The seastead will have 4 foot wide columns that go 13 feet into the water at
a 45 degree angle going out from the corners of a 40 foot by 40 foot platform
with cables from the bottom of the columns to the adjacent corners.
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.

Normal operation will be with 2 submersible mixers with 2.5 meter propellers
using differential thrust but we also want to have a dingy that can be a backup
propulsion method.

I am thinking can have a dingy with the seastead, that we use to go to shore
after parking the seastead in deep water, but we will design it so that in an emergency it has
some ability to pull the seastead, sort of a little tug-boat standin.   

The Yamaha Harmo 3.7 kw electric motors looks nice.
For normal operation the dingy will have one Harmo and a small battery.
There will be 2 more Harmo drives in storage on the seastead and in an emergency these
can also be put on the dingy for a total of 3 drives.

The Harmo is a RIM-Drive electric motor. It has digital/remote stearing and powered raise/lower.
It has a 15 inch ducted 4 blade propeller.  It is 227 lbs static/bollard thrust.
For electric outboards this is is the highest thrust/kw ratio I have seen so the most efficient
at static thrust (have you seen any more efficient?).  
  https://yamahaoutboards.com/outboards/harmo/3-7kw

Yamaha has it so you can set up 2 of these in "twin mode".   Do you expect they can setup 3 as well?

Yamaha says, "Control System: 	Helm Master EX, including joystick, remote control, and Digital Electric Steering (DES)".
Please explain these different options.


So 3 of these should be around 700 lbs thrust.
We can run a power cord down from the seastead.  The rim drives could go for hours.
It should move the seastead at at least 0.5 MPH if no wind (do you agree?).

If we can control the Harmo motors from in the seastead it could be reasonable to not even have anyone 
in the dingy.  What is the control cord for the Harmo like?  Can we make it longer?  

Does this plan for having the dingy be able to pull the seastead in an emergency look reasonable?

Can you find a Chinese boat matching something like “HDPE boat”, “rotomolded polyethylene boat”, 
“PE fishing boat”, “rotomolded utility boat” in the 4 to 5 meter range?  What does it cost?
Please include links.   It could handle 3 of the Harmo motors?

Because the seastead has a small waterplane area the water movement up and down relative to the seastead can be more 
than the height of the outboard motor, so if the motor were mounted directly on the seastead it could go underwater
in waves.   If the motor is on the dingy it will go up and down with the waves and work much better.