designing a fast rowboat

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

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    River Runner: for a rowboat without outriggers the widest point presumably is where the oarlocks are; but we are speaking here of the waterline of course.

    The Banks Dory is a specialized boat for a specific application. It was a very good design for what it was intended to do and cheap and easy to build. However, I don’t understand why it has such a wide following for other, non-related applications.

    Leo: I agree entirely. I might have believed 5% with some difficulty and a lot more justification in the claim but 20% is ridiculous, knowing the way resistance increases with speed.

    HJS: there are several studies of the effect of the moving mass of the rower with a sliding seat in a light boat. Since the resistance is highly non-linear, and variation of speed during the stroke is going to increase the average resistance at the same average speed. Some improvements have been achieved or at least claims made for alternative rowing systems that also harness the strength of the legs but without moving the body. I believe efforts have also been made to use move the body mass in a manner calculated to offset the speed variation due to stroke thrust. I understand these systems were promptly banned form competitions. I don’t recall which thread that was in.

    Correction it is in this thread! see Leo's post below, the discussion starts a few posts earlier and I thought there was a lot of good stuff in it including a power analysis I did at Post 844 . . .
     
    Last edited: Dec 9, 2011
  2. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I don't. :)
    See, for example the pdf in the post earlier in this thread:
    http://www.boatdesign.net/forums/boat-design/designing-fast-rowboat-14250-55.html#post416511

    In some ways, your boat is much easier to model because the centre of
    mass does not move as much and induced accelerations are smaller.
    Unfortunately, you don't have force measurements and other details I can
    use in my models.

    I don't doubt that your new design is better than the old one.
    I just doubt that the 20% speed increase you claim is based on a fair comparison.

    I would love to come up and see your boat during your now cold dim days,
    but I have to go to the Gold Coast in Queensland next week to watch
    kayayers train in temperatures of 27C. You wouldn't like that heat! :)

    Leo.
     
  3. river runner
    Joined: Jul 2011
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    river runner baker

    Revised oar length.

    Naturally the oarlenght is also dependent on distance between oarlocks and distance oarlocks are above water. So I might be wrong about you wanting oars longer than for a Jon boat. But I hope you picked up on the principle I was trying to convey. Given the same distance between oarlocks and same distance oarlocks are above water, the the faster boat or faster rowers will need longer oars and the slower boat and slower rower will need shorter oars.
    I purchase oars for my river dory based on advice I got at a webside and the oars were a full foot too long. Before going to the trouble of making oars or the expense of buying good ones, it might be worthwhile to buy some cheap oars the length you are thinking about and try them on your boat first.
     
  4. HJS
    Joined: Nov 2008
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    HJS Member

    I am interested to understand better why the traditional rowboats go so bad. To design a better boat is not particularly difficult for those who have the knowledge.

    And I think that the low longitudinal stability is one of the causes of great resistance. This is especially true when using sliding seats. Some boats are rocking violently at every stroke. Especially the short two-seaters. And this movement is lost energy.

    Is it possible to define the energy losses in relation to the longitudinal stability?
    Is it possible to define the energy losses in relation to the prismatic coefficient?
    Is it possible to define the energy losses in relation to the wetted surface?
    Is it possible to define the energy losses in relation to the movement of CG?
    Just referring to wetted surface and location of CG is not enough.

    I am only referring to traditional rowboats here.

    I'm not so sure that our simplified calculation methods can provide all the answers.

    js
     

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  5. river runner
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    river runner baker

  6. messabout
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    Location: Lakeland Fl USA

    messabout Senior Member

    HJS boat is an interestig departure from the Whitehall, the Adirondack and other traditional types. Looking across my room I see a shelf with several models, most of them at one sixth scale (that is 2" to the foot). One of them very much resembles the plywood variation of the HJS boat. Its' name is blackie because it is painted..you guessed it..black.

    As I am in my second childhood, I play with the models in a nearby lake. Blackie is better than some of the others in terms of apparent drag. It is very sensitive about athwartships weight placement and it makes a wave train that is curiously different from some of the other models. I have threatened to build a full sized boat along those same lines. Not because it is better than all of the others but because it is a simple build and it looks pretty good.

    And about the Huffington post article; Why would a transat rowboat not have been designed such that it was at least partially self righting? If those madmen had to use 40 minutes to retrieve their emergency gear, something was wrong with the original plan. I am glad to read that they were rescued but puzzled about the inability of their boat to aid in a self rescue.
     
  7. river runner
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    river runner baker

    putting a few ideas together

    Nothing to do today, kind of bored, so I spent some time putting together a design that incorporates some of my most recent thinking on this thread. I still think 4' is about right for maximum beam. I'm not sure what the best length would be, but I thought an 18' waterline would be about right. Going with the idea that the stern should be deeper in the water than the bow (arrow with fletchings effect) I put the maximum wateline length at the midway point figuring this would still give you an LCB aft of middle. I kept the waterline narrow for speed and put a lots and lots of flare in the bow and stern to reduce pitching and help in lifting the ends over waves. For this boat I kept the freeboard low to reduce windage and improve rowing efficiency. Might work well. Something to consider.
    Mr. Wrong Attitude
     

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  8. wolle
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    wolle Junior Member

    nothing new from nvc?

