Masterclasses > 63 FOOT RAF AIR SEA RESCUE LAUNCH
63 FOOT RAF AIR SEA RESCUE LAUNCH by Bluebird
John W E:
On the actual framework itself there are two more pieces of timber to go in. These are for supporting propeller shaft tubes and also rudder tubes and ‘P’ brackets. These were made from 2 pieces of 1/8 ply – 9 ¼ inches long x ¾ inch wide. There is an oval slot cut in these to accommodate the prop tube; the slot was cut to roughly 1 inch longer than required, and also slightly wider than the propeller tube; in our case the prop tube is 6mm diameter and the slot was cut at 8mm wide. These two pieces were notched and then glued into the frames – and the whole assembly was yet again allowed to dry overnight. The next stage in the build is the good bit. :)
Once we have checked and double checked that everything is square, there are no stringers that haven’t been glued properly, there are no pieces that we have missed sanding and we are happy we can commence planking.
Normally, when I diagonally plank, I like to commence roughly in the centre of the hull. I know a lot of people like to begin at the transom (stern) of the boat; but, like I say, I prefer to start at the middle. The reason for this – is, as we work towards the ends of the vessel, we can determine how many planks are going to be required and adjust the width of the plank so we are not trying to fit a ‘tiny fiddly’ piece in at the very last plank.
Now, with a 45° setsquare, I clamped this onto the framework, so that one edge of the square is flush against the keel and is parallel with the keel; and the 45° angle runs out from the keel to the chine so that the angle faces the bow. Across the stringers I marked in pencil a line – it’s a Datum line, which we work from. I mark exactly the same line on the opposite side of the hull, and this is where we place our first plank. Now, for the inner planking, on this particular model, I am using Obechi planks – 1 ½ mm thick x 8 mm wide. The reason I picked Obechi is because it is an easy material to work with; it is fairly flexible; can be bent well with the aid of steaming/hot boiling water and it is also a very tough material. I had considered trying out using Balsa wood for the inner planking; but, after a few trials on test pieces, I found I had a personal dislike for using Balsa as it is a little on the soft side so I opted to go and use the material Obechi which I have used on many occasions and its my preference. I am sure everyone will have their own preferred material to work with for doing their own planking.
The glue I am going to use, it’s the bog standard EVOSTIK (water proof evo bond) and I commence by laying the first plank along my line, leaving a slight gap of about 0.5 mm from the centre of the keel. I then cut the plank oversize at the chine by about 3-4mm. Now, quick note here. If we were going to diagonal plank – single skin – here – we would have commenced our planking on the sides of the hull, this being – when we finished the side, we sand the planks flush with the chine stringer and then when we plank the bottom, the planks overlap the side planks covering up the side plank end grain.
The bottom plank end grain would then be covered up by the running strake that runs around the outside of the hull at chine level. Therefore, effectively, sealing all end grains – so less chance of water penetrating the plank. Water always penetrates quickly through an end grain, so, opting for that method reduces the risks of this.
We are opting for double planking – where we put two layers of plank – one on top of the other. The inner planking – it doesn’t really matter where you start (i.e. bottom or the side). Now, as I say, I started on the bottom. First plank goes along the pre-drawn guideline, while I glue and clamp that in place, I mark off, cut and glue the plank on the opposite side of the hull.
This gives the glue on the first plank chance to dry. I then come back to my first plank; and sufficient clamps allowing :) I glue one plank forward of the first plank I put on making sure it is butted up tightly to the first plank and one plank to the stern of my first plank – so, in actual fact, I now have three planks in all on this side of the hull.
I allow these to dry, by going back to the 2nd side and doing the same. As you have noticed, we are not using nails or pins but just clamps alone. It is a slow procedure, because, it is just normally two planks at a time. It took me roughly 2 – 2 ½ days to plank the hull. That was working roughly about 12 hours a day – with me dinner breaks and of course FORUM BREAKS. :)
Once I had completed the bottom planking; we sand the planking flush with the side of the chine ensuring we maintain a sharp edge on the planking. We then move on to repeat the procedure on the side of the hull, where the plank angle faces the bow – the side planking runs in the opposite direction from chine to deck stringer, but, they actually run towards the stern. Yet again, we mark a 45° angle from the chine to the deck stringer, using our 45° set square & on this line we begin our planking.
As we work our way towards the stern and the bow and we can see we are within 8-9 planks of completing the side, what we can do, we can clamp on several planks without glue, to estimate the distance thus to ensure that the last plank to go on is at least half a plank width. I find the last planks normally end up being put on – right on the corner where the transom meets the chine. It is advisable to try and aim for at least half a plank width, rather than something like ¼ to 1/16 width of a plank.
The reason for this is, you glue and clamp this on, and, you will find (well I did) it’s the first piece to chip off when you catch it with a sanding block. But, if it’s over half a plank wide it does have a greater gluing area. The way you achieve this, is, by reducing the width of one or two planks as you work your way towards the transom and the bow.
Once we have completed planking our sides, obviously we do have to allow it to dry out GOOD AND PROPER and then we sand the edges of the planks so that they meet the bottom planking. This corner on the chine must be kept square – TRY NOT TO ROUND THIS CORNER OFF on the planking but use a short wide-sanding block with small movements along the grain of your bottom planking; working from transom to bow.
