Description of Radio Controlled model of Supramar PT 150 ‘Queen of the Waves’ built by Søren Struntze, Copenhagen, Denmark.
This is a somewhat condensed version of an article which originally appeared in the July-August 2002 issue of ‘Classic Fast Ferries’. While some more recent issues of the on-line journal are still available on http://www.classicfastferries.com, this issue is unfortunately no longer accessible online.
This very detailed 1:40 scale model of the Supramar PT 150 hydrofoil 'Queen of the Waves', has been under gradual construction since around 1975 by Copenhagen based naval architect and IHS member, Søren Struntze. It is one of three hydrofoil models built by Søren, the other pair are based on his own design concepts rather than being scale models of existing hydrofoil types. The full scale 'Queen of the Waves' was the second of three PT 150’s built by Westermoen Hydrofoil, and was completed in October 1970.
The 95 cm long hull consists of a light wooden frame composed of a keel, regularly spaced transverse frames and chine and deck edge strips covered mainly with 0.3mm thick aluminium alloy sheeting. The sheeting was attached to the frame with ‘blue Araldit’. The window recesses for the lower cabins are neatly cut out of the alloy sheeting.
As with the full-scale PT 150’s, the foils are of hollow construction with internal stiffening. Unlike the full-scale hydrofoils, which require high tensile steel for these items, the model foils are of the same aluminium alloy sheet used for building the hull. The foils were assembled with the aid of purpose built jigs to ensure correct alignment when complete.
The bow foil of the PT 150 is equipped with both inboard and outboard flaps on the port and starboard sides. On the model all four of these flaps are radio controlled via an intricate system of mechanical linkages. For gradual turns, the PT 150 hydrofoils only employed their bow foil flaps. It was only for more rapid turning that the rudders were also deflected in conjunction with the foil flaps. The same control arrangement was incorporated in the model such that a single steering servo would initially only activate the bow foil flaps, then, as more helm is applied, the pair of rudders are also deflected. Symmetric movement of the port and starboard flaps is also possible to adjust the trim of the boat. The flaps have a range of movement from 8.5 degrees up to 15.5 degrees down and are controlled via a set of 0.5mm diameter stainless steel wires inside 2.0mm diameter (0.9mm inside diameter) nylon tubes. These flap actuation wires emerge from the hull through the cross tube connecting the foil struts to the hull. They then run down to the foil within the hollow inclined struts. The control linkages for the flaps are completely hidden. In the event of a grounding, the bow foil will rotate backwards about the cross tube which is attached to a pair of shock absorbing springs. A ratchet mechanism has also been fitted to avoid the bow foils swinging forward again after impact.
The aft foil incidence angle is fully adjustable over a range from –2 to +2 degrees. This is servo controlled via push/pull 3mm aluminium rods leading down the rudder support struts in a similar manner to that of the bow foils. The full-scale PT 150 hydrofoils had an aft foil with hydraulically controlled incidence, but in addition were equipped with an air feed stabilisation system which controlled the lift generated by the foil while operating in waves.
The model weight is about 2.6 kg however since savings in weight are possible through changes to newer motors and batteries, ballast has been added in the lower portions of the foils to gain additional stability. This was achieved by inserting about 100g worth of ballpoint pen balls of about 1mm diameter each into the hollow sections of the alloy foils fixed in place with epoxy resin.
Initially twin electric Monoperm Super Special motors were fitted and these were both air and water cooled. The cooling water would be drawn in from the base of the rudders on the aft foils, just as the engine cooling water inlets are arranged on the full scale PT 150. Although these motors provide sufficient power, they had lower than optimum speed making it difficult to match them with optimum propellers. Therefore they have since been replaced with Power 400 series motors.
The battery bank consists of eight SAFT KR 35/44 Ni-Cd cells, each of 2.5 Ah capacity. With the considerable weight of batteries and the otherwise light construction of the model, these cells have been placed within a spring mounted shock-absorbing frame. The battery pack will eventually be replaced with a much lighter 7.2V 1.8Ah Ni-Cd set. The changes to the motors and battery pack are hoped to give an endurance greater than the already significant 20 minutes currently achieved.
