Large Unstayed Masts.

[Chris31415]

Is there any information available on how to build a large unstayed mast, say to fit a Roberts 434.
The reasons for my request are:-
1. I'm costing out building the boat and I just got the quote on the mast, and I don't think my bank manager would approve. The total cost of fitting a stayed mast together with the sails, winches and all associated gear is really beyond belief.
2. An unstayed mast would be much more suitable for short handed sailing than a stayed mast.
3. While most unstayed masts seem to be built of carbon fibre I can see no reason one could not be built of wood. Weight is not a serious consideration for a cruising yacht, but simplicity, reliability and cost are.
4. Wood is inherently suitable for the biulding of a spar that must flex.
To get some idaea of what I am thinking of take a look at:-
http://www.wyliecat.com/yachts/models/wyliecat_39.html
I know I should spend megabucks on professional design and construction but I'd rather find out how to do it myself.

[MarkC]

Yacht designer Eric W. Sponberg has worked with free-standing masts.


Sponberg Yacht Design is the leading expert in free-standing mast design with nearly 60 different mast designs to our credit. Please contact us by e-mail or phone if you would like to discuss a new mast design for your new or existing boat.

http://www.sponbergyachtdesign.com/Copernicus.htm
A retro-fitted yacht with free-standing mast. Ply-wood inner with pre-preg carbonfiber outer.

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

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

[phiil]

I sail a cat-ketch with unstayed masts, and the design does have one serious drawback.

It happens when you are not in a crowded waterway, and the need arises, and you don't want to further burden your holding tank. As you stand by the lee rail, you quickly realize that there's no handy stay to steady yourself.

Panic ensues, and you will shortly find yourself in the ignominious position of kneeling in the cockpit with a bucket in front of you.

Phil

[Jack C]

And there isn't any place to fly the courtesy flag. :eek:

More seriously, I wouldn't build an unstayed spar out of wood for a 43' boat. If you use the Skene recommendations, you're looking at a massive tree trunk. And I disagree about the "cruising therefore weight doesn't matter" philosophy. Almost all of your cruising stores will be raising your center of gravity. Being lighter up top will help keep the metacentric height at a reasonable value.

Jack, owner of an unstayed stick boat.

[ssor]

Aluminum flag poles are unstayed masts.

[Garrett Lowell]

Only in appearance, as there is no stress on the flagpole from driving the earth.

[ErikH]

A large wooden unstayed mast that's light enough to be useful? I don't think it's possible.

You need it long and stiff. Which is to say that you need to either 1) make it out of a material with extreme natural resistance to bending, or 2) make the diameter large enough to be stiff.

If you go with option 1, you're talking about a solid wood mast. Which will weigh a gazillion pounds.

If you go with option 2, you're going to have a very large mast. Which has its own sets of problems.

I think there's a reason that nobody made many unstayed larger masts until aluminum and carbon came out... Wood is great stuff but not for taht application.

[Stu Fyfe]

I have a 22ft wooden mast for a gaff rig. It has a jib stay and two running back stays. It works fine. When I asked Phil Bolger about adding port and starboard stays, he felt the hull was not designed to handle the stress from them. In fact, the running back stays serve only to keep the jib stay taught. The boat can sail without the running back stays in use. As for weight, it takes two-three people to step the mast (or a lift if available. The mast was built in four sections, doug fir and quite strong. I don't think I would build a stayless mast for the height and rig type you showed on the web-page. I think you're asking for trouble when you get that high.

[ 06-22-2005, 11:06 AM: Message edited by: Stu Fyfe ]

[Thad]

Most of Ralph Munroe's boats were unshrouded. They were gaff rigged and often carried topsails. Presto was 41'oa, gaff ketch rigged with the main mast 36' above the deck 8" diameter at deck. She carried backstay runners with purchases for use when needed.

[PVanderwaart]

I have trouble with several of your assumptions.

1) Total cost. Is the cost saving that you forsee really due to going to an unstayed mast, or is it due to a process of simplification that could be applied to the original rig? Remember that the partners and mast step are going to have to be re-engineered as well as the mast itself. Cost reduction by finding a used mast may be at least as great as changing the design.

2) I don't see that an unstayed mast is better for singlehanding. If so, only due to simplicity that can be applied to the stayed mast.

3) I would guess that the number of unstayed aluminum masts is greater than for carbon fiber.

4) I agree on wood as a material. Designer Phil Bolger has written that he thinks that wood is a suitable as aluminum for unstayed masts. There are plenty of examples, and many types of designs, including chinese rigs.

[Venchka]

The mast calculator stops at 40'.

The mast calculator for a 40' stick and 470 sq. ft. of sail area yields a 10" diameter Doug-fir stick that weighs 600 pounds.

Can you say "junk rig"? A Jay Benford Badger 34 with 600 sq. ft. of junk sails would require (and I'm totally guessing) a pair of 40' sticks at 8" diameter weighing 350 pounds each. You might be able to get away with hollow spars on a Badger. Ask Jay Benford.

Cost of Doug-fir in The Swamp for the above examples: $1,000-$1,500.

Pick a different boat or pick a different rig or build your own hollow, stayed, wooden spars. Estimate costs up front before buying plans. Get all the ugly surprises out of the way early.

Wayne
In the Swamp. :D

[ 06-22-2005, 12:14 PM: Message edited by: Venchka ]

[kc8pql]

Even if you decide that you can make an unstayed mast that size work, the partners and cabin trunk are going to need some major redesign to take the load.

