Edinburgh Model Boat Club Page

Beginners Boat Building Part 1 - Balsa Sheet Construction and Stand-off Scale

Basic advice and guidance for the absolute beginner who wants to build a boat but doesn’t know where to start or how to do it.

More advanced hints and tips can be obtained from various model building articles in Model Boats Magazine and in Marine Modelling magazine although these are usually directed at construction of specific models.

Sample plans are available (view only) at the tutorial and information on purchase etc. is provided.

There will be more Tutorials in the Beginners series :

Plank on Frame Hulls; Making your own Boat Fittings; Beginners Box Kit Building; Beginners Yacht Building

Watch the Club Notice Board, the Web Site or read your Club Newsletters for more information. A copy of all Tutorial Notes are available for reference in the EM- BC Boat Compendium kept in the Club House.

Iain Moffatt - Beginners Boat Building Tutorial Edinburgh Model Boat Club Page 1 And in the Beginning ......

Like most things in life, the IDEA is all powerful !! Unfortunately, for most people, the idea is an image of the finished object be it a boat, plane or whatever. This inevitably leads to initial disappointment when you find out how many decisions must be made and how much work must be done to realise the idea.

Many people have houses and garages full of unfinished projects (mine is not quite full yet!!) largely as a result of waning interest when a problem appears that cannot readily be solved.

So my message to you all is ...... PLAN AHEAD In model boat terms this means that a number of key decisions must be made BEFORE anything is bought. 1 What kind of boat do you want ?

2 What are your manual skills like ...... good, excellent, non-existent, don’t know yet?

3 How long are you prepared to spend building it ?

4 How much money are you prepared to spend on it ? Remember ... motors, props, batteries, speed controllers, radio control all adds to the cost of basic materials.

5Are you elderly or disabled? If so you should consider the size and weight of the model you want to build. Remember, it has to be launched and recovered (and carried in a car).

6 The next thing to be considered is the issue of detail. Are your manual skills, eyesight and patience up to dealing with fine detail? If so ...... good for you ! If not ...... consider a ‘stand-off’ scale boat that stands up without too much detail but which can be enhanced if you feel up to it. Remember also that detail costs money - even more if you have to buy it. Fittings kits are very often more than 3 times the cost of the hull & plans. Making fittings yourself is very cost effective but ......

7 Where are you going to build it ? If you have a workshop or garage in which to do the construction, then construction methods can be less of an issue. If however you have to work in the house and move (or tidy away) before meals etc. you don’t want anything that has a multitude of parts and that needs a complex build strategy ...... keeping it all safe and sound during many moves is not so easy!!

Some advice on hull construction to help with the decisions: 1 Stand off scale boats, depending on the size, can be built from balsa sheet wood that is relatively cheap to buy and easy to work with. Also produces a ‘light’ boat and, if constructed correctly, one that is strong and long lasting. Witness a balsa Leander class frigate built in 1975 that is still looking good and sailing to-day. Generally strength considerations limit these to a maximum of about 36” LOA. Light plywood + balsa can easily go up to around 60” LOA with correct construction.

2 Plastic Sheet (Slaters Plasticard for example) is great stuff to work with but the size of sheet produced (12” x 12”) tends to cramp the style where larger hulls are concerned and, although capable of giving an excellent finish, can be very expensive. Always use solvent weld techniques for gluing. Always provide adequate stiffening - sheet is not stiff in its own right. Plasticard is ideally suited to the construction of boat superstructures and detail.

3ABS (moulded plastic) hulls are relatively cheap but require a fair degree of internal stiffening (bulkheads etc) and can be difficult to ‘stick’ to.

4 GRP (glass reinforced plastic) hulls are more expensive but much stronger. Working with the hulls can be messy (lots of glass fibre dust if you have any sanding or cutting to do). You must be very careful not to inhale such dust - wear a mask .. cost pennies. Always use Araldite (epoxy) type adhesives. Car body fillers and repair tape can be used.

5 Plank & Frame or Sheet & Frame hulls can be immensely strong if well built and there is no practical limit to their size. Building requires great attention to the alignment of the hull framing components and sequential application of planks or sheet plates to prevent warping of the whole structure. The resulting hull is very light but very strong. Waterproof adhesives MUST be used throughout. Plank on Frame can produce a wonderful result but takes a LOT of care and patience even though its basically a simple technique. It can also deal with compound curves (round the stern section below the waterline for example).

