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Thread: Drogue or Sea Anchor? What and When?

  1. #1
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    Default Drogue or Sea Anchor? What and When?

    We have a PAratech Sea Anchor, never used it, but have seen some videos of cats using them off the bow. Have also read stories of those that ran from storms, if the speed became too much they ran a drogue (either a true one or makeshift) off the stern. I am curious what the consensus is on what and when, I imagine if the waves are just too big to ride down or surf down, a parachute would be safer? BTW I hope to never need either, but the knowledge could be a lifesaver.

  2. #2
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    Default Re: Drogue or Sea Anchor? What and When?

    Parachute anchor demands very strong attachment points on the bows, and needs to be rigged ready to deploy before the storm. It needs to be big enough that the wind and wave driven speed astern is absolutely minimal, or rudder damage will occur.

    The series drogue provides an alternative approach to the parachute and will also minimise movement through the water, but demands that the aattachments are on the stern. Dinghies on davits are an obvious weakness to this approach.

    single drogues are great for slowing a boat down, but not much benefit in survival conditions.
    Insanity is continuing to do the same thing and expecting different results

  3. #3

    Default Re: Drogue or Sea Anchor? What and When?

    A para-anchor is for stopping (eg to allow a storm to pass over quickly), drogues are for slowing down when conditions are bad but not necessarily survival conditions. Survival conditions for some boats are just nasty or even fun for others so it depends on you boat.

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    Default Re: Drogue or Sea Anchor? What and When?

    Quote Originally Posted by Peter View Post
    ..........., drogues are for slowing down when conditions are bad but not necessarily survival conditions. ...........
    If you are talking just drogues then I agree with you. If you include the series drogue in this, you are totally wrong. Even USCG consider the series drogue to be the best bit of kit in extreme conditions. See the jordan site, and look at some of the tank tests. Read some of the Drag Device Database entries.
    Insanity is continuing to do the same thing and expecting different results

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    Default Re: Drogue or Sea Anchor? What and When?

    As for loads on the attatchment points I have read several articles stating that with a sufficiently long enough line, with adequate stretch, the load on the atatchment points is barely greater than the loads on the same points anchoring in a blow. Our plans are Bahamas Exhmas, eventually Caribbean. At what point would you feel you were surfing too fast and needing to slow down if running with it?

  6. #6

    Default Re: Drogue or Sea Anchor? What and When?

    Quote Originally Posted by Talbot View Post
    If you are talking just drogues then I agree with you. If you include the series drogue in this, you are totally wrong. Even USCG consider the series drogue to be the best bit of kit in extreme conditions. See the jordan site, and look at some of the tank tests. Read some of the Drag Device Database entries.
    I don't think a JSD is the panacea for all extreme conditions. Not wishing to be cynical in anyway but the Jordan site, however upstanding, has a vested interested. The Database also makes specific distinctions between monos, types of monos and catamarans.

    If my understanding is correct Jordan expect waves to break over the stern and into the cockpit and they recommend that the crew go below and strap themselves in when deployed. This may be the best compromise for a mono, that by default presents a small area aft and has a long keel that is likely to yaw to a sea anchor. But I would not like to stop a catamaran (or some modern wide stern monos) stern to wind and breaking waves as JSD suggests. A cruising catamaran, in particular, presents a huge stern area and the impact forces would be worrying to say the least. That is not to say the JSD doesn't have it's place.

    You could simulate the effects next time there is a moderate blow, with breaking waves in your local anchorage set up and anchor stern too.

    There must be members of this forum that have used a para-anchor or JSD and in what conditions?

    I have used a drogue on several occassions in strong winds and NON breaking waves to slow down and time arrivals.

    Richard Woods I think used a sea anchor off Mexico. If I recall correctly Team Phillips towed a drogue at some point but they presented a very streamlined stern and given their "sturdy" bow configuration a sea anchor may not have been a good idea not sure it was survival conditions either.

  7. #7
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    Default Re: Drogue or Sea Anchor? What and When?

    Quote Originally Posted by Peter View Post
    ..............I would not like to stop a catamaran stern to wind and breaking waves as JSD suggests. A cruising catamaran, in particular, presents a huge stern area and the impact forces would be worrying to say the least. .......
    I acknowledge that some catamaran designs are not optimal for a JSD, and I looked at that aspect as much as a lot of others when choosing my boat. However, your comments suggest a lack of understanding of the JSD concept. If you look at the design again, you will notice a significant weight at the end of the rig (in my case 150 cones, and 7metres of 10mm chain). This weight is crucial to the design. As the boat and JSD are overtaken by a wave, and fall off the back, the boat slows almost to a stop, the weight at the end of the rig drops a large proportion of the droguelets out of action by being well below horizontal. This is the situation when the next wave arrives, the first impact of that wave (even a breaking wave) is met by little resistance to boat moving forward because there are very few droguelets stopping it. As the boat increases speed, the rig straightens out and more and more droguelets come into action, slowing the boat and pulling it through the wave.
    That initial impact force is mostly dissipated by the movement of the boat. In a big breaking wave, it is certain that the cockpit will get a good amount of water, so LARGE drains are necessary. If your boat is designed such that the wave would be funnelled into the cockpit, it is probably not a good idea to use a JSD. Personnally this is not a design worry in my boat!

