Free Standing Mast on a Catamaran

Discussion in 'Multihulls' started by Owly, Oct 19, 2018.

  1. Owly
    Joined: Oct 2016
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    Owly Junior Member

    I'm an advocate of free standing masts...... They eliminate a huge number of potential failure points, and the additional material in the mast is often very nearly offset by the elimination of stays, shrouds, spreaders, chainplates, and countless pieces of hardware.
    There seems to be a general consensus that they will not work on multihulls due to the stability characteristics, but I question that....
    A multihull reacts to gusts, etc, by accelerating, or with the daggers up, sideslipping. The shallow draft and relative light weight, lack of ballasted keel, etc, make them a very different animal from a monohull.
    There is also an argument .... fallacious IMHO, that claims that the bridge deck is not strong enough to carry a free standing mast. The truth is that the down pressure is a tiny fraction of a stayed mast, and the step on a mast beam can easily take down pressure as well as lateral loads, and the bridge deck itself is well able to take fore and aft loads at the step. The partner is another matter, depending on the cabin room to distribute the horizontal plain loads that would be taken by stays and shrouds. Bury may be as little as 5', so these horizontal loads are far higher than they would be on shrouds and stays. In some designs, a bulkhead is optimally located just fore or aft of the mast, which spans the entire boat, and could easily be "enhanced" to carry these loads with very little additional weight. Loads in other directions such as fore and aft would need to be carried and distributed by the cabin roof, though often the designs with a bulkhead have a fore and aft bulkhead dividing two berths forward of the saloon, and this could assist by transmitting loads forward to the next bulkhead, where they would become bending loads ... up and down on that structure. I consider this all very doable depending on the structural design of the boat. More difficult would be the situation where a mast beam bisects the saloon, with the roof only to distribute the loads.
    Free standers on cats and tris are almost non-existent. Here are two photos of cats with an Aerorig...... hopefully these will come through as an attachment. The aerorig is hardly the only rig possible with a free standing mast.
    '
    H.W.

    [​IMG] aerorigcat.jpg
     
  2. JamesG123
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    JamesG123 Senior Member

    For one very large failure point. Its possible for a rig to survive the failure of a stay. It is not possible for a rig to survive the failure of the mast.

    The difference in mass between a suspended vs. free standing mast isn't just the standing rigging and the mast itself, but also the structure necessary to support that mast. Down pressure, ie; compression load, isn't an important factor of a mast compared to all the other loads a mast sees. Without being able to spread that load across many points of the hull which generally already have sufficient structural strength to maintain hull integrity, extra mass and volume most be devoted to the roof, bulkheads, and foot step to hold the mast in double sheer.

    The distinction between multi or mono hull configuration is a minor one with the exception that single hulls heel to relieve wind load on the mast and rig. A cat does not, so side loading on a mast gets even more critical if all of that stress is concentrated at the base of only the mast. Which requires a stronger mast and structure mass, up high in the boat where you don't want it. Compared to the above, that you have a column intruding into your bridge salon is trivial.

    If you like free standing rigs, fine. I like them too. But don't pretend there is no trade off.
     
  3. Owly
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    Owly Junior Member

    James:
    I addressed most of the issues you brought up. I don't see the structural challenge as a huge problem on a cat with a bridge deck cabin for the reasons I mentioned above. In the optimal design for this, there is a bulkhead already in place spanning the entire width of the boat, which is designed to take the compression of a mast with standing rigging..... there are obviously virtually no compression loads except the weight of the mast and sails on a free standing mast.... trivial numbers. The use of inexpensive carbon tow to distribute loads out from the partner so it is distributed into the hulls does not represent a great deal of weight, nor does the mast bulkhead require much addition of structure, as the structure designed to carry the compression loads of a stayed mast is fairly well adapted out of the box to handing the lateral loads on the partner. I'm by no means blind to the structural issues, but I believe you are inflating them. I also mentioned the obvious, and almost always ignored fact that cats move under forces applied to the mast, but fore and aft and sideways, rather than rolling. They are known for rather "whiplash" acceleration, so the strain relief is there.... it's just different. Rigging load on a cat do not result in excessively heavy standing rigging, even when the greater angles are taken into account.
    Some, cats DO have a mast column intruding and it's hardly an issue... The same is true of monohulls that often have a compression post.
    Weight high up is a mixed blessing / curse, and assuming a carbon fiber mast, that weight will not be huge........ It does have a dampening effect, decreasing roll rate.

