Masterclasses > VOSPER MOTOR TORPEDO BOAT BUILD

An in-depth build of a GLYNN GUEST plan, for the beginner

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John W E:
VOSPER MTB
An in-depth build of a GLYNN GUEST plan, for the beginner  
The June 2011 issue of MODEL BOATS magazine has with it a free plan and the build article to construct a semi scale VOSPER MOTOR TORPEDO BOAT from which a modeller with average skill should be able to produce a good working model, but to a person who is new to the hobby of model boats and its many ways of doing things, making this model from the free plans may seem a daunting task to undertake.  However, with the MODEL BOATS magazine build article and a build with a few more illustrations it may be possible for the new modeller to understand and undertake the making of this model with fewer mistakes.
As a side note Glynn Guest’s article in MODEL BOATS would be a larger piece of writing to cover all modelling skills    but as you know in magazine space is of an essence.
On with the build.
The first job at hand is to study the plan both sides and to read the build article so that one gets an idea of how the pieces fit together (fig1-2).
The first step is to transfer the required shapes from the plan to the building material.  This can be achieved by various methods - one way is to have the full plan copied - then to cut the required pieces out from the copied plan after that glue the cut out profiles to the building material.
The second method is to trace the shapes from the plan onto either the building material or onto thin cardboard, by tracing the shapes onto cardboard to make templates allows the shape to be duplicated very precisely and this was the my chosen method for this build.  
Materials
All hardware and wood for this build have been obtained from either the web or a local model shop nothing was custom made for the model by a specialist supplier      

John W E:
Medium grade balsa wood is used to build the hull, so what is medium grade balsa?
As a rough guide place your thumb nail across the grain of the balsa wood then try pressing your nail in to the wood and if your nail sinks in easily making a deep indent, we can take it that this is soft balsa.   If your nail is hard to push into the wood and just leaves a small indentation this could be classed as medium balsa.   If there is very little or even no indentation this can be classed as hard balsa
5 sheets of medium grade balsa 900mm x100mm x6mm where obtained for the Maine frame of the hull and 5 sheets of 4mm x 480mm x 100mm for the outer skin
Tools for the job
A good sturdy craft knife is ideal for the job of cutting out as long as it has a sharp blade
Fine tooth razor saw is a good help for cutting some of the pieces out
A 12 “steel ruler is a must-have to aid in cutting out
Homemade sanding blocks of various shapes and sizes.  
For the first part  of the build the two most used sanding blocks where made from ½ ply wood 6” long x 4” wide with medium grade sand paper stuck on with double sided tape on one block the other has fine grade sand paper stuck on to it.    
A good handful of modelling pins or dressmaking pins about 100 will be ample plus a good handful of elastic bands to hold pieces in place whilst the glue dries.
Small set-square or better still an engineer’s small tri-square.
All parts for the hull framework were transferred from the plan onto the 6mm balsa with the use of cardboard templates (tip! Use a ball point pen not a felt tipped pen as the ink from the felt tipped pen will run into the grain of the wood.  Do not press too firmly with the pen when drawing the shapes out) before cutting any pieces double check all the parts are correct (figs 4-5-6).
The main deck pieces are the first to be cut out 2off port and starboard, remember don’t try and cut all the way through in one go, 2 to 3 shallow cuts to slice all the way through, and also cut on the good side of the marked line, start at about the middle and cut towards the bow - then from the middle cut to the stern.  When cutting towards the stern use a steel straight edge as a guide to run the knife blade along to keep the cut straight and square fig 7- fig 8.
When all the parts for the hull frame have been cut out, it is best to check them against the main plan to ensure they are all the right shape and size: note the slot for the prop tube and the main deck hatch have not been cut out at this stage.
The next step is to lightly sand the two edges of the main deck the chine floor pieces.  To do this the two matching pieces must be pinned/clamped together side-by-side.  The edges need to be sanded evenly.  Doing it this way will ensure that both sides are exactly the same in profile (fig 9.)
When both main deck and chine floor have been sanded, the next stage is to join the two halves of main deck together.
Glue
The modeller has a vast choice of glues to choose from but for this build the four mostly used types of glue are:
i)       ALIPHATIC this glue was used for all the wood work.   This glue is very similar to the white PVA glue but is slightly stronger when glue has set dry, has a higher resistance to water, and is normally yellow in colour.
ii)    EPOXY RESIN GLUE
This is used to bond the prop shaft and the rudder tube in place.  There are several types and makes of epoxy resin glue.  However, we need one that sets in about 30 minutes or slightly longer to give us time to adjust the fittings if needs be, most come in a two part equal mix (resin and hardener).  Care must be taken when using epoxy glues as they can cause an allergic reaction to some people.

