After the end of the war the Royal Navy decided to move from gasoline powered fast launches to diesel, to reduce fire risks.
The first major diesel powered boat class was the Dark, introduced in the mid1950s. These were powered by two Napier Deltic horizontally opposed, triangular layout two stroke diesels.

Shortly after this class was introduced it was determined the role of the Fast Patrol boat had been superseded by helicopters and aircraft. The Fast Patrol vessels were then gradually withdrawn.
To retain competence in the use of fast vessels, the RN commissioned three fast training boats (FTBs), the Scimitar class. This was the last high speed RN class of the era.
They were similar to the Brave in many ways. Both were built by Vosper and the lineage is evident. Rather than three Proteus gas turbines, they only had two, although with CODOG diesel units for slow speed operation. They were unarmed and designed to give R.N. crews experience in fast, coastal patrol boats.
The vessels could be armed and converted to three Proteus turbines if circumstances changed.

Our COVID lock-down hastened progress on my Dark class project, so have been trying to find another build for the coming winter. Have decided to model fast patrol type vessels for the time being. They are great fun on the water.

Would have liked to build a Scimitar Class FTB in around 1:32 scale, again using a GF hull from MTB Hulls, but that scale was not in their range. A GF hull is light and robust, well suited to these vessels. MTBHulls did offer a 1:72 scale hull, but that worked out around 16.5” long. Thought it would be too small for a working scale model.

Was in touch with a modeller in Australia who has made similar models. He also pointed out the number of successful “plastic magic” conversions of kits that are around this size. Obviously, it is achievable. Would give an unexpected change as the larger scale would have been similar to my recent Brave Borderer and R.A.F. RTTL projects.
The biggest challenge will be to keep the weight down to around 450g.

Looked an interesting and challenging project and at such a small scale one with plenty of potential for failure.

Contacted the Glass fibre supplier, who offered to mould a lighter hull, at around 100g. Ordered it and arrived promptly. Nice and light at 100g, but somewhat flexible. A thorough dimensional check showed a slight twist in the forepart.

Have found that a gentle application of heat, by electric heat gun, to GF will allow the shape to be worked and adjusted. Warmed the hull and twisted in the opposite direction to straighten it. This worked and the hull became true.
Was concerned that the twist might reappear over the months before can start the build, thus added a light bulkhead and bulwark stringers to hold in position. So far this has worked.
Now trimmed the bulwarks to shape and filled a small strip around their top edges to glue the deck down too.

Concerns over weight encouraged me to weigh every component physically. Biggest challenge came from the choice of brushless motors. An ESC is needed for each one. These are significantly the heaviest items, but have the best performance.
Surveyed scores of ECSs and motors trying to arrive at the lightest combination, but with best performance. Also had to compromise and omit an independent BEC power system to save weight, used the integral ESC one.
The propellors at this size are only available in plastic. Also had to make the shafts out of brass rod with an aluminium tube as could not readily find the more traditional stainless shaft with brass tube in the necessary sizes. Should also be nominally lighter,

Total weight of all these components, along with hull and bulkhead came to 270g.
This is rather less that the 450g target. Have a test 150g battery, which when installed, brings the model to the waterline. If this works well, hope to find a lighter battery with a similar capacity. Does confirm the 450g weight target appropriate.

Just hope the paint, glues and superstructure weight can be contained in the difference!

The next challenge was to ensure the weight distribution corresponded to the waterline, as do not want to add ballast.
Recently dispensed with a bath tub, so the indoor test tank has gone. Fortunately, at this size the hull fits nicely into a laundry sink. Was thus able to carry out trials and locate components to get the best balance. The attached pictures show the final layout.

As the hull and powertrain were assembled, thought might be opportune to do a test run in a small local pool. Using a 2S LiPo battery found that the hull planed nicely, but not dramatically.
Had a 3S battery handy, so thought might be worth trying. Not my smartest idea!

There was no deck fitted (to improve access) and was using plastic tubes as drive shaft couplings.
Certainly, planed really well, but the 3S battery overpowered the brushless motors. Inevitably one of the plastic couplings failed. The model continued to run on the one remaining screw, so this was not readily apparent.

When turning the unexpected occured.
The operating screw caused that rudder to lift the stern corner, causing the opposite bow to dig in. The hull immediately filled with water and sank; the pool is shallow so it was quickly retrieved.

Unfortunately, to meet the weight targets, the ESCs and motors used are designed for drones and aircraft, not marine. There are no pretensions of being suitable for wet operation.
Very carefully dried everything out, but to no avail.
The ESCs emitted the dreaded grey smoke with linked stench and failed. One of the phase wires also pulled out of each motor. The joint could have been overheated and weakened at 3S power.
Tried to repair everything, but was unsuccessful. Only remedy was replacement.

Fitted two more ESCs (these were purchased for another project and are 40 not 20A capacity) and motors. Fortunately, at this size, not frighteningly expensive.
Also found a 2mm x 2.3 mm steel shaft coupling on E Bay, ordered a pair. Due to the earlier failure, thought steel would prove a more robust approach.
Had no previous experience of the plastic sleeves used earlier and was confident steel would work.

Others have used plastic sleeves without problem though, decided to try another type first before switching them out. This was made of surgical tubing which is nice and flexible. Had to fit small plastic sleeves on the shafts to make up the difference in diameters.

Have used steel coupling on other projects, the major downside is noise. This can be reduced by sliding plastic tubing over the joint to stiffen and damp vibrations.
Will fit the steel ones if the next trials bring another plastic failure.

