Light vs Heavy, Soft vs Hard, For Safety

Discussion in 'Stability' started by Wavewacker, Sep 7, 2013.

  1. Wavewacker
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    Wavewacker Senior Member

    What is safer for a small craft, nothing over 26 foot for large rivers and the Eastern ICW. Nothing off shore except a few miles off on very nice days in the gulf.

    For our dear friends outside the US, the Mississippi is America's sewer line, all kinds of trash and debris flow with the current. Telephone poles from floods, parts of houses, trees and whatever can float down stream a foot under the surface.

    People take all kinds of boats out on the river, jet skis to tugs, fiberglass, aluminum, wood and rubber inflatables, even canoes.

    Given that, realize too lakes and other waters will be used as well, here's my thought.

    Getting hit I think I'd rather be light and maybe a soft sided boat, SOF with stringers or planking that gives. I've been hit in a 16' Pamlico kayak and controlled the slam of something glancing off, from behind no less.

    My thought is that heavier, like a 5,000 lb glass boat won't budge so much and could get holed, they do get holed. It happens out there. Hard side boats get damaged, but they also can take a real hit.

    I'm thinking of a freighter canoe, 24' 53" beam, large but not too big, so I'm thinking light and soft.

    Yes, I know steel would be better, not an option. Wood S&G, Wood and glass, or Framed and covered in heavy PVC, or maybe plank and covered.

    What has the best stability and critical area survival in such waters?
     
  2. Deering
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    Deering Senior Member

    In a small boat I'd be as worried about capsize as being holed from hitting something at speed under the surface. If you're really worried about bomb-proof in a small boat, it probably doesn't get much better than this: http://www.safeboats.com/boats/t-top/
     
  3. PAR
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    PAR Yacht Designer/Builder

    It's not hard to "toughen" a boat's bottom enough to accept the occasional bashing, grounding , etc. You can go way over the top for eventualities that will never occur, though.

    I have a 17' skiff design, whereas the heavy duty version has a 1.5" (38 mm) bottom. 1.5" bottom planking, on a wooden 17' skiff is absurdly heavy, but the point is well served when you bash into something at speed.

    Of course speed has a lot to do with how tough something needs to be made and you also have to calculate "reason", for such scantlings. By reason, you have to assume the skipper has some. You can build a tough *** boat, but have a skipper break it anyway, because they didn't possess this ability.

    Simply put the usual options apply - sacrificial runners, toughened/hardened bottom planks, etc.
     
  4. Wavewacker
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    Wavewacker Senior Member

    Thank you PAR, well, I've been pleasure boating a long time and never had a mishap, knock on wood. Not over concerned about the bottom, that is heavily built and Matt's Little Cruiser micro sharpie is 1", I thought that was heavy. I'm concerned with the scantlings with side impacts at. just below and above the waterline. Probably need to consider that as a glancing blow may not be that big of a deal. But I've seen aluminum boats holed at the sides.

    Please continue PAR.

    I'll be checking out your skiff as well! Thanks :)

    Deering, Thanks as well. That's why I mentioned inflatables, the RIB. I do have something in mind, but this is the first issue, hopefully it will lead into a decent design for a very simple build that will be safe, bomb proof and functional. More thoughts?

    Other opinions.... suggestions.....
     
  5. PAR
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    PAR Yacht Designer/Builder

    The lower portions of the topside planks could also receive this level of reinforcement in the scantlings and often do. Topside thicknesses usually vary from heavier at the bottom to lighter at the top, though more of a weight savings thing then toughness, the same approach could be used to harden up the lower areas. In this vain, a layer or two of spectra or Kevlar on the inside, will greatly improve impact resistance, particularly if coupled with a tapered thickening of the lower side planks, while not increasing weight as much.
     
  6. philSweet
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    philSweet Senior Member

    I think if you build to first rate standards regarding durability and versatility, it ends up being plenty strong. For a boat under 26' that is trailerable, events in it's off-the-water life may determine longevity more that it's on-the-water-time. It will probably spent 10 times as much time out of the water, so take special care regarding storage issues. Half inch BS1088 okume with two 10oz drops of woven glass set in epoxy as a skin will win most any naval engagement and if you do battle with civil engineering, it will go the distance and force a decision. It is very difficult to explain just how tough this construction can be.


    Phil's scantling rule -

    Figure out the limiting load case. Add to this the weight of a school bus the same length as the boat. That should cover things nicely. And it's not hard or costly to achieve. But it does tend to force you into better grades of materials. If you were trying to work with lumber from HD, it would probably look expensive or clunky. If you already were planning on using good stuff, not so much. For a versatile boat, you ought to be able to bolt a 10,000 pound breaking load fitting just about anywhere and have it snap before any hull damage occurs. You'll probably be surprised if you build some sample panels out of 4mm, 7mm, and 12mm ply and see just what it takes to rip them apart.

