Say Pollux, I'm curious: do you think that the chine has any practical effect on the hull hydrodynamics? I find it hard to understand its function, other than as a styling statement. Folks talk about "getting down on the chine and becoming stiffer" and things like that, but I don't see how that works in the real world. If anything, it reduces the volume of hull submerged per degree of heel rather than increasing it compared to a smoother shape of heeled waterlines.
I note that the very wide race boats don't have such features...
Yes, that pretty much resumes the effect of a chine of that type: "getting down on the chine and becoming stiffer". When the boat heels till that chine, it will be necessary a much bigger force to sail over it, meaning to heel more than that, compared with what would happen if it was not there and the hull was rounded.
In practical terms helps to maintain the boat upwind on the most favorable heel angle (according to boat design), the one that is determined by that chine. Downwind makes the sailing much easier diminishing the roll and allowing an easy control of the boat. It makes the job of an autopilot
a lot easier.
boats all solo racers use them by the reasons I gave: When a boat is solo sailed it can be sailed faster if it is easier to handle.
Regarding max performance on crewed racing
boats most of them don't use them (I mean chines of this type). A rounded well designed hull allows bigger heeling and helps to maximize the effect of the ballast and the weight of the crew on the rail. Downwind the boat is at fast but much more dificult to sail, needing a dynamic delicate balance of sails
and crew weight. The exception are boats designed to be crewed in extreme conditions, day and night extensively where the easiness of control can have a speed advantage over a needed all time downwind control. That's the case of the VOR:
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!
I don't see them as non intuitive. I look at them and understand how they work in an intuitive way.
If you look to motorboats you will see that they use chines for the same reason, to increase stability, except that while on a sailingboat the chine is designed to work at the best optimal heel angle for a given design, on a motorboat is designed to prevent any heeling:
As I said on a sailing boat they are there mainly to make sailing easier and that's why they are used on all solo racers and that's why they made sense on cruising boats. An easier boat to sail with a short or solo crew is a faster boat.
Regarding This: "There are claims of improved hydrodynamics, primarily in increased stiffness."
it is not a claim, it is a fact: they increase stiffness when the chine hits the water
and if we try to pass over it the resistance increases as well as drag. That's why on boats were absolute performance is searched (top racing with top professionals) chines are not used or it is used a very high chine that allows the boat to heel a lot before it enters in function.
Regarding being useful or not in what regards cruising boats, it depends on the design, if it is a good one certainly they are in what regards to make the boat easier to control. If the chine is to high and only enters in function at high angles of heel, unless it is a cruiser racer
, it will not make sense because a cruising boat is not normally sailed to those angles of heel.
On the Oceanis
38 case it is a low one that will enter in function at a relative low angle, the best angle to go upwind, that is a relatively small angle on that boat. It helps to maintain the boat "on a grove" upwind, it increases stability on a beam reach and will help controlling the boat downwind limiting roll.
if you ask me if it will make a big difference if instead the chine the transom had the same shape but rounded without a chine, I would say no, not a big difference but if it works better with a chine, a chine should be used. A better performance on a sailboat is attained by many little things, none of them having much influence per si but that all put together represent a lot.