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  #31  
Old 02-27-2012
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beej67, Interesting piece on wave characteristics. It's a good explanation of why placement of the chute in the same relative wave position of the boat is important. Another good reason to have a drogue would be to just set a jib and get some sleep if singlehanded in non-life threatening conditions but those that would otherwise require being at the wheel. I have a windvane but it is least reliable on a dead run and especially if surfing down the face of waves. I can definitely see the use for a drogue in that situation: 15' following sea, steady 20 knot wind, the kind of situation making a long passage in Trade Winds where you don't want to stop completely. The other advantage I see in a series drogue is its simplicity as compared to all the things to go wrong in a chute system. Will have to think about making a drogue to keep on board in addition to the sea anchor. I have a pattern somewhere to make the cones. They are actually pretty simple.

Thinking about dragging a drogue, I wonder if big bitey things will come up to take a nip? I know it' s a problem with dragging generator props or pretty much anything that can be mistaken for a meal. Would be an interesting to have a 500# shark grab a 3/4" line attached to your cleat.
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Last edited by smurphny; 02-27-2012 at 07:59 PM.
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  #32  
Old 02-27-2012
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Well, the replacement for the parachute sea anchor isn't a regular drogue, it's one of these "series drogues" they have nowadays, basically thirty drogues on a long line with a chain at the end to weight it down in the water. Effectively, the only thing the chute really does for you from a scientific standpoint is provide drag. Thirty little chutes can provide drag just like one big one can, but if they're distributed all along the rode then the rode never 'snaps.'

I'd love to hear some first hand experience from a sailor who'd used both. All I can relay is what I've heard/read, which is limited because people don't typically choose to put themselves in the middle of hurricanes to test these things out. The one major drawback I've heard about series drogues is that since there's no float at the end, when the storm is over the dang thing hangs under your boat and it's a huge pain in the rear to haul it back in.
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  #33  
Old 02-27-2012
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Quote:
Originally Posted by killarney_sailor View Post

- Jon, my sense is that being anchored and using a midship bridle is not the same, dynamically, as doing it with a parachute since the entire system - boat and sea anchor rig is free too move sideways rather than being tied to a point in space. Also, according to the pictures and diagrams in the Pardey's boat there is a considerable amount of force on the bridle so the angle in the main line is significant, reducing the ability of the snatch block to slide forward and back too much. I get the impression that the purpose of the snatch block is mainly to reduce the potential for chafe.
You could be right, but my sense in my limited experimentation, was that the snatch block tended to ride one way or the other along the main rode as soon as there was any change in the conditions... I could have things aligned fairly well for a certain wind strength, but as soon as a stronger gust would put more pressure on my two furlers forward, the bow would be pushed down slightly, and the snatch block would tend to slide further down the rode.... Quickly, the delicate balance would be lost, and the boat would soon wanting to ride, effectively, stern or quarter-to...

I can only imagine in the chaotic environment of a blow offshore, that tendency might only be exacerbated... Never having tried it, however, I could be wrong... (grin)

One thing lying to a bridle at anchor will make you quickly appreciate, however, is how noticeably the load on the primary rode is increased by presenting your boat in such an attitude to wind, seas, or current... It's one thing to sit in a place like the open roadstead at Rum Cay for 5 days, lying to a bridle in 25-30 knots... Offshore, in storm force conditions, would be a whole different ballgame, especially if you weren't to manage the perfect leeward drift, and resultant slick created to windward...

That's one of the biggest arguments in favor of a drag device such as a series droque, IMHO... The loads on deck gear can be minimized, and with the use of a bridle as Don Jordan recommended shackled to dedicated strong points on each quarter, the issue of chafe can be virtually eliminated... Not to mention, every thing can be tended from the cockpit, having to take regular trips to the pointy end in storm conditions to adjust things and check for chafe could get old pretty quickly, seems to me...

