Favorite rough weather technique

Discussion in 'Sailboats' started by gonzo, Nov 10, 2009.

  1. kistinie
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    kistinie Hybrid corsair

    Multihulls are up to 2X faster than a monohull so escaping is easier when wind blows stronger.

    In heavy short sea, multihull speed offer high manoeuvrability but to the cost of an important stress to hulls and links

    Multihulls structure are stressed by heavy short seas so anything above 50 Kts should be avoided, unless the boat is very light and ultra oversized just like most new racers are.

    Wingover had a drogue, a modified mushroom parachute. it was tested, then used with success when coming back to England from Tortola.
    Since, never again.

    If i can find the available space and $ for a spectra Jordan, it will certainly be a good security improvement for her as Jordan's conception allows the drogue to be lifted in/out from the cockpit.

    From my experience, i never had the need to slow a boat in any weather but i have had the luck to never get more than 55Kts.
     
  2. MikeJohns
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    MikeJohns Senior Member

    It’s a little off topic this, but this is a boat design forum and the tactic adopted in any weather condition depends on the design of the vessel. So in a round about way you can choose a vessel which suits your desired survival tactics best. I still maintain that the better choice is a heavier, high gyradius, high righting moment with a generous GZ curve. I’d like to follow up on BV’s post becasue this is relevent.


    You are qualifiying things at least, and we are a long way from "a heavy rig is always bad or evil‘

    Of course you will always get a higher righting moment if you put more lead in the keel or reduce the weight aloft but that’s not the issue. Naval architecture considers the roll gyradius(k) as a target figure for design similarly the metacentric height (GM) and the static curve of righting moments all are chosen (or compromised) to give the desired characteristics, comfort safety speed whatever. The Roll gyradius incorporates all the elements including the rig, so the decision to incorporate a heavy rig is made early in the design spiral.

    What we should consider if you want a sensible comparison is two boats with different gyradii but identical righting moments. If you have access to seakeeper you will quickly see the effect of changing the gyradius with instant illumination.
    You’ll also find that roll gyradius changes a lot with a mast present or absent but pitch gyradius doesn’t change that much . If you don’t accept this do the figures, or I’ll give you some from a design .

    It doesn't; the acceleration from the wave energy is considerably higher than the natural recovery of the vessel, the inertia resists the knockdown but has little effect on the recovery because it is has a considerably lower acceleration. You don’t actually want a high acceleration in any direction, particularly recovery since the vessel will overshoot and oscillate, ideally you want a strong slow well damped righting characteristic.


    I wouldn’t agree, a knocked down vessel has a lot more water on deck and lightweights often suffers severe damage from the leeside impact with the water. This is ‘solid‘ water not aerated breaking wave. The damage is always worse on the lee side.

    The longitudinal pitch roll gyradius is affected considerably less than the transverse roll gyradius by the weight aloft. If it was a small vessel or a special go-fast boat this would be considered. Once you are over 50 feet on a medium displacement it’s largely irrelevant.

    Again whether or not the mast is heavy or not is something to consider at the design phase. You can choose a longitudinal roll gyradius and design accordingly for the lowest or highest acceleration, or wave piercing or surface following ….whatever. The requirements depend on the entire design from size to intended use and nothing should be considered on its own as a single factor.


    That doesn't fit with observation, for example the 98 Sydney Hobart, by far the majority of injuries result from violent knockdowns and inversions.

    Yes but they are large fast racing machines designed accordingly, ironically they have a large gyradius and high RM from the deep bulbed keel both transverse and longitudinally. However don’t you think their crews show a disregard for prudent seamanship on boats with low freeboard, lean bows and little to impede the waves once they are rolling down the deck. They could be designed to be a lot safer, even if they slowed down it could be quite a different scenario.

    I don’t think Norman Skene is really in the picture but Marchaj certainly is and I think you’ll find him a proponent of a larger roll gyradius as a means of reducing the violence of motion and increasing habitability. It certainly reduces the angle of roll in a knockdown. This in turn lessens the risk of a following wave delivering a coup de grace, but must be considered along with the natural roll frequency and the wave period.

    Sure GM goes up but roll gyradius goes down making the boat considerably less habitable even prone to injure those aboard or completely incapacitate them. High roll angles result from the reduced roll gyradius from an impulse rolling moment (wave strike). A heavily ballasted sailboat sans mast is a very poor craft indeed. The likelihood of inversion has everything to do with the angle the vessel is at when struck and the area of the GZ curve between that angle and its vanishing stability. It has to be considered as a dynamic event.

    I thought it was principally to reduce windage not to increase stability.


