--aj

rPfiflil[#]*il.lr,i#the tropics to the Arctic, Balena - our 42ftgaff cutter with a 5ft draught - has run into an

I lOst,rction at least once a year.

I Forward-scanning sonar seemed a usefultool to warn of lurking dangers in poorly

_ charted waters or when navigating a narrow

I channel I looked at two units suitable for

I yachts.

l. The most economical is the British-desisnedEchopilot Bronze, costing L441 . lt has a clear

display and simple controls but range anddepth are l imited. This is not a problem inshallow waters but l imits the warning t imefor spotting obstructions ahead. Only verticalscanning is possible. The transducer is plasticand reouires a 45mm hole to be cut in theboat. Echopilot also markets a Platinum versionfor f1,499 (see panel right).2. Interphase, based in the USA, offers unitsthat scan vertically or horizontally (or both) withmaximum range of up to 240 fathoms. Thetransducer is mostly bronze and only requires a26mm ho le in the hu l l .

We opted for the Interphase Color

#t-*-tt-- J

Twinscope, costing f I ,857. Modern boats withflat sections can probably mount a transducerused for horizontal scanning just to one sideand slightly back from the forward edge ofthe keel. The best option for an unobstructedview aboard long-keeled vessels like Balenois instal lat ion in the stem, or just to one side.Interphase offers a two-transducer option, onefor each side of the keel, but I was not wi l l ing todri l l two holes in the hul l .

SONARTRIALSAfter we installed the sonar, we practiced withit in Norway, where rocks can appear near

Lt l4 M.yachtingmonthly.com . FEBRUARY 2007

FTTTTNG SONARJ

4 1 .RIGHT: Horizontal scan

of headland (pictured

below) showingit projects furtherunderwater. The cursor

shows range and depth

but not if it will get

shallower than 20m

I

----;;i'lget',o ui

lw' zz'znlwv t76,:4tL

I

a

=6

o

a

ABOVE: Navigating through a narrow channel:

steeply shelving water ahead to port (red

return)and probably gently shallowing to

starboard. The arc of display has been reduced

to speed up the refresh time

Echopilot

This award-winning British company has a full range

of forward-looking sounders, from the square-shaped

monochrome Bronze, with plastic transducer, to an

NMEA compatible, colour TFT Platinum widescreen

model, which has 200m range and video output for

multifunction screens.

Prices: Bronze f441;Silver t62O; Gold f840; Platinum

f'|,499. A Platinum engine is also available for f949

which plugs directly into multifunction screens.

Contact: Echopilot Marine Electronics Ltd

Tel'. 01 425 47 62'll ; www.echopilot.com

. , : l

Interphase (American based)

Andy fitted the Colour Twinscope. Interphase also has

an iScan '180

which boasts a full | 80" forward horizontal

scan. The Probe is their monochrome budget model, but

is forward looking only.

Prices: Colour Twinscope

f '1,857.68;

Probe f898.88

Contact: Mantsbrite Marine

Electronics

Tel :0)162'1 853003;

wwwmantsbrite.com;

www.i nterphase-tech.com

Finding deep waterIt 's fair ly s mple to see where deeper and

shallower waters l ie using the horizontal scan.

To determine actuaL depth ahead, i t is necessary

to face the area of interest and check with the

vert ical view When coming up to headlands or

seamarks, we can assess how far undenrvater an

obstruction extends. Fol lowing a coastl ine, in

the dark for instance, the horizontal view shows

exactly where shallow water s.Warning of rocks and reefs ahead

Using horizontal and vert ical scanning we

prcked up dangers over 320m ahead. When

first met by the horizontal beam, a rock with

J t

'At a range of 32m, I can see where a mudbottom {helves upwards or rocks lie in wqit'

the surface even though the surroundlngwater is hundreds of metres deep. The charts

are excellent, so there was no great risk of

grounding while learntng to interPret the

display. Power consurnPtion was about I A.

We found a shal low, navigable channel

with known dangers and sai led back and forth

tryrng out dif ferent display options. Like radar,

sonar needs ski l l and experience to interPret.

Radar works in a range of mi es while the

Twinscope works in metres and requires either

very slow boat speed or rapid judgement.

When reading the display, i t 's important to

keep in mind that soft mud gives a weaker

ref lect ion than rock and an upward sloping

seabed ahead returns a stronger echo than

a leve seabed. A downward slope gives the

weakest echo, or no return. The colours on

the display are graduated to lndrcate strength

of return whrch is a great aid. I was impressed

and found the sonar useful in the fol lowing

sttua|ons.Survey of a new anchorageWhere a chart lacks detai l , the sonar helped

alert us to obstructions. ln only 3m and at a

range of 32m, I can see where a mud bottom

shelves upwards or rocks ie tn walt. In deeper

water the range ts mucn greater.

