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Old 05-12-2007, 14:37   #31
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one half of mass times velocity squared

Last time I checked Kinetic Energy was one half of mass times velocity squared.

So Kinetic Energy would increase in direct proportion to the mass (or weight) of the boat for the same velocity (or speed).
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Old 05-12-2007, 14:57   #32
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I am a great proponent of parachute sea anchors. I made them and sold them to cruising yachts for years, while I was cruising.
What size diameter do you recommend for a 40 ft, say 15 tonner?

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Old 05-12-2007, 15:04   #33
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Interesting read. I know wave height doesn't really matter, its period and the presence of breaking waves that cause all the problems. If you are fore reaching you can pick where to cross the wave top, that works for a mono, it worked well for the smaller boats in the famous Fastnet. But, thats not really an option for a multi so is the parachute the only option at this point or do you reach a point where the loads are so enormous from breaking waves that something else has to be done? This is really in reference to the situation you outlined where large distant waves collide with shoaling water and steepness causes the wave to break heavily. No, I've never been there either and have no desire to be there.

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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.



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Old 05-12-2007, 15:13   #34
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What size diameter do you recommend for a 40 ft, say 15 tonner?

Mark
15' minimum. 20-25' is better. Ask yourself....."What size sea wall would I want to hide behind in storm conditions?"

I had a 20' parachute for my 45' ketch (20 tons). It worked fine in a hurricane. Some manufacturers recommend a minimum 3/4" anchor rode. I simply don't agree. I used my 5/8" rode and it worked perfectly. It had the right amount of stretch and I had no problem stowing it. I have also seen 600' of rode bantered around. That would also be tough to stow and I haven't found it necessary.

I would be concerned that 3/4" may not have enough stretch.
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Old 05-12-2007, 15:22   #35
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do you reach a point where the loads are so enormous from breaking waves that something else has to be done? .
I don't know. I'm in the brain planning faze

I think the most general point is, that over the last 10 years or so there has been a definite move away from the tactic "run before it", lie ahull, etc, to: turn up and para anchor, heave to in Lin and Larry Pardy style or set a series drogue.

Each of the 3 now (seemingly ) recommended actions
  • Reduces the KE to Zero
  • Makes a buffer of slick water that may stop waves breaking
  • Lowers crew fatigue
Note here that the 3 options are specific meaning: a large para anchor; heaving to in the method described by Lin and Lary Pardy so the boat stays in its own leeway slick; and a series drogue being a propper one not an old style steering drogue.



I think with any of these actions set in a storm how the hell could you cange to another option? I don't think you can (unless forced!), once the, say, para anchor is down and its survival conditions you can't pull it up and swap to heaving to...

Thems my thoughts, I'm interested in yours as its a good way to learn theory

Mark
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Old 05-12-2007, 16:13   #36
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I don't know. I'm in the brain planning faze

I think the most general point is, that over the last 10 years or so there has been a definite move away from the tactic "run before it", lie ahull, etc, to: turn up and para anchor, heave to in Lin and Larry Pardy style or set a series drogue.

Each of the 3 now (seemingly ) recommended actions
  • Reduces the KE to Zero
  • Makes a buffer of slick water that may stop waves breaking
  • Lowers crew fatigue
Note here that the 3 options are specific meaning: a large para anchor; heaving to in the method described by Lin and Lary Pardy so the boat stays in its own leeway slick; and a series drogue being a propper one not an old style steering drogue.



I think with any of these actions set in a storm how the hell could you cange to another option? I don't think you can (unless forced!), once the, say, para anchor is down and its survival conditions you can't pull it up and swap to heaving to...

Thems my thoughts, I'm interested in yours as its a good way to learn theory

Mark
The tactic that the Pardy's use (or at least propose) concern me some.

I have seen drawings of their harness that holds their bow, "off-the-wind". Remember, they had a small, full keel boat. Hoving-to on that vessel would be a simple proceedure.

I have set on my parachute many times in conditions of 20kts all the way up to 60+ with huge breaking seas. My experiance has been that when the vessel is in the trough of a big wave, she will be slung-shot to windward (from the stretch of the nylon rode ). Then when she gets hit by the next gust of wind, her bow may be blown down in either direction. If the vessel has this harness lashed to one side of the boat and that is the side that blows down, that would put the harness lashed to the lee side of the boat and crossing over the boat to windward. I could see that arrangement rolling the boat as it comes taught to the parachute rode.

I have found running the anchor rode directly off the bow to be tremendously succesfull and comfortable. I would never consider anchoring in that position in a lagoon, in a storm, why would I do that out at sea. You have even more forces to deal with out there.

That "Hove-to" position will put increased stress on the entire system IMO and when the boat gets thrust forward in the lee of a big wave it could be increased dramatically. I've never tried it but I remember thinking about it while I was on my parachute one time. My thought was, "That would be crazy". No offense to the Pardy's.
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Old 05-12-2007, 16:37   #37
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The tactic that the Pardy's use (or at least propose) concern me some.

I have seen drawings of their harness that holds their bow, "off-the-wind".
Yes, I agree. As does Alby at Sea Surface Anchors. Para-Anchors Australia Pty. Ltd.

I wanted to diferentiate between their ideas when using a para anchor, and their method of being hove to under sail using their method.

