Mast loads for freestanding masts

Moving on from the irrelevances, semantics arguments and personal insults, here are some scenarios. They are neither best nor worst case, but anyone who has been caught out under full sail in a strong squall at night on a catamaran will relate to them.
For those who haven't been, strong squall wind is cold (the rain cools the air which drops and flows out in front of the squall), noisy as it whistles through rigging and accompanied by rain, frequently torrential. The stronger the wind, usually the less warning you get.
For those who don't sail a cat, add in a couple of broaches as the uneven force from the sail overcomes the autopilot, forget about falling into the cockpit but worry about reaching over the lifelines to reach the end of the boom.

Scenario 1
You are on a stayed rig cat on autopilot on a downwind cruise at 3 am with medium swell in 10 knots of breeze. The headsail is poled out or the spinnaker is up. Your crew is seasick and bed ridden. You're brewing a cuppa when a squall hits.

1) You rush outside and do a ten step back and forth between the winches to ease the headsail sheet a little/pull it over to the lee side until it is blanketed behind the mainl, then furl it. Or you dump the spinnaker sheet, get it behind the main and go on the foredeck and wrestle with the snuffer.
2) You take several deep breaths to recover from the winching/wrestling. The breeze and rain increases, it's getting scary, time to reef the main. You luff the boat, the apparent wind climbs from 20 knots (30 true minus 10 knots boatspeed downwind) to 30, the wind force more than doubles as force is proportional to windspeed squared (400 vs 900)) and your adrenaline level escalates. You reset the autopilot for a reach. Mainsail, sheet and reefing lines flog. You winch the main in to reduce the flogging, then uncleat and ease the halyard, the flogging and the adrenaline levels increase. You winch down the luff and leech in the winch low gear, working hard. The leech reef line tangles or pulls the bunt of the sail into the block and jams. You scramble forward, and work your way aft over the cabin along the boom, but slip on the solar panel and/or get hit by the flogging boom and you are knocked over the edge of the cockpit cover or off the cabin top and knock yourself out (or go overboard, depending on the cockpit cover reach). Make up your own ending.
Or
You keep running square and release the halyard. Nothing happens as the sail is pinned against the shrouds. You alternate between winching the tack and clew down with a lot of effort in low gear, then collapse exhausted in a heap on the cockpit floor, praying it does not increase enough to need a second reef and swearing that from now on, night and squally weather sailing will be done with seriously reduced sail area, despite it being slow and tedious.
5) the squall passes, but you are too cold, wet and exhausted to do anything about getting going again.

Scenario 2
All the same, but the boat has an unstayed rig
1) You release the sheet (on a Harryproa this happens automatically when the stern of the ww hull leaves the water by a preset amount), the boom swings forward and weathercocks, the sail shakes lightly due to the maintenance of leech tension by the bent mast. The boat drifts. You go back inside and make and drink your cuppa and read your book until the squall passes.
Or
You sheet on just enough to provide sufficient speed to steer the boat.
Or
You release the halyard lock (a loop of dyneema around the mast and the top of the sail with bumps on the mast to locate it, cost $10, won't work on a stayed mast) and the main self lowers to the next stop, despite having cheap plastic slides. You take up the slack in the tack line by hand, using the winch to tension the last couple of centimetres/inches and repeat the process for the clew line, sheet on and keep sailing.
2) As the breeze drops, you sheet in more sail or shake out the reef (still heading ddw) and carry on.

No stress, no adrenaline and the option to stop at any stage of the process.

The upwind scenario is similar, but the stayed rig boat has the fear of broaching or capsizing if it bears away to ddw, or a lot more flogging and the risk of an accidental tack if not.

At the end of each season, the stayed rig owner pays a crane to unstep the mast and goes over it with a magnifying glass, looking for cracks and damage. Depending on his insurance and/or his mileage (5 or 10 years usually), he replaces the standing rigging. Spends a day restepping and tweaking the mast to ensure it is in column. Repeats the tweaking once or twice for new ss rigging, several times for dyneema. Before a long trip, he gets hoisted up the mast to check everything is OK and repeats it each week during the voyage. If the boat bangs off a wave, he looks anxiously up the mast to ensure it is all OK.

