Fractional Rig vs. Mast Head Rig - SailNet Community
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post #1 of 67 Old 01-06-2008 Thread Starter
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Fractional Rig vs. Mast Head Rig

Currently have a 26' day sailer. I am pondering a future purchase of a bigger sailboat for coastal cruising. I am looking at boats in the low to mid 30' range. Mostly I would be sailing solo so that is a factor.

I see some boats in this range have fractional rigs while others have mast head rigs.

Looking for some background data on what the real difference is.

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post #2 of 67 Old 01-06-2008
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A fractional rig tends to put proportionally more sail area into the mainsail. Headsails tend to be smaller than on mast-head rigs, so they generally are easier to manage for tacking/jibing. Fractional rigs have been common on racers and racer cruisers for a long time, but there seems to be a trend in the last decade or so to move towards moderately fractional rigs even on performance cruisers. The feeling is this arrangment facilitates over-all sail handling and generally is advantageous to over-all performance.

One thing to avoid is a fractional rig that requires the use of running backstays. Running backs have to be switched from side to side during tacking and jibing, so they make for a lot of extra work and would not be welcome on a boat that is short- or single-handed. You tend to see runners on performance oriented boats that are 3/4 or 4/5 fractional and which race with crew. Most performance cruisers tend to be closer to 7/8 or 9/10 fractional, with aft swept spreaders, so the well-sprung rig geometry does not require runners.

Another disadvantage to some fractional rigs is that it can be tricky to fly a cruising spinnaker (such as an asymetrical) at deep angles if the spinnaker is also fractional. Boats so-rigged will tend to have to steer much higher reaching angles to avoid blanketting the spinnaker with the taller mainsail. Conventional, poled-out spinnakers often work best with these designs. Fortunately, many of the more modern fractional cruising designs have a masthead spinnaker arrangement, which permits the use of the pole-less cruising spinnakers at deeper angles without too much penalty.

Also, if bridge clearances are an issue, fractional rigs tend to be taller than masthead rigs would be for the same size/type boat.

Our cruising boat is a mast-head design that works well for us. But the sketches we have of our "ideal" boat has a fractional rig. I wouldn't recommend making the mast-head vs. fractional issue the ultimate litmus test for your next boat, but I definitely wouldn't disqualify fractional boats from your potential candidates unless some of the issues I mentioned above apply to you.

Last edited by JohnRPollard; 01-06-2008 at 01:13 PM.
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post #3 of 67 Old 01-06-2008 Thread Starter
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Good info. Thanks. My current boat is fractional with no backstay. I was not real sure what a "running backstay" was so I will definitely try and stay away from less thing to worry about.

I also have no experience with a spinnaker so that piece of info is also good to know.

Thanks again,
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post #4 of 67 Old 01-06-2008
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Re: Running backstays

Once you get beyond the dinghy/daysailer size range, most fractional rigs will have a conventional backstay. On performance oriented-designs that are more aggressively fractional (say 3/4 or 4/5), the backstay will usually be very lightweight and is used primarily for adding or reducing mast-bend. In these cases, the primary support for the mast will come from running backstays (sometimes called check-stays and by other names).

The runners are attached on both sides of the mast (port and starboard) at the same height where the fractional forestay attaches to the mast. The runners counteract the force applied by the forestay, just as a conventional backstay would counteract the force applied to the mast head by a conventional headstay. If the forestay was not balanced by the runners, it would bend and pump the mast as it became loaded up in strong winds.

Since the runners are attached on both sides of the mast, and lead from there to the stern of the boat, you can see how they could interfere with the mainsail. So only one can be used at a time -- the windward one. The leeward one, the "lazy runner", is eased to slack so it won't interfere with the mainsail. When tacking or jibing the runners must be switched by easing the working runner and taking up on the lazy runner until their roles are reversed -- in much the same way as we swap jib/genoa sheets.

Like I said, most cruising oriented fractional rigs, and even many performance oriented rigs, dispense with running backstays by using a less fractional rig with a swept spreader and shroud geometry that adequately counters the forestay. Also, fractional boats aren't the only ones that use runner/check stays. Many mast-head, cutter-rigged cruising boats use runners when flying their staysails in heavy going. Hope this helps some.

