Introduction

I hope this site is of value and contains information. I will record my ramblings regarding the green boat projects I undertake. I might entertain those with an interest in the journey over the destination. But let's see.

Please visit again for updates and do leave your comments.


Friday, 10 February 2017

Spinnaker Spun

This is the final spinnaker construction post. There will be something on how it flies, but we'll wait for the weather.

The final tasks were sewing on foot and leech tapes, and the luff tape. The foot and leech are finished with folded strips of ripstop nylon. I cut 20 mm ribbons of cloth from the scraps after cutting the panels. The ribbons were taped on the inside of the marked out lines and cut with the soldering iron. I then used the tape to baste the ribbons on one edge of the sail and then folded the ribbons around and onto the other side of the sail.

This looks difficult, but it worked out well. 

Once the ribbon was tapped in place, it was easy to zig-zag stitch over the ribbons with the machine.

The next task was the luff tape. This is made from a 50mm Dacron strip. This was folded and creased over the edge of a table (see Sailrite Spinnaker videos) then tapped on and sewn. Easy. You can see the luff tape in the picture below.

The luff tape also has a 1.5mm dyneema luff cord inside with small loops of webbing sewn at each end to allow the cord to be tied off as follows:


The final job was to make up the corners. I used a similar construction to that shown in the Sailrite videos. I found the lengths of my panels were not as consistent as I'd hoped, but I was able to cover up and compensate using the corner patches.

I used three colours of webbing in the corners so as to mark the head, tack and clew. 50mm stainless rings were sewn in.


Pudding and eating comes to mind at this stage. If it's a disaster, will I tell you all ? We'll have to wait and see. Only another few weeks until the boat goes back in after the winter. Would I build another sail? Well probably as with experience, another would not be too much work. It's been enjoyable.

For information the sail is: Luff: 6.2m, Leach 5.8m, Foot 4.6m Total area - 21.5 sq m.

Monday, 6 February 2017

Bright Ideas

On and off, I've been working on my navigation lights project for some time. I've created a few 3D model clips for the Guardian Adventure Lights I plan to base my design on. I need to replicate the clip so that the light will fit onto the shield that will create the 112.5 degree light arc.

After the first print, I realised I had simple modelled it to the wrong size. With this corrected, I printed a new clip. After a little fettling I tried it with the light and it fitted perfectly. I like this 3D printing thing.

I then started on a basic light shield to ensure the light is only seen over the correct arc. I needed a couple of goes at this to realise just how much light can be seen even from the tip of the light. You can see the evolution of the basic design here:
It's also worth noting the arc of light you can on the table top. This is caused by the lensing of the light's cover. It measures almost exactly 112.5 degrees.

The next thing to think about is where on the Tiki 21 these lights should be mounted and how. My first thought was to mount on the beam ends. From here it seems the lights would be prominent and perhaps easily mounted. There are a few problems with this position:
  • Nav lights will often be used coming into a port (in the dark!). For a Tiki 21, this is probably not according to "Plan A"! When you arrive at the end on a long day (Plan B), in the dark, the last thing you want it to break out the dock lines and find the beam ends cluttered with nav lights.
  • The beam ends are often close to and at the height of the dock. The light are vulnerable.
  • Moving the lights to the front beam would help, but in the dark and under less than ideal conditions, moving forward to position the lights is not good. 
  • Mounting over the water, means they will eventually get dropped in the drink.
The more I think about position, the more the beam ends are wrong. Next, the gunnels? A small threaded nut, recessed into the wood and a thumb screw on the light? Complicated I think.

Mounted on the top of the mast beam, just back from the cleat seems good. It also allows a better shape for the overall light housing. This is the approach I'm currently following. I've started on a full housing shape and it's looking good. See below and watch this space.

video

Monday, 30 January 2017

Plotting and sewing a spinnaker

With my spinnaker model complete in Blender 3D and the paper cut plug-in generating 2D panels, I'm ready to go. Here's an update on the progress since the last post.

