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John W E:

In this plan build we are looking at a slightly ‘different style’ of building the model hull.  Also, some slightly different materials in the process of building the model hull; and we are delving into the areas of a ‘lot more research’.  By a lot more research we will be researching the history of the full sized vessel to help us in our build.

So, let us cut out the waffle and begin to look at the plan  :)

The plan comes from, yet again, the Model Boats plans catalogue and it was originally drawn by a gentleman by the name of John Pritchard.   John is well known for his drawings of coastal craft such as MGBs, MTBs, Air Sea Rescue launches and so forth.  Along with these plans; I have two articles which were written by John for the Model Boats magazine, one in the year July 1975 and in those days you could purchase the Magazine for 25 pence – eeee and I used to have a full head of hair then  {-).   John also revamped the article and it was reprinted in October 1981 – the magazine had gone up to 60 pence then!!!!

In the October 1981 issue, there are a scaled down set of plans identical to those which I purchased from the Model Boats plan company.

John W E:
So, let us have a look at the plans.  What are the plans going to tell us?   Well, they are graded on the grading system at 4 star **** for the experienced modeller.  When we look at the plans we see at the top there is a side profile drawing of the boat.   To the right of the side profile there is a front view drawn of the boat.

If we look carefully and can make it out; there is a baseline and a water line running parallel through these two drawings.  We need to note this for reference further on.

If we look down from the side profile drawing, we will see a deck view of the vessel; underneath that there are our side profile line drawings.    On this particular drawing which is the one for the time which will concern us; you will see it has been divided up vertically by 7 lines; drawn through the hull.   It has also been divided up 8 times horizontally.   These horizontal lines are marked off as ‘water lines’.   Zero water line or we will call it the baseline also corresponds with the line of the top drawing on the side profile.

So, we know any measurements taken from this baseline will not only correspond with our line drawing; but, it should also correspond with the side view of the vessel.   The vertical lines through the line plan drawing represent the frames or in our case they are going to become our ‘RIBS’.  If we look below the side profile drawing; there is a deck profile drawing.  This again has been divided horizontally and vertically and this time the horizontal lines are marked B1, B2 etc., etc., and these represent what they call ‘BUTTOCK LINES’.

For the purpose of our build; we do not need to really concern ourselves with that too much – we only have to be concerned (for this time being) with the vertical lines which are representing our frames and also our water lines.  If you study the plan closely you can see and this is just for pure reference and information only – the Buttock lines represent, or should I say, they are the squiggly lines drawn through the hull on the side profile.  When I say squiggly they are the lines that go from the deck edge down towards the keel and back up to meet the deck line.

Now then, if we move across the page from the line profile drawings; across to our right hand side of the plan, you will see there is a stern view drawn of the vessel and also, underneath that, there is a line drawing of the frames or ribs.   This line drawing has been divided up again by horizontal and vertical lines and you will see on close inspection – if the scan allows – that the lines are numbered and lettered and they will correspond with the side profile and deck profile drawings.

Now for the time being, what we must do is concentrate and familiarise ourselves with these three drawings, the frame drawings, the hull and the deck profile.  We then know and we can picture in our minds exactly where every frame fits or is located on the profile drawings and on our deck line drawing.

When we are happy with that; we next have to look and say to ourselves – okay – how are we going to power this model? This is because, on close inspection you will see, there are no propeller shaft locations drawn in on our line profile – nor is there any rudder positions indicated.   Our first job is to find the location and transfer these from our side profile drawing and stern drawing to our line drawings.  Also, at this stage, we have to consider – are we going to make the model – a working triple screw model; or a single screw model?  (The screw means propellers in this instance).

For this build – it’s going to be TRIPLE SCREW – i.e. hopefully blinking fast.  ;D

So then; we can either – with pencil and ruler take measurements from our hull profile drawing (side hull) for the position of the propeller shafts and rudders and then transfer these to our line profile or we could actually trace them using tracing paper.   

