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Modifications to the Phantom sails

It is worthwhile making this first check before setting up the yacht to see if there is an issue with the luff on both the main and jib.  Stretch each sail out on a flat table and tape each corner out with just a slight tension on each.  Lay a straight edge along the luff of each sail.  There should be a regular convex curve of about 4mm - 6mm for the sail to set properly.  If there is a concave curve or a variable one then the sail will not set effectively and should be modified to produce that curve.

Modifying Mainsail Luff  Modifying Jib Luff    Improving the sail shape    RC Yacht Supplies

Modifying the mainsail

My mainsail was a typical example with a concave curve of about 4mm.  Needless to say when I had tried to set it on the mast, it had little shape, the leech would fall off, creases would appear across the sail and it sailed abominably

To deal with this I decided to replace the folded and sewn section with hanks as in full sized yachts that travel in the luff groove with the sail completely outside of the groove.  This would make fitting the sail easier as I found feeding it down the mast groove a little difficult.

The first step is to undo the stitching ('quickunpick' from my partners workshop).  Then the sail material is laid flat and carefully stuck down with masking tape so as not to move the rest of the sail material.  A light wooden batten is laid along the luff and using weights and clamps forced into regular convex curve.  Use a straight edge to check the amount of curve - about 4mm - 6mm seems about right.  It is probably better to have the maximum part of the curve higher up the sail say at about 60% of luff height.  To ensure the sail area is not affected the maximum part of the curve was made to touch the line of stitching.  This meant that the curve runs over the two reinforcing stuck on plastic patches.  These need to be carefully removed along with the eyelets set in them.


The curve is transferred to the cloth using a fine point permanent marker.  The cloth may then be folded along the line at this point and stitched back down to reinforce the leading edge or be reinforced using some Mylar tape and then cut off.  I much prefer the tape method.  This tape is available from RC yacht suppliers in their sail making section.  With the sail still fixed to  the table, the tape is applied to the sail just touching the line or slightly overlapping it.  This is repeated on the other side.


The sail material is trimmed to the line using a sharp blade cutter and straight edge working a small section at a time and maintaining the straight edge as close as possible to the line. Always cut with the straight edge over the material of the sail and the exposed section is the material to discard.  The corners of the sail are reinforced with sticky backed sail repair cloth.  Two layers are necessary making the second overlap the first by a small amount.  Two eyelets are then set in the reinforced section.

The slides for the mast track are made using a ferrule from a fishing supply shop (the ones used to secure wire fishing trace) and a small piece of the sticky sail cloth about 35mm X 12mm.  Remove the backing sheet and lay the ferrule across the middle of the sticky side.  Lay the edge of the sail over one edge so the ferrule remains about 2mm proud.  Let the sail grab the sticky material and holding the ferrule with a wire fold the other side over the ferrule and onto the sail. Roll the ferrule between fingers makes a neat finish to the slide.  About 6 or so slides are necessary, one near the head another near the foot and the rest evenly spread.

Modifying the Jib

If modification is necessary then the jib is treated in much the same way.  Once the ferrules are in place a fine wire or thread is passed through each to act as a forestay.  I prefer to use a wire forestay and make a channel for it by sticking a luff tape around the luff using double sided sticky tape.  The materials for this are available from RC yacht suppliers.  This process is outlined on the Stirling site on this page near the bottom.

Improving the sail shape

Despite the addition of the luff curve the sail still suffers on its overall shape.  The leech of the mainsail is particularly difficult to support and not have it fall off and deliver no drive - just drag.  Normally shaped seams increase the sail area in the middle of the sail effectively making the leech tight when the clew is tensioned.  Try tensioning your clew and what happens is a diagonal crease from the leech to somewhere on the mast.  The leech cannot be tightened.  One way of dealing with this in a flat panel sail is to reduce the actual distance along the leech by ever so slightly crinkling it up with thin tape.  Tape the sail on a flat surface so the leech is held firmly in position.  carefully lay some 4mm sail edging tape from the head to the clew positioning it right at the edge.  Lay the tape with just a slight amount of tension and firmly press it down.  Releasing the sail and supporting it by the head, tack and clew should now show the sail to have a curve from the luff to the leech.  If the leech is too tight it will curl in too much.  Simply repeat with less tension with some new tape.

The slight amount of curving at the leech will need to be removed or flattened with battens so the curl in the sail leech moves forward to the body of the sail.  I recommend at least 4 battens.  I have these about 1/3 of the chord and fairly rigid (more so than the ones supplied) and available from the RC yachting suppliers.  A taper over their length and a piece of reinforcing tape over their inner end end helps to encourage a smooth transition from a straight leech to curved sail body.  You may need to try a few times to get things right.  look at the images below to see how the sails can look with this treatment.  The black and yellow bands are there simply to show the curve in the sail and form no function in generating shape.



RC Yacht supplies

See the left hand column in the links page under the 'Play the Rules' section, the three most useful suppliers are listed with links to their address and on-line ordering web sites (click on logo image).

page last edited on 13/05/2012