    Hello,

    i read (nearly all of) this thread during a quite day over christmas and was very impressed, both of the nvc-story and the huge amount of information. (When i finished the reading, i changed the design of my project again). First, i want to know, are there some news from the Nordfijord and her crew? The last post from nvc is several weeks old.

    wo
     
  9. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    still alive

    I'm still out here in a very mild New England winter. Rowing isn't going very well. My brother still has a great deal of pain in his left hand from the table saw accident and rowing hurts it. I'm still noodling on a plan for all my western red cedar strips with no serious candidate for a build yet. We set the Nordfiord with a rudder that is controlled from the aft thwart with a line and a jamb cleat. It works well but we think that a small skeg would be a better bet as it won't snag on any debris in the water such as marsh grass. On our row last Sunday, we got into some shallow water and wound up twisting the rudder around on the rudder shaft until it was at 90 degrees to the centerline of the boat. Talk about drag! Got it straightened out and finished our 3 mile row. The Snow row will be in about 5 weeks so I'm working out on my rowing machine trying to beat my old body into shape. The main reason for my absence is that I've become a bit discouraged with the thread. I had hoped to get some more imput from traditional rowers everywhere; both conversationally and technically as well as news about races and new boats being built. It seems to have fallen a bit flat. I'm glad that you have found the site and read it. With any luck, you will have found some useful information. On another thread, you asked about a hollow bow. On a non-technical note, the hollow bow cheats the prismatic co-efficient a bit for a hulll that cuts the water more easily. Many Herrishoff boats use it.
     
  10. wolle
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    wolle Junior Member

    Its bad about for you not getting enough of what you expected, but
    maybe the things you do are special, and there are not a lot of people around here doing similar things. For me, i found a lot of usefull information in this thread and even more, new starting points of thinking and a lot of input about rough water rowing (wich i never did) and hereto specialy the different demands to the hullform and other design apects in comparison to sheltered water rowing. Thats why i like this expression very much: "in most of our races the whole boat is in the water at times and becomes wetted surface"

    I remember two things to be solved you wrote, the one about steering, the other about getting water out during a race. To the last, would it possible to install some kind of a bellowpump (for water) at the place where you have the support for yor feet, so you can push it with the force of yor legs while pulling on the oars?

    wo
     
  11. Uncle Boats
    Joined: Jan 2011
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    Uncle Boats Junior Member

    Bailing

    I had the same thought the other day about bailing, great minds think alike. I've started up on my dory again,building is the easy part, sanding is terrible, where to give up and paint.
     
  12. river runner
    Joined: Jul 2011
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    river runner baker

    Hollow waterlines

    I've provided a few "sketches" for this thread. In at least one, where the maximum waterline beam was aft of middle, the waterlines curved outward inn the bow and inward (hollow) in the stern, because this is what I've seen done in older sailboat designs and racing canoes and kayaks. I still think that is is the way to go for boats with maximum wateline beam aft of middle. But I've also stated that acheiving a center of bouyancy aft of middle might be best acheived through depth rather than width. That is, give the boat more depth aft, rather than more width. In this case, a waterline aft that isn't hollow (curves out) is probably better.
    Running these designs through a performance (resistance) program would be interesting, but I'm not sure how well it could take into account things such as tracking and pitching. I think it is quite possible that a boat would look faster on paper, but turn out to be a poor performer due to poor tracking or too much pitching. This is where experience and refering to past successful designs is helpful.
     
  13. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    bilge pump

    several boats have small 12 volt bilge pumps that use a small motorcycle battery to power them. They work well enough if the boat is vee bottom, but not so well in a flat bottom. The Nordvind is vee bottom and could use a bilge pump; the Nordfiord is flat bottom and it is questionable if it would work. It may not be a problem as the Nordfiord doesn't ship as much water as the Nordvind. I have modified the rudder on Nordfiord, making it much smaller and eliminated the aspect of it being balanced for better feel. The rudder is only temporary until we get an idea of how much skeg we need and how to orient it. Snow Row is coming up in a few weeks. A good finish is getting more difficult with the younger rowers and boats getting better and better. One of my friends rowed the "Last Chance" in trhe Weir River race last fall. He had never rowed it before and they finished first. He commented that it moves very easily. He's rowed quite a few boats and has a good reference for his comments. ( try googling building last chance ) As always, the difference between slow and fast isn't a whole lot in actual speed but it can be impossible to overcome a 1/10 knot superiority in a race.
     
  14. keith66
    Joined: Sep 2007
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    keith66 Senior Member

    Why not fit a self bailer as fitted to most racing sailing dinghies? they sit completely flush with the bottom, if the water starts to come aboad, just kick it down & starts to suck, a good rowboat is quite fast enough for them to operate.
     

  15. river runner
    Joined: Jul 2011
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    river runner baker

    Hollow or no hollow.

    Wenonah canoes have probably won more races than all other canoe companies combined. They've made sprint kayaks for the US Olympic team. They mave have even made rowing shells for the olympics. They know a bit about how to make a human powered boat go fast. I own two Wenonah singles. I took a couple photos of my Encounter as it sits under my deck. I hope you can get a sense of the bottom shape. This is not a racing canoe, but is designed for fast tripping. I'm inclined to think that a racing model would have less hollow, and I think for your purposes you'd want a norrower waterline with more flam above, but I think this general shape is what you should be aiming for.
     

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