designing a fast rowboat

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

  1. nordvindcrew
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    nordvindcrew Senior Member

    I live in New England (USA) and we have a growing sport of open water ocean rowing racing. Races are from 4N.M. to 21N.M. in length and are only canceled if local authorities won't allow us to go due to bad conditions. Rules are almost non existant and are limited to number of oarsmen,fixed or sliding seat, or general clasification ie: work boat or livery boat. To win, a boat must be able to stand up to some tough conditions yet have enough speed to achieve 6 knots+ in calm conditions. My brother and I have designed, built and raced two boats with some success. I would appreciate a general discussion of design factors from people who are more knowledgeable than myself. Factors such as bottom shape, sections, rocker could all be covered. boats as diverse as a stretched Gloucester Gull and Adirondack guide boats all compete at almost the same level. Our 19' heavy (260 lbs.) Jersey Skiff has been very good at times (18N.M in 3 hrs 47 min), but we need better. Seems like a general discussion could be interesting
     
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  2. skyl4rk
    Joined: Aug 2006
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    Location: Lake Michigan

    skyl4rk Junior Member

    I don't claim to be an expert, but for speed, little to no rocker is good. Beyond that, light weight is important. I built a stitch and glue version of a Banks/St Pierre/Gloucester Dory which turned out very light and could be made lighter.

    http://cruisenews.net/construction.html

    A race boat would have to be longer (the longer the better) and a bit wider (but not much wider). Plywood stitch and glue is a good construction method for the Banks dory types, very little interior framing is necessary, which means light weight. The chine clamp method worked very well.
     
  3. safewalrus
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    Location: Cornwall, England

    safewalrus Ancient Marriner

    Take a look at a gig, they don't come any faster or sweeter (but I'm biased, we've raced 'em in Cornwall for the past couple of hundred years! originally as pilot boats or smugglers, and then they had to be fast!):cool:
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Build her light and put some foils on her, so you can spank the fleet. Expect to get banned or placed in a new class though.
     
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  5. terhohalme
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    I made this rowboat last spring. She took Finnish wooden row boat champion this summer at 2000 m.
     

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  6. nordvindcrew
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    nordvindcrew Senior Member

    Safewalrus, We have the gigs here too. A crew from Cornwall comes over once a year for our early spring race and kicks ***. Only problem, I row double with my brother, not enough crew for a full size Scilly gig. That Finnish boat is a bit more in line with what I'm thinking of. Something a little more traditional in apearance though. I'm learning a computer program for boat design and have a couple of promising sketches worked up. The issues I mentioned initally still need to be finalized. In races, A Gloucester Gull Stretched out to 19.5' gives us fits every time. Watching her, she seems to be trying to climb up on a plane. Whatever she does, it's a fast boat (good crew too ) Does semi-planing happen, is it good or bad? Our 19' Jerset skiff has no rocker and a deep forefoot. Goes fast too, but broaches terribly in a following sea. Current plans are to put some rocker in forward to reduce bow steer and reduce wetted surface. Tons of variables we're working out, That is why this could be a great thread for all rowers
     
  7. nordvindcrew
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    nordvindcrew Senior Member

    Terhohalme, Very interesting piece of work, I'd be interested to find out more about your boat. what little I know about design tells me you've got it right for a single. Looks like a very fine entry and straight run with a lot of flare in the mid sections to get enough spread for oars on gunnels ( a requirement in our class). Thanks for your interest
     
  8. Raggi_Thor
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    I think you could try minimum wetted surface, long waterline and optimize the Cp for your speed. You have probably seen graphs showing how the best CP vary with speed/length ratio. Here's Ted Brewer's numbers:
    Sped/length - Cp
    1.0 and below .525
    1.1 .54
    1.2 .58
    1.3 .62
    1.4 .64

    With 6 knots at 19 feet you are at 1.37
    At 18 feet you are at 1.41

    So it seem like a Cp of 0.64 is appropriate.
     
