Lost power in heavy seas - which hull shape?

Discussion in 'Stability' started by kach22i, Jan 8, 2008.

  1. kach22i
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    kach22i Architect

    Lost power in heavy seas - which hull shape?................. will a retractable keel help?

    Set-up context:
    Picture a flat bottom boat (planing/ sail or motor) which has lost power in heavy seas.

    Comments/assumptions:
    Going to heave up and down like a cork no matter what, right?

    A) Add RIB-like buoyancy collar and you just keep yourself fom sinking, even when inverted (capsized), right?

    B) Add a Retractable Keel and it gives you ONLY some "lateral" stability, right?

    Question(s):
    1. Does it matter if the craft has a mono V-Hull at the bow?

    2. If at idle (like a life raft), would the best shape be all sides of the boat sloping down? Picture a cone pointing down.
     
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  2. Pericles
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    Pericles Senior Member

    Lost power in heavy seas - which hull shape?.

    Gunboat 62 with dagger boards up and streaming sea anchor from bow, well away from land, or sail down wind under bare mast streaming a drogue from the stern to slow the vessel. Serve cocktails and tasty snacks, whilst watching a movie. Wind generator still works, I assume? :D

    http://www.deltayachtsbrokerage.com/news/YWorld_gb62.pdf

    Pericles
     
  3. kach22i
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    kach22i Architect

    I've never heard of "dagger boards" so I did a Google search, this is an odd fish.

    http://home.att.net/~t.l.hansen/Brick_Construction.htm
    [​IMG]

    These look huge!
    http://chepog.wordpress.com/page/2/
    [​IMG]
    [​IMG]
    [​IMG]

    DAGGERBOARDS VS. KEELS – WHICH IS BEST FOR ME?
    by Phillip Berman

    http://www.multihullcompany.com/Article/Daggerboards_vs._Keels
    ...............yikes!

    Daggerboard
    From Wikipedia, the free encyclopedia
    http://en.wikipedia.org/wiki/Daggerboard

    Sounds and looks like a foil to me. What am I missing here?
    .....................................................

    On the other term:

    Sea Anchor:
    http://www.sea-anchors.com/
    http://pubs.usgs.gov/sir/2005/5183/index_toc.html
    [​IMG]
    Parachutes Save a Yacht.....true story
    http://www.duckworksmagazine.com/06/howto/parachutes/index.htm
    [​IMG]
    [​IMG]
    I want to know more about dagger Baords.

    I want to know more about the proposed streaming sea anchor from bow. Why "streaming", and why at the "bow"?

    Interesting stuff, please tell me what you know or point me in the right direction.

    Cheers, George/kach22i
     
  4. Pericles
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    Pericles Senior Member

    The English phrase, streaming a drogue or sea anchor means it follows behind a boat. If streamed from the bow it keeps the boat pointed upwind and slows the backward drift of the boat. There are a number of types.

    http://books.google.com/books?id=LR...ts=HVZFmCao91&sig=dWPcwTZUKZn5PSdFzSjrFZGVCmw

    http://books.google.com/books?id=NB...ts=Pwj689cbrV&sig=RjP8PLZ5EbS6WPYXeg8JeEIGQ_I

    As for dagger boards, the sites you list describe them very well. Foil is another name but it's too generalised a word, I think. There are hydrofoils, Bruce foils and centre boards.

    http://en.wikipedia.org/wiki/Bruce_foil

    http://en.wikipedia.org/wiki/Centreboard

    The cost of dagger boards must be seen with respect to the large gain in performance. Gunboat 62 is a $2 million vessel. :D :D John Shuttleworth designed catamarans with only one dagger board in port hull.

    "This design, like all my cruising designs uses only one retractable daggerboard in one hull. Some years ago I conducted a tank test to find out the validity of this idea, and the test showed that one board in one hull had less drag that one in each hull. The only difference was a loss in tacking angle of 1.5 degrees when the board was upwind. I believe this loss is mostly compensated for by the saving in weight of a board and case.

    The daggerboard and rudder are both designed using NACA sections. The balanced rudders use a section that is tolerant to high angles of attack, while the daggerboard which is mostly at a maximum angle of attack 5 to 6 degrees, has a section which has lower drag and better lift to drag at 5 degrees than the rudder. The advantage of a daggerboard on a multihull, as opposed to a keel on a monohull, is that it does not have to be very low drag when going straight through the water, since it will be retracted when going downwind.

    On this design I have included a shallow stub keel on each hull to protect the propellers of the twin engine installation. The rudders kick up so that the draft of the boat at full displacement is only 0.83 metre ( 2 ft 8 inches ) fully loaded."

    http://www.john-shuttleworth.com/Articles/52AeroDesign.html

    All the best,

    Pericles
     
    Last edited: Jan 9, 2008
  5. masalai
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    masalai masalai

    Many sensible ideas and thoughts have been demonstrated along with a few frivolous posts to add a bit of humour.

    Regardless of the style (heavy/light, mono/cat/tri etc), sensible approach to seamanship and being prepared is not to be overlooked.