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Sheet on Frame will NOT do compound curves easily but works well for the straight sections in the centre half of a hull for example.

6 Bread & Butter Hull construction. Now a days this type of construction is very costly, given the price of reasonably stable, straight and knot free timber. However if you have a ready source of off cuts of old oak or pine floor boards (the thick variety!) ...... Hulls are built of many horizontal layers of pre-cut wood glued together (bit like a sliced loaf on end!). The outer and inner surfaces are hand or power dressed to give the finished hull profile. Hulls are generally heavy. Finish is entirely down to hard work and elbow grease plus lots of filling and preparation. Some beautiful results have been produced however, witness most of the ship models in museums.

Summary of Bread & Butter Construction

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Illustration is for a small yacht hull built from balsa sheet. However the principle is identical no matter what the hull form or what wood is used.

It is essential that a completely waterproof glue be used. Furthermore effective sealing of both the in- side and outside surfaces of the hull is es- sential after carving has been completed.

Iain Moffatt - Beginners Boat Building Tutorial Edinburgh Model Boat Club Page 4 About Balsawood The most remarkable thing about balsa is its light weight - less than 1/3rd of the weight of other woods. It is also re- markably strong for its weight. It is soft, with a marked grain that is not very visible. The strength of balsa is directly proportional to its density. For example 18 lb balsa would be 3 times as strong as 6 lb balsa. It would also be 3 times as hard to cut. The stiffness of balsa is governed by the ‘cut’. Quarter grain sheet with a speckled appearance is stiff and rigid and cannot be bent either end to end or edge to edge without danger of splitting. Normal sheet with a plain grain appearance may have varying degrees of ‘bendability’.

Basic Grading Density (lb/cu ft) Fine Grading Where balsa has to be as strong as possible, a hard grade should be 4 - 6 ultralight chosen - for example flat hull 6 - 8 light sheeting. Soft 8 - 10 light to medium For curved hull sections use a Medium grade. Medium 10 - 12 medium 12 - 14 medium hard to hard hard 14 - 16 hard to extra hard

Where to Start ?

Assuming that you have decided on the boat you want to build, the first step must always be to get a set of plans. The plans will normally be drawn taking account of a particular construction technique (sheet, plank on frame etc.). For a beginner it is therefore important to select a plan set to match your planned construction method.

It is relatively easy to convert a set of lines plans to sheet construction, but, for an absolute beginner, this may be a bit too much to undertake for a first build.

Bow

Transome

Waterline

Forefoot

1 2 3 4

Drawings for simple sheet type hulls will normally contain hull outlines both plan and cross sectional views together with outlines of transverse bulkheads at positions along the hull length. These positions are called ‘frame’ positions. There will normally be at least 2 positions and therefore 2 bulkhead outlines plus the transom.

Material sizes (including thicknesses) are also normally shown. For example, a ‘standard’ length of balsa would be 36” x 4”. For the bottom it would have to be 1/2” thick. The transom would normally also be 1/2” thick. The deck may be of 1/4” thickness and would require the use of longitudinal stringers to add rigidity. The stringers would normally be strip hard wood. If the deck is also 1/2” thick, stringers can be dispensed with. Hull side sheeting will usually be 1/8” (3mm) and when you cut, remember the grain MUST run vertically. Balsa Sheet is normally available in the following widths :- 3”; 4”; 6” and in either 36” or 48” lengths. Thicknesses range from 1/16” up to 1/2” in 1/16” increments. Block balsa can be obtained in sizes up to 4” x 4”.

Balsa is naturally porous (likee sponge) so it MUST be well sealed (inside and outside) before painting. NEVER seal an area that has to be glued later!! Glues do not take kindly to sealers. The best sealer is Sanding Sealer although Fuel Proofer coatings can be used (a high tech balsa sealer resistant to IC fuels). Several coats of sealer are generally required with light rubbing down between coats. The sealer tends to raise ‘nibs’ in the wood and if these are not sanded off, a very poor finish will result.

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Drawings for plank on frame construction are rather more complex. They show the ‘proper’ outline of the hull (curves rather than straight lines) and generally have many more frame stations. They also show the hull cross section at each frame station. The whole is normally called a Lines Plan.

If the drawings have been reproduced from full size drawings, it may be that there are no frame sections shown in which case a bit of drafting work will be necessary to produce the cross sections from the plan and elevation lines. I will not deal with this aspect here ...... if you are interested, watch for the next tutorial (and subsequent ones).

