Hi John Ball To many john's Thanks very much I have a Jig but it has adjustable knife edges so the boat is set on the designed waterline. There is a platform 65mm below the knife edge and a 5mm spacer must pass under the hull. A second platform 425mm from the knifeedge to check the draught.. This set up has the added advantage that the owner can see the ballast/fin But this method does not allow for variations in the water plain due to individual owners weight distribution. So it looks like I must build a tank similar to yours. The only other design I have looked at is the Croatian 2007 worlds tank very high tec. Regards JohnK