Nutin but foam

Discussion in 'Boat Design' started by tarrysailor, Dec 2, 2004.

  1. tarrysailor
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    tarrysailor Junior Member

    Casting the hull as a single piece

    What makes hulls expensive is that they are pieced together out of small parts, each part laborously shaped and attached. But if we cast the hull as a single piece, we bypass the majority of the labor and we also get a single-piece hull that's inherently watertight. In other words, we save a bunch of money. Does that catch anyone's interest?

    Casting a bare hull should be quick, a single weekend's work. I guess a mold could be reused and you could turn out another hull every weekend.

    I accept the criticism that the cabin-on-top is a dumb idea. I guess it's better to have your brains and valuables on the inside.
     
  2. Nels Tomlinson
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    Nels Tomlinson Junior Member

    No, I haven't seen them in person, but I've seen some of Etap's marketing brochures. Their approach seems to be to put quite a bit of the foam up the sides a way, and leave a full-headroom walkway down the middle. That means that if you do somehow fill the boat, it will settle a bit. It will fill if holed below the waterline, and won't self-bail. On the other hand, it will still be more or less sailable when filled. It's a very sensible approach.

    The original post talked about a boat-shaped foam raft, and about the Southern Ocean. The thought of having knee-deep, 0-degree-C water sloshing about inside an Etap boat, with huge seas outside threatening to pitchpole you again, makes the foam-filled bilges idea sound less bad. For less extreme conditions, the Etap approach might be the way to go.

    I agree that their brochures show very livable interiors, but the foam must crimp the storage. They have to have a volume of foam equal to the submerged volume of the boat. That's a fair number of cubic units which can't be used for storage. Don't they use foam cores? That would account for a lot of the foam, but I wouldn't have it for a boat intended for rough service.

    Given that you need a larger boat to regain the storage space for voyaging, the all-metal construction begins to seem plausible, even for a light-displacement design.

    Of course, if the choice is between going in a small, cheap, sinkable boat or not going in a big, expensive, unsinkable boat, going sounds better.
     
  3. mattotoole
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    mattotoole Senior Member

    Aren't Macgregors foam-filled too?

    The only molded styrofoam boat I can remember is the Snark, which was like a hollowed out, rounded Sunfish. I think they were sold through the Sears catalog for awhile.

    Note -- Boston Whalers are the heaviest thing of their type that I can think of. Foam seems light, but giant blocks of it are heavier than you might think. And two hulls are much heavier than one, with a lot of extra material where it isn't needed for strength.
     
  4. Nels Tomlinson
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    Nels Tomlinson Junior Member

    Tarrysailor, I think that you could mold the boat shape, probably with a hollow interior. I think that you could probably make it strong enough to stand up to the strains of bobbing about on the waves with you and your food and water inside.

    I'm not sure that it would be a backyard project (though I'm certainly not knowledgeable about this, and could be wrong). I think that you'd have to cover the outside (and probably the inside) with something to protect the foam. Your mast will impose point loads, if stayed, and will still put some large, localised loads on the structure if unstayed. So would cleats, mooring bitts, et cetera. I doubt that the foam will be able to handle that in a big-enough boat, so you'll need some reinforcements in the foam. I think that by the time you get something that you can sail away, you'll have a lot of small parts, just in the hull. As Mattotoole pointed out, it would probably be quite a heavy hull, too.

    Then there's the fact that only a fraction of the cost of a boat is the bare hull. Better places to cut costs might be in the interior finish, and the rigging.

    In my home, we have painted sheetrock (plasterboard) walls, and cheap wood and masonite furniture. Painted exterior-grade plywood would work fine in a boat, and could be a step up from what I have at home. There's no need for teak and varnish.

    Marchaj demonstrated that low-tech rigs like the crabclaw and the sprit can easily equal the performance of a burmuda rig (see his paper Planform Effect of a Number of Rigs on Sail Power, in Proceedings of Regional Conference on Sail-Motor Propulsion, 1985), and they can be built far more cheaply than a high performance, high tech burmuda rig. Those low tech rigs typically have a lower center of effort, too, which might be a good thing for the sort of hull we're discussing.

    I like the idea of an unsinkable boat, I like the idea of foam flotation and I really like the idea of a cheaper, quicker-built, stronger, safer hull, but I'm not sure that your cast-foam idea is going to deliver. I hope that you'll prove me wrong, but I'm not optimistic.