    I have no argument against the use of drogues to slow the boat in lesser storms, and the example of the Abbott Drogue in "Exit Only's" storm management is a prime example of this. However, these will not be sufficient in survival storm settings, and this is where the JSD is suitable for blue water designed catamarans.
    Insanity is continuing to do the same thing and expecting different results

  8. #8

    Default Re: Drogue or Sea Anchor? What and When?

    I want to get a series drogue before venturing into the wild...

    to that effect I had two eyelets added to our boat while it was in the shop. If you look in the attached photo on the right side of the dinghy you can just see one of them. The boat at that point is about 25 mm solid fiberglass.

    I had the eyelets placed as low as possible while still reachable from the cockpit. I don't think I would venture outside in a situation where drogue deployment is necessary. So one arms length below the cockpit rim it was. The dinghy will be strung about 20 cm higher, so it should not interfere.

    I agree with Talbot in that the appealing thing about the JSD is its variable resistance. Let the breaking wave (or whatever behemoth is lurking behind) accelerate you as easily as possible, but the more you accelerate, the more cones become effective, resulting in a rapid slowdown hopefully before you run into the wave ahead of you.

    ...and I still hope I'll never need it...

    Oliver
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  9. #9

    Default Re: Drogue or Sea Anchor? What and When?

    In extreme conditions, I'd rather have the bows facing the waves. Para-anchor for me.

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    Default Re: Drogue or Sea Anchor? What and When?

    Quote Originally Posted by 44C View Post
    In extreme conditions, I'd rather have the bows facing the waves. Para-anchor for me.
    A very reasonable attitude - but not necessarily the best option for some designs.

    The design of the front of the Privilege is very good for absorbing a breaking wave, and I have also added strong points for a parachute, which will work just as well for the bridle. I am less sure of the vertical lagoon windows, and even less sure about the eyebrows over the windows on the Leopard designs - these have already caused a major problem in one cat in bad weather as they focus the impact of the wave onto the windows.

    Thus choice of para anchor or series drogue needs to be made taking into account the design of the vessel.

    My choice has to balance the admitedly more vulnerable stern, versus the significant reduction in the impact of a breaking wave due to the JSD design.
    Insanity is continuing to do the same thing and expecting different results

  11. #11
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    Default Re: Drogue or Sea Anchor? What and When?

    I have a 1999 edition of Surviving the Storm by Steve and Linda Dashew ISBN 0-9658028-9-2. It is the most thorough publication I know that discusses the use of drogues and parachute anchors in extreme conditions for both monohulls and multis (although multis are not the prime focus) ..... and I believe it is unbiased.

    It includes comments from Eric LeRouge and other notable multihullers.

    It would be very wrong of me to precis the knowledge given in this book in just a few words on a thread.

    My advice .... read and re-read this book before assuming that a drogue or sea anchor is good for your boat.

    If anyone else knows of a better work please let me know. I am NOT interested in biased works and incomplete model tests. The real world adds chafe to the mixture ..... so what happens when a securing line parts on a given system : beam-to and capsize?

  12. #12
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    Default Re: Drogue or Sea Anchor? What and When?

    I am confused.
    The real world adds chafe to the mixture ..... so what happens when a securing line parts on a given system : beam-to and capsize?
    Please explain.
    Safe Sailing
    Paul
    Blog: www.suliere.com

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    Default Re: Drogue or Sea Anchor? What and When?

    There are a lot of things that can go wrong. It is important to consider what happens when they do .... and make sure that the new condition can be handled safely, or would it be better to not be put into that position in the first place.

    Suppose that the conditions are bad: true survival conditions with large cresting and breaking waves. A parachute anchor is used to keep the catamaran bow on to the weather.
    The maximum force on that tether is as the crest passes by. Suppose it breaks due to chafe. The boat is pushed back and beam on to the waves; the very condition that was being protected from. The boat is now left without a parachute, beam on to the waves ..... and vulnerable to capsize.

    Another possibility: the boat is attached to the parachute anchor. It gets pushed back by the crest. As the crest passes the boat is propelled forward because the load is much reduced, enough so there is enough slack that the boat can be turned beam on by the next wave. Hey-presto ... another potential capsize.

    There are case histories in the book of various problems, particularly with parachute anchors. If they are to be used, their limitations should be understood and hopefully countered.

    I prefer to learn from the experiences of other people ..... specially when it concerns extreme weather. I haven't experienced any weather where I needed to use a drogue or a parachute ..... so I have no personal experience.