    This is not the issue with cruising boats only with racers which seems to be flavoring your opinion considerably. You can make a deck drier and safer, or wetter and more dangerous…it’s all in the design.


    [/quote]


    This is a common mistake. Polar moment is not its resistance to angular acceleration. The polar moment is the resistance of an object to torsion or in-line twisting due to torque, eg if you fix on one end and apply a torque to the other how much will it distort. Its got nothoing to do with mass related inertia.
    For future use you’d should call it Roll inertia.
     
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  3. MikeJohns
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    MikeJohns Senior Member

    The most uncomfortable for most vessels downwind is in a sea with the wavelength around 1.2 times the boat length. This tends to produce the worst pitching.

    Coastal sailing often has more challenging wave patterns from winds that produce quite benign waves in deep water.




    Talking of catamarans, running can be quite dangerous in heavy seas for two reasons the first is loss of stability on the wave crests the second is the bridge deck contacting the wave crest and the vessel surging. Both of these lead to a high likelihood of broaching and or inversion.
     
  4. RHough
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    RHough Retro Dude

    NO! The JSD uses NYLON for good reason. Part of the design is based on the line stretching and absorbing/storing energy then releasing it gradually.

    The tension in the system is no constant and the whole premise is to reduce shock loading on the vessel. Using Spectra would defeat this and transfer more shock loading to the cones and the vessel.

    Yes, Nylon is heavy but the material selection is part of the design. Read the accounts of vessel motion whilst using a JSD, it is described as feeling like being slowed by a bungee. The boat is allowed to accelerate as the drogue loads up, there is no shock when the drogue is fully loaded and as the force on the drogue is reduced the drogue does not pull the boat back, the stored energy in the drogue pulls the drogue forward. I don't think Spectra would be a good choice.
     
  5. kistinie
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    kistinie Hybrid corsair

    I used to have the same idea about spectra and a drogue and it remain true for all large drogues

    Jordan is a serial drogue where each drogue slips, so enven if line is hard, the result is soft movement.

    Jordan sales a spectra version that seems to perform exactly the same as nylon version

    Best would be to get a feed back from a spectra Jordan owner.
     
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  6. jonr
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    jonr Senior Member

    In a 60 kt wind, you might head into it at 5 knots or run with it at 20 kts.
    That's about 2.5x the force. 30 degrees deviation can also double the force (increased windage).

    Seems to me that a drogue also provides significant downward force - ie, when you are titled down 45 degrees on the face of a wave, the drogue (off the stern) is helping to prevent pitchpoling or broaching.
     
  7. RHough
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    RHough Retro Dude

    Thanks for that. When I built mine 3 years ago I had never heard of anyone using Spectra. Trying to find good quality Nylon double braid was a challenge. It would have been much easier to use Spectra.

    Do you have a link to the company that sells the Spectra versions?

    R
     
  8. gonzo
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    gonzo Senior Member

    As much as I don't care much for drogues, Spectra has no stretch and would defeat the purpose.
     
  9. BeauVrolyk
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    BeauVrolyk Sailor

    Mark,

    I know a "BS" call when I hear one, and no offense was taken. I've sailed in a number of 60+ knot blows and not seen seas like I saw off of Oregon that time. I was pretty young, so the memory may have enlarge. But, as the data from the storm of 1962 says it can blow true hurricane force out there and there's nothing in the way up wind for a long long long fetch. I think what makes the Washington and Oregon coast so tough is the combination of along fetch coming out of Alaska, no ports to hide in or islands to hide behind, and a counter current that runs up the coast at times in the winter. I seem to remember it being called the "Davidson Current", described as:

    "During the winter, a weak countercurrent flows north- westward, inshore of the southeastward flowing California Current, along the west coast of North America from Baja California to Vancouver Island. This is called the Davidson Current."

    You'll find this described in more detail here: http://www.irbs.com/bowditch/pdf/chapt32.pdf

    I am pretty certain that I've seen the boundary between the California Current, going with the wind, and the Davidson Current, going against the breeze. It's a gigantic version of what we see in the San Francisco Bay when the wind is pushing against and Ebb tide vs running along with a Flood. That time in the '62 we were too close to shore, because we wanted to try and make port, and it took us a long time to get back out to sea. Once we were about 70 or maybe 90 miles off shore the water became much flatter. My guess is that we were in the Davidson and didn't know it. It's the only time I have ever seen waves that big and I hope to never see them again. My other reason for thinking that these were wind-counter-to-current waves is that they were so steep! They were like vertical walls.

    I'm with you, I hope to never see those waves again - ever!

