A blatant Plug

Footy Class General Discussion (Footy)
1

Angus, as well as being a gentleman, scholar and a fine judge of horseflesh, is a prolific designer of boats, as we know.

In my spare time I attempt, in my modest fashion, to turn some of them into reality.

We have just started construction of the plug for a design called Bakers Dozen - for which Angus has swooped the rear deck (for me).

I thought it might perhaps be interesting to describe and show some of the steps in producing a plug for the hull - in Balsa wood. The plug can then be used for either:
Moulding hulls directly (fibreglass or papie mache)
Bottle-shrinking onto the plug
Vacuum forming hull and deck as seperate parts
Moulding a female mould from the plug - so that hulls can be moulded in the female mould with a good outside finish.

Your suggestions and contributions - including STOP welcomed.

BTW this identical process works with:
your own design of hull
Extruded Foam polystyrene
Flavio’s Presto - only once you have carved the plug you sail it!

No photos yet - they are still in the camera
This is what we begin with:


I have altered the profile view to show the Buttock lines (vertical slices) at exactly 6mm spacing, since I am cutting the parts from 6mm Balsa sheet.

Good News (and congratulations, Angus) - I can get all the parts from three sheets of 6mm x 100 mm balsa

andrew

2

Interested to know what sort of computer proram you are using

Cheers

Charles

PS I know nothingof making up vacuum moulds. Can we have a little thread on the subject?

3

I generally like Angus’ designs although both he and I know that the other might do things differently:devil3: but A, what is up with this thing’s sheerline? And why is the keelson so pronounced? I am the first to go for function before form, but what is the goal for this boat?

laughs That being said, I am eager to see how it turns out, I assume due to its name that this is a 13incher?
:graduate:

4

Looks interesting Angus… and thanks for offering up the thread Andrew. Should be erm fun getting it out of the mold, unless it’s a split design maybe?

Quote ‘Your suggestions and contributions - including STOP welcomed’
No no no Andrew definitely don’t ‘pull the plug’, sorry couldn’t resist.

Graham

5

Charles!

The Software is Vacanto Prolines by Vacanti Software. I have very little but praise for it. It is easy to use, reliable and does very nearly everything I want (it won’t draw diagonals, but they are very much out of fashion these days).

If you take the view that everything to do with a Footy should cost roughly zero it’s crazily expensive - from memory it’s about USD 200 - but if you think of all the other things I could have been spending my money on over the three years I have been using it, it is very cheap indeed. Put in terms that will send horrors up you spine, it has so far cost me something like 4 cigarettes a day (Take Snus. Vote for Sweden! Gul och blaa!).

Barrett!

This design of sheerline is called (at least in the Royal Navy), a ‘swan deck’. Its function on a frigate (I think Americans call them something else if they are made of metal and have gas turbines) is to preserve seakeeping ability in a head sea while lowering the main weapons deck. The latter brings weapons closer to the roll centre so that target locking is easier, lowers the centre of gravity, reduces windage, cuts overall weight, etc.

In a Footy, the main reason for doing it is to allow Stollery/Sanderson type ‘surface mount’ technology and cassette electro-mechanicals without giving away any draft.

I take it by ‘deep keelson’ you mean ‘lots of rocker’! If you look at the sections this is nothing like as extreme as it looks - all that has happened compared with Moonshadow, etc. is that the sections have been made slightly more V-ed below the turn of the bilge. The change in prismatic coefficient is actually quite small. The intent (hope? aspiration? rank fantasy?) is that this may reduce heave (i.e. vertical bobbing-up-and down movement) in light weather to which the Moonshadow and Voortrekker types have proved to be unusually suceptible.

:graduate::devil3::devil3::zbeer::zbeer::graduate:

6

Buttocks and section views show considerable tumble home. The ends are full, pehaps to help dampen pitch and minimize submarine. Will probably have a fairly high Cp. I like it. Sure enough has to be a split female mold or it ain’t comeing out. Will look forward to additional info and pix.

7

Given the very light scantlings of Footys it is quite posible to ‘pop’ it off a male mould and add the transom and/or bow block later:graduate::zbeer:

8

Interesting on the “Swan deck” Angus, it will definitely give you some more interior volume to play with. My comment on the “pronounced keelson” was actually more in reference to the “Vee-bottom” you mention; either way, you’ve managed to answer my question. laughs

I like many others, will be interested to see the boat’s progress!