I opted to transfer these with pen and ruler; and I didn’t only transfer the measurements to the side and deck line profile drawing; but, I actually transferred it to the frame profile as well.  The reason for me doing this on the frame profile will become evident later on in the build.

As we stand back and have another look at the plan, it does give rise to a lot more questions which we have to answer.  As this plan doesn’t give any indication of what materials to build the hull from or what motors to power it; we have to find these out for ourselves.   

We also have to work out what scale we want to build this model too, at the scale the model is drawn on the plan which is ½ inch to the foot; this will give us a model of some 31 inches long.  This will be a reasonably sized model, easy to handle and will be fairly light and with today’s generation of brushless motors and LiPo batteries this will give us a startling performance on the water AS LONG AS WE KEEP THE HULL FAIRLY LIGHT.

When I originally purchased this plan and built the hull a good while ago; we didn’t have the brushless motors technology or even the LiPo batteries as we have today and when I built the hull – I made it to the scale of ½ inch to the foot – I powered the model with three Rocket 400 motors; with something like 15 mm diameter propellers.  They were the largest propellers I could fit in and this model would not perform – it used to waddle round – similar to a lame duck   and to increase the size of propellers I would have to do major surgery on the propeller shaft lines.

Armed with the above information, I was looking to build this model using brushless motors.   This is when the first (shall we say) major setback hit me – but the price did!  :)  Two hundred pounds sterling is a lot of money to try and raise from the Banker  {-) when the only thing you can say is well they are very good batteries, motors and speed controllers.  The Banker then says the new bathroom suite will only cost us Three hundred pounds sterling and that is more important – so, I did lose that argument.   We are therefore back to the drawing board.

Next thought was, make it 1/12 scale – 63 inches long – 17 inches beam and it makes a nice large size model.  The only set back there was ME physically.  So I therefore scaled it down, I couldn’t have the motors I wanted; the scale I originally wanted to build it would have been too large for me to handle and I eventually scaled it down to 5/8 inch to equal one foot.   This is what the model is going to be built at – at this scale – we can comfortably manage 3 MTroniks – Vision 600 motors and also 3 NiCad packs.  This will be the power.   Also, we can comfortably accommodate 30 mm – three blade propellers on her.  This should give her a lively turn of speed  :)

That takes care of our ‘rough’ power requirements and we now must look at the material we want to use for the building of our model.

This particular shaped hull, lends itself perfectly to what is known as ‘Diagonally planked’ hull.   Ironically the original boats were double diagonally planked and in between the two planking layers there was a layer of Calico canvas.  The planking, although we could longitudinal as we did on the Cervia build, we are going to opt to diagonally plank this hull.   In actual fact, it will be double diagonally planked.   The inner layer of planking is going to be Obechi and the outer layer of planks is going to be Mahogany.

That takes care of the ‘skin’ of the vessel – but what about the framework to hold the skin.  Here we are going to use a high grade birch ply – of 1/8 inch thick for the construction of the frames; the keel & the motor mounts and several other mounting components.   This particular birch ply I purchased from a Company – you will find that it is slightly more expensive than the standard modelling birch ply because it has six veneers to make up its thickness.  This plywood is extremely strong, for its thickness, and I believe they use it a lot in model aircraft – but hey its ideal for the purpose we are going to use it for  :) so now we have outlined a good few things and we are quite happy with the plans – we can really begin to proceed with taking information from the plans and applying it to our building materials.    Since we are going to scale up these drawings to 5/8 of an inch to the foot – my first plan of attack was to photocopy the frames drawing, which I did do, and that increased the drawings to the appropriate scale i.e. it worked out that they measured about 10.5 across the widest point of the boat and this equated to 136% approximately.  This was fine, because I had to allow 1/8 inch for planking; so, I printed the frames off at this scale.   I then moved on to increase and photocopy the lines side profile.  This is where I hit the first snag.   The overall length of the hull should have worked out in the area of 39 inches or thereabouts.    47 inches was totally unacceptable and that is what they came out at.  O0 So plan B was scrapped on enlarging the side profile on the photocopier.   