    Lastly, your first point...... The likelihood of mast failure is extremely small on a free standing mast...... You have eliminated virtually all of the typical failure points. Dismasting is distressingly common, and it is virtually always caused by failure of some trivial component, of the dozens that cannot be inspected with any degree of certainty. Issues like intergranular corrosion result in a situation where it is for all intents and purposes impossible to determine of a component is sound or not, which means that one must replace ALL standing rigging on a regular basis. While carbon masts can and do fail, it is relatively rare if properly built.

    Assuming a dismasting with a free standing mast, one is in "a world of hurt", but it will remain attached due to running rigging. In that case rigging a jury rig is possible, but could be a considerable challenge, but at least one has a one piece stick, not some flimsy aluminum mast that buckled in the middle. One can be pretty well assured that any failure is going to be at the deck (partner).

    It is very obvious that it can and HAS been done. It is also obvious that it is more suited to smaller cats than larger ones for mast structural reasons, and that it is better suited to shorter masts and low aspect sail plans such as lug or gaff rigs due to the simple math of leverage. It isn't the answer for the 60' "condo cat", but it may be quite viable for the 30 to 36 foot cruiser.

    I was really hoping for a discussion of how to make free standing masts work, rather than the usual arguments that it cannot work, based on what I consider questionable suppositions. When I look at potential problems, I look for viable solutions, until and unless it becomes indisputably obvious that it is entirely impractical. That is clearly NOT the case here. We would not have the array of catamarans that we do today if people had not blown through arguments that suggested that cats were inherently unsafe, found solutions, and moved forward. As an example I direct your attention to this Sports Illustrated article from 1968 titled Hey Ho and Up She Rises. Read and enjoy a good belly laugh!! https://www.si.com/vault/1968/05/06/610714/hey-ho-and-up-she-rises

    Not that I do not appreciate your input on this, but let's look for solutions, not just for problems. I do not recall implying that there was no "trade off"........

    H.W.
     
  4. CT249
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    CT249 Senior Member

    Is dismasting of conservative conventional boats "distressingly common"? As someone who started offshore racing in the late '70s, when rigs were dropping like flies, I'm really impressed with the dramatically lower failure rate of modern stayed rigs. I have yet to see any detailed numerical analysis of failure rates of conventional rigs as compared to freestanding - rhetoric yes, but no numbers. Well, one time we were told of a type that had lost just one mast, but a quick Google showed that was an under-estimate. While that was not conclusive evidence about relative reliability, it was conclusive evidence that some claims about freestanding mast reliability are factually incorrect. By the way, I have a few carbon masts and a freestanding rig, which I love.

    Secondly, the inference that cat's fast acceleration reduces loads appears to ignore the fact that when going upwind or close reaching, fast acceleration will increase the apparent wind which must increase loads. Nor is sideslipping with raised daggers really viable if, for instance, you're trying to sail upwind.

    That article you linked to can be seen both ways - it also reminds us that some people are so full of enthusiasm for developments that they make over the top claims and lie. Piver, for example, claimed that his boats were "seemingly immune to the ravages of the sea", that his Nimble could average 30 knots indefinitely (ie he claimed that his ply 30 footer with '60s gear was as fast as the 130 foot Orange II which set the 24 hour record at 29.4 knots in 2004), that it would be simple to get a 1000 mile run in a day (something the carbon 130ft G class foilers have yet to do), and he insulted monos and cats ("capsized too easily", "sluggish in light airs", and sailed by people whose mind were "closed even tighter than those of conventional boat sailors"). Hedley Nicol's claims were equally over the top - he reckoned his '60s timber tris could d0 27 knots upwind, about 5-8 knots faster than a carbon 135 footer like BPM can do. The article also ignores many of the deaths in that era, such as the entire family, plus three young women, who died on a Piver in the Tasman Sea. What is appalling is that some multi fans (and note, I'm a multi owner myself) were so biased and dishonest that the AYRS admitted it concealed some of the deaths about multis to preserve the type's reputation.

