The Physics of Railmeat - Page 4 - SailNet Community
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post #31 of 51 Old 12-17-2010
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By moving them all to the windward rail, you've increased the ballast significantly over having them scattered all over the boat. The ones that were would have been on the leeward side of the boat may be contributing almost twice their mass to the effort, since they've removed that much mass from the leeward side and added it the windward side.


Also, the average weight of an American male is over 180 lbs. IIRC, so you're looking at 1800+ lbs, not 1500....


Quote:
Originally Posted by smackdaddy View Post


So...in thinking about the huge forces acting on a sailboat in higher winds, I began to wonder what the real effectiveness of railmeat is. You've got maybe 1500 pounds on the rail at a pretty weak lever point - trying to counter acts TONS of force on the sail area and keel. Are these guys really making an appreciable difference? Or is this just more tradition than necessity?

What do you think?



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post #32 of 51 Old 12-17-2010
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I remember reading about an America's cup race where one boat had all of its ballast on two feet. Later this tactic was outlawed.

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post #33 of 51 Old 12-17-2010
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Boats do differ, but another reason I have always heard for maintaining exactly the right heeling angle is that the waterline length is optimized. In the older IRC boats with big overhangs, LWL was maximized with considerable heel. I understand that is less true in the more modern boats with plumb bows, but every boat has an optimum angle of heel for maximum LWL. Experts please correct me if I am wrong.
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post #34 of 51 Old 12-17-2010 Thread Starter
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Okay, so GeorgeB's and Jeff's responses are really good explanations. Jeff, you're saying that despite the fact that you're losing righting torque force due to a decreased moment arm...something like this?



You still essentially get 75% efficiency from the keel with only 55% of the weight (I think) with the railmeat.

I know that something is better than nothing, but it seems that at some point (size of boat, sail area, etc.) you lose any advantage of the meat. I'm just curious where that is.

Or is this, in larger boats, the equivalent of swimmers wearing the shark-skin onesies to get that millisecond advantage?
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post #35 of 51 Old 12-17-2010
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Your drawing is sort of right, but because the center of buoyancy is moving to leeward with the heel angle, the righting arm may actually be the same or greater with the boat heeled vs standing up straight.

And to address part two; typically the larger the boat, the larger the crew, but at some point, the crew weight does have a reduced impact on righting relative to everthing else.

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post #36 of 51 Old 12-17-2010 Thread Starter
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Ah, I see what you mean. So where I drew the centerline of the boat, you're saying the center of buoyancy moves to leeward of that line as the boat heels, meaning that X actually increases and creates even more of righting lever....

Quote:
In the picture, the center of the crew weight is probably something like 5 feet off the center line of the boat. I'm seeing 9 guys on the rail and two on the bow. Assuming, all of the 11 guys are on the rail that is probably something approaching 2,500 lbs as they are dressed.

Again, eyeing the picture, the center of buoyancy at that heel angle has shifted approximately two feet to leeward. So that means a lever arm of roughly 7 feet, which when multiplied by the crew weight results in a righting moment that crudely would be somewhere around 17500 foot pounds (7 feet x 2500 lbs=17,500 foot-pounds).
And that's what creates the efficiency you mention?

Very cool. Thanks dude.
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post #37 of 51 Old 12-17-2010 Thread Starter
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Here's a great article someone over at Sailing World turned me onto...

| Sailing World
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post #38 of 51 Old 12-19-2010
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Of course the boat in Smack's picture would also get some advantage from not having a sail in the water.

A swing keel is essentially railmeat underwater.


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post #39 of 51 Old 12-19-2010
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Do you mean canting keel?

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post #40 of 51 Old 12-20-2010
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It comes down to all the little things. Why do people strip the covers off their halyards? Does that 3 lbs (on a big boat) make any difference? Does the 2 oz. saved by using soft shackles make a difference?

If 2 cars are racing and they're exactly the same, but one has 300 hp and the other has 300.001 hp. Which one will win? No matter how small, everything else being equal, the 300.001 hp car will win.

I have a few issues with the photo, but lets stay on the railmeat topic. The first 2 guys are hiking hard, the others are sitting straight up and looking at the foredeck crew. If your butt is on the deck, you're not hiking hard. The difference between sitting on the high side, and hiking is worth the effort by itself. The difference between being on the low side vs. the high side, is HUGE. That's all you have to worry about. And if the other crew in your photo wanted to help the foredeck guys, they should hike hard and flatten the boat. They should've also been calling puffs so the main trimmer wouldn't be caught with the traveler on center or to windward.

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