Rotating Free Standing Mast Design

[Petros]

what I mean by sudden paranoia is that almost everything you touch, use and eat is usually designed and made to meet some safety standard determined by someone else. It is not exclusive to sailing yachts, rock climbing equipment and hand gliders. Because the car you drive or the electric toaster you use is familiar, it does not mean it would not represent a very large danger if it was not for these safety standards.

You used to be able to get the German Lloyds specification on-line for free down load. It is a massively large document, so you may want to only down load the sections that apply to pleasure/racing yachts. Do a search for it, I am reasonably certain it is still free. It is similar to the other rating agencies design requirements.

 

[cadmus]

Cadmus, If you haven't seen it already, you can read my article on Free-standing masts on my website, "Some Thoughts on the State of the Art" where I make all the arguments for free-standing rigs:

http://www.sponbergyachtdesign.com/StateoftheArt.htm

Eric

Eric, I know your website inside and out, i watch for your name at proboatradio, I always look for updates to your website. I am an advocate of the stayless mast and I could add more good reasons than are in that link. keep up the good work.
Pete

 

[Eric Sponberg]

Eric, I know your website in a out, i watch for your name at proboatradio, I always look for updates to your email. I am an advocate of the stayless mast and I could add more good reasons than are in that link. keep up the good work.
Pete

Great! Thanks!

Eric

 

[cadmus]

what I mean by sudden paranoia is that almost everything you touch, use and eat is usually designed and made to meet some safety standard determined by someone else. It is not exclusive to sailing yachts, rock climbing equipment and hand gliders. Because the car you drive or the electric toaster you use is familiar, it does not mean it would not represent a very large danger if it was not for these safety standards.

I am involved with the creation of safe water quality standards on the national, state and international arena. And safe uses of new chemicals. The way we come up with those standards is not trustworthy or logical and is easily manipulated by industry. One of my undergraduate degrees is in policy analysis and public administration and i focused a great amount of time on the standards and federal regs you are talking about and maybe that is why i do not trust them. Back to the boat "standards" or "class rules" if they do not spell out the logic or how they arrived at them and then publish those in peer review fasion at an affordable price with total transparency and openess about how they calculated them, anyone with a brain would not trust them.
I know how safey standards are made and sometimes it is not logical or trustworthy. Often it is dictated by industry, Look that the STIX A class rating for example. EU class A rating are awarded to many boats that i would never call safe. Some are, some are not. So maybe i am an outlier. Maybe then they say "unlimited use" they are not saying benthology research in the south sea and poorly charted regions for years at a time. Without a good definition of what "cruising" is I fear I will be demanding more from my boat than the average person. But my toaster... I do not think that my toaster is being pushed to the extreams. When i build buildings i often go above the IRC recommendations for longevity, fire prevention or piece of mind. Climbing gear, I use it pretty normally but climbing gear lists the force rating and 95% confidence interval on everything. I do not think it is too much to ask for that on boat equipment.
I am going to put off building for 5 years so i can afford a set of rotating masts (which i plan on) and the associated engineering cost (for Eric) I should make sure this is strong enough for many years of crossings. I need to prove this to myself but really this was inspired by family and other forums questioning the strength of stayless masts. so I am mounting evidence for them, the company that insures my boat, and the children who inherit my boat.

I think if we on this forum took everyone's word on every topic this forum would not exist, it is always aiming to improve and test the status quo. OR to better understand how things are done/calculated/predicted/etc.

You used to be able to get the German Lloyds specification on-line for free down load. It is a massively large document, so you may want to only down load the sections that apply to pleasure/racing yachts. Do a search for it, I am reasonably certain it is still free. It is similar to the other rating agencies design requirements.

THANKS. I will look into it. Hopefully not in German. Do you know what section(s) addresses rigging.

 

[cadmus]

... Usually a metal fitting fails then the mast falls over. By going free standing you remove the problem

yep. i agree. and many others also.

...if this boat is to be a ocean going one then a round section is the best bet...
... If you use a round section then there are many people that can wind or mould your mast as the moulds already exist. Plus if round it will be as strong fwd/aft as it is sideways....

herm? not very aerodynamic.
I see concerns with a foil shape, but the elliptical shape is pretty easy to work with. It prevents delamination of laminar flow, and if you design everything to the weakest/shortest cross section it should be fine... right? Why do you advocate round?