Those that wish to hove to should do so using the Pardy method of heaving to under sail (not with a para anchor)

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No offense to the Pardy's.
None would be taken, I'm sure. they are big enough to listen to all opinions


As for me, I'm with you, gimme a para anchor
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Old 05-12-2007, 17:07   #38
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relative kinetic energy

Great thread, and I have no doubt that this advice is good. As a scientist, though, I'd like to challenge some of the logic in the original post. According to the laws of physics, motion is measured relative to a frame of reference. If you deploy a drogue or other method of slowing the boat by "anchoring" to deeper water, the frame of reference changes from the surface (running free) to the sub-surface. Thus, your speed relative to the waves actually increases, and your kinetic energy would increase as well.

As I said, I wouldn't challenge the advice, but something somewhere in the rationale doesn't seem right to me...
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Old 05-12-2007, 18:11   #39
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I think with any of these actions set in a storm how the hell could you cange to another option? I don't think you can (unless forced!), once the, say, para anchor is down and its survival conditions you can't pull it up and swap to heaving to...
Mark
With the availability of good weather information offshore, hopefully you shouldn't ever get into a situation where you will be forced to switch from one strategy to the other.

You don't wait until it's blowing seventy knots to deploy a parachute. If weather fax and all available information indicates that you will be in serious trouble, it makes sense on a boat like Exit Only to deploy the chute while it's still easy to do. Its similar to preparing for a tropical depression or hurricane when you are anchored in a harbor. You know what is coming, and so you don't wait to go out and anchor until it's blowing sixty knots.

In lesser storms, you may want to switch from one tactic to another more for reasons of comfort and to give the crew a break.

I carried two 18 foot diameter Para Anchor International chutes on board Exit Only. I figured that there was a small chance the system could fail from a blown out chute, or a ship could bear down on us, and we might have to ditch the chute to avoid getting run down.

If it became necessary to change strategy, I was prepared so that deploying it wouldn't be an ordeal. When I headed offshore, I had the chutes, drogues, and all associated gear pulled out and ready to hook up and deploy before I set sail. If I needed it, I would pull the gear out of my salon, assemble it in the cockpit and rapidly deploy it.

Deploying a parachute was easy because I already had a bridle attached to my bow before I headed offshore. Deploying a drogue was easy because I was in a catamaran with port and starboard winches in the back of the boat and setting the drogue was quick and easy.

The ease of deployment depends a great deal on preparation and how you have set up your system. For us, all the components were available and ready to go. All I needed to do was assemble the components with shackles and seizing wire.

Dave
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Old 05-12-2007, 19:00   #40
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Kanani,

Thanks for that. Did you use a trip line with a float or did you motor up to the chute for retrieval?

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Old 05-12-2007, 19:23   #41
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Kanani,

Thanks for that. Did you use a trip line with a float or did you motor up to the chute for retrieval?

Mike
I used a 75' trip line (5/16" polyprop) with my largest fender as a float. It's important to have a float big enough to support the weight of the parachute. As you motor up to pick up the float, the tension is relieved from the parachute and it sinks rather quickly.

When I pick up the trip line, I pull the parachute up from the "Cone" of the chute. The first thing that comes up is my stowage bag, as the trip line goes through a S/S grommet in the bottom of the bag. As I pull up the chute, I just stuff it right in the bag, cone first and it is ready to deploy again. It's really easy.

A word of caution here. If the trip line gets away, for some reason, it makes the chute difficult to impossible to retrieve. Very risky business.
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Old 05-12-2007, 21:09   #42
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Thumbs up Need larger cockpit scuppers/drain size

I want to increase the scupper size on my C&C cockpit.

Routing a PVC pipe 1-1/2 i.d. dia through the cockpit wall and continueing on through the hull sides above the waterline, seems like it should be do able. Anyone else have information on that sort of thing?

It seems like it should work ok.
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Old 06-12-2007, 18:10   #43
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I want to increase the scupper size on my C&C cockpit.

Routing a PVC pipe 1-1/2 i.d. dia through the cockpit wall and continueing on through the hull sides above the waterline, seems like it should be do able. Anyone else have information on that sort of thing?

It seems like it should work ok.
You might be better off adding another (below water-line) thru-hull and ball-valve for your cockpit drain and go striaght down with it.

Putting a thru hull on one side, above the water-line will work OK when you are healed on that side. However, if you are healed on the opposite side, it won't do much good. If you want it above the water-line, you might want to consider running it through the transom.

You may also want to consider that PVC pipe very carefully. PVC pipe can break. Sailboats are flexible and you should avoid anything rigid. IMO, You would be far better off using S/S wire reinforced rubber hose.
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Old 06-12-2007, 20:13   #44
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Thanks Kanani, Points well taken.
While I haven't had a problem yet, other owners have mentioned they wished for better cockpit drainage in heavy sea situations.
Perhaps a check valve and straight down is the better solution.
Thanks for giving consideration to it for me, two heads ARE better than one...
HAwk
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Old 06-12-2007, 20:28   #45
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Thanks Kanani, Points well taken.
While I haven't had a problem yet, other owners have mentioned they wished for better cockpit drainage in heavy sea situations.
Perhaps a check valve and straight down is the better solution.
Thanks for giving consideration to it for me, two heads ARE better than one...
HAwk
While large amounts of water invading the cockpit is rare, when it does happen (and I hope it never does for you) it needs to be evacuated quickly. That is a lot of extra weight. The real problem is, if the conditions are right for it to happen once, it may likely happen more than once in quick succession. If the first batch hasn't drained off, the second batch may well find it's way down below.

Most off-shore cruisers have 2 drains. One just to port of center and 1 to SB of center.
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