    Avoid disastrous sea conditions whenever possible & retreat to a good bottle of your favourite booze and hide inside a vessel like a cork - literally. :D
     
  6. longliner45
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    longliner45 Senior Member

    my computor is slow today,,so I didnt read everything ,,but the drogue is interseting,,,,I have used 3,,,5gallon buckets with the same effect,,,,,7 to one ratio works well,more scope the better to a piont ,also the lighter the boat the better ,,if you had a barrel of water and put a cork in it and shook it around ,,the cork bobs at the top,,,if you put a heavy piece of wood in the same barrel and shook it around the same way you will see it bobs and gets wet all over,also air tight compartments are great for unused area ,,if any ,,longliner,,its all in the design
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

    If using buckets make sure they are "reinforced" model. Just a bucket will eventually fail..
    Light boats tend "rodeo" way too much. More ballast, raw water tanks etc makes it more comfy :D
     
  8. Pericles
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    Pericles Senior Member

    In the same way I would not trust the safety of any boat I owned to inadequate ground tackle (nothing but a Rocna) I would not venture out without other correct safety equipment such as a suitable drogue and a proper sea anchor. No lash ups for me.:D

    The two extracts I linked to, name some products that have found favour with the boating community. Two observations "there is hardly a sail boat of any design that will lie quietly bow-on to the seas in a storm behind a sea anchor---"

    Then "Multihulls will also lie peacefully to an unyielding sea anchor." :D :D :D

    See paragraph headed PACK WITH CARE http://books.google.com/books?id=LR...o91&sig=dWPcwTZUKZn5PSdFzSjrFZGVCmw#PPA198,M1

    Pericles
     
  9. kach22i
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    kach22i Architect

    Lots of good information, thanks guys.
     
  10. longliner45
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    longliner45 Senior Member

    WHAT NO LASH UPS?dont sailors tie knots anymore?I rode many tropical depressions and a few hurricans out,,,,,with good old buckets tied to a rope,,,7 to 1 scope,,counting your freeboard,,,,,never had a bucket fail ,,,,cmon,,,,longliner,,,,,,,,,buy the way,,,,ever try bailing water out of a sinking boat ,,with a drogue?
     
  11. charmc
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    charmc Senior Member

    John,

    Maybe you commercial fishing guys have super strong buckets, but I've never seen one that is all that strong. I've jury rigged sea anchors, and made drogues. The multiple small drogue concept works. I'm not saying there aren't any good buckets, just that I haven't seen any.

    If I were planning to spend weeks or months beyond sight of land, though, I think I'd want to have a purpose designed system with tons of good reference data. I can jury rig a good system if necessary, but if things really go to hell, I want to rely on something made by guys who are much better at it than I am.
     
  12. longliner45
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    longliner45 Senior Member

    I see your point charlie,,,,but buckets are multi purpose ,,and with room on boats the way it is ,I personally have never had a bucket come apart,,and I have used them hard,,,Iv trusted my life to parachutes,,,and maybe even will buy a drogue,,,I also used nylon rope ,,it gives a little ,longliner
     
  13. PAR
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    PAR Yacht Designer/Builder

    I would think the handles would give on the buckets in any rough go. I've had them go just full of paint.

    The key to survival conditions Kach22i, is brains, tactics and knowing your vessel more then hull type, with or without daggers (or any appendages for that matter), sea anchors, etc.

    When conditions deteriorate enough to warrant drastic steps on the boat and your butt, to insure or increase your likelihood of survival, you have several options.

    Knowing what these are, when to employ them and how effective they'll be under a given set of conditions, requires experience, practice, knowledge of your boat, it's location and understanding the storm your in.

    Tossing a drogue on a lee shore for example, is a great way to end up as the following morning's front page headline. There are things you can do, but just doing something generally isn't the best thing.

    The best thing is keeping a cool head. This is key in all emergency situations and very difficult to do, especially maintain over a long period, such as during a storm with a broken boat.

    I've been in some pretty nasty and scary situations, including a bad hull breach with a fire on board at the same time. You have to stay cool. Decision making is very challenging under these types of pressures, so this is where you must rely on muscle memory gained from practice.

    Think I'm kidding? Try a MOB drill for the first time in 20 foot seas with 40 knot winds and see if you'll be successful at bringing that person back aboard (not likely). These drills seem unnecessary when you do them, but trust me folks, when you need them, you better have a clue about yourself, crew, procedures and equipment or people will die.

    This is true of fire suppression, rigging failure, engine failure, hull breaches, collisions and all the things that can screw up your day.

    Prepare yourself, crew, test procedures and equipment and insure they work with practice.

    In short there's no simple answer, no one boat type, no single piece of gear or technique that can be the save all for your butt, especially if you've no-brained yourself into a "catastrophe spiral" (of which there is usually no escape). This catastrophe spiral is common among disaster investigations. It's found a cascade of multiple errors, compounding the events, cause an inescapable sequence to occur that ultimately deeds badly for those involved.

    This is why professionals drill their crews, emergency organizations practice their techniques and the prudent skipper gets a clue before heading into deep water.
     
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  14. charmc
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    charmc Senior Member

    Well said. You expressed some of my thoughts, but more clearly. You're right; knowing your vessel intimately is more important than the particular type of hull.

    Yup, when you find yourself in a true emergency situation, having good instincts and body memory to take over and begin the appropriate response immediately, despite the conscious mind's temporary paralysis while it goes through the "Holy sh_t" routine, can make the difference, literally, between living and dying.
     
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  15. Pericles
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    Pericles Senior Member

    PAR,

    Absolutely correct. Failure to plan is planning to fail.

    Regards,

    Pericles
     
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