• Stern or fin base rudder

    From James HS@21:1/5 to All on Tue Jan 25 07:38:25 2022
    We have a shell (Empacher) with a stern rudder (i.e. it is remote from the fin) and athletes report that it is really hard to steer as a 4- but ok'ish as a 4x

    There has been discussion/debate about moving the rudder to be in the 'traditional' location behind the fin and I wondered what other's views are?

    Are there plusses and minuses to the two locations?

    The athletes steering are 'reasonably' experienced and we use the shell mainly on the tideway and for head races, and occasionally on multi-lanes and the likes of Henley Masters.

    Would welcome the view as to whether swapping from the stern to behind the fin would improve manoeuvrability for our use cases.

    Thanks


    James

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  • From A3aan@21:1/5 to All on Tue Mar 22 07:22:17 2022
    Hi,

    Does "hard to steer" mean that the boat doesn't turn enough, or that the boat is uncontrollable (reacts to quickly and/or unpredictably)?

    I would expect that in the former case, moving the rudder closer to the boat's center of rotation would worsen the situation.
    If the steering is hard to control it might help, but a boat builder would know better.
    I think that having the rudder and fin next to each other is mainly a matter of reducing drag.

    My 2 cts.

    Adriaan.

    Op dinsdag 25 januari 2022 om 16:38:26 UTC+1 schreef James HS:
    We have a shell (Empacher) with a stern rudder (i.e. it is remote from the fin) and athletes report that it is really hard to steer as a 4- but ok'ish as a 4x

    There has been discussion/debate about moving the rudder to be in the 'traditional' location behind the fin and I wondered what other's views are?

    Are there plusses and minuses to the two locations?

    The athletes steering are 'reasonably' experienced and we use the shell mainly on the tideway and for head races, and occasionally on multi-lanes and the likes of Henley Masters.

    Would welcome the view as to whether swapping from the stern to behind the fin would improve manoeuvrability for our use cases.

    Thanks


    James
    "

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  • From Andy McKenzie@21:1/5 to All on Wed Mar 23 03:10:55 2022
    On Tuesday, 22 March 2022 at 14:22:19 UTC, A3aan wrote:
    Hi,

    Does "hard to steer" mean that the boat doesn't turn enough, or that the boat is uncontrollable (reacts to quickly and/or unpredictably)?

    I would expect that in the former case, moving the rudder closer to the boat's center of rotation would worsen the situation.
    If the steering is hard to control it might help, but a boat builder would know better.
    I think that having the rudder and fin next to each other is mainly a matter of reducing drag.

    My 2 cts.

    Adriaan.

    Op dinsdag 25 januari 2022 om 16:38:26 UTC+1 schreef James HS:
    We have a shell (Empacher) with a stern rudder (i.e. it is remote from the fin) and athletes report that it is really hard to steer as a 4- but ok'ish as a 4x

    There has been discussion/debate about moving the rudder to be in the 'traditional' location behind the fin and I wondered what other's views are?

    Are there plusses and minuses to the two locations?

    The athletes steering are 'reasonably' experienced and we use the shell mainly on the tideway and for head races, and occasionally on multi-lanes and the likes of Henley Masters.

    Would welcome the view as to whether swapping from the stern to behind the fin would improve manoeuvrability for our use cases.

    Thanks


    James
    "
    How 'smooth' is the steering foot plate.? I row in a variety of oldish shells, and one thing I have found is that a 'good' foot plate, with bowden cables, smooth movement and with the shoe heel not snagging on the keel, makes steering much easier. It
    might be worth doing all you can in that area first - I assume moving the rudder would involve some structural work to insert a rudder tube.

    Another low cost experiment might be changing the area of the fixed fin? Reducing it would probably make the boat a little harder to sit, less directionally stable and more reactive to the rudder.

    Having said that you might get 'better' steering with a fin/rudder combination. With a stern mounted rudder you are fighting the fin, which will be resisting the turning force, but with an integrated fin/rudder you are getting the fin to do the turning
    work.

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  • From stan livy@21:1/5 to Andy McKenzie on Wed Mar 23 08:46:48 2022
    WIth the rudder at the stern it is a drag rudder- not very efficient except as a brake

    With the rudder immediately behind the fin it works as a crude aerofoil and is vastly more efficient

    With the newer style integrated rudders such as the aerofin, they work as even better foils



    On Wednesday, March 23, 2022 at 10:10:57 AM UTC, Andy McKenzie wrote:
    On Tuesday, 22 March 2022 at 14:22:19 UTC, A3aan wrote:
    Hi,

    Does "hard to steer" mean that the boat doesn't turn enough, or that the boat is uncontrollable (reacts to quickly and/or unpredictably)?

    I would expect that in the former case, moving the rudder closer to the boat's center of rotation would worsen the situation.
    If the steering is hard to control it might help, but a boat builder would know better.
    I think that having the rudder and fin next to each other is mainly a matter of reducing drag.

    My 2 cts.

    Adriaan.

    Op dinsdag 25 januari 2022 om 16:38:26 UTC+1 schreef James HS:
    We have a shell (Empacher) with a stern rudder (i.e. it is remote from the fin) and athletes report that it is really hard to steer as a 4- but ok'ish as a 4x

    There has been discussion/debate about moving the rudder to be in the 'traditional' location behind the fin and I wondered what other's views are?