Plan C was to draw out on the 1/8 plywood we were going to use, the side profile at the correct scale.   This I did; by starting off drawing a base line; to correspond with the base line on my plan; then followed by the water lines drawn parallel to the baseline at the correctly spaced intervals for the scale.

John W E:
This was followed by the vertical frame spacings drawn onto the plywood on the correct place.   I then plotted out the shape of the keel onto the lines which I had drawn.  This gave me a side profile of the hull to the correct scale.

Then the next step in the procedure was to turn back to our enlarged copy of the frame drawings; mark in the centre line between the frames and the baseline and then add our building board line which is parallel to the base line and is 1 inch above the tallest frame (I did this on the Cervia build).  This baseboard line, as we know, represents our building board.

Every frame we trace off now, we also trace this building board line; plus, two legs or 4 lines drawn down from the baseboard line, touching the deck line of the frame we are going to trace.   These lines become support tabs – and support our finished frame on the building board.     

On this particular model, we traced all the frames out first; on separate sheets of tracing paper; we then drew the opposite side of the frame onto the tracing paper – so in fact we were producing the full frame per sheet of tracing paper.  The reason for this is the frames are large (some being over 10 inches across and over 7 inches deep) and we needed to shuffle the frames around on our plywood to ensure that we could accommodate them all onto that piece of wood without being too wasteful of the plywood.   It took me several attempts and the best I could achieve was having one frame slightly cut into the top of the keel which does no harm apart from the cosmetic value of the frame.

Sometimes it is advisable to use this principle of tracing full frames out, rather than half frames – when we know we have limited materials.

Once I was happy – I began to mark out the centre areas of the frames; requiring a light hull I kept the thickness of the sides of the frames as thin as I dare possible.   In some cases the side width of the frame was just over ¼ inch wide; also, on the bottom areas of the frames, I have left slightly thicker but you will note that holes are cut in and these have several purposes.  Apart from making the frame lighter, they also give passage of cables between frames; also, if needs be the movement of water  :)  between frames HOPE NOT ;-)

Also you will see, as well I have drawn in the motor mounts; and also the servo mounting.  These are marked in, if you look closely, in the centre of the frames which will be cut out later on.   Once we are happy with all that we have drawn onto the plywood, and we have ensured that we have copied all of the frames correctly; and we are pleased we can proceed to cut the frames out.   We have mentioned this procedure before, but, for those who are reading this for the first time – I prefer and this is my personal choice – not because it’s any better or any worse I like to use a hand fretsaw to cut all my materials out with.   The other thing is, when we cut our frames, keel and motor mounts out try and cut out at least 1/16 of an inch away from the finished line.  Personally I do not try and cut the frames straight out, size for size; I try and cut the plywood /frames out into manageable chunks.   In other words, one piece of plywood which I have cut off may have two frames drawn on it.

At this stage, once we have cut the frames out we sand them to near enough the lines; leaving our line left on.  When we have cut all the parts out i.e. the frames & the keel; note at this stage I have not removed the centre of the frames yet.  This will be done after I have cut the notches for the keel fittings.   This is what I did next.  O0

John W E:
I cut out the notch for the first frame in the keel and then I cut the corresponding notch out of the frame.   When I cut the notches out; I tend to make them a ‘slack’ fit whilst working with thin plywood and when I say ‘slack’ I don’t mean a RATTLING GOOD FIT  :) aye to give you an example if we mate the two parts together – i.e. the frame and keel and then pick the keel up – the frame should just barely stop in place.   If I shook the keel, the frame would in fact drop out.

The reason I do this is when we come to do the final assembly, and we apply the glue to the joint I have had situations where, for some unknown reason either the timber has expanded with the glue or just with adding the glue, the joint becomes extremely tight – and forcing the joint in place can in fact smash the frame.  So, to overcome this, we make the joint a little bit on the slack side.

So, we have cut the joints out for the keel, and the next set of notches or joints to cut out are the ones to take the motor mounts.   These notches are parallel to the keel notch, either side.   Then, when I have cut them out, I removed the centre of the frames.   I then finish dressed with sandpaper the insides and outsides of the frames – set them to one side and now we have to work on the keel itself.

