|Aug 19, 2010, 03:41 AM|
BOTTLE! - Entry Level Yacht for the Footy Class
It's time we had a build thread for an entry level yacht that the youngsters can make and sail successfully, and costs within their pocket money.
If the yachting pastime, and kids, are to prosper, we need to learn to make and fiddle with things. It was a New Zealand birth right, the right to have a shed and to tinker. The first aircraft, jet boat and the fastest motorcycle were made in sheds and kitchens in NZ, but today I go to parks and no kids are flying a kite they have made, or a plane or sailing their yacht in the beautiful lake at the local park. This is more than building a simple yacht, it is the future of the inventive world!
This project came out of a need expressed by kids and their parents who watch me sail my little Footy all round the lake, for an entry level yacht.
The toy store ones don't sail, the model stores kits are expensive, and none of them think they can scratch build something from plans.
So why a yacht made out of a bottle?
Model Bottle Boats have a long history:
The success of this design depends on the use of a PET soda bottle as hull material.
And here may lie the problem for most of you...
In NZ the majority of the soda bottles are made in one factory to one design - they are not the bottles available in the rest of the world.
The bottle is 1.5 litre PET plastic with a very plain shape and a narrow sloping neck, measuring about 95mm x 330mm to the top of the cap. A quick search online has not turned up such a simple shape overseas. It appears that bottle design is subject to marketing forces that favour very convoluted moldings with un-boat like shapes.
So your first task, dear reader, is to go to the Mart and inventory bottles.
Report your findings back here, and I'll see you tomorrow.
* Footy Rules:
|Aug 19, 2010, 11:37 AM|
Rusty, A 2 Litre UK Coca Cola bottle is 95mm x 340mm... as I don't intend to race my Footy this might be "ok" if I can't find better a match...but the bottle does not have long sloping neck..
|Aug 19, 2010, 06:38 PM|
A community build? What a concept, I like it. Browsing the marts here the best I've come up with is a 1.48L Coca-Cola bottle, roughly 90 x 290.
The bottle doesn't have the long neck but pretty close in size. Comes in twin packs at the local grocery store.
|Aug 20, 2010, 05:13 AM|
Step One - The Hull:
I think we can say 'no' to the Vitalis bottle, but fond memories!
The USA Coke bottle is a possibility. The wasted shape so beloved of their designers is absent?. The lack of a long neck means more buoyancy up front which is not entirely bad. The US designers tend to the wide beam Footys. The length is ideal for a legal Footy.
The UK Coke length could be a non-legal design (max 12 inch) unless a larger ball is placed in the bow, and do you have that waist?
We are going to heat treat the PET to re-engineer its shape to some extent. Whether there is enough plasticity to remove the waist is in question. The treatment will expand the bottle in length by about 2cm, and remove minor molding ridges and fill out the bottom flutes.
It is possible you may find a bottle that is good to go unmolded, and this is even simpler for the young builders amongst us. The bottom flutes may not be detrimental to the hull performance. There are five flutes on my bottle, so you can have one at the bottom of the hull.
Partially submerge your candidate in the bath tub and look at the waterline shape.
Let’s get started.
If you follow these easy steps, measuring and cutting carefully, you will quickly end up with a simple but very innovative yacht that will sail well and give you great pleasure!
Each step is graded in importance: (1 'easy' to 3 'get this right!').
If you feel you need help with the most important steps, please ask for assistance!
Step One - The HULL: (2)
We are starting with an important job.
However the materials are free and you can have several attempts until you get one you like.
The hull treatment is quite simple and follows Andy Trewin's Bottle experiments:
Find an old cycle inner tube and remove the (car type) valve.
(Many of the items required may be obtained for free if you go to your local outlet and explain with enthusiasm what you are doing. The bike shop should have an old unrepairable tube or two they can give you. Most places will have a rubbish bin!)
Drill a slightly-too-small hole (approx 8mm) in the top of the bottle cap and force the valve into it.
Retain the plastic bottle top washer in the cap. Screw the cap back on tightly.
Use your hand pump to put around 40psi into the bottle. It should ring when hit on a bystander’s head!
Remove the pump.
Place the bottle 100mm from an electric space heater and slowly rotate.
The bottle will expand a little and the ridges and moldings will gradually reduce. The base flutes will fill out, the bottom will round, the neck diameter will increase and the length will grow.
If you have some leather gardening gloves it can help with the heat!
Watch the length so with a 40mm table tennis ball in the bow extending a cm, the total will not exceed 300mm.
Concentrate the heating finally on one face. It helps to mark this face with your marker pen. This is the top.
Heating this face may decrease the length, pulling the face more level and leaving the bottom more rounded.
