Airmar B175M vs B175HW: depth reach or wider coverage?

Investigate B175M when depth reach and a narrower footprint matter; investigate B175HW when wide coverage in the upper water column is the objective. These are editorial interpretations of their specifications. Neither is a universal upgrade over the other, and neither can be evaluated independently of the sounder driving it.

#Side-by-side specifications

Shaded rows contain different values. On a small screen, scroll the table; model names stay visible within it.

Sources: Airmar’s B175M and B175HW pages, checked 3 October 2026. Airmar lists 150 m and 152 m in different places on the HW page; neither is a guaranteed working depth. Published depth limits are not a promise of fish detection under your boat’s operating conditions.

#Decide what you need to see

Write down the depths you normally fish, the depths you occasionally visit and what you are trying to distinguish. Looking for bait across a broad area is a different task from placing a lure beside a small piece of bottom structure. A recommendation that ignores this distinction can be technically accurate and still lead to the wrong purchase.

A wider beam samples more of the water around the boat at a given depth. A narrower beam provides a more local view. That trade-off is not a quality ranking: more coverage can help search, while a more confined footprint can help relate returns to a particular position. Use a demonstration that resembles your fishing rather than an attractive screenshot from unknown conditions.

#Check the sounder as carefully as the sensor

A chartplotter may need a separate sonar module to drive the intended transducer. Confirm supported frequency bands, power, identification and connector variant against the exact display or module documentation. An adapter changes the connection; it does not create a sonar capability that the electronics lack.

If you intend to share sonar across two screens, also check the display network. Sharing a numeric depth value is not the same as sharing the sonar image or controlling the sounder. Ask for a diagram identifying the transducer, sounder module, network link and screens. That makes the package easier to quote and troubleshoot later.

#Installation can reverse the value calculation

Both listed bronze models require particular attention to hull suitability; Airmar identifies fibreglass and wood applications. Discuss an appropriate housing option with the installer for a metal hull. Do not improvise a material substitution or assume a similar-looking model carries the same installation instructions.

Choose tilt from the measured deadrise at the mounting position. Also check access inside, hull thickness, flow and nearby turbulence. A sensor located where it loses clean water at cruising speed can be frustrating regardless of its specification. Replacing it later involves more than swapping a screen, so settle the mounting plan before ordering.

#Request comparable Australian quotes

Include the complete part number, tilt, connector, sounder module if required, cable arrangement, hull work and commissioning. No Australian supply or installed price was verified for this comparison. A quote for the bare transducer should not be compared with a package that includes installation and electronics.

Choose according to the job: the M is the candidate for medium-frequency reach; the HW is the candidate for wide high-frequency coverage. Ask the installer to document the selected sensor setting and test bottom retention through your intended speed range. If your actual requirement is simply a dependable depth number for sailing, start with cruising depth instruments instead of a fishing transducer upgrade.

#Worked geometry: coverage is not the same as fish detection

For a simplified flat bottom and a vertical conical beam, footprint diameter is approximately twice the depth multiplied by the tangent of half the beam angle. At an assumed 50 m depth, a 25-degree beam spans about 22.2 m, while an 11-degree beam spans about 9.6 m. These are geometric illustrations, not measured detection footprints; frequency, target strength, settings, bottom shape and conditions change what the display reveals.

This helps explain the buying tradeoff. A wider view can include more water but also more structure within a single return. A narrower view samples a smaller patch. Do not describe one as universally better without specifying the fishing task. The B175M beam changes across its band, so choosing one angle for this example is not a claim that it always operates at that angle.

#Two owner briefs that point in different directions

An owner searching a broader water column at suitable shallower depths may investigate the HW’s coverage. An owner whose planned work favours medium-band operation and a narrower sampled area may investigate the M. Both still need a sounder that supports the exact unit and a mounting position appropriate to the hull. The published maximum-depth statements do not promise reliable fish detection at those limits.

Ask the supplier to explain the recommendation using the owner’s actual depths, speed and fishing method. If the explanation is simply “1 kW is best”, it has not resolved this comparison: both units carry that rating. A demonstration or relevant installation history may be useful context, but it should not be presented as a controlled test under your boat.

#The purchase record that prevents an expensive mismatch

Record full sensor model, housing material, tilt option, connector, sounder/module and supported settings. Have the installer assess deadrise, internal access, cable route and acoustic location. Do not infer suitability for an aluminium hull from a bronze-housing product name; obtain the appropriate manufacturer-approved housing and installation guidance.

Define an acceptance run in representative safe conditions and note where bottom or useful returns are lost. Investigate aeration, mounting and configuration before blaming the screen. For a budget project, correct siting and a matched sounder deserve priority over buying more nominal power. For a premium project, adding sensors requires a documented coexistence and source-selection plan, not simply another hole in the hull. See Furuno versus Simrad for the broader system choice.