The British 'Dark' class

[Pioneer]

The Royal Navy’s ‘Dark’ class had quite a long gestation period having been ordered in the mid to late 1940s. The rather severe box like design had had its origins on the drawing boards of the Royal Naval Constructors at Bath (UK) however, Messrs Saunders Roe were awarded the detail design contract for what was then known as the Admiralty Type ‘A’ Fast Patrol Boat. The specification required that it should be diesel powered; the power units chosen were to be a marinised version of the powerful Napier ‘Deltic’ engine. Using a combination of alloy frames and decking, with traditional wood for hull sheathing, we are indebted to David Mills for this image of the final stages of construction of P1101 HMS Dark Adventurer – we hope to show you more from his collection of archive material from Messrs Saunders Roe. (click image for full view).

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[Dave Mills]

Ted, thanks for dropping in the photo of P1101 Dark Adventurer outside the main hangar with the old Fryars house shown in the background. The low building next to it was the drawing office where my father Victor Mills worked from late 1945 to 1974 and where I spent a few years too. This photo is of the first of the Dark Class to be built at Saunders-Roe (Anglesey) Ltd.
I will add photos of the Dark's starting with this general arrangement drawing of the Type A FPB (Fast Patrol Boat) They were designed to be like the Black & Decker drill by being able to add various attachments, like a pair of 20mm Oerlikons on the aft deck, torpedo tubes making them MTB’s, or a larger Cannon as seen on the pair for Finland, Vasama 1 and 2. Saunders-Roe (SARO) also built a series of five riveted aluminium hulled FPB's for the Burmese Government (T201-T205) and were fitted with a bespoke alternative electric drive in addition to the twin Deltics. These were known as Slow Speed Drives. My father said they were for enabling the Burmese Navy to creep silently along the many creeks to catch smugglers and bandits. It all sounded very exciting to hear such things when I was only a young lad at the time. All the RN Dark Class were of timber diagonal planking over an aluminium frame structure with the single exception of P1120 Dark Scout. This was a unique model with an all-welded aluminium hull, simplified bridge design (no spray deflectors) and the used transom exhausts. Photos of Dark Scout become easy to spot even at a distance with that 'box' of a bridge. She was also the last to be built at the Beaumaris works and was launched 20 March 1958.
The last 'foreign' FPB that SARO built to the Dark Class design was shipped to Japan 29 July 1957. I found only a couple of very hazy photos on the internet, but have just found four more while scanning through eight to ten thousand surviving Saunders-Roe negatives. Many are superb, but equally, many are in very poor condition. I will choose a small selection of the better ones for you all to see. (click on images for larger views)

[Julie]

The Japenese boat was in yokohama in 1957 Scout was accepted into the RN in 1958 would'nt that make Scout as the last to be built??
nice to see this change to the forum best wishes
Julie

[Dave Mills]

Yes Julie, the FPB for Japan was shipped out 29 July 1957 and P1120 Dark Scout was launched 20 March 1958.
Scout was therfefore the last Dark built at SARO for the RN as the rest of the order was cancelled.
There is also some info on the BMPT forum.
As this subject has come up so soon in the new Dark Class section I will drop these photos in of her.

Dark Scout with all welded aluminium alloy platework.

P1120 clearly showing transom exhausts

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P1120 outside workshops

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P1120 on the Menai Strait

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[Dave Mills]

Having mentioned the SARO built FPB for Japan I found this page from the company magazine of 1957. The four negatives I have found so far are in particularly poor condition and very badly wrinkled. I will try to repair one or two some time when I'm not scanning the rest of the comapny magazines or surviving negatives.

[justaveteran]

Great pictures but, to me, 'tin' MTBs do not appear to be so 'workmanlike'.
I'm sure the designers have got it right, but try convincing us riders of the wartime wooden variety !

[Dave Mills]

I think Dark Scout's welded hull was an experiment for the navy as the company had built the 72ft all welded aluminium motor/sailer 'Morag Mhor' for the British Aluminium Co. Dark Scout may also have been an experiment to further reduce cost, time of construction, weight and complexity and possibly increase hull stiffness over the aluminium/timber composite that the RN originally specified. She was more of a Ford "Consul" than a "Zodiac".
The Dark Class may not have been very elegant (pointed shoe box!), but they were designed to be a versatile tool with interchangeable bits.
The earlier and more eleganet experimental riveted aluminium MTB 539 (later P1602) launched 1948 is today under around 43m of the Irish Sea off Anglesey and said to be 'polished shiny' by the action of tide and sand although she went down almost 60 years ago. What would a wooden hull be like after 60 years? I'm hoping to have a diver down on her this summer to check her out with a view to possible rescue. [click image for full view]