Every ten years the unstayed mast owner repaints his mast if he cares about it staying shiny. 20 years if he doesn't. In the unlikely event a bearing wears, he notices the mast is getting sloppy and he has at least another couple of thousand miles to remove the mast, replace the bearing and carry on. Plain plastic bearings wear slowly as the bearing rotation speed is low and the diameter far higher than the loads require. Add a grease nipple and grease them occasionally and they will outlive you.

Doesn't need a psychiatrist (or a psychaiatrist) to see which is more stressful.

CT, are you going to give us your list of advantages of each rig for cruising, or shall I do that as well?

skaraborgcraft, why would your money no object rig choice have a stayed mast?

 

These are some of the nightmarish scenarios that go through my head when I think about stayed masts.

 

I would certainly like to hear your perspective on the matter.

 

I don't doubt it, but the discussion is a comparison between stayed and unstayed masts, solo and the description was far harder, riskier and more stressful than the unstayed rig scenario above. It pretty much supports the stayed rig scenario above. Thanks.
Nothing on Google. I remember reading it, but wanted to quote it. Not a problem.

The first of those is potentially lethal (centring the boom while running square in big breeze), but they all support some or all of the stayed rig scenario above. Thanks.

Not quite bashing upwind offshore at night, solo in a strong breeze.

I'm sure they did 'include' that, but in the interests of safety they should have (and I bet they did) included a heck of a lot more.

Big deal. It happens automatically on an unstayed mast, and/or you can use the topping lift to the end of the boom. Almost no cruising cat sailors these days have backstays, and those that do would not consider tweaking them in a gust.

Nowhere near as silly as someone who can'tdifferentiate between gradual and obvious wear on a solid plastic bearing and the possibility of failure of 50 different components holding up a stayed rig.

You said, and keep saying, they exist. If you want to be taken seriously, you should list them.

I must be "extremely arrogant", as few spring to mind for a shorthanded cruising cat, which is what we are talking about.

So list them.

So you keep saying, but won't list them. A peculiar way to conduct a discussion.
What's in this 6 boat fleet of yours, please? A Laser, couple of windsurfers and a dinghy or 3? Which are about as relevant to mum and dad cruising in a cat as Ultimes and foiling moths.

 

Actually, the engineering of a self-standing mast is more complicated.

 

Wow, I would say precisely the opposite but, of course, one never knows and you always have to be willing to learn something new.

 

Yeah, ok...

 

A self-standing mast has no redundancy. Claims that stayed rigs require consistent attention and maintenance has no basis on reality. Stayed rigs are routinely neglected, but millions of sailboats are not demasting.

 

I totally agree, but is that what makes the engineering of a self standing mast more "complicated"?

 

Sorry Skaraborgcraft, those remarks about inexperienced people casting aspersions at others were NOT aimed at you - I said I was annoyed about an inexperienced person casting aspersions at other rigs, and you don't fit that description. You are extremely experienced and didn't case aspersions.

I didn't say that the OP had to have bearings; I referred to "bearings and structures" and unstayed masts needs structures to hold them up. I said they can and do fail and your tale of the superyacht that failed twice is yet another example. The point is sometimes this issue is written about as if it was a contest between one rig that was always suspect and one rig that was always perfect, and we all know that is not the case.

I only bring in handicap statistics to try to provide independent numerical analysis when some people appear to be making over-stated claims or asking for information. I fail to see what is apparently wrong about trying to provide such information on a boat design forum.

 

You asked for further input, so here's some.

The claim that it is more efficient is a sail can act "as a foil at greater angles downwind" is a myth - and it's a myth that is proven every day by the world's most popular classes, sailing in their thousands. The sail on the Laser, the most popular boat in the world, is regularly sheeted out a little bit beyond 90 degrees. This is done so that the boat sails by the lee with the flow moving from the leach to the luff, as in this pic from the Improper Course blogspot;



The Optimist (the Laser's rival for the most popular boat) and the Finn (also extremely popular) use the same technique. The Finn and Laser are long-time Olympic classes - they are the subject of university studies, they are analysed endlessly by coaches and Olympic sailors, and they have been sailed by many of the world's greats.

