Dangers of open bow 'heavier than water' boats

Discussion in 'Boat Design' started by parkland, Feb 19, 2015.

  1. parkland
    Joined: Jul 2012
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    parkland Senior Member

    Hi guys, me again.
    I had a question, that I can't seem to find the answer to.

    OK, with open bow boats, what danger factor is faced in reality, when it comes to swamping the craft?

    I know a lot of smaller pleasure boats have foam installed in the boat, so in a way they are not sinkable.
    But, some commercial boats, and small pleasure boats made of steel or aluminum, have open bow designs where there is seating or open deck.
    Even going down to tiny aluminum boats, the entire boat is just wide open.
    So there are lots of boat designs, where there is no flotation foam, and if swamped, the boat could just sink to the bottom.

    I guess I am just wondering, is this design considered more dangerous, or is the hull height engineered to be higher than say if the hull was covered and didn't allow water to enter?
    It seems like a dumb question, I'm sure an open bow would sink easier in lots of situations, but just wondering if the design is considered just as safe as a covered bow if engineered right, or if it's more "gotta watch the bow on this boat, she'll sink if we swamp it".
    The reason I even ended up thinking about this, is that for a smaller boat, to make the hull covered, means to get inside to repair or service anything, there would be barely any room.

    Consider a 24 foot steel boat, with 8 ft bow section, 8 ft cabin, and 8 ft stern section.
    Maybe the hull would be 36" to 48" from keel to side rail. If there is a floor welded on top, water washing over would run off the sides, but the space and height inside the hull and stern would be hard to go inside to do anything.
    If the bow and stern is open, access is a lot easier, but too much water = you sink.
    With the bow and stern open, the center of gravity would also be lower, along with weight. The floor installed on the hull bottom would be simple and removable, and the hull sides eliminate the need for railings.

    So basically, the way I see it, open hull design is better, until a wave comes and floods the boat.
    I have seen boats built like this though, but just wondering how dangerous it is considered, over having the decks covered to protect against getting swamped.

    I worked commercial fishing on a open hull design boat, much like I described, and it had zero flotation foam, and other than a 12v bilge pump getting rid of water that splashed in, there was never an issue. It was a home made aluminum boat with an outboard, about 28 ft and 14 ft wide, 44" from keel to top sides of hull. It seemed to handle about 3.5 ft waves without even worrying about any water washing into the hull.

    I know if comes down to design, what body of water it's used on etc, but generally speaking, how dangerous is an open hull design compared to a hull with the deck over the hull to prevent swamping?

    Is there a statistic somewhere that says "open hull boats are 10x more likely to capsize than closed hull boats of the same size."? Or something similar?
    Is an open hull boat without flotation considered a death trap? Is it considered perfectly safe? The boat I spoke of that I worked on, has been around since the 60's and is still floating today, on a large lake. Obviously it's not a terrible boat.

    Just wanted your guys opinions or thoughts.
     
  2. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    A decked over boat is only invulnerable to flooding if the decking seals the boat off. Other than that, decking makes the boat less vulnerable to flooding.

    For instance, a bow deck may keep water out of the bow of the boat, but not its mid hull. In fact, the bow deck could simply dump whatever water come aboard into to the mid hull. This is why you see sail boats, which have bow decks, with splash boards. The splash boards are to divert the water over the side.

    Small sailboats are often half decked because of the desire to keep the free board ( hull above the waterline) low to reduce windage. There are a number of small sailboats which have very little of no decking. They usually have higher sides (more free board). So, as the free board increases, the need for decking decreases.

    A major motivation for adding decking on a small boat is to provide dry storage space. Decking also tends to strengthen the hull.

    A decked boat may look safer than it really is.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    There is a very widespread belief among boaters that "high sides" keep the water out, and thereby make for a safer boat. This is a simplistic, and not especially accurate assumption. In fact, it is sometimes a negative, as it increases windage, and raises the centre of gravity, and even sometimes leads to people falling out of boats because it is a stretch to reach down to the water ! Which it not to say that it is good to have little freeboard, but like everything with boats, you have to look at the whole design, and its intended usage, to arrive at the best compromise. You have the option of a self-draining cockpit to keep water out, but that is not always desirable either. So much depends on the whole picture of what the boat will need to be used for, and where.
     
