Like just about everyone else, I wrangled with the weight issue, and the truth is that it's just about impossible to get absolutely right.
The poblem comes from the fact that in its' unconverted form, the model is too light for its' size. This is due in part to the size and weight of the RC gear and powertrain originally installed, as it's far lighter than would be any proper RC and propulsion / steering gear (remeber also that the model originally had no rudders or steering servo). To compensate, the designer(s) made three simple, but significant alterations to the original design.
Firstly, they altered the underwater profile, substantially reducing the deph of immersion at the transsom, threby reducing the displacement.
Secondly, the first mod was only partially successful, so they proceeded to paint the waterline quite a bit lower down, particularly at the stern - the unconverted model floats noticably higher by the stern than does a full size Severn.
Then finally, they positioned the exhaust ports about 10mm lower on the transom to make the model look right.
All this adds up to a model which when converted is invariably a little overweight, and goes stern down when full power is applied. You will all be glad to hear that mine is no different ! Therefore, I came to the conclusion that even a 380 motor was going to be too heavy. So initially I went with a pair of 25mm brass props on M3 s/s shafts (from Raboesch), driven by a pair of 280 motors, running from a 7.4v 2200 mAH Li-Po, through a Viper marine ESC, and Hi-tec Zebra 3 RC gear (40MHz), and a micro servo for the rudders. This gave great speed, and good endurance, but on only the second outing I managed to melt the backs out of both motors ! - Back to the drawing board !
Anyway, after much headscratching and surfing of the interweb, I found a great compromise between the power of a 380, and the weight and efficiency of the 280 - a motor that IMHO is too little talked of outside heli circles - the 370: Only 10 grams heavier than a 280, with a steel back, ventilated can, and quite happy at 7.2 volts.
The battery that I ended up with (quite by accident) fitted the modified battery compartment like a glove, and allows room for the leads which connect to a deans plug, bonded into the side wall. The compartment stays almost completely dry, and even if it does get flooded, does not allow water into the bilges. It also means that I don't have to remove the suerstructure to recharge. As regards the height at which the battery is mounted within the model, I can confirm that the model corners flat at all speeds when not planing, and even when I sent it out on Fareham Reach in a blow (with chop!), although it was a real cow to keep head to wind, even with the wind and waves abeam, the model showed no signs of being anywhere near capsizing. To complete the working side of the model, I made the original on/off button waterproof, and reisnstated it, so that there is no need to remove any covers to switch the model on or off.
The final plan now is to re-paint the hull above and below the waterline, then apply new decals and stripes.
Finally, does anyone have any suggestions for a suitably scaled radar fitting ? as my boat is currently doesn't have one !