Bow

Transome

Waterline

Forefoot

1 2 3 4 5 6 7 8 9 10 11 12 13

13 10 1 4

Some Basic Terminology.

In full size terminology, LOL (length on waterline) is, as it says, measured on the waterline; Likewise LOA (length overall) is measured between perpendiculars dropped from the extreme stem point and the extreme stern point; Beam is the width of the hull; Draft is the depth below water's surface of the lowest part of a ship or boat; Draft can also mean the degree of curvature in a horizontal cross-section of a yacht hull; Sheer is the degree of curvature of the deck along its length as compared to the load water line; The transverse (port to starboard) curvature of a deck is known as the ‘camber’. Flare is the degree of curvature of the hull side plating at the bow and hence the rake of the stem post. Stem - the Bow or front end; Stern - the aft or after (back) end; transom - a flat back end; Port - the left looking forward; Starboard - the right looking forward; Bulkheads running fore and aft are called Longitudinal Bulkheads. Those running from side to side (port to starboard) are called Transverse Bulkheads. Transverse ‘beams’ are used to support the deck and are attached to the hull frames using ‘knees’ (triangular brackets fixed to the deck beam and to the frame). Beams running fore and aft and joined to each bulkhead are known as ‘stringers’ and are used to stiffen the hull shell plate and add rigidity to the frame and keel structure. The ‘keel’ is a very strong and rigid beam running the full length of a hull to which frames are attached at their lower ends. A Strake is the term used to describe a horizontal set of hull side plating. The dimension of any plate in a strake is normally limited by the ability of machinery to shape it. The first row of plank or hull plate either side of the keel is known as the ‘Garboard Strake’. The last row of plank or hull plate below the upper deck is known as the ‘Sheerstrake’. The extension of the hull upwards above the deck is known as the ‘Bulwark’. The inward slope on the sheerstrake and bulwark is known as the ‘tumblehome’. Navigation light colours - Port = RED (port is never left on the wardroom table) and Starboard = GREEN

Rubbing Strake Sharp transitions between sections of hull plating are known as Hard Chine Hull ‘chines’. These are normally encountered in small fast boats (PT boats etc.) and the hulls of such craft are termed ‘hard chine’ hulls or in TID Tug hulls manufactured from plate bent in one plane only. Chine Strips Re-enforcement of the join uses ‘chine strips’ or stringers notched into the frames.

Iain Moffatt - Beginners Boat Building Tutorial Edinburgh Model Boat Club Page 6 Glues to use

1 Balsa cement gives good, waterproof joins and sets quickly. However it can be expensive (lotsa wee tubes at £3.60 each) and the rapid hardening reduces the time you have for alignment etc.. My preference for fittings & small structures. Sands easily.

2 Water Resistant PVA adhesives, although not water proof, produce more than adequate results, provided the model surfaces and properly sealed and painted before immersion and provided any in-service damage is promptly dealt with. It is cheaper. It also takes longer to set and so allows for alignment. My preference for hulls and large structures (not Tugs!) that can be sealed and painted both inside and outside. Sands easily.

3 Epoxy Resin Adhesives - in the 5 and 20 minute variety is my preferred adhesive for strength joints like bulkheads, keels and Tug superstructures where the tow hook is attached to the structure. However it does NOT sand easily so you need to use only as much epoxy as can be trapped within the joint.

4 Cascamite - water proof, water based urea-formaldehyde adhesive. My preference for all boat gluing where slow drying is not a problem and joints are tight (I.e. no gaps) and where clamping is possible. NOTE : Never over tighten a clamp on a glued joint - you simply force all the glue out of the joint thereby weakening it. Clamping should be aimed at maintaining the position of the parts. Tools you will need ......