    If you want to get out on the ocean quickly and cheaply in an unsinkable boat, get a small, older fiberglass boat, with a trashed rig and a trashed interior. Fill the bilges with foam to the waterline, reinforce the hull-deck joint, and off you go, with very little money invested.
     
  5. tarrysailor
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    tarrysailor Junior Member

    more foam = more volume = more length = better sailing

    I think we're all on the same wavelength, here --- a ship you trust the lives of yourself, family and friends to, shouldn't sink.

    Foam takes room. Let it. That means the boat has to be bigger. Let it. And from everything I've heard, it's better to have 'bigger' mean longer. That improves top speed and means for a more seaworthy ship, too. So a result of making the ship safer, we get a better handling ship. That means we are making the right choices and decisions all along.

    On the other hand, look at what happens if we make the wrong choices.

    Every containership that puts to sea carries hundreds of containers that are not securely attached. Many of those containers will float a few inches above or below the waterline and you can't see them. They can be anywhere, even in open water that is apparently safe. I've read about boats that hit them. With no warning whatsoever, a sudden crash throws everyone forward to slam against a wall, a mast or whatever is in front of them. A hole is torn open in the hull a foot wide and three to five feet long. In thirty seconds to a few minutes, the boat fills with water. There is no time to close hatches, no time to grab life perservers, no time to launch lifeboats. If your boat will not float filled with water, you are going down right then. If it will float, you had better hope it is warm water rather than icy water. Five minutes in icy water, even inside a boat, and your hands will not work.

    Incidently, I'm an accomplished woodworker, a third-generation carpenter, and I can easily build a boat from the raw tree, if I have to. And, in case you didn't know it, it is amazingly easy to cast your own metal parts in your own back yard, using nothing more complicated than old buckets, clay pots, propane and sand. You can find out about it on the internet.

    As for high-tech versus low-tech, I agree that high tech makes better ships. If you are Bill Gates, you pick up the phone, you say "I want a safe, modern, one-hundred foot ship," and you slam the phone down. Bill Gates can afford high tech. The shipyard that does his ship can be trusted to do an outstanding job. He will get a better ship.

    For those of us who can not afford the price, high tech means no ship. There are plenty of shipyards that churn out pieces of crap as fast as they can and can't be trusted to do any job right. That's the only kind of shipyard I could afford. No wonder people like me are wondering if maybe there isn't a better way, like maybe using rock foam as a building material that we could work with in our own back yards. When you can't trust your builder, you have to do it yourself, or else forget it.

    That's the reason I was looking at rock foam and casting the whole hull as a single piece. No, foam will not support loads like masts, towing lines, anchor lines, etc. My question was --- what will it support?
     
  6. PAR
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    PAR Yacht Designer/Builder

    Clearly, Tarrysailor you need to bone up on at least some of the concepts of material properties and their application in structures, general yacht design, a bit of chemistry, physics and math would be helpful as well.

    Floatation is a difficult issue once your little yacht gets large enough to provide standing headroom. In fact over certain sizes, the issue isn't treated with foam, but compartments as you would loose way too much interior volume with the foam necessary to keep all but rather small yachts swamped, but afloat.

    Then there's the problem of the correct type of foam, not all are structural nor closed cell and this could spell disaster if not paid attention to, let alone the location and placement inside the hull. It can't be just stuffed in all the out of the way places and work as floatation. You may float if swamped, but turtle, which, as a general rule, isn't good.

    I design easy to build boats. Craft that don't require anything more then an average person with average skills, tools and experience, some materials and the perseverance to attach one piece to the next. until it's complete.

    The construction of the hull accounts for such a small amount of the total effort in the building a little yacht that frankly it is the least of your worries. A real fancy hull may run as much as 20% of the building effort, but realistically it's below 10% of the total building process. Typically the hull requires the best materials and craftsmanship, so short cutting in this area, in the hope of saving money, time or effort isn't wise, especially when the hull marks the small footprint of the total build, but is the element most required to be stable and watertight, not to mention look and perform like you'd intend.

    In short, foams are used as a core material, relying on other materials and their specific properties, along with applied engineering principles to provide panel dimensions to the qualities required.