    So arguably, the article doesn't show that people were in general biased against multis, but that they reacted in a sensible fashion to an appalling death toll and a huge barrage of dishonest hype from many of the leading multihullers. The early history of multis (a type that I and most of those closest to me have owned and sailed) shows that claims about designs are often wildly over-hyped. That means that it's reasonable for us to ask for objective evidence about designs, rather than claims.
     
    Last edited: Oct 19, 2018
  5. Owly
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    Owly Junior Member

    The point here is to find ways that the supposedly inherent problems of a free standing mast on a catamaran can be overcome. The advantages of a free standing mast are huge, though a Bermuda rig is not the optimal rig for a free standing mast, as sail tension governs camber, and that presents a challenge.... at least to the sailmaker due to the flex. A free standing mast eliminates a great of maintenance, and eliminates the need for highly stressed chain plates.... a notorious point of leakage on many boats. It also allows the sail to be set at any angle, and eliminates the need for preventers to keep the boom from slamming into the shrouds, or the need for running backstays, etc. It does remove hand holds (shrouds), but that is pretty much a non issue. A free standing mast could be braced to take the whip out in storm conditions by running something part way up the mast with jury stays and shrouds using a halyard.
    Yes there are problems / issues, but there are also solutions. Key here is to keep things reasonable. A shorter mast with lower aspect ratio rig is a no-brainer, both reducing mast stresses due to leverage, and cost, hence my comment about using a gaff, lug, junk rig, or similar low aspect rig. If ultimate performance / speed / racing is the object, then it's a no-go as far as I'm concerned. For cruising / voyaging, the liabilities are less of a concern. Speed and comfort do not go together anyway.... Going 18kts may be exciting, but it involves riding the "bleeding edge", and that conflicts with safety. The larger the boat, the less viable this would seem to be. It's clear from the photos I posted that I'm not the only one who thinks this is viable. It clearly has been done, and apparently works??

    I'm not against looking at the problems.......... That's how solutions are found.... That was the point of the link in my previous post. The problems were identified, and have been solved. Virtually all capsize issues these days involve sailing the edge.... racing. Sailors fearing for their lives still abandon multihulls, but those boats are nearly always found right side up and intact. We see this in incidents around New Zealand, such as the Queens Birthday Storm, and and a few other incidents that have been recorded, not to mention Richard Woods Eclipse, abandoned off Central America, and later found upright and virtually undamaged. The Freedom yachts with their free standing carbon masts have had a few failures, but the mast technology was not "mature", and in reality their dismasting record is (said to be) better than many boats with stayed masts.
    The structural issues of the mast step and partner are fairly easily solved. The other issues are clearly solvable also. Such things as sheet releases may be part of the solution, and of course as with multihulls in general, reefing when you should is HUGE.

    This could become a useful discussion of the ways and means of making a free standing rig work on a cat. The liabilities and limitations are part of it that must be looked at honestly. It's important to keep in mind that different sailors have different priorities. Case in point being the fact that my own interests involve smaller cats and voyaging, and ultimate performance is very low on my list of priorities, while safety and simplicity of sailing rate very high. I enjoy sailing, have no interest in racing from one tiki bar to the next, and don't see the ocean as an obstacle between me and my destination...... For me it is about the journey, more than the destination, or I would fly.

    H.W.
     
  6. upchurchmr
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    upchurchmr Senior Member

    There have been multiple threads dealing with this.
     
