designing a fast rowboat

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

  1. Guest625101138

    Guest625101138 Previous Member

    NVC
    I have been following this thread with interest for some time.

    I took a stab at modelling your current boat based on the photos and dimensions given.

    I then had a look to see what Godzilla would produce for similar hull constrints but optimised to do 6 knots.

    Both boats modelled displace 250kg and are approximately 6m long.

    I am working on the basis that the power input is 300W with a rowing efficiency of 60%.

    The attached chart compares the expected speed of the two different hulls. I believe you would be able to get about 0.4 knots better by using the Godzilla hull.

    I have attached the linesplan for both hulls. The main difference is that the NVC_6IA is fuller in the ends and I have aimed to maiximise the waterline length for the overall length. Also NVC_6IA is more stable.

    If my modelling is close then you should find your existing boat moves very easily up to 4.5 knots then the wave resistance starts to kick in. To push the existing hull to 5.8knots would take almost 50% more effort than that required to push the Godzilla hull.

    Based on my experience with slender hulls the result makes sense.

    I did not get too concerned about the height of the gunwale in the modelling.

    I have seen foam used as gross fairing to dramatically change hull shape so this could be an option rather than total rebuild.

    Rick W.
     

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  2. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    ch-ch-ch changin

    Well, we moved my stretcher forward 3 inches, big improvement. Tried moving the buttoms out 2" towards the blades; mistake. Easier to pull the oars but too fast a cadence for us. We're going to try to get back to a really long pull and a slow cadence. To do that, we really need to be able to hang on the oarss at the end of the pull to get our backs and weight into the pull. The stations have to be set up right or this doesn't work for us. I think we're getting close to having things where they should be. A little more tinkering will have us pretty near there. During our experiments, we were able to push the hull up to 6.9 knots for a short period of time and keep a constant 5.2 knots without too much problem at all. After examining the hull, we have decided to make some major changes. The keel we added has almost 4 square feet of surface area and is crreating too much drag. To correct this, we will re shape the bottom to create a deeper VEE section and eliminate the need for the keel. This will get rid of the extra wetted surface and still keep us tracking. At the bow, we're going to lift the first chine to create a far better entry and a little deeper fore foot. These changes will add some bouyancy and float the hull a bit higher with a resulting narrower waterline. When we built the boat , we massaged almost all of the VEE out of the hull, and the entry wasn't so hot to begin with and we thought we were stuck with it. Two or three sessions with the glass should result in a far better hull. To Rick Willoughby, I saved your analysis and will study it later on. Thanks for the interest in the project and the help. I'll keep everyone up to date as we make changes. Right now the plan is to get the stations spot-on-right then put in some serious time rowing ourselves back into shape. Charlie is right, if you think you're not in shape, you aren't! I have to get to a large copy machine to copy Tad Roberts drawings, and when I get them, I'll mail them to anyone interested.
     
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  3. sailing canoe
    Joined: Sep 2006
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    sailing canoe Junior Member

    Nvc

    Good see you are still fighting the good fight. Newsweek had a story a few weeks ago about men in their 60's running better marathons than they did in their 50's. So just go for it. Yeh changing the overlap can make a big difference. occationally I grab a different pair of oars with the button in a different place , it can feel very strange. I have no way of tracking speed so I have never Known how the speed changed. Keel -- I was suprised when you put such a large one on. I was thinking more fin like. Your hull changes seem major!! Aren't you worried about changing to many things at once? What is your target speed? I think you have mentioned it above but almost 7 knots sounds fast. Was the snow row a typical race length? It seams at that length that it would be a sprint from start to finnish. Did I just do the math right ? the winning boat was going almost 10 knots!
    Count me in for a copy of tads plans. I was going to sugest scanning them and posting them here, but if they are already large fomat it would be a pity to lose the detail. Expenses reembursed of course. Thanks for doing this - nick
     
  4. Clinton B Chase
    Joined: Mar 2005
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    Clinton B Chase Senior Member

    Drake Progress

    Well my rowboat is progressing slowly...I am actually in the process of shaping the keel. I am going with 3/4" tapered to 1 3/4" at the sternpost. Will be a fun job and I should easily get rails on this weekend which means I'll be posting turnover shot soon. Can't wait to put her in...I get nervous just thinking about it.