You don’t need many, and it is worth while spending money to get good ones that will last. The unit prices and numbers quoted below are from the Squires catalogue (PLEASE check as my prices may be out of date) 1 12” Steel Rule (NOT plastic - cause its no good for cutting along) 2 12” flexible steel rule for measuring curved surfaces (very useful) £2.95 040-014 3 Engineers adjustable combination square £7.95 160-422 4 Coping Saw frame plus fine blades plus £5.95 SA0094 5 V-Block & clamp to use in conjunction with the coping saw (you can make one up if you want) £4.95 VBC366 6 A Zona Razor Saw (32 tpi & cutting depth 30mm) £6.95 ZON500 7 1 fine 12” hacksaw blade and if you feel flush a handle 8 A craft knife (I use Swann-Morton No.3) with straight blades (No. 11 and No. 16) £2.95 + £0.60) SMH003 9 A heavy duty craft knife for bigger cutting jobs (replaceable blades) £1.00 about 10 Set of Compasses £2.00 about 11 A pair of Jenny-aw-things (if you can afford them) 12 Assorted spring clamps (around 10 if you are building a large hull) pack of 6 £2.95 CL340 13 A couple of needle nosed spring clamps (for longer reach) £0.75 CL356 14 A miniature 12” sash clamp for joining wide pieces edge to edge £2.95 CL0030 15 A 3 jaw pin vice to hold small drills (up to 3mm capacity) £7.95 PC0030 16 An 8” long quarter inch round file (making prop shaft holes) £3.95 160-024 17 Packet of construction pins (NOT the ones with small plastic heads - heads can come off) 18 4 or five right angle jig plates (2” wide sections of 2” x 2” ally angle bar) 19 A building board - 3 or 4 foot long by 10” wide by 1” thick offcut of MDF. (stable, flat & dosen’t warp or bend)

Obviously how many of these things you buy is up to you as are any substitutions you may want to make. However, remember that the right tool does make things easier and building should not be a chore. As you become more experienced you will doubtless come across many other tools and gadgets that you simply can’t live without! (I know ...... I have a garage full of the things, a lot of which I have used once in the dim and distant past. Ne’er mind .. I’ve got one if I could only find it !!)

4 8 14 9

5 15 6 3 12 11

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Construction Pins

On the right shows a building board with jig fittings for building a keeled boat. This one happens to be a plank on frame construction, but the same method can be used for a sheeted hull. The jig clamps (marked 1, 2, 3 etc) hold the frames (or bulkheads) both perpendicular to the board and at right angles to the length of the keel. Provided that the frames or bulkheads are cut over height, the whole hull except the deck can be built without re- moving the assembly from the board. The surplus material is then trimmed off before decking is fitted.

This picture is courtesy of Alan Johnston and is part of a full set of construction photographs for the steam launch ‘Branksome’, that have been posted on the Web site.

Sheet Construction

In the majority of sheet hulls there are common sets of components cut from sheet balsa. A typical set of these is shown below.

Hull Bottom

Make sure grain runs this way

Bottom notched, bent upwards and glued

B 3 Transom B1L B1R B2

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When notching the bottom sheet, try not to cut all the way through. TIP : Take a very fine hacksaw blade and wrap 6 turns of electrical insulating tape around each end. Cut the groove until the tape sections rub on the cutting surface. Cut the Vee groove from the upper side of the bottom sheet. If you are fitting a Keel use it as a template for getting the angle right otherwise you will have to pin a piece of scrap balsa to the transom edge to keep the angle whilst the glue sets. Use araldite type glue for this joint.

When fixing bulkheads, always use a building jig to keep everything at right angles. (see next page)

If the beam is greater than 4” (100mm) you will need to make the bottom in two parts, glued along the longitudinal centre line.

NOTE: If you are using a balsa deck of the same thickness as the bottom (½” or 12mm say) you can miss out the longitudinal stringers and fix hull side sheeting directly to bottom and deck edges.

If you use a thinner deck then you will need these stringers to support the side sheet to deck join. Make sure that the bulkhead notches are no bigger than required to accommodate the longitudinal stringers . The strength of the boat hull depends on how well you build this whole structure.

Transferring outlines to the bit of wood ..

No matter what ...... have a copy made of your drawing BEFORE you start.

A rather neat way of doing this, for anything smaller than an A4 sheet of paper (or A3 if your copy shop can do it) is to have a photocopy made of the section of the drawing. Take the photocopy and place it on the wood in the correct position. Using a domestic iron on the hot setting (but not on the steam setting!!) press over the outline. This will melt the toner and transfer it to the wood. Clearly the smoother the wood, the better the effect. Also try to do the transfer within an hour of having the copy made (the sooner the better) otherwise the toner will have ‘cured’ so to speak.

Failing this, carbon paper and draw over the outline or you can use tracing paper (local Smiths or art shop can provide). If none of these grab you ..... try a fine point biro (NOT a gell pen) and poke through points on the line with the plan lying on the wood. Then join up the dots.