9

By any Angus standards this is hardly any tumblehome at all! I have no worries about removing either an epoxy-glass moulding or a vac-moulding from the plug:D

It says here

SOOOOO,

We have a side view, as in the last picture with 6 buttock lines (each side of the hull) so we will be laminating 12 pieces of 6mm Balsa to give a block which will, of course be 72mm wide before sanding, etc.

(probably worth saying - there is a free demo version of Prolines. It lacks bells and whistles - you can’t save or print, but I can receive one of the Master’s designs, adjust anything I see fit:p. (actually I only record the overall dimensions and adjust the buttock spacing to suit the wood I have))

To get full size patterns what I do is:
[ul]
[li]Using the last picture I “print screen” to put the picture onto the clipboard, then set up a word document with A3 paper in landscape format and
[/li][li]Paste the side view into the document
[/li][li]Then I crop (picture menu) to the bow and stern lines (and remove most of the junk at the top and bottom of the picture.
[/li][li]Using picture menu again I adjust the overall length of the picture (and hence the hull to the Prolines overall length (13 inches - welll done that person)
[/li][li]Now I have a full size side view with all the buttock lines the correct size and relationship.
[/li][li]I mark three holes down the length of the boat - you will see why later
[/li][li]I then copy the drawing 3 or 4 times on a sheet, and print several
[/li][/ul]

Then its time to cut out enough paper patterns (its a VERY good idea to label them 1 to 6 since they are similar looking


Stick them to the balsa sheet (or MDF or Extruded polystyrene) - I use spraymount and cut them out
A bandsaw would be ideal, but for balsa a sharp knife and sanding block are sufficient

YES - I have used pictures from another plug to illustrate the process - I have not taken enough photos of all the stages for Bakers Boz.

So now we have 12 labelled buttocks for the plug - each with 3 holes in them for registration.
At this point I coat the inside of each piece of balsa with a fairly dark acrylic paint

You will see why later

In the picture I have already peeled the paper patterns off the parts, and there are 3 barbeque skewers ready to act as dowels to assemble the buttocks in the correct location.
This is particularly important for this design, as the dropped rear deak gives an non-level deck line (in fact I aim to make the plug with a level deck line, and cut away the mouldings later - which is why the buttocks don’t show the dipped deck)

andrew

10

Nice work and a nice tutorial Andrew. Using buttock lines when you have them certainly makes for cutting many fewer parts than using the cross sectional lines drawing.

11

Hey Angus, about your description of the intent of a swan deck “… to preserve seakeeping ability in a head sea while lowering the main weapons deck. The latter brings weapons closer to the roll centre so that target locking is easier…”. I hope you are not planning to mount cannon aboard, say to clear space on the starting line with a broadside into the fleet.

This brings me to a technical question about deck mounted servos. I am thinking specifically about diagonally placed boats that tend to be narrower than conventionally placed ones and tend to carry their radio gear and batteries aft of center. In the case of Brent Carter’s boats the winch’s swing arm extends over the rail at certain points of sail. Does the swing arm have to have full rotational clearance of the (interior) sides of the box just as the sail must have clearance for full deployment on all points of sail above the rim, or is it to be measured in a static position only, perhaps trimmed for a beat? This may never be an issue, however it would follow that deck mounted servos are exposed to the elements and the inclination would be to move them aft to avoid deck wash and dunking in a nose dive (as well as increase their use as leverage against nose down sailing). If the winch arm had to clear the sides of the box in all points of its rotation that would be something to be aware of in the layout of a builder’s electronics.

12

Neil - don’t joke about clearing starting lines by gunfire.

A very long time ago, I went on a sail-training race that started in Cherbourg (France). It was largely run by the French navy and the sailing instructions were in French. According to them the race was to be started by a ‘coup de canon’. And they meant it - a 4" naval shell whistling overhead in the general direction of England (what’s the French for ‘collateral damage’?)
:zbeer::zbeer::devil3::devil3:

13

So now its assembly time:D

Before doing this give some thought to:
How you are going to clamp the parts together till the glue goes off
What type of glue to use - it needs to be sandable

I have used three methods of clamping - with varied success.
The least successful was the one I expected to work best - clamping up in a Workmate (not sure if they are called this in the US - folding workbench where the whole top acts as a vice) This led to some skewing of the parts as they were clamped.

I have also used spring clamps and pins, and most recently three lengths of screwed rod (2mm) clamping through the dowel holes.

For glue I have used dilute PVA (white, woodworkers glue), Polyurethane glue and would also be happy with balsa cement.