John W E:
more pics

John W E:
iii)    CYANOACRYLATE OR SUPER GLUE
Yet again there are many makes and types of this glue but experience has shown the ones that are sold in model shops for the modeller work the best for us    
In this build super glue is used to bond different materials, such as plastic to wood and cardboard also your fingers to the model SO BE VEARY CARFULL WHEN USING THIS GLUE IT WILL BOND YOUR SIKN IN SECONDS AND THE FUMES CAN IRRITATE THE EYES PLUS HARMFUL WHEN INHALED SO DO BE WARNED ABOUT THIS HEALTH HAZARD
iv)   LIQUID POLY
This glue is used to bond plastic parts of the build such as the gun bandstand.
Once again lots of companies produce this type of glue, but I have found that the HUMBROL one works the best for me on styrene card.
Let’s get back to the building of the model    
The two halves of the main deck were laid on a flat surface and lined up, a strip of cellotape is applied along the length of the joint from bow to stern - this is so it forms a hinge joint in the two halves of the deck.  The deck is then hinged open and glue applied to the two mating faces.  The hinged joint is now closed and the excess glue is squeezed out.  This also pulls the two halves of the deck together and the deck is then placed on a flat surface (extra cellotape may need to be applied across the deck to help prevent the deck from pulling open).
It would be advisable to place something such as a piece of polythene/grease proofed paper or similar on your working surface to prevent the deck from being stuck to the surface.
Weights are then applied on the top to keep the deck flat whilst the glue dries.
The same method as above is used to glue the chine floor together - they are then set aside until the glue has fully dried (fig. 10)  
As the glue is drying we can move on and begin to assemble the keel and appropriate pieces.  
As the keel was cut out in one piece we require the hole for the prop tube to be put in and this is first done by offering the keel to the plan and very carefully marking off the position of the prop tube angle plus the positions of the supporting cheeks either side of the keel.  When this has been done we can cut the main keel where the prop tube goes through. (fig.11)  before reassembling the keel with the side cheeks it may be best to make a strong back-up for the supporting of the keel and this will also keep the keel level whilst it’s being glued.  The strong back was made from a square bit of timber approx 6 inches long and about an inch square and is covered completely with cellotape to prevent the keel from sticking to it. The keel is then glued and assembled then clamped onto the strong back (fig.12) ensure that the keel is the right length and also the hole for the prop tube is the right size before the glue has set.  
Assembly of the keel to the chine floor
First a light sanding to remove all overspill of glue on the keel and the chine floor and then mark out the location for the hole in the chine floor for the motor.  We first draw a centre line down the middle of the chine floor using the stern as a datum - we can work out various lengths along the boat.  After cutting out the hole for the motor in the chine floor we next have to locate and glue the keel into place along with the bottom tapered ribs, (use a small setsquare to keep the ribs square with the floor and  keel ) (fig 13)  