The keel has the centre prop shaft running through it, so, we must cut it into two at an angle and this is where we require our information from the side profile line drawing, to give us the position of the centre propeller shaft on the keel.

Once we have marked the propeller position out, we cut the keel and then I added ‘packing pieces to either side of the keel’ to make it the same width as the propeller shaft in other words the propeller shaft was 6mm and so either side of the keel which is roughly about 4mm thick, I added one piece of 2mm plywood either side of the keel giving a total thickness of 6mm.   I then cut another two pieces of 2mm plywood twice as long as the tapered cut through the keel; and these pieces become the cheek pieces that hold the keel together.   I have included a photograph and also, if we are unsure of exactly what it is, we did a similar thing on the plan for beginners; so this takes care of our keel assembly.   The only other thing was, where this propeller shaft cheek assembly was on the keel, bang in the centre of it is mounted a frame.   So, the notch in that frame had to be widened accordingly.   The next stage in our build we do a dry fit of all the frames to the keel, checking that they all sit in position properly and there are no frames out of alignment.

Once we are happy with this setup, we can now start marking off the notches for our chine stringers and our deck stringers.  What I do with these, is, I use a scrap piece of wood, the same size as the chine and deck stringer and use this as a template when I cut the notches out.  For reasons of not wanting to make big mistakes and drop clangers as we all do, when I cut notches out I cut all the chine stringer notches out first, checking with a scrap piece of timber the same size of the chine that the notch is cut squarely on all of the frames,   when we have finished doing that – we will then move on to the deck stringers; cutting and checking as we go.  This to me does save embarrassing situations, where we have cut all the notches out and find we have cut some of them in the wrong place and IT HAS HAPPENED TO ME  :).

At this stage, you will notice that we have not marked out the location nor cut for the stringer notches this, I personally leave, until a little bit later on in the build.  So, the next stage in the build now is to manufacture a building board.

We will use the same principle and system for the building board as we did with the Cervia build.  One piece of chipboard preferably ¾ inch thick, two or 3 inches longer than the hull we are about to build – in our case the building board will be 44 inches long.  Ideally me building board should have been about 14 inches wide; but, I could only get a piece of chipboard that was 10 inches wide, so I made use of that.

0n the reverse side of the building board, I glued and screwed two lengths of timber down the length; which were 2 inches x 1 inch x 44 inches long.   This serves the purpose of preventing the board from twisting and distorting.  As a side note; I know I used chipboard, but, I suppose if you have it you could use thick plywood or even MDF (high density chipboard).

John W E:
On the plain side of the building board we mark a line down the centre, and then this line is divided into spaces which correspond with the spacing on our keel for the frame positions.

At the frame positions, marked on the centre line, there is a right angled line drawn through at 90° to the centre line.   I then started to assemble the support blocks onto the frames ensuring that the support blocks also had a centre line on, which corresponded with the centre line of the frame.  I then began with the centre frame mounting this onto the building board.  Once I had checked that the first frame on the centre board was mounted at right angles to my centre line and also vertical – checking this using a set square/engineer’s square.   I moved on, one frame either side locating and fixing frames until I had all frames positioned and mounted onto the building board; apart from the last frame which is actually transom.  This transom is set at, I believe, at a 15° angle, the reason I believe – it’s a little while since I actually did this and I am just catching up on the writing.  :)

We now do our final check to ensure that the frames are square with one another and parallel – and when we were happy with that, the next thing is to insert the rudder servo mounting which I made from 1/8 ply and it is mounted mid-way between the 2nd and 3rd last frames from the stern.

I fitted the keel into position (with no glue – just a temporary trial fit).  When it was in place; and set home; ensuring it was sitting snuggly in all the frame notches, I laid a 3 foot steel straight edge along the side of the full length of the keel.  This was to ensure that the keel was not bent like a banana when viewed from the top – or looking from the bow down the length.

