Masterclasses > 63 FOOT RAF AIR SEA RESCUE LAUNCH
63 FOOT RAF AIR SEA RESCUE LAUNCH by Bluebird
John W E:
The final coating of epoxy resin was applied; and the hull was allowed to stand and harden for good 24 hours. Then I gave it a final rub down with fine-very fine wet n dry. It was thoroughly washed off with warm soapy water and rinsed and given to me son Andrew to spray for me. The first two coats were Halfords grey primer undercoat and these once dry were lightly rubbed down. Then, there were three top coats given of Halfords acrylic satin black paint. This was thoroughly allowed to dry for a couple of days; and to be honest with you – as normal – IMPATIENCE GOT THE BETTER OF ME – and I gently removed it by cutting it from the building board. :)
John W E:
Prior to cutting the hull from the building board, I had made a building stand for the hull to sit in. On the building stand the support faces which come into contact with the hull, I had lined with a very soft sponge; this prevents the paint from being ‘chipped off’. Once the hull was off the building board and into its building stand, examine all the inside for any large blobs of glue that may have dropped/amassed on the inside of the planking and remove them with a scalpel taking care not to damage the planking on the inside.
Then I gave the inside of the hull with polyester resin mixed just pure polyester resin and work it into the planking and into the frames; the reason I used polyester resin here rather that epoxy (on the inside of the hull) is because its cheaper and also its there mainly to protect against absorbing any water that does find its way into the hull (polyester resin does absorb water over a period of time) unless it is coated with either paint or another protective barrier over the top.
Once this polyester resin on the inside has dried, we can set about installing the hardware/running gear. On this particular build, with it having three motors, I installed the centre prop shaft first. The prop shafts I used on this model are bog standard off the shelf ones. I cut the outer tube so that it just long enough to emerge from the bottom of the hull; as it would do in a real life size boat.
We make a ‘P’ bracket up – first of all. We select several pieces of tubing, the smallest one fits over the propeller shaft – in my case 4mm diameter. The next piece of tube fits over the first piece snuggly and the 3rd piece of tube fits over the top of those two pieces snuggly – so in actual fact we have made a small telescopic tube and these are all soldered in place to make a rigid body.
I acquired 4mm nut and bolt, which fitted snuggly into the tube. This in turn was to become a mandrel which held the brass tube snuggly and I fitted the whole assembly into an electric drill.
With the aid of a file and emery paper I profiled the brass tube into a shell shape. We made three of these shell shapes, i.e. one for each shaft; and, after we they had been completed, I cut the legs from 1mm thickness brass plate. This was soldered on squarely to the shell shape, along its length. This now forms the ‘P’ support bracket at the end of the shaft.
John W E:
We now assemble the ‘P’ support and the propeller shaft into the central location in the hull ensuring that it is square along the length running true with the keel and also at the correct angle. We have already pre-cut the whole to take the ‘P’ bracket but we do not Araldite this in first, we Araldite the main propeller shaft in first.
Araldite is a thick 2-part Epoxy resin.
Once this has hardened, we then ensure that the propeller shaft can turn freely. This in turn centralises the ‘P’ bracket at the end of the shaft, centralising it and making sure it is true with the shaft.
When we are happy with it, we then epoxy the ‘P’ bracket in place. The centre shaft now is our reference shaft for the marking off the distance for our two outboard shafts. They must be parallel to the centre shaft and also at the same angle.
The same is procedure is what was done with the central shaft i.e. epoxy the outer tube in first, followed by the bracket at the end.
Normally, I personally move on to fit the motor beds next. I think I have mentioned before, I made a jig up a while ago which replaces the coupling and, basically it is a solid coupling, this is located on the end of the propeller shaft inboard side and also locates on the motor spindle shaft. This gives a perfect alignment between the motor and shaft (sometimes) :) then; the motor mount is set into the hull with wedge shaped pieces of timber and glue and when the glue has hardened on the motor mounts – the solid coupling is replaced with a flexible coupling – and a trial run of the motor and the shaft is then done. This ensures that it is in line.
Once we have all three motors lined up and set in place; I normally run them in – hey this is a good time to drop the phone in on top of the motors when someone next calls you as happened to me. :)
When we are happy that there are no tight spots in the propeller shafts etc., we can then move on to installing the rudders.
This is where the set up, in this particular model, becomes interesting; on the original full sized vessel, all the propellers turned in the same direction. (Left hand – as we stand at the back of the vessel – they would all turn anti-clockwise.)
