Sharper Pic­tures

Marine elec­tron­ics is an ex­cit­ing area for any­one with an in­ter­est in tech­nol­ogy, and the un­der­wa­ter im­ages now avail­able on a MFD are as­tound­ing. To get op­ti­mum re­sults, though, you’ll need a hot trans­ducer.

Boating NZ - - Diy Boating - with NOR­MAN HOLTZHAUSEN

What would pre­vi­ously have been just a ‘fishfinder’ is now a Multi-func­tion Dis­play (MFD), and usu­ally in­cludes mul­ti­ple fishfind­ing and sonar ca­pa­bil­i­ties as well as GPS with chart­plot­ting, engine man­age­ment, radar and au­topi­lot in­te­gra­tions.

Most ex­cit­ing for fish­er­men, though, is the range of ul­tra­sonic ca­pa­bil­i­ties avail­able. Rather than just a sin­gle sonar beam point­ing down­wards, there are now nu­mer­ous tech­nolo­gies avail­able. Con­ven­tional two-di­men­sional fishfind­ing dis­plays have been en­hanced with Broad­band and CHIRP (Com­pressed High In­ten­sity Radar Pulse) tech­nolo­gies.

Both tech­nolo­gies take the same idea of a down­ward pulse of ul­tra­sound, but by varying the in­ten­sity, fre­quency and du­ra­tion of that pulse the clever elec­tron­ics are now able to pro­duce a much clearer pic­ture of what lies be­low.

Broad­band is a so­lu­tion that varies the pulse width ac­cord­ing to the con­di­tions and depth to pro­duce an op­ti­mal sig­nal. CHIRP trans­duc­ers, by com­par­i­son, trans­mit a longer du­ra­tion pulse that changes fre­quency, re­sult­ing in greater res­o­lu­tion and depth ca­pa­bil­ity.

In ad­di­tion, side-scan­ning and down-scan­ning sonar pro­vides a 3D view of struc­tures be­low and to ei­ther side of the boat. This al­lows the skip­per to not only see what is di­rectly be­low the boat but also po­ten­tially in­ter­est­ing struc­tures to ei­ther side. For scuba divers this is also a great fea­ture, since points of in­ter­est like caves can be iden­ti­fied be­fore jump­ing over­board.

The trou­ble, though, is that each of these tech­nolo­gies re­quires dif­fer­ent trans­ducer ca­pa­bil­i­ties. While broad­band and CHIRP can be sup­ported by the same con­ven­tional type trans­ducer (pro­vided it sup­ports the re­quired fre­quen­cies), the side-scan­ning op­tion re­quires a pair of long trans­ducer el­e­ments mounted lon­gi­tu­di­nally with the hull.

Down­scan­ning, which pro­duces a 3D im­age of what is di­rectly be­low the boat rather than to the side, also re­quires a spe­cial trans­ducer which can fire a sonar beam in a spe­cific pat­tern.

De­pend­ing on the brand of MFD you’ve fit­ted, your dis­play may al­ready sup­port the ad­di­tional tech­nol­ogy. You may have the op­tion to add an ad­di­tional trans­ducer, or re­place your

De­pend­ing on the brand of MFD you’ve fit­ted, your dis­play may al­ready sup­port the ad­di­tional tech­nol­ogy.

ex­ist­ing one with a multi-func­tion trans­ducer which pro­vides two or more tech­nolo­gies in one unit. In some cases an ex­tra in­ter­face is re­quired, such as the Sonarhub mod­ule for older Lowrance dis­plays, or a soft­ware up­date may be re­quired.

If you have one of the lat­est-gen­er­a­tion Lowrance or Sim­rad MFDS, you can get all four main func­tions in one sin­gle ‘To­talscan’ trans­ducer. This means that in­stead of two or more trans­duc­ers, a sin­gle unit can pro­vide all four func­tions as well as mea­sur­ing water tem­per­a­ture.

The only down­side is that the com­bined unit comes in one size (and thus power range), which is ideal for recre­ational boat­ies but may not suit those who like to fish re­ally deep. In that case a high-power trans­ducer, such as the 1kw units from Air­mar, may be more ap­pro­pri­ate.

IN­STAL­LA­TION Hav­ing de­cided you need a new trans­ducer, the next step is in­stalling it. This is ab­so­lutely the most crit­i­cal part of the en­tire fishfinder so­lu­tion, and get­ting it wrong will lead to poor re­sults and frus­tra­tion.

To func­tion well a trans­ducer re­quires undis­turbed water, and while this is easy when the boat’s at rest, many boats pro­duce aer­ated water along the hull when un­der way. The tra­di­tional tran­som-mount trans­ducer is the eas­i­est to in­stall on most ves­sels, but may also give the poor­est per­for­mance.

At high speed the tran­som-mount trans­ducer may not even be fully in the water, and many boats suf­fer from this prob­lem. If you have no­ticed that your ex­ist­ing fishfinder won’t give a pic­ture when the boat is moving fast, this is the prob­a­ble cause. For larger ves­sels, an in-hull or through-hull in­stal­la­tion may be bet­ter than a tran­som mount.

