Model Boat Mayhem

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Author Topic: R.T.T.L. 2751  (Read 65888 times)

Perkasaman2

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Re: R.T.T.L. 2751
« Reply #25 on: November 22, 2009, 08:40:48 pm »

Here's a stern pic. :-)
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riggers24

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Re: R.T.T.L. 2751
« Reply #26 on: November 22, 2009, 10:32:45 pm »

Its been a rough week me southern pal.
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John W E

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Re: R.T.T.L. 2751
« Reply #27 on: November 23, 2009, 07:29:23 pm »

hi there

Mike thanks very much for putting that link on - that is a very interesting link with regards to double-diagonal planking  :-))

I have spent a bit of time today, trying your idea Mike of assimilating the calico between the plank layers.   I have abandoned the idea now, to be honest, because with it being a chined hull - I couldnt get it to stretch evenly into the concave areas of the bow; I tried using tissue and a very light cotton - but at least I tried.

Whilst on the subject of double-diagonal planking we must realise that there are several versions of this boat, which were built at several different yards.   The planking arrangement therefore differs, so, not all of these may have had the horizontal stern planked.  

Some vessels, or should I say 2 vessels with the E after the numbers, were the experimental vessesl and these were built with aluminium bottom and fibreglass sides.  Later in their life, this was stripped off and was replaced with double diagonal planking.

The other thing to remember is that the Mk Ia 's had 3 Napier-sea-lion engines.  So did the Mk Ib 's  but, the Mk 2 's only had 2 main Napier-sea-lion engines.  The thing that is confusing is that the 2751 there are reports saying that she is a Mk 1 with 3 Napiers and other places she is a Mk 2 with 2 Napiers - I am going to get this clarified first though.

aye
john e
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DickyD

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Re: R.T.T.L. 2751
« Reply #28 on: November 23, 2009, 08:06:12 pm »

Vosper 68ft Rescue Target Towing Launch Mk.1B
RAF Numbers    2751 - 2755
Builder    Vosper, Portsmouth
Displacement    Light......25.68 Tons
   Loaded....44.675 Tons
Dimensions    LOA.........68ft
   Beam.......19ft 0.75in
Draught    Light - FWD....2ft 0.25in, AFT.....4ft 10.75in
   Loaded - FWD....2ft 10.5in, AFT.....5ft 11.75in
Main Propulsion    Triple Napier Sea Lion
Horse Power    500 BHP
Number of Shafts    Three
Maximum Speed    40 Knots
Cruising Speed    33.3 Knots @ 2000 rpm
Range    530 miles
Fuel    2200 Gallons
Construction    Hard Chine - Mahogany Skin, Planking - Double Diagonal
Crew    8 - 9 Men
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John W E

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Re: R.T.T.L. 2751
« Reply #29 on: November 23, 2009, 08:11:35 pm »


RAF Numbers 2751 - 2761 & 2767 - 2771
Builders Vosper Ltd, Portsmouth
 Grove & Guttridge
 Saunders Roe
Displacement Light......25.68 Tons
 Loaded....44.675 Tons
Dimensions LOA.........68ft
 Beam.......19ft 0.75in
Draught Light - FWD....2ft 0.25in, AFT.....4ft 10.75in
 Loaded - FWD....2ft 10.5in, AFT.....5ft 11.75in
Main Propulsion Twin Rolls Royce Sea Griffon Mk.101
Number of Shafts Two
Maximum Speed 39 Knots
Maximum Cruising Speed 33.3 Knots @ 2000 rpm
Contiuous Cruising Speed 30 Knots @ 1800 rpm
Range 530 miles
Fuel 2200 Gallons
Construction Hard Chine - Mahogany Skin, Planking - Double Diagonal
Crew 8 - 9 Men
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DickyD

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Re: R.T.T.L. 2751
« Reply #30 on: November 23, 2009, 08:28:50 pm »

Confusing isnt it ?  {:-{
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cdsc123

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Re: R.T.T.L. 2751
« Reply #31 on: November 23, 2009, 08:29:23 pm »

