Heavy Weather Sailing

[GreatWhite]

Excellent blog there SD...thank you for the information!

[AdamLein]

Originally Posted by smackdaddy

However, my smarty-pants-physicist-nephew corrected my thinking that waves in water are actually "moving forward" as they appear to be... he explained that the standard non-breaking wave is simply an up/down movement of the water - not the forward motion that it appears to be.

Individual water molecules move in a circle: in the direction of wave motion at the crest, then downward as your nephew points out, then in the direction opposite wave motion in the trough, then back up to the crest.

If a breaking wave poops you, the water is not only moving forward, it's moving forward faster than your rudder is.

And that forward "surfing" motion of the boat is due to its sliding down the face of the wave - it's not really being "pushed" because this type of wave has no velocity, just amplitude. (I think that's all right).

The wave has two velocities: the velocity at which the geometric shape that you perceive propagates along the sea's surface (called the group velocity) and the velocity of individual particles. It's the group velocity that determines whether or not you're surfing... surfing is sailing on the leading edge of a wave at approximately the wave's group velocity.

He went on to say that breaking waves were a completely different set of equations that got very complicated very quick. That water IS moving and has a lot of "forward force".

He's right that the math is a lot more complicated for breaking waves, but there's still a straightforward lay description. The main difference is that normally when a water molecule arrives at the crest of the wave (moving forward), there's some water in front of it and below it to support its weight and to resist its further forward motion. In a breaking wave there's just air there. So the water has some kinetic energy from its forward motion like it always does, but it also has its potential energy from towering high above your boat. When a swell passes under you you don't experience that energy. When the waves breaks on your transom, all of that energy is converted into heat, sound, and deformation. It's the deformation you're concerned about.

But, as someone said earlier in this debate, as long as the rudder stays in that lower "strata" of water, it's fine.

The water continues to be affected by surface waves quite deep -- to a depth equal to twice the wavelength... or maybe it was half the wavelength, I don't remember. Either way the water just below the surface (where your rudder is) is still moving about quite a bit, and in a 15' breaking wave you can expect that that water will be tossed about quite violently when the wave crest breaks on top of it.

Imagine pouring some red water from one container into another which already contains clear water. The red water won't just stay at the surface, it'll plunge down below the surface of the clear water and mix things up and create lots of turbulence... and you're pouring a small amount of water from a few inches away. Now imagine pouring tons of water from ten or twenty feet above you... you will not find shelter just below the surface.

[smackdaddy]

Now THAT'S a great explanation, AL. Thanks.

I now remember him mentioning the circular motion - and that makes perfect sense the way you explain it.

This was my favorite line of yours (with a bit of embellishment by me):

Originally Posted by AdamLein

When the waves breaks on your transom, all of that energy is converted into heat, sound, deformation....and soiled foulies.

So now that you've explained the sub-surface velocity in a breaking wave - 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?

A couple of other questions:

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

Thanks for taking the time.

[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.

[smackdaddy]

I just noticed you sail a C27 too AL. Man, you're smart.

Heh-heh. Thanks for the great explanations.

One question I still have for Dog is...when you say that the JSD negates the need for active steering of the boat...what's happening at the helm to protect the rudder? Assuming you don't have AH - do you lash the wheel/tiller to protect it from the scenario AL lays out above?

[St Anna]

Originally Posted by smackdaddy

I just noticed you sail a C27 too AL. Man, you're smart.

Heh-heh. Thanks for the great explanations.

One question I still have for Dog is...when you say that the JSD negates the need for active steering of the boat...what's happening at the helm to protect the rudder? Assuming you don't have AH - do you lash the wheel/tiller to protect it from the scenario AL lays out above?

Dont have experience with the jsd - but always lash tiller/ lock wheel [with some give]

Keep a safe boat, do all the right stuff and when you gotta do the praying/kissing thing, go below and wait it out - no lee shores...
Thats the risk you accept when you head off!!

[AdamLein]

Originally Posted by St Anna

Dont have experience with the jsd - but always lash tiller/ lock wheel [with some give]

Keep a safe boat, do all the right stuff and when you gotta do the praying/kissing thing, go below and wait it out - no lee shores...
Thats the risk you accept when you head off!!

Do you lock the helm to leeward or amidships? Do mean that you heave-to? Care to describe your experience a bit more?

[St Anna]

Originally Posted by AdamLein

Do you lock the helm to leeward or amidships? Do mean that you heave-to? Care to describe your experience a bit more?

Other peoples experiences wont help on the day - different weather/boat proximity to ships/lee shores.

