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post #11 of 19 Old 03-04-2016
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Re: Ease worries on night watch

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Originally Posted by hellosailor View Post
Very nice. Now, how about taking it rock hopping at six knots with some good New England granite to run into, instead of flimsy hollow stuff?
What are you talking about? They ran it right up onto the rocks at 4:20-4:30!

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post #12 of 19 Old 03-04-2016 Thread Starter
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Re: Ease worries on night watch

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That was pretty cool. Can we try this at home?
Lets take the C&C and have some fun. In reality I think I would be sick doing that to a perfectly good boat.
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post #13 of 19 Old 03-04-2016
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Re: Ease worries on night watch

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Originally Posted by virtualground View Post
[Ignore what I'm about to write if you're allergic to pedantic posts.]

Momentum is the product of mass and velocity. Nothing exponential comes into it. However, taking the boat size from a linear dimension of 31' to 38', making the simplifying assumption that the mass of a vessel is proportional to the cube of its length, would in fact multiply the momentum by about 1.84. So yes, the momentum roughly doubles for that change in length.

Momentum shouldn't be confused with kinetic energy, which is the product of mass and the square of velocity. Once again, though, an increase in mass (keeping the velocity the same) will result in only a proportional increase in kinetic energy.

It's the kinetic energy that does the damage - it takes energy to crush a hull. And in the example above, for the same change of 31' to 38', the kinetic energy would also almost double.

The difference between momentum and kinetic energy:

- Momentum is the tendency of a mass to continue moving forward at a constant velocity unless acted on by a force (as in Newton's second law of motion).

- Kinetic energy is the energy that it has as a result of its motion.
Come on! VirtualGround! Everybody already knows that!!! Kevin
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post #14 of 19 Old 03-04-2016
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Re: Ease worries on night watch

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Originally Posted by Minnewaska View Post
Cool vid. But momentum grows exponentially with weight and speed. Take the boat size from 31 to say about 38 and momentum will double, even at the same speed.

Still, FRG is tougher than some think.
lend me your boat and let's find out

BTW - either those guys sail around in my home harbor or someone has seen the video and figures they can sail the same way

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post #15 of 19 Old 03-04-2016
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Re: Ease worries on night watch

What, no one plays baseball?

They all switched from hardwood bats to aluminum, because a lesser mass (the aluminum bat) moving at a higher speed, imparts more kinetic energy when it hits. Force equals mass times velocity squared. So if you keep the mass the same, i.e. a smaller boat, but increase the boat speed, you impart a great deal more force in the collision than you would have by simply using a larger boat at the same (original) speed.
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post #16 of 19 Old 03-04-2016
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Re: Ease worries on night watch

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Originally Posted by hellosailor View Post
What, no one plays baseball?

They all switched from hardwood bats to aluminum, because a lesser mass (the aluminum bat) moving at a higher speed, imparts more kinetic energy when it hits. Force equals mass times velocity squared. So if you keep the mass the same, i.e. a smaller boat, but increase the boat speed, you impart a great deal more force in the collision than you would have by simply using a larger boat at the same (original) speed.
Right, that's why I kept velocity a constant in the point I made, as a 31 ft boat is rarely going above the reported 6.5 kts in that vid (would hull speed be about 7ish). However, the larger boat will have both more mass and more likely to have more velocity.

My gut tells me the FRG is not as exponentially stronger.


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post #17 of 19 Old 03-04-2016
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Re: Ease worries on night watch

"My gut tells me the FRG is not as exponentially stronger. "
All depends on the boat.
If you took a vacuum-bagged modern FRP hull, it could be lighter than an older non-bagged one, and still stronger. Or the glass layup could be stronger. Or, a "we don't know how strong this is and frp is cheap" 1960's hull and compared it to a newer one, it just might be stronger.
Of course if you T-bone a J/24 you're going to find out just how lightly a racing boat can be built.(G)
So maybe we need to take Louis and Vinnie to a boat show, with a couple lead pipes, and ask them to test the impact resistance of various bows?(G)
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post #18 of 19 Old 03-04-2016
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Re: Ease worries on night watch

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Originally Posted by Barquito View Post
That was cool. Maybe the only more demanding test would be to hit something that was a little more pointy. I'm sure a lot of blue water sailors would be interested to see them hit a shipping container at hull speed.
So is that a real problem, like in the film "All is lost", for blue water sailors or is just a matter of really bad luck to find one of those containers?
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post #19 of 19 Old 03-04-2016
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Re: Ease worries on night watch

Containers are pretty rare, but I've hit a temporary buoy placed out by the military. No damage, but scared the crap out of me.
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