  9. safewalrus
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    Location: Cornwall, England

    safewalrus Ancient Marriner

    So go for a smaller version! down yer we have sometninh called a 'flashboat' 'tis a gig of some 16 feet LOA, rowed randan, that is stroke single oar, big bloke in the middle two oars, bow single oar (opposite side to stroke) gives 'ee two oars a side, plenty of power, goes like the wind -you could always do two oars each if only two of you! fun too! No need to reinvent the wheel if you don't have too! Might put a look of dismay on the Cornish boys faces - to be beaten by a yankee 'flashboat' 'specially if they don't know you have one! proper job!
     
  10. nordvindcrew
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    nordvindcrew Senior Member

    Safewalrus, That Flashboat, VERY interesting can you point me to plans? Without seeing any plans, 16' seems too small for three people to be rowing. 19' would be more like it for speed and room for seating even for two. I'd love to give the Cornish crew a good go some spring soon
     
  11. mike1
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    Location: Cape Town

    mike1 Junior Member

    Hi, I live in Cape Town South Africa , and am about to start builing a 5.4 m (8 ft?) stich and glue.
    I have had a problem trying to find information on Coastal water rowing.
    The world rowing body (www.worldrowing.com/index.php?pageid=12)will host next years worlds , and there are many fotos of the 2006 worlds held in Guernsey. very interresting.
    What program are you using , id be keen to hear more of your ideas.
    Kind regards
    Mike
     
  12. nordvindcrew
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    nordvindcrew Senior Member

    Mike, I'm using Pro Surf 3. It is not too well known and I am struggling to learn even the basic use of it. I have no CAD experience or formal boat design training. My ideas come from eight years of racing and constant observation of our own two boat as well as the boats we race against. I had hoped that this thread would bring out the real designers and a discussion of general design theory. Raggi Thors post was the sort I'm looking for. Tad Roberts,a designer in Washington State, a forum contributor, was kind enough to send me a set of limes showing his concept of a fast row boat, and they gave me a lot to think about. A large part of his ideas will show up in my next boat if I can just get the station molds to print out on my program. I think skin on frame is where I'm heading as well as doing a light weight lay-up in the mold I already built for a 16" 8" hull. Give me an E-mail address and I'll scan some pictures and forward them to you
     
  13. mike1
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    mike1 Junior Member

    Ok , Some comments,
    Row boats don't plane , unless they're surfing down a wave.
    Length must be an important part of the speed equation,a long narrow boat will always be faster than a short wide one. For instance rowing sculls.
    1 ) A fast rowboat will probably be as long as possible and because of its length will be able to have as narrower beam as permitted by the required displacement.

    Maybe 16" 8" is on the short side and 19 ' sounds much better.
    Bow steering ,yes like you guys I am concerned about bows digging in and directing the issue.
    2) we should find a suitable method of lifting the bow as the speed increases.

    We're not rowing an scull because of its seaworthyness and stability.
    3) we need to find a way of increasing stability without effecting speed.

    4) Uffa Fox once said .. wieght is very good in a steam roller , not so in boats.

    I am going to think about construction and will comment later

    I Hope some of these folks who know the answers will chip in with ideas.
    mike
     
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  14. Raggi_Thor
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    As long as possible, but not longer than you have power for :)
    Two rowers can't keep going at 7 knots in a 49 feet boat.
    There must be a point where the trade off between wave making and wetted surface is at an optimum..
     

  15. nordvindcrew
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    nordvindcrew Senior Member

    I'm aiming for 20' with a waterline beam of about 38" ,slight hollow bow and flaring side for a maximum bean at the gunnels of 52". Windage is also a concern. Often 15-20 kt winds are part of race day. Weather prediction for our 4 mile race on Saturday is for temps to be 53 degrees F and winds to be 10-15 kts. there has to be enough freeboard to keep the waves out, but not too much for wind resistance. Many days the wind is the biggest obstacle to making good speed.
     
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