Hi chaps

The MKI 68ft RTTLs were the old wartime Hants & Dorset HSLs (3 x Napier sea Lion) stripped of armament and fitted with target towing winches powered by 10hp petrol Fords. The numbers fell between 2552 and 2746 inclusive. The post-war design MKIAs were a beamier design, and to start with were (under-) powered by the 3 Napier Sea Lion set up until the Rolls Royce Griffons came available. The numbers were 2747 to 2750. The subsequent five were designated MKIBs and were also built with 3 Napiers, but had slab sided aluminium superstructures with improved internal layout.  These were numbered 2751 to 2755. All these boats were upgraded to MKII spec when the new engines came available. The MKIIs were built with the RR Griffons and were numbered 2756-2761, and 2767-2771. The experimental MKII was 2762E, later re-numbered 2772E and when re-planked to standard spec she became 2772. She was never 2762 because there was another RAF rescue vessel with that designation.
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Re: R.T.T.L. 2751
« Reply #32 on: November 23, 2009, 08:31:50 pm »

Nice one Christian, could you repeat that please ?  ok2
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John W E

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Re: R.T.T.L. 2751
« Reply #33 on: November 23, 2009, 08:42:30 pm »

So Christian  2751 started life with 3 engines then  she was up upgraded to MKII spec  having the centre Napier engine removed  and 2 Griffons  engines fitted only   , have i got that bit correct ?


john e
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Re: R.T.T.L. 2751
« Reply #34 on: November 23, 2009, 08:53:20 pm »

Think she ended up with 2 RR Griffons John, I think.  ok2
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cdsc123

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Re: R.T.T.L. 2751
« Reply #35 on: November 23, 2009, 09:05:00 pm »

Yep, spot on  8)
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John W E

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Re: R.T.T.L. 2751
« Reply #36 on: November 23, 2009, 09:16:18 pm »

 :-))
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Re: R.T.T.L. 2751
« Reply #37 on: November 23, 2009, 09:17:47 pm »

Now the next question Christian   

both props were left hand and the rudders had trim tabs fitted to them to help steerage as thay were prone to pull to the starboard   so thay say  do you have any pics of the rudders fitted with the trim tabs ? pleas

john e
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cdsc123

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Re: R.T.T.L. 2751
« Reply #38 on: November 23, 2009, 09:51:05 pm »

Sorry, no. I'm not convinced the RTTLs had these though, I think the Brave Class which were a larger and faster version of the same hull design had them though. The RTTLs were famous for needing an experienced helm to prevent slamming onto one chine on re-entry after wave jumping, due as you say to the torque effect of having same handed props. The trick was to apply helm on take-off to counter the torque effect.
They did however have transom wedges retrofitted to bring the nose down, a comparison photo showing one boat with and another without can be seen here, close to the bottom of the page;
http://www.bmpt.org.uk/boat%20histories/brave%20class/page_two.htm
BTW I have seen a rear view of 2751 which shows the external transom planking to be horizontal.
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Perkasaman2

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Re: R.T.T.L. 2751
« Reply #39 on: November 23, 2009, 11:21:41 pm »

Some great info here - it seems that a third (additional) diagonal layer was retro added to their 'bottoms' to resist the stress of prop torque slap/pounding mentioned by cdsc123.
My winter build plan of a 1:16 RTTL finished in Medit. colours (white) might kickstart earlier. These craft make fine looking models - keep up the fine work John. (I'm making a lot of notes.)  :-))
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John W E

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Re: R.T.T.L. 2751
« Reply #40 on: November 24, 2009, 09:36:06 am »

http://www.bmpt.org.uk/News/Brian%20Mutton%20Memories%20of%20RAF%20Marine%20craft.pdf

some good stuff hear to have look at regarding trim flaps

john
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John W E

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Re: R.T.T.L. 2751
« Reply #41 on: November 24, 2009, 07:22:22 pm »

hi all

just a quick update, started on the exterior planking there are 30 mahogany planks on there - and its taken me the best part of the day to do this much....but both sides are done - I have calculated there may be 360 odd more planks to go on.....the steel tubing that you see in the foreground is what I am using to roll the planks over - to get the bend in the planks.  Also, when I have put the glue on the back of the planks I use the tube similar to a rolling pin - this removes all the air bubbles from underneath - it also beds the plank in.  :-))

so here goes....planking away

oh - and I have added a front view to show the flares of the bow.

aye
john
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John W E

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Re: R.T.T.L. 2751
« Reply #42 on: November 25, 2009, 06:30:32 pm »


Some great info here - it seems that a third (additional) diagonal layer was retro added to their 'bottoms' to resist the stress of prop torque slap/pounding mentioned by cdsc123.
notes.

