Hidden fluxgate box?

Thank you for keeping our spirits and hopes up while our boats were languishing in the yard awaiting release from lockdown.

As ever, I enjoyed the ‘Skippers’ Tips’ section. Jonty’s item about ‘Fluxgate Compass interference’ (YM, June 2020) got me thinking, as I don’t recall fitting one when I installed my Lowrance plotter some years back. So I set off to look for the box with a ‘yellow sticker’ on it but came up against a problem, or was it a bulkhead? – I can’t find an aft cabin or even a wardrobe on my Colvic Countess 28, Moonfleet.

I checked with two mates who both have Westerly 31s, to which they have fitted chart plotters, but they too had problems locating an aft cabin or a ‘yellow stickered’ box.

Please don’t take it personally Jonty – I am just envious of your Southerly. Mike Cooke

Jonty Pearce responds: I’m glad to see you are engaged fully with the joys of older boat ownership. Not only did original designers often think ‘out of the box’, but owner upgrades may have changed electronic equipment, bearing in mind that a fluxgate compass may never have been fitted new! I too fitted a Lowrance plotter when I owned an E-boat, and frequently such small standalone plotters (and larger ones) may not indulge in the electronic delights of a fluxgate compass input; they deduce the heading from changes in the GPS position.

Autopilots usually incorporate a fluxgate compass, and if wired into the plotter, a more accurate heading can be displayed. In these cases any search for an external fluxgate compass will be fruitless; the yellow sticker warning of the nearby sensor will only be found on boats fitted with a discrete fluxgate unit – positioned as far as possible from magnetic influence and large lumps of metal, hence the placements in aft cabin wardrobes. Unfortunately, it can be a frustrating search aboard yachts without aft cabins! In fact, aboard my Southerly 105 Aurial, I discovered the fluxgate (with no yellow sticker) below a saloon bunk.

I trust that you and your mates are soon able to go sailing again aboard your own enviable Colvic and Westerly craft!

Mike Cooke’s Colvic Countess 28, Moonfleet has a chart plotter, but no fluxgate compass, which is normally required to provide head and movement data to a built-in autopilot