Masteheaded Vs Fractional rig

Discussion in 'Sailboats' started by mholguin, Oct 2, 2006.

  1. mholguin
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    mholguin Junior Member

    Can somebody explain in plain english waht are the advatanges a fractional rig has over a mastheaded and viceversa?

    Nothing too deep...
     
  2. Finlander
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    Finlander Junior Member

    Ok, nothin' too deep here, otherwise I'll drown rather quickly... :)

    It is my understanding that the most efficient stayed-rig is one that has a jib without overlap. Instead, the sail area should be weighted toward a big mainsail. Large, overlapping Genoa's are used for certain types of racing, but that's because the overlap isn't counted toward total sail area; otherwise they're not especially efficient.

    Hence, a fractional rig helps to satisfy the goal of having a small non- or only slightly- overlapping jib and large mainsail, because the mast can be placed further forward.

    Someone please correct me if I'm wrong; this is only derived from something I've read. I'm not an expert in the theory of rig design.

    Kristian
     
  3. jarhead
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    jarhead Junior Member

    sounds good,kristian. no jib at all is even better, in my view. on a boat up to about 7 metres, you can use a cat rig and forget about jibsheets and backwind. for bigger boats a small jib on a club will take you up to 9-10 metres.
     
  4. RHough
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    RHough Retro Dude

    A single element foil ala cat rig cannot develop as much lift for the same area as a split sail plan. In conditions where the boat can use the maximum lift for a given area a large main, small jib combination will produce more power. A single foil has a CL limit somewhere in the .9 - 1.1 range. A multi-element sail has a CL max of 1.6-2.0, the potential for almost twice the power for the same area.

    If you look at classes that have a sail area limit, after some extreme experiments, they all end up with the fractional rig, large main, small jib configuration. In classes like 18 foot skiffs, even though there is no limit to sail area, they have chosen the large main, small jib combination also.
     
  5. gggGuest
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    gggGuest ...

    Actually that's not quite true. There are several single handed dinghy classes where a single sail is preferred, notably the A Class Catamaran and the Moth.

    But agreed, you never see big overlapping jibs or masthead jibs.
     
  6. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    For upwind work, tacking, it's convenient to have a small jib.
    For downwind sailing maybe a large genoa or two, one on each side is easier to manage than a spinnaker.
    So masthead rigs may be good for cruising while fractional rigs are better for racing, also because you can trim the main with a backstay (bend the mast top).

    Just my impression :)
     
  7. mholguin
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    mholguin Junior Member

    Good answers. I think I understood. But of course, a follow-up questioon:

    In a boat rigged as masthead, using a smaller jib (say a No. 3 or 2) is not as efficcient as the No1 for winds around 15 KNots... this would be because a masthead rig places the head sail too forward? Or can any boat benefit from using a smaller jib?

    Before somebody asks to test it myself, we are currently restoring our boat, a Tartan 30C. There are no plans to re-rig her, just curious to see what would be faster....
     
  8. Vega
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    Vega Senior Member

    They say it better than I can, but I agree with those Guys:

    “In my sailing experience I have learned to prefer a fractional rig to a masthead version, whether cruising, racing or daysailing.
    .................
    So why are so many cruising boat built today with masthead rigs? For one reason they are simple and cheap. The mast is usually just a straight un-tapered extrusion. For another reason, builders seem to be reluctant to change, a problem in our industry that has stifled growth and innovation. The masthead rig is largely an anachronism left over from days when the racing rules gave favored treatment to boats with masthead rigs. This is no longer the case, but cruising boat design was adversely influenced for years by handicap rules, even though most boats never see the starting line”.
    ................

    http://www.rcryachts.com/fractional.htm


    .... “The fractional rig was first used on race boats, as it gives more control in raking the mast with an adjustable backstay giving more control with mainsail shape.

    These rigs are used mainly because they offer better performance. The larger mainsail increases performace downwind and in light airs. The downside is that the big mainsail can overpower the boat in heavy winds and you should reef sooner rather than later. However, because of the greater control you have with mainasail shape, by tightening the backstay, the draft of the sail moves farther forward, increasing stability to windward in heavy conditions. In light air, releasing the backstay puts more camber back into the main and it offers plenty of power.

    The fractional rig makes for a very good racing rig and cruising rig. The headsail is smaller and there is no inner forestay, forward lowers or large overlap to slow down tacking the jib. The smaller headsail means faster tacking and less physical effort for the crew - good for racers and cruisers! Many fractional rig boats sail nicely under main alone which is another bonus for cruisers.”

    http://marina42.net/cgi-bin/p/m42p-custom.cgi?d=passage-yachts-inc&id=615


    “I like the simplicity and strength of the masthead rig but I like the versatility of the fractional rig. My own boat has a fractional rig. Fractional rigs are pretty”.

    (Robert Perry)


    Perhaps there is one case were I would prefer a Masthead Rig, and that’s if that rig is for a Cutter.
     
  9. RHough
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    RHough Retro Dude

    You are right of course. I should have said ... Except for single handed boats ... :)
     
  10. mholguin
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    mholguin Junior Member

    Veda:

    You made me realize that is not simply a matter of headsail size... the fractional rig has clear advantages over a masthead, when it comes to shaping the mainsail thru mast bend. That would be hard at best with our masthead as the mast is quite old and with an elipitical cross section.

    Question still remains on on a mastheaded being able to perform better with a smaller jib...