Keep the bottle moving, rotating it slightly back and forth, and watch that the neck diameter does not grow too large to accommodate the ball (35mm), or the base too rounded so that it sticks out way past the waterline. Cover areas that you do not want to grow with a cloth. Do not expose the bottom directly to heat (just the sides) to minimize stern bulge.
Video Link to how it should go when you've finished! -
|Aug 20, 2010, 10:26 PM|
Ahoy there Rusty and Skippers!
I made the first attempt for step one. First off I used a bicycle hand pump to put air pressure in the bottle, worked. Second, I used my gas stove to expand the ridges and molding, way too hot here to break out the space heater.
The bottom expaned nicely and the bottom face rounded and protruded out just a tad. The bottom still had corners and I continued rounding them out. I may have went too far as the bottom face started to protrude further out and taper.
I set the hull down next to my rule and used a tennis ball and gauged my length. I'm roughly 301mm/11.875 inches, close. Also, I'm not sure how this tapered end would affect rudder operation?
Well if anything my daughter and I will drink this second liter of coke and try again. I was planning on building two of these, one along with my daughter.
Lessons learned for step one: Make sure to completely remove the bottle label before putting heat to it.
As for Coca-Cola Rusty: "The wasted shape so beloved of their designers is absent?."
I hear you!
By the way, is that a message in your bottle?
|Aug 21, 2010, 07:15 AM|
Gary, you don't have a failed footy hull - you have a successful rocket!
Just put the valve through a rubber bung and quarter fill bottle with water - pump away and presto, a water rocket! There are no mistakes, only disguised opportunities...
You make a good point on the label. If you leave it on it will inhibit the expansion on that face. This may stop ridge moldings from filling out, but may also allow greater expansion on the other side thus giving some rocker to the hull bottom.
In any case it is a PITA to remove. Heat does seem to help, and it does not catch fire with my heater. I think solvents are the final solution.
Being greedy or perfectionist in the molding is not productive. The stern will not be perfectly round, but the flutes become small bumps, one of which we pass the rudder tube through. If you spend just a little too much time it will get too round and protrude too far past the waterline. We want as much waterline as we can get on such a small hull! Similarly if the heating is too prolonged the length and bow diameters become too large. The ball bow is a 40mm table tennis ball - not a tennis ball, lets keep it light!
For reference, I use a small fan electric heater rated at 10 amps - 2000 watts. It is quite powerful but the fan assists the heat to flow evenly over the hull and it takes some time to achieve the molding. However once the bottle reaches its plastic stage, it flows quickly. If you are quick you can mash the stern down on a flat cold surface and reduce some of its roundness.
Any heating attempts at modification once air is let out of the bottle are disastrous.
The above contents of the Bottle!, apart from water to establish the waterline, is a cunning spine. You are welcome to write messages on it.
I don't want to encourage the over quaffing of soda in order to get a usable hull. Especially as the next step involves you in the search for confectionery!
It appears you have been drinking Coke for a long time...
|Aug 21, 2010, 07:56 AM|
Let's make sure you have everything to hand you will need:
May I raise your consciousness to the next item you need to find. Keep an eye open on your walks for a few of the white or yellow plastic tubes that lie all over the pavement. I finally figured out what they are - confectionery support sticks - what we call 'lolly pops', though they don't make any sound...
|Aug 21, 2010, 07:24 PM|
Thanks Rusty for your feedback. As model builders we sometimes tend to be our own worst critic. Now that I look at this hull it reminds me of an egg plant, I put a piece of silicon tubing on the end and it gave me a big chuckle.
In reference to the Footy box diagram, can it be made from a cardboard box? That would save me a couple of dollars and make some good use of those boxes I have piled up in the shed. Looking at the Footy rules I ran into some photos and I thought this one was interesting, now is this boat legal?
I'm on the hunt for those white "lolly pop" sticks. I don't see the hollow ones here just the solid plastic ones. I'll keep looking.
|Aug 22, 2010, 05:13 AM|
It's legal 'cause its in the box.
Developmental Class so anything not specifically prohibited is allowed.
The box rule is based on the rule for the British 36R class, which has been around since about 1935. It has always been accepted in that rule that diagonal boats are allowed.
Most current designers are striving for the longest waterline. The theoretical longest hull in a 6x12x12inch box is over 15 inches! But you have to have double diagonal hulls, which leads to short coupled rudders (can't stick out the back of the box if they are not inline with the slot), and rigs that have highly inclined booms to clear the box top, and skinny beams.
Jury is out on whether this practically results in a faster boat or not - too early to tell.
The double bottle yacht shown above is similar to the Stollery bottle yachts (not Footys, his are fat) where two slim bottles (and a beer can) are joined by a wrap around molded skirt that holds the fin. It is a single diagonal boat with the rudder under the stern - nothing can protrude outside the box.
Actually if your hull is a few millimeters longer than 305, it can still probably fit in the box as the round bow can be slightly off centre and the rudder will still fit through the slot.
