MAINSAIL CUTDOWN for DIY sailors. Also add a reef to...

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People who would like to develop some basic skill in cutting down sails to fit their boat, please read on. These skills are easily adapted to repairing sails, and replacing the uv protection on furling genoas, but before we get started, I couldn't resist the temptation to put in a couple of snaps from my recent cruise.Can you see that box to the right of the last photo; It's a waterproof box for my 850 watt petrol generator. I made it out of thin hardwood ply. The interesting thing about it is that the top is kept on with webbing strap(blue). The two ends of the webbing terminate in ss shackles. The red cord is a lashing pulling the 2 halves of webbing together. Because the webbing is so strong, the lid retaining setup, doubles as a carry handle for the generator and box. See the end of this guide for other uses for webbing....

and Now back to the topic....


Sailmakers Awl used for punching needle holes through thick sail cloth and pinning sailcloth to plywood.

Needles required for hand stitching on sails.

Sailmakers hand stitching thread (whipping twine).

Sewing palm. For use with the above needles & thread.

If you need help with terminology, use a googl- search on the word sail. Click on Wickip--- the free encyclopedia and scroll down the page. There is a diagram of a mainsail with excellent nomenclature. Sorry about the cryptic clews but this guide does not allow links outside ebay.

If you are looking for a small mainsail, smaller than luff 9.9m x foot 3.4m, for example, Tophat25, Hood23 or 20, etc, a common solution at a reasonable price is to cut down an Etchels mainsail. The the total cost for this this work to be done by my sail-maker including a good Etchels mainsail, starts at $475 depending on the features required. Estimate correct at time of writing, updated 8.12.13. (Etchels mainsails in stock, winter prices, not just before Xmas) Etchels mainsails are usually made from a hi performance style of dacron which will last well. There is generally a good supply of these mainsails on the secondhand market. They are typically replaced after a couple of years of racing. A new mainsail will usually be slightly faster than a 2 year old sail and competitive Etchels owners are constantly up-grading.

The methods described in this text have all been used by me in my commercial activities. To some sail makers the methods would be described as a bit "agricultural". That's fair enough; if  you're making a new sail to sell, it will need a high standard of finish. That same high standard is not required to the same degree in cutting down second hand sails in my opinion. My focus is on functionality and DIY methods. However I cannot take responsibility for work that is not my own. If you use the methods outlined here, you must take responsibility for the result including any subsequent failure. This information is given in good faith with no guarantees.

           If you're in some remote area and your sail fails, the methods and products referred to in this guide can be a life saver. Or if the kitty is running low and you can't afford to buy a new sail, this guide can save you thousands and get you heading over the horizon with a feeling of confidence and self sufficiency. A tip; if you are about to throw away an old sail, keep the corners especially the clew and tack. Below the surface layer, is cloth that hasn't seen the light of day. It's almost as good as new cloth, and there is often a selection of weights, ideal for repairs and alterations. Some of my customers have sailed around the world, using the old sails to repair the new ones. A can of contact cement and a needle and thread can go a long way!


Cutting down a main as if reefing, is a relatively simple matter, well within the ability of the average handyman. This involves cutting a new shorter foot and of course a shorter luff. The alternative is to cut down a main by either re-cutting the luff or the leech. These two procedures are vastly more labor intensive than the former cut down.

The important criteria to be considered when trying to fit a main to a mast and boom setup. Neither the luff nor leech of the sail can be longer than the space available on the mast and boom. The luff measurement must be sufficiently less than the space available, to allow for stretch when the main is in use. A Cunningham eye is useful in adjusting luff tension, although not essential.

TOOLS: I plan to make available a range of sailmakers hardware, generally not available at chandlers, for the purpose of sail repairs. I only sell stuff that I use myself. To do the job properly and quickly, you will need the right gear. Don't try to save money on cheap gimmicks. It will cost more in the long run! and there may be no store in your favorite remote cruising destination.

Obviously a sewing machine will speed things up but is by no means necessary. A sewing palm and needle is sufficient for the stitching required. A good quality whipping is highly recommended. An awl or spike is required to punch holes through thick layers of sail cloth. Glue is required to hold components in place for stitching. Seaming tape is most favoured for this, although a hot melt glue gun can be very beneficial in some circumstances. These glue guns are available in most hardware stores and of course eBay. Cutting tools include large scissors and Stanley knife or box cutter.


    I frequently draw my sails out on A4 paper using a scale of 1cm to the 1m. Most sails will comfortably fit on the page using this scale, and it only takes a minute or two. Battens will generally be equally spaced apart. If the sail has 4 battens there will be 5 spaces between them. Divide the leech by 5 and mark the battens in position. Using a bit of artistic license you can easily approximate the roach and hence calculate the foot length you will end up with after cutting down (as if reefing the sail). It will help to get your head around the job and even to decide which sail can provide you with the desired result. You can see if the there is a batten pocket or reef patch in the way, and plan what to do about it. Most often a batten at the bottom of the sail can just be eliminated, if it clashes with the clew reinforcing. The clew reinforcing patch should be positioned in such a way as to leave no unsupported roach. 



Once the calculated luff length has been established, the sail can be marked. Similarly the leech can be calculated using Pythagoras or simply approximated to the desired angle of the boom. the approximate foot line can be marked using long batten or similar. the foot line should have a downward curve, to allow the foot to contact the boom. In the case of a loose foot setup, slightly less downward curve is desirable. If a dart is going to be built into the foot, to add additional fullness to the foot area, more curvature in the foot curve is required. I position the dart about 1/3 of the length of the foot, measured from the luff.  After the dart is created, a new curve must be cut.


