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Old 21-11-2007, 18:21   #16
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Agreement sometimes looks like dispute :)

Everything in your article and in your response I find entirely valid. I wished to merely supplement your excellent points to encompass additional vessels and conditions. As can be seen by the postings in this group, you have instigated substantial reflection by a number of captains on possible strategies for coping with heavy weather and beyond. That is a good thing. The sea is a demanding and rarely forgiving mistress.

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Old 22-11-2007, 00:59   #17
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Hi Dave...I printed off your article last night to sit down and read. I find I absorb it better than staring at the computer. I climbed into the pilot berth of my new boat, (which is still sitting in a padock) and read it . It all made good sense to me and was writen in a manner that I call " forget the lawyer speak I need to understand this language" ! I then reached across and grabbed my 1950 copy of cruising under sail by Eric c Hiscock. and turned to the chapter called "management in heavy weather". And blow me down,...Under waves he says "The water in a wave does not move forward in a horizontal direction any more than does the bunting of a flag which is rippling in the breeze" . And further reading is so much akin to what you have writen. His slight deviation with parachute anchors is , i think , as much to do with the gear quality and the "style" of sailing of that time. Congratulations ..it just goes to show that common sense, stated commonly is still the best kind of information. (And I am quite sure that Eric would agree !)
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Old 22-11-2007, 09:06   #18
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Cooper,

Thanks for citing that good information from Eric Hiscock. I never saw it, and it would be a good resource to retrieve from Amazon or elsewhere on the internet.

If you want to read a good book that tells about heaving to as a way of decoupling your boat's energy from the energy of stormy seas, read "The Ventursome Voyage of Captain Voss." It's an awesome story by a man who sailed in the high southern latitudes and mastered the art of heaving to. He did it often, and he did it well.

Heaving to works well because it does two things. It reduces your boat's kinetic energy as close as possible to zero, and it creates a protective slick to windward (a zone of turbulence in the water on the windward side of your boat) as you slide to leeward in a square drift. Energy waves don't propagate well into that slick zone of turbulent water and plenty of mariners will testify that approaching waves die out when they hit that turbulent zone of water to windward when they are properly heaved to. They report that breaking waves pass in front of the boat and by the stern, but the waves coming toward their beam diminish significantly in the zone of turbulence. That zone of turbulence is a killer of breaking seas, in a similar manner to the zone of turbulence behind a ship where the seas are quite flat although surrounding seas are large.

I think that the protective effect of parachutes comes from three factors. First, the chute takes your kinetic energy down close to zero since your speed is close to zero. Second, because it holds you relatively stationary, it's harder for the seas to transfer their energy to your yacht. And third, the parachute creates turbulent water - a turbulent slick - directly to windward, and seas coming from that direction lose their power when they traverse the disturbed water created by your chute. When you look at an aerial photo of a parachute sea anchor at work on the cover of the Drag Device Data Base book, you can see the parachute close to the surface being slowly dragged through the water in front of the yacht. When we used our chute we dragged the chute about a half to three-quarters of a mile in 19 hours. I am sure the chute created a zone of turbulence to windward directly in front of our yacht, and I suspect that it helped diminish the power of oncoming seas. It kind of puts you in an "Alley of Lower Energy" that saps the strength of oncoming seas. You are in the zone of disturbed water that becomes your port in the storm.

Parachutes work extremely well on our catamaran, and I am not sure which of the three effects are most powerful during a storm. It's likely that all three effects are important to some degree, and they are cumulative as well.

Anyway, read the Venturesome Voyage of Captain Voss and be amazed at the power of heaving to. I am sure that Captain Voss would say reduce your kinetic energy as close as possible to zero by heaving to, and then watch the turbulent slick to windward protect your boat from the power of oncoming seas.
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Old 22-11-2007, 12:01   #19
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very good information! thanks.
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Old 25-11-2007, 15:23   #20
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For me, the secret has been learning to "depower" early. i.e. shorten sail while it is still comfortable to do so.

