I continue to try to learnt as much as I can about sail design. A thread running here on the Wooden Boat Forum is providing terrific knowledge about sail shaping and broad seaming. Todd Bradshaw’s post are just so helpful and incisive.
Here is the link to the thread
And a couple of images from the thread, the first is a lug sail design posted by Todd Bradshaw
This second image is also by Todd and shows where broadseaming starts, as you machine from the leach and run towards the luff of the sail.
Picture by Todd Bradshaw showing start positions for broadseams
I have also tried different panel layouts using Sailcut4, one an unusual radial cut just for fun, and the other a rather nice traditional vertical cut panel layout. The vertical cut would require my cutting the cloth in half and then re-sewing. Looks nice though.
Here is Todd Bradshaw’s wonderful radial lug sail. What a beauty, having to hold back with all my might from simply getting on with ordering one
raid41-vertical-panel-lug-mainsail
Here is the PDF file for each individual panel for the vertical cut version
raid41-vertical-panel-development
In order to show the vertical panel layout in different rotational views to illustrate the shaping, I have taken two screen dumps from Sailcut4, and converted them to PDF files.
Having looked these various options and listened to feedback, a simplified vertical panel layout might meet our RAID41 class needs. A 4 panel design keeps seam cutting and sewing to a minimum, still gives good shape. Costs are reduced as well, purchasing a wider cloth, it may need only 8m to make the sail.
raid41 700mm vertical panels
Having decided on a 4 panel vertical cut for the main and a two panel vertical cut for the mizzen, I printed out the Sailcut4 individual panel developments. Laying these shapes onto 140cm wide “scale” cloth showed that I needed 8 metres of cloth for the main and 3 metres of cloth for the mizzen. The vertical layout is somewhat wasteful of cloth for the mizzen, but there will be plenty left over to make corner patches.
So, today (18/12/08) went to see what sail cloth remnants were available with my chosen supplier. There were some very nice tanbark lengths but narrower and heavier than I planned to use.
I have found with previous boats that a heavy cloth looks good but makes reading the wind more difficult and seems to take up “a lot of space” when dropped into the boat. Since Trim is to be a cruising dinghy, I need the sails to be compact when dropped.
The “Sailmaker’s Apprentice” recommended 3.9 oz, my current Scow sail is over 5 oz, with the Gannet sail over 6oz. Decided something 4 oz to 5oz should suit this first trial at sailmaking. I could go heavier later on if need be.
The creams were also heavier, so had a look at the white cloths. A 4.2 oz white cloth was available, with enough cloth on the roll end to make this first suit and a second suit later on after lessons have been learnt. This was purchased.
So, that’s good, my roll of cloth is sitting there challenging me to make it into the “engine” to drive Trim. Back to reading now about the details. How best to cut the cloth, what tape to use to hold the panels together before sewing. Obtain the correct thread, and sail hardware.
I had been wondering how it would be possible to see the sail set on spars which have not been made yet. Realised that it will be possible to use the mast and spars from my Scow to set the sail on and examine the set and look of the sail when made whilst there is still time to adjust things.
Grommets, double side tapes and thread
Again, after great help from the members of the WB forum, more details are resolved.
Cutting the cloth can be achieved using a standard soldering iron with a flat blade, but there is a tendency to leave black melted beads in places and that simply cutting with a metal ruler and a utility knife is best.
No “0″ spur grommets will be used for edge lacing and small reef patches.
No “2″ spur grommets for corners and end of reef lines
3M Super Seam Stick for joining the panels together before stitching. It should be possible to check the shape of the whole sail by using this tape before sewing.
V-46 or V-69 thread.
Learning about “Mould” shaping in Sailcut4
One of the more deeply hidden features of Sailcut4 is that the type of aerodynamic shaping of the sail can be chosen in the feature “Mould”, which is found by clicking on “View” and the “Mould”. Here is a pdf file of a screen dump of the page.
Their software allows the aerodynamic shaping of the sail to be adjusted at the top, middle and bottom of the sail. At each level, three settings are used to adjust the shape. It then also tells you where the maximum draft position is for those settings.
The luff setting increases the roundness of the sail entry as the number chosen is increased. I had been using a value (3) which gives a flat entry. Increasing that to (9) produces a much rounder entry and increases the broad seaming introduced into the first panel seams.
Adjusting the leach value then can be used to obtain a maximum draft position at 40% back from the leading edge.
The depth value I have used are 8% for the top, 9% for the middle and 10% for the bottom. That is that the draft depth should be a percentage (8,9 or10%) of the cord length.
