Having served as Navigator on a yacht fitted with one of these seat arrangements in the daze before all this electronic stuff such that one actually had to spend time at the nav station doing navigation
, a couple of things.
1. If the swing arm comes directly to the base of the seat from the swivel post under the nav table, it's nearly impossible to face the nav table as the swing arm interferes with one's leg so the one finds oneself sitting more or less sideways. The swing arm needs a bend in it so that once swung out into position, the supporting arm for the seat is roughly parallel to the front of the nav table.
2. If the table is arranged cross-wise in the yacht in such a fashion that one is facing outboard
while working at the table (i.e. one's back is toward the opposide side of the yacht rather than fore and aft) when the table side of the yacht is to windward, unless the swing arm can be locked in place with a sturdy pin, the seat is unusable as one cannot sit and brace oneself against swinging backward unless one holds onto the edge of the table with one hand or, one can curl ones leg under the seat and brace with one's toes--which is difficult and will be exacerbated by a straight swing arm as described in 1, above. Moreover, when the seat is not occupied, unless it can be locked, it will tend to swing out without warning in a sea-way no matter how tightly one ties it in place and regardless of the knots one uses!
3. In a manner similar to case 2, above, if the seat is fixed on the post and not free to "roll" as it would on a ball joint, when the nav table is on the windward side of the yacht any heel at all requires that one sit on the edge rather than top of the seat, exacerbating the situation described in 2, above.
In conclusion, when we got to Mexico
, the seat top was dismounted from the swing arm, the swing arm removed and chucked into the sea (by the yacht's owner and co-navigator), and the seat bolted to an approximately 30" piece of tubing with a rubber cap on the bottom end. With this, one could place the seat under one's bum and angle the affair forward or aft, port or starboard, as necessary to keep ones balance. This "modified" seat had the further advantage that it could be taken into the cockpit
for use by the helmsman who otherwise had to stand for long hours. Of course, there was always a battle to get the seat back to the navigator where it belonged, when necessary.