Now, nothing stops the thousands of Laser, Optimist and Finn sailors from easing the mainsail out well beyond 90 degrees so that the sail will "act as a foil at greater angles downwind" apart from two things - one is the knot on the mainsheet (which can of course be adjusted easily) and the other is the fact that the sailors of some 400,000+ boats sailing over 70 years have proven beyond dispute that it is SLOWER than keeping the sail in no further than about 95 degrees.

The concept that a sail could be let out to (say) 130 degrees to the apparent wind to "act like a foil" and be more efficient at driving a boat downwind seem to be problematic in simple physics and geometry. Here is a standard diagram of basic sail trim at different angles; tt's pretty accurate.



Note the boats in the illustration headed "beat" and "close reach" have their sails at about 135 to 120 degrees to the true wind which would seem to be about the angle that fits the claim that they could be eased well beyond 90 degrees "to act as a foil" sailing downwind.

But as the drawing shows, a sail at 13 to 120 degrees from the true wind sail drives a boat UPWIND. A sail setting that creates a vector that can push a boat UPWIND efficiently is not going to also efficiently push a boat DOWNWIND.

Get out on a windsurfer or small boat and try "setting the sail like a foil" at such angles downwind and see how well it works against identical craft sailed conventionally and well. It doesn't work well, and I've tried it many times both on purpose and inadvertently. It's slower than going downwind with the rig stalled or semi-stalled at about 90 degrees which is why hundreds of thousands of people who could have done it, didn't.

Secondly, where is the independent evidence that a soft wing sail is significantly, if at all, more efficient than a standard rig of similar weight, cost, heeling moment, etc? The more efficient hard wing sails have been used in experiments for about 100 years in a bunch of classes - some people claim that they have been banned from all classes or other rubbish like that, but it's complete crap. Outside of fast tris cats and some speed record boats, where different factors apply, the wings haven't proven to be sigificantly faster and have often been slower. Yes, we can seen claims and diagrams ad nauseum on the web showing that wings are dramatically faster even outside the very fast boats - but where is the actual independent evidence provided by disinterested sources?

This forum used to have the benefit of the late Tom Speer, a Boeing wing designer who was also involved in the design of America's Cup solid wing sails. Tom had reason to be a fan of wingsails but he was also an expert - and he regularly pointed out that they did NOT have major overall advantages for most boats. Here's some quotes from Tom about the benefits and otherwise of wing sails;

"the notion that because aircraft wings are very efficient and have thick sections, while sails have thin sections and generally lower lift/drag ratios, and therefore a thick sectioned sail will aerodynamically superior to a sail rig with a thin section simply because it is thick, is a mistaken idea. Airplanes have thick sections because they are structurally stronger and because they have to operate efficiently at low lift coefficients in cruise. This is generally not the case for most sailing craft, except for very high-speed craft like landyachts and iceboats.....A sail rig can operate at comparatively high lift coefficients even in high winds because it has the luxury of being able to reduce area. This makes the narrower operating range of the thin section acceptable."

and;

"at a given operating point, a thin section will out perform a thick section. The reason is simple. When you add thickness to a camber line, you raise the velocity on both sides. Higher velocities mean more skin friction. A higher peak velocity means it is harder to slow the flow down without separation. So, from an aerodynamic point of view, thin is good."

and;

"If a softsail rig is given the same height as a comparable rigid wing rig and designed to avoid separated zones, then there's no fundamental reason why it would be less efficient. Those are two big "ifs" though. The flip side is also true. If you design a rigid wing to have a low aspect ratio, it may not give you any performance edge over a soft sail.....The ability to adapt the soft rig to the sailing conditions can give it the edge over the rigid wing rig - adaptability through wing twist was the key to Cogito's success. The ability to add sail area or to reduce it through reefing makes the soft rig the better choice for most application."

Finally, having built up a stayed rig for a 28'er and re-done it a couple of times, I know it doesn't actually require sophisticated engineering. There is an enormous amount of experience to learn from, and it's actually very simple.