It is not necessary to make a box for a simple straight design - you can measure the length and height well enough with a ruler.
I made one out of corro plastic held together with bamboo skewers!
How is your bottle search going, Dekan? UK Andy likes the 1.5 l Liptons Iced Tea, (got to be better for you), Icelandic mineral water flat bottomed 1.5Ltr and the 1.25Ltr Coke.
|Aug 22, 2010, 06:00 AM|
Once you have a hull that looks good and is not too long, we are going to do the first of some design steps.
The maximum design displacement (total weight) of our yacht is around 500 grams (although the hull will take twice this).
You can use the original gear that came with the old 2 channel radio sets: 2 x 40gm servos, 40 gm receiver, 4 x AA batteries and holder - 125gms . The yacht will sail ok in normal conditions, but will lack stability in higher winds or with larger sails, unless you use a larger 9-10 ounce bulb. You are encouraged to at least get a cheap 9gm rudder servo and use AAA cells.
If you have (hopefully) lighter radio gear than the old standard 200 plus grams, you may use either a lighter displacement or use a heavier fin bulb.
A lighter displacement may be more manoeuvrable and a faster accelerator, or more suited to lighter winds. A transference of the radio gear weight to the bulb gives a higher bulb to total weight ratio meaning a more stable hull: one that can take more sail area or higher winds, higher speeds and maintains speed better on changing tacks.
A heavier bulb can mean a shorter keel length giving less drag and pitching, but then we must retain keel area in relation to sail area and ours is already quite narrow.
This is where your design skills come into play.
With this yacht you can easily change the keel and bulb weights and positions to try many combinations.
Because this yacht is so lightly constructed at less than 100 grams, with readily available, light weight and cheap radio gear of as little as 30 grams (5gm receiver, 5 gm rudder servo, 9 gm sail servo, 10 gm 1S LiPo battery, wiring etc) it is possible to make a stable yacht weighing less than 350gms with a 200gm bulb!
Mark a centre line all around the hull top and bottom. This is very important for the accuracy of our build so do it carefully using a flexible ruler and with reference to the symmetry of the hull (the top may be curved differently from the bottom).
Fill your bottle hull with the amount of water you choose for your displacement (1cc = 1 gm) and go take a bath with it.
We want the hull slightly nose high at rest as the hull will drop forward at speed. This will put the waterline just below the ping pong ball.
Because the bow is so bullet shaped it will go well downwind!
Mark the position of the waterline all around the hull with an indelible marker pen.
You can see how very buoyant our hull is, and how little force it takes to propel it across the bath! (compared to the duck)
|Aug 23, 2010, 03:26 AM|
STEP TWO: THE RUDDER (1)
The Footy rules allow a rudder to extend up to 51mm past the stern for a 305 mm hull. This is possible with a transom rudder hinged on the stern, but a more aerodynamic rudder that requires less force to move it, is a balanced rudder with a hinge line 20-30% further back. This requires the rudder to be more forward and gives less hull leverage. You can choose either but I will describe the balanced rudder installation.
Take a drill, or better, your soldering iron and with its hot, sharp tip, melt a small hole on the centreline at the waterline or slightly under and at a slight angle so that a straight line connecting to the top of the stern clears the bottom plastic of the bottle. Try your lolly pop tube for size. When you have a tight fit, push the tube up until it contacts both the rear of the hull and the top. Mark the place on the centre line where the tube is touching and melt another hole to accommodate it. I like to go through one of the flute bumps. You now have a slightly rearward sloping rudder tube that places the rudder 50mm past the stern.
Take some 3mm or 1/8th inch plastic corrugated sign board (Coreflute, Correx ...) and cut a rudder shape from it aligning the flutes with the rudder tube.
You can try different shapes with card patterns but keep the perimeters similar to about 100mm long and 60mm wide, and the hinge line in from the front. This will place the leading edge of the rudder forward of the stern.
You can easily cut the rudder smaller if you find it is too large later.
Take a spoke and place it into the rudder tube and thread the rudder on it. Secure the rudder temporally in place with tape or plasticine so it is central and resists moving.
|Aug 23, 2010, 10:23 AM|
Joined Apr 2010
1. Compressed air in a bottle can be dangerous. Do not attempt to break a record of how much pressure a bottle can hold. If you use an air compressor to pressurize your bottle, adjust the pressure regulator to avoid over pressurizing the bottle.(Rusty recommends 40 PSI. I would not exceed that)
When these bottles are over pressurized they can explode violently and can cause serious injury. For best control, a bicycle tire pump may be your safest choice.
2. Avoid most drinking water bottles. They are made of a much thinner material and will not hold the same pressures as carbonated beverage bottles.
You can feel the difference in the flexibility of the material of the lighter weight bottles.
Be safe first and enjoy the whole experience.
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