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Old 27-03-2017, 22:04   #1
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Interesting keel shape

There is a picture of Hugo Boss keel on facebook. I'll try and post it here.

https://www.facebook.com/AlexThomson...type=3&theater
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Old 27-03-2017, 22:09   #2
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Re: Interesting keel shape

Looks like a canting keel....

https://www.google.com.au/search?q=c...&bih=643#spf=1
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Old 28-03-2017, 10:36   #3
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Re: Interesting keel shape

I think he is referring to the swallow tail shape of it. The bulb is not just a rotated NACA section or torpedo shape. As I understand it this shape is used to act as a better end plate, increasing the keels lift. What I don't understand is why you would use it on a canting keel since they are normally set to generate very little if any lift.
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Old 28-03-2017, 14:45   #4
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Re: Interesting keel shape

I would think that with the very narrow(?), is that the right word, keel stem that the bulb will provide much of the lift when the keel is canted. That and I guess, if I understand it correctly, the foils. Imagine the force on the keel box when that thing is fully canted and the boat is bashing along at 30+ knots.
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Old 28-03-2017, 15:02   #5
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Re: Interesting keel shape

Ahh, got it now, I didn't notice this view of it on FB. Am guessing in profile it would look very similar to a "wing" hence would generate lift as Stumble states, must be more to it, it would be interesting to learn the reasoning behind the design....
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Old 28-03-2017, 15:09   #6
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Re: Interesting keel shape

Do you think any engineers were involved in the design of that sucker?
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Old 28-03-2017, 15:25   #7
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Re: Interesting keel shape

http://www.sname.org/HigherLogic/Sys...0-a89c32f8c122

I am going to have a nice couple of hours trying to digest this, but it covers the question asked.
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Old 28-03-2017, 23:38   #8
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Re: Interesting keel shape

Quote:
Originally Posted by Stumble View Post
What I don't understand is why you would use it on a canting keel since they are normally set to generate very little if any lift.

the canting keel shaft is fore and aft angled so that when the keel is fully canted it creates a positive angle of attack to the sea surface
therefore the keel does not provide any side force but does act as a foil creating vertical lift, therefore the bulb with a flat tail might well serve as a winglet in a foil
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Old 29-03-2017, 00:02   #9
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Re: Interesting keel shape

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Originally Posted by marcofailla View Post
the canting keel shaft is fore and aft angled so that when the keel is fully canted it creates a positive angle of attack to the sea surface
therefore the keel does not provide any side force but does act as a foil creating vertical lift, therefore the bulb with a flat tail might well serve as a winglet in a foil
I was going to say I think you got the lift in the wrong direction. Turns out it depends. Some older designs like Red Herring apparently had negative lift to help the righting moment, newer designs have positive lift to reduce displacement or work towards foiling.

Canting Keel as a Lifting Foil - Boat Design Forums
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Old 29-03-2017, 07:31   #10
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Re: Interesting keel shape

Good point, my impression however is that these foiling monos behave more like a "dynamic trimaran" than a keelboat
A so large footprint in the water makes lead bulbs useful to start going, after that the "off center of gravity" lift helps a lot the righting moment
My two very humble cents
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Old 29-03-2017, 09:41   #11
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Re: Interesting keel shape

Quote:
Originally Posted by marcofailla View Post
Good point, my impression however is that these foiling monos behave more like a "dynamic trimaran" than a keelboat
A so large footprint in the water makes lead bulbs useful to start going, after that the "off center of gravity" lift helps a lot the righting moment
My two very humble cents
This is just a wag. my guess I should that the negative lift of the foil is to counteract the boats trim angle. Basically so the keel generates zero lift in the as sailed position when running.

This gets really tricky because as we have seen on A-Cats even a very slight mistake in trim angle for horizontle foils can make a huge difference on the water. A 1.5% Dow angle on rudder winglets for instance cost me 3kn in boat speed. I just couldn't get the stern out of the water. Litterly five minutes with a file and an inclinometer fixed a 3kn problem.

This is even worse on a foil forward of the max rocker...

Frankly these boats are so overengineered it's hard to take one thing in isolation, and you know they have all been tested within an inch of their lives so someone has spent massive amounts of money getting to this shape. I would love to have someone I need the know explain it though.
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Old 29-03-2017, 19:32   #12
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Re: Interesting keel shape

What exactly broke on the recent Vendée Globe race? Was it one of the foils, and this was what made it possible for him to continue sailing? Looks fairly hefty.
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Old 29-03-2017, 21:15   #13
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Re: Interesting keel shape

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Originally Posted by psk125 View Post
What exactly broke on the recent Vendée Globe race? Was it one of the foils, and this was what made it possible for him to continue sailing? Looks fairly hefty.
The starboard lifting foil on Hugo Boss broke off after a colission. The Vendee boats are not really designed to generate much lift from the keel, instead the lift to windward primarily comes from daggerboards. In the latest version the foiling boats not only generate lift to windward with the daggerboards they also lift the hull, or at least part of the hull weight.
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