At the bottom you just have a fairly solid few bits of boat structure, but you need that with a freestanding mast too. The chainplates are simple - normally just bits of stainless steel with bolt holes, attached to the hull. What's hard about that?

The rigging wires are essentially the same ones used on balustrades in many houses - dead easy. The spreaders are really just struts that are have bases that are rivetted etc onto the mast section - simple. The tangs can just be holes in the mast walls - dead easy. Or you can have standard fittings and a compression tube for the bolt - against, something you can knock up with hand tools in an hour or less. This is all basic stuff that would be almost boringly simple for someone with your background.

If you choose a wingsail or freestanding rig and it works for you, cool and best of luck. I love freestanding rigs, wingmasts and similar devices, which is why I own and use so many of them. But some people choose to dramatically over-state their advantages and exaggerate the problems of other rigs.

The point is that while it's great if you end up with a rig you love whatever type, it shouldn't be chosen based on spurious claims and on equally incorrect insults about those who choose other types.

 

My thoughts on the perceived/claimed pluses of stayed rigs. All of which pale into insignificance on a cruiser when compared to the ease of use and lack of stress that goes with owning and saiiing an unstayed rig as shown in post
1) The stayed rig has something to hold onto!
Stated as if it is impossible to put a handhold on the deck, and ignoring the need to avoid the stays when moving around the deck, the inherent danger of being sliced if the boat hits something while sailing fast and stops while someone is standing behind the stay and the lack of need to go forward except to tend the anchor.
2) The rigging can be used to 'tune' the rig
I'm not sure how this works on a cruising boat. Once the rig is set up amidships and straight or slightly bent, there is not much 'tuning' possible. Apart from a few rare examples, even racers don't alter their standing rigging once the race starts, or even from week to week during the season. An unstayed mast is 'tuned' when it is designed. Once built, there is no need to alter these characteristics.
3) It's what the racers (Moths, skiffs, etc use)
Comparing race boats and cruisers is like comparing F1 cars to family sedans. Irrelevant and ridiculous.
There has been thousands of hours and millions of dollars spent developing unstayed Finn rigs. Still a microscopic amount of each compared to developing stayed rigs, but it would be interesting for our resident racer to put a stayed rig on a Finn and see how it compared.
4) Lighter
An alloy mast with ss rigging will be about the same weight as an amateur built vac bagged or infused unstayed carbon mast (~120 kgs for a 12m cat). The stayed rig boat will be heavier overall, due to the need for a forebeam and seagull striker, chainplates, tracks, traveller, etc and the beefing up they require.
5) Redundancy
All the items that might break on a stayed rig can be doubled up, but rarely are these days. I don't understand how this is better than having something that won't break, but I guess it is a mindset thing.
An unstayed carbon mast can (and should) be bench tested before it leaves the factory. If it meets spec, it will do so for it's entire life due to the excellent fatigue properties of carbon and the structural simplicity. A stayed mast is dependant on rigging tension being correct, so this peace of mind is not available. Aluminium and stainless have poor fatigue and stress related properties in comparison.
6) A stayed mast and it's rigging can be neglected and still work.
This concept is best employed on boats that don't go beyond swimming distance from shore. An unstayed rig is designed to be neglected.
7) Easier to engineer
An unstayed mast is a simple cantilever, built from materials with reliable, easily tested properties and few variables. It can then be bench tested to ensure they have been met.
A stayed mast is a compression member with many components, including the deck fittings and the reinforcing required to hold it up. It needs to be engineered for each panel and component.
The unstayed rig requires the deck and heel to be strengthened, which is a simple exercise as the loads are all in the horizontal plane.
The stayed rig needs the entire area between the shrouds, forestay and backstay to be engineered, plus the mast beam to take the high down loads.
I'm not sure which is 'easier', but the stayed one definitely takes more time.
Buying off the shelf items to build a rig is a totally different subject to engineering it and has the same relevance as 'It's what the racers use'. And unless you are confident in the item's provenance should be treated the same as neglect in #6 above.
8) Less windage
On a modern 12m cruising cat with hounds 10m off the deck, there will be ~66m of 12mm dia rigging (3 x 10m of diamonds, 3 x 12m of shrouds and stays): 2.5 sq m of frontal area. Add the spreaders and you are near enough the same frontal area as a sheet of ply (2.8 sq m). Add the forebeam, striker and furler and it is more. The unstayed mast will have more frontal area than the stayed mast down low, less up high as it is a tapered tube. It will have less windage overall.
9) Stayed rig is more rigid
True, but not an advantage on a cruiser. A squall hits, the unstayed mast flexes and the effect is similar to a first reef. The slightly slower acceleration from the flex would not be noticed on most cruisers. The flex and low cog reduces the shock loads and crew discomfort when/if the boat slams.
10) The stayed rig has more sail options
True, all of which have to be paid for and stowed somewhere. When you are fighting them on the foredeck at 3 am because a furler has failed, a sheet fouled or the breeze has increased, the advantages of a single (or 2) mainsails and no extras on an easily depowered or reefed rig are overwhelming.
11) Better downwind
It's not about the miniscule gain from hotshot racers sailing their Lasers and Finns. It's about Mum and Dad cruising downwind. A rig with 30% of the area (all the headsail or half the spinnaker) blanketed by the mainsail is not an efficient use of sail area. Dropping the main to fill the spinnaker is cool until the breeze picks up or changes and it has to be lowered. Poling out headsails works, but is more work. A mainsail rubbing on shrouds chafes. A boom that can't be let out past 75 degrees is more likely to accidentally gybe than one that is at 90 degrees.
12) Cheaper
The stayed rig, it's fittings and the extra sails and gear required will be way more expensive than the unstayed one. The difference will be increased if the carbon masts are built to easily achievable boat building standards (ie, vac bagged or infused) rather than the aircraft quality (autoclave) required for carbon race boat masts.
The materials in a 17.5m long unstayed mast for a 12m catamaran in Aus are ~70 kgs of carbon @ $US30/kg $2,100 + 10 kgs of fibreglass at $4/kg $40 + 40 kgs of epoxy at $10 per kg $400 = $US2,540. Build it in 2 halves and join them and it is a couple of weeks work. The carbon track and cars cost less money than you'll spend on fastenings to hold an alloy track on.
Maximum satisfaction comes from building it yourself (easier than many other parts of the boat), but if not, the trick is to find a builder who doesn't build or warranty it as it as an America's Cup spar, but as simply another item to build using standard techniques.

