Effect of flare of sides??

Discussion in 'Boat Design' started by itskens, Dec 11, 2012.

  1. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    From a technical stand point, flare can slow both sailing and to a lesser degree rowing or pulling craft. Simple wetted surface increases, as well as less favorable entry angles can lead to this. The transition from working sharpie to racing, as well as several other craft types, like moths have borne this out repeatedly, with the faster designs having plumb or nearly so topsides. Of course, the amount of loses are fractions of a knot, but in shape/size and weight limited classes, this can be a front of the fleet or mid fleet difference.

    As to your needs, efficiency isn't really a term that's appropriate for those shapes. That type of boat would be best suited by refining rocker to it's needs and speed and enough flare to make her comfortable (relatively). I'd also look at matching her plan taper, especially aft, to match it with here wave making qualities (similar to her bottom for example). Point being, that anyone can pen up a simple boat like that, but the good ones have a lot more "thought" placed in volume distribution and shapes employed, then you might currently realize. Simply put, she's going to be constantly working in a "hole", so if the hull form adopts a similar shape, she'll do well, if not, she'll dig in and have bad habits.
     
  2. El_Guero

    El_Guero Previous Member

    Water flows slow .... around anything in water. That is why deep "v's" want to be on plane. And fast 'ships' want to be wave piercing.

    You might want a balance between flair below the water line and above. Maybe look at a modified flat bottom?

    Wayne
     
  3. itskens
    Joined: Aug 2012
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    itskens Junior Member

    Yes, I have looked at The Stubby before. I think a Vee shape of any kind is out, for me, as some of the places I'll beach this are gravel bars, made of rounded river rock. Our driftboats, here are flat-bottomed and nice for "sliding" over the rocks in the shallows... sometimes, so shallow that we are sliding over wet rocks, basically.

    Load: Yes, in thinking about driftboats over the years, I've come to think of them, or any boat, I guess, as having three "basic" parts: the surfing, or piercing nose, facing the opposing flow; (in driftboats) the bow, which greets the standing wave; and the load-carrying compartment, which from my reading, should be centered a bit aft.

    So, as I'm thinking 'bout where to put the flare and the seat, or seat "zone", I have to think 'bout weight distribution and where I can put my big dog and how to center the design of the hull 'round that.

    I've come to view driftboats, much like a cowboy boot, which one can spin on the ball of the foot, if they wish. The bow can be made, like a ski tip, to either carve, as with older skis, or just slide 'round, like the newer, round-tipped skis.. Same is true with the upstream transom.

    Ya,, I've thought about this a lot and I could just build a box, but I'd rather design some more custom elements into this little pram. Weight will be a consideration, as I'd like to put it on top of my pickup and drag it into the marsh.

    I really appreciate everyone's posts/thoughts!! Please feel free to correct me on any misconceptions I have, 'cuz I'm making a lot of this up, though from drifting experience and bouncing off my very elder guide friends, who knew Keith Steele and gave input into the design of his boats. Actually, what I've come up with, is very much what Woody Hindman was doing. But,, that's another boat....
     
  4. troy2000
    Joined: Nov 2009
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    troy2000 Senior Member

    If it's a flat bottomed drift boat with rocker you want, there's no sense reinventing the wheel. Or rather, reinventing the Rogue River dory... which despite its name, also gets used a lot on the Colorado River.

    http://www.riverstouch.com/Book.htm
     
  5. itskens
    Joined: Aug 2012
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    itskens Junior Member

    I agree. But, there's tweeking that can be done. Many driftboats are for loading gear and big clients and some, for pulling plugs. Some are Cadillacs and others are Porsches. Some have flat spots/regions; others full rocker. Some track and some cut. It's fun!!
     
  6. El_Guero

    El_Guero Previous Member

    Go a little longer and narrower than you first want. It will handle a little better.

    You could run ribs down the center for going over your rocks ....
     
  7. itskens
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    itskens Junior Member

    If I go to 12'ply(11'-6") x 44/45", will it still behave well in the river? Can I keep a SNG version under 100#?
     