    Ordinary boats are probably a lot stronger than you think. Have you seen this?

    http://www.youtube.com/watch?v=b-MDnwzTJR8
     
  7. Wavewacker
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    Wavewacker Senior Member

    :D LMAO

    In all my years in bubba country I have never forgotten my trailer one time. It does make me wonder why I need a trailer now...

    Yes, with prudent and sober operation, planning along with common sense, I'd think any production boat that meets regulatory standards should do.

    I probably should not have stated the original question as I did, but was hoping to see comparisons between the methods and materials mentioned.

    As the kids say, "my bad".

    As I stated a freighter canoe. However other functional boats are not out of the question as a camper, like a dory.

    I just bumped a year old thread Jeremy started on his SOF using aluminum tubing. I might be able to assemble a frame such as his in about the same time as the gluing and curing time invested in a wood or glass boat of similar size, it's the quickest boat build I've seen that can be adopted to different styles. In boat design, SOF dory.

    As pointed out above, inflatables are certainly safe with a level head at the helm.

    I was thinking of tubing, sized to scale, with planks or plywood sides and covered in a heavy PVC rip stop material (a swimming pool cover 32x18 or so used one season) maybe gluing it to the panels. It can also be welded and glued for low pressure air chambers. I also have a large rubberized military style raft that can be donated to the project.

    I'd call this a light build, certainly less than thicker scantlings of wood or glass. I can't go the quarter million for a 26' aluminum RIB.

    Power would be 20 hp or less. 60# thrust trolling motor at times. Hopefully too something that could sail.

    Along these lines, is it doable, reasonable, safe and stable?

    It's very economical as I already have most of the materials, need the tubing and rivets and small hardware. And, if the covering was damaged, I'd have enough left over to do the whole thing again, after that I could buy more.

    Perhaps I didn't pose this initially as a comparative analysis but now we're on track. Thanks for the replies!

    PS. PAR, couldn't find the boat you mentioned, what's the name....thanks.
     
  8. SamSam
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    SamSam Senior Member

    Even on a small boat watertight compartments or flotation can be used to lessen the consequences of holing the hull. To compromise the design of a boat with an extra heavy or extra floppy build in anticipation of an event that may never happen seems to be having to live with a boat that is not quite suited for it's intended use.
     
  9. Wavewacker
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    Wavewacker Senior Member

    Thanks SamSam, that is food for thought, but can you better define that, the first issue would be some deign for the intended use, the second consideration would be the safety and stability of such a craft under the desired design.

    As far as I can find, this has never been done before.

    I'm no engineer, but tell me how it could work or why it won't.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    I agree with SamSam, you can build a boat that can be practically immune to holing, but it will be costly in terms of $ and operational usefulness. Flotation is your best option imo.
     
  11. Wavewacker
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    Wavewacker Senior Member

    Thanks, that just make sense to me. Several separate air chambers, any one or even two remaining that could keep you afloat seems to be the ultimate solution even on a budget build. Redundancy ! Holed or not you're not sinking.

    I'll take the other issues to the more appropriate threads such as to designs.

    I do apologize for being so unconventional, I think an inflatable collar on a canoe would look rather odd, I've never seen it, at least there is a motor so it might make sense to some. I understand that to most it would add an expense to a similar boat and that most wouldn't go there, but I have the materials at hand.

    Please let me know if there is an issue with such an arrangement. I'm aware of inflation issues, expansion, contraction and air loss of inflatables, they can be a pain to maintain.

    PS. Going up river I try to stay close (not too close) behind a larger boat letting them plow the debris field. The strategy has worked so far.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

  13. Wavewacker
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    Wavewacker Senior Member

    Thanks Mr. E ! I see how it's done. I also see why I don't see it very often (ever really) the mini would probably do at about $65 a foot and the larger at over a 100 bucks foot. I could cut up a lot of Wal-Mart life jackets for that (LOL). But who said boating was a cheap......

    It's not real ugly, can't really see it that well until you get close.

    Looks better than my inflatable tubes, they are rather large. Probably overkill.

    It seems such secondary stability could be in the design especially with a fore and aft deck with interior compartments.

    Now, self righting? I've rolled a decked kayak but never a canoe! :)
     
  14. SamSam
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    SamSam Senior Member

    For whitewater boating in kayaks and canoes, they have inflatable flotation (air bags) that you put in when it's needed. Canoes are light and speedy craft, but if they swamp and fill with water and then get carried into an obstruction, they are destroyed. Air bags keep them empty of water and light, so they bump into obstructions and then move around. Filled with water this happens. There is no way to build a canoe to resist any forces like this and still have a good canoe.
    [​IMG]


    .
     

  15. SamSam
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    SamSam Senior Member

    .

    Here is what I was talking about...

    [​IMG]

    Whoops, that wasn't it.
    Here it is...

    [​IMG]

    No, that's not it either.
    I have it now...

    [​IMG]

    Well, dammut.

    [​IMG]
    [​IMG]
     
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