sailboat hull transducer

Please verify you are a human

Access to this page has been denied because we believe you are using automation tools to browse the website.

This may happen as a result of the following:

• Javascript is disabled or blocked by an extension (ad blockers for example)
• Your browser does not support cookies

Please make sure that Javascript and cookies are enabled on your browser and that you are not blocking them from loading.

Reference ID: 4d28569e-2ec3-11ef-8faa-c3ce22145351

Powered by PerimeterX , Inc.

• 2024 BOAT BUYERS GUIDE
• MIAMI BOAT SHOW
• Email Newsletters
• Fishing Boat Reviews
• Fly Fishing
• Marine Electronics
• Fishing Tackle
• Fishing Destinations
• The Bahamas Fishing Guide
• Boating Safety

Transducer Insight

• By Jim Hendricks
• Updated: February 22, 2016

We were cruising at 17 knots some 22 miles off Cabo San Lucas, Mexico, when the sonar screen lit up with returns from a massive school of fish. “That’s tuna!” said Capt. Eduardo Gonzalez. As he pulled back the throttles, three crew members scrambled to grab rods and cast metal jigs. Seconds later, we were in the midst of a triple hookup on school-size yellowfin.

This is the way sonar should work: You see the fish, you catch the fish. Yet it’s not always so easy. Fast-moving game species, such as tuna and kingfish, as well as forage species, like squid, can be notoriously tough to detect on sonar, especially when the boat’s underway. What’s the secret to seeing these on sonar? Whether you have a CHIRP or conventional fish finder, the answer often lies in the transducer you choose, where you place it and how it is installed. No matter what type or brand of sonar you have aboard your boat, if you are serious about finding fish, there are truths about down-looking transducers you must consider.

THINK IT THROUGH

There are three basic kinds of transducers: transom-mount, in-hull and through-hull. When it comes to down-looking sonar (as opposed to side-scanning sonar), forget the first two. Through-hull models are the choice of the more experienced captains.

A through-hull transducer has direct contact with the water, and that eliminates the signal loss you experience with an in-hull type. Because an in-hull transducer sends and receives sonar through a fiberglass hull, the signal degrades, impairing your fish finder’s ability to pick up details.

While a transom-mount transducer has direct contact with the water, it is more likely to be bathed in foam as water exits the stern and mixes with air while the boat is underway. “Aerated water interferes with a transducer’s ability to send or receive sonar signals,” says Peter Braffitt, general manager of Gemeco Marine Accessories, a distributor for Airmar Technology Corp., a leader in transducer development and manufacturing. “Clean water flow over the face of the transducer is critical to the proper operation of the system,” Braffitt adds.

A properly installed through-hull is more likely to stay in clean water than a transom-mount transducer, according to Braffitt. What’s more, through-hull ’ducers are available in larger sizes than transom-mount models. Why is that important? Read on.

If you are serious about finding fish, such as tuna and kingfish, Braffitt says not to scrimp on size when it comes to choosing a transducer. Larger models feature bigger ceramic elements. Elements are what send and receive sonar signals. Simply put, as size increases, so does signal strength and sensitivity. “The larger the ceramic elements, the more energy a transducer produces and receives,” Braffitt explains. “As a result, you see more fish and see greater detail on the sonar screen.”

In years past, many boats under 30 feet could not readily accept large through-hulls because these transducers protruded too far below the hull, creating drag, adversely affecting handling, and interfering with trailer bunks. On planing hulls, such transducers had the effect of a trim tab, disconcertingly lifting one side of the boat while underway.

More recently, however, Airmar introduced large through-hull transducers for both CHIRP and conventional sonar systems that mount relatively flush with a boat’s running surface. Flush-mount, low-profile installations help to prevent damage to the transducer from it striking underwater objects. Big, low-profile transducers, such as the Airmar B175, are available in tilt versions that look straight down, even when installed on the angled surface of a V-hull.

