Water accumulating at the transom while at rest

Discussion in 'Boat Design' started by Loveofsea, May 19, 2007.

  1. Loveofsea
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    Loveofsea New Member

    I maintain that the most substantial cause of small vessel capsizing can be attributed to the buoyancy characteristics of a hull whereby water runs to the transom while at rest. This design flaw is common to virtually all small production boats.

    If manufacturers were to redesign the hull to shift the moment from the transom to the center of the hull, it may save lives in the event of unintended water intrusion.

    I would appreciate any arguments to the contrary.
     
  2. Guillermo
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    Guillermo Ingeniero Naval

    Do you mean small open boats....? With outboard engines?
    Under the CE RCD open boats under 6 m are obligued to be buoyant when flooded. I don't know in the USA. Over 6 m they use to be partially decked and have self-draining cockpits. For these last the use of authomatic bilge pumps is quite common.
    Most of the open small motor boats with outboards are planning ones, so they need the kind of hulls they have, and weight when empty tend to concentrate backwards.
    Nowadays cabined planning ones use to have big wide sterns and CG more forward than open ones; in fact some of these boats float with a somewhat nose down attitude when empty. But reasons for this designing has little to do with flooded flotability concerns.
    I'm afraid I don't realize exactly what's your point....
     
  3. messabout
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    messabout Senior Member

    Loveofsea;
    You are correct in the case of most, perhaps not all, small open outboard boats. I have demonstrated this sinking phenomena on model boats several times. None of the episodes were intentional for the sake of meaningful research. Additionally, I have seen this happen on full sized boats

    Enclosed transom extensions that straddle the engine might help. The scheme involves putting some positive bouyancy aft of the the power plant such that the boat does not assume a transom down attitude when swamped. Some balancing must be contemplated. The boat is just as likely to sink if the bow end becomes seriously flooded and that end has too much weight, as in heavy ground tackle and other accumulations.

    It would seem that both ends need some watertight compartments and careful balancing. Carried to extreme, there must be a need for bouyancy chambers along the sides too.

    A while back there was a thread that dealt with transom straddle extensions (squat boxes). Some of the participants thought that those would be a great place to put batteries and fuel tanks. Of course that negates the whole safety aspect.

    Go to any small boat dealer in Florida and observe the 16 or 18 foot boats with huge 150 and 200 HP engines that weigh too much. Not only that but the coolest ones have platforms high above the engine. People stand on those platforms to scan for fish and sometimes for poling the flats. Worse than that, the dealers all seem to sell little narrow assed tin Jon boats and rig them with anything from 20 to 50 HP engines. These things are famous for swamping when the boat has been planing and the throttle is suddenly chopped. I shudder at the sight of those suicide boats. This past weekend just such an occasion arose in Tampa Bay. Two guys spent 11 hours in the water before the Coasties saved them from dwelling in Davy Jones locker. They're lucky to have survived.

    So Guillermo, All those tales that you've heard about crazy Americans are true. We are also dead set against design regulations because we don't like legislation that tells us what we can and cannot have.
     
  4. charmc
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    charmc Senior Member


    In fact in the US there are similar regulations. Under Section II, Title 46 of the US Code (Federal Laws), enacted 1971, latest revision 2003, USCG regulations for small boat safety require that outboard boats 20 ft/6 mtr long and under have sufficient flotation built in and located so the fully loaded boat, including motor and passengers will float "approximately level" when flooded, with limitations on heel angle even if passengers move to one side of the boat. Are you saying that boats are being built which are not in compliance? I haven't purchased a boat of this size in years. The question may sound naive, but my impression was that all manufacturers were in compliance.
     
  5. kengrome
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    kengrome Senior Member

    These are requirements for commercial manufacturers only, not for home builders, and they apply only to new boats sold to the original owners. If you buy a boat that a home builder constructed, or if you build one yourself, or if you buy a second hand commercially built boat, it does not need this flotation. That's my understanding of the regs anyways.
     
