Depth finder showing wrong depth (Auto Helm)

[Foster]

I have an array of Auto Helm instruments and I don't know if they are stock on the 4588 Bayliner (1993). I had the bottom painted and now the Auto Helm depth is off by ~60 feet. It doesn't track actual distances (So I can't say 45 == 6', 55 == 16' etc). There is a sensor in the stairs leading down to the staterooms that is embedded in the hull. There doesn't appear to be any damage to it.

There is a second depth finder, it's one of the round gauges that match the other instruments. I think that's the stock one. And it's working. Is that the sensor that's in the stairs?

If I was to go on a hunt for the second depth sensor, where would be the first 5 places to look?

[purduepilot]

Some PO put a bunch of thru-hull transducers on my boat. I've got some under the engines, in front of the engines, under the stairs, next to the holding tank, and in the VIP stateroom closet.

[brad4550]

You stated hull was just painted could the yard have painted over the transducer and now cannot read depth or speed/distance.

[higgins_jr]

Try getting a diver to scrape the paint off the transducer. My secondary depth sounder (the transducer being under the stairs as yours appears to be) had been playing up, and I cleaned off the surface with a scraper and some acetone when it was on the hard last week, and it’s working much better now!

Cheers

[Foster]

It's possible, but they have painted a number of times and it's not seemed to have made a difference. As far as I know neither one of the hull sensors are below the hull.

[Foster]

Hey Higgins, is that sensor part of the Auto Helm (do you have Auto Helm?) or is it the round gauge on the pilothouse and flybridge panels, they are both working.

[higgins_jr]

I’m getting a tad confused with your terminology. When you say “Autohelm”, do you mean Autopilot? That is separate from any depth sounder transducer. Pics of the round gauges you are talking about would help.

Yes, I have “Standard” brand depth “round” gauges on the pilot house and flybridge. They are linked and get their reading from a single thru hull transducer under the breezeway stairs. Often when antifoul is applied, they paint over the sensor that comes thru the hull.

More info, preferably pics to know exactly what you are referring to!

Cheers

[MonteVista]

I am thinking that a thru hull transformer whose surface is solidly covered with some kind of paint it would show less, not more than actual depth if the signal bounces more quickly from the paint layer. Given your symptom I would guess that the bottom paint contains tiny air bubbles (pockets) in it and the signals travel more slowly through that. Just scraping ANY thru hull transducer that may be covered with any kind of paint should cure this. You may try to follow the cable from the gauge to determine where the transducer is attached to and get someone to get in the water to scrape its surface.

[Woodsea]

Foster,
we have two transducer locations. One is under the the bottom stair at the aft end of the companionway. The other is under the floor of the vip guest room closet.

[Foster]

Hey John H, that is the same depth finder that I have! It's the one that works, and there is a sensor under the steps that lead from the companionway to the salon. So that all makes sense.

The brand name on the devices are AutoHelm, they are a precursor (or maybe was bought by Raymarine. I was trying to not confuse people by using the brand name. They have orange branding on them.

Thanks for the hint about the mid-cabin closet, it makes sense that the sensor would be in that area, it would be easy to get the wires to the pilot house. I'll dig around there when I go down this week.

I'd also think that the depth would drop with the paint stopping the sensor.

Thanks for all the help, I'll report back when it get's resolved.