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Old 13-02-2012, 18:03   #1
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Series Drogues & Heaving To

Why do the makers of Series Drogues give instructions not to deploy from the bow?
It would seem that a SeaAnchor and a Series Drogue both do the same thing and would be to the same benefit while Heaving To as a storm tactic.
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Old 13-02-2012, 18:18   #2
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Re: Series Drogues & Heaving To

A drogue is not designed to stop you ,merely to slow you enough to retain control. A sea anchor is designed too arrest as much as possible any drift.

Anyway in my view sea anchors are dangerous, difficult to deploy and recover, expose the rudder to damage, exert huge snatch loads and cause you to visit the most exposed part of the boat in a blow.

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Old 13-02-2012, 18:25   #3
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Re: Series Drogues & Heaving To

Drogues and Sea Anchors are not the same thing and are not deployed in the same way.

A drogue (regardless of design) is normally deployed off the stern. It's purpose is to slow the boat down (not stop it) and increase directional stability.

A sea anchor is normally deployed off the bow. It acts very much like an anchor. When riding on a sea anchor the boat sits bow to wind and waves and is effectively stopped.

Heaving-to is a term you may sometimes hear applied to riding on a sea anchor or even a power vessel just maintaining position in a storm, but more commonly it is used to describe a technique for stopping (or nearly so) a boat under sail. This same technique can be used as a heavy weather tactic, but normally by itself and not in combination with either sea anchor or drogue.

All three options are applicable to different heavy weather scenarios.
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Old 13-02-2012, 19:25   #4
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Re: Series Drogues & Heaving To

Quote:
Originally Posted by Dpoissant View Post
Why do the makers of Series Drogues give instructions not to deploy from the bow?
It would seem that a SeaAnchor and a Series Drogue both do the same thing and would be to the same benefit while Heaving To as a storm tactic.
It's a long answer. Check out the following link to get some answers:

Blue Water Catamaran - Exit Only Sails Offshore Around The World.* Captain Dave - Privilege 39
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Old 13-02-2012, 19:51   #5
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Re: Series Drogues & Heaving To

Galerider Drogue Launched Off Bow Stops Wave Strikes While Heaved-to
The link above outlines deploying the drogue from the bow during heaving to.
What is the danger in using this device in this manner?
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Old 14-02-2012, 10:06   #6
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Re: Series Drogues & Heaving To

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Originally Posted by Dpoissant View Post
Galerider Drogue Launched Off Bow Stops Wave Strikes While Heaved-to
The link above outlines deploying the drogue from the bow during heaving to.
What is the danger in using this device in this manner?
There is nothing per se dangerous about using a drogue in this manner. But it is atypical of how they are normally used.

Related note: on vessels which heave-to well (and not all do) you should not typically need to use a drogue this way.
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Old 14-02-2012, 11:38   #7
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Re: Series Drogues & Heaving To

Quote:
Originally Posted by Dpoissant View Post
Galerider Drogue Launched Off Bow Stops Wave Strikes While Heaved-to
The link above outlines deploying the drogue from the bow during heaving to.
What is the danger in using this device in this manner?
never ina million years would i use what is described above as a serious storm tactic. wow, where to start...

...and havent they disproved the myth about a boats slick helping to prevent wave strikes? I can imagine it stopping the windwaves that exist on top of the larger swells, but I cant imagine a 4m+++ breaking wave being in the slighest way affected by the slick?
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Old 14-02-2012, 12:21   #8
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Re: Series Drogues & Heaving To

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...and havent they disproved the myth about a boats slick helping to prevent wave strikes? I can imagine it stopping the windwaves that exist on top of the larger swells, but I cant imagine a 4m+++ breaking wave being in the slighest way affected by the slick?
I don't know... I have seen wind waves fall onto themselves (sort of collapse and dissolve at the same time) when they hit a slick, but have (thankfully) never been in breaking waves and have no idea if they'd be affected.

But, I am just making this up, it's hard for me to believe that 'the slick' could be a significant enough effect on breaking waves to make it a real part of a strategy. As in "the slick is a significant part of our strategy" and not just an incidental advantage of doing something else. But I don't know, I am curious what other people have learned or seen.
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Old 14-02-2012, 12:41   #9
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Re: Series Drogues & Heaving To

The slick created by a hove-to boat or a sea anchor is actually a series of vortices called a "Von Karman Street". Google that term and you'll find a lot of stuff on fluid dynamics. The vortices divert energy from the cresting waves, knocking some of the power out of them.

I once read a statement attributed to Larry Pardy where he reportedly said that the waves start to lose their power in the slick created by the Von Karman Vortex Street as much as a 1/4 to 1/2 a mile to windward while drifting downwind at 5/8 to 3/4 knot in 70 knot winds.
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Old 14-02-2012, 13:15   #10
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As the energy displacement effects of a Karman vortex street would extend no deeper than the keel of the boat generating it and that depth would decrease rapidly as it got farther from the boat? And over 90% of a waves energy is contained in the depth from surface to 1/2 the wavelength of the swell.