This means that the strength of the mast will be huge for its purpose even in the event of the fwd accelerations you seem to be worried about.

Of if i am worried about roll i rotate them transverse, if worried about pitch(bow pounding) i rotate them forward. Or i just use the short/weakest direction as the weakest link and try to figure out what it should be... which was the original plan, certainly this can be done.

A wingmast is designed to provide more power. Something that a cruiser can acheive by adding a bit of sail area vs making a more fragile mast.

yep. But it has many other advantages. So is that statement saying that stay less rotating wing masts are more fragile?

Plus when the time comes to build your mast the mould will cost the same as the mast

If female molding, yes. If buying it from someone with an existing female mold, no. If using a male mold/mandrel, no. If using a wood/foam/composite internal structure, then it depends.

...and you will not build your wing mast due to its large total cost.

correct. although i have glassed all my life i will not be investing in the equipment needed to do CF properly. I am already wasting too much time learning to weld aluminum. However, since much of the cost of a CF mast is fixed the small boats seam to have a greater marginal cost and end up avoiding them. So perhaps i will be forced to DIY as I am trying hard to stay small.

When cruising you will not be interested in continually trimming your mast to get the most power.

Why do you assume that? It is part of sailing? You clearly do not know me. I have itchy hands. I am always trimming the sails. Even when i should be sleeping. I regret that i can not rake the mast with a stayless, i regret having less things to play with. But the advantages outweigh losses (I will post on some of these later as it sounds like everyone assumes i know nothing about wing masts) and trimming for lift rather than drag is so much more refined and fulfilling.

...then the project falls over when the mould costs come in.

Yeah, Eric tried to scare me already. I think it should be spelled: $tayle$$. But that being said in the long run there is some cost savings. Talk to freedom owners.

...By the way I'm a yacht structures engineer who has been designing masts for over 25 years. All of the scenarios you describe can be calculated for and understood and designed to if required, good naval architects and engineers can estimate all that you speak of.

perfect, so how? and why is everyone saying it can not be done? What do i read?

for a monohull of course!!

how does it differ for a catamaran? obviously it is initially super stiff.

CF mast or hybrid CF glass mast

I though mixing fiber types was bad in the long term as they flex differently putting too much force on the more ridged one. forcing us to over build the ridged component and making things heavy.

 

[cadmus]

This also is based on a CF mast or hybrid CF glass mast as the strength of fibres are much bigger than say aluminium.

are we talking tensile here? I am assuming so.

the strength of fibres are much bigger than say aluminium. eg a typical laminates that I build have UTS > 1000Mpa whereas 6061-T6 al has a YS=300Mpa. So we are 3x in front already and much lighter.

3x but that is not a good analogy as you should be making comparisons to the stays and shrouds.
I like where this is going, however.
So lets pretend the backstay is the hypotenuse and the deck is the base. If we make analogies to the stayless we can make that base infinitely small? is that what you are saying? Then compare the tensile strength of the CF mast to the tensile strength of the backstay of a boat i trust?
Is that fair? That is not how you do it is it? no.
I would think the buckling of the compression forces in the traditional mast are the limiting factor and a traditional mast. not the backstay.
Also I would have to include the compression on the CF mast (on the leeward side or the side where i keep bashing the bow into waves). I assume that is the weaker link.
And this changes every meter up the spar, right?

I know i am clueless but i am slightly less clueless than before.
This is good stuff, keep it coming. What should i read? thanks. pete

 

[cadmus]

simple comparison to traditional rigs

Look. A Westsail32. an Ingred 38. Bristol Channel cutter. These are well rigged boats. Slow, but that is defined buy other things more than the rig. Lets just use this as the boats my family and friends call safely rigged. They are heavy and since i am building aluminum mine will be heavy. They are incompatible lengths and sail area but they are similar displacement to SA ratio. similar righting curves (if normalized to length). I am looking at ~38' and an ingred is 38'. If i can do the math to see that a stayless wingmast is as strong as these and can take a beating as well as these, I am happy. and my friends and family will have to 'eat it.'
Does that better define what i am looking for? i want them to eat it.

