Practical Boat Owner – June 2019

Q

How do you work out

the holding strength of

a mooring?

My mooring is on hard

sand in the north-west of

Scotland. Designed by

Gaelforce it has two 60kg

Sampson anchors joined by

12m of 32mm ground chain

to 11m of 16mm risers plus

swivels etc. I see moorings

indicating 15 tons or 20 tons

but Gaelforce didn’t indicate

the strength of my system. It

was designed for a 28ft

Westerly, all up probably

three tons and in an

exposed spot so I believe it

was over specified but

would welcome advice on

how to estimate the holding

power. It would be useful if a

friend were to drop by with a

bigger boat!

As you can see from the

photo, the mooring is quite

remote, on Loch Moidart. I

use it in summer only – in

winter she’s on the hard at

Arisaig. Even so storms

rattle through at any time of

year so the mooring has to

be strong. Kelpie D is a

Westerly Merlin, and we

belong to the Moidart

Mooring association.

Martin Whitehouse

Hale, Cumbria

ANDY LANCASTER

REPLIES:

The holding strength of the

mooring depends on so many

variables. The rating of any

mooring will vary with the

seabed conditions, water

depth, weather, time of year,

condition of each component,

marine growth etc.

Your mooring is well

over-specified for your yacht –

which is a good thing and

means that you can sleep well

on breezy nights, even if you

live a distance away.

If your (wealthy) pal visits with

his much bigger yacht, it will be

fine as long as there is room

for it to swing. Obviously it will

Martin

Whitehouse’s

Kelpie D is

moored in

Loch Moidart

Q

I’ve replaced the

alternator on my

20-year-old Beta 20 engine.

The company that sold me

the new alternator replaced

the connection to one of the

brushes for the Sterling

smart charger and soldered

a connection to one of the

stator coils for the

tachometer. I gave them the

old alternator and they

assured me that they have

made the connections

identical on the new

alternator. The old alternator

was a Nippondenso and the

new one is an identical,

genuine Denso replacement.

On starting the engine, the

needle on the tachometer

immediately spins round to

full deflection hard against

the stop at 4,000rpm. Even at

the slowest tick-over the

tachometer is showing

1,200rpm and any increase

in revs sends the needle to

the 4,000rpm stop. The

alternator is charging at

14.5V as shown on my

battery management meter.

I have not made any

adjustments to the

tachometer or to the boat’s

wiring. I do not really want to

start altering anything until I

have a clear idea as to where

the fault may be, so your

help would be very much

appreciated.

Ian Dodsworth,

Barbon, Carnforth

DUNCAN KENT REPLIES:

The wire for the Sterling smart

alternator regulator should be

attached to the alternator’s field

coil, which is what controls the

alternator’s output.

The tacho connection to an

alternator requires a wire from

one of the stator coil outputs

(often marked with an ‘R’ and

soldered onto the input side of

one of the rectifier diodes),

which will supply an output of

around 8.0V AC. Make sure you

do not confuse the two wires.

The tacho should be

adjustable to suit the engine,

either by DIP switches or an

adjustment screw, and should

be carried out while the engine

is at typical cruising revs – circa

2,200rpm for a Beta 20.

require more space around the

buoy. You should discourage

him from staying there in really

bad weather though.

To specifics, these anchors

are certified to have a holding

power of ten times their weight,

(when new) and in hard sand

they will hold way more than

that. The actual amount will

depend on the characteristics

of the seabed. Naturally, this

type of anchor has to be laid

correctly. If it is laid upside-

down it will be useless.

The heavy ground chain is

an essential part of the

system. It is designed to be

heavy enough so it is not lifted

off the seabed, and even if

there were no anchors on the

ends it would be hard to drag

it. It also ensures that the load

on the anchors is in the

design direction, horizontal

and away from the blade. The

ground chain has to be

stretched out tight on the

seabed with the anchors laid

in line, and the right way up.

The riser chain will be

continually clanking and

dragging on the seabed, so

this is what sustains the most

severe wear and tear.

You should remember that

your mooring is basically a

simple machine holding your

valuable yacht in place. It is

operating 24 hours every day

whether the boat is on it or

not. It is working in vile

conditions, with no lubrication

in corrosive salt water against

an abrasive seabed, so

regular inspection is essential.

■ An expert in his field,

Andy Lancaster spent 22

years working as a mooring

contractor.

MOORINGS AND BERTHS

PAINT AND

ANTIFOULING

Richard Jerram is

former UK technical

manager of

International Paint

50 of the most frequently asked boating questions are answered by our experts on the PBO website. Visit http://www.pbo.co.uk

GAS FITTING
Peter Spreadborough,
of Southampton
Calor Gas Centre,
has 20 years in the
industry

TRAILER-

SAILING

Colin Haines is a

design engineer

who has trailer-

sailed for 25 years

ELECTRONICS

Andy Haines of

Greenham-Regis

Electronics is an

expert in marine

instrumentation

TOILETS AND

PLUMBING

Karl Sutcliffe of Lee

Sanitation knows

about holding tanks,

toilets and plumbing

YACHT DESIGN

Andrew Blyth is a

naval architect with

interest in stability

and buoyancy

WOOD

Richard Hare is a

wood technologist

and long-time

wooden-boat owner

BOATBUILDING

Tony Davies has

been building and

repairing wooden,

GRP and steel boats

for 40 years

ELECTRICS

Mooring holding strength

Wayward tacho