designing a fast rowboat

Discussion in 'Boat Design' started by nordvindcrew, Oct 13, 2006.

  1. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    Thames skiff

    Looking at the pictures of your boat, a couple of things struck me. I noticed that the oarlocks are mounted high on extender shafts and look to be a bit weak. In the pictures of the boat being rowed, it seems that the seating is very high relative to the sheer line. A lower seat position would eliminate the need to raise the oarlocks and the lower center of gravity will make a new and vastly better boat. She will be much less tender and react to motion a lot less
     
  2. EStaggs
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    EStaggs Senior Member

    The seating location dictated the oarlocks. The frames as designed are made to be under thwarts, which was within about 2" of where I needed my seat slides to be. Structurally they could not be moved or modified a great deal, so the seating units had to be built into them. I didn't have a great deal of experience building at the time, so I put the seats about 8" higher than I would have liked.

    The oarlocks are actually remarkably strong and sturdy. The only deflection I get during rowing is in the gunnels, which would easily be remedied by adding cross-gunnel supports at the aft edge of both riggers. The scantlings for the inwales and outwales are just not large enough, but the deflection is probably about 1/2", and doesn't result in much loss.

    If you were to build the same boat for offshore purposes, Id say those are good modifications to make, absolutely. On the other hand, we are on smooth water, so she will be getting a lightweight single shell as soon as I can get it finished (and started for that matter).

    E
     
  3. messabout
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    messabout Senior Member

    Nordvincrew;
    Nifty article in Wooden Boat Magazine Sept/Oct 07 issue. Titled Dory Stroke. A rather scholarly piece about rowing efficiency. You may be well past this with all your experience, but it is still worth a read. The technique is claimed to smooth out the power stroke and cause the force to extend over a longer period of time within the same stroke cycle. I have thought of the possibility of grafting some load cells to the oar shafts for the purpose of identifying the variables in rowing techniques. Alas someone a lot smarter than me has already done that.

    Many of us are interested in your boat and your success in defeating those other guys. The best boat is only part of the equation. Human power and its' most advantageous application is the rest of it.

    Any one out there sufficiently practiced with the dory stroke technique to qualify as a critic?
     
  4. nordvindcrew
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    nordvindcrew Senior Member

    rowing technique

    Thanks for that Messabout, I haven't got my new issue of rediculously expensive and esoteric wooden boats yet, but will be interested to see it. We constantly examine and re define how we row, in different races diffferent stratagies come into play depending on the length of the race and weather conditions. Constant adjustment as we row can be the key to speed. Right now, we're hoping to have the boat ( no name yet, got to be Nordic) ready for the Weir River Race in late October. We're so close to the Carter Brothers in the Daniel J murphy it's not funny. Last race we rowed 96% of their time, finished only a little bit behind them. This new boat has the potential to get us up there. I have a sticker in the rear window of my truck that reads "row hard, no excuses". That is our Secret weapon". I appreciate your interest and encouragement, it's good to know there's a little group of people rooting for us two old farts in this bit of foolishness.

    Boat is off strong back and all bonded together on the outside. It stillneeds some major fairing then get turned over and bond the inside of the hull and add some extra material to stiffen the chines and sheer. Hull weight is just under 80 pounds as it sits. Finished weight is still a guess, 120 would be great
     

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  5. nordvindcrew
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    nordvindcrew Senior Member

    Dory stroke

    I just read the dory stroke article in wooden boat. At this time, our oars are not suited to that technique. They are composite with aluminum shafts and a moulded plastic blade that is cupped in both directions and is also set at an angle to the shafts so that the blade is more nearly parrallel to the surface of the water. the blades are balance so that there is no twist induced by the offset in the blades. they seem to move us along pretty well. I've got some hollow wooden oar shafts all glued up and faired, maybe a conventional blade on them would be something to try. Even if we bought new oars, simple straight blade oars might not be too expensive. Right now, I've got about $500.00 into the boat including disposable supplies, glass cloth, mat and resin. I'll need to buy a little more mat and resin and some material for the seats, inwales and outwales as well as fairing material and one part epoxy paint. Maybe another $150.00 shoulld do it. $650.00 for a 20' rowing boat keeps it in the very affordable range. Long range plans are to use the same mold next year to get a 16-1/2' boat, essentially a double ender but with a very minimal transom to set up as a sail boat; galvanized steel centerboard and maybe a ketch rig with sprit sails. I get a big kick out of this whole process: we went from a wooden 8' dinghy to a 16'9" wood boat we pulled off the dinghy molds to a fiberglass 16'9" boat to the 20'3" double ender we're building now, with yet another varient planned. It baffels the living hell out of some people how we keep getting a "new" boat from the same basic shape that originated as an 8' dinghy.
     
  6. charmc
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    charmc Senior Member

    Well said. That's one thing I noticed about your boat from the first picture, and I agree totally. Beauty of line counts for a lot. Good thing bathtubs are so slow!
     
