Yachting

PHOTO: GRAHAM SNOOK/YM

TECHNICAL

74 http://www.yachtingmonthly.com MAY 2016

We rely on bow rollers and cleats

without giving them a second

thought. Should we be paying them

more attention? Alastair Buchan investigates

W

hen a yacht

suffers gear or

engine failure off

a lee shore, her

crew’s last lines

of defence are getting a tow or

throwing the anchor overboard

and hoping it holds. However,

even the world’s best anchor and

strongest chain count for nothing

if your deck fi ttings are not up

to the job. Often overlooked and

rarely included in the annual

maintenance routine, your cleats

and bow roller could be your

weakest link that let you down

when you need them most.

Unless you’ve had the boat

from brand new or replaced

your bow roller or cleats, it’s

impossible to know what forces

have been exerted on them

before you bought her – or even

if they were really up to the job

in the fi rst place. There is no

guarantee that they are the right

size, correct design or able to

safely take the considerable loads

imposed by winds, waves and

swells. Additionally, when used as

a fi xing point for forestays, bow

rollers must cope with the mast

whipping about too. Finally, they

must take high downward loads

when you break out the anchor.

Taking the loads

The loads on deck gear vary

according to whom you ask. The

American Boat and Yacht Council

(ABYC) has a table of anchor

loads from the combined effect

of wind and seas for various boat

lengths and Professor John Knox,

inventor of Anchorwatch, reckons

that the force on an anchor in
kilograms is (1/500) x (boat’s
overall length in metres)^2 x (wind
speed)^2 , but this doesn’t take
into account freeboard and gives
different answers to the ABYC.
Well-designed bow rollers share
a number of common features that
make them suitable for anchoring,
lying to a mooring and towing. A
lot depends on the size of the roller
in your bow fi tting. In turn, that
depends on the diameter of your
anchor cable, be it chain or rope.
Since choice of anchor cable is a
personal preference, boatbuilders
ought to fi t the option demanding
the most space, which is rope. The
rule of thumb is a anchor rope
should have 1.5mm diameter for
every metre of the boat’s overall
length, with a minimum of 10mm.
Chafe protection doubles this and
adding some extra space for a
comfortable fi t means that even
the smallest bow roller should
handle a 25mm rope with ease,
but many can’t.
The cheeks of the roller that hold
the cable in place as the boat yaws
around must be strong enough to
resist bending or breaking from
side loadings they’ll experience.
Bow rollers overhanging the bows
create frightening horizontal and
vertical loads, but the forces are
manageable by taking them onto
the hull via a tang on the yacht’s
stem. This arrangement has the
SOURCE: ABYC bonus of eliminating the hinge

LOA (m) BEAM (m)

Mean Wind Speed

13 knots

MODERATE BREEZE

Mean Wind Speed

30 knots

NEAR GALE

Mean Wind Speed

44 knots

STRONG GALE

Mean Wind Speed

60 knots

VIOLENT STORM

8 2 57kg 222kg 445kg 889kg

9 3 79kg 318kg 635kg 1,270kg

11 3 102kg 408kg 816kg 1,633kg

12 3 136kg 544kg 1,089kg 2,177kg

15 4 181kg 726kg 1,451kg 2,903kg

18 5 227kg 907kg 1,814kg 3,629kg

Load acting on your anchor

Are your deck fi ttings

the weakest link?

Your bow roller

has to suit your

style of cruising,

the more you

use it the

stronger it

should be

PHOTO: ALASTAIR BUCHAN

Bow rollers are vulnerable to

horizontal loads as the distorted

cheeks on this fi tting show