and I've thought about it for my boat. But there are drawbacks -- windage, for one -- a very serious problem, since sails on furlers have far more windage than bare stays. This causes drag and extra heeling moment, hurting upwind performance. The second problem is balancing tension between the two forestays. Some superyachts designed by Bill Dixon with this setup have hydraulic tensioners under the deck with strain gauges, to solve this problem.

I don't know what rig you use on your boat but the most usual on modern boats of that size and type for offshore work with a small crew or solo is two furlers, one with a Genoa, other with a much smaller jib and a removable geenaker or code 0 on a light furler, a cutter rig. Some are using instead of a true cutter rig the two sails rigged very close on the deck and near the same point on the mast to avoid the use of additional backstays.

HR, Najad, older Oyster, RM, Allures use the normal cutter rig for offshore work:











Some like Jeanneau, CNB and the new Oysters are starting to use two furlers very near and not far away in what regards the place were they meet the mast:








I agree that for performance it is better a single furler and a change of sails when needed or having installed another sail on a removable stay is better regarding sail performance and windage but that only works well with a crew, not with a solo sailor, at least in demanding occasions that is normally when the smaller sail is needed. It is also less flexible because it is a lot more difficult to reef a frontal sail without a furler.

The geenaker on those boats is a separated sail mounted on a light removable furler, as you can see on the allures 45. The bigger sail on the furler is a 140/150% Genoa.

[neilpride]

Paulo, those 2 furlers close each other is called Solent rig, not a true cutter, a true cutter have the mast positioned aft from the center and a jib or genoa furler with a second inner forestay , hanked or with furler.. far away from the jib furler. Cutter rig.

[Polux]

Originally Posted by Dockhead

Well, there are two different things going on here.

Righting motion from form stability comes from buoyancy, not from any hydrodynamic effect (that would be a different kind of stability). We figured out in the course of this thread where that comes from -- flatter bottom. Chines allow the bottom to have a larger curve radius, giving more form stability. That form stability falls off rapidly when you reach the chine, which however, can be compensated for with ballast stability to give you a not bad overall stability curve. So as far as that's concerned, it's all about the shape of the bottom -- the chine itself doesn't do anything with regard to righting moment.

The other interesting question is whether the chine has any hydrodynamic effect. It certainly does on seaplane pontoons and power boats -- as the chine can redirect the water jet downward producing lift which helps with planing. But those are chines of a different shape, and full planing does't occur with normal keelboats.

Does an immersed chine act as a runner or a another keel, if it is immersed? That would be a different hydrodynamic effect, and I can't say whether it exists or not. I have not found anything written by a naval architect which indicates that this is a significant consideration, but my mind is open. I rather doubt it, myself, as the chines on cruising boats are too shallow to make a significant projection into the water like a keel, but I am not a naval architect (and would like to remind all of you who are not naval architects also not to pretend that you are and fantasize that you have technical knowledge which you don't) so can't say for sure.

You never heard about Matt Layden and Paradox sailboats?

https://www.youtube.com/watch?v=LkaW-fu022w

Matts boats

Those boats answer clearly your doubts about chines having an hydrodynamic effect. They don't have a keel and chines give a fundamental contribute to stability and to to go upwind and if you think it does not work is better to look at the voyages those little boats have made.


Elusion

[Polux]

Originally Posted by neilpride

Paulo, those 2 furlers close each other is called Solent rig, not a true cutter, a true cutter have the mast positioned aft from the center and a jib or genoa furler with a second inner forestay , hanked or with furler.. far away from the jib furler. Cutter rig.

Yes you are right. Did not know the name of the rig, but I never said it was a cutter rig, quite the contrary:

Originally Posted by Polux

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I don't know what rig you use on your boat but the most usual on modern boats of that size and type for offshore work with a small crew or solo is two furlers, one with a Genoa, other with a much smaller jib and a removable geenaker or code 0 on a light furler, a cutter rig. Some are using instead of a true cutter rig the two sails rigged very close on the deck and near the same point on the mast to avoid the use of additional backstays.
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