Chine at bow

[frank smith]

I notice that there has been a lowering of the chine at the bow on sailboats over the years. In the past there was much effort into fairing the chine into the bow a smoothly as possible . but chine designs that I see today seem to have a rather straight level chine from midships forward .
How is this an improvement ?

Frank

[gonzo]

There aren't really many new modern designs with hard chines. Some designers that cater to DIY still work on them, but they are rare.

[Paul B]

There aren't really many new modern designs with hard chines. Some designers that cater to DIY still work on them, but they are rare.

You need to get out more.

Many modern designs, especially ones aimed at fast reaching and running, have chines.

Everything from I14 dinghys, to Sportboats from 5.5 meters to 9 meters and more, to fast IRC boats in the 40 to 45 foot range, the TP52 fleet, the Volvo 70 fleet, the Mini Maxi fleet, and even the latest 100 foot canting keel weapon (pic attached).

Your location says you are in London. Pick up a copy of Seahorse magazine from a local magazine stand and flip through it.

[frank smith]

because of the inherent qualities of damping and construction I am thinking of chine hulls made from sheet material . Thus the question of chine action at the bow.
Frank

[gonzo]

I understood it is a question of hard chine hulls with rather flat panels.

[apex1]

You need to get out more.
Many modern designs, especially ones aimed at fast reaching and running, have chines.
and even the latest 100 foot canting keel weapon (pic attached).

Hmm, and when you would tell me where you see any chine at the bow of the boat shown? (above waterline of course)

Can we see that when going out more?:D

[Paul B]

Hmm, and when you would tell me where you see any chine at the bow of the boat shown? (above waterline of course)

Can we see that when going out more?:D

I'm not the one who made the claim that chines seem to be running all the way to the bow more often in modern designs, am I?

Some do, like the Humphries Volvo 70 design, others do not. The photo of Speedboat was handy to illustrate the use of a chine on a modern design.

[apex1]

Nono, you did´nt, but that was the issue, was´nt it?

[Paul B]

Nono, you did´nt, but that was the issue, was´nt it?

No, that wasn't the point I was taking issue with. There was a claim that "There aren't really many new modern designs with hard chines."

The fact is, there are.

For example, this sportboat design by Paul Bieker is currently in build in Houston, Tx.

[frank smith]

Hmm, and when you would tell me where you see any chine at the bow of the boat shown? (above waterline of course)

Can we see that when going out more?:D
That is a nice boat with a nice chine . Dose that help with separation?
But that is still not what I am getting at

Yes, flat panels . It could be multi chine or single chine . What would be the best way to shape it so as to have the best effect on water flow.

In days of old the ides was to have the chine disappear after it left the water.
think in terms of an origami design . Now it is the current fashion to leave the chine in the water , more or less parallel to the water line .

[Rick Willoughby]

That is a nice boat with a nice chine . Dose that help with separation?
But that is still not what I am getting at

Yes, flat panels . It could be multi chine or single chine . What would be the best way to shape it so as to have the best effect on water flow.

In days of old the ides was to have the chine disappear after it left the water.
think in terms of an origami design . Now it is the current fashion to leave the chine in the water , more or less parallel to the water line .

Frank
If you look at the waterlines on a hull with an immersed chine the angle of flow around the chine is not very severe. Once you bring in the boundary layer it is softened further. The water does not mind if it is making a slight turn or following a very gentle curve.

An immersed hard chine can improve the block coefficient so you get more displacement for the beam and this will reduce wave drag for any given displacement.

Then there is the benefit you get from the better planing ability of a flatter surface. Works better reaching and going downwind than a rounded section.

The more severe immersed hard chine also provides a cushioning deep "V" when heeled going to windward.

Post #71 on this thread is a good example:
http://www.boatdesign.net/forums/sailboats/flat-bottom-vertical-sides-flat-deck-flat-everything-26770-5.html
A boat like this is simple to build and will perform very well. You see the trend to length and slenderness as this equates to easily driven. Curves are harder to make and add no performance advantage.

At displacement speed there is very little advantage to a round section hull over a rectangular section hull - of the order of 1 to 2%. At speed the flat sections will provide lift much earlier so the boat will get up and go faster.

Rick W

[Ad Hoc]

"..An immersed hard chine can improve the block coefficient so you get more displacement for the beam and this will reduce wave drag..."

er.....so let me get this right. More displacement for the same length, ie decreasing L/D ratio improves the residuary!!!

