CONTINUOUSWAVE

Q1: if a GARMIN SideVu GT56 SONAR transducer is mounted in the center recessed pocket in the transom at the stern on the hull of a 1999 180 DAUNTLESS, would the walls and hull angles block the [port and starboard SONAR] beams?

See Figure 1 for the location of the current transducer and the recessed pocket in the hull under the transom.





Q2: will the [center recessed hull] pocket collect turbulent water [caused by] the hull shape?

Q3: [will the] water separate [from the SONAR transducer active faces when the boat is underway] at high speed?

Q4: is there any disadvantage [to mounting the GT54 transducer in the center recessed pocket of the 1999 180 DAUNTLESS]?

BACKGROUND
I am replacing a HUMMINBIRD fish finder with a GARMIN unit and GT56 transducer. The current [SONAR] transducer is smaller than the GT56, and it is mounted in center recessed pocket [of the hull at the stern of a 1999 180 DAUNTLESS], which seems very protected and almost perfect for it. None of my previous boats had that space.

My concerns are:

• the GT56 transducer is physically larger, and
• SideVu [SONAR] requires unobstructed left-right projection [of the SONAR acoustic beams].

I would mount [the GARMIN GT56 transducer on] the [starboard] side of the [transom and not in the] pocket. My previous Dauntless 16 had a pocket similar to the pocket on your 180. When I installed an transducer I used the space [on the transom] to the starboard. Later that proved to be a wise choice as I found it much easier to fine tune the transducer angle and exact depth for optimal operation. Adjustments could easily be made while in the water.

Also, Garmin's mounting suggestions are often very helpful.

[Figure 3 shows the location of a SONAR transducer on] my 1999 18 DAUNTLESS. The transducer location worked fine.

Without seeing the size of the GARMIN GT56 SONAR transducer in the proposed position in the recessed center hull pocket under the transom of the 1999 180 DAUNTLESS, to come to a judgement about how well it will work in that location is difficult. All readers know about the GT56 is that it is "larger", which is really not much information.

Based just on what can be seen in the illustrations, the transmission and reception of SONAR signals athwartship from the recessed pocket does not appear to be blocked. Mounting in the recessed pocket would provide a clearer path for acoustic signals aimed athwartship than mounting to the un-recessed face of the transom to starboard. I do not seen any advantage in moving the SONAR transducer far out to starboard and close to the hull chine, as was shown in Figure 3.

A further consideration in mounting any SONAR transducer in the recessed pocket location is the possible introduction of turbulent and airy water by the transducer interfering with the clean flow of water to the outboard engine cooling system intake ports, which might cause problems with engine temperature due to insufficient water flow at higher boat speeds.

It appears that even if you moved the transducer mounting to outward from centerline, and mounted it to the face of the transom, not in the recess, you would still have useful side-scan SONAR results, although towards the port side there might be some attenuation as the SONAR beam becomes closer to being horizontal. And as JEFECINCO notes, you will have more room for vertical mounting height adjustments. And mounting the larger SONAR transducer to starboard of the center line will remove any worry about creating airy water flow into the outboard engine cooling inlets.

qbantek wrote:Q3: [will the] water separate [from the SONAR transducer active faces when the boat is underway] at high speed?

As long as the active faces of the SONAR transducer are mounted so as to be below the actual hull, I do not seen much chance that they will not have water flowing over them and be working into air.

ASIDE:

Q5: why is there so much rust coming from the hull drain in the center of the transom recessed pocket?

You should look into the cause of that rust.

ASIDE

jimh wrote:Q5: why is there so much rust coming from the hull drain in the center of the transom recessed pocket? You should look into the cause of that rust.

I’m concerned [about the rust color stain]. The thru-hull is plastic, so it shouldn’t be the source, and there’s nothing in the bilge showing rust or stains of the same color. This boat is new to me, and I don’t have much information on it other than that it had a single owner since 1999 and was used mostly in lakes and rivers in North Carolina. Perhaps the water in that area was high in tannins or other materials that can cause staining.