Mast loads for freestanding masts

Forgive me for saying this but I think that's one of the dumbest posts in history. What sort of biased propaganda do you base your claim on? From some of your comments it appears that you are basing your criticism on sitting on your couch watching videos. Do you honestly think that is a reasonable basis for such insulting remarks?

Do you honestly think you know more than the people who design the foiling Moths, the round the world singlehanded tris, and the America's Cup boats, apart from many highly experienced cruising sailors who choose stayed masts? Stayed masts work - stays in tension are a very elegant, efficient engineering solution.

For some reason, unstayed mast and junk rig promoters seem to write lies quite a bit, and sadly many people fall for them. For example the Eric Sponberg piece on unstayed rigs linked to earlier contain plenty of claims that are simply untrue and insulting. For example, Eric admitted here that his claim that rating rules require wires that force mainsails to be triangular is simply untrue - and yet he left the piece on the web. Eric, like some JR promoters, uses insults and false claims in a way that seems to sucker in those with poor critical thinking skills.

The vast depth of your ignorance is shown by the fact that you say you don't know about the Laser 4.7 rig. The Laser rig is THE most popular rig in the world - and it's unstayed. If you don't know about the most popular version of an object in the world then it is ridiculous to claim you know anything significant about such objects. To abuse stayed rigs when you do not know of the Laser rig is is as stupid as abusing all cheeses when you do not know of cheddar, or insulting all gases when you don't know of the existence of oxygen.

Your ideas for rig weight seem to show some major misunderstanding, or the problems with your rig concept. A 12' high rig weighing 120lbs? Considering even a basic 14' alloy and dacron unstayed Laser rig weighs about 24lb and my 38' alloy stayed yacht rig with sails weighs less than than 120lb, it's strange that you appear to consider the unstayed rig superior in such an application.

By the way I own a lot of unstayed rigs and like them, just as I own stayed wingmasts and stayed conventional masts and like them - the point is that they are different, not better. The most popular classes in the world have unstayed rigs so vast numbers of sailors have had years of experience with them, and yet we choose stayed rigs for most applications because stayed rigs normally work better. Only the arrogant would think that most of those who choose stayed rigs do so for the wrong reasons.

 

So your "analysis" is partly based on the completely unscientific method of watching videos?

Having done plenty of offshore miles (Sydney to Hobarts, etc) I can say I have never "risked death" to "mess with a rig". A mainsail on a stayed mast CAN be reefed when square running quite easily, despite what biased people say.

Did your "research" bring up Loic Caradec, Lock Crowther and the other people who died offshore arguably because they had wingmasts?

Oh, and when you were doing this deep research that overlooked the world's most popular unstayed rig (which is quite well known for high failure rate by the way) how did you calculate the proportion of unstayed masts that are found in the world's cruising fleet? After all, anyone with a brain would know that you can't compare the failure rate of two different systems unless you know their relative popularity. So how many junk rigs are there out there cruising, how many miles do they do, how many conventional rigs are out doing the same thing, and how many of each are failing? If you can't tell us those numbers then you have NO proof for any claim that stayed rigs fail more often.

So why do you think your rig will be immune from the problems that are blamed for the loss of the unstayed and junk rig masts on Sabra, the Trolobite that lost two masts, Lexia, a Challenger 35, a Westerly Konsort, a Virgo Voyager, a Coromandel, Pete Hill's Freedom 33, etc etc etc?

 

Hundreds of videos of for real sailors, don't bother with skin and drama videos. Along with MANY rough weather sailing articles, books, etc. And as someone who has spent my entire life building and fixing things (meaning I understand how thing function very well) there are blindingly obvious drawbacks to conventional rigs. Like everyone says, there are tradeoffs to every design decision. Just watch that part of the video I referenced, that's crazy, who would want to go through that in rough weather?

I'm not listening to biased people, I'm listening to all people. Almost all the accounts are from people with conventional rigs. The biased people, owners and builders of freestanding rigs, have some good points. You have to admit that.

No I did not see that, but I will look it up for sure. Do you have links? I will not have wing masts or hard wings. The whole basis of my sail design centers around easy reefing, reliability and ease of operation. The decision to go with soft wings is all based on those criteria, performance is secondary. Except for running and close to the wind I'm actually expecting that my sails will have similar or worse performance than conventional sails, and I'm ok with that.

You are making an unsubstantiated claim to refute the claim that you are supposing I made, which I did not. What I do know is that making an unstayed mast strong enough to withstand whatever conditions is a relatively easy task compared to a stayed rig. Yes, it may be a little heavier, but oh well. My unsubstantiated opinion is that people are obsessed with saving every last ounce and that's why they fail, or that manufacturers are trying to save money and make larger profits, at the expense of people's safety.

There have been countless boats with unstayed rigs, or partially stayed. And there are many still, we just don't see many on cruising boats. You are making an appeal to popularity, which is evidence of nothing. From watching all those videos(and articles) I have seen many times people's rigging on stayed rigs fail, sometimes resulting in complete failure, commonly resulting in a really dangerous situation. Most of the time it was from some little part, one of many such parts.

When I post the design you can tear it apart and tell me all the ways it can fail.

To be continued...

 

I'm not "making an unsubstantiated claim" in that passage you quoted. In that passage I claimed that the Laser is the world's most popular rig (which is supported by data) and that you had no actual data on which to base your claim that stayed rigs are inferior. Both those are correct and substantiated.

Of course I know that there have been many unstayed boats - for heaven's sake in the passage you criticised I noted that the world's most popular boat is unstayed. So is the second most popular, and the most popular sailing craft of all (by some measures). I own examples of all three of those classes, incidentally, because I like unstayed rigs I just don't like BSers throwing abuse at the vast numbers of boats that have other rigs for very good reasons, and the people who choose and create those rigs.

