thanks everybody for the info .I will get 2 -6 volt batteries and fit them in the hull so that Ican work out the necessary extra ballast.
I never thought of using a mixerbut will probably do this as well but nearer to when the build is complete .I am on with the drawings now scaling them from pictures /photos on the internet.
I will then produce the templates -make the bits in cardboard then when they look ok finally out of plastic sheet .I have had one or two comments doubting my ability but as the bionic man said 'we have the technology we will rebuild it'