Depth sounder woes: solid/composite hull? What's the common depth sounder used?

[Paul Beardsell]

The depth sounder on my BayCruiser 23 stopped working some fortnight after I got it afloat late March and it was intermittent the initial fortnight anyway. I was initially bamboozled by terminology. Apparently "in hull" and "thru hull" mean the opposite of what I thought. "In hull" means the sensor/transducer fires thru(!) the hull and "thru hull" means the sensor is in(!) a hole in the hull. The sensor is from Raymarine and attached directly to the Raymarine a98 chart plotter.

Yesterday a Raymarine dealer sent their engineer to have a look. He told me what was later confirmed by Raymarine UK. The cable is permanently attached to the sensor and cannot be replaced. A simple cable fault requires a new sensor even if the sensor is fine. The sensor is £300 or more. And labour would be extra. And maybe the fault is with the chart plotter! And fault finding is difficult as no one has anything actually in stock in the UK. Order first.

I could get a much cheaper sensor, the Raymarine CPT-S, an "in hull" one that fires thru the hull, rather than the "thru hull" which is in the hull. But this only works if the hull is solid fibreglass, not of composite/sandwich construction. Is the BC23 hull solid or composite?

And what kit do others use for depth sounders on their BC23s? And in swallow Yachts generally?

[Graham W]

On my BR20 I've got a Garmin GPSMAP 557xs, a plotter/fishfinder that was discontinued a while back.  The transducer (a "transom-mounted" model) is secured in an underwater gap in front of the centreboard slot and the transducer cable runs up the front of the slot and out of the top.  I don't know how that arrangement relates to the BC23. 

I've never had any luck with the newfangled CHIRP depth transducers and have gone back to the older kind, which is dual frequency.  They don't provide quite as much screen detail but are cheap and very much more reliable.  The problems that you describe sound similar to what I experienced with CHIRP (two of them) before I went back to good old dual frequency.  Corroded pin connections where the transducer cable plugs into the unit can also cause problems.

[Rob Johnstone]

Do we know what is meant by a composite hull? Does it mean a lamination of wood, epoxy resin and glass fibre matt and gel coat finish, a lamination of epoxy resin and glass fibre matt with gel coat finish or  just straight epoxy and filler with a gel coat finish?

If it means either of the first two, then the BC23 hull is a "composite hull" because it is made of layers of glass fibre cloth bonded with epoxy resin between outer coats of gel coat.

I think you should be able to remove the transducer from inside the hull without too much trouble - you could fill the resulting hole with resin and filler then fit the transducer that fires through the hull at the same spot. But will that transducer be compatable with the chart plotter? Nowadays, the transducers are a bit like the human eye - they do quite bit of primary processing before sending the data to the info to the chart plotter.

Are you (and is the Raymarine chap) sure it's a fault with the transducer or the cable? Was he able to demonstrate that the magic box of the chart plotter wasn't at fault, or that there was some interference from other sources?

I could blether on about how the current fashion having all the instruments providing output though one controllers provides a wonderful single point for castrophic failure .........

[Graham W]

Nowadays, the transducers are a bit like the human eye - they do quite bit of primary processing before sending the data to the info to the chart plotter.

I wonder if the dreaded CHIRP transducers are in this category?  My favoured dual frequency transducer probably does a lot less pre-processing and comes out ahead as a result.  Plug compatibility is nearly as big an issue as the electronic signal kind.  Airmar seem to make the transducers for most of the major players and it may be worth checking their website to see what they have available in terms of plug/technology/mounting options for the specific Raymarine model.

[Paul Beardsell]

By "composite"/"sandwich" construction I meant "cored". Is BC23 hull solid fibreglass or is it cored?

[Martijn]

The hull is cored with what seems to be app. 8mm thick blue foam.
Except for the upper strake, which is just solid fiber glass.

[Julian Merson]

I've always used NASA clipper instruments.  On my previous Coaster (fibreglass hull) initially, I inherited a clipper duet which was fine for a decade, and when it started misbehaving, I replaced it with the same thing but just the depth sounder on its own ( since the paddle for the hull speed, which did go through the hull, kept getting clogged up with weed, so I stopped using it, filled in the hole and resolved never to purposefully stick a hole through the hull again - not that it was me who cut the hole in the first place...)
Both of these used the same echo sounder inside a pot of oil bonded to the inside hull.  The only issue was when the pot started leaking oil from where it had been epoxied to the hull - which was, ultimately, a messy job to clear up but fairly easy fix - more epoxy, more cooking oil.

On my BC20 (Marine ply construction and, probably, some other stuff - not quite sure, not overly interested in finding out) I purchased the same nasa depth sounder, new for around £120 - much less than the £300 for your Raymarine thingy - and just have the echo sounder bedded in a lump of blutack on the inside of the hull, and it seems to work really well. 

No plans for a BC23 upgrade but, if my numbers did come up, I'd try the same thing again.