How do I mark out large cloth panels? I considered a number of possible approaches:
  • Generate a series of vertex coordinates and manually plot them, then and join the dots;
  • Create a scale drawing and linearly extrapolate each vertices then joint the dots;
  • Project the image onto a large board at full size and plot;
  • Build, borrow or buy a giant plotter;
Of the possibilities the manual approaches all seem too laborious, buying a second hand plotter is not a bad idea but they are huge and might cost a bit too much.



If the projector approach can work, it seems the best approach, but there are a set of possible problems:

Size: The digital projector in my office is fixed to the ceiling and the screen is about 2m (6ft) by 1.2m (4ft). I need an image about 3.5m by 1.5m for cloth and largest panel. The room is too small. I need to move the projector further away and need a bigger wall or high ceiling with clear floor space.

Accuracy: How do I know a 1m square projected onto the wall will be the same size wherever it occurs in the image (i.e. vertical and horizontal linearity)?

Marking out: How can I mark the cloth according to the projected image? The edges will be long sweeping curve.

Cloth Use: How do I know that I can fit all the panels on the size of cloth I've purchased, especially if I want the warp of the cloth generally aligned with the panel lengths?

Scaling: How do I ensure the shape projected onto the cloth is the correct size?

Below are the detail of what I finally did.

Plotting and sewing a spinnaker

I set up a projector in my office where I screwed a 2.4m x 1.25m MDF panel to the wall. I marked out the wooden panel with a 500mm grid. I set up the PC with Adobe Illustrator and created the test grid. I scaled the drawing until the projected grid was close to the marked out grid on the wall. I then fine tuned the projector position until the grid was aligned. To my delight I found I could achieve a gird which aligned to within a few millimeters over the range both vertically and horizontally.

Next I imported the 2D panels into Illustrator and set about moving the panels into position. Illustrator allows a maximum drawing size of 5.75m X 5.75m. Some of my cloth is over 5m long. It won't fit, so I worked at half scale.

I set up illustrator with a page size of 5.5m by 0.75m. The next problem is to ensure the imported Blender drawing is the correct size. I had anticipated this, so when I created the sail panels I also create some simple 1m by 1m squares as references. Once the panels were imported, I scaled everything until the reference square was 0.5m X 0.5m in Illustrator. When projected onto the wall, I checked the reference square size on the wall, and it was spot on at 1m x 1m.

The panels were still much longer than board. You can see one of the smallest panels in the picture below.


The procedure for larger is as follows:
  • Project one end of the layouts onto the cloth. Mark the centres of the reference grid on the cloth as registration marks.
  • Use an awl pushed into the board to press the flexible ruler (I used 2.5m long UPVC angle bead) against at two points on the panel. This gives a nice smooth curve which follows the projected edge. Mark out the panel with a soft pencil.
In the picture you can see the panel, the awl and some red lines which were added to the Adobe file to show where the seams go. A seam is where an extra 8mm is added to overlap the next panel. This is taped and then stitched. The procedure is:
  • Stick a bit of masking tape to the panel and write on the panel numbers and mark the seams and the numbers of the adjacent panels. This will help with cutting and sewing later.
  • Once the panels are marked, shift the cloth along and move the image left/right to get the remainder of the panel onto the board. (This might require a few steps to complete the whole thing).
  • Carefully align the registration marks on the cloth with the projected image reference grid. 
  • Continue marking out the panels.
  • Shift the cloth up/down to complete the process for the whole vertical extent of the cloth.
With the cloth marked out, the question is how to accurately cut it out. Nylon should be cut using a hot knife to seal the edges and avoid fraying. I experimented with a temperature controlled soldering iron turned up high. The pointed tip worked well and easily cut the cloth, but a guide edge was required.

The cloth is first stuck together using basting tape. This double sided tape is a very thin acrylic tape with a paper backing. I found the soldering iron will run along the backed tape and create a good clean cut. I used the tape for all edges, ensuring I cut the inner edge where the panel has no seam, and the outer edge where the panel has a seam.

