78 November 2017 Canal Boat canalboat.co.ukTrimming the rudder for better handling... it’s a black art
Trimming rudders is doneWeed hatches
are baffling...
We have just bought a second-
hand canal boat and on checking
the weed hatch there isn’t a baffle
plate. I could easily make one, but what are
the benefits of having it and how far down
the weed hatch would it need to be placed?
GREWIGGY, via the CB websiteTONY REPLIES: Not all
narrowboats have a baffle plate.
When they are fitted they are
supposed to help reduce hydrophonic noise,
help combat cavitation and help prevent
eddies building up as these make the water
flow to the prop turbulent and less effective.
If you are going to fit one try to get it about
level with the bottom of the weed hatch trunk
so it is in line with the uxter (swim) plate. As
long as the boat handles well without excess
noise I would leave it as it is. A correctly fitted baffle plateI have a 57ft Jonathan Wilson hull with a Beta
1903 engine and balanced rudder. My boat is
coming out soon to be blacked and I am hoping
to correct two problems I have.
Problem 1. The tiller wobbles while travelling along.
At certain prop speeds this stops but it is there most of the
time and is very disconcerting.
Problem 2. When turning the boat around, say when
winding, the stern does not respond as readily as I would
expect; she goes around in the end but not as easily as you
would expect. I have been advised to take some metal off
the leading edge of the rudder, say one inch. I have also
been told to add a couple of inches to the trailing edge.
Can you help?
JOHN ROSCOE, via emailTONY REPLIES: First of all the wobble - I
thought all boats did that and with the very direct
connection to the tiller on narrowboats it is more
pronounced. My understanding is that it is vortices in the
water from the prop hitting the side of the rudder. It all
depends upon the degree of wobble. Wobble also gets far
worse when you try to go too fast for the width and depth
of the canal.
If the prop is clear of fouling and is not bent or has part
of a blade missing, you are very much into the ‘black arts’and might spend a long time and a lot of money failing to
solve the wobble.
Taking an inch off the leading edge would move the
rudder away from the prop so might help, but at the
expense of needing more force on the tiller. Likewise, taking
some off the trailing edge may help if the vortices are hitting
the back of the rudder but at the expense or turning force
and having a rudder that is lighter or tends to pull out of
your hands
The same is true with the difficulty in turning. I can see
no reason why removing an inch from the leading edge of a
balanced rudder should help the turning (although it might
put the rudder into a different part of the prop wash and
reduce or enhance the wobble).
I was told that my ten-year-old boat needed the rudder
extending upwards, but I re-trimmed the boat.
Much of handling depends upon the trim. If the stern is
down the boat tends to pivot further back than one trimmed
flat. I used scrap lead (insulated from the steel hull) to trim
my stern down by about half to one inch. This made a fair
difference, but it’s all to do with gut feeling about the set-up.
The first thing I would do is try to use anything I could
get easily (bags of sand perhaps) to ballast the stern
down and see if that helps. If not, then I would go back
to the hull-maker – he has a good name so should be
able to sort it out.Q
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