Practical Boat Owner – May 2018

for 350-400 miles in flat water at around five
knots, and still had enough fuel left for 10
hours’ motoring when we reached Muros,
but had we been significantly further
offshore it wouldn’t have been possible to
motor to port. Given the strong to gale
force easterlies forecast to stay for several
days, the Galician coast would most likely
have been out of reach under jury rig, but
we at least had enough spares and tools to
make a watertight repair to the deck.
As for a jury rig, with the stump of the
mast left it would have been a relatively
simple operation to lash the spinnaker
pole against it, with the head supported
by Dyneema stays, to create a spar
around 5m off the deck. We had enough
water and food on board for a further
fortnight at sea, so even at an average of
only three knots we could have reached
Lanzarote, or a closer harbour in Portugal.

We can only speculate on the size of the

wave that hit Zest, but the science of

wave predication can help to ascertain a

possible maximum limit on how large it

might have been.

My long-standing belief had been that

the maximum wave size that you had

any chance of experiencing was twice

the significant wave height – ie double

the average height of the largest 30% of

waves – which in our case would have

been around 7m. Latest scientific study,

though, suggests a rogue wave can be

much, much larger.

Normally if a chainplate pulls out of a

bulkhead it’s a result of water ingress

that has weakened the timber, but

subsequent surveys showed the material

on both sides was perfectly intact and as

strong as when Zest was built.

We think the most likely cause relates

back to when the mast was replaced

two years before Kass bought the boat

• the spar that broke was only four
  years old. It seems the new rig had
  stronger standing rigging than the
  original, possibly as a result of changing
  from rod to the nearest (stronger)
  equivalent of Dyform wire. This may
  have been sufficient to move the weak
  point in the system from above the deck
  into the structure of the vessel. So
  beware of unintended consequences if
  you beef up only one element of a boat!

LESSONS LEARNED

1

Keep waterproof head torches

to hand.

2

A cordless angle grinder

was useful to cut the shroud

that was in tension. We’d

already tested the bolt cutters

in Zest’s original inventory and

discovered they were not up to

the task. Sharp knives put paid

to the internal halyards.

3

Good pumping arrangements

are reassuring.

4

Engaging a professional

weather router would

have been beneficial. A

knowledgeable person ashore

who is able to gather data

with ease – and has the time

and skills to make an in-depth

analysis – can bring benefits out

of proportion to the relatively

modest cost.

5

It was reassuring to know

that we both had recent sea

survival training, along with

first-rate emergency equipment,

plus a very comprehensive set of

tools and spares.

6

For serious offshore use

I’m now more sceptical of

monohulls with low bridgedecks.

Even if washboards are stowed

ready for use, it’s all too easy

to be complacent. The same

applies to multihulls with patio

doors and no way to stop water

in the cockpit from flooding into

the hulls.

7

The knowledge that rogue

waves are more prevalent

than was previously believed

reinforces the dangers

associated with entering a port

with a shallow bar, such as

many on the Atlantic coast of the

Iberian peninsula, in an onshore

swell. It only needs a big wave

to appear at a critical moment

to flip what initially appeared to

be a manageable situation into a

life-threatening scenario.

ROGUE WAVE AND STRUCTURAL FAILURE

The scene at dawn
after Zest’s
dismasting. The sea
state was well down
and, after a final tidy
of lines, we were able
to motor towards port

Drying out in Muros after making it safely

to port – Kass standing up through the hole

torn out of Zest’s deck

Following the dismasting, Zest was

repaired in Cowes, with a new rig

installed ready for the 2017 OSTAR

transatlantic challenge, in which Kass

participated and survived a 70-knot

storm that resulted in the loss of four

competing boats.

Find out how it went at PBO Ask the

Experts LIVE! at Beaulieu Boatjumble

on Sunday 22 April.

Hear more about Zest’s

offshore sailing adventures

Practical Boat Owner • http://www.pbo.co.uk 57

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