HI David
Dynamic positioning is fairly advanced technology for a model boat. Do you have a particular model / purpose in mind?
The VP system seems to be much favoured for use in tugs / ferries in the real world, as your research has found, where small spaces and instant changes of thrust are necessary. On a model the real problem is the draught required by the blades.
Many of the more recent large passenger/cruise vessels use multiple Kortz nozzles both fore and aft and I assume they can achieve good control as well as providing economic thrust for use at sea, or they would not be so popular.
Water jets sound interesting but I suspect the technology would be complex to produce reliable jets. A fellow modeller used a water jet on his model and found that he had to strip the unit right down after each sail as the bearings and shaft were seized.
Electronics are already available to control and mix two propellers to control speed and direction so if you can find or design 360deg rotating Kortz nozzles the solution may be in sight.
Apart from the cost I believe Graupner may be up for sale so supplies may not be easy to come across.
I'm all for british brains and innovation 😀

Dynamic Positioning means staying in the same place despite any wind and current so yes you do need thruster that could thrust in any direction. To make the project worthwhile I think you would need to have some sort of objective that really required precision positioning.

From what I have found so far , yes deep pockets would be required for a suitable hull, VSP thrusters and a control system.

What might be more fun would be to devise a way of producing vectored thrust in any direction at much lower cost e.g. with a variable direction water jet. I feel a bigger pull towards the more british way of more brains and less money approach. Buying two or three of those £200 a time VSP just seems too easy.

All depends on how deep your wallet is as to how complicated you decide to build, plus would you realistically need such a high rotation of prop movement on a model boat?

Sometimes simple is more longer lasting than expense.
A lot can be achieved with kort nozzles and a bow thruster in model boats, both very reliable items with little maintenance in service.

Since making my original post I discovered that a model version of the Voith Snieder thruster is available.

e.g. http://www.cornwallmodelboats.co.uk/acatalog/voith_schottel.html this is a complex piece of kit and will produce any amount of thrust in any direction.

Information on how it works in full size can be found at

http://voith.com/en/products-services__power-transmission__applications__voith-water-tractor-14322.html (see the PDFs on that page bottom right).

This is a type of thruster that is used very effectivly in Dynamic Positioning systems see

http://en.wikipedia.org/wiki/Voith_Schneider_Propeller

and

http://www.dynamic-positioning.com/dp2012/thrusters_jurgens.pdf

It would be pretty amazing project to use the model scale VSP thruster to build a model with the same degree of computer control as is fitted to the full scale systems.

Has that ever been done?

Graupner "schottle drive", albeit with limited angle of rotation, but thats only due to having to use a servo to rotate the drive unit, but serves to good effect.