Wrong.
Increasing the L/D ratio decreases the residuary.

"..At displacement speed there is very little advantage to a round section hull over a rectangular section hull - of the order of 1 to 2%..."

At low Fn's a bilge with a hard chine can add as much as 10% to the total resistance compared to a soft round bilge. But of course does depends on the size of the radius and the Fn.

A hard chine is ostensibly only for 1) higher Fn's or 2) ease of construction hulls. There are other minor benefits, as noted for yachts - if at 'ideal conditions' when reaching (since the chine is still underwater and creating drag, but now offset by some minor lift), but these are not the principal reason for going hard chine or not.

[gonzo]

Some old chine designs, like the Sea Bird, would plane at over 12 kts. The chine is hard almost to the bowstem .

[frank smith]

Some old chine designs, like the Sea Bird, would plane at over 12 kts. The chine is hard almost to the bowstem .

Heeled over the flat bow panel would provide a lot of lift . It is also a LDB ,
so the chine may help to control water .

Ben Seaborn , the designer of the Thunderbird 26 said that he used paper to rap around an existing hull model to see how it might work . Ther have been versions scaled up to 32' that worked well .

But the question remains . How would it be done today ? would you pull the water line out and lower the chine.

[gonzo]

I think that all the successful hulls have the chine above the waterline. Some, like Frer's Supercadete, had a chine in the center which faded fore and aft.

[Brent Swain]

because of the inherent qualities of damping and construction I am thinking of chine hulls made from sheet material . Thus the question of chine action at the bow.
Frank

With polyconic bows, such as we use on origami boats, there is no advantage in having a chine at the bow or stern. Best just eliminate it and drastically cut the amount of extra work involved in building a chine, as well as eliminate the possibility of a chine inducing turbulence and drag when beating into a head sea.

[ancient kayaker]

In my admittedly limited experience keeping the chine low at the stem(s) makes for an easier build when using sheet material. It also seems to reduce drag, at least it maximizes the LWL. So maybe it's just a reflection of the trend for home construction and faster boats combined with modern materials.

[BobBill]

Curious exchange got my curiosity going.

I am primarily a small boat sailor. I had a 110, then an Ensign. I guess you could say one was a (soft) chined hull, the other not at all.

I thought the difference between chines and no chines was, aside from building issues, lift versus displacement on beats, assuming planing on other points, with chined hulls.

The trend toward wide and chines is very interesting and, to me, a bit scary for ocean sailing. I think the jury is still out on durability when the hulls are so wide that the chine function changes in those big rigs. It almost seems it loses its original function.

I am simply in need of some education here.

[BobBill]

I will have to amend the above.

The boat I saw on SA (A 950 something) is super wide, flat and chined to the max. Likely the only way it could work. so, the chine does come back to be what it is designed to be under way.

Am learning.

[MikeJohns]

I notice that there has been a lowering of the chine at the bow on sailboats over the years. In the past there was much effort into fairing the chine into the bow a smoothly as possible . but chine designs that I see today seem to have a rather straight level chine from midships forward .
How is this an improvement ?

Frank


There has been a lot of testing of chined sailboat hulls over the last 10 years, It appears that if the chine is aligned with the flow then there can be a reduction in drag probably due to the chine entraining and flow modifying effects. If the flow is across the chine then vorticity occurs and the drag goes up. For this reason forward chines appear to be much better if close to parallel to the static waterline rather than being swept up as in many designs in the past.

An interesting problem with multi-chine is that as the overall shape approaches that of a round bilge you tend to get more cross chine flow. Odd as if may appear in smooth water tests a single chine hull of equivalent vital statistics seems to produce a lower drag if properly designed than a round bilge. I know designers in the racing fraternity who are currently quite interested in this. Whether there would be a net advantage or disadvantage in smaller displacement vessel in a seaway may be a mute point but overall a single chine vessel can be very successful. They have been given a bad name because the hulls need designing with some care and knowledge.

In cargo ships there is currently research indicating a definite reduction in drag from adopting a harder chine. It’s very interesting.

[BobBill]

Here is pic of the French 950 I saw on SA, with its double chines...awesome it is.

I wonder how it goes heeled in 12+ pressure?

Is it good thinking to view chines as a way to provide driving surface with all that weight in the air when heeled, maybe even providing a bit of lift?