You can see a panel below, where the tape has been set out along the pencil lines and the cut made with the soldering iron. Note that the iron doesn't really burn the MDF board.


Here's another set of panels, taped out ready for cutting. Note the green tape labels that indicate the panel numbers and which edges are seams.

Here are some of the finished panels all ready to be stitched and a printed out plan with panel numbers for reference.

The panels are now assembled. I did this in three large triangular sections; the whole head section, the clew and tack sections with the natural vertical break. These were then to be sewn together. When assembling a section, I taped a panel and then stitched, then added another and stitched. This way only one panel, the new one, has to pass under the machine's arm as shown below.

I'm used a 3 step zig-zag machine which gives me a 6mm wide zig-zag. This is smaller than a pro-built sail, but I can't rip the seam apart so I think it is strong enough. Stitching over the tape is not a problem and fears of the needle gumming up have come to nothing. I'm using a fine point needle and V46 bonded polyster thread. Here are the finished seams:


You can see how the clew corner has not quite come together here. More on that later. Here's the finished assembly. Just the luff, leach and foot seams and corners to do.




Friday, 6 January 2017

Part Spun Fun With Sail Panels

Here's an update on the progress since the last post on designing the spinnaker.

Creating appropriate 2D panels

After some thinking I realised the way the 2D panels are created is important. The model I initially created in Blender was a "perfect" smooth curved surface (a nurb surface). This was based on a real sail design the I borrowed! and scaled a little to the boat.
Tiki 21 with an A2

To make 2D panels, I first needed to create a mesh representation from the perfect surface. But it occurred to me that the type of mesh was important. Each panel in the sail should be something which can be folded out flat without any stress in the panel. This is not the case if the initial mesh shown below is used.
The problem is the software simply cannot make a flat 2D panel using the mesh made of the back grid cut along the red seams. It can only approximate this. i.e. in the resulting panels the mesh edges lengths will not be the same when flattened as they were the curved model. i.e. the panel must be stretched a little to make it flat. This results in errors in the panel 2D shapes.

To solve the problem, I first converted the perfect sail into a near perfect fine mesh. Then I cut the sail into the panels. I then took each panel and deleted the internal mesh leaving only the perimeter vertexes for a panel as show below.

It should be understood that the edges of the panel (hole) are not straight, so the cut out is not flat (see below). I then created a new mesh of triangles using the perimeter vertices. This gives a mesh that can be laid out flat without any stress. i.e. it could be made from paper panels.

This might seem a bit complicated or over the top. Perhaps it is? However, I arrived here after lots of experimentation and only this way can I create 2D panels that when sewn in cloth and flown from the boat, should, in theory, adopt a shape close to the model shape!

Here's a single panel that can be flattened out, shown in its original position within the sail.


So how to mark out 3.5 meter long panels from the computer models ?

Sunday, 4 December 2016

Spinning the Spinnaker

I wonder if the meaning of the expression "it's taking shape" comes from sail making?

After a number of dead ends, I think I am making way. I now have a 3D model of an A2 spinnaker sized to the model of my Tiki 21. I can mark out the seams and make a 2D surface development of the panels for cutting. I've tested this by cutting out paper panels to make a model.

Here are a few notes for those that are interested on the journey and lessons learnt.

Sail Design

The first thing I need is a good sail shape. Then I need to realise the design in cloth. Both tasks are difficult. I need to know what shape is right, and then how to make this from flat cloth.

I don't know what shape is exactly right. Clearly I can look at lots of pictures and guess, but I don't want to spend too much time and money on a guess. My approach is to copy an existing shape for the design and use a computer to build a 3D model and develop the necessary 2D panel shapes from the model.

There's plenty of detail on all this in Brian Hancock's excellent blog and website.

Sail Shape

To obtain a good shape, I've been a bit naughty. If you search the web you can find 3D visualisations of sail designs. You can't download these, you can just "look". But that's enough for me. If I look from three orthogonal axes and take screenshots, I can reconstruct a 3D model. I did this in Blender 3D.