“The invention of the flush-mount transducer has revolutionized sonar use for boats under 30 feet,” Braffitt says. “Boats as small as 16 feet can now run big through-hull transducers with no issues in handling or trailering.” A number of boatbuilders also incorporate pockets along the keel of their hulls to facilitate flush-mount installations of large transducers, such as the Airmar CM599LH-W or R109LH-W.

An increasing number of saltwater fishing boats now feature step-hulls that usher a cushion of aerated water under the running surface to increase lift, boost efficiency and increase speed. Yet step-hulls have also created an issue that negatively affects transducers. When all that aerated water travels across the face of the transducer, it interferes with sonar signals, as discussed earlier.

The solution in this case is to install the through-hull farther forward than you would on a conventional V-hull (traditionally, through-hulls are positioned as far aft as possible). “On a step-hull, placing the transducer just in front of the steps, as close to the centerline as possible, helps keep it in clean water,” Braffitt says.

Because step-hulls tend to run relatively flat, the forward transducer location stays submerged most of the time. This allows the transducer to operate properly, even while the boat is running at high speed. In fact, the boat cited in the opening paragraph is a step-hull model — the new Mag Bay Yachts 33 — with an Airmar B164 through-hull, low-profile transducer for conventional 50/200 kHz sonar installed just forward of the front step.

LED DILEMMA

Another kind of interference comes from other electrical instruments. I recently installed LED navigation lights and discovered that my sonar was unreadable due to “hash” obliterating the screen. After I turned the lights off I realized the LEDs created radio frequency interference (RFI).

More separation between the wires for the lights and the transducer cable solved the problem.

Many marine LEDs are CE rated, shielded to prevent RFI. So if you retrofit your boat with LED lights, make sure they are CE rated. Should the fish-finder screen still suffer from interference, just separate the wires from the transducer cable.

For top fish-finder performance, choose the biggest and most powerful transducer, and ensure it’s installed in a manner that minimizes interference and maximizes sonar transmission and reception. Pay attention to these ’ducer details and you will find more fish.

• More: Gear , Marine Electronics , Transducers

How to Catch More Fish Using Soft Plastics

NextMarine: The Future of Saltwater Angling

The Benefits of Gyrostabilized Binoculars

8 Top Soft-Sided Tackle Bags and Backpacks

Using Weedless Baits to Catch Calico Bass

Popping for Tuna

Fun Fishing at the Historic Flamingo Lodge

The Mission to Make Custom Boat Gear Convenient, Easy & Fun

• Digital Edition
• Customer Service
• Privacy Policy
• Cruising World
• Sailing World
• Salt Water Sportsman
• Sport Fishing
• Wakeboarding

Where Is The Best Place To Mount A Transducer? (Top 5 Locations)

UPDATED 03 NOVEMBER 2023

by Robert Ceran

Are you wondering where to mount your fish finder transducer?

As you probably know, it’s essential to install your transducer correctly in order to get good performance from it.

Table of Contents

But choosing the right location to mount a transducer is more complicated than most people anticipate, since each location comes with its own set of challenges and pros and cons.

In this article we’ll go over the 5 best places to mount a transducer on a boat, and what you need to know in order to choose the right location for your transducer. 

Where to mount a transducer on a boat

The top five transducer mounting locations on a boat are:

• Transom mount
• Trolling motor mount
• In-hull mount
• Thru hull mount

Out of these five transducer placement options, the most commonly used ones by far are transom and trolling motor mounts, though the other three can also be great options for specific situations and applications. 

When choosing the right transducer mounting location, it’s important to keep in mind that all of these options come with their own pros and cons, and you should weigh these carefully before choosing the right one for your purposes.

Screwless transducer mounting kit

Pad for mounting your transducer without screwing into the boat hull.

Where to mount transducer on transom

Now let’s talk about choosing the best transom mount transducer location, since this is one of the most commonly used places to mount a transducer on a boat. 

Unfortunately, many anglers choose an incorrect transducer placement on the transom, and as a result they experience problems with their sonar imaging.

That’s why it’s so important to get the transducer placement right in order to achieve the best results.

What is the best transom mount transducer location?

