The British 'Dark' class

Post-war development of Coastal Forces craft covering the Proud, Bold, Gay, Dark or Brave Class boats, as well as experimental craft
Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Electric drives for Burmese 'Darks'

Postby Dave Mills » Sat Apr 02, 2011 7:40 pm

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]
Attachments
Slow drive 1.jpg
Arrangement of drives located in the auxillary machinery compartment each side of the accoutic control cabin
Slow drive 2.jpg
technical drawing of battery electric "Slow Speed Drive".

Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Napier Deltic engines

Postby Dave Mills » Sun Apr 03, 2011 6:46 pm

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)
deltic_animation-small.gif
A neat animation of the opposed piston Napier Deltic engine.
deltic_animation-small.gif (75.83 KiB) Viewed 3382 times

Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Re: The British 'Dark' class

Postby Dave Mills » Thu Apr 21, 2011 10:27 pm

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]
Attachments
419-3 x1000.jpg
Vasama 1 on the slip
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419-5 x1000.jpg
Vasama 1 about to go on trials
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419-6 colour 2 x1000.jpg
In all her colourful glory
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419-6 x1000.jpg
Entering the Menai Strait
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420-3 x1000.jpg
Fixed pitch propeller showing considerable tip curvature, possibly to help reduce tip cavitation. Note cavitation erosion at blade root. They Dark's generally seemed to suffer from these problems. The earlier experimental aluminium MTB 539 (P1602) suffered from considerable cavitation problems with her triple ROTOL variable pitch propellers (not to mention hydraulic pitch control failures in service)
.

Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Re: The British 'Dark' class

Postby Dave Mills » Thu Apr 21, 2011 10:53 pm

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]
Attachments
444-6_V1.jpg
Vasama 1 on trials showing the striped paintwork below waterline (Thomas Telford's World famous Menai Suspension Bridge is in the background)
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465-13.jpg
3 May 1957 on the Menai Strait
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465-23.jpg
3 May 1957 during the naming ceremony with Christening bottles raised over bows. These were electrically released from a control desk on the pier head.
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465-40.jpg
3 May 1957 after the naming ceremony with guests taking a 'cruise'
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465-41.jpg
3 May 1957. An excellent view of the bridge structure with guests.
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Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Japanese ENGINELESS 'Dark' ?????

Postby Dave Mills » Sun Sep 18, 2011 11:41 pm

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
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Engineless Dark for Japan?

Postby Dave Mills » Sat Nov 26, 2011 3:37 pm

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)
Attachments
447-1 x550.jpg
PT9 on the slipway
447-1 x550.jpg (74.34 KiB) Viewed 3172 times
447-2_JAP_FPB x600.jpg
PT9 during launch
447-3 x600.jpg
PT9 on the Menai Strait
447-4 x600.jpg
PT9 sitting at normal depth

Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Burma Dark Class Hull construction

Postby Dave Mills » Fri Dec 23, 2011 9:43 pm

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.
Attachments
T201 riveted hull.jpg
Burmese Dark Class - Round head riveting down to the chine. Countersunk below [photo Ted Else?]
T201 riveted hull.jpg (21.74 KiB) Viewed 3075 times
T201 riveted hull 229-3.jpg
Burmese Dark Class - Round head riveting down to the chine. Countersunk below.
T201 riveted hull 229-3.jpg (79.79 KiB) Viewed 3075 times

Pioneer
Moderator
Posts: 289
Joined: Sun Oct 19, 2008 12:48 pm

Re: The British 'Dark' class

Postby Pioneer » Sat Aug 24, 2013 3:29 pm

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'
Attachments
deltic-engine-fit.jpg
Photo Courtesy of Dave Mills.

Dave Mills
Chief Petty Officer
Posts: 53
Joined: Mon Mar 14, 2011 2:35 pm

Re: The British 'Dark' class

Postby Dave Mills » Sat Aug 24, 2013 8:12 pm

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
Seaman
Posts: 3
Joined: Sun Jul 23, 2017 9:52 am
Location: Poland

Re: The British 'Dark' class

Postby Romanov » Sun Jul 23, 2017 10:21 am

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
Moderator
Posts: 289
Joined: Sun Oct 19, 2008 12:48 pm

Re: The British 'Dark' class

Postby Pioneer » Sun Jul 23, 2017 7:24 pm

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
Seaman
Posts: 3
Joined: Sun Jul 23, 2017 9:52 am
Location: Poland

Re: The British 'Dark' class

Postby Romanov » Mon Jul 24, 2017 10:02 pm

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

Image
Image

Romanov
Seaman
Posts: 3
Joined: Sun Jul 23, 2017 9:52 am
Location: Poland

Re: The British 'Dark' class

Postby Romanov » Thu Jul 27, 2017 10:08 am

Hello
I found these photos online
Attachments
206898.jpg
206900.jpg


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