  14. #14
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    Default Re: Drogue or Sea Anchor? What and When?

    As far as I know, I have read every reported use of a parachute on cats and never come across such a case as you mention.

    If conditions are so bad that you need to use a parachute due to the risk of capsize would it not be just as risky not to use one?

    I am intending to make a video on this subject and I am very interested in it.

    So I ask - if conditions are such that not to have a parachute is to risk capsize then is it not more risk not to use one?
    Safe Sailing
    Paul
    Blog: www.suliere.com

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    Default Re: Drogue or Sea Anchor? What and When?

    I'm not going to precis Surviving the Storm ... It's a good book and addresses the issues you are raising.

    If you need more advice I suggest you actually contact those that have used the devices in EXTREME weather ..... or indeed have not used any.

    Erik Lerouge would be a good start in your research, and he may well put you on to others.

    The assumption that a drogue or a parachute anchor needs to be used in extreme conditions is not one that sits happily with me, but it remains an option.

    I instinctively feel that the best way to guard against capsize and breakage it to travel with the wave system, but not faster than it, and not directly down the wave to cut down the extreme acceleration/deceleration cycles and avoid overtaking the wave. Drogues may help reduce the speed .... but then again they may not be required. Drogues by their nature will restrict maneuverability ..... so not to be considered lightly. I certainly don't want to anchor myself in a sea with a parachute anchor with in steep seas traveling towards me at 20 knots.

  16. #16
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    Default Re: Drogue or Sea Anchor? What and When?

    I have read extensively including Dashew.
    I have read all the official reports on the use of drogues - real life events with the good and the bad. I am not seeking advice, I am trying to engage in a discussion.

    I certainly don't want to anchor myself in a sea with a parachute anchor with in steep seas traveling towards me at 20 knots.
    That seems to miss the whole point of the parachute anchor. Waves do not travel towards you - they simply go up and down.... you travel towards them! When you sail and you think you see waves travelling towards you it is an illusion. They are simply move up and down and if you stop then basically you move up and down with them.

    If you remove the energy from the boat then you remove the energy bashing into the sea but if you stop like that you will broach hence to keep you bow to the weather you use the sea anchor.

    So waves will never travel towards you at 20 knots unless you are doing 20 knots into them!
    Safe Sailing
    Paul
    Blog: www.suliere.com

  17. #17
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    Default Re: Drogue or Sea Anchor? What and When?

    Also
    I instinctively feel that the best way to guard against capsize and breakage it to travel with the wave system, but not faster than it
    That means you have to stop because the wave system as such is not travelling as you assume
    Safe Sailing
    Paul
    Blog: www.suliere.com

  18. #18
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    Default Re: Drogue or Sea Anchor? What and When?

    Paul ..... go to sea. It is no illusion that the crests are traveling with the wave system.

    The water particles don't travel with the wave .... but they don't just go up and down. In open water wave theory they are considered to have a trochoidal motion. In reality there is always a wind driven surface current ..... but certainly nowhere near 20 knots.

    If you anchor your boat with a parachute anchor it is assumed that the parachute anchor remains stationary in the water because of its size when related to the size of the trochoidal motion. It is a good approximation. However the energy is in the wave and can be delivered very effectively by the wave crest. I'm sure you know this ......

  19. #19
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    Default Re: Drogue or Sea Anchor? What and When?

    I did state basically up and down and realised they travel in a trochoidal motion but that does not change the point I am making.

    There is always a current but that current can be considered as the sea moving -so even if you are 'still' you move with the sea at the speed of that current - it can be ignored when discussing the energy hitting the boat.

    Yes there is energy transferred to the boat from the wave because the wave itself has motion within it - we agree on that BUT the wave as a whole is not moving and the least energy situation between you and the water is when the boat is still in the water - the parachute will travel with the current just as the boat will but will in effect keep the boat still in relation to the waves so the least energy that can be transferred to the boat is when the boat is still. Move the boat in relation to those waves and you add energy to that wave hitting the boat.

    if the water in the wave was purely up and down then the wave energy transferred to the boat would be minimal but its not and hence there is some energy transferred to the boat.

    So when you write of motoring at some speed with the system all you are doing is adding to the amount of energy that can hit you. This is whey heaving to is so nice - you can stop and have a cup of tea or on the other side of the pond a cup of coffee. You are removing energy from the system.

    Any speed adds to your problems in those severe conditions it does not reduce them..
    Safe Sailing
    Paul
    Blog: www.suliere.com

  20. #20
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    Default Re: Drogue or Sea Anchor? What and When?

    Thinking about the subject a bit more:-
    The only way you can reduce the impact of the top of the breaking wave would be to move back and then forward after it passed..... not possible, so any speed forward must just to the relative speed at which you hit the crest ..... agreed?
    Safe Sailing
    Paul
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