The straight edge was then lifted on top of the keel to ensure there was no hog/hump in it; when I was happy with that I removed the keel, I then repositioned it using glue.  The glue I used was EVOSTIK (water proof evo bond) and before the glue had set I re-checked the keel with the straight edge ensuring that it had not distorted.   When the glue had dried; I moved on to very carefully sand the frames to make sure that they were fair with one another.   I say very careful because anyone building a hull like this must remember that the frames are very fragile.   Where the deck stringers fit into the notches and also the chine stringers, on the first three frames in from the bow; the notches were angled with a file so that the angle faced the bow taking the sharp corner off the notch.

Next procedure was to actually fit the chine stringers; and then the deck stringers.   The deck stringers were laminated 1/3 of the way from the bow – two pieces 1/8 x 1/8 laminated together.   The last 2/3 to the stern were a solid piece of Obechi 1/8 x ¼ - the chine stringer was put in as a one piece of Obechi 1/8 x ¼ which was steamed, stuck in the spout of a boiling kettle, with me finger stuck on the switch and if there are any youngsters reading this YOU ARE NOT TO DO IT you must get a grown-up to help you.  BOILING WATER CAN KILL – if you are lucky it ‘just’ peels your skin off – SO TAKE CARE!!!

Happy with this, they were glued and clamped and then allowed to dry; and whilst these were drying, I fitted the 4 motor bearing mounts, these were made up similar to the keel; but, only in 2/3 lengths and they run parallel either side of the keel – 1 ¼ inches apart.  (Spaced roughly 1 inch from the keel).

These 4 lengths of timbers will eventually become part of the motor mounts; and supports of the batter packs and speed controllers.  I set the whole assembly aside and let the whole assembly dry overnight – not removing any clamps until the morning.

When I had removed all the clamps  I faired the frames in with fine sand paper and a sanding block – the sanding blocks were one large square lump of wood – about 12 inches long by about 1 ½ wide.   The other one was a scrap piece of waste pipe about 6 inches long and about 2 inches diameter – this is for fairing in where the hull flares at the bow.

The next stage was to add the stringers; the first four stringers to go in carry on from the front of the engine bearers to the bow and the way this was done - the stringer was laid over the top of the frames so it was in an even position and then temporarily clamped onto the frames; where the stringer touched the frames, it was marked with a pencil either side of the stringer.

When I was happy with the positioning of the stringers; and had marked the positions on the frame, I removed them and with a razor saw cut the notch out.    If you look at one of the photographs you will see how I set the depth of each notch, to stop me from cutting too far down.

Some of you may not be able to afford this expensive piece of equipment and also it is extremely difficult to get a hold of because an electrician doesn’t like giving up his electrical tape without a fight.    You guessed it a piece of electrician’s tape stuck to the side of the saw the correct depth in other words 1/8 of an inch from the tip of the teeth and when I reached the edge of the electrician’s tape that is when you know when to stop! SOMETIMES  :)

I cut inside the pencil marks, because – always remember it’s always easy to remove material, but, much more difficult to put it back in.

So, I ended up putting 4 stringers in the bottom of the hull; and 4 stringers in the sides of the hull.   Where the stringers on the hull bottom are relatively evenly spaced; the stringers on the sides are closer together towards the deck level.   The reason for this; there is a fair amount of flare at the bow and with the aid of the stringers it makes bending the planks into the flare a lot easier.

Now we have all the stringers fitted, we must once again give a gentle light sand to remove all the high spots on the frames and stringers.

Last but not least either side of the main keel; there are supporting timbers.   The reason this is put in, is to give extra width to the keel for the planks to be glued too.  These two pieces of timber, which go from bow to stern, are yet again made up of 1/8 x ¼ Obechi timber clamped and glued – slightly proud of the bottom of the keel (so the reason for this is when you sand – and on your final sand – you sand this level with the keel and it will also be at an angle with the frames).    If you imagine the apex of a roof of a house – the top ridge tiles – and that will give an idea of what the shape should be like.


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