    Paul Gartside, my design teacher and hero, said that he STILL gets nervous when he sees his own boats go in the water for the first time! Makes me feel better :)

    Cheers,
    Clint
     

    Attached Files:

  5. lazeyjack

    lazeyjack Guest

    Built two like this, for exercise, 7 foot oars, row abt 600 strokes 4 days, not much exercise that, but the sun, is the problem, already had one nose cancer job
    I kept it down by the local marina, on grass by high water, marina manager comes along says"1050" a year to leave it here
    This place is the pits, there are a few kayaks, the rest is yuppies and thugs on personal water craft
    I called him a prick, and he threatened me and boat, I should really have called local TV station, made a story of it
    Stead of that I rowed it to a place which is sorta no mans land
     

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  6. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    race length

    The snow row is about the shortest race we do, and it is a killer! Too long for a sprint but too short not to sprint. I don't do the math to get the speed for the "Murphy" it's just too discouraging. I'm not sure if the race length is in stature or nautical miles, I should step it off on a chart with dividers some day just to be sure. The best time We've ever done on that course was on a training row in the "We're Here": 38 minutes and 14 seconds. We're going to make changes slowly. First, get our stations right then change the bottom of the boat. We made the bottom too flat and found ourselves skating off sideways with any wind on the beam at all. A rudder held our course but still let the bow be affected too much by wind. The full kength keel was the only answer, and it worked, but creates too much drag. Adding 2" of vee to the bottom will only add a very slight amount of wetted surface and should provide enough draft to keep us on course. Quick, VERY rough math indicates maybe 3 cubic feet of volime will be added to the hull which will float us higher and reduce waterline beam. We'll wait for warm weather before starting to change the bottom. during that time we can row the Nordvind to keep getting back into shape. Clint,, The Drake is looking great! Yup, that first float is always kind of nerve wracking but very satisfying too. Our down and dirty methods of construction make it easy for us to take a sawzall to the hull and make changes. No gelcoat, only flat finish marine one part epoxy that can be sanded and repainted easily when repairs are needed. Lazyjack, great little dory! probably fun to row. It looks much like A Gloucester Gull; a favorite boat around here and a competitive single in the hands of a determined rower. some of the guys around here just put their boats in the back of a pick-up truck and transport them back and forth to the water. the "Murphy", all 22' of it comes to the races on the top of a Chrysler mini van. It's light enough that the two guys that row it can get it up there with only a little help.
     
  7. lazeyjack

    lazeyjack Guest

    some requested design so here tis for all,
    i spaced frames 450, used 8mm on topsides 12 on bottom, 2 layers 8 for thwarts, kwila stem,.kwila rubbing strakes and clashing, one rowing position
     

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

    I thought it was the Francis Kinney designed dory out of an early edition of Skene's Elements of Yacht Design.

    This is a nice boat...I have some students building one out of plywood and epoxy. She is very pretty, very slender and seems so small in the shop. Great boat.

    Clint
     
  9. Clinton B Chase
    Joined: Mar 2005
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    Clinton B Chase Senior Member

    Drake gets turned over

    Photos of some final hull construction and then turnover yesterday. I am pleased with the results.
     

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

    More shots...

    The boat was actually drawn at 16' LOA so when I first saw the hull upright the first thing I noticed was the sheer was less bouncy because I stretched it by 1'3". But she looks fair and like a fast boat and I am pleased not to mentioned ready for building the interior. In fact I was so uplifted by the turnover that I got going on refining the drawing of the next boat! Enjoy. Can't wait to race....probably won't launch until August so I will miss the Blackburn and Essex R. race but maybe not the Southport race. Anyone do that one?

