Canal Boat — November 2017

78 November 2017 Canal Boat canalboat.co.uk

Trimming the rudder for better handling... it’s a black art

Trimming rudders is done

Weed 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 website

TONY 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 plate

I 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 email

TONY 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.

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