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ContinuousWave: Small Boat Electrical
HUMMINBIRD 570 Depth Sounder: Poor Shallow Water Performance
|Author||Topic: HUMMINBIRD 570 Depth Sounder: Poor Shallow Water Performance|
posted 09-16-2011 03:49 PM ET (US)
I spent a week in Beaufort NC this August - we actually left a couple of days early with Irene coming in. We spent most of our time boating between Beaufort, Cape Lookout, and Shackleford Banks. There is a lot of shallow water there, and we were in our 1984 Outrage 25 with twin Optimax 150s. As with all of our trips there, I need to paint skegs again and the twin Rev4 props are getting less shiny with some more time in the sand. The east end of Taylors Creek was particularly shallow this time, so much so that all navigation markers there have been pulled out
I've had a vexing problem getting good depth readings once the water is less than 3-4' deep under the keel. The keel is about 1.5' down, so that is about 5-6' overall. What happens is the depth finder will peg at 0.6, the minimum reading. I've fairly well determined that it is due to interference/turbulence related to the engines, as if I cut power and tilt the engines up, the problem goes away. I'd think with the engines on 5" jackplates that I'd have less problem. They are a counter-rotating pair if that matters.
This is only a problem at the coast. At the lake if I'm in water that shallow I'm about to hit shore. But at the coast, 4' of water may be the deep channel, and you really would like to know if you have 2.5' under your keel or 1.5' or what. I can do fine in 3' of water (1.5' under keel), but that is getting close to the minimum without dragging bottom some.
I have a Humminbird 570 depth finder. I've talked with Humminbird and have the transducer in as good a position as possible. It is about 6" to the starboard of the bottom of the keel. I get good readings at all speeds as long as the water is more than about 5-6' deep. I've adjusted sensitivity and other settings as directed by Humminbird but without changing the problem. In most usage, it works great - it just does not once it gets fairly shallow.
I'm interested in suggestions for a different depth finder that might do better at shallow water with a stern mount.
The other option I've considered is drilling a hole through the foam in the "inner well" inside the massive front storage locker - the same inner well has a drain hole. I've read of people drilling down to the outer hull layer and glueing a thru-hull transducer there. I'd really rather get a transom mount working well.
I appreciate your suggestions.
posted 09-17-2011 09:55 AM ET (US)
Try an experiment. Move the SONAR transducer to the deepest point of the V-hull. Angle the transducer so it points forward a few degrees. This should help avoid the false reading from the engine gear case.
We had a similar problem on our sail boat. When we were in really deep water, over 200-feet, the depth sounder would loose bottom echoes. It would suddenly get an echo from the boat's keel, and indicate we had only four-feet of water below us. This was quite unnerving until we recognized the pattern of its occurrence.
posted 09-17-2011 09:57 AM ET (US)
Is the SONAR transducer being used a particularly special design to have a very wide cone of coverage or have side-scan features?
posted 09-17-2011 03:42 PM ET (US)
Thanks for the suggestion jimh. I've talked to other owners with the same hull and twins but it seems few go into very shallow water with them.
When you say put it to the deepest part of the hull, I presume you mean directly under the keel?
Before I do that, I'll also try angling it slightly more forward and see what that does since I can do that without moving the mounting holes.
The transducer is the standard one that comes with the unit. It is a dual-frequency unit but with nothing special about it.
posted 09-17-2011 05:46 PM ET (US)
For a test, get a piece of wood, say a 1 x 3, and mount the transducer to it. Then use a C-Clamp and clamp the 1 x 3 onto the transom, right between the engines, and position the transducer right in the middle at the apex of the V-hull.
posted 09-19-2011 11:42 PM ET (US)
Another strategy to help the SONAR find the bottom: switch the depth range to a specific range from AUTO. For example, if you are in 5-feet of water, set the depth range manually to be 10-feet. Once the unit finds the bottom, return the depth mode to AUTO.
Also, sometimes a power-cycle of the depth sounder will help it reacquire the bottom once it has lost it for a while. It seems like the automatic algorithm sometimes gets lost and cannot recover. A power reset starts everything fresh.
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