The best compass I’ve ever had for a boat was the Sowester Bosun Grid Compass. A grid compass beats all others for steering a yacht because the helmsman does not have to remember the boat’s heading. He simply keeps an eye on the compass to make sure the north/south needle is central between the sides of the grid. He must also ensure that the north end of needle is pointing to the north end of the grid which is usually identified by a ‘V’ or arrowhead shape.
The rotating 360 degrees bezel is turned until the desired compass course is set by lining it up with the indicator at the forward end of the compass. Allowances should be made for variation, deviation, and tidal vectors. Deviation can be a bind if a yacht is built from iron, when it is best to employ a professional compass adjuster to do the job of setting up the ship's compass. If there is any deviation after the compass has been adjusted he will supply you with a deviation table - even in some instances allowing for the heeling of the yacht.
For the past few days I’ve been keeping a lookout on Ebay for a Bosun compass. Four of them were available. I deliberately bid for one that had a bubble under the glass, knowing that the competition would not be fierce. In all, there were 15 bids, but it went for less than a third of the average winning bids for the other compasses. I was chuffed, and I hope I shall be more pleased when I have eliminated the bubble by adding fluid from an old, unwanted compass.
I like the large size of the Bosun - 104 millimetres diameter across the viewing glass - which helps when steering the yacht, because all the markings are clear. At night the compass does not require a light, as it is illuminated with phosphorous markings. Very conveniently the compass can be attached to a bulkhead by slotting it into a small bracket which has a retainer thumbscrew. The total width of the supporting frame is 195 millimetres. Mine has a second bracket that can be fitted within the cabin where the compass can be securely stowed when not in use.