Of course, you could simply measure off the drawing ......

Sequence of Building

1 Mark out and cut the components and clearly draw in the centre lines; 2 On the bottom, mark out the position of the bulkheads on the bottom making sure that the position lines are at right angles to the centre line; 3 Check fit bulkhead slots on the keel and mark position lines for bulkheads on the keel; 4 Notch the bottom, bend it up to correct angle to fit the transom depth, glue it and clamp it until glue dries; 5 Clamp a jig block to the bottom in line with the longitudinal bulkhead position; 6 Fit the longitudinal bulkhead (LB1) in line with marks with glue on lower edge, holding vertical using clamps until glue has dried; 7 Fix the second transverse bulkhead (B2) to the rear face of LB1 and hold with construction pins until glue has dried; 8 Move the jig block to the position for B3 and clamp it; 9 Fix B3, holding it in place with construction pins until the glue has dried; 10 Mark out and cut the deck together with any openings; 11 Check fit the deck to the bottom/bulkhead assembly; 12 Fix the transom (B4) gluing it to both deck & bottom; you will have to chamfer the transom edge of the bottom to the correct profile before fixing;

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You should now have a construction that looks like this :

The next step is to dryfit the motor/propshaft assembly. You MUST do this before any sheeting is applied to the sides - you won’t have ac- cess otherwise.

So get out the propshaft, loosely fit the prop and offer it up to the hull so that the prop clears the hull bottom and is clear of where the rudder will lie.

Drive Train & Rudder Setup

Make up a solid coupling Measure distances between motor block to hold motor and casing/mounting bracket and the bottom. shaft perfectly in line. These will be used to make up a base block

Motor

With the hull frame on its side, lay the motor/prop shaft assembly on the edge and position it so that the prop clears the hull bottom by at least 5mm. Mark position lines on the frame edges. Do the same with the rudder tube.

Section of 2" x 2" A simple angle jig made up from scrap offcuts aluminium angle. of 2 x 2 ally angle. I use a couple of cast lead weights to hold it down and either cheap plastic clamps or clothes pegs to hold the component to be glued.

Glued join You could use a tin of something from the kitchen cupboard, but they generally tend to be Cast Lead weight rather large. approx 1.5 lb File a bevel on this edge Position the jig at the edge of the work to avoid to clear any glue overspill from the joint. the need for deep clamps.

When making up the rigid coupling, make sure it is sized to match the length of the flex. coupling that will eventually replace it. If you don’t do this, then the sizes for the motor mounting block will be incorrect.

TIP :...... Any misalignment between the motor shaft and the prop shaft will give a noisy drive train and, since in mechanics, noise equals power loss, you’ll get a higher current drain from the battery. It is well worth spending time on the issue of alignment.

TIP : ...... Keep the motor as low down as possible in the hull. The ideal is to have the prop shaft parallel to the boats waterline. Raising the motor creates a downward thrust on the boats bow and a considerable reduction in propulsion efficiency. Fast electrics use external flex. couplings or flexible drive shafts to achieve this.

When you have the line up markings done, extend the line across the bottom until it crosses the centre line. This is where you will pierce the bottom for the prop shaft tube. Also extend the line on the rear face of B3 until it crosses the centre line, giving the position of the second hole. Always start small when doing this work !! On balsa, I use a sharpened bicycle spoke held in a pin vice (spokes are hard and rigid). Gradually open out the holes using round files, continually checking alignment. Do not use drills for this - they have a tendency to produce oval, oversized holes in soft wood when used by hand.

It really is worth spending time on this ...... I’ve seen many a boat that turned in circles with the rudder amidships simply because the prop tube had been badly placed, and not in line with the hull centreline.

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Sheeting the Hull

Before sheeting can begin, you will have to sand the deck and bottom edges as shown below.

Grain running vertically Sanding line means sheet can be bent round curves

Bulkhead

Use sanding block to eck dress off edges D of deck and bottom plank until they are flush with side (as on right) g in nin run in ion Gra ect dir this 12" ttom Bo

Glue HERE

HULL SHEETING Make up a sanding stick around 1 1/2" (35mm) wide and glue a strip of medium grade glass paper to one side and another of fine Direction of grain at bow flare. grade on the other side.

