F28/30 CK instrument transducer location

[andygc]

Good morning.

I'm having some trouble with my log and echo sounder - fitted by the previous owner. The echo sounder appears to be troubled by air bubbles running over the hull surface under way - it reads perfectly well on the mooring, but has intermittent signal loss when sailing in the river (where I really need to know the depth!). The log impeller doesn't seem to want to rotate when the boat is moving, or when the tide is running past the mooring at more than 1 kt. I have cleaned the log impeller and its shaft and I know that the bottom of the boat is clean. If I flick the impeller with the transducer removed the display gives a low speed reading, as you would expect. The transducers originally fitted to the boat (in 1980) were well aft - in the galley cupboard just forward of the companionway steps. The current ones are fitted about 2 feet forward of the aft end of the centreboard trunk and about 3 feet port of the centreline.

I would like to know where the transducers are fitted on other people's F28/30 cat ketches. I'd also welcome comments from anybody who has a F33/35 CK centreboarder on where their transducers are mounted.

Thanks for your help,
Andy

[Castaway]

On our F 35 (UK), the depth transducer is in the centreline, about 2m aft of the bow, and the log to starboard of that, about 15cm away. I think the log reads a little differently on each tack when sailing. If you flick the paddle wheel of the log, it ought to give quite a high reading, so perhaps you need to adjust the gain or damping, and the same might apply to your depth transducer; on mine it needs extra to give accurate depths in deeper water whilst underway. Have you got any antifouling on it? That can make a big difference. I use a thin smear of lanolin to good effect on both, but too much on the log can cause it to stick (literally).

[andygc]

Gerald, thank you for your reply. I had hoped there would be others here who sail a F28/30 CK and who could tell me where their transducers are mounted. The log suddenly started working at a bit over 4 kts, and then continued to work at lower speeds, including the tide going by on the mooring (but that was 1.5 kts). I think the echo-sounder must be experiencing bubbles coming from the centreboard slot. There's no antifouling, the bottom is newly copper-coated. It seems to be much more reliable on starboard tack, when it is downhill from the slot, and misbehaves on port tack, when it is uphill. It looks as though I shall be peeling the transducer off the hull later in the season and then be experimenting with moving around a plastic bag full of water. Not something I can do while tacking up the River Exe - I need to be in the cockpit, not in the bilge!
Regards, Andy

[Castaway]

Andy,

Are you using a transducer stuck to the inside of the hull? On the UK built Freedoms, the balsa core extends a long way down,to what might be the garboards if it were wooden, and this will probably cause poor transmission of the ultrasound. By the time you get to solid fibreglass there is a lot of thickness, and it is angled quite steeply.

We have a through-hull fitting in the centreline, forward between the tops of the V-berth, and we don't have problems with flow or bubbles, just fouling. We would like forward looking sonar, but that location is too exposed if we ground.

I would be surprised if air is being entrained from the centreboard casing, since there is about half a metre of water depth (in ours), and the slot is almost filled when the board is down, though I expect you will have it raised if tacking up-river.

I'll be interested to hear your eventual solution.

Regards,

Gerald

[andygc]

Gerald
The original and subsequent echo transducers (three of them) before the present one were all in oil baths. One of the two below the galley sink (ie portside aft) was set into the hull, the other was surface mounted. The third was next to where the current one is, also surface mounted. The current one just sits on a pad of silicone. So, if it is cored that far down, three out of four have been pinging through balsa. I had some holes filled by the yard and a skin fitting replaced as part of the preparation for coppercoat and I'll ask them if they found balsa in any of them. Short of drilling test holes, I can't think of a way of finding the edge of the core, and I don't want to do that. I'll let you know the eventual outcome.
Andy

[Castaway]

Andy,

When we had the boat epoxied, the yard peeled the gel coat, which left the hull translucent, and the outline of the balsa core was visible. I replaced a through hull (toilet outlet) with a wider one, and found balsa there, which I replaced locally with epoxy, so It might not be obvious with a 'same size' replacement. I have no idea whether the UK built F30 is the same as the F35, but it seemed an idea for consideration. However, if transducers have worked in the past through the hull as you have it, then there is no reason to believe the balsa degrades the signal. I was just speculating.

I suspect you'll just have to spend some time trying different locations. Have fun!

Regards,

Gerald

[ScottBBrown]

On my F28 CK, the depth and knot meter are located port side just aft of the head under the forward seat for the table.
Hull # 30