Rowlocks for rowing boat

Discussion in 'Boat Design' started by Frosty, Jan 27, 2011.

  1. Frosty

    Frosty Previous Member

    Is there a position the oars should be on a rowing boat in terms of length from stern or the like etc?
  2. michael pierzga
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    michael pierzga Senior Member

    Hmm....are you asking the position of the seat in the boat ? or the position of the oarlock ? Very long time since Ive rowed boats, but I remember the general rule for the oarlock is 300 mm aft of the aft edge of the seat..

    The seat position ? Beam max ?.. I like a working rowing boat to be very slightly bow down.... the seat and your weight just forward of Beam max and the oarlocks at Beam max. Depends a bit of the shape and type of boat. Important that the boat float on its lines when underway. Stern down is to be avoided.

    Most good boats have two oarlock positions and the seat has two or three mounting positions depending on the size of the oarsman, how many people are onboard and wind, sea direction. .

    Upwind in a seaway I like to slide the seat forward and use the forward oarlock positiion .

    How high is the seat in relation to the oarlocks ? Hmm...depends. I like it when oars are perpendicular and level with the sea and the grips at the bottom of my rib cage . Seat too high and you hit your knees.. seat too low and you waste mechanical advantage.

    Best to give the oarlock seat position a good guess, then modify after seatrials .

    If you are using wooden thole pin style oarlocks, its easy to have two or three oarlock positions. Thole pins are really nice to use with a workboats style craft.

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  3. Chuck Losness
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    Chuck Losness Senior Member

    When I made my dinghy I originally put the oarlocks 12" aft of the rear edge of the seat. That was a little too far aft and I now have the oarlocks 9" aft of the seat which seems better. My oars are a little short, only 6' long which could have some effect on the placement. I would prefer a 6'6" to 7' oar. Dinghy beam is 4', LOA 9'9" and the rear edge of the seat is 5' aft of the bow.

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  4. Frosty

    Frosty Previous Member

    Its an 8foot 9 inch planing dinghy.Im not racing or anything just thought I would put some oars on it for a bit of exercise.

    I cant move the seat either, its moulded in, in fact its not really meant for rowing.

    I hav'nt got any rowlocks yet but will probably get the ubiquitous pin with a horse shoe type.

    It has a moulded in seat about 18inches from the transom so ile probably have to row in reverse unless I glass in a new seat which is not out of the question.
  5. viking north
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    viking north VINLAND

    On page 18 of the Reverse engineering thread, page 2 of boat design, you'll find a photo of my 18ft. Shelbourne rowing dory. You'll notice three sets of oarlocks. This allows 1 to 3 people to row but this was not what it was set up for. It was primarly set up for 1 rower with an option for 2. The idea with 1 rower is the center position with the seat approx CB location on her lines. This rowing position when rowing in calm weather, beam weather, or running with it. The forward position when the weather picks up and it's hard to control direction(the wind on bow is blowing you off course), you change to the forward rowing position. OR if you are carrying a passinger in the stern seat, OR if 2 people are rowing. The 2nd rower is in the aft rowing position. The oar locks are positioned (i think 12 to 13 in )(confirmed) aft of the aft edge of the seat. I will confirm this today and reply. Your arm length does play a role here for comforth of rowing so a little trial and error is in order with some means of using a C clamp as the oar lock. Also you can fine tune your boats trim with a rock or bag of sand.This dory design is a real rowing machine. I can maintain 3.5 to 4 kts over a 5 mile course. I row approx. 25miles a week excellent non boring exercise. Geo.

    A yacht is not defined by the vessel but by the care and love of her owner.
  6. TeddyDiver
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    TeddyDiver Gollywobbler

    It depends a bit of the beam and how long oars you get. To start with some 30 cm from your chest when sitting on the seat is about the min. With dinghies the hight from seat to freeboard might be the biggest issue. If it's limited shorter oars help some..
  7. Frosty

    Frosty Previous Member

    Well If I have no seat yet or rowlocks where do I start . I mean is there an optimum point on the hull that rowlocks should be. Is it as simple as --in the middle of LOA?
  8. Squidly-Diddly
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    Squidly-Diddly Senior Member

    "single OR double" rowing sculls have never been mentioned as

    seriously suffering from different positions in same hull.

    You can row as double, single, or single with passenger in stern seat.

    I think you row from stern seat if just carrying cargo (the rear passenger seat is all about the girl getting the best view and seat....view of you that is).

