Practical Boat Owner - February 2016

reefing work with a fractional rig
that needs pre-bend? What about
maintenance, what happens if it all
goes wrong, and how long will an
in-mast mainsail last? Can you
convert a conventional mast
by adding a bolt-on-the-back
system? What difference does
a tensioned luff-spar make, and
is it worth having?
Then there’s the question of
battens. If the sail doesn’t have
battens, can you change it for one
that does? Will the system work
with a battened sail? Some will,
some won’t. And are battens a
good idea anyway?
The questions continue. We will
be looking at all these and more
in the following pages.

Performance first
Let’s start by looking at
performance, because that’s one
of the most fundamental factors.
In-mast reefing is a compromise
not only because of the flat sail
but also because a sail without
battens has to have a hollow
(concave) leech. That makes it
up to 20% smaller than a
conventional alternative. With
short vertical battens you can have
a straight leech, while full-length
vertical battens allow you to claw
back some of the deficit by having
a positive roach.
Regardless of the battens,
however, you will have more
weight aloft. This, combined with
the reduced drive from a flat-cut
sail, means that performance
suffers. Also bear in mind that you
can’t bend the mast to depower
the sail, so you have to forget
about playing with the backstay.
Despite all these factors, it’s not
all bad news on the performance
front. The ability to adjust sail area
quickly and easily means that
you’re less likely to be hanging on
to too much or too little sail. And,
significantly for some sailors,
in-mast reefing allows them to
continue sailing when declining
strength or mobility might
otherwise force them to stop.
Yet another factor sometimes
cited is that many cruising boats
carry a significant amount of
weather helm, and the only way to
get rid of it is to reef the mainsail.
On that basis, an in-mast sail is
at less of a disadvantage once
the wind reaches a Force 3 to 4
because it’s like having a reefed
sail to start with.
If you’re buying a new boat and
have no firm views either way,
whether you end up with in-mast
reefing or a conventional mainsail
might come down to the builder.

In-mast mainsails need

looking after if they’re to

give good service

One mast specialist points to

two large European builders of

mainstream cruisers. Both build

boats of a broadly similar nature

designed to appeal to a broadly

similar market, yet one sells 75%

of its production with in-mast

reefing while the other sells 75%

with conventional mainsails.

Progress and

problems

Potential in-mast converts are

sometimes worried about whether

they’ll one day find themselves

with a sail jammed halfway in

or out. In decades past, many

sailors were hesitant to switch

to roller-reefing headsails for the

same reason, but reservations

now tend to centre on the

compromise in sail shape

rather than on reliability.

In-mast mainsails are often

viewed with more scepticism

than roller-reefing headsails,

both because they haven’t

been around for so long and

because the mechanism is inside

the mast. That means it’s harder

to get at and, if the system does

jam, you don’t have the option of

spinning the boat in circles to furl

the sail away.

Many of us will have experienced

problems even if we haven’t sailed

extensively with in-mast systems.

I was on a boat years ago when,

with the (nearly new) sail flapping

around as it was being reefed, the

clew tore out. True, that was the

sailmaker’s fault, but the point is

that we were left with no useable

mainsail. In the unlikely event that

you lose the clew of a conventional

main you can still sail with a reef.

On another boat test the sail

wouldn’t furl in as we were

approaching a narrow and busy

harbour entrance. It took several

minutes of persuasion with a

hammer and a wedge of wood

before it cooperated. Experiences

such as these will inevitably

determine how readily any of

us will embrace the whole

notion of in-mast reefing, but the

manufacturers have been steadily

refining what they have to offer,

even if some have gone in

different directions from others.

It’s also important to bear in

mind that problems are not

necessarily the fault of the

manufacturer of the reefing

system. Other significant factors

include the type, age and

condition of the sail, the way it’s

furled and unfurled, the deck

hardware and, of course,

maintenance by the owner.

Tolerances with in-mast

reefing are finer than with

conventional sails.

Evolution of

the species

In the early days of in-mast

reefing, the luff spars (the

aluminium extrusions, otherwise

known as mandrels) were all

untensioned: they simply ran

inside the mast from the drum

at the bottom up to the head.

About 15 years ago, however,

Seldén decided to make a luff

spar that could be tensioned. They

had found that the system didn’t

always work particularly smoothly

or produce a neat reef, particularly

in the middle of the sail. When

the luff-spar was pulled aft by

weight in the sail, the sailcloth

made contact with the inside of

the mast. That led to friction,

often making it hard to wind the

sail in or out.

Seldén’s systems have now

been through several evolutions,

some using a furling line on a

helical worm-drive and others a

drum with an endless line. The

current Furlin RB system is the

most refined yet and the one

most commonly fitted to new

production boats with in-mast

Dunreefin: a hollow-leeched,

battenless mainsail came with

this Bavaria when the owner

bought her, but he has since

abandoned in-mast reefing and

switched to a conventional sail

Partial battens

allow a straight

leech or even a

small roach

Seamanship