Topic: SI Transducer Mounting Location – Stepped Hull with Strakes

[snooktarpon]

I know transducer placement has been discussed a lot but I could not find a thread that would help my situation.

I have a 18’ Lowe aluminum hull bass boat with a stepped hull and strakes. The step is about 4 inches forward of the transom. When looking at the transom towards the bow, the step is triangular such that the size of the step is decreased as you go port or starboard.

I just purchased a Hummingbird 598ci HD side imaging unit. I am trying to determine the best location for the transducer.
I have an existing transducer for an old Hummingbird Xtreme 160 with Temperature (mounted by the dealer).  I’m not sure how well this transducer is performing since the boat is new to me. I’ve come up with 3 potential mounting locations for the SI transducer and I would like to get some feedback.

I’ve attached pictures that should help explain my situation.

Mounting Location A (existing transducer location):
Initially, I was going swap out the old transducer and mount the SI transducer in its place. Then I looked closely at this mounting location and I noticed several reasons why I don’t like it:
1)   It’s mounted on the transom so it’s 4” aft from the step. Turbulence will be coming off the step so I’ assume the 4” distance should be minimized.
2)   It’s a mounted almost in line with a strake. Again this will cause turbulence.

Mounting Location B (mounted on hull aft of the step):
I’ve taped the SI transducer in a potential location (mounting location B). It’s located just in front of the step so it’s underneath the hull between the step and the transom. It’s also located between strakes. There are several issues in my opinion.
1)   Using the mounting bracket that came with the 598ci HD, this location would force me to mount the transducer on the bottom of the hull between the step and transducer. As a result, there is no height adjustment and the transducer is positioned to low (protruding below the hull line). I’m afraid that the transducer is prone to getting damages by hitting a stump or causing rooster tails when on plane.
2)   The  transducer is about 10” from the edge of the prop (when looking directly forward from aft) and I know 15" is recommended by Hummingbird.

Mounting Location C (mounted on hull aft of the step but closer to hull centerline):
Another potential spot is mounting location C. Since the step is deeper, the transducer will not protrude below the hull as in location B. In fact, I think the horizontal centerline of the transducer will almost line up with the bottom of the hull line. The issue is that the transducer will be about 4” from the edge of the prop (when looking directly forward from the aft) but it will be forward of lower unit by 10” and 20” from the prop.

In my opinion, I like location C but is it too close of the prop? Any other comments/suggestions?

Additional question: Is is OK to mount the transducer on the transom with the step (location A or location B but transom mounted, not step mounted as I have in the pictures)? My intuition tell me the turbulence off the step is going to cause problems but am I just paranoid? Transom mounting offers more flexibility if I use a transom plate since I can move it around without drilling additional holes.


Thanks in advance!!!

[Humminbird_Greg]

Maybe someone with the same or similar boat hull will see this and comment but my two Lincolns on this are that you should try mounting it in position “C” or even a few inches to the left of that location as this gives you a better chance of adjusting the transducer.  Forget about the 15 inch deal as that is the minimum recommended distance from the prop to the transducer but it was really meant for boats with inboard motors and propellers that are forwards of the transducer, which yours is not.  The only clearance issue you have to worry about with the prop is if the transducer is mounted in front of the propeller and creates an air cavitation pocket that will not allow water to flow through the prop.  This does not happen very often.  The problem with mounting the CSi (Compact Side Imaging) transducer on this step face is that there is a water inlet cover to the left of the transducer. Depending on how far out it sticks from the hull it could block some of the left Si sonar beam. Transom plates are great and I would recommend using one.  It would also help with the water inlet cover blockage by moving the transducer back away from the hull.

It would have been nice to know how well that old XT-6-20 transducer from the Xtreme 160 works at faster boat speeds.  It could have opened up some transducer mounting options.

[Fast Eddy]

Greg,   Here is the stern of my Cape Horn 17.  You can see the light and dark areas where the the outer edge actually angles forward.   Can I mount my 598 lower below the one strake?

[Fast Eddy]

close up

[Humminbird_Greg]

Are you meaning at about the 10 to 12 inch mark?

[Fast Eddy]

Thanks Greg  yes 10" it sits on a strake or hull ledge that ok?   Do you think that would be the best spot?   Can I go even closer to the center line? I want to hit the optimal spot the first time rather than making my stern look like a colander!

[snooktarpon]

It would have been nice to know how well that old XT-6-20 transducer from the Xtreme 160 works at faster boat speeds.  It could have opened up some transducer mounting options.

Greg,

I took the boat out last week and the Xtreme 160 with XT-6-20 transducer in Location A losses its reading when going faster than 10 mph.  So based on that, I 'm assuming Location C is the best location.

If the transducer is the properly located, what is a typical max speed I can go while still getting good readings? My boat probably does 35mph-40mph.

[Humminbird_Greg]

Thanks Greg  yes 10" it sits on a strake or hull ledge that ok?   Do you think that would be the best spot?   Can I go even closer to the center line? I want to hit the optimal spot the first time rather than making my stern look like a colander!

Behind the strake or closer… it all depends on how the water flows off your transom while the boat is underway.  I’m guessing here but I would start with behind the strake.  If you can, install a transducer mounting board over that whole area and then you can move the transducer around if needed without adding more holes to the transom.

[Humminbird_Greg]

Greg,

I took the boat out last week and the Xtreme 160 with XT-6-20 transducer in Location A losses its reading when going faster than 10 mph.  So based on that, I 'm assuming Location C is the best location.

If the transducer is the properly located, what is a typical max speed I can go while still getting good readings? My boat probably does 35mph-40mph.

I think location C would be your best option.
If properly positioned you should be able to run wide open and not lose the bottom reading – that is saying that your boat hull has such a sweet spot on it.  Not all boats do and this is especially true with aluminum hulled boats.