All riveted aluminium experimantal MTB 539 (later P1602)

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[Dave Mills]

After the loss of the experimental all aluminium MTB P1602 in early 1952, Saunders-Roe won the contract to detail design and build the next generation of FPB known as the Dark Class. They were somewhat ‘chunkier’ and box-like around the rear quarters than the more elegant P1602. The Darks were of a composite hull construction using riveted aluminium alloy frames and stringers over-clad with laminated timber strip planking. There were bolted to the metal frames and the decks were plated with riveted aluminium sheeting. They were powered by two Napier Deltic 18 cylinder 2-stroke supercharged diesel engines of 2,500 BHP each. Saunders Roe built Dark Adventurer, Aggressor, Antagonist, Biter and Avenger. During the building of these five vessels SARO shopped out components to other shipyards for the building of the rest of the series for the Royal Navy. The last that SARO build for the Navy was a variant on the design in the form of P1120 Dark Scout. She was the only all-welded aluminium Dark and was somewhat simplified by the looks of her. No doubt it was a cost cutting exercise to appease the Government as the remainder of the order for the Darks was about to be cancelled.
SARO also won a contract to supply two very similar vessels to Finland, Vasama 1 and Vasama 2. There appear to have been of conventional composite hull construction.
The Burmese Government also ordered a set of five all riveted aluminium clad FPB’s complete with a bespoke auxiliary battery-electric ‘slow-speed drive’. My father said it was for silently creeping up the many river creeks to search out pirates, smugglers, bandits and gun-runners – all exciting stuff for a youngster to hear! The aluminium hulls were specified to withstand marine worm attack that would have been a problem in the warmer tropical waters.
Following this series was one for Japan, service number PT9. There is a strange rumour that she was supplied with only one of the usual two Napier Deltic engines. It seems a strange tale and I can’t imagine why anyone would want to spread it. If the Japanese wanted a Deltic engine for some other purpose I would have though they could have obtained one by a less devious and expensive route. The company magazine article does mention two engines, so the rumour may be just that.
On the subject of tales and rumours there is a 1951 Saunders-Roe advertisement that illustrates P1602 and proudly proclaims she is the World’s First Aluminium Alloy MTB. This has been found to be untrue/incorrect. The Americans has an alloy MTB No PT-8 in 1934 and is today restored and for sale for around $1.4M
Long before PT-9 was a pair of aluminium hulled steam torpedo boats built by the Scottish Yarrow Co., one for France, Le Fourde in 1894 and a larger one for Russia, Sokol (Falcon) in 1895.
P1602 may be more accurately described as either Britain’s or the Royal Navy’s first aluminium MTB, unless that is proved incorrect? [click to enlarge]

[Dave Mills]

I have just asked a friend about the rumour of the Japanese ‘Dark’ class being fitted with only one engine, but he had neither heard about it or could suggest any reason for it.
He did, however, tell me a story about the Burmese T201-T205 series. One of them was moored at Menai Bridge pier during some particularly rough weather. When they came to start her up the next morning they spun over one of the Deltic’s engines that promptly wrecked a piston or con-rod (NOT cylinder head as I wrote earlier as there are none on the Deltics) due to seawater having entered into one of the side exhaust ports and getting past the protective flap. Pairs of pistons must have come together in one or more of the cylinders (probably an inclined bank) and met seawater that caused the damage. It had to be taken back along the Menai Strait to Saunders-Roe for an engine replacement!
After this incident all Deltic engines had to be taken through the additional start procedure of manually turning the engines over by one revolution to check that no water had entered any of the cylinders. It had also been said that the early Deltics had problems of cooling water leaking into cylinders, so the start up procedure could also detect this earlier problem. Napier's made changes to mak them into reliable and widely used marine and locomotive power sources.
Could this seawater ingress through the side exhausts be why P1120 Dark Scout was fitted with higher transom exhausts giving greater protection against sea water ingress?
[click to enlarge]

[Pioneer]

A very evocative view of the Burmese T201 for me - as I was onboard when this image was taken. At that time I was a Stoker 1c in the 7th Ferry Crew from HMS Hornet.
We had just arrived to witness the launch - shortly before the shot was taken - those Naval personnel present - I was one - boarded for a very short trial (with the Saro crew).
After further short sea trials that lasted a couple of days, she was 'signed for' and the 7th Ferry Crew finally sailed her down to Weymouth for shipment as Deck cargo for Rangoon. A very cushy number for the Stokers (2 plus 1 Leading Hand) as we were not allowed in the Engine Room control booth for the whole journey South - overnight stop at Falmouth - Happy Days

[Dave Mills]

Another evocative couple of photos of the Burmese 'Dark' T201. One on the inclined slipway at Saunders-Roe Beaumaris. The slip way built in 1953 on the funicular system where the boat starting on the level at the top of the inclined rail tracks, but ending up at a small angle to help them roll across the coast road to Penmon. The other photo was taken by my father Victor Mills of me on the bridge of T201 before having a wonderful trip along the Menai Strait to Port Dinorwic.