So wouldn't a huge portion of the waves energy be out of reach of the surface effects of the karman vortex street?
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Old 14-02-2012, 13:19   #11
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Methinks I would love an engineers input on this as it seems to me to be a bit of a wives tale brewed from both science and a bit of anecdotal old salt wisdom.

That said I would never question larrys story, and I have never used the technique choosing instead to use my series drogue to great success...
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Old 14-02-2012, 14:05   #12
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Re: Series Drogues & Heaving To

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Originally Posted by foolishsailor View Post
Methinks I would love an engineers input on this as it seems to me to be a bit of a wives tale brewed from both science and a bit of anecdotal old salt wisdom..
If you can get your hands on Tony Marchaj's "Seaworthines the Forgotten Factor" read it..
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Old 14-02-2012, 14:57   #13
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Re: Series Drogues & Heaving To

Quote:
Originally Posted by foolishsailor View Post
As the energy displacement effects of a Karman vortex street would extend no deeper than the keel of the boat generating it and that depth would decrease rapidly as it got farther from the boat? And over 90% of a waves energy is contained in the depth from surface to 1/2 the wavelength of the swell.

So wouldn't a huge portion of the waves energy be out of reach of the surface effects of the karman vortex street?
Yes and no. One good reason for crossing blue water in a deep full keeled boat.

Second, well yes; the bulk of the waves energy is deep below the surface, but,... it is the surface of the wave you're worried about. That is where the water driven by the wind overtakes the waves and forms vertical peaks that overrun the waves velocity in fluid, and breaks collapsing down the front of the wave and flips you're boat.

That is the water you need to slow down, so the wave passes under you're boat as a large swell, instead of a breaking wall of water.

So does heaving-to and forming a slick affect deep long period ocean waves?....NO, does it force a breaking wave to break early in front of you, instead of on top of your boat? According to experienced mariners, and fluid theory, yes.

According to Pardey stalling the hull by heaving-to, or by sea anchor, (in conjunction with heaving-to), is a critical skill to surviving a storm with breaking waves greater than 40% of you're boat's LOA. He also stated the tactic you use should depend on your boats stability, characteristics, and strength of storm, wave period, etc...

Running before a storm, was NOT recommended as a storm can increase without warning overunning the boats, (helmsman's), ability to steer, breaking waves on the stern can force a boat beam to the breaking waves and flip you, and you spend more time in the worst part of the storm, and can be driven miles off course or onto a lee shore.

Using a drogue, (off of the stern), while preventing surfing down the waves subjectes the rudder, and the stern of the boat to breaking waves, it may not flip you, but it may break something.

Using a drogue off of the bow is a sea anchor by another name.... I may have to give it a try. Having 1 device that serves two purposes has several benefits. A series drogue may not be as effective in stopping a boat, as a large sea anchor, but if it helps keep the hull centered in the slick, it MAY be a usefull survival tool.

If not you can always move it back to the stern.
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Old 14-02-2012, 14:59   #14
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Re: Series Drogues & Heaving To

Sorry for the long post, but the long and short of it is, it doesn't matter where in the whole big ocean the waves break as long as it is NOT on top of your boat. Affecting them, even a little, can turn a hit into a miss.
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Old 14-02-2012, 15:16   #15
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I will have to concede the fact of the slick working as I don't have any evidence otherwise, however if you know of any links that show the mechanics of it I would be interested as even in marchaj's book referenced above it is based on formulas and was before computational fluid dynamics and therefore is not necessarily accurate when scaled up to real life and also the real conditions of large swell activity in which the vortex street is acting on something other than a plane of water. I read somewhere that it had been debunked in a simulation however I can't for the life of me remember the link nor find it when googling so it might just be only in my mind.

However when talking about being hove under a drogue/para anchor and comparing it to a series drogue from the stern. They are very different. A series drogue is expressly designed NOT to stop you but to slow you down and to keep the stern presenting to the waves, the same as a normal drogue. The difference between the series and single drogue is the issue of line tension and acceleration. With a single drogue the line can slack and allow the boat to accelerate with a potential for broach or shock loading of attachment points. This doesn't happen with a series drogue.

My current boat won't hove to with out fore reaching, but even if it did I would still use my series drogue. I used it extensively on this boat during a long troublesome passage and found it to be the best option in my experience. You will take green water on you companionway, but it is not the same as getting pooped and definitely better than presenting your beam to the sea. Even if the slick stops the breaking wave the steepness of a near breaking wave won't be diminished and the oscillation issues in seas like that would be better dealt with by changing your presentation angle.

Just my opinion based solely on my personal experience and the boat I currently haves design characteristics. My last boat was a double ender with a full keel and I still would only heave to up to a point and then toss out the series drogue...
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