Shoot-through trans­duc­ers (mounted in­side the hull) can be used on solid hulls, ei­ther solid glass or alu­minium, al­though not on timber hulls or those with soft-cored fi­bre­glass con­struc­tion. Prop­erly in­stalled, this trans­ducer type is ar­guably the best op­tion since the trans­ducer it­self

does not dis­turb the water flow, and it can be lo­cated for­ward of the engine and so it’s al­ways in clear water.

Also, since they do not re­quire a hole to be cut into the hull, there is no potential for a water leak at the mount­ing point. An­gled units can be pur­chased to match the hull pro­file, and they can be in­stalled off-cen­tre so long as the keel is not in the line of the sonar beam.

When choos­ing a place­ment, make sure the unit is not try­ing to shoot through a chine or is close to a hull fix­ing, both of which will also af­fect the re­sult­ing im­age.

Through-hull units are the next op­tion, and these can ei­ther be flush-mounted on a suit­able hor­i­zon­tal sur­face, or fit­ted into a fair­ing block to cor­rect for the an­gle of the vee on the hull.

A hole needs to be drilled through the hull for the trans­ducer mount­ing screw, and the ca­ble is fed through this with ap­pro­pri­ate sealant. Many high-power trans­duc­ers are avail­able as through-hull mount­ings, since their tar­get mar­ket is of­ten larger com­mer­cial ves­sels.

The fi­nal op­tion, which gen­er­ally ap­plies to the large, flat side-scan­ning trans­duc­ers, is to sur­face-mount the unit. Again, this is only an op­tion if a per­fectly hor­i­zon­tal sur­face is avail­able since the side-scan­ning ca­pa­bil­i­ties re­quires a clear view to ei­ther side of the boat.

A sur­face mount does leave the trans­ducer ex­posed and li­able to be dam­aged if that part of the hull ever touches an ob­ject such as a trailer, or if the boat is ever beached, but that shouldn’t con­cern a launch owner.

Our project boat was com­ing out the water for new an­tifoul – a per­fect op­por­tu­nity to re­place the ag­ing fishfinder which came with the boat.

We spent some time de­cid­ing on a unit, even­tu­ally se­lect­ing the lat­est Sim­rad XSE pack­age, which in­cluded its To­talscan trans­ducer. Space al­lowed us the lux­ury of a larger dis­play, so we opted for the largest model in this range, the GO9 with a 9-inch touch screen.

Be­cause the boat is a glass-over-ply con­struc­tion, a shoot­through in­stal­la­tion was not an op­tion. Also, the very nar­row cata­ma­ran hull meant that the only tran­som mount op­tions were very close to the pro­pel­ler, so clear water while un­der­way could not be guar­an­teed.

On the other hand, each hull has a per­fectly flat bot­tom which runs hor­i­zon­tally while un­der­way, so ei­ther a through­hull or a sur­face mount were the best op­tions.

So we chose to sur­face-mount the To­talscan trans­ducer, or­der­ing the op­tional mount­ing bracket with the pack­age. This trans­ducer is not yet avail­able in a through-hull ver­sion, al­though the sep­a­rate Struc­tures­can unit pro­vides sim­i­lar ca­pa­bil­i­ties with a through-hull mount op­tion. With a rel­a­tively thin ply­wood hull the potential for trans­ducer dam­age would be the least of our wor­ries if we ever beached the boat!

The bracket could there­fore be screwed to the hull us­ing short stain­less screws that did not pen­e­trate through the ply­wood skin. Sikaflex sealant was ap­plied to each screw hole and the unit was at­tached.

Be­cause the To­talscan trans­ducer can be mounted with the ca­ble ex­it­ing ei­ther end, we po­si­tioned it with the ca­ble to the rear so it could be run up the tran­som the same way the pre­vi­ous tran­som-mount trans­ducer had been. It was then a fairly easy job to feed the ca­ble through to the helm and dis­play unit.

Job al­most done. It is im­por­tant not to ap­ply a sol­vent-based an­tifoul to the face of the trans­ducer, since the chem­i­cals can at­tack the plas­tic. Also, a soft (ab­la­tive an­tifoul) sur­face may ab­sorb some of the sig­nal and re­duce ef­fec­tive­ness.

West Marine pro­duce a spe­cial water-based trans­ducer an­tifoul­ing, which is rea­son­ably priced and works well. We ap­plied this to all ex­posed parts of the trans­ducer sur­face. We used nor­mal an­tifoul over the steel bracket and on the ca­ble.

Now we can’t wait to get her back in the water and see our gorgeous new dis­play show­ing 3D colour im­ages of every­thing around the boat. BNZ

Don’t ap­ply a sol­vent-based an­tifoul to the face of the trans­ducer – the chem­i­cals can at­tack the plas­tic.

BE­LOW Side-scan­ning sonar trans­duc­ers are long and flat.

RIGHT Po­si­tion­ing the trans­ducer for a sur­face mount on the bot­tom of the hull.

ABOVE A shoot-through hull trans­ducer is bonded to the in­side of the hull.

BE­LOW A fair­ing block is used on through-hull in­stal­la­tion to ad­just for the an­gle.


The fin­ished in­stal­la­tion. It just needs trans­ducer an­tifoul be­fore go­ing back in the water.

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