Here is the plug assembled “dry” using barbeque skewers as dowels to keep the buttocks aligned
When happy that the result is “boatiform”, repeat it with glue and your clamping mechanism of choice

picture of another plug at the glued stage (this is Vooooortrekkkkker)

Now comes the FUN part:zbeer:
MAKE HAMSTER BEDDING!:smiley:

This is a slightly posed picture (in the middle of a genuine process)
The only tools I use are shown - razor plane (find one with a skewed blade if possible)
blue razor blade - infinitely sharper than any stainless blade. They are still made and sold
snapoff blade craft knife - when new the blades are agressively sharp, and will sweetly carve balsa and foam - as soon as the sharpness declines I replace, and retire that blade for general use

Partly smoothed plug - the paint marker becomes a coloured line the exact shape of the Buttock (when you have smoothed it perfectly. You can readily check that the two sides are staying in step and the same shape. When you have planed out the “steps” you have pretty much achieved the grand concept of Angus. You are close to perfection:D

andrew

14

And this is where you are going

These are again VT, BYKT because of the red tell-tale lines!

VT plugs (I made 3) are finished with 3 coats of water-based acrylic varnish, but this is a bit thermoplastic, and softens when I heat-shrink PET onto it.

Bakers Dozen will get 2 coats of epoxy laminating resin - the first thinned with alcohol to enable it to penetrate the wood and the second to give a hard finish

andrew
more as it happens

15

The Story so far:

Bakers Dozn Plug glued, smoothed with the plane, sanded smooth and fine sanded. I was wondering what to seal the wood surface with, and had decided on epoxy.

I then realised that bare balsa is just fine for most of the processes I aim to try - and it takes no time at all to be ready to use:D

First I am going to plunge-mould some hulls, or at least try to. This is the very simplest of hot moulding techniques. The Plug is held in firmly while a frame (with sheet of plastic) is heated to softening point and plunged firmly down over the plug while the plastic is soft

This is the sheet which is going to become the carrier plate - when you do this yourselves - USE thicker ply!

Plug mounted on a plank so that it sticks up high enough - in an ideal world you carry the plunge far enough to go well past the plug - then the plastic cools within a second or two and can be removed and trimmed to suit

(BTW this is how cockpit canopies, engine cows and many other parts for model planes have been made since time immoral)


The "carrier plate with hull-shaped hole is beside the plug

Now I moved into the kitchen, so as to be near the heat source (cooker) and set up the workmate conveniently near it. You have got the message that this is a process that has to be done swiftly, havn’t you?

see next part for what happpened

andrew

16

In the previous picture I have attached a sheet of pastic to the Frame using lots of bulldog clips (some people use double-sided tape and some use staples)

For the purpose of trails I am just using whatever plastic sheet I have - usually I would do trials with plastic covers from business files or any other convenient sheets of plastic, This time I had a look around the garage and found several sheets of foam PVC, about 1.5 mm thick. I know that this is used for thermal forming, so it should mould quite well. I have also got lots of scrap styrene sheet of various thicknesses which I can use


This is the outcome of the first trial, I had tried heating the plastic over open hot plates on the cooker (holding it (with insulated gloves) a few inches away from the heat). This was impossible to get even heating, so I turned on the Fan oven to 150deg C and place the board with plastic in the oven for a few minutes.

This is the result. Not perfect, or deep enough, but very promising for a first

andrew

17

Are you using a vacuum to pull the plastic sheet down on the plug? I remember playing with a little vacuum forming toy when I was a kid. You could not sell those for kids these days!

18

hew565
No, at this stage I am using andrew-power to push the frame down over the plug. The two trials that I did recently both suffered from the problem that I did not get the plastic soft enough the form completely. If it won’t plunge-form it probably won’t vacuum-form either. Vacuum forming will be the subject of one of the future trials with this plug

Vac-forming note:-
A) I will use my home-made vac-forming equipment (but this is a relatively large and deep moulding)
B) I have cunningly made the plug in two halves around the vertical join so that I can vac-form either
(1) the way it is now - to make a one-piece hull or
(2) by laying the two halves down flat on the backboard and moulding a single part which is cut into two hull halves