The next stage is to sand out any imperfections/unevenness on the planking on the hull. Also, you will find, on some of the photographs you will be able to see a photograph which runs down the centre of the keel. I have done this deliberately to avoid an air gap between the planks and the bottom of the keel. This gap is now filled in with car body filler along with any hollows in the planking. The filling was sanded down smooth – but not too smooth as we need a ‘keying’ surface for our next layer of planks. Once we are happy with our inner planking and we have no imperfections and it is nice and smooth. REMEMBER WE MUST BE SURE HERE – BECAUSE ANY IMPERFECTIONS NOW IN THE INNER PLANKING WILL BE TRANSFERRED STRAIGHT TO OUR OUTER PLANKING having less material to play with (thickness wise) on this particular model.
John W E:
We come to do our exterior planking – now; the initial idea of this build, was to try and keep it as close as possible and my idea was to try and keep it as true as possible to ‘real life’ on the exterior.
On the actual real vessels it was planked with 4 inch wide x ¾ inch thick mahogany. For my mahogany I used 0.5 mm thick x 3 mm wide strips. The first plank to go on was in the centre of the hull on the side, set at 45° from the chine At the end of the day, I had put 70 meters i.e. 35 meters of planking on each side. Wow that is an awful lot of planks – near enough 8 days solid planking – side and bottom. In total there was 170 meters of planking put on the hull.
The method I used was to apply first of all, gently pull the string of mahogany through my finger and thumb nail – so that the plank gently curled. The glue was then applied on the back face of the mahogany strip and then this strip was placed into position on the hull and then pinned down with dress makers pins until dry. The excess glue was wiped off with a damp sponge, but, not too wet so as to the soak the plank; this procedure was done until the complete hull was covered.
It was then allowed to completely dry. Once it has stood there for about a day or so, I sanded the hull in the direction of the planking – with various grades of sand paper; working from medium grade sand paper down to a fine sand paper. Any gaps were filled in with a mixture of dust from the mahogany planking and a little drop of PVA glue and also any prominent pinhole marks were filled in using the same method. Once the planking and everything had been thoroughly dusted off, I moved on to the next stage in the build.
The next stage was to coat the hull with an Epoxy finishing resin (PACER Z-POXY finishing resin).
Pause for thought; if we had built the hull and just used the single layer of diagonal planking – personally I would have followed this route – I would have coated the hull with a polyester resin and then, with a layer of tissue mat, following by two further coats of resin – with a final sand.
This does have its advantages and also its disadvantages; with it being a ‘largish’ hull; we are basically only relying on the thickness of the planking plus a few stringers for the hull strength – as the polyester and matting mixed will give a percentage of strength, it will not withstand a sharp impact very well. I cannot comment about – if we had replaced the tissue with the material that the ‘flyboys’ use; because to date I have never used that yet. but hey I do plan to use that material in a future build.
If we had used say, thin plywood for planking on a single plank, this would have given us a much stronger hull. So, for those who are contemplating building a diagonal hull there are a couple of ‘pointers’ to think about. In this particular build, where we have double diagonalled planked it; we have actually increased the strength numerous fold, because we are actually producing a form of a plywood where the grain in the planking run at 45° to one another and this produces an extremely tough hull.
John W E:
...... couple more pictures for the planking process ..... :)
John W E:
To move back to coating our hull with epoxy – so basically the strength is already in our hull and all the epoxy will do, apart from bonding it all together, is produce a very water resistant barrier between the elements and the wood. So, the instructions on the epoxy say – mix equal amounts – I moved the hull into the nice warm kitchen, covered everything up – where I was going to be working – with old towels etc., no matter how one protects something – one always manages to splash with paint or resin – at least I do :) and, you can guarantee that it will be your better half who will find it – not you.
So with this finishing epoxy you do get two containers, each containing 6 fluid ounces – one of hardener and one of resin and what I did was – I acquired the little tumblers that you use for measuring out cough medicine etc., I used two of them. I measured out 15 ml of hardener in one and 15 ml of resin in the other one. I poured this into a cap top that you get from a spray can – mix thoroughly which gave me 30 ml of mix – it was a little bit too much (believe it or not) to cover the whole of the hull. Bear in mind the hull is 40 inches long x 10 ½ wide…..it covered it amply leaving a little bit left. This was set aside and allowed to dry for two hours and what surprised me was there was no smell whatsoever from this epoxy.
Once the mixture had hardened off on the hull thoroughly, and I had left it overnight; I rubbed it back with coarse wet n dry and rubbed it nearly to the grain of the planking once again, removing all brush marks and ‘ripples’.
I also used various blocks of wood as sanding blocks along with the wet n dry.
I then washed the hull thoroughly and dried it in the airing cupboard for a couple of hours and then gave it another coat of epoxy resin. This again, was allowed to dry overnight. The procedure of applying the epoxy to the hull was repeated; and once again when this had dried – it was rubbed back with medium grade wet n dry – not forgetting to use the sanding blocks as well.
John W E:
moulding a plank to shape.......with fingers....
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