designing a fast rowboat

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

  1. nordvindcrew
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    nordvindcrew Senior Member

    Terhohalme, looks very good. I'd like to know more about it also: dimensions, projected weight etc anticipated speed and rough water capability. Melong mentioned rules. we don't have any rules to speak of in open water rowing here in New England USA, other than number of crew general type of boat, out riggers and sliding seats are all that is considered
     
  2. terhohalme
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    terhohalme BEng Boat Technology

    Dimensions just fit in the rule, few millimeters on the right side...

    Length 6.49 m, beam 1.26 m, weigth 39 kg, material 6 mm Joubert okume plywood and epoxy glued.

    Top speed at race is about 7.0 knots (2 km in 9 min 14.8 sec)

    They haven't define "raked" bow or stern, so in my point of view anything that is not vertical is raked. Bow and stern are raked about 10 mm.
     
  3. melong
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    melong Junior Member

    6.49 metres with a 1 metre beam just above the waterline? That's a lot of wetted surface. Pity they aren't more reasonable about the beam restriction. Taking it down to 800 mm would leave plenty of stability and carrying capacity and knock a stack off the wetted surface. Still, rules are rules.
    You also appear to have a sliding seat in it. I would have thought that with the short oars you're restricted to on a 1.26 metre beam there wouldn't be much advantage in a sliding seat. Normally the pin to pin width is of the order of 1.6 metres or more.
    Why didn't you give the upper plank a stack more flare and get yourself some extra beam at the rowlocks? You could easily get 1.4 metres, even if 1.6 was too much of a stretch. There doesn't seem to be any maximum beam restriction in the rules and when using a sliding seat any extra oar length is going to help.
    My idea would be to go as much flare as you can without getting banned. Any boats designed to rules always end up being distorted by them to some extent.
    Still, lovely boat anyway and 7 knots is certainly a decent speed.

    @ Nordvindcrew: She looks like a flat water boat to me. With that deep forefoot and no rocker I think you'd have broaching problems under the conditions you race in.
     
  4. nordvindcrew
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    nordvindcrew Senior Member

    broaching

    The pictures don't show the bottom very well. the run is mildly rockered through the mid section and picks up 4" of rocker at the ends. Fore foot is very minimal. The 16' boat that we used as a basis for this boat is a little more heavily rockered and is very capable in rough water. Our Jersey Skiff has a tremendous forefoot and is a beast in a following sea. Future plans include i re work to grearly reduce the fore foot.
     
  5. nordvindcrew
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    nordvindcrew Senior Member

    wetted surface

    Melong, you frequently refer to wetted surface, and obviously reducing it is a good thing. The problem, in my mind, is that in my boats and in most of the weather we row in, the entire boat is wetted surface. The choppy waves cover almost all parts of the hull at different times , including an occasional break over the low part of the sheer. seems to me that the static number on wetted surface is sort of irrellevant to what actual conditions produce. our 16' boat has a lot of counter in the stern and picks up a huge amount of wetted surface as soon as the waves kick up even a little bit. On the computer, its mumbers look very good, but not so in the real world. I would guess that total hull area and shape might be just as important and more useful than the static wetted surface number. The hugely flaring top strake you suggest would only be a positive attribute in calm conditions where the waves don't get up under it. No formal education here, just 10 years of rowing and trying to observe what is going on with the boat as we row and hours and hours of conversation trying to come up with conclusions. All we have come up with is that all the rules and numbers only work all the time on the computer or drafting board. We'll see how it all works out when we get to rowing the new boat.
     
  6. melong
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    melong Junior Member

    Sorry, must have caused some confusion here. When I commented about the rocker and forefoot I was replying to your question about Terhohalme's boat and its rough water abilities. Like I said, to me that one looks like it's predominantly designed for flat water racing. It'll still handle a chop but running down waves like you seem to do would be likely to cause problems I think.
     
  7. melong
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    melong Junior Member

    Once again this was about Terhohalme's boat. He's using a sliding seat with a 1.26 metre beam and IMO the more beam he can get the better off he'd be. I agree about your comments re rough water, but I don't think that's a problem for him.
    Since you're using a fixed seat you don't need as much beam and I agree having a narrower hull will make things easier in rough water.
     