    Thanks guys, this is going great...
     
  11. Finlander
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    Finlander Junior Member

    masthead v. fractional

    I also wouldn't switch to a fractional rig if the boat wasn't originally designed for it. There's probably not much advantage unless the mast was placed far forward in the first place. Then again, consider this....

    <begin slight digression> But first, my preference---and I plan my next boat using this concept---is to have a small, boomed, self-tending jib. Perhaps it will be extended by a bowsprit. However, a boomed jib and bowsprit might not easily work in your case. That's because you have to consider the geometric center of effort---it might mean changing the mainsail-traveller's position further aft, etc.... <pardon my digression>

    Nevertheless, a moderately-sized working jib is still a good idea. I always prefer it over a Genny for upwind and close reach conditions---even in light winds. But for a broad reach in light conditions, I prefer a cruising spinnaker or blooper (I can't remember the correct terminology these days). Not a full spinnaker in any case.

    And for dead-downwind sailing, consider that mainsails aren't great because the boom can't extend beyond the sidestays (generally, free-standing masts rule in this regard, but they appear to be very expensive). Hence, many stayed-rig sailors prefer to tack downwind to improve speed and comfort and also to avoid jybing.

    So, to enable acceptable, dead-downwind performance, I'd want dual wing to wing headsails (as was mentioned in a previous post), but with no mainsail. For example, it could have a cruising spinnaker, plus the small working jib opposite. If the working jib jybes, then it's no big deal; just keep focused on the cruising spinnaker.

    In any case, this is where I see a benefit to a fractional rig: The short jib would probably interfere less with the cruising spinnaker---assuming that the cruising spinnaker is pulled to the masthead.

    No matter whether you ultimately choose fractional, masthead or a combination of both, you might consider dual-headstays, depending on the type of cruising spinnaker you choose (some attach to a headstay, some don't), and of course, dual-halyards. IMO, a good downwind rig will increase your sailing enjoyment more than anything else. Plan accordingly :cool:
     
  12. mholguin
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    mholguin Junior Member

    I think I was misleading in the way I formulated my questions.

    we are currently restoring a Tartan 30C. We are not considering any modification onf the rig. I was wondering, if first fractional rigs had any advantage over mastheads, and -back to our boat- using smaller than 150% jibs and trimming the mainsail better would yield better performance.

    Back in the days we used to race, we used the 150% as much as we could, by reflex if you will. I guess the question is now, considering that in a fractional, the small jib/big main works so well, if the same can be applied to a masthead, using a smaller jib to get better? performance.... I guess I'll have to wait to have the boat fully repaired....
     
  13. Finlander
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    Finlander Junior Member

    double headsail

    You're not planning on racing are you?

    I know I'm not exactly answering your question, but here's how I dealt with a similar issue as you're facing....

    First, I'm a cruiser; not a racer. One thing that I never liked about 150% Genoas is that the low foot tends to obscure viewing. Naturally, the clew can be raised, but then weatherhelm suddenly increases. Care must be taken to keep the rig balanced.

    In my case, I trimmed both foot and leech to make the the whole thing smaller. Scary! And to counter weatherhelm and also to maintain adequate sail area, I added a boomed staysail to effectively transform the rig into a double-headsail ketch.

    It was a relatively simple task, but before cutting and drilling, I first tested the rig by adding a temporary staysail and fastening the jib-sheet blocks further aft, etc. to simulate the intended balance.

    Ultimately, the smaller jib and self-tending staysail made things easier to handle and improved visibility. Plus, the sail area actually increased. Since the smaller sails seemed to hold their shapes better, sailing characteristics improved under all conditions. There was probably some extra speed, too.

    So, to answer your question as specifically as I can: Yes, IMO, a small masthead jib is better than a Genny. But keep overall sail area in mind---think about adding a staysail if necessary and possible. I know you stated that you're against modifications, but this isn't a big one ;) And it only works if you're not confined by racing rules of course.


    Kristian
     
  14. gggGuest
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    gggGuest ...

    Arguably any gaff or gunter rigged boat is effectively a fractional rig.
     

  15. sharpii2
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    sharpii2 Senior Member

    The biggest advantage I see I a fractional rig is balance. In every one Iv've sailed on, the first step in reefing is dropping the jib. In every occasion I have done so, I have successfully shortened sail without creating a monster weather helm. The next step in reefing is taking a slab out of the main. But if merely dropping the jib will do, it's easy enough to hoist it again very quickly.

    With a masthead rig, I don't think you can get away with that. Once the jib, which is usually larger than the main, is dropped, The Center of Area (CA) of the rig moves way aft which can create a wicked, maybe uncontrollable, weather helm. The cure is to hoist a smaller jib, or reef the original jib, then take a slab out of the main. Without roller reefing, this can be a lot of work. Especially when you are out alone.

    The main advantages of the masthead rig are that:
    1.) it can carry more sail on the same height of mast and
    2.) it is enormously strong for its weight and level of materials technology. It is possible to make a masthead rig that is all but indestructable with relatively inexpensive materials. George Buehler claims that a masthead rig of his design was hit by a seaplane and was still standing afterward. (the seaplane didn't do as well). I have read accounts of vessels with such rigs being rolled completely over and having the rig still completely in place.

    Also, the CA problem can be easily solved by going to cutter or ketch rig. Maybe thats why you occasionaly see very small, under 30ft, masthead cutters and ketches.

    I hope this helps.

    Bob
     
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