While we were involuntarily moored in Friday Harbor, this unusual work boat (the aluminum one with the I-beam supported above the foredeck, not the white one behind it) dropped anchor near us. On board were a diver, a man, and woman: the crew. And two hefty gentlemen who did not participate in operations except to look over the side. With nowhere to go, we speculated what they were up to...
As we watched, a diver went down with a heavy line. When the diver returned to the surface, the woman used a heavy windlass (not visible below the bulwarks) and routing the line over a block on the bow she hoisted up... a concrete block some 6 or 7 feet square and perhaps 18 - 24" thick. Trust me, this was HEAVY - the bow of the boat dipped a lot. Obviously a quite substantial mooring anchor.
With the concrete hanging from the bow, the man attached a brand new pennant line, looking like at least 1-1/2", to the anchor block (with a chafe guard of course!). He then manoeuvred to a good spot and she lowered the anchor to the bottom. He then attached a (very) used buoy to the pennant, and they all went home.
The old mooring pennant had parted, releasing the buoy, which apparently fetched up on shore somewhere in Friday Harbor and was retrieved. The action we witnessed was the reattachment of the buoy to the anchor on behalf of one or both of the observers, using a new pennant.
That boat was ideally designed for mooring installation and maintenance. We witnessed the maintenance part. For a new installation, the new anchor would be placed in the bow, and then once transported to the desired location a hoist rolling along the I-beam would be used to retrieve it from the foredeck, roll it out forward above the water, and then lower it to the sea bottom. Pretty clever design.