It’s essential to mount your transducer in an area of the transom that doesn’t have any turbulence, since even a little turbulence can negatively impact the quality of your sonar image. 

This means you should avoid areas with turbulent water flow aft of rivets, strakes, or ribs in the hull. Choose a transducer placement spot on the transom where the hull in front of this location is flat and smooth.

Also, make sure that the transducer is at least 15 inches away from the propeller of your outboard motor, and check whether the outboard can rotate fully in all directions without bumping into the transducer (which needs to be checked in the fully trimmed position). 

What is the best transducer mounting height?

The best transducer mounting height is at the bottom edge of the transom, with the lower surface of the transducer protruding about 1/32 to 1/16 inches below the bottom of the boat.

It’s important to avoid mounting the transducer too high on the transom, since this will cause it to be out of the water at planing speed (keep in mind that the water level of the transom drops when the boat is on plane). 

If you mount your transducer too high on the transom, this will still allow it to function at slow speeds under 2 to 3 mph. But as soon as the boat gets faster than that, the transducer will stop working. 

Secondly, you also want to avoid the transducer being too low on the transom, as that will trigger turbulence and rooster tail formation, which also negatively affects the quality of sonar imaging. 

So the ideal transducer mounting height on the transom is with the bottom surface of the transducer just slightly protruding below the bottom of the boat (see diagram above). 

How far should a transducer be in the water?

The transducer placement needs to be deep enough so that its piezoelectric crystals are fully covered by water.

This can be accomplished even if the top of the transducer is flush with the water level, but if its crystals are out of the water, the sonar can’t function, and you won’t get an image. 

One thing you need to keep in mind is that the water level of the transom goes down at planing speed, and if your transducer is mounted too high, the crystals will be out of the water when you’re going fast.  

Should the transducer be flush with the bottom of the boat?

No, it’s actually better if the bottom edge of the transducer protrudes by about 1/32 to 1/16 inch below the bottom of the boat.

This is just enough to ensure that it is covered by water even at planing speed, but not low enough to trigger turbulence and rooster tail formation.

If the transducer is flush with the bottom of the boat, it will still work at slower speed, but not at high speeds. 

Can you mount a transducer too low?

Yes, if you mount a transducer too low, it will trigger turbulence and air bubble formation around the transducer, as well as rooster tail formation behind the transducer.

This turbulence decreases the quality of the sonar imaging, especially when your boat is planing at higher speed. 

What side of the boat do you mount a transducer?

A transducer should be mounted on the side of the boat with the downstroke of the outboard propeller, which is usually on the starboard side.

An easy way to check this for your boat is to observe the direction of rotation of your propeller. If it’s clockwise, then your transducer placement should be on the starboard side, but if it’s anti-clockwise, then the transducer should be on the port side. 

The side of the transom with the downward stroke of the prop has less turbulence than the side with the upward stroke, which is why it is the best transducer mounting location. 

Where to mount a transducer on trolling motor

The best place to mount a transducer on a trolling motor depends on the type of transducer you’re using.

A forward facing transducer (such as LiveScope, Active Target , or MEGA Live) should be mounted on the shaft of the trolling motor, as that gives it an unobstructed view in the forward direction.

The great thing about this type of transducer mount is that it will automatically point your transducer in the same direction as the trolling motor.

However, you can also achieve this with a trolling motor barrel mount if the transducer is placed on the side of the lower compartment.

If you want to mount a 2D or down imaging transducer on your trolling motor, the best way to do this is with a barrel mount, which uses a circular mounting bracket that fits around the lower compartment of the trolling motor.

This mounting location is ideal for pointing the transducer downwards without obstructing its view.

The best locations to mount different types of transducers

Now let’s take a closer look at different types of transducers, and the best mounting locations for each of them.

Where to mount a side imaging transducer

The best location to mount a side imaging transducer is at the transom, since that usually allows its sonar beams to shoot sideways in both directions while you’re driving the boat around, which enables you to scout large areas of water to both sides without having to slow down.

