4100 SCB Electronics

[Mike459]

My boat was equipped with Raytheon electronics circa 1998. Radar, GPS, autopilot, depth sounder, etc. What is interesting is I have 3 thru hull transducers wired up but apparently only one is in use to a depth display. They apparently can be removed from inside the boat, because they have plastic plugs attached at each location to fit inside the thru-hull. I'm at a loss to figure out why the 3 transducers for a simple depth display and don't see any evidence of any other chartplotter/fishfinder type electronics. Any ideas?
Thanks
I'm in the process of installing a new simrad NSS EVO3s system and about to add a 4th transducer.

[shrew]

Why would you install a 4th transducer, when you already have 3 throughhulls.

1) I would trace the transducer cables to find out where they route too.

2) I would replace an unused transducer with the Simrad.

Don't drill another hole in your hull unnecessarily.

[Mike459]

Originally Posted by shrew

Why would you install a 4th transducer, when you already have 3 throughhulls.

1) I would trace the transducer cables to find out where they route too.

2) I would replace an unused transducer with the Simrad.

Don't drill another hole in your hull unnecessarily.

Shrew, Thanks for the reply. (I'm about 5 months in on my first large twin diesel boat - I'm still doing research on the best path forward)
1. Tracing wires results in 1 3 wire cable hooked up to the depth display and a bundle of similar cables wrapped up under the dash. Useable or not, I don't know...
2. I'm looking for 3D views of bottom structure for wreck diving. I'm not sure a new transducer in the old hole / receptacle would be capable but I intend to check if one is available. The new simrad I want is a different boat shape with 2 bolts and needs a much smaller center hole. I was hoping to replace it in the water, but don't know if that is feasible with a cored hull.
Adding another hole to the hull bothers me also but the new holes are much smaller. If I haul the boat and pull the 2 extra transducers and convert the holes to fit the newer design transducers, I think the repairs would be extensive.

[shrew]

You're going to have a tough time replacing a through hull transducer in the water. They are typically installed from the outside with a lock collar on the inside.

The antifouling paint around the transducer needs to be removed down to bare gelcoat, then the old transducer needs to be removed. The old caulk needs to be cleaned up, then the new transducer bedded with a sealant like 3M 4200. Then the hull anti-fouling paint needs to be re-touched up.

If you have all of your materials ahead of time, you can get the job with 2 people during a short haul. If you can, talk the yard in to doing a short haul late in the afternoon and leave you either blocked or in the slings until the next morning. That way you can spend a few hours that afternoon and into the evening and have early the next morning to finish things up. Otherwise short hauls are only for a few hours.

[Mike459]

Shrew, Thanks for the advice!

[SteveP]

Not that it would change pulling the boat to re-use an existing hole, enlarge it, or drill a new one but I believe your hull is solid not cored.