  8. Petros
    Joined: Oct 2007
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    Petros Senior Member

    that would make a much better performing boat in my experience, and should be easy to keep under 100 lb. Material costs would be about the same. I might go out to 48" beam, seems L/b ratios for dinghys of about 3:1 are popular and well balanced.
     
  9. El_Guero

    El_Guero Previous Member

    Coleman 12 foot aluminum skiff is 128 pounds: http://www.canadiantire.ca/AST/brow...eman 12-ft Aluminum V-HULL Boat.jsp?locale=en

    If you use the plastic core boards, you are looking at 9lbs per 4'x8'. About twice that for balsa core; balsa would not be as good against the rocks. And Okoume marine grade is heavier.

    Plus epoxy, tape, and finish.

    You can fashion in carrying handles, and seats, etc.

    What are you looking at?

    3 sheets tops?

    Use a narrower bottom beam than you first think, bring the sides up at a 45 degree, use a hard chine about 2 to 4 inches up - I would base that on your expected displacement. Bring that out with maybe a slight curve up. Then corner it and bring it the rest of the way up at a slight angle.

    3 foot by 10 to start? And if you want it wood on the outside/inside, they veneer some of the plastic boards with it as well.

    Where was all these fancy products when we were making plywood boats, and 8x8 rafts as a kid .... ?
     
  10. El_Guero

    El_Guero Previous Member

  11. itskens
    Joined: Aug 2012
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    itskens Junior Member

    Not a jon boat.....

    Uh,, yes and no... Jon boats are nice, but I'm wanting more of a drifter and something smaller to take my large dog and dekes 'round the lake margins. Very much like this Smith Bro's Pram, but I'd like to rake the downstream transom a bit more and maybe raise it a hair.
     

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  12. philSweet
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    philSweet Senior Member

    So looking at this the other way around, if you wanted to make a practical, versatile, easy-to-live-with vessel out of a race boat, you would add a nice amount of flare to it.

    Also, I disagree that an increase in flare is associated with an increase in wetted surface area. It is precisely the high powered race boats that have an increase in wetted surface area. They tend to trade this off against lower wave drag, which is a bigger headache for them than more modest machines.
     
  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The racing versions of several sailing and rowing craft, have found removing flare a beneficial thing. I can think of several working craft, that evolved with racing, where their sides became more plumb. With sailing craft, their LW's fatten with heel, which in some forms, particularly long, shallow ones, doesn't help their wave making particulars. A look at kayak and rowing shell evolutions bears this out, as well as many other relatively low power craft. As speeds increase this becomes less a concern, because drag encumbrances (concerns) shift. The same is true of wetted surface, but to a lesser extent, unless talking about craft with extreme flare, like some dories. A boat with plumb sides will not gain as much wetted surface underway, as it pitches with a stroke or a sail press, as a craft with flare. Again these are marginal increases, but if against the same type, one with, one without flare, the plumb sided craft will tend to be faster. I realize this isn't a terribly important point to consider, for the OP's ideas, but . . .
     
  14. itskens
    Joined: Aug 2012
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    itskens Junior Member

    So, it's sounding like since this is a little row boat, I can do a flare of 20-30/70-60/110-120 degrees and not encounter a greater difficulty rowing,, but/and might gain some stability and purchase for hauling the dog in.
    I've seen some designs in driftboats and prams, which are more flared in the upstream transom; I'm thinking that this allows more floatation, but may reduce tracking a bit?

    Thanks again, all! I'm most impressed with how helpful, considerate, and knowledgeable the forum members are!!

    Also,, looks like the more flare I add, the more rocker and the less bottom on the boat,, unless I dish out the bottom of the side panels.
    Since this isn't for major wave running, couldn't I go with a minimum of rocker, compared to the true "Drift Prams", i.e. this Don Hill Mini Drifter:
     

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  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The shape of any boat (rocker, WL's, chine profiles, amount of flare, etc.) all are dependent on what you want from the boat, which seems thus far, pretty "wishy washy" to me (no offense intended). If you don't nail down what you want, then designing for any goals is a futile exercise.
     
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