:-))
Hi ya Brian this is interesting, I havent managed to find any facts to back this up yet.   The only thing I can find on the web and in a few books which I have is where it mentions strengthening the starboard side chine and adding extra supports to the affected areas - logically thinking I cannot see them adding an extra layer of diagonal planking over the bottom of the hull as this would increase the weight of the vessel and dratrically decrease its performance.

I would have thought that if they were that concerned, they would have just reduced the govenor settings on the engines.   I did, however, find reference to strengthening the hull at the chine on the experimental boats which had aluminium bottoms on the hull and they were prone to cracking around the chine where stress was caused, but, this was later rectified where they stripped off all of the aluminium and fibre glass and replaced it with double diagonal planking.

aye
john e
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Perkasaman2

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Re: R.T.T.L. 2751
« Reply #43 on: November 25, 2009, 09:37:25 pm »

Stengthening/adding frames after skinning x2 and final fitout would be a nightmare/uber expensive exercise (Vosper liability - design unfit for purpose i.e. 40knots?????) After the inexpensive final trim wedge solution (a la' E or S BOOTE fashion) adding a third 'stiffening' bottom layer of 15/16" must have been a hugely cheaper/getout for Vosper. The waterline on the mk11 rttl's is very interesting/revealing. Don't forget that these structural issues ocurred in only certain sea states and general governing of the throttles would have been inappropriate/unnecessary in all other sea conditions where the full monty ok.
You are not seriously intending to add  an extra skin if you verify the fact :o :-)
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cdsc123

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Re: R.T.T.L. 2751
« Reply #44 on: November 26, 2009, 09:20:26 pm »

Hi John

This is a superb treasure trove of RTTL photos, the 2751 gallery has a few good views;

http://www.asrmcs-club.com/BoatsWebsite/rttl1ab2.html

I took this photo of 2753 when she was being broken up, you can clearly see there are 2 layers of planking despite what I have read on the subject.

The really interesting thing is the cross section of the trim wedges;    
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HS93 (RIP)

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Re: R.T.T.L. 2751
« Reply #45 on: November 26, 2009, 09:23:10 pm »

is that one of the wedges and if it is how far across does it go and have you any other pictures of the wedges

thanks

peter
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cdsc123

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Re: R.T.T.L. 2751
« Reply #46 on: November 26, 2009, 09:28:33 pm »

Hi Peter

Yes, all the way, and no, not in cross section.
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HS93 (RIP)

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Re: R.T.T.L. 2751
« Reply #47 on: November 26, 2009, 09:41:50 pm »

Thanks anyway.

peter
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John W E

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Re: R.T.T.L. 2751
« Reply #48 on: November 26, 2009, 11:35:26 pm »

 Hi Christian thanks very much for putting that link on  :-)) so can we say that no boats of this class had three layers of bottom planking ?

john
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Re: R.T.T.L. 2751
« Reply #49 on: November 27, 2009, 06:37:54 pm »

Hi John

I suppose some must have, as lead historian T Holtham says they did in his published work (RAF Marine Craft Directory).

Perhaps 2753 slipped through that net. The thing to look for is the direction of the outer layer on the bottom, as a 3rd layer would surely have gone in a different direction to the 2nd layer. I note from recent photos that 2751's outer layer of bottom planks runs parallel to the stem, i.e. "leaning forwards", whereas 2753 had the opposite. This could mean 2753 never got the 3rd layer but 2751 was one of the boats that did (this assumption is made safer as they both came from the same builder).

Pure conjecture, but a theory nontheless.
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