[Dave Mills]

Some more photos of Burma T201 at Saunders-Roe. 29th December 1955. What! - No Christmas holidays?

[Pioneer]

These photo's certainly raise a few questions for me Dave -
Can you remember any RN crew present on that trip down the Menai Strait to Port Dinorwic? - if so, then I was one of them. If not, this craft had 2 launchings - maybe this craft was the one that needed the engine change - and it was the second launch that I witnessed?? Super clear images Dave - thanks for posting them.

[Dave Mills]

I can't be 100% sure it was T201 that I got my ride on as a kid to Port Dinorwic. I remember it being towed stern first into the outer dock. I have some other photos of T20? at the port but they are from the damaged company negatives.
This article is from SARO Progress magazine for Autumn 1954.
I've completed the DVD with hyperlinked index for the thirty-five magazines that I managed to find so far. These will be available during my talks on MTB 539 (P1602). - More articles will follow -

[Dave Mills]

Another couple of SARO Progress articles on the Dark Class.
Note that Dark Aggressor also went to Port Dinorwic dock as did the Burmese T201, but this time to take on stores for her journey south presumably to HMS Hornet.

[Dave Mills]

The Burmese T201-T205 series had these purpose designed electric drives for slow speed working as mentioned earlier.
I havn't reproduced the full article, but these two illustrations show where they were fitted to the for'd end of the Vee gearbox. [click to enlarge]

[Dave Mills]

The Dark Class used 18 cylinder Napier Deltic diesel engines. They were producing 2,500bhp in the early to mid 1950's but finally produced 3,100bhp. These higher powered engines were used in the Norwegian 'Nasties' and an even more powerful version in the amazing Japanese PT-10 that used three of these monster engines providing speeds around 50 knots.
The IME (Institute of Mechanical Engineers) web site has some excellent photos of the engines and one of PT-10. (dont forget to browse all three pages)

A neat animation of the opposed piston Napier Deltic engine.

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[Dave Mills]

FINNISH DARKS
An order was received by Saunders-Roe, Beaumaris in late December 1955 to build a pair of FPB's of the Dark Class type for the Finnish Navy. They were of conventional composite aluminium frames and mahogany planking and powered by twin Napier Deltic engines each of of 2,500 bhp. The boats were completed ahead of schedule and were named Vasama 1 and Vasama 2 at Menai Bridge Pier on the 3rd May 1957. They set out on their 2000 miles journey 8th May and arrived in Helsinki 15th May. 'Vasama' translates as 'Arrow'
These photographs appear to be of Vasama 1 before her name were painted on the hull and when the hull flair was painted red and white. In the later photos it appears they did away with this curious striped paintwork. [click to enlarge photos]

[Dave Mills]

Some later photos of the Vasama 1 and 2. Note that the names were applied to the hulls. Vasama 1 also appears with name and still carrying the striped painting to the flair in this first photograph. It was soon changed to remove the white stripe as can be seen before her handover. [click to enlarge photos]

[Dave Mills]

I recently heard a curious rumour about the Saunders-Roe built 'Dark' for Japan being shipped out without any engines. It was so bizarre that I dismissed it, but a few days ago another friend told me he worked on the boat at the factory and that the Japanese cancelled the Napier Deltics and the boat went out with an empty engine room! He couldn't remember if the gearboxes were fitted as he is now suffering the effects of Alzheimer's. Some other things he told me about seemed highly questionable such as the Darks being fitted with four engines. His claim about the engineless Japanese Dark does, however, correspond with the previous similar claim, so maybe his claim was right.
If anyone has further information or confirmation about this strange situation I would be most interested to hear about it as I intend to make my next illustrated talk about the 'Darks' and it would be a most fascinating fact to include.
I would appreciate any help and advice, especially reminiscences and anecdotes about experiences with 'Darks'. I only stightly remember them roaring along the Menai Strait when I was just a nipper in short pants!