Reefing the mainsail in 25 knots of breeze is a helluva lot easier than in 35 or 40. Going to the bow to drop a big headsail / raise a smaller one is the same - easy in less breeze, horrible in more.

It is often tempting to think that the increased breeze is just temporary and that you will be able to get by with the sail area that you have, and most times it probably will be ok too, but that odd occasion when the breeze continues to build and build and you end up in 40 knots and you haven't put in your reef yet and you still have that 135% headsail up, you will sure as hell wish you had downsized.

It isn't like it takes much to shake out a reef or even change headsail back up a size (most of you probably have furling headsails anyway). Frankly, a lot of people sail with too much sail up anyway... it feels fast, but often, even though you might be seeing good numbers on the speedo, you have a lot of leeway and no ability to point. Carrying less sail area will probably give you as good VMG (or sometimes even better VMG) and you will be more comfortable and your gear/sails will thank you for it.
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Old 25-11-2007, 17:29   #21
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Our Genny is about a 150%. As soon as we start to see white caps we furl it in to about 100%. When the white caps begin to shed spray we take in a reef on the main.

Very quickly after that we'll take in the second reef and get the jenny down to about 50%. If we know we are going to penetrae a thunderstorm - common here - we'll go with main alone and get the engine in forward idle.

Finally met someone here who has taken the Maxi out in the open ocean. I picked his brain a bit and plan to get a lot more insights from him next weekend. I am feeling a bit more inspired about going offshore in a 27 foot boat...
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Old 25-11-2007, 17:42   #22
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I recall first reading about the concept of heaving to with a parachute in the Pardey's book, Storm Management Tactics. Even came with a DVD. They certainly made a convincing case for the method, but I was left to wonder whether it would also work with a catamaran. I'm glad to hear from Dave that it does, or at least with his.

In thinking over the whole matter, it certainly seems that setting up several options to employ, and being able to do so at the time and place, efficiently and safely, is the key. However, also knowing how my 50+ year old brain is working these days, it isn't remembering the concept that is the problem! It is remembering and executing the details. Unfortunately, in the excitement of the situation, simply having a checklist (however helpful it might be) won't be good enough. Having enough repetitions of practice, though, would be very helpful. So, we need to practice setting out all the options, and do it enough times, repeated occasionally, so that if we ever should actually have to do it out of need, we can hope that it will go smoothly.

On to my question: I bet that some of you thought along the same lines and did some practice runs with your storm strategies, first. How close was the real experience, when you finally had to do it? Any tips you learned? In your practice runs, did you set out to find conditions that were at least a bit more challenging than a pleasant day sail?

Thanks, again.

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Old 04-12-2007, 23:28   #23
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Hi Dave,

Thanks for your great piece on kinetic energy and how it affects yachts in a bit of a blow. Its interesting to see things from a perspective of another analogy as it certainly reinforced your points on my mind. The kinetic energy chart certainly shows what we all "know" in a very strong way.

Also in my few days on this forum I came across a link to a tragedy in the Bay of Biscay some 10 years ago with an offical enquiry report. The actual thread on this forum had degenerated into a brand slagging match where otherwise intelligent minds shuttered closed and critical lessons were missed.

I needed to flick from your speech to the report a couple of times in my mind and then came across another piece of valuable 'evidence' supplied by you in your video of your yacht in the Red Sea.

So let me bring the points out I think are interesting:

The tragedy had 45+ knot winds for over 24 hours with an unlimited fetch running into a continental shelf producing substantial breaking waves. The yacht involved was running before it at, one would assume, above hull speed, without warps etc.
Previously in the voyage the skipper allowed a spinnaker to blow out with a boat speed of 14 knots, where the hull speed would be 8 to 9 knots. So we could assume the boat was surfing down waves in the Force 9 storm at 14kts. That’s 175% of its hull speed.

Using your kinetic energy calculations thats 196 at 14 kts. However the Kinetic energy at hull speed 9 kts is 81. So the amount of kinetic energy above hull speed is 115!! Remembering that we get much higher instability above hull speed.

The yacht in the tragedy is a light production yacht of low degree of vanishing stability. But this is not root cause of the problem.

