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Old 28-04-2018, 08:38   #1
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knuckle

In looking at small cat designs for a possible build, I've looked mainly at Richard Woods designs, and at Bernd Kohler's designs. I love the simplicity of Kohler's flat bottom trapezoidal hulls, but in almost every other respect, Richard Woods boats are a better fit for me, though their hull designs are considerably more complex, and time consuming to construct, and have more draft per inch of displacement / less payload.

Maximizing performance is not as important to me as maximizing payload. I have no interest in setting speed records, or racing, so I consider the differences in wetted area trivial, in fact they become a non-issue as the weight increases in my opinion. Over loading even if one is very careful, is likely on a long voyage.

We all have our priorities, and mine are no doubt different from yours.....

One glaring difference between the two hull designs is the knuckle which is a distinct feature of all of Richard Wood's designs. The knuckle is above the WL, and presumably serves two purposes. One being to deflect spray to a more horizontal trajectory, and the other is to transition the hull shape, widening it rapidly at the sole. Presumably the area below the knuckle is bilge, the area above it is cabin.

In real life, how much value does the knuckle have in terms of spray....... I'm not fond of a wet ride, but in reality, the cockpit is well aft. In the center, the bridge deck is going to block a lot of the spray, and the tramp, depending on it's construction, may break it up a lot. Spray outboard may be wind driven into the cockpit. Without sailing both boat designs in similar conditions, it's difficult to say weather this difference is significant.........

Any real world experience based wisdom on this??


H.W.
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Old 28-04-2018, 11:26   #2
smj
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Re: knuckle

The knuckle also ads buoyancy when the boat is hard pressed.
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Old 28-04-2018, 12:00   #3
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Re: knuckle

Quote:
Originally Posted by smj View Post
The knuckle also ads buoyancy when the boat is hard pressed.
Alain Colas added sponsons to all three hulls of the racing trimaran Manureva, which has long thin bows to "Cape Hornize" it, and prevent the boat from burying bows.
https://en.wikipedia.org/wiki/Manure...1978-11_2.jpeg

A knuckle rapidly widens a narrow V hull, and creates a transition point from a rounded of V hull to a wider hull better suited to accommodations. It is generally considered that narrow bows (within reason), little rocker, and broader sterns, results in less hobbyhorsing. Increasing displacement at some point forward will resist burying the bows, and the knuckle or sponson can also create lift, in addition to increasing the displacement rapidly.

I'm interested in what effect it has on spray............ A dry ride is a desirable characteristic..... but does it have a significant effect?

H.W.
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Old 28-04-2018, 12:52   #4
smj
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Re: knuckle

I would suggest contacting Richard Woods with your questions.
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Old 30-04-2018, 19:11   #5
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Re: knuckle

Owly, have you looked at Simpsonís? 8.3 and 9 both use knuckles.
Apart from adding to the build complexity knuckles are a win all around, although I have heard anecdotal stories of wave slap noise at rest when knuckle is too close to waterline.
Basically they break the stiction of water sliding up the sides of the boat.

https://boatcraft.com.au/Shop/index....ex&cPath=32_33

The 8.3 comes up on the used market quite often, the 9 not so much.
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