I am NOT making an appeal to popularity at all. What I pointed out is that you are not using any data that provides any evidence of comparative failure rates of stayed rigs v unstayed rigs. You are claiming that one rig is grossly inferior but providing no evidence that it has a failure rate of X% and that a supposedly superior rig has a failure rate of less than X%. That is simply not logical.

As you said, there are not that many unstayed rigs in cruising boats, therefore it is far less likely that they will post videos of incidents, therefore it is far less likely that you will see videos of unstayed rigs having trouble, therefore that is not a logical way to decide that one rig is terrible and the other great. You appear to be completely ignoring that very basic and logical fact.

You have also spoken about your experience with practical things but completely ignored the fact that vast numbers of people with enormous practical experience in sailing, rigging and design prefer stayed rigs. If you rate experience with practical things as so important then it is simply dishonest and hypocritical to ignore the vastly greater and vastly more relevant experience of people like the enormous majority of the Moth, America's Cup, production boat, racer and offshore multis designers, who choose stayed rigs because they work so well.

I don't know what you're talking about re the video. I can, and have, reefed my 36'ers mainsail, on a stayed rig on a square run, quite happily. I don't know why some people make a big deal about it.

 

Reefing while going downwind only requires to sheet the sail in to as close to center as possible; piece of cake.

 

Mr. Herdiman,
We should all be thankful for your help and if you are a little testy somedays that is fine with me.
I am always amazed at how well you deal with some of our stupidity on this forum. In the past I have acted as if I could just through a few number around and come up with a design with just a little help. Truly delusional thinking on my part.
I am humbled by your intellectual prowess.

I owe much for expanding my knowledge.
John Howland

 

I'm still trying to work out how anyone could be so wrong.

 

Yup. And this is where the confusion is. Righting moment is the resistance of the hull(s) to resist external load applied and is usually expressed in lb.ft or kg.m. per degree of list. So a maximum righting moment is the resisting force needed to counteract a maximum angle (designed or derived) of heel. This will determine how many degrees the cat is allowed/designed to tilt.

The force on the sail 200 lb @ 40 mph wind (multiply by 2) as this is a biplane rig is the designed external force which exerts pressure at a distance (moment) away from the VCG (the point where the hull rotate at its center. The VCG is not mentioned nor the distance of the mast away from the center of the cat.

The force required required to break/deform the mast is designed below the Yield point of the material, not the Ultimate stress. Since most alloys would yield at at about 60% of its ultimate strength, max force is designed below that 60%. Say about 50% of ultimate stress, that will give a safety factor of 2. A safety factor of 3 would mean it is about 33% of ultimate strength. This is the designed/allowable force.

 

Does this mean that the mast is designed to fail at 1/3 of the righting moment? I can't see how dismasting is a safety feature in a design.

 

I believe you are misreading.

If we had some numbers; it would make more sense, but to do so means we need to know the righting moment,

 

Righting moment depends on heel angle. What righting moment are you talking about?

 

I'm imagining that Sponberg is using the righting moment as expressed by 1/2 beam times the weight(6000lbs in my case). The actual restoring force would be much lower than this...?

Centerline to centerline beam = 11'
Fully loaded displacement = ~1200 lbs
Sail area = 100ft2 divided between 2 masts in biplane configuration
The sail's center of pressure = 9' off the water
Don't know exactly the VCG but about 24" off the water

To my understanding, maximum righting moment occurs on a catamaran just as one hull exits the water, assuming around 3 to 5 degrees.

The mast would be about 14' tall from it's uppermost deck support to the uppermost batten at the top of the sail.

To be honest I don't see the direct relevance of the righting moment if the maximum force ever applied to the sails(or masts) cannot exceed the righting moment. Design the masts for the actual maximum force expected and apply the appropriate safety factor to account for fatigue, etc and call it good. If the sail force can exceed the actual righting moment then there is no point in making the masts stronger than this. Apply a suitable safety factor.

As I understand everything now a mast 3" diam with 1/4" wall of 6061 aluminum will be more than strong enough for my application. A 2.5" diam would probably be enough.?

 

Why do people with standard rigs talk about it so much? It seems the problem comes when you don't get the sails down *before* the wind builds up. At that point sheeting in is not possible or safe, or rounding up may not be safe? Sounds like it comes down to seamanship to avoid such problems in the first place. Also, the sails don't just fall down on their own with much pressure on them, which necessitates pulling them down manually.

 

Er.....nah. I got caught in a "white squall" with an already single reefed mainsail going down wind. I did manage to roll the genoa away, but it was impossible to haul in the mainsheet, and despite letting the main halyard go, the sail stayed up. That boat sailed faster than hull speed in wind driven flat water for the next 15 minutes. I triple reefed the mainsail every night after that, and of course, it never happened again.

 

There is no evidence needed, as many of my points are self evident, along with many of the points made by proponents of unstayed masts. There only 3 possible failure points on an unstayed mast; 2 points at the mast base and the mast itself. The only way it can fail is through significant design error. As you indicated, there is simply not a lot of data to draw from.

I think tradition and popularity are pretty big factors there. Over the many years in my profession I realized that a lot of "professionals" don't actually know what they are doing(more specifically, why), they just know "this is the way it's done", and continue on that path never questioning the basic principles they are working from. The long term result is lot's of work for me.

Did you watch that portion of it? Does the answer not seem just a little bit ridiculous? From the way he answered it seems that this is a common occurrence for sailors and something he has experienced himself.