aft hull chine for sailboat afecting performance

[Ferman]

Hi,

I have seen lately some inovations in sailing desingns that make me wonder if they really work in a beter performance of sailboats like the aft hull chine or the doble ruder or doble dagger board with swinging kell, i realize that this work in performance but specially the aft chine does it really make the diference.

[messabout]

It can make a difference on some, but not all boats. We usually see that feature on boats that are capable of sailing above standard hull speed. The hard chines aft help keep the boat from squatting so badly at or near transition speeds. Some of these boats can achieve a mushy planing speed.

Twin rudders and twin daggers are canted outward to make the foils more nearly vertical when the boat is heeled. All these nifty design features need to be able to work in concert with one another. None of those features should be added to an existing boat except on the advice of a knowledgeable design person.

[Eric Sponberg]

Originally Posted by Ferman

I have seen lately some inovations in sailing desingns that make me wonder if they really work in a beter performance of sailboats like the aft hull chine or the doble ruder or doble dagger board with swinging kell, i realize that this work in performance but specially the aft chine does it really make the diference.

These features aren't new--they've been around for decades. Yes, they do work. Chines help keep a boat on plane a little longer and maintain speed better than if it did not have chines. The boat must be quite light in order to achieve planing speeds for these to work. If the boat can't plane to begin with, the chines might not help that much. Hulls with chines have more wetted surface than boats without chines, so if the boat is always sailing in displacement mode, it might be slower than its non-chine counterpart, particularly in light air.

Double-rudders are a no-brainer--the leeward rudder is left down while the windward rudder is withdrawn. Such boats have built-in redundancy--break one rudder and you have another right handy. The downside is extra cost to have two rudders instead of one.

Swinging keels with double-daggerboards--they generally go together because a boat with a swinging keel has poor windward ability. It loses lateral plane when the keel is canted. The daggerboards make up for that lost lateral plane. Such boats are harder to control, they are more expensive to build, and the keels and daggerboards take up interior space, all of which is why you see them on racing boats but not on cruising boats.

Eric

[alberto88]

aft chine is work when planing, but when not plane then chine is slower sometimes, especially in the light.

Fashion more than function; the quickest sportboats around many still not have chine.

[Steam Flyer]

Originally Posted by Eric Sponberg

These features aren't new--they've been around for decades.

Heck yeah.

Anybody remember the Force 5, a competitor to the Laser (and in the opinion of many, a better design)?

Originally Posted by Eric Sponberg

Hulls with chines have more wetted surface than boats without chines

True, but it's a complex trade-off between wetted surface area and increased form stability at low heeling angles.

More righting moment = more horsepower = more speed. If the designer is clever enough to place the chine such that the boat isn't dragging a corner thru the water at normal sailing angles, yet gains a significantly higher metacenter, the boat can definitely be faster once out of "light air" mode. And a partial chine aft (such as the Force 5 had, and many skiffs have, and some sportboats are starting to wear) doesn't generate the awful helm forces that a full-length chine does.

Aft chines.... a fad, but with some reasoning behind it

FB- Doug