But when mounting a side imaging transducer on the transom, you need to take care that you put it in a spot where it isn’t blocked on one side by the outboard motor when it is fully trimmed down.

Where to mount a down imaging transducer

The best location to mount a down imaging transducer is either the transom, or the trolling motor.

Which transducer placement is best for you depends on whether you plan to use the down imaging while you’re driving around (in which case a transom mount is best), or while you’re fishing (in which case a trolling motor mount is best).

If you mount your transducer on your trolling motor, the best option is a barrel mount, since that allows you to position it at the very bottom and pointing downwards with an unobstructed view.

Finally, Humminbird offers several thru hull down imaging transducers that you can mount inside your boat without drilling a hole.

This option is great if you want to use down imaging to scan the water below while driving around with your boat at planing speed. 

Where to mount a LiveScope transducer

The best location to mount a LiveScope transducer is on the shaft of your  trolling motor, which is ideal for a forward facing sonar. This also holds true for other brands of live sonar, including Lowrance Active Target or Humminbird MEGA Live . 

However, an alternative option is to use a transducer mounting pole , which was specifically designed for live sonars, and can be positioned at the front of your boat similar to a trolling motor.

The nice thing about using a transducer mounting pole is that you can point your transducer in different directions independently of the trolling motor, simply by rotating the handle of the mounting pole.

The same mounting locations that are ideal for live sonar transducers are also a great choice for Humminbird 360 or Mega 360 transducers.

Where to mount an in-hull transducer

The best place to mount an In-hull transducer is as close as possible to the centerline of the hull and towards the aft end, since this part of the hull remains in contact with the water even at high speed.

If mounted correctly, this transducer location will allow you to get high quality sonar readings at high speed with an in-hull transducer.

But keep in mind that in-hull transducers can only be used on fiberglass boats, since fiberglass has sonar characteristics that are similar to water, which enables an in-hull transducer to shoot its sonar beam through the hull. 

When choosing the right location to mount an in-hull transducer, choose an area that has no ribs, rivets, or other protrusions on the outside of the hull, in order to avoid water turbulence.

You also need to avoid locations with cables or other sources of interference. 

Where to mount a thru hull transducer

The best place for mounting a thru hull transducer is as close as possible to the centerline of the hull and towards the aft of the boat.

Choosing an aft midship transducer placement ensures that the transducer will be in contact with water even when planing at high speed.

Also, if you have an inboard motor, make sure that the thru hull transducer is mounted forward of the propeller.

Where to mount a transducer on a pontoon boat

The best place to mount a transducer is at the bottom edge of the bracket at the back end on one of the pontoon tubes.

Since pontoon boats are built on top of pontoon tubes, they don’t have a transom like other boat types, and so require a different using a different location to mount a transducer.

When mounting the transducer, make sure that it is just under the water line, and parallel to the water surface.

If your cockpit is on the starboard side, it’s a good idea to mount the transducer on the same side, to make it easier to run a cable to the cockpit.

And when you lay down the cable, make sure to keep it away from any other wires or electronic devices that can cause interference.

Leave a Reply

Your email address will not be published. Required fields are marked *

• 2024 BOAT BUYERS GUIDE
• Email Newsletters
• Boat of the Year
• 2024 Freshwater Boat and Gear Buyers Guide
• 2024 Boat Buyers Guide
• 2024 Water Sports Boat Buyers Guide
• 2024 Pontoon Boat Buyers Guide
• Cruising Boats
• Pontoon Boats
• Fishing Boats
• Personal Watercraft
• Water Sports
• Boat Walkthroughs
• What To Look For
• Watersports Favorites Spring 2022
• Boating Lab
• Boating Safety

Installing a Transom-Mount Transducer on a Boat

• By Jim Hendricks
• Updated: April 6, 2020

It don’t mean a thing if ain’t got that ping. With apologies to the first lady of song, the late great Ella Fitzgerald, that sums up fish-finder performance. The world’s finest sonar is useless without a transducer that pings and receives the echoes in an effective manner. Ultimately, pings paint the picture of the underwater world. To work well, a transducer requires immersion in water that’s free of air bubbles that cause aeration and result in sonar interference.