Orthogonal Screenshots as a template design
Tiki 21 with an A2  Tiki 21 with an A2

The sail design shown has the following dimensions: Luff: 6.2m, Leach 5.8m, Foot 4.6m Total area - 21.5 sq m. 

With my sail shape defined, I need the panel layouts.

Software

1. Sailcut CAD

Sailcut CAD  is a program with a long history and allows a sail design to be specified in terms of a set of parameters, e.g. foot curve, luff curve, twist, mid girth etc. It takes the design and creates 2D panels with seams. These are cut from cloth and the sail assembled. Sailcut allows head and fore sail designs in various panel layouts, including radial designs.


I took my desired shape and made a set of measurements according to the parameters required in Sailcut. All looked good. I exported the 3D design from Sailcut to Autocad DXF and imported into Blender 3D. In this way I can compare my desired design with the generated design from Sailcut.

After a number of iterations, I found that Sailcut simply will not give me the shape I want. It is expecting the luff to be bent on to a forestay with a small curve in it due to the wind load. It doesn't expect a flying sail, fixed at the head and tack. No matter how hard I try I cannot make it work. Time to rethink.

2. Blender 3D

Blender 3D is an amazing tool. It's also free! It's primary purpose is to develop 3D games. It supports 3D modelling, photo realistic rendering, animation, physics models and plenty more. The image below was create using blender.


It is so good that you can use it for many 3D CAD applications. Since I have a 3D model of my desired shape, can I use Blender to create the 2D panels? If I can, I don't need Sailcut.

A bit of searching on the internet and I found an add-on for Blender called Sailflow. This add-on allows sail shape development using parameters a bit like Sailcut, and panel development. But I don't need the shape development, as I already have a design. I tried this add-on and although it looks promising, the panel development doesn't quite work. I created 2D panels, but it makes a mess of some panels. It's just not working for me.

3. Dynamics of Cloth

It is clear that a smooth 3D surfaces can be approximated with a mesh. The finer the mesh, the more accurate. If the mesh is used to define flat panels, cut out in cloth and assembled, the stretch in the cloth means that the sail, when flown, will take up the smooth shape. To make this work exactly you need the panels to be the right size according to the expected wind strength and cloth stretch characteristics. Working that out is too difficult. After all, it's a Tiki 21 and not an America's Cup trimaran.

If I assume that for the panel sizes I want, the stretch etc. will work out, then I can disregard the dynamics and just flatten out my 3D panels into 2 dimensions. It turns out that Blender has the ability to do this using a feature called UV unwarp. I tried this out and compared the output with a Sailflow panel that did work. They are the same. So I can ignore the add-on scripts and just use Blender's built in tools, but there are 25 panels and it will take time to do. Surely there's a short cut?

4. Paper Model

More searching the internet. This time for a Blender add-on for surface development. I found Paper Model. This add-on tool allows a mesh to be cut with seams and the panels exported to an SVG file.




It's purpose is to make a layout for assembly into a paper model. It is very close to a sail panel layout, just a lot smaller. I tried it and here's the result




Conclusion

I'm making steady progress. It's fun and I'm learning a lot. The following considerations are still to come:
  • How smooth a model (how fine a mesh) should I use?
  • Double check the tack sheeting angle alignment with sail's radial panels.
  • What seam layout do I need?
  • What detail do I need at the seam junctions between 3 or 4 panels?
  • What is the best order of assembly?
  • How to best mark out the panels on materials?
  • Do I need to make a test sail to gain experience?

Watch this space for more ramblings.









Tuesday, 15 November 2016

Some History

Scott Brown of the MultiHulls website was recently in touch to see if my green Wharram was the same Gratitude that he knew of. I am aware of the history of the boat, and Scott confirmed much of the detail. Kindly, Scott then sorted this out for me ....

Sea People article mentioning Gratitude
Sea People article mentioning Gratitude

Sunday, 13 November 2016

Noss Mayo Return - South Hams


Noss Mayo Return - South Hams

I should apologies for this indulgence. It's over the top, but was fun to make. Hope you like it.
I'm not quite sure what I can do next?