A Cunningham eye or reef patch can sometimes provide a new tack or Cunningham for the cutdown main, if it's in the right place. Usually the whole tack patch, including all the multiple thickness part, will need to be removed from the sail, in a form suitable for restitching in the new position. If you are shortening the luff by a small amount, say 0.3m, then there may be a case for leaving the reinforcing where it is, and placing a new ring attached to what is left of the reinforcing patch. You can use a stainless ring or large shackle for this and stitch it onto the sail using webbing. Similarly the clew will generally have to be relocated to its new position. Often the leech line can be kept intact, and be used in the new cut down position. By opening the leech fold to keep the leech line in tact, the corner patch can simply be moved up the sail to its new position and the leech line pulled thru the corner patch and trimmed later. Notes: Unpicking zigzag stitching can often be done with a pair of scissors. If the lower blade ends in a point, this point can be pushed under the stitching to cut it. The blades need only be apart enough to pick up the stitching. I use a jerking motion to cut a few cm at a time. An oil stone or fine file can be used to keep the blade sharp.


Once the leech line fold is opened up, the corner patch can  be slid up the sail to the required position. The leech must be kept straight ie, in the same alignment. Sufficient overlap of cloth on the corner patch is required, to allow a minimum of three rows of stitching between the sail and  the corner patch. Generally some trimming of cloth from the sail is required to avoid covering the leech line exit and cleat or eyelets for securing same. If the corner patch needs to overlap a reef point, the corner patch may need to be trimmed to avoid covering the reef eye. this is easiest done with a Stanley knife close to a stitching line if possible. Once the corner patch has been located in its new position, it will be necessary to fix to the corner patch to the sail using various types of glue. A hot melt glue gun available at hardware stores is very useful for this, especially in damp weather. Double sided seaming tape is a little bit quicker to use in dry weather, available on eBay or sailmaker suppliers. Lastly contact cement can be used. Spray can glue is most convenient although not essential. Use news paper between the components to keep them apart until positioned correctly. If you are having difficulty flattening out he sail cloth, it can be fixed to a sheet of ply or custom board etc, using press pins. I have used medium sized nails for this in the past when I ran low on press pins. Just sharpen up the tips a bit so they go in easier. If the area of the sail you are working on is left flattened out for a while, say for a few hours or overnight, it is generally not necessary to fix the working area to ply in my opinion.


Generally the zigzag pattern of stitching looks most at home and professional. Don't load the needle with too much thread. No more than a meter, initially, and it's doubled through the eye of course and the ends tied in a simple thumb knot. This becomes the stop for the thread on the first stitch. You can rule a pencil line on the sail to get the stitching nice and straight. Since this method of stitching is so strong, there is no need to put your holes too close together. I seldom spaced holes closer than my little finger, and sometimes as wide as 2 fingers. The real secret to a very strong and good looking line of stitching is to double back through the line of stitching, back to the beginning. On the way back to the beginning, the thread is going back through the same holes in the opposite direction.If a nice tidy job is done this way, the line of stitching will resemble a very heavy machine stitch. It's always rewarding to complete a professional looking job, and once you develop a rhythm, it can be completed surprisingly quickly. The sail makers palm can speed things up where there is only a few layers to push the needle thou, not enough thickness to warrant  punching holes with a spike or awl. There are few new sails made even today without some hand stitching. If you are trying to get your needle through many layers and it won't pull through with fingers, then a pair of pliers is handy just to grab the end of the needle and pull it through.


I've got an awful lot of stuff that I need to sell. It's just a matter of time before it hits the store. If you need anything in particular please let me know. The stuff that has made it to the store so far can be viewed by selecting the category; "Sail Repair Hardware " after clicking on the red store icon. The store icon is towards the top right of this page.


One of the most common problems with second hand sails is the problem of eyelet corrosion which can lead to a major eye pulling out of the sail. eg clew or tack eyes. Webbing is frequently used to overcome this problem. The following photos show a recent tack eye reinforcing that I did to a #4 storm jib. The tack eye and wire were starting to rip away from the foot tape. It's not real pretty but I was in a hurry, and I left my palm and glue gun on my boat. So this is what you can do in about 15 to20 minutes even without all the proper tools. I am using an old bit of ply as a backing board to make the needle holes through the sail cloth using an awl.

These photos are not that good, and I will get some better ones when I can. It's important to glue your repair materials in place before you start sewing. Any type of glue is ok but my preference is the hot melt glue gun, but any contact cement will work, maybe even superglue.  


I guess if you have read this far, you may have got something useful out of it. Don't be afraid to get an old sail and have a go. That's how you're going to become a pro. My first alteration was on an Etchells main. It was pretty crude thinking back to the early 1980's. Still, it worked for many years on my first 35' Wharram cat. I eventually converted it to full length Battens and added reefing points and it was still going strong when I sold the boat many thousands of miles later. Each sail job I have done since, has looked better and been done quicker. It's the practice that makes the difference. I've earned a lot of money doing sail repairs and alterations and have enjoyed it. Skilled people are in very short supply in this country. If you develop these skills you will be in demand. That's partly how I started this business. Good luck in your endeavours.

      Thanks for reading this guide and if you have any feedback it's most welcome. Sailing is one of the true adventures still available in the modern world. Enjoy! 

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