  7. melong
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    melong Junior Member

    It does look nice. Can't wait to see some pics of it underway.
     
  8. nordvindcrew
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    nordvindcrew Senior Member

    beauty

    Thanks for the support. Most if not all of the credit goes to my younger brother who drew the original dinghy plan that every version has come from. He's got a great eye and is a natural when it comes to design. I look for his approval before I go ahead on any changes to the design or construction. I'm jumping way ahead, but have got myself really enthused about doing a sailing version, it will stretch our knowledge trying to come up with a centerboard and sail plan that is well balanced. Help from the forum will most certainly be needed when we get to that point. The Boat will get her first taste of the salt water this weekend ( still no name, a bad omen ) so we can determine where the rowing stations need to be. Then we can build in the thwarts which will also be flotation compartments, add flotation bow and stern then rub rails. Lots of fairing and sanding in between before it can be painted ( color scheme is still undecided too ). God,grant me strength!
     
  9. nordvindcrew
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    nordvindcrew Senior Member

    seat height

    I keep looking at the beautiful Thames River Skiff That Estaggs built. With the addition of two longitudinal stringers notched down over the frames,and a bit longer than the length of the rowing stations the thwart height could be set as low as desired. The job wouldn't be too intimidating and wouldn't compromise the strength of the boat. If the boat were mine, I'd seriously consider the change
     
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  10. EStaggs
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    EStaggs Senior Member

    You know, its a relatively quick build, and pretty cost effective. I have about $1300 into the boat with okoume ply (4mm), plans, a 20' mahogany board, some purpleheart, some teak, the alu rigger work, cedar for the seats, and the glass. Id say its a 100 hr project with a yacht finish and your suggested mods. Plans are $100 or so from Selway-Fisher. He is also willing to do redesign work to your specs for a fee.

    Here are a couple shots for the mental exercise:

    During construction:

    [​IMG]

    [​IMG]

    [​IMG]

    As you can see, its pretty basic, and lends itself to any number of outrigger and oarlock combinations. The beam is 39".

    Any questions, just let me know.

    E
     
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  11. RHP
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    RHP Senior Member

    Great pictures E, many thanks.
     
  12. nordvindcrew
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    nordvindcrew Senior Member

    seat height

    I can see how the frames dictated height. A change to full height frames, maybe a couple more frames and the supports for the sliders could go at any height you want. It's a pretty boat, and as you said, not too expensive. How much did you pay for the oars? For me, they tend to be kind of pricey. I'd like to have at least two sets of different lengths for varying conditions. I've got 10 hollow wood shafts done. They're Alaskan Yellow Cedar cut just under 3/8" thick by 3/4" wide, tapered and joined with birds mouth joints. They're very light and strong enough that I've set them on supports 5' apart and hung on them ( 170 pounds ). Next question is blade type. Traditional may be a good choice to try to learn the " Dory Stroke ) as reported in Wooden Boat this month. the plans I worked from have measurements for curved blades and the laminating jig is made and ready to go. Time to make a decision and finish the project
     
  13. EStaggs
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    EStaggs Senior Member

    I have $350 in both sets. I bought some used sculls from a local racer, one set (mine) are cf shafted, wood handled, poly bladed; the other (wife's) are Draeger cf racing sculls, hatchet bladed, cf handled. Hers are VERY light.

    Id say for the type of rowing you are doing, a traditional macon bladed oar is what you want. They are not as sensitive to position in the water, esp proximity to the surface. You can also manipulate those oars a little better in rough water. Hatchet blades are great for sculls and fast flatwater boats, but they do have their peculiarities in rough water. Efficiency is lost at a staggering level when you put the oar too deep, so with the rough water service you would have problems aerating the blade often.

    Id love to have a set of birdsmouth oars, and I might try to put some spruce or yellow cedar ones together, but Im up to my *** in the NINA project and need to bang out a SOF kayak soon as well (kayak season is back and we only have 3, no couples can come with us).

    E
     
  14. nordvindcrew
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    nordvindcrew Senior Member

    0ars

    I'd like to get in touch with some of the flaat water scullers around here to see if I can get any damager oars to put conventional blades onto and shorten up for my needs. might be a way to get light and inexpensive oars. The birdsmouth oars are both easy and a pain in the *** to do. I can't stay out of the adhesive no matter what and wind up a mess. lots of peretive cutting and a couple of jigs to make up then it's all ahead full.
     

  15. Ramona
    Joined: Feb 2007
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    Ramona Senior Member

    I have been searching for a couple of windsurfer masts to make a set of oars. Used to be plenty of damaged ones about. The idea being to add epoxy/plywood blades and timber hand grips. This is to be used on a Windrush catamaran which I will be using as a yacht tender and general fishing platform. Nice easily driven hulls and plenty of room to enable wide rowlock positions.
     
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