[AdamLein]

Originally Posted by smackdaddy

(with a bit of embellishment by me)

Can always count on you for that

what do you think about the issue of potential rudder damage using the JSD...that is the boat being essentially held in place stern-on by the drogue as the energy of the water moves past the rudder? From a physics perspective is rudder damage more likely with this orientation than bow-on?

Far be it from me to actually apply my amateurish knowledge of theory to a real-life situation and draw a practical conclusion, but since you asked...

I first wrote a really long response and then realized that you asked a slightly wrong question. It should be, "Stern-on and bow-on boats are both exposed to rudder damage if the conditions are just right -- breaking wave and shock-loading, respectively. Given the necessary events have occurred, which boat's rudder is more likely to survive?"

In other words, suppose a stern-on boat is pooped by a huge breaking wave, and a few miles away a boat hove-to a sea anchor with a slack rode is suddenly dropped back on her rudder. Which is more likely to lose her rudder?

Beyond knowing that lots of water crashing down on my rudder is probably bad for the rudder, I couldn't begin to estimate how bad it is.

I would point out that if you're hove-to, your tiller is probably lashed alee and that should help protect the rudder, whereas running requires active steering and I doubt the helmsman could hold onto the tiller if the rudder is hit just right. Probably a good way to break an arm.

1. In actual surfing, in other words where you're on your board riding all the way into the beach - I assume you're NOT riding the SAME group of particles, but actually the "slope" of the wave made up by progressive "groups" as the sine wave moves. In other words - it becomes gravity, not "forward motion" or continuous "velocity" of the wave...is that right?

Precisely. The water on the surface is blown downwind, and drifts along with the prevailing current, for sure, but for the most part seawater stays in the same place over short periods of time.

If you laid out your garden hose and lifted one end and flung it down really hard, you'd get a wave moving along the hose. The actual rubber material of the hose doesn't go anywhere, of course. But if an ant on a skateboard happened to be on that hose, he could ride the "hill" all the way to the other end, if he timed it right. That's surfing.

2. I think I understand the potential energy of the breaking water - that is the group velocity multiplied by the gravity and lack of resistance you mention.

No, it's the weight of the water times its height above you. The group velocity of the water doesn't contribute to the energy of the wave.

So I assume that the breaking water is both falling and essentially "surfing" as well - just at a much higher velocity than the boat. Is this right?

Kind of. I can't say I've ever seen breaking waves at sea and I'm mostly imagining ocean beaches here. Remember that the plunging breaker doesn't float on top of the smooth water like your boat does, so I don't think it could really surf. Instead it's got some kinetic energy from its circular motion so it's really just being flung forward, with nothing to catch it except fiberglass.

If so - why is does it have so much more velocity and power?

Why it has more velocity - not sure. Maybe because you're using a drogue to slow your boat down? Also because with nothing to catch it, potential energy is rapidly and efficiently converted into kinetic energy through a process called "falling"

Why does it have more energy - mass and height. Water weighs more than your boat (by the definition of "boat") and in situations we're concerned about, water is much higher. Also there's a lot of it.