Read Next: Airmar TM165HW Wide-Beam Chirp-Ready Transducer (Transom-Mount)

Many transducers are mounted with a bracket on the transom — a convenient location that requires no large holes in the bottom of the boat and eliminates interference with trailer bunks. But this zone is also prone to excessive aeration as H₂O streams out from under the hull and props agitate the water. These transducers demand careful installation. Here are tips for mounting one of the most popular transom-mount models, the Airmar P66 dual-frequency ’ducer (available with a speed and temp sensor)on a sterndrive boat with a 12-degree transom angle. Make sure the connector plug on the cable matches the transducer port for your particular brand of fish finder.

Skill Level: 2 of 5

Finish Time: Approx. 3 hours

Tools and Supplies

• Airmar P66 transom-mount Triducer with speed and temp sensors ($159.99, westmarine.com )

• Power drill, drill-bit set and countersink

• Phillips screwdriver

• Straightedge

• 3M 4200 marine sealant

• Electricians snake (for routing cables)

• Masking tape (to secure template)

• Measuring tape

• Stern Saver mounting block, to avoid drilling into the transom ($49.99, tacklewarehouse.com )

On single-drive boats, Airmar recommends locating the P66 on the side where propeller blades are moving downward, which is usually the starboard-side of a single outboard or sterndrive. It should be as close to the centerline as possible but at least 3 inches outside the swing radius of the prop blades. For twin drives, mount the transducer between the drives. Avoid areas abaft through-hull fittings or pickups that create turbulence. If you opted for a speed sensor, connect the cable to the fish finder and spin the paddle wheel to ensure it reads. Make sure there is a relatively accurate (ambient air) temp reading. If not, return it to your place of purchase.

Tip: An alternate to drilling holes in the transom, especially on aluminum boats, is to use a King Starboard (poly) block such as a Stern Saver to accept the retaining hardware. The block gets glued to the hull with a special adhesive, and hardware gets screwed into the block.

Cut out the supplied template and position it so the arrow at the bottom is aligned with the bottom edge of the transom. Be sure the template is parallel with the waterline, then tape it in place. Using a 9/64-inch bit, drill three holes 7/8-inch deep at the marked locations. To prevent from drilling too deeply, wrap masking tape around the bit 7/8-inch from the point. To minimize gelcoat cracking, run the drill in reverse until the gelcoat is penetrated. After drilling, lightly chamfer each hole with a countersink bit to prevent further cracking. Drill holes 90 degrees to the angled transom surface, not horizontally, to ensure that the screw heads sit flush with the bracket.

Tip: Drill the holes at position B on the template for hulls with reverse transom slopes of between 16 and 22 degrees. Use position A to drill holes if the slope is between 2 and 15 degrees.

With the bracket removed, apply marine sealant such as 3M 4200 (suitable for below-the-waterline applications) to the supplied three No. 10-by-13/4-inch self-tapping stainless-steel screws. Also squeeze sealant into each of the three mounting holes that you drilled in the previous step. Use a manual Phillips screwdriver to screw the bracket into the transom, but don’t completely tighten screws at this point. Slide the bracket up or down in the slotted adjustment holes until the distance from the bottom left corner and bottom of the transom is 11/2 inches. Then make sure the bottom of the bracket is parallel with the waterline. At this point, tighten the screws.

Open the retaining cover on the top of the transducer bracket by depressing the latch and rotating the cover downward. Then insert the transducer’s pivot posts into the slots on the top the bracket. With posts in position, push down on the transducer to click the posts in place. Rotate the transducer downward until it snaps into the bracket. Close the retaining cover. Install the paddle-wheel speed sensor, if you have one. Route the transducer cable to the fish finder. If it is necessary to drill through the transom to route the cable, be sure to use the supplied cable cap and sealant to prevent water intrusion. Use cable clamps to secure the cable along the length of its run.