The advantages of having less parts to fatigue is well stated above and on other threads. If we could simply keep this to design strength of new boats who's parts will take what they were designed for during my imaginary 6 days of force 9-12 bow bashing that would be great.

(but if petereng and others wants to keep teaching me how to calculate this stuff i am more than interested in doing it right)

 

[Skyak]

It is interesting to see the conversation about assuring safety in a universe of unknowns. I have a question. Has anyone ever done a formal 'design failure mode effects analysis' on a sailboat they designed? It is kind of the basis of all safety analysis. If you are designing a mast to the righting moment of the boat you are assuming that it will result in a higher safety factor in all of the other failure modes that you are not considering. A DFMEA is what you need to prove it.

Some of the other severe loads that might be considered -getting rolled, impact, stress risers/notch sensitivity, fatigue life.

Your choice to go with the unstayed CF rig is a classic bet that the most reliable chain is the one with the fewest links. In today's world of global manufacturing and counterfeits I think it will gain popularity. I second the motion to stay with a round section.

The last thought I had was how sailboat design is still so based on traditions, guidelines and estimation techniques. Autos, airplanes, even bicycles have gone to computer modeling and virtual prototyping/testing. I suppose the insurance like Loyds has a lot to do with that.

 

[cadmus]

Some of the other severe loads that might be considered -getting rolled, impact, stress risers/notch sensitivity, fatigue life.

Yeah, that is what keeps me up at night.

about rolling, i was once told that the floatation in a stayless wing mast make it unrollable. That is nice.
But how does it behave underwater. Are those forces greater than when upright? A keel is 1/30 the size and of your sail but it is counteracting the same forces.

 

[Skyak]

The key is a 'sealed' masthead. When you do the boat design the stability curves will show a big spike in righting moment when the mast hits the water and a peak ten or twenty degrees further as more mast is immersed. To get an idea what it's worth take the top fifth of your mast and multiply it by the sectional area to get volume times the density of water to get force then multiply by the distance from the midpoint of the tip to the middle of the topsides. This long distance is what makes it effective. The tip might only displace 200lbs of water, but at 50ft from the middle of the topsides that's 10,000 ft*lbs of righting. That's significant compared to a 6000lb keel that might only have 6ft of leverage to the topside center or 36000ft*lb. The keel moment is diminishing but the mast righting is still increasing to about 130. It is great insurance that a knockdown doesn't result in a rollover.

If that doesn't make the sale consider the stability of your boat around 180. Some wide offshore racers were shockingly stable upside-down.

As for the forces it depends on the waves and the sail. If the sheet is free and or the waves are not much larger than the boat it should pop right back up. If the waves are much larger than the boat and the lines are fixed it's a DFMEA question of what breaks. This is why the analysis is done. It would make sense to design the sheet to give at a force lower than what it takes to break the rig. Waves have too much force to overcome. Did you see the tsunami videos of big steel ships squirting under bridges like toothpaste?

 

[cadmus]

I see the reason it prevents rolling.
My questions was will that hurt the mast? Waves breaking is not wind blowing. Water is not air. one compresses the other doesn't. one has much more mass and viscosity.

(hope fully all sails have been heavily reefed in this situation)

 

[Tanton]

A couple of things.

-For cruising and for a construction in composite, the rounded shape is probably the best approach. Being flexible by nature, the load is distributed around and takes account of the sides, lateral and fore and aft forces on the mast.
-Instead of a stub mast, I prefer to have the turning mast itself to penetrate the deck to the bottom mast step. Now, with the venue of having a jib, I do not mind to have a turning mast with a diamond and outboard shroud set up, and the turning ball on deck.

