What transducer should you mount on your boat?

It’s all well and good that you’ve found the perfect fishing boat, but getting the most out of those expensive marine electronics on the dash means knowing where and how to fit a transducer.

Believe it or not, there is more to transducers than just a screen, a bit of wiring and attaching a transducer to the hull.

WHAT TRANSDUCER IS RIGHT FOR YOU?

The Trade-a-Boat Haines V19R project boat (since called the Nautek N19R) was kitted out with a state-of-the-art Raymarine electronics package. We used some of Raymarine’s excellent online information on transducers and fishfinders.

Even if you’re not fishing, having a fishfinding sonar unit is a handy bit of equipment to have, doing more than just sound depth. These systems work by transmitting a radio frequency in pulses or pings from their transducers. These sound waves echo back to the boat once they strike the bottom and the stuff in between. This information is interpreted providing an accurate depth reading, a visual representation of the sea, dam or river floor, the structure above, plus the fish of course.

Then there’s the environment in which transducers work. Raymarine lists salt, minerals, plankton, algae and other plant life as some of the things that absorb sound waves, particularly at higher frequencies where they can affect transducer performance. The same applies to bubbles created at the surface, meaning the unit should be kept clear of this type of instability.

Fortunately, there is a measure of control over the performance of a transducer. Here are three things you can control when fitting a transducer:

• Power | The strength of the sonar ping, where more power equates to deeper penetration, clarity of structure and fish, and good response in murky conditions.

• Frequency | On our Haines V19R project boat, the Raymarine fishfinder uses a low 50kHz frequency for deep water penetration to more than 60m, and a high 200kHz for under 60m.

• Sonar beam cone angle | A wide angle at lower frequencies covers more area out from the boat but at lesser resolution, while a narrow beam at higher frequency images a smaller portion of the area but with more clarity. We use both on our V19R project boat.

With that in mind, now it’s time to consider the material of the transducer. Raymarine recommends the following materials:

• Plastic | Moat suitable for fibreglass and metal hulls.

• Bronze | Best for fibreglass and wooden boats. This is especially important for the latter, as expansion of the timber can damage a plastic transducer.

• Stainless steel housings | These are best for steel and aluminium hulls.

HOW TO MOUNT A TRANSDUCER ON A BOAT

There are several ways to fit a transducer on a boat. Each has distinct advantages and disadvantages.

TRANSOM MOUNT

Generally plastic and the cheapest option. Our V19R project boat has one of these.

PROS

• Cost
• Easy to install and clean 

CONS

• Best for boats less than 8m (27ft)
• Performance not as good as thru-hull.

IN-HULL

Fixed to the inside of the hull, for solid fibreglass hulls only. Our V19R has one of these also.

PROS

• Inexpensive
• No holes in hull
• No obstructions in water
• Low maintenance

CONS

• Reduced depth reading
• Poorer fish detection
• Can only be used in fibreglass hulls

THROUGH-HULL

Provides best performance for transducers. Recommended for displacement boats and shaftdrive inboards.

PROS

• Best performance
• Can operate at faster speeds

CONS

• Needs a hole drilled in the hull
• Requires a fairing block
• More maintenance  as it’s susceptible to fouling and marine growth.

TILTED ELEMENT

Flush-mounted to hull and doesn’t need a fairing block. Not affected by the recommended angle range of the boat, with an internal self-levelling element always directing the beam down. Performance of these transducers is similar to a through-hull mounting.

PROS

• Flush mounted
• Available in two versions: 12° tilt for boat deadrise of 8° to 15°, 20° tilt for boat deadrise of 16° to 24°

CONS

• Needs hole drilled in the hull
• More maintenance with susceptibility to marine growth
• Needs to be mounted in a position that’s always underwater

See the full version of this story in Trade-A-Boat #459, November / December 2014. Why not subscribe today?