designing a fast rowboat

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

  1. Clinton B Chase
    Joined: Mar 2005
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    Clinton B Chase Senior Member

    That is what I was thinking...low wetted surf area at the length of the Savo 575 should mean very fast. It almost seems unfair to the GB rowers.

    GBs have VERY low freeboard and I think that is a big advantage in open water windy conditions as long as the hull has good secondary stability to keep the waves out. Drake is great in these situations. The very fine ends can be somewhat unnerving, however, when the waves and chop gets up. This is a big difference between a boat designed for sheltered vs open water. The Savo definitely strikes me as a sheltered water boat. We'll see what the Savo 575 fixed seat version ends up looking like.

    The other very strong contender is Clotilde, a St. Lawrence River Skiff drawn by Steever, plans at Mystic. As some folks know, I've been getting these beauties into the computer with huge help from a forum member here. We've modeled the Bobby, Annie, and a 15-footer I call the Fry Skiff. The Fry and Bobby have been built from CNC cut molds.

    I am having trouble seeing why Clotilde would not be very competitive with a GB, esp. if the weight is similar. The hull is symmetrical, but I tend to like a little asymmetry, so that may be the first tweak.

    Clotilde
    LOA 18' 1"
    Beam outside planking 42 13/16"
    Beam WL ~33" with 1 person
    depth amid 14 1/8"
    Freeboard~10" with 1 person
    Cp = ~.52-.53 loaded with 1 person
    hull weight good question....not the lightest even in strip composite.
    I know one SLRS builder has his Annie around 105lbs...I'm thinking it could get down to 95 with some careful planning.

    The hull would look a lot like this beauty but shorter. These shots are the original Bobby at 20 1/2'. I'm finishing one of these currently with students. Fall launch if things go to plan. Isn't it the most beautiful thing?

    [​IMG]
    skiff760 by Clint Chase Boatbuilder, on Flickr

    [​IMG]
    Bobby by Clint Chase Boatbuilder, on Flickr
     
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  2. NoEyeDeer
    Joined: Jun 2010
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    NoEyeDeer Senior Member

    The last bit. I supsect that amount of BWL is going to push the wetted surface to an uncompetitive level. The Savo 575 only has a BWL of just over 26".

    You're working with Terohalme on this, right? He'll be able to crunch the numbers and figure out what's needed for the critical parts.

    Things like stem profile, transom and topsides flare you can have however you like (within reason) so you should be able to get what you want. On the Savo's he pinches the ends right in to minimise planking area and therefore weight, but if you don't mind an extra pound or two you don't have to do that.

    And yes, the SLRS are very nice boats. For a family/picnic boat they'd be very hard to improve on.
     
  3. DickT
    Joined: Apr 2008
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    DickT Junior Member

    "My goal in life is to beat a Guideboat"

    Not to brag, but I have beat guideboats with this one. It's basically a Herreshoff without rocker.
     

    Attached Files:

  4. SailorDon
    Joined: Apr 2013
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    SailorDon Senior Member

    This thread has been going for over 6 years. Has someone come up with the definitive answer to the best performance rowboat for coastal rowing?

    I'm a rank amateur having bought my first rowboat, a Selwin-Fisher Mandarin 17 from the builder about a month ago. I think that the addition of some spray covers forward of the rowing position would make it suitable for coastal rowing. At 17' overall length, it is a bit short for achieving 6 knots. I can do 6 knots for about 5 or 10 seconds, but the wave making resistance is a killer. Perhaps a 20 ft. version of the same design would be more competitive.

    Here are a few photos.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    And a video clip.

     
  5. NoEyeDeer
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    NoEyeDeer Senior Member

  6. NoEyeDeer
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    NoEyeDeer Senior Member

    Got a lines plan for that one? I've seen some of your other shots of that boat, and it looks like it'd do the business.
     
