designing a fast rowboat

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

  1. mike1
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    mike1 Junior Member

    John, a lot depends on the athlete, just how old and how supple he (you) is/are, here are some for flat water
    Span between rowlocks ( to c/l pin 159 cm , scull ( blade) length 288 cm inboard 88 cm gearing is therefor 2.350
    However this gives an overlap of 170 and if you are not an accomplished rowr ( scull) this might be too much, Its worthwhile remembering that most often sliding seats do have an overlap. this present some tactics for both stroke and recovery, one hand above the other,, in in south Africa where I live , its right over left, I suggest that you contact a local club if you are confused. I started rowing at 65 and found that I could manage about 60mm so you may want to rearrange these figures, if you do you should try and keep the gearing the same , ie shorten the blade.
    sill to seat between 17 and 19 cm depending on your body shape, tall( long bodies) and thigh thickness, might want more or less. the stroke would finish somewhere at the lower rib , and the blade should be submerged to the depth you want,
    Seat to feet 18 to 22 cm the more supple you are the higher you can have this, but the catch is supposed to both drive your body towards the front of the boat , and to lift you a bit ( from what I remember,
    sill to water26 to 28 cm, this will of course depend on the length of the blade, chosen and the distance between the seat and the sill .
    You would need to draw this out full size on the garage floor, or a piece of plywood,
    The gearing is quite important, these boats are made for racing 2000m and the gearing should leave you exhausted at the end of the last meter, if you are rowing for and hour or so you'd want lessor outboard to make the pull easier and less exhausting .
    Its all about how comfortable you are with the stroke, and how tired you get and how fast the stroke is, and of course just how flat the water is, the more waves the more clearance you'd need for the blade to clear the water on recovery.
    If I was doing this now I'd make allowance to adjust everything , this would need the sill of the oarlock to be able to be moved up or down a few cm perhaps just 2 or 3 cm, the you can fiddle with the rest.
     
  2. mike1
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    mike1 Junior Member

  3. John Perry
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    John Perry Senior Member

    Thanks for the helpful replies. I may now have a bit better eye deer.

    The webpage at biorow is clear and detailed, although it is probably for flat water race boats. I will use most of those dimensions but I think the freeboard of the boat and the height of the rowlocks above the water probably does need to increase for water that may have small waves.

    The pictures below show where I have got to now. The change from one person rowing to one person rowing plus a passenger does make quite a difference to pitch trim if an immersed transom is to be avoided. I guess that the reason that wineglass transoms are often seen on row boats that can carry a passenger aft is that a stern down trim does not initially cause much immersed transom area. I have drawn a transom with a flat base, so transom immersion probably needs to be avoided altogether but this shape of transom will give a bit better pitch stability and I would think that must help with a short boat with a sliding seat. The sheerline is such that the height of the rowlocks above the water remains almost unchanged when a passenger is added.

    I may be over complicating things with the fancy rudder and steering - drawing with a computer makes it almost too easy to just keep adding more bits and pieces.

    I have drawn the rails for the sliding seat extending further aft than they need to for conventional rowing. The reason is to allow for the option of a sliding rowlock arrangement, although with this boat that would only be feasible without passenger.
     

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  4. mike1
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    mike1 Junior Member

    Wow , John you have done quite a bit of work, I have some friends who row coastal in flat to some quite decent wave condition (they ar a bit nuts) I could ask them what their settings are if you'd like, But it would be better if you contacted a similar club near where you live,, their site address is http://capecoastalrowing.wordpress.com/ so you can see what they row.
    There boats are built locally in Cape Town South Africa where I live. and are built to Fisa coastal rules, the rules are perhaps not quite what you're after. anyway.
    well done
    You mentioned the weight earlier as 38 Kgs , quite light , what will you be using to build it with.
     
  5. NoEyeDeer
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    NoEyeDeer Senior Member

    With a boat this short, sliding riggers would have to be better. Here's a thought: maybe you could contact the bloke who built the Clovelly Scull. It's not in production at the moment, but was set up with a sliding rigger for open water. The rigger set up seems to be very good and could probably be adapted to other boats, which may save you building your own riggers.
     
  6. mike1
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    mike1 Junior Member

    No eye deer has a very good point , sliding riggers have a massive advantage , there is not bot rotation / oscilation especially in a short boat, good idea NoEyeDeer
     
  7. John Perry
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    John Perry Senior Member

    Mike1 asked about construction material. I would be building this almost entirely from best quality 3mm plywood plus a few bits of plain timber (what do you call timber that is not plywood?). Glass taped seams and epoxy coating inside, glass/epoxy sheathing with the lightest glass I can find on the outside, no external seam taping. I did similar years ago when I built a sailing hydrofoil. I have based my weight estimate on a figure of 2.23 kg/m2 for the coated, sheathed and painted 3mm plywood. This is of course much more than the weight of the bare plywood. I really ought to make a test panel to check this weight - different builders will probably get different results depending on how they slap on the sticky stuff. I have drawn the bottom of the boat strengthened amidships with internal stringers and a couple of cross members, without that I imagine that one could step right through the bottom of the boat when getting on board. The outriggers and other bits and pieces would be fabricated from various bits of aluminium alloy that I already have lying around.

    I agree that sliding rowlocks are likely to be better for a short boat than a sliding seat. My plan, dependent on household chores etc., is to get the boat afloat with a sliding seat then build a sliding rigger later on. I think it will be interesting to compare the two methods of rowing in the same boat, this may even be something that has not been done before?