  4. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Your write about swamping by waves to the point of sinking, which may not be the greatest widespread consideration for most boat applications. Doesn't make sense to build all boats for the highest possible wave- which would be sub design. There are other factors which may be of higher consideration for wave swamping, like loss of power/maneuverability etc. Taking waves from the sides or stern may be more of an issue than having a covered bow.

    FWIW.

    PC
     
  5. Rurudyne
    Joined: Mar 2014
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    Rurudyne Senior Member

    That or an X-bow craft.

    The sub would be prettier. ;)
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    With small boats, the risk is less about water being taken aboard, and more about being overwhelmed by waves and high winds. Of course, having free water on board only increases that danger, but many small boats go over with the first ingress being when they get turned over, by, for example, breaking waves.
     
  7. philSweet
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    philSweet Senior Member

    Really small boats will respond fast enough to follow the waves. But at 24', you are somewhat in no-mans-land from a seaworthiness point of view. It is a very popular and affordable size, but very difficult to make seaworthy. For a sailboat, it is usually too big to beach and too small to handle a dingy. It is also a challenge to provide the boat with everything it needs to fend for itself. It's also a challenge to keep your junk in the boat (meaning not lose important stuff like navigation, communication, charts, food, water). My take is that the boat ought to be able to fend for itself, to be left on a mooring for a couple of years without attention and do ok. The idea that the boat needs a couple of people to keep it floating doesn't appeal to me. If it's a lifeboat and has 40 people on it, then fine, 40 people probably can keep it floating. The list of really seaworthy 24'ers is a pretty short one.

    Then there's Jerzy - http://www.booksandbooks.com/event/jerzy-tarasiewicz-open-boat
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    The "nut behind the wheel" is, of course the crucial part of the boat, that can make up for many deficiencies, or negate any inherent advantages.
     
  9. portacruise
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    portacruise Senior Member

    Add self bailing cats...
     
  10. parkland
    Joined: Jul 2012
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    parkland Senior Member

    This is just the thing, the human variable.
    The thing with the closed in hull, is that even if it's not water tight, the bilge pump has a chance to recover.
    With an open bow, or open hull, if a wave makes it's way inside, you could be sinking in a matter of seconds.

    I find myself surprised that I really had not considered this danger before, but on the flip side, there are plenty of boats just a single swamp away from being on the bottom, and they're still here.

    I was reading last night, that most boats sink while parked, from water line issues, or through hull fittings.
    Problem with that, is that while parked, chances are you can just jump off, or likely nobody is even on it.
    So most boats sink while not under supervision.

    It would be nice to have a product or design for an open hull, that includes some safety device that could provide emergency flotation, but not be permanent like a deck covering, or welded shut compartments which are hard to enter.
    Sure, there is foam, but then it's taking up space, and making anything underneath hard to access.

    To make the deck or cabin self bailing, means you create all sorts of cavities and closed spaces which are hard to access.

    Whats worse, statistically only 8% of boats end up on the bottom from swamping. So, would it make sense that an open hull is better because inspecting condition is easier?
     
  11. Rurudyne
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    Rurudyne Senior Member

    My cats don't do much of anything besides sleep,eat and poop. :p
     
  12. portacruise
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    portacruise Senior Member

    Some ideas for emergency floatation discussed in this thread:
    http://www.boatdesign.net/forums/boat-design/unsinkable-boats-realy-51641.html

    Perhaps something like the inflatable PFD concept that inflates to the top outside perimeter might be the way to go?

    PC

    PS: Rurudyne most boats including catamarans do the same: sleep (average use 3X per year?) eat (your $$$) and poop (disperse smoke, oils, as well as some biodegradables)


     
  13. Rurudyne
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    Rurudyne Senior Member

    Well, yeah. Boat is an anachronism for "Break Out Another Thousand". (old joke alert!)
     
  14. messabout
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    messabout Senior Member

    The design of the boat plays into the probability of having, or not having, the boat become swamped. Heavy boats need different configurations than light boats. Where and how the boat is to be used is also a dominant consideration when design is contemplated. Does the boat have a wide transom, is it a double ender, rounded bottom, hard chine, and more. A boat whose roll period happens to be the same as the wave interval is in trouble. How the boat is loaded plays into the equation, a bow heavy boat in big seas will invite trouble for example. Keeping weight, as nearly as possible, concentrated near the middle of the boat will let her be lively, less likely to scoop up a green one........................There are too many variables.

    Not to forget that skillful boat handling is one of the major factors, maybe even the most important one.
     

  15. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Anachronism, acronym, sounds like a malapropism ! :D
     
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