    I imagine the relation of seat and foot holds to the oar locks (in both horizontal AND vertical) is what counts......and well as putting your weight in best position (just aft of center of buoyancy?).
  9. Ike
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    Ike Senior Member

    When I was building my dinghy I was building from plans so I put the seat where they said, but if I had to do it over again I would lower the seat about 3 inches. After finishing the boat I first sat in it and determined where I would put the oarlocks. For me it was where the oars would be straight out from the boat when sitting and holding the oars in a natural position. Not extending the arms or pulling them back to the body. I later moved the oarlocks about 2 to 3 inches farther aft. The oar length has a lot to do with it. Oar length is generally about two times the beam. But i went with a little less. The beam is 4 feet but the oars are only seven feet. They seem to balance better that way. As I said, I wish I could lower the seat because now the oars hit my knees if I raise them just a little above level. I would like to have a couple more inches of clearance. For my wife who is a much shorter than me, the height of the seat is ok.

    First determine where to put the seat so the boat balances for and aft. then determine where to put the oarlocks.
    Last edited: Jan 27, 2011
  10. viking north
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    viking north VINLAND

    Ok, i'm a little confused, I thought the seat was fixed in place and we needed to locate the position of the oarlocks. ah, you have a fixed seat but can install another one if necessary, Ok got it now. So here are the basic steps i used on the Shelbourne dory to locate the center one man rowing position.
    Step #1 draw a chaulk line on a leveled floor to represent the center of the boat stem to stern.
    Step #2 about half way along that line draw another line at 90deg to represent the beam of the boat.
    Step #3 lay a 2x4 on edge along this beam line using it as a reference and fix the 2x4 so it remains on edge. Nail, screw or throw a bag of sand over each end but keep it alined and on edge.
    Step #4 locate the center of the transom beam wise and draw a line down to it's bottm edge.
    Step #5 place the boat on top of the 2x4 like a see saw alinging the bow and transom center line up with the stem to stern line in step #1.
    Step #6 balance the boat see saw style on the 2x4 on edge and you have located the approx center of boyancy.
    Step #7 on the exterior of the hull mark the location of the 2x4 where it exits from under the hull. Transfer this to the inside of the boats sides and you have the approximation of the center of the width of the rowing seat. However I would make this the forward edge of the rowing seat to allow the boat to sit better on her floation lines.
    Step #8 measure back between 12 to 13 in from the aft edge of this rowing seat on the gunnels and there is where i'd put my oar locks.
    Note, you might want to do a mock up on seat height, oarlock position, to fine tune to compensate for body trunk length, arm length, and the length of the oars you will be using. 1in, change can make a world of difference so take the time to do it.
    Hope this helps, Geo.

    A yacht is not defined by the vessel but by the care and love of her owner.
  11. Frosty

    Frosty Previous Member

    Ok I put a piece of 1 inch PVC pie under the 1 inch keel. Its center of balance is right on the join that I have glassed together. I reduced a 12 footer into a 8 foot 9 so it will fit on the swim platform.

    12 /13 inches back from that is almost in the middle of the original glassed in seat and 2 feet from the transom.

    I could extend the seat a few inches forward and use that, it would mean that I could use the transom to brace my feet but the oar position looks very far back at 2 feet from the transom in a 8.9 footer.
  12. viking north
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    viking north VINLAND

    That puts your body approx. over the cent. of boyancy about 3ft. forward from the transom on say a 6 1/2 to 7 ft. waterline, if you've went thru the proceedure quazi carefully it sounds about right but i thought it would have been maybe a little more say 3ft. 6 in. Not having a photo or hull plan of your modified hull makes it a little difficult, You,ve now got a good approximation, install a temp. seat put her in the water and try it. Sit up straight on the seat, have someone view how she sits on her lines and fine tune from there. While you're at it set up temp. oar locks and fine tune their location also as i said prev body height, arm length, oar length. oarlock height from the water play a big role. The proceedure is not an exact science but does give you a good starting point and once located can be used for similar shaped dingys. ---Geo.
  13. DCockey
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    DCockey Senior Member

    This appears to be a proceedure for determining the center of gravity and therefore the center of bouyancy of the empty boat. It may or may not be the center of bouyancy with one or more passenters in the boat positioned so the boat floating with the desired trim. Center of buoyancy depends on load and trim.

    If the empty boat floats close to the desired trim AND the waterplane is close to symmetric fore/aft about the unladen center of gravity, then positioning passenger(s) at the unladen center of gravity will keep the boat trimmed about the same but floating deeper. The effect of the passenger(s) on the trim also depends on the weight of the passenger(s) relative to the empty weight of the boat.
  14. DCockey
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    DCockey Senior Member

    This is good advice.
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  15. Carteret
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    Carteret Senior Member

    Yep, you can't beat getting in the boat and trying them out before a permanent installation. Very important to set them up so they are comfortable with your arm reach. I built the thole pins design that Michael used. With the Thole pins attached to the oars by a spliced lanyard (donut) the oars cannot be dropped overboard. Attached is a link for building your own oars. They (oars) have gotten really expensive.
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