    Are there plusses and minuses to the two locations?

    The athletes steering are 'reasonably' experienced and we use the shell mainly on the tideway and for head races, and occasionally on multi-lanes and the likes of Henley Masters.

    Would welcome the view as to whether swapping from the stern to behind the fin would improve manoeuvrability for our use cases.

    Thanks


    James
    "
    How 'smooth' is the steering foot plate.? I row in a variety of oldish shells, and one thing I have found is that a 'good' foot plate, with bowden cables, smooth movement and with the shoe heel not snagging on the keel, makes steering much easier. It
    might be worth doing all you can in that area first - I assume moving the rudder would involve some structural work to insert a rudder tube.

    Another low cost experiment might be changing the area of the fixed fin? Reducing it would probably make the boat a little harder to sit, less directionally stable and more reactive to the rudder.

    Having said that you might get 'better' steering with a fin/rudder combination. With a stern mounted rudder you are fighting the fin, which will be resisting the turning force, but with an integrated fin/rudder you are getting the fin to do the turning
    work.

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  • From carl@21:1/5 to James HS on Wed Mar 23 20:48:08 2022
    On 25/01/2022 15:38, James HS wrote:
    We have a shell (Empacher) with a stern rudder (i.e. it is remote from the fin) and athletes report that it is really hard to steer as a 4- but ok'ish as a 4x

    There has been discussion/debate about moving the rudder to be in the 'traditional' location behind the fin and I wondered what other's views are?

    Are there plusses and minuses to the two locations?

    The athletes steering are 'reasonably' experienced and we use the shell mainly on the tideway and for head races, and occasionally on multi-lanes and the likes of Henley Masters.

    Would welcome the view as to whether swapping from the stern to behind the fin would improve manoeuvrability for our use cases.

    Thanks


    James

    The shear force between water & a hull's surface falls from bow to
    stern, so a shell's drag centre lies ahead of its centre of mass. With cross-sections approximating to flattened semi-circles, shells have
    side-slip easily &, having less resistance to side-slip at stern than at
    bow, are easily deflected from their intended course when a boat's axis
    departs from its direction of motion. As stern swings out of line, the
    the opposed force vectors of forward momentum of boat & sternwards drag
    on hull go increasingly out of line, amplifying the initial yaw rate.

    Optimum performance requires a system giving proportionate, controllable side-force, first to control the stern's tendency to swing, but also
    able to be steered.

    In a single-scull a simple fin, towards (but not at) the stern, resists
    any initial swing and the sculler varies blade loads to over-ride &
    maybe stall the fin. But safety & speed require a crewed boat to be
    steered, by 1 person rather than a committee, by some form of rudder.

    How best to steer & control a crew shell? With a fin-sized 1-piece
    rudder; with a fin towards the stern (as in a 1x) and rudder right at
    stern; will flat plates so; or can you have an efficiently-combined
    fin & rudder?

    A fin which stalls readily at a small angle of attack (a flat plate) can prevent that initial yaw, allowing a separate rudder to over-ride it.
    But when a rudder forces a direction change that stalls the fin inducing
    lots of extra drag. To steer well in this situation a rudder needs a recognisable & relevant aerodynamic section as it must operate over a
    wide range of loads & angles of attack in which conditions a flat plate
    will just stall.

    The close-coupled, but separate, plate fin & rudder is currently the
    most common system - a large plate fin with a much smaller, less deep
    rudder right behind it, or even cut into it. Here the plate fin resists turning while the little rudder must be heavily rotated to get the fin
    to stall, wholly or in part. The 2 elements do not cooperate. So cox
    rides on a knife-edge, between no useful steering & over-steer as they
    increase rudder rotation. And, of course, the crew always blames the
    cox who can't fully control their nearly 1 tonne of boat-plus-crew with
    that £20-worth of tatty tin plate!

    You can do far better. Aircraft wings are shaped & aligned to generate
    lift with minimum drag. Their hinged trailing edges (flaps & ailerons) continue the smooth shape & can be drooped to increase the wing's
    effective camber (curvature) & thereby modify the flow over its top
    surface, increasing the lift with almost no drag increase.

    The value & function of "foils" (as wings of all kinds are properly
    termed) being poorly understood in rowing, we blindly waste part of our
    effort on the "parasitic" drag from inefficient steering systems &
    resulting poor directional control whose side-slip adds further drag.

    A well-designed, articulated, aerofoil-section steering foil gives cox
    perfect boat control - able to make fine course adjustments or major
    changes with minimal parasitic drag. The response is precise & almost immediate. And the boat is more stable - an added bonus.

    Our "AeRowFin" is exactly that - a retro-fittable foil-based steering
    system which has been improving boat speed & course control ever since
    Sydney 2000.

    As an add-on, we offer a forward-mounted "CanardFin" - a much smaller
    foil, mounted around bow's frontstops position on an eight. It keeps
    the bow on track so that, when cox steers/changes course, the bow now
    goes immediately where you point it rather than side-slipping &
    generating leeway drag which slows the boat & delays the turn. We call
    this combined system "HyperSteer", for obvious reasons.

    Cheers -
    Carl

    --
    Carl Douglas Racing Shells -
    Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
    Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
    Find: tinyurl.com/2tqujf
    Email: carl@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
    URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells

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