Object lesson in rudder efficiency

[Henry Law]

I was at stroke in a bow-loading four this morning, with a young rower
pressed into service as cox. I try to avoid rowing stroke so it was my
first opportunity to observe a rudder in use. I was interested.

We had a number of "sticky navigational moments" (poor cox had agreed to
do it to get us on the water but she didn't have a very good morning);
most of them required rapid and decisive course adjustments. So the
wires moved past me, round went the bar to about 80 degrees from the
direction of travel, and whoosh! there was a kerfuffle of disturbed
water several inches below the surface as the rudder stalled. I'm quite
sure that the steering input from it at that point was next to zero;
certainly that's how poor cox saw it.

An eight we once bought second hand came fitted with one of Carl's
fin/rudder assemblies. Some careless crew broke it off at some point
and it was replaced with the usual flat tinplate affair because "it
stuck down too far and was always getting broken". If the people who
made that decision saw what I saw today (and bothered to think about it)
they might possibly have made a different decision.

(And no, I'm not Carl's marketing agent; presumably any boatbuilder
could put in a rudder that wouldn't stall; it's just that the Sage of
Chertsey seems to be the only one that cared enough to do so).

[m***@gmail.com]

It wasn't a Janousek was it?

I row at stoke in our 4+ and often cringe as I watch plumes of water coming off the rudder almost perpendicular to the boat at max deflection just acting as a brake. In most coxes defence, the design of the steering on the Janousek 4+ boats we use (high aspect swept blade with a fin also) somehow makes it very easy to get into the position of high deflection and zero rudder authority and we have had some bank/bridge collisions because of this. The cox is late steering and uses a lot of rudder, when the boat them doesn't respond they use even more and the boat just ends up going straight. I have coxed the same boats and tell them never to use more than half the deflection and steer little and early.

A lot of new coxes also think it is like a car, more rudder = turns more. Different boats are also quite different to steer even in the same brand and they get used to max deflection being OK to use.

[Carl]

Post by m***@gmail.com
It wasn't a Janousek was it?
I row at stoke in our 4+ and often cringe as I watch plumes of water coming off the rudder almost perpendicular to the boat at max deflection just acting as a brake. In most coxes defence, the design of the steering on the Janousek 4+ boats we use (high aspect swept blade with a fin also) somehow makes it very easy to get into the position of high deflection and zero rudder authority and we have had some bank/bridge collisions because of this. The cox is late steering and uses a lot of rudder, when the boat them doesn't respond they use even more and the boat just ends up going straight. I have coxed the same boats and tell them never to use more than half the deflection and steer little and early.
A lot of new coxes also think it is like a car, more rudder = turns more. Different boats are also quite different to steer even in the same brand and they get used to max deflection being OK to use.

The concept that the flow over a foil (e.g. fin, wing, oarblade, sail,
etc.) can 'stall', & that this is a bad thing, is wholly alien to most
coxes, who were never told that to over-rotate any supposed steering
surface, in particular the typical flat plate rudder, simply stalls it
which results in major turbulence & drag.

But rowing, ignorant & fearful of the mechanical sciences, prefers to
ignore their direct relevance to shell performance.

Cheers -
Carl

[Henry Law]

Post by Carl
But rowing, ignorant & fearful of the mechanical sciences, prefers to
ignore their direct relevance to shell performance.

Quite so. But in this case one has to observe that the coxes never tet
to see this rudder-as-brake problem in practice.

Anyone who saw what I saw on Saturday morning could see with complete
clarity that the hard-over rudder wasn't having much effect, if any,
even if they had no clue that what they were observing was the result of
a stall in the fluid flow sense.

[m***@gmail.com]

Post by Henry Law

Post by Carl
But rowing, ignorant & fearful of the mechanical sciences, prefers to
ignore their direct relevance to shell performance.

Quite so. But in this case one has to observe that the coxes never tet
to see this rudder-as-brake problem in practice.
Anyone who saw what I saw on Saturday morning could see with complete
clarity that the hard-over rudder wasn't having much effect, if any,
even if they had no clue that what they were observing was the result of
a stall in the fluid flow sense.
--
Henry Law Manchester, England

There is certainly some ignorance if they have a cox box or other means of seeing speed or 500m splits. I remember the first time I coxed being very surprised at the huge increase in split with even modest steering inputs.

An an aside I also like coxes who make a 'rudder on' call and what adjustments to make when a large steering input is required so the crew can keep the boat set.