OOOGY
I’m sorry; I failed to explain how you know when the plastic is read to mould; it needs to be OOOGY. This is a common, but flexible description of how the plastic is when it is soft enough to mould.
To find the correct point to mould at you:
Clip (staple, tape or nail) the plastic sheet to the former
Heat the sheet and observe it
(this description of stages applies to cellulose acetate and styrene sheet - others are similar but may have slightly different stages and appearances)
Support the former so that the plastic sheet can hang down as it goes soft and stretches.
As the sheet heats up it will go through the following stages
[ul]
[li]Goes tight (this is the rolling stresses coming out)
[/li][li]goes slack - slightly
[/li][li]tightens a little
[/li][li]gradually goes increasingly slack and baggy (this is the plastic becoming nearly molten and stretching under its own weight)
[/li][li]when the plastic sheet is worryingly baggy (old aeromodelling magazines used to say “commencing to smoke”) This is the OOOGY state you need.
[/li][/ul]
Swiftly (with insulated gloves) grasp the carrier and push it down over the plug. If the plastic was soft enough - it will pass right over the plug and go hard within a few seconds.
Remove the clips, wangle the carrier off the plug, draw a felt tip pen line round the inside of the moulding at the top of the plug (bottom as you have it held) so that you know where the deck line is
Remove moulding from plug (it should come off even with some tumblehome, especially if the moulding is still a little warm)
Trim moulding, complete and sail!

Now for more heat
andrew

19

Andrew,

Just a few questions from a Luddite.

  1. You mentioned in an earlier post that the finished hull wasn’t deep enough. Was this because you just hadn’t pushed down far enough or had the plastic cooled preventing any more stretch ?

Presumably some form of stop could be attached to the pattern support plank about 0.5 inch below the deck level so that you could push down quickly without having to worry about when to stop.

  1. Do you find that all the plastic in the finished hull form comes from that which was covering the hole in the frame, or does it get pulled from the excess as well ?

  2. Do you make your frame hole just the bare max hull shape all round plus the plastic thickness, or do you add some working clearance ?

  3. Since some of your readers may not have unlimited supplies of miscellaneous plastic sheet lying about the shed, would the standard modeller’s Plasticard of 0.5 or 0.75 mm be O.K. or would local thinning require something thicker ?

Finally, please don’t tell Angus I’m asking about the new technology - I might lose all my balsa cred :lol:

Cheers,

firstfooty

20

Firstfooty,

I would never think of you as a Luddite. I more associate you with craftsmanship, scholarship and hand-crocheted Footys:D

Thanks for the questions, I’m glad that the class is attentive.

  1. You mentioned in an earlier post that the finished hull wasn’t deep enough. Was this because you just hadn’t pushed down far enough or had the plastic cooled preventing any more stretch ?

There are only a few seconds of “workability”, and I did not get the plastic hot enough, so the plastic cooled before the hull was the full depth.

Presumably some form of stop could be attached to the pattern support plank about 0.5 inch below the deck level so that you could push down quickly without having to worry about when to stop.

This would work, as long as the stop did not interfere with the “push”

  1. Do you find that all the plastic in the finished hull form comes from that which was covering the hole in the frame, or does it get pulled from the excess as well ?

Stone me, an Engineer!:smiley: I don’t know and have never measured, but I WANT the whole sheet to contribute material to the hull, so I put a very generous rounded chamfer on the bottom side of the frame, so that the plastic can flow round it easily if it feels so inclined.

  1. Do you make your frame hole just the bare max hull shape all round plus the plastic thickness, or do you add some working clearance ?

More the latter. The whole process has a certain air of urgency about it - and with opaque plastic you proceed firmly by feel. I aim to leave about 2mm clearance at all points

  1. Since some of your readers may not have unlimited supplies of miscellaneous plastic sheet lying about the shed, would the standard modeller’s Plasticard of 0.5 or 0.75 mm be O.K. or would local thinning require something thicker ?

Certainly. I have done one trial using 0.5mm styrene, and the resulting hull was perfectly satisfactory as regards stiffness, etc. (Bakers doz has a lot of curvature everywhere, so does not need a lot of thickness). I would be quite happy to add stiffness on the inside of a hull if this seemed necessary.
It gets expensive if plasticard is bought from model outlets - finding a local supplier of HIP (High impact polystyrene) sheet is a good idea. Last time I BOUGHT a sheet I paid £6.00 for 1.5mm sheet 8 ft by 4 foot (thats why I drive an Espace)

Finally, please don’t tell Angus I’m asking about the new technology - I might lose all my balsa cred

He won’t hear it from me:D

I hope to make some progress this weekend - possibly try hot moulding balsa and depron sheet on the plug, as well as perfecting the plunge-moulding

andrew