As I understood chines years ago, they offered simple building (wood) and strength, and also efficient hull shapes---Star, I-110 (soft chine), Enterprise, Wayfarer (I think, and double hard chines?), I-14s (single, double and none), Lightning, Penguin, Fireball, and others. Some were screaming planers.

I do not recall many boats larger than the Star or I-110 having hard chines. Might have been a cruiser or two. Certainly no America's Cup boats, which seemed to thrive on lift.

Lots of these mega-wide boats showing up recently, and most have chines.

Now I am wondering what an old America's Cup formula would produce in chines, and if that would have changed anything??

[HJS]

I have used a chine on nearly all my designs since the late sixties, from the smallest Marblehead racer to the multihull cruisers. If possibly, I would never do something else any more. You will get a dry boat with high stability and ability to go fast.
The chine should go horizontal as long as possible out in front and be smoothed out at the stem where it meets the bottom in a natural way. But try not to have a hard chine at the bow, because in a steep wave the water can come from above and suck the front part down. That’s also why the rounded bottom in front has to be designed very carefully.

Yacht design is still an art!

JS

[frank smith]

Thanks JS ,

the file you sent did not open for me in Freeships

[HJS]

Thanks JS ,

the file you sent did not open for me in Freeships

the file is in Delftship format
download Delftship Free

js




www.sassdesign.net

[Rick Willoughby]

[

In cargo ships there is currently research indicating a definite reduction in drag from adopting a harder chine. It’s very interesting.

This agrees with my recent experience. I am finding that the slight lift I get from a hard chine hull, even at moderate displacement speed (froude 0.4), actually provides an advantage over a rounded hull.

As noted earlier in post #11, you can achieve a narrower hull for a given displacement and length with a hard chine because the block coefficient is higher with a near rectangular section than a rounded section. This reduces wave drag that almost offsets the slight increase in wetted surface but once the speed gets into a range where lift or sinkage is a factor the hard chine has an advantage.

Rick W

[frank smith]

Thanks for your replies.
Very interesting stuff , it will take time to digest it .
I am working on something that is just in thought faze right now.
Light disp. and narrow not unlike a Thunderbird but bigger.
the trick being to maintain minimal draft , and have power to carry sail .
Not at all sure what that is right now . I should say that this is a hobby
for me , and the boat is a learning tool , as I dont absorb abstract info well .

[Perm Stress]

If chine forward is reasonably high above the water, it helps making the decks dryer, as the sheet of water, traveling up the topside, brake up in droplets and lose speed, when passing a chine. Smaller droplets, again, experience more intense air resistance in their travel, and reverse their motion downwards earlier, also helping dryness of decks.

[ancient kayaker]

Stress: I have a small plastic kayak that takes high chine forward to extremes as it reaches the deck at the stem stem. This does not make for speed. Since it has extraordinary stability compared with my faster boats I put a sail on it a few years ago. It was a dry ride even in a stiff breeze; it refused to plane, prefering to absorb the energy by throwing a monstrous bow wave far above the gunnels (I have to keep my elbows in to avoid getting soaked) but not a drop came on board. It was mostly white water. Thanks for the explanation.

[Brent Swain]

In my admittedly limited experience keeping the chine low at the stem(s) makes for an easier build when using sheet material. It also seems to reduce drag, at least it maximizes the LWL. So maybe it's just a reflection of the trend for home construction and faster boats combined with modern materials.

With sheet metal, eliminating the chine at the bow eliminates a lot of work, and is much easier to build than having a chine at the bow. I eliminated 64 feet of cutting , grinding and welding when I eliminated the chines at bow and stern on my 36 footers.
When beating into a rough head sea, the flow of water at the bow is contantly changing diretion, depending which part of the wave is hitting the bow at the moment. So how is it possible to put the chine in the same direction as the constantly changing water flow direction? To believe that possible is extremely wishful thinking. Regardless of which direction the chine is , the choppy water will always be constantly crossing it, inducing turbulence, and drag.

[gonzo]

Hard chines, on V bottoms often produce wet boats. The water splashes out and over.

[ancient kayaker]

I don't get to use my boats in rough conditions so this is only my opinion. It seems that at whatever angle the waves hits the stem it would be deflected down to a degree determined by the amount of flare where it hits. The surfaces below the chine have more flare (read deadrise if it's the bottom) than the sheer. However, that's all relative.