Why are rowing boats wider in the aft section

Discussion in 'Boat Design' started by mike1, May 16, 2008.

  1. mike1
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    mike1 Junior Member

    Hi All,
    I've noticed from plans and boats, that many rowing boats and paddle ski's seem to have the maximum beam aft of halfway,, why is this so when many of the older boats are true double enders with both ends beign identical?, for instance the Adirondack Guide boat, and the Gardner , Herreshoff 17 ft row boat.
    I have often wondered , and now, look forward to finding out why.
    Thanx
    Mike
     
  2. Fanie
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    Fanie Fanie

    Hi Mike,

    The shape of a boat has to do with many things, hydrodynamics, space, stability, speed, comfort to name only a few.

    If you have a shape that is widest in the centre and both ends are identical, it is firstly to discard the frustration of having to puzzle out which end is which :D as long as you can remenber the other four sides, L, R, up and down :rolleyes:

    But there are other reasons, if it slits through the water with little resistance it's for speed or ease of rowing, the water is gradually opening up to the centre and then gradually let back in behind the hull centre.

    Unfortunately there are compromises. If you want to have a fast row boat it may not have much space in it. If you want a dry ride and you make the same narrow rowboat's freeboard more, you will sacrefice stability.

    Many small boats are often designed for one purpose only, and in many instances just to help you fill the garage up :D
     
  3. rwatson
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    rwatson Senior Member

    I have always remembered the rough rule of thumb for canoe design - maximum beam ahead of midships for a dry ride, maximum beam behind midships for speed.
     
  4. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    I'm tempted to say because we are wider in the aft area... :D

    Mother dearest bought a Kayak once, it kept going in circles, the max beam (I think?!) was well aft, she later learned that the shape was designed to be stable paddling down stream and it was not a still water boat. You'd need a spurt to explain, which I am not but with canoes and kayaks its a horses for courses thing I think.

    MBz
     
  5. rwatson
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    rwatson Senior Member

    In Kyaks/canoes the 'going in circles' thing is a function of no skeg or rudder, combined with a short waterline.
    In small boats, skegs and rudders get hammered during launching and in shallow water, plus manauvarability is reduced.
    Even 16ft canoes with a fairly flat bottom wander all over the place unless you have skilled paddlers at both ends.

    Any boat with two sharp ends suffers from lack of bouyancy at either end, in an attempt to avoid being pushed around by strong water. Unless the craft is used where the water is fast and variable, I would always go for a wide stern just for the ability to climb back into the boat - which is almost impossible in a canoe.

    Perhaps the rule should be - the further you are from the shore, the wider the stern should be. So in a fast flowing stream, having a pointy end makes sense when you are nearer a shore. If you are going to sea, you better have a wide stern in case you need to climb back aboard as the shore will be a long way away.
     
  6. ted655
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    ted655 Senior Member

    I You "row" backwards & paddle looking /sitting forward..
    Try sitting backward in a Kayak & paddling to a far off point.
    A heavy load is better moved if the oars are pulled.. A wide stern carries a load better & tracks better.
     
  7. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    I'm a good paddler and I tell ya this thing would not go straight easily... man it was work, like no other kayak I have used. I thought mum was just being mum at first, but she was right... never tried the boat in a river but the guy who filled us in was supposedly a spurt and sounded very knowledgeable.

    Candos are a sinch to keep straight in comparsion... I'm talking about a boat that really wanted to loop LOL, not just wander.

    Cheers
    MBz
     
  8. rwatson
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    rwatson Senior Member

    Rowing a canoe is easy - racing shells are canoes in every sense of the word.
    The reason they track properly is that they have a skeg, not because they have a wide stern.

    The other big reason that canoes are soooo hard to keep in a straight line is that the 'steering' is much closer to the centre of effort. Its much easier to change the direction of a boat from the extreme ends, where rudders live.
    In a centrally seated craft, the poor paddler has to make the ends rotate around the centre with very little leverage to work with, making the job twice as hard.

    Oars make a much better job of steering from the centre, as the blades are much further away from the edge of the hull, and have extra leverage. Its much easier to 'steer' an oared craft than a paddled craft, but you cant see where you are going a lot of the time.
    I remember driving my sister nuts by spinning her little dinghy, for several sick making minutes, on its axis with oars, which could never be done with a paddle.

    Back to Mikes observation - "Many boats have identical ends". Dont forget that you only have one set of frame designs to make with that style. Boat designs are not all performance driven. Often its just aeshetics or convenience.
     
  9. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    U not listening... anyway, on with the show.
     
