So far, all of the lifting devices having the garrison gin style have been tripods. The advantages over a gin with more than three legs goes way back to the "Milking Stool" principle, that of the device being steady on surfaces which are not perfectly flat.
In California we found the exception to the rule at Sutter's Fort in Sacramento. This fort has four bastions at the corners of an irregular rectangle. In one bastion a lifting gin was set up and shown in the process of mounting a tube on a 4-truck carriage which can only be described as a fortress carriage, having a center of gravity which is too high to be a naval type 4-truck. This lifting gin is smaller than other garrison gins we have seen, but is ample for lifting the smaller artillery of the far west common in the 1830s, 40s, and 50s. The artillery assembled by the fort's owners came from a variety of places, but the Russian field artillery and naval artillery of that era was well represented, because the Russians owned tracts of land and several forts in California at that time.
The pics from our visit in 2009, are displayed below,
Mike and Tracy
Two carronades flank the Sally Port of this fort with it's large, heavy, wooden doors. Note the spikes to repel invaders.
The 4-pole gin with the winding drum, the capstan and the ratchet on the right side of the drum.
The upper area of the gin showing the blocks, the shears, the tackle and the end hardware which holds everything together.
A view of the lower gin showing the rope craft used to secure the tube. Also, it looks like a second ratchet is located at the left side of the winding drum. That feature would be good insurance.
The guns and equipment of a bastion. A seacoast style water bucket is there and carriages of different heights.
One of the high 4-truck carriages used to get the tube up to the center of the high embrasures.
The bastion showing the position of the embrasures for cannon. Note the lack of safe, 'dead space' except directly below the openings. The only place for a scaling ladder would be at the bastions corner, not the most secure place for a tall ladder.
Unless the defenders are throwing 4 pdr. or 6 pdr. fused shells at you, the space below the embrasures is fairly safe. The old infantryman is always judging a fort's worth based on how easy it would be to defeat it due to architecture or armament.