FEBRUARY 2007. www.yacht ingmonth y .com 45

t-30m over i t wou ld look the same as one w i thon ly 1 - r . T l -p deeper roc l wou d d sappear[ r n m l h c \ . r c o n ) \ | r n i : q : n n r n : e h p d r n r h c ' e ; c' " - " - r r

the sha lower one would move closer. Weprefer the vert ical view for spott ing bottomlsnge 's d le . t l y ahead, as ' t c lear ly shows t l -ei o n t h r t r t h r r h n h o r t < e

Warning of surface dangers aheadWir i ve ' t i ca l scan, sh ps pass ng a iead ar r ieimit of our range show up as a surface echo,evel t l -e wash 'Ton a fasr -ovrng powerboa l car be seen. We have t ' ,ed de l ibera te ly, , , ^ i ^ - ' - . . . ^ , ! . \ , - . r . . . a n e a r L h e l i m L

of range and i t shows up immediately andcreany.

WHAT ARE THE PRACTICALTIMITATIONS?I. The angle of the horizontal beam means thatr s r r : l es a leve ,eabed a t a d i - tance ahead o Iapp o" i -a te ly [ i ve to s ix t imes lhe dept l - . Sothe range is l , - i ted . ospec ia l l y rn s la l low waterand there can be a problem decrding howdeep an obstructron is.2. Scanning t ime imits the speed at whichthe d ispray is L ,pda ed . Ob ecrs can sudder lych :noe nns i f i n r o r ' l - e r e r egp w l -e^ r he boa r

i . m n v ; n p o l l r . l n i n p l , \ e l \ . a n s e l e c t a s m " l l e t' - ' b b - " _ " '

arc to scan or use a shorter range, whichspeeds up the scannrng rate3. Surface clutter and noise is a problem. Withhigh gain sett ings and long ranges, there iso F c n r h p : a n t r ) r ) n a c n f : n n h . t . 'u r H L u , u l

ahead of the boat and rn rough weather it's/ t f { i e . t t o I s r i ^ o . . . q l - n h i c c r 5 6 O , e t O t l - e

surface.

HOW COUTD THE TWINSCOPEBE BETTER?Alarm is too quietThe in-bui l t alarm is so quiet you need to f tan ex le rna a la rm. l l -e cor r ro l : fo se t t ng thea aTm aTe rather crude and only al low forc o l o - n n . t a , c | n ' l d c n r h n V e l t i - a l V i e w o t

forward drstance in horizontal view. t wou dA ^ A ^ r ' ^ . ' ^ A ^ . A l ^ r ^ . ^ l ^ - , . ^ . . ' - , 1 . . . , ^ .I i F I i r l r F r ( ' 1 , t s d L , t t s t r ) \ F l t s ' L d

P a t u t d a t * a

of the scan to be monitored by the a arm

What comes in the box - the transducer,manual, and control/display head.

Ulla and Andy fit and seal the recess for the transducer with epoxy and a layer of glass cloth

Ufla appfies bottom paint to the installed and faired transducer in Bal@na's stemt,

func t ion .Changing range

I Tre co^srar r neec ro c^drge d^ge a1o

I eadtusr ga i r - wo- rd oo imo ovec oy arau tomat rc op t on .Gain control

l -

I Because ga i^ has -o oe ad jusrec "eq le rL v

I a rd t le dJ tomdt ic se t t ing is o f ten 'a r f 'o -idea l , I wou ld l i ke to see an op t ion fo r a garncor t ro l tha ts a lways immed a e ly avar lab p .

a '

I Depth function

I Because o f r re range a^d ga i r^ p rob lems lheu n I d d n t - a t c l u p r o o u r s - p l e f i s h ' r d e .as a deptn sounder

I s"l".tion of unitsI I r e m a ' i m l m u p p ^ r - a n g e w t h d l l e r r g - n t

i s ( a p p ' o . i m a r e n e t r p s r r b a c ( e t s ) : M e t r e - :

r nqd . r . p r r : t ho nn t i . n o e " t end t he sha fu" r ' ' " " "

for f i t t ng through the th ick stem of a wooden

boat. A

The Interphase Colour Twinscope is in

daily use aboard Balena. I believe that

conventional depth sounders will rapidlygive way to forward-looking sonar. The

Interphase has a greater range but Echopilot

claims a much quicker update, which could Ibe useful for rock hopping. j

f20m;Feet: I ,200ft (366m) and Fathoms

Preparing the transducer

Andy chisels a recess for the transducer

'Surface clutter and noise is a problemand in rough weather it's difficult todistinguish objects close to the surface'240 fathoms (439m). This means that usersof fathoms can 'see' I I 9m further ahead thanthose who choose metres. This rnstrument sr 'ndr .ecd i r - he I l (A rvhcrp met r ca t on isn tused.Display ratioIn shal low water the vert ical image isr r : m m c d r r n : o : i n . r t h c r n n n f r h c r i i < n l : r ,- r - o - ' . - r

and can be dif f cult to read, unless youd o e r a a c a t h o r : n o o r a r h i r h r. . , , _ , , n a y m e a ^o v p r l o o L n q d : n q c r q : h p : d

Transducerwould have iked a more st reaml ined

!,o

I

46 www.yacht ingmonth y .com. FEBRUARY 2007

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