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bmcald 05-28-2004 05:02 AM

crazy depthfinder
Just installed a Raymarine ST40 depthfinder this spring and find it unreliable. I ran aground in what the depthfinder assured me was 8 feet of water beneath the keel, which draws 3 and a half feet.

Or it steadily displays a tenth of a foot of water below the keel in a channel that the charts say is 5-8 feet deep.

Can turbulent, choppy water confuse a depth finder? That hasn''t always been the case when a reading was clearly wrong, but it is usually what I get when I cross the bar outside my canal into the shallow bay.

2 possibilities? The manual recommends that the depth finder get wired to the house battery instead of the engine battery, but I don''t have a house battery and there''s no place to put one, so its on the engine battery. Manual says that the settings can be lost when the engine is turned on, but so far the settings I programmed are still there.

Other possibility may be that air is trapped in the silicone caulking I used to stick the transponder to the hull. There''s a level place in the hull with no core that was intended for an inboard transducer. But if it worked fine initially, how would air have been introduced?

Any thoughts? I haven''t called Raymarine service yet.

39512 05-28-2004 05:15 AM

crazy depthfinder
I assume that you used mineral oil to fill the housing? I have installed a few of these inboard transducers and found them to be unreliable. It is possible that you are getting RF ''noise'' from the engine. There are filters that can be installed to eliminate the problem. I''m sorry to say that the only sure solution in my opinion is to install a thru-hull.

Sailmc 05-28-2004 05:16 AM

crazy depthfinder
I would double check my installation for air bubbles. Be sure that you have sited the transducer in an appropriate place. Also you should calibrate your depth sounder. I did so with a steel tape mesure in my slip. Make sure you have the keel offset set properly. With that said my opinion of depth sounders in general is that they are only usefull for confirmimng the fact that you are aground.

bmcald 05-28-2004 05:22 AM

crazy depthfinder
Unfortunately, in my case, it didn''t even confirm that I was aground!

The transducer is fixed to the hull with silicone caulking on a level area designed for the purpose, with no core material in the fiberglass. Isn''t the tube filled with water or oil only necessary if a level place on the keel isn''t available?

hamiam 05-28-2004 07:58 AM

crazy depthfinder
I wonder if there is a way to adjust the depthfinder such that it knocks 5 feet or whatever off the reading. Sorta a fine tuning at the display head?

mikehoyt 05-28-2004 08:06 AM

crazy depthfinder

I purchased ST40 BiData last season and had a similar problem with the depth unit. Basically was unreliable in shallow water.

Contacted Raymarine and they said it was likely the display unit (which contains all the electronics). The shop where I bought it loaned me a transducer and a depth only display unit. I connected the transducer to the existing unit (hanging over the side) and had similar readings. Then I connected the new depth display unit to my existing transducer and the problem disappeared.

I took back the loaners and the one I purchased and the shop and Raymarine had a replacement display unit for my ST40 bi-data in 4 days. I installed it and it worked perectly. The service from the local shop was outstanding and the replacement unit works flawlessly. We were so happy with it that this year we installed the ST40 wind.

The symptoms of my problem were :
a. unreliable shallow water readings (usually reads high)
b. The depth reading would change while sitting still. It would vary by about 5 feet over a period of 5 minutes while sitting at the finger pier!

Contact thje place where you bought it and try a new display unit. Will likely fix your problem.

Also maybe contact Raymarine but try the other first if you can. I think this was a known problem to Raymarine.

Best of luck


bmcald 05-28-2004 11:20 AM

crazy depthfinder
Hamiam--there is, its called offsets, so you can get a reading based on the waterline, the bottom of the keel or from the transducer location. I''ve got it set for the bottom of my keel.

bmcald 05-28-2004 11:24 AM

crazy depthfinder

What frequency did you set it for readings? I set it for the max, 14 a minute I think, because there is nothing but shallow water in the Great South Bay off Long Island. Any idea if it would be more reliable at a lower reading frequency rate, like 1 or 2 times a minute?

I hope you''re not saying that depthfinders can''t work reliably in shallow water...


mikehoyt 05-28-2004 11:33 AM

crazy depthfinder

I tried all frequencies.

I sail in very shallow water (avg depth 13 feet).

The original unit was malfunctioning. It was replaced by Raymarine under warranty. The computer is in the diplay unit which was where the problem originated. Raymarine is aware of this problem with some of their units.

Contact Raymarine and they will suggest that you try a replacement. This is how I found my problem last year. Once replaced there was no longer any problem.

Last Saturday I had the keel offset set to the depth from my hull to bottom. It worked reliably right to the point where it said 0.4 feet when I realized my offset was off by 0.4 feet. As it was a rising tide and the bottom is sand and mud we simply heeled the boat over and kept on going til we were out of the channel. We dragged the keel pretty much the whole way. The unit worked properly the entire time. The depth was about 3.5 feet.

Replace the instrument not the depth transducer and your problem will be solved under warranty.

Best of luck


bmcald 06-01-2004 04:23 AM

crazy depthfinder
Raymarine responded to my inquiry. They recommend fixing the transducer to the hull with 3M 4200 instead of silicone, which can cause the echo to bounce back.

Is 3M 4200 what everyone uses to fix their transducers to the inside of their hulls? This is when a tube with oil is not needed because a flat place with no core material is available.

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