  7. SailorDon
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    SailorDon Senior Member

  8. DickT
    Joined: Apr 2008
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    DickT Junior Member

    No specific lines per se. I had John Gardners lines for the Herreshoff rowboat in his book, but found a small clip of Herreshoff's original 1947 drawing online. I liked the asymmetrical swedeform look better and guesstimated some molds based on the two sources and mounted them on a ladder for a strongback. I used a 13/16" pine bottom board and started planking with edge glued 2 5/16" x 5/16" pine brush handle stock. At some point I noticed that the ladder had sagged and drawn out the rocker. I realized it wouldn't be true to form so I flipped it and finished it by eye Norwegian Faering style.

    I have since cut away the forefoot and extended the stern to help it track. It weighs about 85 lbs. I can hold 5 1/2 mph in a 3 mile race on Lake Champlain and have seen 7.5 on my gps. I'm 65, though, and may not be able to make good on that this year.
     
  9. KJL38
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    Location: Tasmania

    KJL38 Junior Member

    That's the overall beam but it's the part under the water that counts which is only 26.4" on the Savo 575.
     
  10. flo-mo
    Joined: Jul 2010
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    Location: Vienna, Austria

    flo-mo Junior Member

    Here is a link to Gaco Oarlocks, an interesting website for many reasons.

    If you click at "Herreshoff speaks" you open a PDF titled "Origin of the Herreshoff Rowboat" with an extract of his book "Common Sense of Yacht Design" containing the lines plan.

    Here is an interesting quote from this extract comparing his design and the St. Lawrence River Skiffs:

    By the way the Gaco Swift Dory evolved from these lines and sure is a fast and versatile rowboat (though she has an unusual sheer line).

    [​IMG]
     
  11. NoEyeDeer
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    NoEyeDeer Senior Member

    No, it isn't. :)

    For a start, you're making the mistake of comparing beam at the sheer. The important part for resistance is the part that is in the water. The Savo has a much narrower waterline beam, and therefore far less wetted surface, which of course translates into less resistance.

    However, even if you do want to compare beam at the sheer, the Savo is two feet longer. So in terms of overall length/maximum beam ratio it's about the same as the Mandarin. Either way, it's not tubbier.
     
  12. NoEyeDeer
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    NoEyeDeer Senior Member

    The Swift is a direct flop off a Gardner/Herreshoff 17 footer. I know the exact boat he took the mould from. It was cold moulded from two layers of 1/8" mahogany, and John took the mould off it before it was completely finished. That's why his boats don't have quite the stem profile of the H/G boats. The boat he took the mould off hadn't had the external stems fitted at the time.

    Anyway, as far as what's in the water his boats are effectively identical to the H/G 17. The differences are so tiny that they wont matter in practice.

    I do like his rowlocks though. I'm thinking I'll get myself a set. They're well thought out and very reasonably priced.
     
  13. acp1934
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    acp1934 Junior Member

    And not only is that a big advantage but the fact that the Savo 575 has more beam at the sheer means that longer oars can be used, assuming neither boat is using outriggers.
     
  14. Clinton B Chase
    Joined: Mar 2005
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    Clinton B Chase Senior Member

    OK, you got a point. When I wrote those specs out I predicted the response!

    Tehro did the design with Ruud Van Veelen, but it is with Ruud with whom I've been working.

    I need to poke Ruud about the fixed seat design. I'm not absolutely crazy about the sterns of the Finnish craft, and I am crazy about the SLRS, visually. A boat has to be a something I can't take my eyes off of because of it's beauty in every aspect.

    Maybe D Cockey will come along. David, I wonder what the WSA is of say the Annie. The ends of the SLRS's are quite fine, so it may not be so bad.

    I have not found the boat yet....but I find a little bit of something in the other designs that I love...I am officially on a trek to find my Mecca.
     

  15. DCockey
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    DCockey Senior Member

    Depends on displacement. For 250 lbs in seawater (64 lbs/ft^3) not including outer stems or keel:
    Volume Displacement = 3.8931
    Wetted Surface Area = 25.7812
    Waterline Length = 15.7768
    Maximum Waterline Beam = 2.65599
    Water Plane Area = 23.3744
    Dimensions in feet​
     
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