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post #5 of Old 05-25-2004
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Fractional vs. Masthead Rig

I think that Silmaril hit the nail on the head, if you are looking for a rig that is simple and requires the least amount of ''fussing'' then a masthead rig makes sense because there is less that can be done to alter its sailing characteristics (without reefing or changing sails). This simplicity comes at the price that for any particular sail combination there is a vey narrow range of windspeed that works for that sail combo at least as compared to a fractional rig.

For any given actual sail area, properly sailed a fractional rig will offer better performance and be easier on the crew on all points of sail. The key phrase there is "actual sail area". When you look at race boats, many racing rules result in masthead rigs getting an advantage in ''unrated sail area''. Masthead rigs are a little faster in races sailed in a narrow range of conditions under rating rules that under penalize unrated area.

This means that in real life, if you are buying a boat mostly to go racing and want to race under a rule that underpenalizes overlapping jibs and spinnakers, then a masthead rig makes sense as long as you can afford to sail with a larger crew and maintain a more expensive sail inventory. (The C&C 99 has a masthead rig as a racing rule beating ploy more than any other reason.)

If you want to go cruising, or choose to race under a rule like the IMS rule (or to a lesser extent PHRF) that treats all sail area more fairly, then a fractional rig would makes more sense.

I did want to comment on Silmaril''s points:

Silmaril says that "a masthead rig is faster on all points of sail", all of the wind tunnel and actual in the field testing literature disagrees with that when taken on an absolute sail area basis. For a given actual sail area, fractional rigs with non-overlapping headsails, are actually the most efficient sailing rig meaning offering the best performance per square foot of sail area. So I think when Silmaril says that the masthead rig is faster on all points of sail, it is not that a masthead rig offers better performance for a given sail area, but as mentioned above it has a rating advantage under some racing rules. That advantage really goes away quickly in the case of rating rules that permit fractional rigs that use masthead spinnakers but then the smaller crew and easier handling advantage of a fractional rig goes away as well.

I also disagree that fractional rigs by their very nature need to be more complex. Racing masthead rigs are argueably more complex if they are to match and the performance of a fractional rig. While it is true that fractional rigs benefit more than masthead rigs from having a wide range of backstay adjustment. Backstay adjustment on a fractional rig quickly powers up and down both the jib and mainsail with one adjustment. Once you get used to having that tool it is very easy to use (Too much helm pull it in, too little speed, let it out) It is actually easier to use and far simpler than the combination of a babystays and adjustable backstays which is the masthead rig''s equivilent of a fractional rigs mastbend control systems.

With regards to running backstays, most traditional and modern fractional rigs do not use running backstays, any more than masthead rigs continue to use checkstays. It is only on boats that are designed with very bendy rigs that runners are still employed to fine tune forestay tension but then again, masthead rig boats with very bendy rigs end up with checkstays which in effect are less forgiving running backstays. (Most bendy rig frac''s can live without their runners but few bendy rig masthead righs can live without their checkstays being handled.)

That said cruising fractional rigs will sometimes rig running backstays in heavy weather in much the same way that cutters and sloops with a storm jib mounted on its own stay will rig runners in heavy going.

Anyway, here is my reply to an earlier discussion on this topic. Much of it is similar to Silmaril''s points and it was aimed at a person who was not clear on the definition of the two rigs.:

"These terms both derive from the point at which the forestay hits the mast. On a masthead rig the forestay hits the mast at the masthead (top of the mast). Masthead rigs are far and away the more common of the two rigs. It came about as a rule beating method for racing sailboats. Under the CCA and IOR racing rating rules, jib size was under penalized. This promoted small mainsails and big jibs.

On a fractional rig, the forestay hits the mast somewhere below the masthead (or a fraction of the overall height of the mast. It is not unusual to see fractional rigs referred to as a 2/3 (Folkboats), 3/4 (J-24) or 7/8th’s (Triton) rig, 90% (Farr 40).

Each rig has it advantages and disadvantages. There are some big advantages to a fractional rig for cruising and racing. For cruising you are dealing with smaller and easier to handle headsails Not only are the headsails smaller because of the shorter headsails but, because the headsails represent a smaller percentage of the overall sail area, you don’t need to have overlapping jibs. The sail area is made up in the mainsail.

Fractional rigs often have purposely designed flexible masts and, when combined with a backstay adjuster permits quick, on the fly, depowering of both sails. On either rig, mainsails are easier to slab reef in a manner that results in an efficiently shaped sail for heavier conditions. On a fractional rig that means that you don’t have to take the expense, complication, maintenance and performance hit of a mainsail furler. Controlling mast bend you can often avoid reefing the mainsail or furling the genoa as the winds build. Roller furling genoas have notoriously poor shape when partially furled. The smaller jibs of a fractional rig rarely need reefing and when they do the fact that they are often minimally or non-overlapping results in a better partially furled shape.

Masthead rigs typically have larger running sails and so can typically point closer to dead down wind. They are a little more forgiving. Because Fractional rigs permit such a large range of easy adjustment they can be trimmed through a range of adjustments that results in a bigger range of speed both slower or faster than a masthead rig of similar sail area. The limited adjustment of a masthead rig means that you more or less live with what you have. Therefore a masthead rig neither has the opportunity for going really faster and with less heel, or going all that much slower either (although jib sheet lead angles are way more critical on a masthead rig and require more skill from a performance standpoint than any other adjustment on either rig) as a result if sail trim is not your thing, then the masthead rig''s lack of adjustability would perhaps make more sense.

My biggest problem with Masthead rigs is that you really need to carry more headsails and make more headsail changes. This is partially a function of the responsibility of the jib for drive. If you take a Fractional Rig 100% jib on a 28-footer it might be 150 s.f. and its 150% Genoa would be 225 square feet. But on a masthead rig 28 footer the 100% jib might be as much as 225 to 250 square feet and its 150% Genoa would be 337 S.F. to 375 s.f. That is a really big sail to manhandle and the when you increase a sail by 125 S.F. vs. only 75 s.f. there is a much smaller wind range that the bigger sail can be carried in so you might end up also carrying a number 2 Genoa as well as a working jib and a 150% #1 Genoa. With roller furling you end up sailing more frequently with (much less efficient) partially rolled up sails.

I strongly favor Fractional rigs for coastal sailing because the are so much easier to tack and jibe, you are not carrying around the big winches heavy weight rigging, and as many large sails, and lastly are not subjecting the boat to the much higher rigging loads of a masthead rig."

I was a little disappointed in the ''Sail'' magazine article. It seemed a little dated and seemed to be light on discussion.


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