We are working on a seastead design that will have a 40 by 16 foot living area above the water.
There will be 4 foot wide columns that are about 20 feet long going out from 
from the 4 corners of living area and down into the water at 45 degrees, which half of
each column under water.   The bottoms of the floats will make a rectangle about 44 feet wide and 68 long.
From the bottom of each column there will be 
2 cables going to the adjacent corners to hold it in place.
There will also be a cable making a rectangle betwen the bottoms of all the floats so we have some
redundancy in case one cable breaks.
The seastead is about 30,000 lbs I think but this is NOT a normal boat hull shape,
it is more like a tiny oil platform as far as drag.

We expect to use 2.5 meter diameter propelers on two submersible mixers and solar power to move
at around 1 MPH plus any help from using eddies.

It will all be made out of duplex stainless steel.
The floats will be 1/4 inch thick.

Lets assume the owner does a selective cleaning of barnicals every month on his own.

Please discuss lifecycle cost of ownership issues.  Lets say we sell this for $500,000.
What sort of ongoing costs would customers have and how long should it last, etc.
For this just ignore insurance and depreciation/replacement of the whole structure.