PolySail International

High Performance/Low Cost Sails for Small Sailboats

 

 

BERMUDA and MARCONI SAIL

 

 

The modern Bermuda sail, sometimes called a Marconi, is usually a high aspect, jib-headed, triangular mainsail carried on a tall, stayed mast and is known for its ability to help boats point more closely into the wind. Often made of high tech synthetics, Bermuda and Marconi sails today are often shaped and heat shrunk over hydraulic forms by high end sailmakers such as North Sails™.  The Bermuda sails usually depend on a heavy boom along the foot of the sail to help pull the sail into shape. Control lines include an outhaul near the clew which is used to help control the shape of the foot, a vang located on the boom and attached to the base of the mast to help pull the boom down, a halyard used to haul and douse the sail, and a mainsheet to control the angle of the sail relative to the wind. For more details and history about this sail and rig, go to this site: http://en.wikipedia.org/wiki/Bermuda_rig

 

This sail is said to have developed from a leg o’ mutton sail, but unlike the leg o’ mutton, the foot was more horizontal and it was initially flown boomless. Flown loose-footed on an unstayed mast with only a mainsheet for control, it is probably the simplest of all sails to fly, but without that boom, the sail requires that the mainsheet come off the clew at an angle that splits the load evenly between the leech and the foot in order to function properly. Having a boom eliminates the problem of having to place the sheet so that the load on each sail edge is evenly divided.

 

Bermuda and Marconi sails are one of the more difficult sails to construct from polytarps. Proper rounding and carefully placed darts are especially important with these sails. Begin as shown in the instructions by stretching out the tarp, weighting the corners, and marking out the dimensions of the luff, leech and foot with an erasable marker or with a retractable metal measuring tape of suitable length. Roughly cut out the sail shape allowing about 10” of material beyond the marked dimensions so that you can place V-Darts in the sail before taping the edges. Next, place a V-dart in the tack that roughly bisects the foot and luff. I usually make the length of this dart approximately 1” for every 1’ of luff length so that a sail with an 18’ luff would have a 18” long dart. The closed base of the dart is about 1” for each 10’ of the foot, so that a sail with a 10’ foot, for example, would have a closed base of 1”. Thus, for a sail with an 18’ luff and a 7’6” foot, the polytarp sailmaker would cut a long triangle of double-faced tape that would be 18” long and ¾” thick to form the dart. In smaller Bermuda sails, a few inches of rounding in the luff and foot will usually provide enough camber (wing shape) for the sail to work well, but with sails having the combination of a luff of over 15’ and a short foot, I recommend placing small additional V-Darts in the sail as indicated in the diagram. Generally, these darts will be less than 1/2” x 8” for a sail with an 18’ luff.  On some larger Bermuda sails, I sometimes have to add a very small V-Dart in the foot and/or leech, as well. Much depends upon the weight of the tarp being used, how much wrinkling there is in the body of the material, and how well the reinforcing rope draws up the edges. The heavier the weight of the tarp material, the more these extra darts seem to be needed. Do not be too quick to add extra darts, however, because we only want about 10% camber in a Bermuda sail.

 

The leech can also be rounded in a Bermuda sail. However, if you choose to round the leech for additional power, you will need to support this extra roach with battens. If the roach (or rounding in the leech) is fairly small (not more than 5” from the straight baseline), then you can make a simple batten pocket out of the edge material from the tarp, then use one or two bamboo skewers (available from WalMart for about $1.00 per hundred) for your batten as shown in the pictures below. Note how these battens support the leech in the lightweight (3.1 oz./sq. yd.) sailboard-type sail below. These batten pockets are added after the sail has been completed and must be sewn down.

 

After completing the darting, the next step is to outline the sail perimeter with double-faced tape. If you’ve chosen to have a straight leech, place double-faced tape along the leech without any rounding from head to clew. If you’ve chosen to have some roach in the leech, round the leech by about 3” for each 12’ of leech length. The greatest rounding will be about 40% of the way down the leech from the head of the sail as shown in the darting diagram above. In the luff of the sail, add about the same amount of rounding (3” for each 12’) so that the largest amount of rounding is about 35% up from the tack of the sail. Make certain that the tape shows a fair curve in all cases. For the foot, use about 3” of rounding for each 6’ of foot length. Place the apex of the tape curve about 45% back from the tack. For triangular sails, it is also a good idea to square off the head by about 3”. Note the edge rounding in the Bermuda sail for a Holder 12’ below. The window is necessary because this sail nearly sweeps the deck on this little boat.

 

Once the taping is done, follow the instructions to place the rope reinforcement line and reinforce the corners with edge material and tape. Using this tested technique will allow you to make very strong corners for your sails. Follow this link to see a humorous YouTube video on how these corners have been thoroughly stress tested: http://video.aol.com/video-detail/sail-testing/3738715166  Make certain your sound is turned up so that you can appreciate the vocals of Eileen Quinn. Some of the photos in the section below show alternate taping and window techniques that can give different looks to your finished sails.

 

Striped, squared-off head on a Holder Bermuda Sail.

Rectangular window and striped clew treatment on a Bermuda Sail

Angled window and tack taping in an 85 sq. ft. Leg O’ Mutton sail.

Tack treatment on a smaller 65 sq. ft. Leg O’ Mutton Sail

Head and luff treatment on a high aspect Bermuda sail being carefully inspected by the family cat.

Clew taping on the 85 sq. ft. Leg O’ Mutton sail. Look carefully and you will notice that the leech overlap is narrower than the foot.

 

 For small dinghies, you might need to add a jib and/or a spinnaker to get the best performance from a Bermuda sail, especially on a downwind run.

 

Because Bermuda sails are difficult to make from tarp, I strongly recommend modeling these sails to scale with graph paper before beginning the build. Click on my sail shaping article for directions. However, keep in mind that any modeling or math-based programs for darting or shaping polytarp sails do not take into account such factors as the wrinkles that remain in the body of the sail when it is being constructed, the edge stretch resulting from the use of different weights of tarp material and different types and sizes of reinforcing rope, and the methods used to form the edges and corners of the sail. All of these factors enter into the final shape of a polytarp sail. But the beauty of a tarp sail is, you can afford to experiment to find the perfect shape.

 

 

 

PolySail International

2291 SE Gaslight St., Port St. Lucie, FL 34952-7332

 Email polysail@polysail.com or call Dave Gray at 317 385-3444

PolySails–Sold on the Web since 1996. Customers in all 50 states and around the globe.

 

This page updated on 10/30/2009