TIP : When you cut the side sheeting, always cut it around 3mm too deep. This gives a little allowance to ensure that the vertical edges of each sheet form a close fit with the one before. (see above)

Watch for depths when sheeting at the bow and stern ... the hull curves will mean that the side sheet is not a true rectangle!! Best to dryfit sheet, mark deck and bot- tom lines and then cut. The flare in the bow section can be dealt with by inclining the grain in a forward direction

TIP : When cutting balsa (or any wood) always cut with the grain NOT against it. All woods, particularly balsa, will split easily along the line of the grain.

Super-structures

Since most sheet based hulls are stand-off (I.e. viewed from a distance) great amounts of detail are un-necessary. However it pays to identify the key features of any boat and attempt to replicate them thus lending a sense of reality.

Superstructures can generally be made ‘box like’ and, where possible, should be made in one piece and removable. To accomodate this, any deck openings need to be fitted with a ‘coaming’, the overall dimensions being such that the superstructure slips easily over the coaming. The coaming should be made of thin ply or hardwood strip and not balsa, which is too soft and likely to ‘chip’. Make the coaming as deep as possible - this helps to retain the superstructure in windy conditions and when putting the boat in the water. Many a superstructure has happily bobbed away on the pond to the horror of its owner!!

DO not skimp on the quality of finish. Despite the lack of detail, a poor finish sticks out like a sore thumb and completely destroys the overall effect.

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Tips on Structures:

Keepum LIGHT and keepum STRONG !! Reinforce corner joints. Whats underneath can’t be seen so don’t skimp but watch for coamings. If building a tug with tow hook attached to the superstructure - make sure to provide a means of ‘bolting down’ the structure and make sure it is sufficiently strong!!

fig. 1 fig. 3 fig. 2

fig. 4

fig. 5

If making ‘curvy’ deck houses (figs. 1& 2), use thin (0.5mm) ply with grain running along the curve. If it needs to be thicker, add a second layer, sticking it down with PUR or EvoStick. For curvies, always leave surplus material on edges and when dry, trim to shape. You can spot glue to hold things in place using thick Cyano.. Fig, 4 & 5 - strong tug structure, with 4 internal bulkheads of 1/4” ply. All joints re-inforced. Side panels are cut in one piece from 3mm ply.

STEP 1 - Mark out and cut one side of the Always fit the bottom edge of superstructure, leaving surplus material on Superstructure the superstructure to the deck what will be the curved side. curves before finally cutting the upper profile. Cut the ply to the Trim off this bit Trim off this bit correct length and mark deck line (left). Mark heights and cut the profile. Curved deck line STEP 2 - Set a pair of compasses to equal the largest gap. Always build structure to match Draw a line parallel to the deck.. deck opening !! It’ll be OK pro- STEP 3 - Use the side of the superstructure to This is your cutting line. mark out two pieces of 2mm ply forthe fore vided you cut the opening the and aft coamings. right size ... ah hum .. erewell

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I prefer to use strip hardwood for hatch coamings, usually a min. of When building the structure remember that the internal bulkheads need to be notched at their ends to avoid 3mm and glue with araldite. fouling the coaming. Why? Well any deck opening is a source of weakness and can easily lead to warping of the deck unless the edges are reinforced by a coaming. Openings are often used to lift a boat out of the water etc. so they need to be strengthened. Last but not least, a coaming keeps water out of the hull and locates the structures. Coamings are therefore important !! Structure should be a close fit on the coaming.

Rudders & Steering Linkages Coaming

Rudders only work when there is a flow of water past them. So if a rudder is in line with the boat prop, the rudder can be used to turn the boat with little or no forward movement. If the rudder is NOT in line with the prop, you will only get steering when the boat itself is moving forwards .. the higher the speed the greater the turning effect of the rudder.

Why is this important ? Stand-off scale models nearly always have a single screw regardless of how many the prototype has. So, in a twin screw full size boat, there will normally be at least two rudders. Likewise 3 screw .. 3 rudders. If you decide to fit the ‘correct’ number of rudders your model will not steer well at all. So my advise is - single screw = single rudder.

Rudders develop maximum turning effect when rotated 35 degrees either side of centre. Any more rotation simply slows down the boat thereby reducing the turning effect.