 

[petereng]

Hi Cadmus - This is the beggining of a long journey.
a) a soft sail with any mast in front of it is not very aerodynamic full stop. A round mast soft sail at best can give you a Cl=1.5. A wing mast soft sail at best will be 1.8. Its much cheaper to be smart with 20% more sail area then a high tech wing mast. But you have to figure this out for yourself. Especially for cruising b) if the wingmast mould exists then get a quote for its build.
c) I've helped lots of amatuer builders build their masts and only one out of 10 acheive the laminate quality required to acheive the design stiffness.
d) No, wingmasts are not less fragile it comes down to what safety factor you want to design to and realising that design in reality for any mast
e) for instance all the large free standing wingmasts I have designed have had problems going from wing to round to accept a bearing. They buckle really easily at the transition. If you build the wing on a post vs burying it the post is really heavy because is quite a bit smaller then the wing. It can become quite complicated.
e) building a mast like this by yourself I'd only do it if you can infuse very well (carbon is not easy to infuse) use prepreg or very good wet preg. Making the stick is easy, you have several issues to solve with tracks, nav lights and do you have a jib?
f)You will be unhappy with a wood/foam/timber internal structure. It will be heavy. The best design will be 100% carbon then use 100% H-Glass. Hybrids (CF/Glass) are possible and they do reduce material costs by 10-15%.
g) I am not saying it can't be done, it should be done but if you go into this trying to save dollars then you will probably fail. You need to truelly cost it out right, allow 25%-50% overrun then compare to a conventional rig bought from a reputably rig builder. It may be easier to buy a std rig and go sailing vs the super angst you will go through doing a bespoke mast. Giving you a heads up here.
h) You really don't want to be on a cruising catamaran at 30 degs heel!! Cats develop max righting moment when they are flat. The usual discussion here is not designing at 1.5xRm (mono) but say 0.8xRm or 0.6xRm. Its unrealistic to expect a mast to support the full Rm of a large cat!

If you are cruising you will not sail close hauled all day so the extra bit of lift the wing gives you will not be useful. You need to find someone who has done extensive wing sailing on a cruiser, talk to some of jeff schionnings customers.

I really can't get into the structural mechanics of free standing masts here. Lets just say you are completly correct in going down this path you just need the right cheque book and right people to have it happen.

Enjoy the journey as you may not end up at the destination you thought you bought the ticket for! Peter S

 

[petereng]

Hi Cadmus - This is what I usual tell my clients on a mast project
1) find the builder that you are comfortable with, if its yourself tick it off the list
2) build a test laminate to my spec, a 600x600mm panel is usually what is required
3) send it to a test lab that I use and get a "basic" test done for $800 AUD. A full test is about $2500 and includes compression and shear numbers. basic gives me tensile, flexural strength and modulii. It also gives the fibre ratio by weight. If these acheive the figures I think they should be, we are on our way. If they fall short we have to figure out why and perhaps do this again or use the knocked down values.
4) During this time I get a sail plan and a Rm curve or just the max Rm
5) I get the client to sketch what they have in their head. Your wing maybe 200x300mm but someone elses maybe 500x200mm etc etc. Bearings or post? etc etc as many wish list items as possible
6) I do a preliminary design with a SF=1.5, 2.0 and 3.0 I make them as light as I can within the scope. I present these findings to the client and they digest it. At this point they pick the design to develop and go away and talk to the builder to get a budget quote as now we know a shape, weight and a laminate
My charges up to now could be $1000, it could be $10,000AUD depending on the scope. Once the quote or quotes come in and the client knows what budget to set, I can then work out the finer details if the client wants me to do this. The biggest cost free standing mast I've done is $25k which included the engineering of an in boom furler (the CF 21m mast cost about $100k the mould cost $25k) the least is about $500AUD. The $$ spent on the laminate test are really worthwhile. Peter S

 

[cadmus]

The above is some great info and advice.

Although not the building standard route, and not the modeling route the repost below would satiate all fears.

Look. A Westsail32. an Ingred 38. Bristol Channel cutter. These are well rigged boats. Slow, but that is defined buy other things more than the rig. Lets just use this as the boats my family and friends call safely rigged. They are heavy and since i am building aluminum mine will be heavy. They are incompatible lengths and sail area but they are similar displacement to SA ratio. similar righting curves (if normalized to length). I am looking at ~38' and an ingred is 38'. If i can do the math to see that a stayless wingmast is as strong as these and can take a beating as well as these, I am happy. and my friends and family will have to 'eat it.'
Does that better define what i am looking for? i want them to eat it.

The advantages of having less parts to fatigue is well stated above and on other threads. If we could simply keep this to design strength of new boats who's parts will take what they were designed for during my imaginary 6 days of force 9-12 bow bashing that would be great.

I realize there might be pros and cons as that is 2 very different materials.