Fast Patrol Boat: Vosper P150 Perkasa

23rd November 2007

5th April 2007

Here's fun.  Build a three foot FPB (fast patrol boat) out of balsa and plywood, paint and decorate, fit a huge motor and connect some serious NiMH batteries, a propeller, rudder and radio control system and find the nearest pond - this picture is a neat summary of the end result:

Yes, it's very fast and very deadly.  A fast patrol boat is perfect for high speed patrols, intercepting other ships or making hit and run attacks.  This one is configured as a Motor Torpedo Boat (MTB) with anti-submarine 21-inch torpedoes and is designed to close the distance, fire torpedoes and then turn and run.  Yes having a 40mm gun is nice for intimidating drug smugglers etc. but won't hurt a submarine unless forced to surface.  The high cruise speeds of these boats make planing an everyday occurrence...so the fact that the front third of the boat is out of the water in the picture above is completely prototypical!

Prototype

The prototype is the Vosper gas turbine powered FPB 'Perkasa' delivered to the Royal Malaysian Navy from 1967.  (Vosper delivered a selection of similar designs to navies around the world including the RN.)  Gas turbines are more costly and consume more fuel than diesel but have a number of significant advantages such as greater power/weight ratio, are lower maintenance, allow very fast acceleration/deceleration and top speeds of ~50 knots (58 mph or 93 km/h).  That is seriously fast!  It is not necessary to worry about achieving un-prototypical scale speeds with too big an engine in your model...splendid!

The Model

Built from a 1:32 scale (I measure 1:31!) Precedent kit (code SWP or PPSW?) that came in two varieties (wood or fibreglass hull), the wooden hulled version is built by overlaying curved strips of plywood onto a wooden frame, using filler in the gaps and sanded balsa blocks for the complicated front hull geometry.  I must confess that getting the hull to be smooth and symmetrical was challenging and without the woodworking skills of my Father the end result would have been much less impressive.  The fibreglass hull version may well be an easier project for those without an expert to hand!  

Nevertheless it was immensely rewarding to see the hull take shape over several weeks, with an hour or two put in a few evenings each week, in a way that can't be achieved from just building a plastic kit.  (Although of course building plastic kits is still much more satisfying that buying a finished model.  Which in turn is more satisfying than just looking at a shop window...)  Something about the way the design 'grows' out of the wood makes it feel more organic and satisfying, but obviously not everyone feels this way about balsa!

The curves of the superstructure are again achieved using a mix of plywood and balsa blocks on a wooden framework.  All the details visible in the pictures were made from sub-kits of balsa, dowel and thin strips of wood, including the torpedoes and stands, gun, hatches and lockers etc.  The finished model was then masked and sprayed red below the waterline and a selection of military looking greys were used above.

'P150' stickers that with hindsight are rather too big were added and the torpedoes secured with black tie-wraps.  Delicate hand rails were left off and windows were not unfitted because it was always the intention to motorise and use the boat on the water.  Why glue on what will only snap off at a later date?  Details still to be fitted (because they were purchased separately) include an anchor and chain/rope, mooring stanchions and life raft cylinders.  An aluminium carry frame was also made:

Propulsion

But what about the interior?  An electric motor is very simple to install, clean, quiet and it is easy to recharge batteries.  Petrol engines although powerful are dirty, noisy, produce clouds of fumes and are likely to die in the middle of the pond/boating pool/lake without warning when they suddenly run out of fuel.  With batteries and an electric motor the boat will just get slower as the batteries begin to run out so it is easy to pilot back to the side.  (No waders needed...!)

I decided to go for a nice big Torpedo 850 12V 157W electric motor and large capacity nickel metal hydride batteries (NiMH) in two packs of 10, each to last about 30 minutes during operation (impressive at 13 Amps!).  These batteries although expensive are lighter than a conventional lead acid battery and can also be split into two groups of five and nestle snugly between the bulkheads on either side aft of the motor, ensuring excellent balance.

Steering and Control

The speed control is a RCLINE SP-RF20 (with the purple heat sink in the picture above) and connects to the batteries and motor, and was designed for use in model racing cars originally.  This and the servo (Futaba S3003) for the rudder are controlled by a Futaba FP-R115F receiver also located in the water-tight box.  Remote radio control is provided by a 4 channel Futaba T4VF (of which only two channels are actually used, one for throttle and one for steering).  All the Futaba stuff came in a big box called 'Skysport 4'.  I also had plans to motorise the 40mm gun so that it could rotate but this idea occurred too late in the construction process to be implemented easily because of the internal bulkheads.

Performance

The model thus equipped enjoys rapid acceleration and deceleration, a top speed allowing it to plane, a small turning circle and high manoeuvrability.  Just like the prototype.  It's also extremely stable in the water with a very light superstructure (I once saw a large and highly detailed Kirov battlecruiser oscillating from side to side drunkenly in a most comic way, no doubt because the owner had over-detailed the superstructure with all manner of brass fittings.  It was a real shame because it made what was otherwise a superb and dignified model look completely daft!) 

Also if the model goes out of range of the radio control then it shuts down (instead of speeding into the sunset on its last known course...!) although the range of the control appears to be at least 100 m, and it is designed for model planes so it probably has a much greater range than I've tested.

Video

Here it is in action, captured on my DSC-V1 camera on a boating pool. (Watch out for the very tight turn a few seconds after the duck/goose quacks loudly...) The video could do with enhancement to focus more on the model so I will re-upload it at some point!