    You could carve a boat out of foam, lather it with goo, stuck-um and cloth and wait for this to cure. Then what will you have? A hole in the water, that you know nothing of it's abilities. How much will the safe loading be, how big an engine can I hang on her, will it turn at speed or trip over a poorly shaped chine and capsize (another thing that's generally not good) Will she plane, be stable during the plane, walk on her chines, hobbie horse like a bucking mule or plow like a school bus. If she does any/all of these things can you fix the design flaw(s) that caused it?

    You could highjack a known design (if it's one of mine, I will not pursue you in court, I'll drive up to GA and hurt you) and run the risk of copyright infringement and law suits. You could use a public domain design (there are hundreds available) and hope for the best. You could purchase a set of stock plans from one of the many design firms or stock plans houses on the market or have a custom or semi custom design drawn up for your needs. Then again, you could get the education you need for successfully designing your own vessel.

    The last general rule of thumb would be, not to risk folks you care about greatly, in a craft who's qualities or abilities are unknown, farther from shore then THEY may be able to swim back to, if you screwed up some of the guess work you've anticipated using, for the design, development and construction of this little boat of yours.
     
  7. gonzo
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    gonzo Senior Member

    Containers are properly secured as other cargo is. Accidents happen, but are not the norm. I have studied quite a lot of so called "colission with containers" in home build and designed boats. It seems like a structural failure in most cases. The loud noise they claim to have heard is caused by catastrophic failure of materials. As for containers floating inches above or below the water, do the math on displacement. They are routinely loaded to 50,000 lbs, how can it float? I agree it may happen with a partially loaded one, but those are the least likely to break loose of their attachments.
     
  8. Skippy
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    Skippy Senior Member

    Okay Gonzo, here it is,
    from
    http://www.export911.com/e911/ship/dimen.htm
    and
    http://www.damcomar.com/useful/equipment/drycargo20.html:

    Max tare: 5290 lbs
    Max payload: 62270 lbs
    Capacity: 1175 cubic ft

    So with max total weight of 67,560 lbs, and minimum volume (inside, ignoring volume of container materials) of 1175 cft,
    Max density = 67,560 lbs / 1175 cft = 57.5 lbs/cft.

    Since fresh water is 62.5 lbs/cft and seawater is 64, these containers should always float as long as they're dry and loaded within the specified limits. :!:
     
  9. gonzo
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    gonzo Senior Member

    40'x8'x8.5'=2720cu.ft.
    62,5760lbs/2720cu.ft.=230lbs/cu.ft
    Ergo it won't float.
     
  10. MikeJohns
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    MikeJohns Senior Member

    I have examined collision damage from floating objects often enough. I am sure that some of the terrible losses with all hands have been through massive and instant structural failures from collisions with floating hazards. The weaker your boat the less impact it takes.

    One foam cored GRP vessel sank in Australia a couple of years ago after hitting a domestic fridge, and that had a few layers of GRP on either side of the foam.

    In 20 years I have reported on and heard about collisions with logs, whales, miscellaneous garbage but never yet on one with a container. Although many people have reported seeing them floating out there.

    The commercial cruise boats that operate the Canadian coast, count on several collisions a day with logs escaped from the logging industries rafts.

    I think the only safe way of using foam would be a raft type vessel made up of foam "logs" a racing equivalent of Kontiki !
     
  11. Skippy
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    Skippy Senior Member

  12. I MIGHT AS WELL JUMP IN TO. For all the foam gang supporters. It is great to fill dead space to make a safer boat. As in everything designed there are exceptions. NEVER put foam lower than 1/2 the way down to the WATER LINE. When the boat starts filling and setteling with water, topside cabins fill also. Now we have no idea what is going on as she gets tossed. When she rolls over every crack and popped seam takes in water each time. There is no way to prevent a sinking -- except to, never risk bad weather conditions. Ships have been built that will not sink in the worst weather. They are in a shipyard. All of the unsinkables all sink once. Rich
     
  13. tarrysailor
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    tarrysailor Junior Member

    All boats sink?

    No, I don't agree that all boats sink, not even all the sinkable ones. No more so than all aircraft crash. All things have a productive life and after that time, they are just worn out and not worth repairing. Then they get retired.
     
  14. I, agree. You can design my boats. Rich
     

  15. gonzo
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    gonzo Senior Member

    Yes 40'x8x8.5=2720
    67560/2720=24.84lbs/cu.ft.
    I added an extra zero and came out wrong:(
     
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