Your video on your website has you in the Red Sea saying "50 Knots of Wind. It doesn't get any better than this." Of course, you wouldn’t be saying that except for having a lovely flat sea of limited wind duration over a short fetch and the breeze up your clacker.

Your speech also mentions notoriously dangerous areas “Black Holes” you call them. I think the Bay of Biscay has rated as one for a millenia.


The conclusions from these different sources are neatly drawn and they are as obvious as us as a Homer Simpson: D’oh!

50 kts of wind is fun when the sea is flat. “It doesn’t get better than this”.
To 50 knots doesn’t get worse than this when there is a fetch and duration to give breaking waves.

The Kinetic Energy of a 10 tonne boat and a 30 tonne boat are the same, but the momentum of the heavier boat is much more. So it doesn't matter if you are in a plastic fantastic or a Swan once your KE is too high you're in trouble.

That reducing the kinetic energy to zero is the safest option.
However if that is not possible at least ensure the kinetic energy is below that of hull speed even when surfing. I.e warps, drogue etc keeps your speed at or below hull speed at all times when conditions deteriorate. (I don’t see how warps could ever suffice)
Then if you can’t keep below hull speed in one method you know you have to try something else to keep stability.


So:
As a ‘rule’: when the weather deteriorates significantly to make breaking seas keep the boat to hull speed. If that’s not possible, Stop.

Of course, if the breaking seas are overhanging, stop.

Thoughts?

Mark
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Old 05-12-2007, 12:17   #24
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Quote:
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Hi Dave,
...
The Kinetic Energy of a 10 tonne boat and a 30 tonne boat are the same, but the momentum of the heavier boat is much more. So it doesn't matter if you are in a plastic fantastic or a Swan once your KE is too high you're in trouble.
...
I don't see how you come to this conclusion. Are you saying that at the same boat speed they are the same, or are you saying that you can accelerate a light boat to speed higher than a heavy boat and thus end up with the same KE? If it is the latter, then you could take the argument and say that the light boat is clearly safer in those conditions, as it has much less KE when kept to a reasonable speed.

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Old 05-12-2007, 12:37   #25
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I think you also have to factor in the height of the breaking wave. When is it no longer prudent to face them?


Quote:
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So:
As a ‘rule’: when the weather deteriorates significantly to make breaking seas keep the boat to hull speed. If that’s not possible, Stop.

Of course, if the breaking seas are overhanging, stop.

Thoughts?

Mark
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Old 05-12-2007, 13:42   #26
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accelerate a light boat to speed higher than a heavy boat and thus end up with the same KE?
Paul L
Hi Paul

No the KE is the same for a 10 tonne boat as a 30 tonne boat at the same speed. Its only the Momentum that changes. Doesn't Momentum = Mass x Velocity? ( I dunno, I'm too old to remember my girlfriends name, let alone what I failed at University 30 years ago!).

So, say both boats were rolled by a wave while they were doing 14 kts then the momentum of each would be:

1 knot = 0.514444444 meters per second
14kts = 7.196 meters per second

Momentum = Mass x Velocity

10 tonne boat = 10 x 7.196 = 71.96 tonnes m/s
30 tonne boat = 30 x 7.196 = 215.88 tonnes m/s

So, if a light weight boat and a sturdy cruiser are both in the same storm doing the same speed and get rolled by the same way: the light weight boat will be pummled, but the sturdy boat will have 3 times to impact and thus could be damaged as much as the more lightly constructed boat.

Yes, I know theres obvious differences between a uldb getting to 14 kts and a heavy cruiser getting to 14kts But the point remains that one shouldnt think that because they are in a production boat they are going to die any more easily that someone in a heavy cruiser. BOTH need to slowdown.



But I need someone smart with engineering to check those figures.

Mark
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Old 05-12-2007, 14:14   #27
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I think you also have to factor in the height of the breaking wave. When is it no longer prudent to face them?
As Dave says, when the particles of water stop moving up and down and start moving horizontally i.e the waves Potential Energy converts into Kinetic Energy.