  8. RHP
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    RHP Senior Member

    I'm currently looking to buy something similar to the craft under discussion, a long, slim sea worthy carft for exercise and fun.

    The Annapolis Wherry seems pretty close to what I have in mind: Length: 17' 9", Beam: 38", Weight: 65 lbs.

    http://www.clcboats.com/boats/wherry.php

    What do you guys think? I like the way its self-build as well.

    Richard
     
  9. melong
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    melong Junior Member

    Yeah it looks like a nice boat. Similar to Ken Basset's Firefly and Liz designs. Same overall length and beam.
    I've rowed a Firefly and they go well, but they're definitely a solo boat if the water's at all choppy. They could also be a tad longer for best results with a sliding seat, but if you're not worried about racing this wouldn't matter.
     
  10. EStaggs
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    EStaggs Senior Member

    My wife wanted a boat to complement her running routine, so I went through this all about a year and a half ago before I knew this forum existed.

    I built a Selway-Fisher Thames rowing skiff, which plans are developed for 12-20' lengths. Ours is 17' LOA, 3'3" beam, 4mm plywood, mahog gunnels, purpleheart transom, and sliding seats/outriggers of my own design.

    She wanted something she could get a good workout in, I wanted something stable for her to learn in and able to take 1 or 2 rowers. The boat has never shipped green water (wakeboard boats in the area have taken to wake surfing, which produces monstrous 3' wakes at very short intervals), pitches minimally, and would make an effective racer or pleasureboat for this type of requirement.

    Note the hollow turn of the bilge. With two rowers, the 2nd panel is immersed:
    [​IMG]

    [​IMG]

    And on the Oar:

    [​IMG]

    [​IMG]

    Just a tidbit for you RHP, add a little heat to the fire.

    E
     
  11. terhohalme
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    terhohalme BEng Boat Technology

    Hi Melong,

    In the rule 1000 mm beam is inside 200 mm below sheer line and outside 120 mm above keel line it have to be 750 mm wide. So the waterline beam at 120 kg displacement is only about 610 mm.

    These boat are for long distances, 30 - 65 km at constant speed of 6.2 knots (5 hours/58 km). Wide sheer line would be too heavy in windy conditions. Narrow beam is compensated width crossed oar handles (150 - 250 mm).

    I am just a designer and builder, not a rower. But thats how they want it.
     
  12. melong
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    melong Junior Member

    Ok, 610 on the waterline sounds good. I thought it'd be a fair bit more than that. I was assuming the freeboard would be about 250 or so which would put the 1 metre width about 50 above the water, so I thought BWL would be around 800. The boat must be a fair bit deeper amidships than I assumed.

    Wouldn't have thought the extra flare would matter in a breeze, but as you say if that's the way they want it.....
    Personally I hate having oar handles severely crossed. It's a bugger in rough conditions when you often need to do a quick heave on one handle to keep the boat on course.
     
  13. RHP
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    RHP Senior Member

    Mr Staggs, many thanks your pictures, a truely lovely location and boat. My concern seeing the picture of boat 2-up is there doesnt appear to be enough freeboard for sea rowing?


    Terohohalme, as a designer what would you say is a safe minimum freeboard for a sea rowing boat once loaded? (Definition of 'safe' = for a father and son). Thanks. 30 - 65 km at constant speed of 6.2 knots sounds fansicating by the way!

    Richard
     
  14. EStaggs
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    EStaggs Senior Member

    I think you would find the boat needs a bit more height in the bow to defend from waves, but otherwise it would be quite apt at sea. An easy change to make.

    Thanks!
     

  15. nordvindcrew
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    nordvindcrew Senior Member

    fast row boat

    I've seen an Annapolis wherry submarime on one race and be pulled out on a couple of more by the harbormaster or race committee. nice flat water boats, but not too good in rough water. It would be great if chesapeake small craft would design something similar with more beam and freeboard. That Thames skiff looks much more capable, and good where outriggers are permitted. For us, the problem is we have outriggers, then we would compete with Alden double shells. New boat getting closer to the water. Possible trial launch to see where she floats and balances on this weekend. That is if I get some time during the week to bond the new panels into place. One further thought on this whole subject of boat design. If a bath tub could somehow win every race, I'd still want to row a good looking boat even if it meant I'd never win a single race. Something in there about tradition and beauty in the eye of the beholder.
     

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