The propeller shafting is of 2mm diameter stainless steel rod. Since this is less than the scale diameter of the actual shafts, for static display the shafting will be sheathed with 3.5mm diameter aluminium tubing between shaft bearings to give the correct scale appearance. Since the foil mounted shaft bearings rotate when the aft foil angle is adjusted, an intricate cardan shaft arrangement is incorporated to accommodate this movement. On the full scale PT 150 spherical bearings and sliding shaft couplings had been fitted to accommodate shaft deflections. The multitudes of hinged shaft support struts are all faithfully recreated on the model.
Construction of the hull and foils and the installation of running gear and radio equipment was complete by 1986, though the superstructure still needed to be built. None the less, it was now possible to test the model. To ensure it was watertight, and to simulate the additional top weight and windage of the final superstructure, a temporary ‘box’ superstructure was constructed and fitted to the model in preparation for the trials. After experimenting with different propellers to overcoming an initial teething problem of achieving a stable ride, the trials revealed the model would run in a manner just like its bigger sisters. Smaller faster running two blade propellers of 40mm diameter and 34mm pitch gave the best results with a considerable reduction in the current drawn from the batteries over the original propellers that had been fitted. With reassurance that the model would run properly, effort has since concentrated on adding details and building the superstructure.
The superstructure was fabricated largely of balsa wood and 0.5mm aeroplane plywood, but suitably toughened with resin applied to its surface. Some portions of the upper superstructure, where scale details would be revealed, were again fabricated from aluminium sheeting. The upper aft cabin and bulwarks at the bow and upper aft deck incorporate the intricate stiffening that would have been apparent on the full-scale vessel. The mast structure was also carefully fabricated from alloy. Elsewhere miniature stainless steel handrails are fitted.
Søren has gone to extraordinary lengths to model features of the interior of the hydrofoil. Ready for incorporation in the model are rows and rows of seats painted up in the various bright colours of their time, complete with miniature headrest covers made of tissue. Steps and bulkheads in the cabins are also modelled. On the upper deck, the bridge contains a comprehensive layout of scaled instrumentation with throttle levers a clearly distinguishable feature. On the aft bulkhead of the wheelhouse, further circuit boards and a radiophone can be spotted. A crew rest area is provided aft of the wheelhouse. Three hand made figurines representing the skipper, engineer and radio operator are at the controls. The radio operator is in a relaxed pose reclined back in his seat with feet up on the console reading the paper. Søren reports that the radio operator had the most time to spare on a typical voyage and so this was an appropriate snapshot of his life on board!
The larger windows around the wheelhouse and upper front saloon make it relatively easy to see inside those sections. Realising that it would not be as easy to see the details inside the remaining sections of the model, Søren decided to make all but two of the exterior doors functional so that they can be opened to peer inside the model. All doors come complete with working door handles!
The model is designed to be able to be separated into many sub-parts for ease of maintenance and repair. Several hidden latches on both the port and starboard sides secure the superstructure to the hull and these are simultaneously locked or released via a single actuator.
One of the neat features of the model is that there are few external indications that the model is radio controlled. The first impression is that the hydrofoil is purely built as a detailed static display model. The switch for the radio control gear, the bow foil adjustment jack and the central locking actuator for securing the superstructure are all neatly hidden under a scale hatch on the foredeck.
Photos included are:
1. The framing of the hull completed. Note the extensive use of lightening holes in the keel and transverse web frames. Circa 1975 (Søren Struntze)
2. The overall hull structure completed. The aluminium alloy sheet ‘shell plating’ can be clearly seen, as can the window cut-outs. Circa 1976 (Søren Struntze)
3. The bow foil being fabricated from thin aluminium alloy sheet with the aid of a construction jig. Circa 1976 (Søren Struntze)
4. Close-up of the bridge and crew accommodation area on the model taken in about 1995. Radio unit can be seen in the upper right while a matchstick in the upper left corner illustrates the small scale of the instrumentation (Søren Struntze).
5. A trial run of the model with the temporary superstructure fitted and insulation tape covering the incomplete window recesses in the hull. Antenna cable can be seen aft. Circa 1990 (Hans Jørgen Hansen)
6. The model as it stood in about 1995 (Hans Jørgen Hansen)
7. Another perspective of the model from around 1995. One can’t help but admire the details (Hans Jørgen Hansen)
The model constraction has advanced further since these photos were taken, however no more recent photos are available for the album at this stage. More details can be obtained from Søren Struntze by posting a message on the IHS Bulletin Board at www.foils.org. Be patient in awaiting a reply.
File written by Adobe Photoshop? 5.2
File written by Adobe Photoshop? 5.2
File written by Adobe Photoshop? 5.2