When the real boat is turning, the coxswain and the engineer would use a combination of speeding up, or slowing down either of the outboard engines to assist in the turn. The centre engine would be dropped down to low revs and therefore not to interfere with the turning thrusts of the propeller. Along with this manoeuvering there would be assistance from the rudders. Now, on our model, we do not have the facility (as yet) to reducing the centre motor’s speed through the mixer. It runs at the speed that has been set by the throttle on your radio handset.
I am going to get a ‘tighter’ turning circle either to port or to starboard (possibly to port more than likely). To compensate for this I have altered the linkages between the three rudders so that; when I turn to port the port rudder virtually blanks off the port propeller. The centre rudder only blanks off half of the thrust of the centre propeller and the starboard rudder blanks off only a third of the starboards propeller thrust. When I say ‘blank off’ it directs the thrust of the propellers. This system works both on both port and starboard movement.
The other alteration I made – originally I produced three scale-sized rudders – these looked rather small – so…I increased the size by wrapping them in Plasticard and this should also add in the turning circle. The rudders themselves are made up from brass bar 1/8 inch diameter – inserted into two plywood cheeks, which form the shape of the rudder. The tiller arms are all manufactured from 1/16 of an inch brass; cut and shaped, along with the use of parts from a three-pinned plug. The linkages between the arms are all plastic to prevent any electrical interference. At this stage, I have tested all of the electrical fittings – I have had a trial fit of the Electronic speed controllers, along with the mixer unit – so far so good.
Now I am very happy with this set up and it works well.
I can move back on to the build of the hull; the hull itself is basically finished now – there is the deck to go on, which I am busy with now. The superstructure to build along with the deck fittings, guns and so forth. As this is turning out to be a slightly longer and more enjoyable build than I ever anticipated – I have decided to put this part of the build on first, followed by the rest of the build – which will tag along after this. :) :D
..... I'LL BE BACK
aye
John e
bluebird
John W E:
Hi there,
Here is a scribble to explain the method/possible method of constructing the cut-down prop shaft and the P bracket support - this is a method I have used several times, when we didnt have the facility of a lathe to manufacture the parts.
We commence by obtaining a 'shop purchased' prop shaft of the correct length that we require for our prop shaft. We remove the prop shaft from the tube; mark off on our tube the required length for our new prop tube - and, then cut it at our mark.
I normally cut the tubes in half with a small modellers pipe cutter - this does give a nice clean cut. I then remove all the burrs and dress the prop tube up.
The next stage is to remove the bush from our redundant piece of prop tube - what I normally use to remove the bush is a tube which fits pretty neatly inside our prop tube, or, I have used a discarded knitting needle (from the Mrs) and I tapped the bush out from the inside.
The next procedure is to warm up gently, normally on the cooker top, the end of the tube where the bush is going to fit. Prior to doing this, I normally put the bush into the freezer compartment of the frige and I divvent mean a bush from the back garden :) so while the bush is being frozen and contracting, the tube is going to be expanded with the heat. This makes it a lot easier to fit the bush back into our new section of tube. Let it cool down naturally, out of harms way......... yes I have tried to pick the tubing up when its still been RED HOT and yes, it does bring tears to the eyes.
The next stage, as you will see by the drawing, is to make the support bracket - this is basically 3 pieces of tubing. The inner tube must be the correct diameter to fit over your prop shaft and it must be not too tight of a fit, you must be able to spin the shaft in the tube.
Then, its a case of two pieces of tube which will fit over the tube over your first piece of tube. These are all cut to length slightly longer than one another - inner tube being the longest and these are then soldered - just with normal soft solder - then I make a mandrel up and shape as has been mentioned previously in this build - with a file and emery cloth and then I add the support leg.
I do hope this makes it a little clearer - and - I will add further scribbles as we go along - but, just as a side note - the rudder and rudder tubes are made up basically the same way as we make the P bracket up - and I will add a drawing to explain later on.
Now....just going back to fit the deck.
aye
john e
bluebird
John W E:
2nd part fitting the deck – now we have to sit and think about the deck and if we think about when we did the deck on the Cervia, although we used a light ply on the Cervia’s deck and this was to facilitate the bends in the deck – the one going from bow to stern (the rake) of the vessel and also the bend that goes across the deck from port to starboard (Camber) – Light ply easily took the shape we required, with the use of a lot of weight and a lot of cellotape sticking it down while the glue stuck; now then, if we look back at our plan that we are building from and look at the side profile – we now know why she is called ‘the Whaleback’ because of the shape of the deck line.