After this retrofit also loosely fitted the deck. Held this down with the Handyman’s secret weapon (duct tape) so it can be removed to improve access if more issues are found during the next test runs.
Quick test in the laundry tub showed everything was working.

Back to the outside pool and found that these new plastic sleeves worked fine. Decided not to replace them. They are certainly quieter and smoother than steel couplings.

Also confirmed the hull planed nicely on 2S, so fought off the temptation to use 3S again!

Although the battery used was overweight, it was adequate for test purposes. The waterline was slightly above the correct position, but with good trim.
Under power the hull planes well, but the bow eventually lifts excessively. Think this could be overcome with transom trim tabs. These were fitted originally, so would eventually add them anyway.
After about ¾ hour of mixed speed running the 2S 2000 mAh battery had lost about .2 volts. Can now confidently order a smaller capacity and lighter weight battery.

The 40A ESCs, robbed from a future project, were used for the test runs referred to in the previous Blog. These ESCs are heavier than the 20A required, so replaced them to realize a weight saving as have now received the replacements
A future weight saving will be from fitting a lighter Li-Po cell. Will order one early next year to minimize deterioration during the winter.

All now installed and embarked on more test runs, also with trim tabs. The model performed flawlessly, it planes nicely and, with the trim tabs, nice and flat. The plastic couplings show no deterioration so have dropped any thoughts to replace them.

As I reflect on this first attempt to build a small, lightweight model one lesson stands out. The structure is quite traditional, so tried to fit a .020” thick styrene deck. Not the usual .060”, thinking this would save weight.
After two attempts to get the aperture sides straight without distortion and by then bracing with stiffening strips gave up.
The deck sides sagged slightly and it became difficult to get the removable access section correctly aligned.
Reverted to the thicker material which fitted perfectly and remained straight. Probably turned out lighter too as dispensed with strips and adhesive!

The practical sailing season in this part of Canada is drawing to a close.
Will now move towards finishing the model as am confident the powertrain works.
Future blogs will be limited to describing any significant steps that arise during this process

Turned to the superstructure. This is essentially a multi-curved cowl to allow copious amounts of air to flow into the Gas Turbine engines. The forward portion of the cowl is shaped into the wheelhouse and there is a recessed bridge cut into the upper deck.

First thoughts were to make this from styrene type foam and then coat either with glass-fibre or some similar material. Have used this approach before but because it tends to be heavy, was doubtful of the results. Nevertheless, embarked on making a male buck out of foam.
Was surprised by a couple of things that arose during this:

1) Have previously cut foam with a sharp knife as do not possess a hot wire cutter. Because of curves and size of the superstructure, even a fully extended new box cutter blade was not long enough.
Decided to try and cut carefully using an electric coping/fret saw. The cut worked out well. Think the reciprocating blade heats the styrene which seals the cut.

2) Sectioned styrene can be smoothed with sand paper to again give a smooth surface.

Ended up with a nicely shaped block. Planned to cover it with GF cloth or similar so could impregnate and seal with resin.
However, had a couple of sheets of .020” thick styrene available. These were originally purchased for the deck, but decided they were too thin and flexible. Wondered if they could now be used to cover the buck, using it as a former.
Embarked on a series of trials. These will be described in the next article.

With careful planning, shaping, cutting and heating to bend into shape, this thin styrene was wrapped and fitted around a styrene foam buck made for the simpler rear section, to cover the engine room hatch.

This turned out quite well. Was encouraged the approach might also work on the main section. Although this is an infinitely more complex shape, if it worked the saving in weight would be considerable. More in a later episode.

After thought and planning, the superstructure began to take shape. Started with the rear of the cowl first. It is the simpler section and would confirm if the approach was suitable. Would also give a basic section from which the more complex bridge and wheelhouse could be made.
Again, used the styrene buck concept and started to fit a thin styrene sheet over it. Quickly realized that, although the buck made making the cowl easier as could heat and bend sections around it. Once had reached the multiple curved sections of the wheelhouse it could be dispensed with. Easier just to cut and fit the sheet then heat as necessary and manipulate into shape.

As there are no model builders plans available, was using the General Arrangement drawings. These have several drawbacks, one of which is at the intersection of two curves giving a blended joint, the intersection point has to be estimated. The front of the wheelhouse thus became inspired guesswork!

Have attached pictures of the rough assembly of the superstructure. These show how it is made up of various smaller sections. That is one of many techniques have gleaned from this website. Break complex items down and they become much easier to make.

Onto the final stages of railings, deck hardware and painting. Will give a further update once complete.

Finished, apart from some minor display touches.
The final weight is 470g, that is 20g above the 450 target.
As the waterline looks fine, have decided to leave well alone.
If the performance is as it was earlier, will be satisfied.
Now, onto the next challenge, the H.Sw.M.S. Visby

Model was finished some time ago, but as there were no unusual problems during assembly or finishing did not update this blog.

Due to the small size of the model was able to test ballast and batteries in our laundry sink. To try to minimize the battery weight obtained a small 2S 1000 mAh battery.
Was unsure how long this would last, but as it helped bring the waterline up thought worth a try.

Much to my relief the model performed well. Slightly faster than scale would guess, with in excess of 20 minutes running.

Have uploaded a video on the media section, which shows it nicely.
Decided this model has worked out well and was an enjoyable build.
Quite challenging trying to minimize weight yet retain the scale appearance and performance.