There are two ways we can do that:
1) When we look at the breaking wave and think "thats no white-cap, that sucker could roll me if it hits"
2) When the wave face forms a vertical wall and the top portions starts to roll over like a dumper on a beach.

I don't think I have been out in either and I don't think I ever wanna see a 2)

But please note: I don't think I have seen a 1) and I know I havent seen a 2)! So I am feeling in the dark, and like you, I'm looking for things I can guage when at sea.

As for wave height, it doesnt really come into it. If the wind, and fetch have been enough to make a 1) or 2) then the waves will be high enough. A wave can be 100 feet tall, taller, but wont hurt your boat if its not breaking.



Mark




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Old 05-12-2007, 14:18   #28
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IIRC,

KE = 1/2 m v2,

Momentum = mv.

So weight (mass) is a factor in both. But KE in creases exponentially with velocity.
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Old 05-12-2007, 14:19   #29
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the light weight boat will be pummled, but the sturdy boat will have 3 times to impact
Sorry, a couple of typeos. Should read:

the light weight boat will be pummeled, but the sturdy boat will have 3 times more impact
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Old 05-12-2007, 14:29   #30
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Hi Dave,

Very informative article.

I am a great proponent of parachute sea anchors. I made them and sold them to cruising yachts for years, while I was cruising.

It should be emphasized that practicing with the parachute anchor is paramount. Also, a good discussion could be held on how to switch from a drogue to a parachute in deteriorating conditions. I have only done that once and I will NEVER do it again and I don't recommend it unless someone can come up with a viable plan to do it safely.

As for myself, when conditions dictate a switch to "Storm tactics", it is time to deploy the parachute and ride out the storm in complete comfort and safety.

For those of you that have ever sailed in 50+kts of wind and heavy breaking seas, there is no feeling in the world like falling back on a parachute. It is utter chaos one minute and a complete feeling of comfort and security the next. It allows you the freedom to really lay back in the cockpit with a cup of coffee and enjoy the beauty and majesty of the storm with narry a drop of water coming on board. It's almost like sitting behind your own sea wall. I never once saw a wave break over my 20' parauchute. With my (chain on bitter-end) system, I didn't have to be concerned about chafe either. (BTW, I ran a pin through the chain, just before the bow roller).

Having said that, just having a parachute on-board does little for one's ability to use it. It does have it's risks. Rounding up, timing deployment and falling back to a tightening rode takes practice to keep from getting pooped or worse.

I would suggest that anyone with a parachute on-board, practice using it in 25kts of wind, then 30, then 40. Have the parachute bridled and ready for deployment when you leave on any passage over 3-days in length.

I remove my anchors and chain from the bow before leaving. It's a funny feeling, leaving a harbor without the ability to stop your boat if an engine fails or something. I, usually keep a small Fortress anchor in a bag with 20' of chain and some rode.

I attach 20' of 1/2" chain to a member in my chain locker that is specially constructed for taking the full force of the yacht, bitter ended, at anchor. I attach my 400' of nylon anchor rode to that chain. I attach another short piece of chain to a heavy S/S swivel that is specially constructed with ball bearings. It's actually made for under sea lifting cranes. That is attached to a 5/8" S/S "D" ring on the parachute.

I leave the bitter end (1/2" chain) in the chain locker. I stop that chain just before the anchor windlass rope gypsy. I make a few turns on the gypsy with the nylon rode then run the rode back to the cockpit (being very careful to be outside of all stansions and rigging). I then attach the rode to the parachute in the cockpit where it (hopefully) makes the entire passage untouched. However, I do try to make it a habbit to deploy it once on every long passage, just for the practice.

If you don't practice with the parachute, it may be a waste to even have it. Most people are intimidated by deploying it the 1st time. By the time that they get to where they MUST deploy it because all hell is breaking loose, they could be in big trouble because they don't have the experience or confidence to complete the task safely.

The last few years of cruising, I would often just pull up on the parachute to take a days rest or wait for daylight to enter a port (be careful of traffic on that one).
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