Chine at bow

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.

 

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.

 

Chines

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.

 

Learning

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.

 

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.

 

Chines

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??

 

Yacht design is still an art

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

 

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

 

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.

 

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 .

 

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.

 

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.

 

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.

 

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