    BV
     
  10. bntii
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    bntii Senior Member

    In speaking of Jordan series drogues:

    My thought as well but in talking to Ace sail makers it appears this is not the case.

    His explanation is that the elastic properties of the series drogue is provided by the change in position of the drogue in the water, from a j curve behind and below the vessel to straight back.
    Apparently the highest load case provided for in the design is not dependent on a elastic response of the line.
    He reports that this was all outlined by the designer before he passed away.

    Unless I hear differently before I get it purchased, I will go with the spectra version to save weight and bulk.
     
  11. RHough
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    RHough Retro Dude

    I wish that had been explained to me when I built mine! The bulk/weight of the Nylon rode is considerable.

    When the relative ease of splicing the cones into 12 stand Spectra is considered the time saved compensates for the added cost of the line.

    I'm going to ask Dave at Ace for Spectra sizing used to replace the Nylon and for his permission to post that information here.

    R
     
  12. jonr
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    jonr Senior Member

    You might look at "Amsteel Blue" - way lighter/thinner/stronger.

    I see that what is used for weight on the end doesn't matter - might be nice to use an anchor. Hopefully won't matter, but if it does get shallow...
     
  13. RHough
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    RHough Retro Dude

    That is just what I do. I rig my lunch hook and a bit of chain as the weight.
     
  14. claverton
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    claverton New Member

    Hi BeauVrolyk

    Thank you for your considered reply. I'm not an expert on this topic but it is of great interest on various levels to me, not the least that I expect to be sailing into areas where this topic is very relevant.

    I went to the web site you've referenced, thanks for that. I would like to point out that this is a web site promoting the product, not an independent source.

    Sure, the site does promote the product in an intellectual sense, but the Jordon family make no money out of the product, the design of the Jordon drogue is in the public domain and there is no patent over it. There is a sailmaker on the bottom of the site who makes them, but you can get them made up anywhere or make them yourself. Jordon donated the IP of the product the the sailing community.

    That said, some of what he's saying does make sense. However, there are a number of factual errors.... This means that the absolute fastest the water could be moving would be at the speed it would pick up falling about 12 feet. The water isn't falling the entire height of the wave, but only the height of the breaking crest. This is a speed of about 15 miles per hour. As an example, people jump off single story buildings all the time without hurting themselves.

    Incorrect (with respect). The breaking part of the wave will move at the same speed (or slightly faster) than the wave speed. If the wave is moving at 30mph, then the breaking part of the wave will be moving at atleast 30mph. If you are for example a body surfer and catch a breaking wave, you will be moving at the speed of the wave. A yacht caught within a breaking wave will be moving at the speed of the breaking wave.


    But, there's a second problem with this. Water is not solid. As a result, as it falls it breaks up into foam. Again, observe the top of a wave at the beach. The foam is billions of small droplets and globs of water that are trying to move through the air. The movement through the air is what breaks it up and as the water attempts to travel through the air it slows down. Of course it also speeds the water up, you see the foam moving along with the wave at the beach, but that foam is NOT ever going faster than the wave. If it were, the foam on the waves would arrive at the beach first, long ahead of the wave. It doesn't do this.

    We agree with each other. The foam is travelling at the speed of the wave.

    On the basis of these simple observable facts, which you've seen at the beach, you know that this persons calculations are simply wrong.

    A big call. The person in question was a senior aeronautical engineer and lecturer, and got into drogue design when he retired.

    While gigantic breaking waves are terrible - we'll all agree - the danger is the weight of the water crushing the boat and the circular action causing the boat to roll over. It is not the speed of the wave or boat, and it is certainly not crashing into the trough.

    The speed of the breaking wave is the issue. A yacht travelling with the sea with drogue off the stern will rise over the breaking swell at very slow speed. But in serious stuff without drogue if it gets çaught in the break it will for a period of time be travelling at the speed of the wave. The winston churchill was an extreme case. but rollovers >180 degrees are not uncommon in seas such as the southern ocean and to my mind the series drogue off the stern is the most sensible strategy to prevent knock downs and rollovers. Their disadvantage is they are hard to retrieve, but it is a minor disadvantage.
    Regards Ian
     

  15. RHough
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    RHough Retro Dude

    Here is the reply from Dave at Ace sailmakers:

    This gives a 70% weight savings and a 75% reduction in the bulk of the line.

    The JSD for my boat is a storage problem, I keep it in the lazerette in a bag packed like a spinnaker so it is ready to deploy. The bag is heavy and unwieldy, saving about 50% of the total weight and bulk would be great.

    Thanks to kistinie for posting about a Spectra version! There is always something to learn here!
     
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