  6. charmc
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    charmc Senior Member

    US Coast Guard Publication, "Safety Standards for Backyard Boat Builders"

    http://files.dnr.state.mn.us/education_safety/safety/boatwater/backyardboatbuilders.pdf
     
  7. kengrome
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    kengrome Senior Member

    This publication was created as a set of guidelines or safety suggestions for individuals to use when building their own boats, it is not a set of regulations for individual boat builders.
     
  8. charmc
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    charmc Senior Member

    "We refer to people who build a boat for their own use as "Backyard Boat Builders". They are expected to comply with the same safety standards and administrative regulations as regular boat manufacturers."

    http://www.uscgboating.org/about/faqs/regulations.aspx

    Looks like I am correct and you are wrong, Kengrome,





    Until I read further.

    "Failure to do so could affect their insurance coverage and make them vulnerable in a liability suit."

    Not much in the way of enforcement here. You're right, they really aren't much more than guidelines and suggestions. :(
     
  9. Frosty

    Frosty Previous Member

    Just putting the regs aside a minute. The thread was--Water accumulating at the transom while at rest.

    So you dont like water accumulating at the transom? where do you want it to accumulate?--thats where the drain bung is.

    If you take the bung out and get it on the hump it will drain itself.

    Do you want it to sink horizontaly?

    What do you mean unintended water intrusion?--rain? -- wave?

    As Guilermo says --whats your point?
     
  10. kapnD
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    kapnD Senior Member

    Interesting to note that the CG assumes the average adult is only 160 lbs. Not a realistic figure when compared to me and my usual crew!
     
  11. charmc
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    charmc Senior Member

    The investigation into the capsizing of a tour boat on a lake in the Northeast a few years ago found that a contributing factor in the tragedy was the fact that the passengers were " quite a bit heavier, on average" than the 160 lb standard used to calculate stability when the boat was built. That standard really needs to be changed.
     
  12. messabout
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    messabout Senior Member

    There are, in fact, meaningful regulations that prescribe the requirements for commercially built boats. Apparently those regulations are being systematicly ignored, or the builders are unaware of the regs. I am thinking of relatively small recreational boats here.

    I dare say that the majority of people who participate in this forum are knowledgeable boatmen. Many of you are engineers, physicists, naval architects, and just plain smart boat builders and users. Contrast that with the masses of people who actually buy and use boats that the market offers. The majority of those innocent people have not a clue about stability, seaworthiness, power application, and general safety rules.

    I have a close relative who lives in another state. He is an intelligent human being and a genuine nice guy. During a visit, he suggested we go boating in his Z drive 23 footer. I said: where is the switch for the bilge blower? He said: what is that? Yikes! Nice guy that he is, he did not know sh*t about boats. He would not know a safe boat from a hole in the ground. Manufacturers can sell him anything as long as it is sexy looking and it goes fast.

    The ubiquitous Jon boats, that I mentioned, do not have sufficient flotation to support themselves in such a way that the users could self rescue. No way ? With a hundred pound motor they'll sink like a rock. Stern first of course. Add to the problem the propensity for the users to add swivel seats mounted well above the thwarts. These guys know nothing about metacentric height or archimedes principle. They just want to go fishing. Most are decent citizens that do not deserve the reckless abandon with which the manufacturers risk the users lives.

    Jack Frost you are right. Take the bung out and get the boat on the hump and it will drain. Thats all very well when you have a few pounds of water in the boat from rain or spray. That process falls short when you have taken a big glob of green water over the bow or have been caught in the wake of a big boat. If you ship a couple hundred pounds of water you are in deep trouble. The water may tend toward the stern and the farther it goes aft, the more weight is concentrated aft of the CB and as the boat is depressed at the stern then more water rushes aft until.....
    We'd need a much bigger drain opening than a conventional bung.
     

  13. Frosty

    Frosty Previous Member

     
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