At any rate, in my experience, fixing the secondary bridle line to the main rode works like a charm, very easy to fine tune the boat's attitude using a cockpit winch, and one certainly should be able to attach one line to another without creating a major chafe issue...
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  #34  
Old 02-27-2012
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Quote:
Originally Posted by MedSailor View Post



If the anchor is of sufficient size there should be little load on the rudder as there is little drift backwards. Correspondingly though, the loads on the line and bridle are massive.
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In a 40 knot blow!
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  #35  
Old 02-27-2012
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i have friends who have used a series drogue and they were very pleased with the results, but that was in 40-45 knots so I can't comment on efficacy in nastier stuff. I seem to remember that they had something like 120 cones for a heavy 38' steel cutter.
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  #36  
Old 02-27-2012
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Picking up 120 cones wouldn't be so bad! least you be alive to do the picking!...Dale
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  #37  
Old 02-27-2012
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Quote:
Originally Posted by Flybyknight View Post
In a 40 knot blow!
You have never been out in one, now have you.
Thank you for your useless comment, which doesn't appear to have added anything to the discussion. I'm assuming, based on your highlighting, that you are challenging the assertion that a boat won't move backwards significantly with a parachute anchor set.

Based on my readings from the Pardeys, and all the first hand accounts from the DDDB and Adlard Coles book there indeed is very little strain on the rudder and little movement aft with a parachute appropriately sized and appropriately deployed.

Typical drift rates for a boat in a storm or hurricane laying to a parachute are 0.5-1.5knots. Does that sound like enough to damage a rudder?If your parachute is undersized I would expect drift aft and damage, but not for a correctly sized one. Here's a thought experiment for you. Imagine a 500foot diameter parachute sea anchor, tied to a 21ft boat in a storm. Now do you think it'll drift back severely and damage the rudder? Scale down the same thought experiment and use the correct size of parachute and you have a regular yacht, such as mine.

To directly answer your question, yes I have been out in a 40kt blow where a parachute was deployed, winds 25-35 gusting in the 40s and we did deploy a sea anchor. Care you share your first hand experience?

Not sure why I responded to that.....
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Last edited by MedSailor; 02-27-2012 at 11:19 PM.
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  #38  
Old 02-28-2012
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Quote:
Originally Posted by smurphny View Post
beej

Thinking about dragging a drogue, I wonder if big bitey things will come up to take a nip? I know it' s a problem with dragging generator props or pretty much anything that can be mistaken for a meal. Would be an interesting to have a 500# shark grab a 3/4" line attached to your cleat.
I've heard that repeatedly over the years, but I'm wondering if there isn't a bit of urban myth to that one - perhaps from people simply looking for an excuse not to bother with a towing generator? (grin)

First of all, they are pretty rare out there, hardly anyone uses them, in my observation... I've towed a spinner for thousands of miles offshore, have never noticed any "bite marks", and my only loss of one was due to my own stupidity, passing up-current of a large fishing buoy in crossing the Bay of Fundy... The 2 other people I personally know who've used them, one has used his on a passage from Oz to Chile, the other on 3 transatlantics, neither has had one stolen by a shark...

In each year's debrief of the ARC by one of the Brit boating rags on gear that works, water generators repeatedly score very highly, and I can't recall any significant mention of loss due to "predators"... One of my favorite pieces of gear, I'm mystified why more passagemakers don't use them (walking the docks prior to the Caribbean 1500 this year, I didn't see a single towing generator rigged on anyone's stern, though I suppose some boats could have had them stowed at that time. I tend to doubt it, however - water generators don't seem to go hand-in-hand with a dozen jerry jugs of diesel lashed to the rail (grin)) But, I can't help but wonder whether it's due to the fact that some folks out there just "know" that losing those props to big, hungry creatures is a real problem... (grin)

Last edited by JonEisberg; 02-28-2012 at 08:46 AM.
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  #39  
Old 02-28-2012
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I suppose the Jordan Series Drogue should enter the discussion here, though as far as I know it's generally considered an active, rather than passive technique. i.e. you need to be steering, and standing in the cockpit (with stern to the waves) in order for this system to work. The Coast Guard does recommend streaming JSD from the stern unattended, though I haven't heard of that nearly as much as using a JSD or other drogue as part of an active steering tactic. If that is a sound tactic, then I would seriously consider it.

