Practical Boat Owner — January 2018

Practical Boat Owner t http://www.pbo.co.uk 37

ENGINE EXHAUST

COLREGS

PAINT AND

ANTIFOULING

Richard Jerram is

former UK technical

manager of

International Paint

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

Chris Ellery of

Greenham-Regis

Electronics is a

former Merchant

Navy officer

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

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

BOATBUILDING

Tony Davies has

been building and

repairing wooden,

GRP and steel boats

for 40 years

ASK THE EXPERTS

Q

I’ve decided that one of

my jobs this winter

should be to install an

anti-syphon valve since my

engine is well and truly below

the waterline.

Having looked at the

suggested installation by a

well-known manufacturer, I’ve

wondered whether a simpler,

cheaper but possibly equally

effective installation may do

the trick?

This would involve tapping

into my injection elbow from

the heat exchanger to the

exhaust with a single tube

(fitted vertically up from the

elbow and satisfying the 40cm

above the line requirement),

which in turn has a non-return

valve somewhere along its

length. So when the gases

inside the exhaust cool and

Q

Could you please clarify

the COLREG rules

regarding steaming lights?

My Hunter Horizon 27 has

never had a dedicated

steaming light fitted to the

mast from new. It has a

masthead tri-colour and

anchor light, and there is a

bi-colour fitted on the bow

and a stern white at deck

height. All these are fine

under sail, but under motor is

it preferable to travel with the

lower nav lights on?

Robert Smithyman,

Grimsby

contract enough to create a

syphon effect, air is drawn in

through the non-return valve,

releasing the negative

pressure formed.

You may well say: what if

the syphon effect is so

powerful that somehow water

from the water lock (which I

drain very regularly) is drawn

up the exhaust? Then I’m

really stuck, I suppose!

Stelios,

by email

STU DAVIES REPLIES: If I’ve

got this right, I think the idea is

based on the assumption that

STUART CARRUTHERS

REPLIES: There’s often

confusion about what is a

steaming light and a masthead

light. The proper terms defined

in COLREG are masthead light

and all-round light. COLREG

doesn’t define a steaming light.

A ‘masthead light’ means a

white light placed over the

fore-and-aft centreline of the

vessel showing an unbroken

light over an arc of the horizon

of 225°, and fixed so as to show

the light from right ahead to

22.5° abaft the beam on either

side of the vessel. This is often

called the

steaming light.

An ‘all-round

light’ shows an

unbroken light

over an arc of

the horizon of

360° (often

referred to as

a masthead

light).

A power-driven vessel under

50m in length underway is

required to exhibit a masthead

light forward, sidelights and a

stern light. A power-driven

vessel under 12m may exhibit

sidelights together with an

all-round white light in lieu of

the masthead and stern lights.

A sailing vessel underway is

required to exhibit sidelights

and a stern light. In a sailing

vessel of less than 20m in

length these lights may be

combined in one lantern at or

near the top of the mast where

it can best be seen.

I don’t know how old your

boat is, but provided the

various lights can be

independently switched on

and off you should be able to

select the correct combination

for motoring or sailing. If you

wish to use the sidelights and

stern light while motoring then

you need to fit a masthead

light on the mast, on the

boat’s centreline.

Shed light on confusion

Water in

the engine

worries

raw cooling water. If this loop

isn’t high enough then sea

water can come back along

the hose and flood the engine

when the boat is heeled.

The silencer’s water trap

plays a part here as well in

acting as a reservoir to absorb

some flow back. High rise

elbows are an option, playing

a part in the system by raising

the height of the exhaust at

the engine, in relation to the

hull. If you’re concerned then

perhaps take a look at the

diagram as well as checking

the height of your exhaust as

it traverses the hull.

cooling components cause a

suction-effect that sucks back

cooling sea water from the

silencer water trap. I’m not sure

this is the case and you may be

trying to solve a problem that

doesn’t exist!

The exhaust gases push raw

water out of the silencer water

trap and along the exhaust hose

until it exits the boat. There’s

usually a loop in this hose which

gives it some height for the

water to go over and out. This is

where the characteristic blub,

blub, blub comes from as the

exhaust gases create enough

pressure to push out slugs of

Normal sea

water level

12 inches

minimum

Anti-siphon

or T-piece

Waterlock

muffler