Ask the experts
Q
With no reefs, the main and genoa
of my 8.5m (28ft) Westerly Merlin
bilge-keeler Fauve are nicely balanced,
so I wish to mark the genoa with the
appropriate points to reef so as to balance
the mainsail with one, two or three reefs in.
I estimate that the genoa should be reefed
to 0.6, 1.25 and 1.92m from the tack to
provide the equivalent areas of the mainsail
when it is set with one, two and three reefs
respectively (ie, the reefed genoa will have
the same proportion of sail area as the
reefed main).
However, the act of reefing moves the
centre of effort forward on both sails,
so with a reefed main there will be less
weather helm due to both a reduced
sail area and the centre of effort moving
forward. I have countered the first element
by reducing the genoa’s sail area by an
equivalent percentage. However, the
second element should require a further
reduction in the genoa. In addition, the
forward movement of the centre of effort on
the genoa will increase rotational moment,
thereby requiring an even greater (third)
reduction in genoa area. Are these factors
sufficient to worry about, and if so, how do
I calculate the required further reductions
in genoa sail area for each reef of the
mainsail? Or could I simply just guesswhat further reduction to apply?
I appreciate that perhaps the only
accurate method of achieving a balanced
rig is to finely adjust the genoa reefing
to the specific conditions at the time of
setting the reef in the main. The same
logic could be used for identifying the
approximate genoa reefing points: ie, go
out in the conditions appropriate to those
necessitating one, two or three reefs and
mark the genoa when an appropriate
balance is achieved, but life’s too short.
Besides, should I really be messing
about outside when conditions are
such that three reefs are necessary?
Surely sailmakers have an approximate
rule of thumb to follow?
Alan Pemberton
PlymouthIAN BROWN REPLIES: Some interesting
points are raised here. Yes, the centre of effort
of both sails (and the relationship between
them) will change as the boat is reefed, and in
theory this will affect the boat’s overall balance.
No doubt sufficient time and expertise could
be brought to bear in calculating some sort of
theoretical optimal ratios, but these would fail
to take into consideration a whole host of
other factors that will combine to determine
the overall feel and balance of the boat.For example, a furled genoa – even with a
luff flattener fitted – will become a less efficient
aerofoil as it is furled, which will have a
bearing on how much drag and heel it
generates relative to the actual area. An
unfurled blade jib of a given area will be more
efficient than a larger headsail that has been
reefed to the same area. The same applies to
the mainsail. As the sails are reefed, therefore,
the useful ‘drive’ component of the sails as a
proportion of the area (and relative to each
other) will change and this will influence the
overall balance. A sail that is in better shape
or made from better materials to begin with
will behave differently to a poorer/older sail.
The way the sails are trimmed will also have
a huge bearing on how the boat behaves, as
of course will the degree of competence of
those on board. Other factors will include sea
state and point of sail. In other words, relying
on sail area alone to work out how the boat
should be balanced is in my opinion far too
simplistic an exercise.
As you suggest, the best practical solution
is to use your experience of the boat to know
whether you need one, two or three slabs
in the mainsail and then tweak the genoa
accordingly. Fitting marks along the foot of the
genoa at regular intervals will provide you with
a reference point so that you can recreate
comfortable settings next time around.SAILS
A balanced rationale for genoa reefing marks
Keeping a third
battery for best
Q
My Westerly Konsort has
two 115Ah leisure
batteries, and as the boat now
has a fridge I would like to be
able to use both as house
batteries, installing an extra,
smaller car battery to ensure
the engine can be started. All
three batteries would be charged
when on shore supply with a
Sterling Pro Charge Ultra, which
I believe will keep them all in
excellent condition.
To avoid having to change
battery switches every time I
wish to start to engine, I would like to keep the third battery
not as the starter battery, but for ‘emergencies’ – ie, when
the house batteries cannot cope. Is this a satisfactory way
to treat the third battery, being kept charged but only being
used very seldom? Will it be there when needed?
Doug Pattison
PristonPAUL HOLLAND REPLIES: It will be fine to use a battery in
this way. An alternative would be to dedicate the new battery to
engine starting and add a VSR to your system. This would
remove the need for you to switch batteries, and ensure the
starter battery is topped up first by your engine alternator.ELECTRONICS ELECTRICS
Q
My VHF radio is around 10
years old, and due to water
damage I’ve recently had to
replace the Vtronix antenna of
the same age. I have a new
Vtronix Raider antenna including
the cable, but find it is now
impossible to stop the squelch.
This noise stops when a signal
comes through loud and clear,
but returns when the signal
stops. On reinstating the now
dried-out original antenna the
set works as normal.
Has the new aerial got too
much gain? If so, is there any
gadget to reduce the gain so
I can use the new antenna?
Nigel Fentiman
Cobham, Surrey
CHRIS ELLERY REPLIES:
It sounds like something on board
is radiating noise which the old,
waterlogged and faulty aerial
couldn’t receive. Now that you
have a good aerial, it’s picking
it up. I suggest you switch
everything off on the boat to see
Stop the squelch
if you can isolate whatever is
generating the noise. Also,
route the aerial cable away from
other cables if possible.
Does the squelch lift on all
channels or just some? Does the
problem disappear when you go
to different areas? The interference
may not be from something on
board, but from, say, a local
paging transmitter. Here in Poole,
for instance, there is a signal that
lifts the squelch on Ch28 close
to my office. It may be that the
new antenna by its design just
happens to be good at picking
up noise from something local
which isn’t even transmitting in
the marine band.
The other thing to check is
whether you have made the push
and screw connection into the
Raider aerial correctly. Another
option is have the radio and
antenna tested away from the
boat. There’s no clear-cut answer
to your problem, and only by
eliminating things will you get to
the cause. I have sold hundreds
of Raider antennas and not
heard of this problem before.