    Cheers,
    Clint
     

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  11. charmc
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    charmc Senior Member

    Clinton,

    Very nice! Congratulations, you've done a good job so far.
     
  12. lazeyjack

    lazeyjack Guest

    yes clinton nice job, and so few temp frames to build over, fair chines too,
     
  13. nordvindcrew
    Joined: Sep 2006
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    nordvindcrew Senior Member

    It's a Faering!

    What a beauty! Great lines and the real look of a Faering. I see what you mean about the sheer being a bit less springy than you might have wanted, but it' a beauty, none the less. The manner that you carried it out of your shop indicates to me that it's a very light boat. Any idea of the current weight? You mentioned your desire to do the Blackburn, We,ve only done it once and that only after we'd been rowing for three or four years. It is a grind and requires a lot of practice and determination to do it. I am wondering how much rowing you have done to want to challange yourself to that extent. The pull from Thatchers island to the breakwater at Gloucester Harbor is seven miles with the twin lighthouses on Thatchers kind of mocking you as they ever so slowly receed in the distance. It can be kind of demoralizing! We have the Nordfijord sorted out better now. the stations are more to our liking and feel much better. The oars still need work, and I think that I need to finish the hollow shaft wood oars I've been working on to get something that may be a bit better for us to use. Work has taken a new course for me, I am no longer a salesman but am back out installing fences. The work is hard and my body is going to take some time to re-adapt to it.The good part is that it will toughen me up a lot and help get me back in shape to row with some real power in my stroke. At this point, amost all the wood to start the skin on frame boat is in my sheds. I've pretty much decided to build a 17' version of the model that I posted pictures of way back in the forum. My biggest concern was strength in the gunnels to deal with the stress that rowing would put on them. To eliminate the problem, I'm going to buy the plans from Glen_L for a sliding seat with built in outriggers for the oarlocks. I'll make the seat fixed and make sure that the riggers don't exceed the beam of the boat so that I don't have go up another class higher. The beauty, to me, is that the whole rigger unit can be moved fore or aft to get the balance that is right for the conditions on a given day. Sounds like an idea and it might even work. Rowing with my brother is a Sunday tradition that is 10 years old and one that I won't give up, but I do want a single to get out on those summer evenings or clear winters days when a row would give my soul a needed lift.
     
  14. mike1
    Joined: May 2004
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    mike1 Junior Member

    Hi Nordvindcrew,Go Slowly with the sliding seat Idea,, The rowing geometry is very different to a fixed seat.. if you measure your stroke ,, catch to finish , at your thumbs,, for a fixed seat it will be some what less than a sliding seat,, in turn if the "span " gunnell to gunell , remains the same this will increase the angle at the catch and finish ,, In a flat water single optimum for high performance world cup style would be to catch at 70+- deg and finish at 40+ degree. I dont think this could be handled with waves. the span of a single for someone at about 6"6" would be about 5'3" I can let you have all the details , but you should be very cautious. regards Mike Henry
     

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

    Charlie, I will definitely work slowly up to the Blackburn, but I don't doubt my skills and determination but know enough to ramp up over the next couple years.

    The sheer I have realized is going to look better on the water and one good thing is that the windage of this hull should be minimal without the high bow...the flare I hope will still keep things dry inside. Interestingly, the sheer looks bouncier in the drawing....that is b/c I drew it at 16' originally and stretched it to 17'3"....so that may explain some of it. Yes, she is a prototype and I look forward to modifying the lines next winter.

    In the meantime I am working on the Maine Coast dinghy an 18 1/2' x 6'2" transomed row-and-sail dinghy made for the family and a small crew to go out and enjoy...she will be fast and seaworthy I think.

    Have fun with your project!

    Cheers,
    Clint
     
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