This is what 35 degrees looks like The turning effect of a rudder blade is propor- on a standard rudder. 35 degrees on a balanced rudder tional to both the speed and the blade area. gives around about 30% more In models, high speed craft like PT boats and turning effect fast electrics have small blade areas whereas

3 tugs have large areas. On a fast boat, too large 50 2/3rds an area can make the craft uncontrollable and in extreme cases can cause it to overturn (flip 1/2 over) in a tight turn at high speed. 1/3rd Balanced rudders give more turning effort sim- Maximum 50:50 balance gives optimum results ply because they re-direct more of the propeller wash.

Outline of stern of boat However this means that, when running astern, allowing clearance for rudder large rudder movements can mask the water arm flow into the propeller, leading to cavitation and Turn to Starboard (right) a reduction in propulsion efficiency. If the rud- der leading edge is too close to the prop, the effect can be quite dramatic.

Centre line of Hull Turn to Port (left) In medium and slow models, rudders are fre- quently over sized compared to their proto- types. This has to do with the fact that the MUCH EASIER than the sprung links used in model aircraft. Length of push rod equal to centre distance characteristics of water and water flow between servo and rudder arm axis of servo arm (hydrodynamic effects) can not be scaled. Florists wire wrapped around parallel to rudder push rod - end hooked here arm

Rudder control linkages in models are generally grossly over sized since the main con- cern is for stiffness of control rods etc. However do not forget ...... flexible cable run in a nylon outer sheath will happily do the job and has the advantage that 14 G Flexi bowden cable run be- hind the cockpit side panel and the steering servo can be Servo in forward cabin glued to one bulkhead only mounted anywhere in the boat. Twin rudder horns connected by adjustable link

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Purpose Acrylic Cyanoacrylate Epoxy Loaded Epoxy HotMelt Polyurethane (PUR’s) Silicone SolventBased WaterBased (PVA’s) Gap Filling F P-F E E G-E G-E E F P-F Bond Strength F-G G-E E G-E F-M F-G F-M F-G F Impact Strength F-G P-F G-E G-E F-G G-E E G-E P-F Humidity Resistance F F G-EG-E G F E G P-F (E equals waterproof) Metal Bonding F-G G G-E G-E P-F F-G F G P-F Glass & Ceramic Bonding F-G G G-E G-E P F-G G G F-G Elastomer Bonding F G F-G G-E F G G G P-F (Silicon; Natural Rubber; Viton; Butyle) Plastic Bonding F-G G-E F-G G P G F-G F-G P-F (ABS; Styrene; GRP) Wood Bonding F NS G G G-E F-G NS F-G E Paper & Paperboard F-G NS NS NS G-E F-G NS F-G E

KEY

P= Poor F = Fair G = Good

E = Excellent NS = Not Suggested

Example Trade Names : Acrylic Glues - Fusion & Fusion 500; Tensol; Cyanoacrelate Adhesives (thicker glue gives stronger bond strength) - ZAP; Grip; Epoxy Adhesives - Araldite; Super Epoxy etc. (all two pack and all in different curing times) Loaded Epoxy - any of the plastic steels or plastic metal range (all two pack) Hot Melt Glues - a wide range available from DIY stores - sticks for plastic, wood etc. PUR (Polyurethane) Glues - Gorilla Glue (Chronos Ltd.); Excel; Titebond Poly; ProBond Poly. Solvent based Glues (one pack) - Balsa Cement; PVA (poly-vinyl-acetate water based) Glues - Polyvinyl Acetate Emulsion; Yellow Glue; White Glue; MPA; Titebond; Carpenter's Glue; Elmer's; Aliphatic Resin; Cross-Links; SpeedBond; DBI. A truly waterproof water based wood glue is ‘Cascamite’ (a urea-formaldehyde adhesive) and is available from Humbrol. Mixed 2 parts water to 1 part glue powder so it goes a long way. Slow setting (like overnight) but great stuff for wood hulls. Gorilla Glue (a PUR glue) is also said to be waterproof and comes ready mixed - I’ve never used this so can’t comment.

Known Issues : PVA’s tend to creep when the joint is put under continuous stress. Don’t use for plank to frame joins unless the plank has been steam formed. When used on end grain, joint tends to become glue starved because grain absorbs glue. PUR’s expand on setting so can deal with end grain joins and they don’t creep under load. Cyanoacrelate Glues - thick are better at gap filling than thin. Big gaps (up to 2mm) can be filled by pouring in a suitable amount of ‘micro-ballons’ and adding Cyano glue. Easily sanded.

Iain Moffatt - Beginners Boat Building Tutorial