John W E:
MOTOR, PROP TUBE, AND COUPLIING  
When selecting the prop tube for the model a standard M4 X 228mm propeller tube with bronze bush bearings was chosen along with a standard DYCO coupling - these are ‘off the shelf’ from the local model shop.  When trying to obtain a solid coupling as referred to in the model boats build article, the ones that were available needed to be altered to fit the prop shaft.  Whilst this is not a difficult task, it was felt to be outside the build for beginners expertise parameters for this particular model build (all materials to be standard and off the average model shop shelf).
The prop tube size refers to the length of the tube but it will be noted that the shaft is longer (approx 267mm in length)  it will have a 4 mm thread on one end of the shaft the other will be plain.  The propeller fits on the threaded end of the shaft with a lock nut and washer to secure the prop on.  
The plain end of shaft is where the coupling is located.
The DYCO coupling is in three parts; two brass inserts and a flexible plastic centre body - one brass insert will need the 4 mm hole in it to match the prop shaft diameter and the other brass insert will match the motor shaft 3.2 mm.  You will also need a small Alan key to fit the locking grub screws in the inserts.
MOTOR
The motor in this build came from the spare box on my work bench and at the time I thought was about the right RPM (17000) for this model but it was discovered to be of a lot lower RPM so a Graupner speed 500 has been ordered to replace it.  The new motor has a RPM of 17600 which will be ample.  
Back to the build
To work out the motor angle, we need to temporarily fit the prop tube in to the keel at the correct position and angle.  You may have to open up the hole in the keel with a round file a little but do not make the fit of the tube too slack - a nice push fit is what we want.  Next we have to make an alignment jig to help with setting up the motor, the easiest method is to temporarily remove the plastic insert from the coupling and replace it with a neat fitting piece of solid tube of the same length as the plastic insert.  This when fitted between the motor and shaft will hold the motor rigid and at the same angle as the prop shaft.  At this stage you will see the motor mount is different in this build compared to the one in the MODEL BOATS article. Again this was done NOT as a better way of fitting the motor but to keep it in the parameters of off the shelf build for the beginner.  A standard motor mount supplied with the motor is used but this time the motor is mounted upside down.  The motor was held in place with the use of a small piece of bluetack placed between the top of the keel and motor. The motor mount was squared up and the angle of the mount marked onto two pieces of cardboard - this was then cut out to make templates.  These were offered up next to the motor to ensure that the angle is right, when happy ¼ plywood was used to make the two mount supports, ¼ square Obechi is then glued to the inside of the top angled edge of the ply wood.  This is then glued to the chine floor in the right place (figs14-18) at this stage you may wish to follow the MODEL BOATS article and glue the prop tube in place, but for ease of skinning the hull and sanding, I removed the prop tube and motor until later in the build.
The next step is to fit and glue the transom in place, use a set square to help keep the transom square and vertical to the chine floor (fig.19) when the glue has dried move on to fit the forward bulkhead and stem post (fig. 20) move onto the next stage of fitting the deck only when the glue has fully dried on the last two stages.  Apply a small bead of glue to the top edge the transom and the forward bulkhead plus stem post and with the deck sitting on a flat sturdy surface, line the edge of the transom up with the top inner edge of the stern of the deck.  At this stage ensure the stem post lines up with the centre of the bow on the underside of the deck - when the two parts are correctly aligned, temporarily pin and apply some weights on top to hold the structure in place until the glue has set  (fig. 21).  At this stage it was found there was a slight flex in the deck,  so two additional supports were added to hold up the deck (arrow is pointing at them in photo).  As the model is built out of mainly balsawood and if untreated balsawood comes into contact with water - it is a bit like a sponge - it soaks the water up and expands splitting joints and so forth, so it is best to seal all the areas with sand and sealer now as we cannot access these parts of the hull when it is skinned, a total of 3 coats were applied to the bottom of the chine floor and underside of the deck.
The step on the main deck is next to be constructed and this is made from 4 pieces of 6mm balsawood, the shape and size is transferred from the plan onto the material and then cut out - but it is left 2mm oversize on the outside edge do not cut out the torpedo scallops at this stage these 4 pieces are glued and pinned into place at the bow (fig. 22).  If you have the use of a small set of clamps it will be helpful.  When all the glue has dried recheck all joints for any gaps or splits and if there are any fill them in with glue.  
Next we have to sand the angles on the edges of the main deck and the chine to match that of the stern and the mid bulkhead, this is achieved with the use of a long sanding block, sand a little bit at a time and check often with a straight edge along the hull and across the sides to ensure that you are not sanding hollows into the hull sides.

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