Not only do we have the camber of the deck, but, also we have a hump and a hollow in the deck. This is going to be difficult for us to form out of plywood in one single sheet.
One option is open to us - using very thin plywood – say 1/16 inch thick – we could lay it across the deck in say 3-4 sections, to give us an area to call the deck and where the joints are in the plywood we could fill and smooth in. We could put the plywood on in 4 pieces, 2 at the stern and 2 at the bow.
There are 1-2 options as a I say, to look at using plywood, however, along with the plywood we are going to have to put some sub-structure underneath – this would hold the shape. This is because, relying on the frames to produce this deck shape, is not going to be enough. We would get hollows between the frames.
So, knowing that we have to put some form of sub-structure underneath – and this is going to add extra time to our build – let us have another rethink. How was the original boat decked i.e. what materials were used? According to all information I have – she was double-diagonally planked with mahogany planks with a canvas membrane between the planking – the same as the hull bottom was constructed. This sat on deck beams and deck frames of varying sizes; supported by laminated gussets and elbows; so, we can take this and we can construct deck beams similar to the ones of the real boat for our deck to be laid upon.
Also, we could double diagonally plank the deck – this would give us a more realistic and closer to true scale hull.
So, our first job then, after we have smoothed off and obtained the correct deck edge shape and size; our next stage is to re-enforce the frame tops which we did with 1/8 inch x ¼ inch Obechi strip; one piece clamped either side of the frame at deck level, slightly proud of the deck by about 1/16 inch.
This was done on all of the 8 frames, including the transom.
The transom only had one support timber put in and that was on the inside. Once all the glue had hardened on the frames, we then sanded in the correct deck camber, using a flat sanding block; some 10 inches x 4 inches. This sanding block is just a flat piece of plywood with coarse sand paper stuck on the one side and fine sand paper on the other side. The reason it’s so wide and long – this prevents one from sanding ‘hollows’ into the work. Sometimes though it can be awkward to use, but, once you get the knack of sanding with it, you can see the benefits.
Now we have completed sanding the camber; we can think about putting the longitudinal deck beams in first; the first thing we must do is mark a centre line down the centre of all of the frames so we can work from the centre line – out over to each side.
Mark off on the frames that are appropriate – all of the opening areas (in other words all of the areas that are going to give us access to the inside of the hull).
We then work around these openings inserting our longitudinal deck beams in. These deck beams are notched into the support pieces that we put into the side of our frames. I commenced at the stern, working to the bow, putting the longitudinals in.
Then, I commenced putting horizontal stiffening beams in (these are the beams that run from the deck edge to our longitudinal beams). Then after I had finished putting these deck edge beams in, I marked off the main opening area for the cabin and wheelhouse.
Where this is marked out, we have to insert the combing strips; this is where we have to cut out the tops of several of our main frames. This is a genuine case - of marking out once, checking 5 times – then re-checking and then eventually cutting once you are 100% sure. Then, after we have cut the frame tops out we insert our combing strips. What I did then was set the hull to one side for a while to allow all the joints and glue to harden up.
Whilst it was in the process of hardening I double checked all of the hardware in the hull – the motors, couplings, rudders, rudder couplings and linkages etc., ran the motors once again and checked the steering servo. The reason for this is once the deck is on; if something does go on with one or two items, it may be major surgery to get at the item to correct the fault. So rather check now whilst I still have reasonable access to the hull the better.
The glue has hardened and we go back to our sanding block and very carefully level and blend in all of the deck joists with the camber of the deck and also, the whaleback shape.
It is always adviseable now (says he) to remove the dust out of the inside of the hull SAYS he again! Thinking oh can I get the vacuum nozzle in here. :)
Okay what method are we going to use, plywood, or double diagonal. I really like the idea of double diagonal. It gives the best option to produce the lovely shape of this deck on this boat. So, we are opting to double diagonally plank the deck – we aren’t going to put the calico membrane in though; we are going to use Obechi for the first layer of planks 1.5 mm thick x 8 mm wide. This will give us a rapid build up of planking for our first layer and then we are going to plank using our friend the 3 mm x 0.5 mm thick mahogany planking.
Start the process – we commence at the centre of the deck; at an area between the bridge front and the bow – roughly half way between. We draw a 45° line across the deck support beams; to the deck edge. This is done both port and starboard and this is the line that we used for our first plank.
We then glue on our first plank, exactly the same way we glued our first plank on the hull and we use the same procedure. Five planks forward of the first plank and five planks astern. When we have 10 planks on, we swap over and do the other side.; so this is where I am up to now O0
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