If the time comes and it is not a given that you will get stuck in a nasty piece of water and wind, but if so you will feel very much alone and have to remain as cool as a cucumber especially if there are others on the boat - they will look at you as the skipper - you cant lose it.

I was on and only have as seaworthy a yacht as can be. Then a Van de Stadt, now a Peterson. Again, my experiences are very minimal in comparison to many on SN.

On one occasion, I locked the wheel slightly leeward to amidships. I left a small storm jib just in front of the mast (about a 4' foot). On this boat this was 'heaving to' We went below, keeping a watch every 15 minutes and then lying back on the cockpit floor. This lasted 2 days.

Another time I locked the wheel amidships and we ran with the breeze (a 65kn breeze). We adjusted the storm jib (this time forward for CE reasons) until she sailed herself. This storm lasted for about 18hrs before it abated to a what appeared to be a mild 40kn.

Both these times I let the boat run on a coarse for searoom - away from reefs and in the general direction I wanted to go.

Now, we are confident in the boat and ourselves - and ensure our safety - after all we are all doing this because we LIKE cruising! I better blog a lot as in a short time, we are off again. I expect I have learnt from my experiences and probably will make different stupid mistakes (but have a great time in between) We do plan a lot and always have plan B if weather etc no good. At the moment I am a marina bound liveaboard - tied to a dock and a job.

[PCP]

Great thread. There are on these forums a lot of very experienced sailors that seem to enjoy sharing information. Thanks to them.
I have never been in such a bad weather that needed survival tactics. Just a couple of times with force 10.

Originally Posted by johnshasteen

... Rule of thumb is above 40 knots of wind you shift from sailing to surviving and every boat is different and requires different defensive tactics. ...

But I know that 40kn of wind is not always too much to sail safely. It depends on the boat. Sure, with a 20ft boat, but not with all sailing boats.

I have learned a lot with my friend Armand. Armand was a Flemish sailor that lived aboard with his family on a 15 m steel ketch : Horoscoop. 30 years ago his boat was at my home port and he enjoyed it so much that he stayed for some years.

I had at the time an 80-year-old 22ft traditional sailing boat and one day, when I was going out, he asked me if he could come with me. Later on the day he said that he loved my boat. It turns out that it was very similar to a boat that he had sailed in his youth (he was 60 years old) from Antwerp, around British Islands to Finland where he was shipwrecked by a big storm.
We became good friends and almost every time I sailed out, Armand joined me.

One stormy day, I was looking at my boat, seeing if everything was alright when I was surprised by Armand. He came and said to me : let’s go sailing. I looked him and said: Are you crazy?
He said: No, not on yours, today let’s sail mine.

It was at least a force 9, perhaps more, and it was a wonderful sailing. Armand was a great sailor, I was just doing what he told me to do, but between the two of us we had no difficulty in sailing his boat, and what a sail.

It became a habit, when the stormy winds were blowing, we sailed his boat, not mine. I have very good memories from that time. Armand built some reputation among the fishermen. When they were returning for shelter on their 70ft boats, we were going out for having some fun. I learned in those days that a sailboat well managed is much safer than a motorboat. I remember to pass those fishing boats doing over 10k and feeling comfortable, while they bounced on big waves, doing very little speed, sometimes with their propellers out of water.

Of course his boat was so heavy that on normal days the best he could do was motorsailing.

Bottom point, 40ft winds for survival tactics, for an oceangoing boat, it seemed to me a bit excessive. After all on the last Mini Transat the Minis (6,5m) get over 40k winds and all of them (70) went on racing…and with just a solo sailor. No casualties.

Regards

Paulo

[johnshasteen]

Originally Posted by PCP

Great thread. There are on these forums a lot of very experienced sailors that seem to enjoy sharing information. Thanks to them.
I have never been in such a bad weather that needed survival tactics. Just a couple of times with force 10

But I know that 40kn of wind is not always too much to sail safely. It depends on the boat. Sure, with a 20ft boat, but not with all sailing boats.
'
Bottom point, 40ft winds for survival tactics, for an oceangoing boat, it seemed to me a bit excessive. After all on the last Mini Transat the Minis (6,5m) get over 40k winds and all of them (70) went on racing…and with just a solo sailor. No casualties.

Regards

Paulo

Paulo, for the average sailor in the typical boat on this thread, and not just 20-foot boats, 40 knots of wind is a lot of wind and can be dangerous. I've sailed Paloma through two force 10 storms (one in which we kept racing)exciting rides, with experienced, bluewater sailors. But far from sheltered waters, when the wind pipes above 40 knots and the seas start to build, you have to become a much more careful sailor if you don't shift your mindset, you will get in serious trouble.