Ah yes, SWATHs. I remember them!!! I ran a small 38' SWATH boat as a video platform for the '95 America's Cup in San Diego. It was magic when at speed (~16 kts), as all it's dynamic stability systems (interceptors, foils, water ballast, etc.) had significant dynamic pressure to work with. At speeds less than ~8 kts, it was an absolute dog, having very little transverse and fore-and-aft stability, due to the self-same small waterplane that makes SWATHs such able platforms within their (very) narrow design envelopes.
For example, underway at slow speed, a person walking forward would require immediate re-ballasting to compensate. Given I couldn't pump water fast enough, she would inevitably dip her bows, allowing green water to flood the walkway on whatever side that person walked upon. Ditto when walking aft. If the crew stayed put, all was well, at least in the benign sea states I worked in.
Fortunately, I had an engineer that was a little, tiny, skinny guy that could crawl down into the submerged hulls for engine service. Me, I could SEE the engines, I could (with difficulty) TOUCH the tops of the engines, but no way, no how, could I work on them.
I also worked at the Naval Undersea Center, when one of the 1st SWATH ships (KAIMALINO) was built by the Navy for evaluation. With two gas turbines on deck, driving the propellers via daisy-chained chain drives down the aft legs of the hulls, the noise underway was truly epic! Again, magic when operated in her very narrow range of speed and load parameters, but ultimately unsuccessful as a general work platform.
Be careful when you think of "stability" and "SWATH" in the same moment. They act much more like aircraft than ships. As with aircraft, when they're out of their operating envelope, with little dynamic pressure available to augment stability, they behave more like bricks.
Regards,
Pete