  10. mike1
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    mike1 Junior Member

    Thanx folks,, I think I'm getting there, ask my wife what L , R, up, down , ment, we figured out up and down bit and think that R stand for Red, still working on the L bit.
    I can see the bennefit of having similar frames radiating out from the middle, and the ease of climbing over transoms, However most times it seems that on the water line , row boats are double enders , maybe not symetrical , but sharp at each end.
    Someone once told me that with the max beam just aft there was better for trackin?? is this so ,,
    Also of you look at sites like Paul Gartside , his rowboats are all shaped so that the max beam is aft,
    Thanx folks
    Mike
     
  11. the1much
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    the1much hippie dreams

    L= Lavender,,,,long leash,,or,,LOOK OUT,,,is what we came up with,,,,,thanks for the up, down part,,,,that 1 was confusing,,hehe,,,,and beanzy,,,i know what ya talking bout,,,i think my friend had 1 of those messed up kayaks,,,,man i hated it,,hehe ;)
     
  12. SamSam
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    SamSam Senior Member

    To the original question, possibly the availability of outboards changed the shape to support the weight of the motor and operator. With a motor, maybe effiency in moving through the water was less important and cargo capacity became more desirable. For the inexperienced, a wider boat is more initially stable also. It would seem to be a market driven change, as it is far easier to motor a boat as to row it. Of course it sort of depends on what you are referring to as a rowboat. Searching "rowboat" under google images, 95% of what's shown are motorboats that can be rowed. It's like you can beat something with a shovel or dig a small hole with a sledgehammer, but there are better ways.

    As for the kayak that wouldn't steer, perhaps it had extreme rocker to the bottom. A fast water kayak is not meant to be propelled and steered so much as pulled along by the current and pointed as fast as possible in the direction wanted. Lotsa rocker allows them to pivot in place as opposed to turning a corner like a car.

    Only more amateur type canoes have actual skegs. They have a big disadvantage in added drag and catching crosscurrents or catching on rocks and stuff, which is especially bad when drifting sideways to the flow of a river, as when heading for shore or when turned around by events such as current, winds, riverbends etc. Canoes and kayaks vary their tracking ability with the amount of rocker, from none to a bunch, and also with the introduction of a very slight, shallow v to the bottom. The fineness or fatness of the entry and exit lines also effect tracking.

    I used to make them and studied their design a bunch. As far as asymmetrical design, I seem to remember reading that maximum beam ahead of midships was actually faster than having it behind midships, sort of like the big bulb on a real ship, or a whale or most, if not all, fish. The disadvantage was loss of tracking and it was much harder for the front paddler for paddle clearance. I also think I remember it was not allowed by the ACA in competition canoes.
     
  13. Chris Ostlind

    Chris Ostlind Previous Member

    There is something to the issue in all the responses posted. OK, not all of them, but it goes something like this when speaking of asymmetrical hull forms for human powered vessels.

    1. There's a performance advantage when one provides for a slender entry as wavemaking drag is diminished. When you pull the widest part of the hull aft of the COB, you are sharpening, to some degree, the angle of the bow entry. This slenderness thing has to be balanced by some measure of form fullness forward, or the boat will tend to dive in anything save for flat water. This is typically addressed through a modest degree of flare.

    2. Assy. hulls have a nice tendency to track straight all by themselves as the hull is acting in a weathervane manner when power is applied to the forward stroke. This feature allows the designer to enhance the rocker, just a bit, for additional responsiveness to turning inputs.

    The result is a boat that tracks smoothly and turns readily with the smallest corrective stroke. It is always better when paddling/rowing to be able to have most of your strokes focused on delivering forward thrust than taking the time to apply course corrective strokes. If you've ever paddled, or rowed, a squirrelly boat before; one that kept taking another course than the one intended, then you know how tiring it can be to get it back on track.

    Yes, you can fit a rudder or skeg, but then you add appendage drag to the boat. Of course, a misbehaving craft may benefit from such a mod, but the additional drag has to be offset by the enhanced enjoyment/performance or you've simply spun your wheels to no effect.

    Allowing for the addition of an engine aft, along with the needed buoyancy for same, may have been a part of the designers brief in these types of boats, but that is probably a different discussion as to original intent.
     
  14. Brent Swain
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    Brent Swain Member

    Excessively wide sterns on sailing craft drasticaly reduce directional stabilty regardles of skegs etc, even when motoring upright in calm waters.
    Brent
     

  15. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    I was trying to remember what it was about the kayak that went in circles on flat water. I think that the max beam was just behind the paddler but it was at deck level and the boat tapered quite quickly to quite narrow at the waterline. I think that the boat was designed to do slalom in rivers allowing the paddler to heel the boat quite dramatically to achieve a tight turn (not sure about that). On flat water if your weight was not perfectly central the boat tended to go the way you lent... at least I think that was the way it was... many many years ago now. Sound plausible? Dredging the memory here :D

    Anyway off topic so back to the show.
     
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