  7. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Owley, I like the idea of free standing masts as well. I'm not a marine engineer, but it seems with most sails with a boom to the stern is that all the force and weight is on the mast. The next is that masts are mostly very tall to add sail area. I have been playing with a different idea for a while, but it is a very different setup altogether and may not be to your liking, you can look at it here.
    Sail Angle to the Wind https://www.boatdesign.net/threads/sail-angle-to-the-wind.61288/
    There are many reasons for it.
    One is a free standing mast in the stern of each hull which reduces the length of the mast, while larger sail surface is achieved with two sails, the shorter mas is especially suitable for trailing applications.
    A trimaran is (almost) a single hull with it's own sail, which is why they are generally fast. The ama's is there to keep the hull upright as we all know, for guys that cannot sail, like these small bicycles with the two side wheels for kids who cannot keep their balance :rolleyes:
    Putting the mast up or taking it down is also easy to do.
    I fish, and if you spin then rigging is always a pain, especially if you snap your favorite rod tip on a cable that gets in the way.
    The mast carries only about one third of the sail force since the sail is connects to the mast, the bow and the claw to the deck. The force on the mast is hence always basically towards the bow and some degrees either way.
    I built a small tri to play with the sail, and something that was fascinating is how little the tri canted. That gave me the idea that it would be very nice for a catamaran.
    My friend has a small tri with a basic conventional sail on it. We tried to see how fast it would go in a storm, and the best we could get was around 25km/hr because the wind pushes the hull in under the water and you'd get submerged. Even with someone on the windward ama we could not keep it from getting submerged as a result of the sail's down force. The sail I show does the opposite, it tries to lift the hull up, and the few times I sailed in a good wind, I got the impression that a larger boat with a larger sail can be made to plane.
    The (shorter) masts and sails can also be left at home and you can take the boat out with an outboard and trolling motor if you do not want to do sailing, so it makes the application versatile, although we discovered that if you go fishing, then the wind blows, if you go sailing then there is no wind. The obvious solution is to go fishing with a sailboat, and you get the best of both worlds.
    I'm sure one can calculate the forces for a free standing mast to work...
     
  8. Owly
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    Owly Junior Member

    Fanie:
    I'm familiar with that thread..... There have been many biplane rigs built, and while they have their advantages, they also are inherently heavier and more complex. The single central mast has the advantage of being simpler, and additionally of being stepped about 4 feet higher up, meaning more elevation per mast length... small but significant. It also doesn't put the mast down the middle of a narrow hull, as is the case in either a single mast trimaran or a biplane cat. Invariably in either of those cases, one is putting the mast down where there is a bulkhead to bear the lateral load, and that means bisecting a doorway opening..... not good in a narrow hull. I've looked at that, and in particular with the Searunner trimarans, and to have adequate space to move past the mast, it would need to be offset 8 to 12 inches to one side or the other.... not something I find particularly disturbing. Trimarans unfortunately lack the payload I need until one gets very large... larger than I want, and of course the rig grows with the boat.... heavier mast, etc.
    I find the Aerorig as shown in the two photos excessively complex as far as having to have a pivoting mast, though they would be great to sail. having the main and jib pivot together is attractive.
    Reaching for the sky to get the higher level winds is popular, but I think there is a reasonable compromise to be had. The Bermuda rig is so common that it accepted as the best rig, and probably is for many purposes.
    H.W.



     
  9. rob denney
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    rob denney Senior Member

    Free standing catamaran masts have been around on 50 and 60' cruising multis for a decade or so. They work well. No reason why they wouldn't work on a condomaran. Team Phillips in 1999 had 42,000 kg m of righting moment, about the same as a Gunboat 90 and far more than most condo cats and had no problems with their 40m/130' high free standing masts (had some problems with their hull and the mast bearings) 20 years ago.

    What "problems" are you referring to?
     
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  10. BigCat1950
    Joined: Nov 2018
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    BigCat1950 Junior Member

     
  11. BigCat1950
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    BigCat1950 Junior Member

    I have seen many post their opposition to an unstayed rig, and none of them had experience of an unstayed rig. I built a monohull with two unstayed masts. I sailed across the Pacific with them. The next owner circumnavigated. The third owners sailed to S. America. The original masts still stand, 40 years later. The deck was only modestly reinforced 1/4" glass over foam, and the mast steps were maybe 1/4" thick fiberglass. The mainmast was about a foot aft of the main bulkhead. The sail area was huge, the boat was very stiff, and yet still they stand. The SAILS were stayed by the sheeting system which attaches at the leach, per Blondie Hasler's design.
     
  12. JamesG123
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    JamesG123 Senior Member

    So not really free standing. Making a pole stick up on a boat isn't hard. Its the loading of sails and attachments that is the tricky part.
     

  13. BigCat1950
    Joined: Nov 2018
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    BigCat1950 Junior Member

    Most people would describe a mast with no stays or shrouds as free standing. I'm not sure what you mean by the comment that the loading of sails and attachments is difficult. The Chinese have been doing it for centuries.
     
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