Stayed rigs are not the stupidest idea on a cruising boat. That distinction goes to dagger boards and rudders that don't kick up in a collision and saildrives which are unprotected. Interestingly, the arguments for stayed rigs are usually by the same designers and owners who think this makes good sense.

The advantages of soft wings on cruisers are not performance related. Most of the boats that have, and love them are comparative slugs. The benefits are low cost, low loads, easy reefing and repair and balanced rig/low sheet loads. And in my experience with these owners, there's also a big lump of trying to improve the breed, rather than doing what everyone else does, which makes them very interesting and challenging to design for.

 

No worries. You do far more racing orientated sailing than i have ever done, so performance statistics is information you commonly share, its all good.

I found a gaff main on a downwind run in strong wind and big seas caused a much heavier helm steering imbalance, than a lug rigged main in the same conditions. Having 30-40% of the sail on the other side of the mast did give far greater helm control and less heave on the hull. I find having the centre of effort of the sail over the hull, rather than outboard by some way is a better ride.
To be fair to stayed rigs, the bermudian cutter with a double reefed down main and poled staysail on the opposite side was just as comfortable.

And although many luggers use freestanding masts, some of them are set up so that the yard halyard becomes something of a backstay/shroud.

 

All data from racing boats show that is not true

Nice claim, but there is no data supporting that one rig type is designed to be neglected while the other one isn't.

Either structure has to be engineered properly, with appropriate reinforcements. In fact, literature on stayed rigs is extensive and they can be easily calculated from similar designed. Unstayed rigs are semi-experimental which requires more knowledge and time to engineer them.

In conclusion, this is another of your long list of unsupported claims.

 

Might want to study some Chinese maritime history.