Confederation Marine Modellers
Frank's newest model is of the USS Crockett, an Asheville class gunboat which saw service in the Vietnam War. She was commissioned on 24th June 1967, transferred to reserve in July 1975 and decommissoned in 1976. She was 165 ft long, and 24' beam. Powered by two 725hp Cummins diesels and one 1370hp GE LM1500 gas turbine, she was capable of 50 knots. She was armed with one 3" and one 40mm guns, plus two twin 0.5" machine guns.
The model is two Dumas kits, one comprising the parts to make the hull and superstructure, and the other the hardware and fittings. The model is 51" long, 5/16" to 1ft scale, or 1:39. This makes the scale speed for the model, corresponding to 50 knots, to be 11.5 km/hr.
Frank found this to be a learning experience for him and he now has a greater appreciation and understanding of the skills required to build a boat of this size and detail. The instructions were very poor, consisting entirely of text with no diagrams or illustrations to help. Youtube and Bill M were able to provide more help. Frank built the hull and applied the fibreglass and Bill M. helped him with the finishing of the hull. The hull was too flexible with the 1/8 " thick ribs supplied and these were replaced with 1/4" ribs. The main deck was supplied as two halves in the same sheet of wood, so these were replaced with a single piece. The bridge front was too thin and flimsy and all of the bridge structure parts were replaced. The guns were poorly designed, so redesigned by Bill and built in a completely different way. In addition, the railings were made from stainless because the material provided in the kit was not strong enough. On the whole the kit was poorly designed and without Bill's help and guidance it would still be sitting on the work table.
The model is powered by two 12 motors from a 2.9 Ah gell cell battery, using a Viper speed control and an Attack 75MHz radio. The lights are powered from a AA battery pack.
Click on pictures to enlarge
The forward / aft trim looks OK, although I was surprised by the draft. The model weights about 6 lbs and is already close to the waterline. I added ballast weights to see what would be needed to bring the model down to waterline. This shows that rather less that 3 lbs was available for the deck, superstructure and detail. I'm going to have to watch my weight again!
I decided to increase the top speed by overpowering the ESCs using a 4S battery. The ESCs must have a high voltage limiter as they cut out. From a box of bits I found a voltage reducer and installed it. Providing the voltage is adjusted to below about 14 volts, the ESCs operate fine. I settled on using 13.25 v to give a slight margin. The increase in voltage gave a marked increase in performance, and I decided to use this set-up permanently. I think the model is slightly overpowered, but at least it can be quickly moved out of conflict situations!
Rowen's Her Majesty's Air Force Vessel "Seal" - Parts 1 & 2.
Click on pictures to enlarge
After the shafts were correctly located, the motor mount position was established. I made up a mount using wood and aluminium plate. The motor shaft spacing is determined using the shaft centre lines. The longitudinal location can be measured from the shaft slope and height.
Two brushed, 550 type motors were then fitted to the mount, followed by the shaft couplings. The mount location can be fine tuned by slightly sliding the mount around until the motor and shafts could be rotated with the minimum force. The mount was then glued into place.
The shaft couplings used are steel, which tend to be noisy. I find that if a rubber or plastic sleeve is pushed over the coupling it quietens considerably. The inner coupling cavity/sleeve can also be filled with grease to ensure the joint is lubricated. I had earlier installed “oiler” fittings to the shafts for periodic lubrication.
I decided to try the Quicrun 1060 series ESC on this model, one per motor, to improve control. So far they work well, although the installation would be eased if the wires were longer.
I made up rudders by wrapping styrene sheet around a flattened brass rod and gluing together. The doubled over sheet was then cut to the rudder side profile and the section sanded to shape. Once compete the shafts were lubricated and inserted into the tubes. The rudder servo was fitted with a control linkage made up using old bicycle spokes and tested. I set the radio up to the “elevon” control sequence and tested the systems. Nice thing about brushed motors is everything usually works right the first time! No programming of ESCs etc needed either!
The hull was now watertight with the powertrain fitted; time for trial tests on the local pool. This may appear awry chronologically as I wanted to get the hull sailing properly before adding the superstructure etc as a winter project. I am using 3 S Li-Po batteries and I found the performance adequate. Nice bow and wave patterns, similar to the actual vessel photographs.