The latest model started as a suggestion that I ought to look at the US Navies new LCS vessels in particular the USS Independence. I duly looked and, boy, is that one ugly vessel! Well, it might have some functional attraction and frighten America's enemies but would not look out of place on an industrial estate amongst the other warehouses.
But, the idea of a slim hull with two sponsons for stability intrigued me and out came the sketchpad. My original idea was to use a small waterjet unit to propel the model. No matter how I tried, no practical way could be seen to fit it into the hull. The use of a "surface piercing" propeller was then considered, the spray they generate would have made the model look quite impressive. However, with the experimental nature of the trimaran style hull, a surface piercing prop was going to be an extra complication I did not need. So the model ended up with a conventional submerged propeller.
A lot of paper was consumed until a sensible layout of internal items was achieved with a simple but hopefully strong construction. The centre hull is about 30 inches (75cm) long with a beam of 2 inches (5cm). The deck to which the sponsons are attached is 8 inches (20cm) wide. The model was designed with the idea that the hull would not attempt to plane at high speeds, hard to do with such a narrow beam anyway, and the sponsons should just "kiss" the surface and supply the necessary stability.
Built mainly out of balsa with a liteply deck, the completed model weighed in at around 3 pounds (1.4 kg). A "545" motor with direct drive to a 30mm diameter (P30) propeller and a six cell battery provided the "umph". The final appearance was aimed at a fast coastal craft, the sort that smaller nations might employ to protect their coastlines. I also enjoyed the excuse to build a plastic helicopter kit for the flight deck and try my hand at a camouflage scheme.
In terms of handling it was perfectly normal at low speeds and could even be steered when moving astern. The first high speed runs showed a tendency for a sponson to drop with no warning causing the model to suddenly heel over at an alarming angle. Luckily the instinctive responce of cutting the power always allowed the model to recover. Numerous experiments were carried out and it was found that by angling the sponsons outwards, the model was stable at high speeds. Well, stable in a straightline or gentle turns but too tight a turn and the sponson would start to drop. This effect occurs with turns in either direction and just in case the rudder was the cause, a smaller rudder was tried. This did not cure the problem and actually lost the astern steering, so the big one when back on. On reflection this type of handling is not unknown in planing hulls, especially when overpowered. In fact it seems quite realistic to avoid tight turns when travelling at full speed anyway.
I remain impressed with the effortless way the slim hull slices through the water at speed producing no significant bow wave. It does however generate a nice wake wake behind the three transoms.
Glynn Guest