[Dave Mills]

While going through my 1000's of photos I found these very badly damaged negatives of the ellusive Japanese Dark.
I compared the waterline with other Darks and they all seem very similar. Either the Japanese one had its engines installed, or was simply balasted to depth.
There is no dirt around the exhausts, but that could be because she hadn't been fired up when the photos were taken. The mystery continues.
Sorry about the wrinkled negs, but when they are this rare - - - -

(Click image to see all)

[Dave Mills]

The five Burmese Navy Dark Class (T201-T205) were constructed of riveted aluminium alloy sheet on Aluminium hull frames.
These two photos show the round-head rivets clearly visible above the chine. Below the chine the hulls were flush riveted with countersunk rivets to reduce drag and the heads being eroded off. I assume it was considered unecessary to flush rivet up to the waterline (higher than the chine) as they would be normally clear of the water when the boat was under way.
The 1940's experimental aluminium MTB 539 was all flush riveted and suffered some rivet loss near the propellers. I think there may have been similar problems with the Burmese Darks as I remember as a child my father bringing home a handful of countersunk rivet heads that he told me had corroded off MTB hulls.
I was recently told by one of the Saunders-Roe inspectors about a Burmese Dark being brought out of the sea and he could see the rivet heads 'fizzing'. They were corroding before his eyes and the whole lot had to be removed and replaced with a different grade of aluminium. It sounds like the early days of understanding the electrolytic corrosion of metals in seawater.

[Pioneer]

Another rare image, courtesy of Dave Mills, that gives a true impression of the size of a Napier Deltic motor. Not sure of what craft this is being fitted but would suggest possibly an early 'Dark'

[Dave Mills]

Thanks Ted for posting this image. I have just returned home after celebrating a friend's diamond wedding anniversary in Beaumaris, just one mile from where this photo was taken in the mid 1950's. I spoke to one of the guests who worked on the Dark Class when he was an apprentice as I was trying to find out what method was used for secure the mahogany planks to the aluminium frames. Unfortunately he couldn't remember, but he confirmed the decks were riveted aluminium sheet as I have seen among my photos. He also worked on the experimental all riveted aluminium hydrofoil Bras d'Or for Canada that I have opened a section on. Talk about coincidences in a matter of hours!
I'm giving a talk on the development of the Canadian hydrofoil and Bras d'Or in Llangefni 3 Setember 2013.
I will also be giving a new talk on the Dark Class 10th October 2013 at the Gwynedd Engineering Society, Bangor, N. Wales. All are welcome.

[Romanov]

Hello,
My name is Roman.
For many years I was building model ships. It Has been some time since I am considering to build a multi purpose fast patrol boat of DARK class.
The problem is that despite the big quantity of available documentation it has serious lacks In quality. Available sources are not detiled nor precise.
I am looking for any materials regarding this type of boat – photos, drawings In order to create the good model.
I will be gratefull for any help.

Romanov

[Pioneer]

Hello Roman
I'm glad that you found us. Welcome aboard.
This Topic has been very quiet of late but as you will have read there is quite a lot of information within.
The detail that you require may now be difficult to trace but there are quite a few modellers who may be able to point you in the right direction. There is of course the general arrangement drawing within the second post on page 1 of this Topic.
Please let us know of your models progress Roman, with some images of the build if possible
Best of luck
Regards
Pioneer

[Romanov]

Hello :)
Thank you for very nice reception.
I am drawing model plans of this boat
Currently I am drawing model plans of Dark-class speed boat. I have a documentation from late 70', the same one where even technical details are not correct.
Currently I am looking for photos of deck details such as wheelhouse and others.
One of photos in your thread shows front of wheelhouse, but I am missing both sides. Most of photos show the whole boat, the photos of small item are quite rare. I would be grateful for all more detailed photos

romanov@autograf.pl

Romanov

[Romanov]

Hello
I found these photos online

[verithingeoff]

Hi Guys
Not an ex mariner but an old brylcreem boy.
I lived in Beaumaris for many years with my parents moving there from Manchester in 1954. My dad worked at Saro. When he retired in 1981 he was given a model of P1101as a retirement present. I had it after dad died and I gave it to my son who has recently had it restored.

Here are a couple of pics, and a message to David Mills, I'll be in touch directly with you via your website

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[Dave Mills]

Thanks for getting in touch Geoff. I'll email back.
I knew your dad when I was an apprentice.
I believe there were a few Dark class models made for customers to get a feel for what they were getting.
I'm pleased your son now has it in restored condition.
I gave a talk in Moelfre last Saturday on the late 1940s experimental aluminium MTB that was designed and built at SARO. I also have a model of MTB539 on long term loan that was built in 1950. It also needs some repairs to get her up to scratch.