Tip: If you need to release the transducer from the bracket, use a sharp upward blow with your palm on the underside of the ’ducer. This allows access to the mounting screws if you need to adjust the height. If the transducer accidentally gets latched before mounting to the transom, slots on each side of the bracket allow a screwdriver to be inserted, releasing the bracket.

• More: diy projects , How-To , transducer , Weekend Workbook

More How To

On Board With: Brian Grubb

Installing Clear Acrylic Livewell Lids

Captain of Dive Boat That Caught Fire Sentenced to Four Years

How to Make DSC Fully Functional on a VHF Radio

Boat Test: 2024 Checkmate Pulsare 2400 BRX

Cox 350 Diesel Outboard

Suzuki Marine Unveils New Stealth Line Outboards

Boat Test: 2024 Zodiac Medline 7.5 GT

• Digital Edition
• Customer Service
• Privacy Policy
• Cruising World
• Sailing World
• Salt Water Sportsman
• Sport Fishing
• Wakeboarding

Many products featured on this site were editorially chosen. Boating may receive financial compensation for products purchased through this site.

Copyright © 2024 Boating Firecrown . All rights reserved. Reproduction in whole or in part without permission is prohibited.

• Forums New posts Unanswered threads Register Top Posts Email
• What's new New posts New Posts (legacy) Latest activity New media
• Media New media New comments
• Boat Info Downloads Weekly Quiz Topic FAQ 10000boatnames.com
• Classifieds Sell Your Boat Used Gear for Sale
• Parts General Marine Parts Hunter Beneteau Catalina MacGregor Oday
• Help Terms of Use Monday Mail Subscribe Monday Mail Unsubscribe

Transducer through hull size

• Thread starter Suntala66
• Start date Mar 15, 2022
• Forums for All Owners
• Ask All Sailors

I recently bought a 1991 Hunter 37.5 Legend and I need to replace the depth finder transducer. I am told I will need to have my boat hauled out in order to install it in the same location, so I need to order one before haul out. I do not know the size of the original through hull so I can order the correct size to replace it. The manual says it is a ST50 but does not give the size of the through hull, so I need to make sure it is the correct one. If any Hunter Legend owners can advise me on this I would be most grateful.  

SBO Weather and Forecasting Forum Jim & John

Instrument Transducers | Raymarine

Welcome to the forum and congratulations on your new sailboat!! Thru hull should be 2-inch diameter and the transducer should be retractable. Confirm the diameter, manufacturer (Airmar?) and model.  

Ralph Johnstone

Time to go modern and install an "in-hull" depth transducer. Transducers are usually an extra to the display instruments so you can hold on to your display if it's not too old.  

Suntala66 said: I recently bought a 1991 Hunter 37.5 Legend and I need to replace the depth finder transducer. I am told I will need to have my boat hauled out in order to install it in the same location, so I need to order one before haul out. I do not know the size of the original through hull so I can order the correct size to replace it. The manual says it is a ST50 but does not give the size of the through hull, so I need to make sure it is the correct one. If any Hunter Legend owners can advise me on this I would be most grateful. Click to expand

Barnacle Bill

Buy the instrument of your choice with the transducer(s) and if the existing hole is a tight fit, use it as is. If the existing hole is too large, then fiberglass up the too big hole and recut another hole to fit the new transducer size. If your existing hole is smaller than the hole needed for the new transducer, then make the hole bigger. To do that, get a hole saw the size of the existing hole and have someone inside the boat place a piece of wood over the hole and hold it in place and then drill out the pilot hole into the wood from outside the boat. A long piece of wood works best because your inside person can place each of his/her two feet at the ends of the wood with no worry that it will move because pressure will be applied to hold it in place, and not worry about drilling a hole in a foot. With the wood inside still in place and secured with the pressure of the feet of your inside person, you can use that pilot hole to drill out the larger hole saw size. Obviously the boat has to be out of the water and also you need to use the appropriate caulk to bed the new transducer(s).  

• This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register. By continuing to use this site, you are consenting to our use of cookies. Accept Learn more…