Speed and depth sounder reliability

Electrical and electronic topics for small boats
ConB
Posts: 172
Joined: Fri Oct 09, 2015 2:52 pm
Location: Suttons Bay, MI

Speed and depth sounder reliability

Postby ConB » Sat Jul 06, 2019 12:56 pm

I am wondering at what speed I should be able to expect a reliable depth sounder reading.

I have a 1987 Outrage 18 and have installed a new Garmin GT 23 transducer. Around 25 mph I loose depth readings. My old Garmin lost readings in the high 20s mph.

It seems to me that the depth sounder should be reliable at higher speeds.

What are the experiences of other CW readers?

Con
!987 Outrage 18 / 1987 150 hp Johnson & 1969 13 / 30hp Johnson tiller

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: Speed and depth sounder reliability

Postby jimh » Sat Jul 06, 2019 1:49 pm

I have a Lowrance HDS-8, the original version and now at least three generations into obsolescence. To the SONAR I have connected the basic Lowrance Skimmer transducer. They now call it "83/200 kHz Transom Mount Skimmer with Temp." There used to be a model designator--HST-WSBL--but they seem to have dropped those designations and just use SKU numbers.

My experience with the HDS-8 and the HST-WSBL is to get good solid bottom echoes with depth indication at any boat speed, including all the way up to the top speed of the boat around 44-MPH. The deepest water that I can recall being able to get a bottom echo was in Lake Superior. I think the little transducer was holding the bottom echo at over 800-feet depth while underway.

Before I got the HDS-8, I had a lower-tier Lowrance SONAR that used the same transducer. When out in the Pacific northwest in the waters around Vancouver Island, I found that the maximum depth of that system was about 150-feet. Since the Pacific Ocean in the large open sounds around there is very deep--the Canadian Forces use that area for submarine warfare games--the little Lowrance sounder was essentially useless about 90-percent of the time. It was only when we came into some shallow anchorage that a bottom echo would appear.

Some years ago in the winter, when I cannot go boating and I tend to think about boating projects, I bought a much larger and much more expensive transducer from AIRMAR, their model P66 (as I recall). This was compatible with the HDS-8, and I had spent the winter reading testimonials from anglers about how much better the P66 was compared to the HST-WSBL. I got the P66 mounted on the transom, but I did not have a switch to quickly switch back and forth between two transducer. To change transducers I had to disconnect one and reconnect to the other.

I soon discovered that my installation of the P66 was flawed, and the darn transducer would lose bottom as soon as there was any way on the boat. It was quite frustrating. The problem was likely all due to the location I mounted it. It was too far off the keel centerline, and there was probably aerated water coming off the hull. After a short time I removed the P66 and repaired the several holes in the boat transom from its mounting screws. The P66 went back in the box. I planned to install it on the other side of the transom, but I never got around to it. Maybe I should find the box and give it another try. I am sure the cause of the poor performance was related entirely to mounting position.

As a result of these experiences, I believe that any SONAR transom-mount transducer will be sensitive to degraded performance if the location on the transom is not carefully chosen and then the precise amount of immersion under the hull tweaked for best results.

Image
Fig. 1. A Lowrance HST Skimmer transducer mounted on the transom of a SPORT 15 hull.

ConB
Posts: 172
Joined: Fri Oct 09, 2015 2:52 pm
Location: Suttons Bay, MI

Re: Speed and depth sounder reliability

Postby ConB » Tue Jul 16, 2019 2:58 pm

I will try moving the transducer between the keel and were I have it mounted now and report back.

Thanks, Con
!987 Outrage 18 / 1987 150 hp Johnson & 1969 13 / 30hp Johnson tiller

ConB
Posts: 172
Joined: Fri Oct 09, 2015 2:52 pm
Location: Suttons Bay, MI

Re: Speed and depth sounder reliability

Postby ConB » Tue Oct 22, 2019 4:22 pm

Before I put my Outrage 18 away for the winter I removed my transducer.

On a calm day with my wife driving the boat at different speeds I observed the water as it left the transom while on plane.

It was obvious that I had put the transducer in a bad spot from the air bobbles in that spot. Just six inches toward the keel looks a lot cleaner. I will try that spot next spring and report back.

I should have looked over the transom while on plane years ago and moved the transducer then.

Con
!987 Outrage 18 / 1987 150 hp Johnson & 1969 13 / 30hp Johnson tiller

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: Speed and depth sounder reliability

Postby jimh » Tue Oct 22, 2019 5:20 pm

CON--that sounds like a good strategy.

But on my boat, with a big engine mounting bracket appendage with a buoyancy box (called a Whaler Drive) it seems like there is airy water coming out everywhere. But I will give it a closer look next season. The boat has gone into storage until May 2020.