I would also consider more cones than recommended in order to make a drift stopping device (same function as a sea anchor), rather than slowing device, which could be streamed from bow or stern.

I have a hard time with the idea of streaming a drag device from the stern in breaking waves, without steering, though. It just seems intuitive to me that the bow is what's designed to go into, and safely over, waves. The stern, not so much. I would also argue against the point made that when streaming a JSD from the stern that tending it from the cockpit is an advantage over going forward to tend a para-anchror. In both cases you're going towards the end of the boat with oncoming waves. The companionway hatch (look at the picture in my avatar) would also be a point of potential vulnerability, whereas my bow has no vulnerable structures and has more freeboard as well as being "pointy" and possessing sheer to direct wave forces away from the boat.

The series drogue tests by the coast guard (which make excellent reading) argue against deploying a JSD up forward, and don't think much of parachutes for the same reason. While I'm inclinded to trust their test and methods, I still have a hard time understanding how it is fundamentally better, by boat design, to present your stern to waves rather than the bow. Where's Bob Perry when you need him....

Here's what the coast guard's series drogue test has to say on the matter (notice that they estimate the drogue's loads to be between 60-100% of the boat's displacement) not any lighter than a sea anchor.:

Link to Coast Guard report HERE:
http://seriesdrogue.com/coastguardre...oguereport.htm
------------------------------------------------------------------------------------------
6.4 Boat Design
Back Forward Index

With a drogue deployed, a well-designed and properly constructed fibreglass boat should be capable of riding through a Fastnet type storm with no structural damage. Model tests indicate that the loads on the hull and rigging in a breaking wave strike should not be excessive.

There are three areas that require special attention:

The attachment fittings for the bridle of the drogue towline at the corners of the transom must be capable of carrying 70% of the towline design load. For a 7500 lb. displacement boat each fitting must be capable of carrying 5300 lbs. Many yachts are equipped with a Genoa track which runs aft to the transom. Such a structure, which distributes load along the hull, could be provided with a special eye at the transom for attaching the bridle.
If the nylon towline is led through a chock instead of attaching directly to an eye, experience suggests that chafing may occur even with good chafing gear installed. Consideration should be given to the use of a short length of wire cable running through a stainless steel chock before attaching to the nylon line.

Many sailors are reluctant to deploy a drogue from the stern because they fear that the boat may suffer structural damage if the breaking wave strikes the flat transom, the cockpit and the companionway doors. The model tests do not show this to be a serious problem. The boat is accelerated up to wave speed and the velocity of the breaking crest is not high relative to the boat. The stern is actually more buoyant than the bow, and will rise with the wave. However, the boat may be swept from the stern. The cockpit may f ill and moving water may strike the companionway doors. The structural strength of the transom, the cockpit floor and seat, and the companionway doors should be checked at a loading corresponding to a water jet velocity of approximately 15 ft./sec.

When a boat is riding to a drogue no action is required of the crew. The cockpit may not be habitable and the crew should remain in the cabin with the companionway closed. In a severe wave strike the linear and angular acceleration of the boat may be high. Safety straps designed for a load of at least 4g should be provided for crew restraint. All heavy objects in the cabin should be firmly secured for negative accelerations and drawers and lockers should be provided with latches or ties which will not open even with significant distortion of the hull structure

AND:
6.6 Sea Anchor Deployed from the Bow
Back Forward Index

The foregoing recommendations and discussion apply to a drogue deployed from the stern rather than a sea anchor deployed from the bow. A large sea anchor would be required to hold the bow of a modern yacht into the wind and sea in a survival storm. The required diameter of the cone or chute would be 2 or 3 times the diameter shown on Figure 25. The design load would be 50 to 100% greater than that shown on Figure 26. Even with a large sea anchor the bow of a modern yacht will tend to yaw away from the wind when the towline goes slack as it will when the boat passes through the trough of the wave. For these reasons the use of a sea anchor deployed from the bow is not recommended.


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Last edited by MedSailor; 02-28-2012 at 11:57 AM.
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  #40  
Old 02-28-2012
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Have a look at this. This guy did some interesting work with a para-anchor on his small catamaran in Australian waters


KatieKat ParaAnchor Index
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