I discovered two small hydro-jet units (NQD type) and, needing something to occupy me during "lock-down" eventually hit on the idea of a small short sea type of ferry. Lots of inspiration in the Baltic and Mediterranean.
Two previous models powered by these units had shown them to be tricky to install in a wooden hull. Add the fact that they incorporated no means of making the model move astern and quite a few designs had to be sketched out and discarded until a practical layout was created. This was a flat bottomed hull with the jet nozzles set into a cut-out at the stern.
First sailing trials of the bare hull were OK. The model handled safely even if the speed was none too impressive. The hull being ballasted to an all up weight of around 5 pounds (2.3 kg) to ensure the impellers were fully immersed and would start reliably. Astern was not found to be essential provided you could avoid jamming the model into the bank-side.
A simple superstructure was made to match the sort of vessel that might only have a short run between ports. Some full-size vessels have rather garish hull decorations, I settled for a simpler scheme using self adhesive vinyl sheets. I pays to have a friend with a vinyl cutter!
Sailing trials of the completed model showed the same characteristics as before, including the modest speed despite the twin hydro-jets working hard. I tried removing some ballast and the speed did improve. Eventually all the ballast was taken out and the model now zipped along at a more impressive 5-6 ft/sec. The hull was not quite fully planing but didn't have the stern sinking as most over driven displacement hulls would have done. I guess the flat hull bottom lifted the stern. The hydro-jets still self primed when starting, although with the odd momentary "gurgle". In this final state the 31 inch (78 cm) long model weighs in at 2.25 pounds (1 kg).
Overall, an interesting challenge to design, well it's too easy to become boring if you only do the same things time and time again. But, now something different is needed for 2021.
Glynn Guest