    Mentioning the Clovelly skiff, the only quick rowing boat I have ever rowed happens to be the prototype Clovelly skiff that was purchased by a friend of mine. There is actually a picture of me rowing it towards the bottom of this webpage: http://www.hostellerssailingclub.org.uk/index.php/2013-second-file. I did find it a nice boat to row, although I have no experience of other comparable boats.

    Chris Partridge who has the nice blog at http://rowingforpleasure.blogspot.co.uk/ has a 'Sprite' which is a plywood sliding seat row boat the same length as the one I have drawn. There is a group called Home Built Boat Rally (HBBR) that has done some trips in company rowing down the Thames in the UK. Josephine and myself participated in one of these trips rowing our heavy sailing dinghy from Lechlade near the river source to Tower Bridge in London. We left the others behind at Beale Park near Reading, then after Tower Bridge we put the sails up and carried on to Holland and eventually Friesland. Chris Partridge was with us on the upper Thames in his 'Sprite' and I noticed that it does pitch somewhat as the sliding seat moves but despite that Chris reckons it is an excellent boat and he uses it for much of his rowing. Mind you, it does not carry a passenger, that is the requirement that I have found makes the design much more of a challenge, especially when it is combined with a requirement for a short overall length.

    When it comes to making the sliding rigger for my boat, light weight may be even more desirable than for other parts of the boat. I might have a go at resin infused carbon on a foam core, probably unnecessarily fancy but practice for possible future sailing hydrofoil experiments.
     
  8. NoEyeDeer
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    NoEyeDeer Senior Member

    I put that last bits of paint (non-skid patches for feet) on mine yesterday afternoon, so got some final weights this morning.

    The bare hull is exactly 28 kg (61 lbs 11 0z).

    Hull + main thwart + footrest is 30.4 kg (exactly 67 lbs).

    Hull + main thwart + footrest + oars is 33.9 kg (74 lbs 11 oz).

    The last number is minimum race weight, plus me of course for actual displacement. Me is currently heavier than ought to be, but will work on that. However, as weighed this morning, including jeans, belt, t shirt and wallet, I'm 83.4 kg. This will put the boat about 1 mm below the (salt water) DWL I used when designing, so that's close enough. Once I'm back in shape I should drop about 10kg off that.

    Should also be able to save about a kilo with a better set of oars, and could trim footrest and thwart weights if I really wanted to, but as is it's pretty damned good.

    I'll give the non-skid paint a bit more time to cure (overnight isn't really enough for oil-based) but will probably throw the thing in the water tomorrow.
     

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  9. SukiSolo
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    SukiSolo Senior Member

    Looking really nice NED, very good job, good luck with her.
     
  10. NoEyeDeer
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    NoEyeDeer Senior Member

    Gave her a trial run this morning. Knocked off an enjoyable 7 nautical miles without trying, which is a lot further than I was thinking of going. So yeah, she seems to row pretty well.

    Trip report here: Nice rowboat, nothing fancy
     

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  11. John Perry
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    John Perry Senior Member

    I think it is a lovely looking hull, and very nicely built.

    You mentioned modified Gaco rowlocks. I noticed those on the internet, looking at the photos it looks as though the modification you made was to cut the top off?
     
  12. NoEyeDeer
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    NoEyeDeer Senior Member

    That was the main part of it, although I did do a bit of minor reshaping on the insides, just to smooth things up a bit. They're still heaps strong enough.
     
  13. Clinton B Chase
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    Clinton B Chase Senior Member

    Lovely! What is your butt pad? You like a narrow thwart! I've heard they can be better for hard rowing. What is the width?
     
  14. NoEyeDeer
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    NoEyeDeer Senior Member

    My butt pad is a foam car wash mitten that I happened to have lying around. I was gearing up for my first row in several years and thought "Damn, I'm gonna need butt padding!". Search ensued, and the mitten seemed to be the best thing I had handy. Fairly dense foam (not closed cell, of course) and just the right size to cover my butt bones handily.

    Unfortunately, after a couple of hours of rowing, I found it not really adequate. I'll be thinking about better solutions. The rest of me was fine at the end of the trip, but my butt was feeling a tad abused.

    One possibility is to ditch the (very nice looking) Norwegian-style thwart and make up a contoured seat like the sculls have. This could be lighter too, for whatever that's worth. Another is just to grab some better foam.

    The thwart is 180mm wide (just over 7"). Making it wider wouldn't really save my butt bones anyway.
     

  15. SukiSolo
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    SukiSolo Senior Member

    If you do make a contoured seat (certainly recommended for sculls) it is worthwhile creating relief for where the ischium part of the pelvic bones sit. One good technique is to bore a hole (each side) then chamfer it pretty accutely. The effect is to stop the bone (lower pelvis) squashing the flesh too hard locally. Basically you spread the load across more of your bottom flesh which allows the blood to flow better. Definitely works for most people.

    The key to a comfy shape is just try a load of different scull ones, 'til you find a really good comfortable one. Copy it and get the hole centres right for you. Used to make ply ones in a hot press arrangement donkeys ago, and I've carved out way more than a hundred of them....;) We used to sell them to people to fit to eights, not just fit them to the sculls and doubles we made.

    I suspect the geometry of the seat will work just as well for your fixed seat position as scullers use a fair bit of fore/aft movement anyway.
     
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