Last edited by JohnRPollard; 01-06-2008 at 02:25 PM. Reason: clarity
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Thanks again.
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post #6 of 67 Old 01-06-2008
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Good posts, John, as usual.

We have owned both masthead and fractional boats, and esp for shorthanded cruising prefer the fractional rig. I'd agree with JohnR that when cruising you should avoid "necessary" running backstays, because that is a chore that pretty much requires an extra body.

By "necessary", I'm referring to boats whose rigs are so spindly that the integrity of the rig is compromised if the runners are forgotten or mishandled. This mainly applies to straight-on race boats (but many "out-of-date/noncompetitive racing designs end up being converted to "cruisers") so you may run into this scenario.

Most more moderate fractional rigs will use runners, but their job is primarily to provide and maintain headstay tension. In a masthead boat the backstay can provide this function.. on most jumper-less fracs tensioning the backstay will mostly bend the mast, little of the force is transferred directly to the headstay. Runners do provide that tensioning force as the wind pipes up. This aids pointing ability and keeps the sail shape as the sailmaker intended it to be.

Our 35 footer with a 3/4 frac rig came with runners, but the rig is robust enough to use without them. The price of the convenience of not using them is some pointing ability as mentioned above. Since we do not race this boat we, so far, have been satisfied with using the boat this way.

However we recently added a furler, so it may prove to be more advantageous to replace the runners... we will see, but prefer to sail without them if we can (we are almost exclusively doublehanding)

We like the frac rig because it keeps the headsails smaller, lighter and more manageable (sheeting loads are down as well) and, more importantly, the spinnakers are much smaller and easier to handle than their masthead counterparts. As a result we fly our spinnaker MUCH more than we ever did with our previous boat, a 40 foot masthead boat, whose kite could be a real bear to deal with.

The other advantage (IMO) of many fractional rigs is that since there is more power invested in the mainsail, the bulk of your sail area can be well managed with a good mainsheet/traveller system. These types of boats will also tend to sail better under main-only in more extreme conditions.

Nothing wrong with either, as John says frac/masthead should be a secondary consideration beyond other more important criteria such as construction, layout, equipment and condition, but it was on our "nice-to-have" list this last time after dealing with huge genoas for 12 years.


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post #7 of 67 Old 01-06-2008
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Like Faster, we have a fractional rig that doesn't require using running backstays most of the time. We do bring them out when the wind gets up to about 30 knots and the seas build above 5', making the mast start to pump. We find the smaller jibs easier to tack quickly (for racing). The large main is easy to reef if we need to reduce sail without having to go out onto the foredeck.
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post #8 of 67 Old 01-06-2008
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I also own a fractionally rigged boat which does not require running backstays. My boat was sailed in from South Africa on her own bottom without them. I typically sail with a 110% jib except in the lightest breezes at which time I shift up to a 130% jib. The boat is fast and easy to handle on all points of sail. The following was a piece that I wrote for another purpose on this subject.....

Fractional vs. Masthead 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. Historically cruising and racing boats were fractionally rigged. The Masthead rig came into popularity as a racing 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 masthead jibs and spinackers.

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.

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 often do not 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. Mainsails are easier to reef in a manner that results in an efficiently shaped sail for heavier conditions. It 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 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 non-overlapping results in a better partially furled shape.

Masthead rigs 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 much slower either.

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 and as many large sails, and you are not subjecting the boat to the much higher loads of a masthead rig.
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post #9 of 67 Old 01-07-2008
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I kind of had a slight idea of the differences. but this thread is very instructive. thanks for starting it and thanks for the answers.
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post #10 of 67 Old 01-07-2008
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We have a masthead rig with a baby-stay. Both the backstay and the babystay are adjustable, allowing us to induce mastbend and have the same adjustable sailing characteristics as described above.

We use hanked-on sails and a downhaul to drop headsails in virtually no time flat if we need to.

Honestly, up to about 25-28knots, she is fine with a no.1 heady... If it looks like a day that is likely to deteriorate, we will just start with the working jib, and have the no.3 blade standing by in case things get really bad.

At 26 feet our boat's biggest baddest headsail is still a manageable size...though if the boat was a 38footer I would likely be less enthuised about the masthead rig.


Last edited by Sasha_V; 01-07-2008 at 06:34 AM.
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