Your math probably isn't off.

One of the biggest marina owners in Seattle is now Joe Diamond, the
same guy who has made $bazillions putting parking lots on empty sites
in the central business district. He is pricing everything up as high
as he can- and probably would be doing so even if the marina
association's advisor had never addressed the meeting.

I'm currently aware of several rates in Seattle that have increased
20-25% this year. People are getting upset and blowing out of Marina X
when the rates shoot through the roof, and move to a vacant slip at
Marina Y. However, even though you are expected to stay at least a year
to get your
security deposit refunded when you leave- the marinas put everybody on
a month to month.
John Q Boater blows out of a place that raises his rates from $10/ft/mo
to $12.50, and scurries off to a new spot across the lake at $10.50.
When the rate across the lake goes up to $13.00- there isn't a lot poor
old John Q can do about it.

I heard a rumor that moorage at Marina Del Rey is something like
$24/ft/mo. A $giesel a month just to park a 40-footer. Ouch. I'd like
to think it won't go that high in the NW, but who knows?

When they first built Shilshole Bay Marina back in the early 60's, the
moorage rate was 35 cents/foot/month. One of the old time brokers on
the lake likes to recall how about a year after Shilshole opened they
raised the rate to 50-cents. He said there were howls of protest, and a
lot of people went back inside the locks to look for moorage at 35-40
cents. I could stand 50-cents a foot. Heck, I'll pay up several years
in advance. :-)