[Bob Cleek]

Read the Sponberg information carefully. Only one of their unstayed masts has been put in as a retrofit. In that instance, they had all the design specs and got lucky in that the hull design was suitable. As for what has been said above, it's all true. Unstayed masts are an option for hulls which are light and easily driven. Beyond that, you are looking at junk rigs, which are a different set of physics altogether.

If you want to visualize the engineering problems simply, think of it this way. Take a foot of 3/8" dowel and stick it in a shoebox. Lift the shoebox by holding the end of the dowel horizontally. Now do the same thing with a brick instead of a shoebox. Ask yourself, what does the dowel have to look like to hold the brick horizontal the same way it holds the shoebox?

However, go back to your original problem: COST. Your interest in an unstayed mast is cost considerations, not design, right? Okay, think about solving the cost problem. We've already established that after you've paid for the engineering, which is very important, you've got to pay for all that carbon fibre and so on. (Sorry, solid wood IS too heavy.) First, an unstayed mast done right (like you've done with the rest of your boat, correct?) is probably going to cost you as much as a stayed rig.

Now, have you considered a USED rig? There are lots of boats that are cut up and sent to the landfill. They all have rigs which are usually in a lot better shape than the hulls. If you can find a yard that's cutting up boats, they will often have some salvaged rigging around. You should be able to find spars, or at least fittings, to suit your needs. Certainly, you should test the wire and fittings for strength, or have a new gang made up, but the bulk of the expense in fittings can be saved by recycling!

When the road gets steep, sometimes the better solution is to find another way around the mountain rather than trying to reinvent the wheel!

[Dan McCosh]

I don't see why an unstayed mast would be any less expensive than a stayed mast. The wire itself is pretty cheap, and results in a lot less material in the spar.

[Philip Maynard]

I'd get a smaller boat, one that you can afford.

[Jay Greer]

I did an article for wooden boat some fifteen years ago called "Black Cat'. Richard Black of Ventura CA designed and built a beautiful unstayed cat ketch that is very impressive. Contacting him might be worth the effort. I understand he still lives in Ventura.
JMG

[Chris31415]

I don't understand why the calculator stops at 40, or why it is easy to build an unstayed mast for a 17' boat but a 43' boat is impossible.
I think that a combination of mono directional fibreglass and very thick walls would be needed but the weight would come out very similar to a stayed mast.
Hal Roth in "How to sail around the world" quotes 1200lb for the mast, rigging and fittings down to mast step on a light weight 50' boat. I don't think that figure includes winches, chain plates, sheets etc.
Thats a lot of weight for the mast. A 10' x 50' solid telegraph pole would weigh in the order of
1400lb with no attempt to taper or lighten.
So, tell me, if I built a mast of western red cedar, 10" square tapered to 5" at the top, 3" wall tapered to 1.5" at the top, with mono directional fibreglass epoxied down the forward end to take the tensile loads, diagonally wrapped with mono drectional fibreglass, blocked solid at the base, deck and top how and where would it fail?
It would be possible to use a slightly smaller sail area as the large high roach would increase efficiency, and the winches, chain plates, furlers etc. would be smaller in number and much lighter.
I do not think that the comparison with a brick is valid. An unstayed mast with a single sail has its loads spead over its entire length. The stress from the downhaul would be identical to that for a stayed mast, though the points where the chokers connect the wishbone to the mast would need some localised reinforcing.
I think that if I epoxied a 12" piece of 3/8 dowling covered in fibreglass matt into a hole drilled right into a brick the combination wold be almost indestructible, unless I put the stick into a vise and hit the brick with a hammer.

[ssor]

Let's see a 12 inch x3/8 dowel scaled up to forty feet = a fifteen inch diameter stick forty feet long, solid, made of hard wood. It could work.

OR it could break. If you want to roll the dice, go for it.
The weight per foot for wire rope and sta-lock fittings is easily figured.

[Bruce Hooke]

There was a good discussion here recently about reinforcing the outside of a mast with things like carbon fiber or unidirectional cloth. The short story is that for it to work you need to carefully engineer the whole thing or, as I recall it, either the wood or the reinforcing material ends up taking the full load until it fails and then the load gets transferred to the other material, which, not being strong enough to take the full load, also fails.

Skene's Elements of Yacht Design gives a very simply (if somewhat vague) formula for a solid spruce mast:

P = Wind Preassure = sq. feet of sail area * 1.5

L = Length of mast in INCHES

Safety Factor = 1.5 for small boats up to 3.5 for large catboats with gaff rigs

15,700 = pi * fiber stress of spruce, which is 5,000

Diameter (inches) = Cube Root of (16 * P * L * safety factor/15,700)

You can substitute other suitable woods for Spruce in the equation if you know the fiber stress.

It would take a bit more work to convert this equation to a hollow mast. Skene's just deals with hollow masts in the context of stayed masts.

[mbogo]

Why not keep the boat and its general rig design, but go with a simple wooden mast (aka telephone pole), 6x7 galvanized wire, galvanized turnbuckles, and galvanized cable clamps. Find the pole or cut down a tree and let it season as you build the rest of the boat, and buy the rest of the stuff at the local Fleet Farm store cheaply. Constructing your own rig from these materials is not any harder than building the rest of the boat!

It might not be the most elegant rig, but very simple and strong and easily repaired to boot. A little too Buehler-ish for some, but it got Moitessier around the world more than once on Joshua. That's exactly the kind of rig he had. Roberts boats are all deck-stepped if I remember rightly, so there should be little to no work in redesigning the deck step, especially if you are building the boat yourself - just make the step fit the mast when you come to that point.

[ 06-23-2005, 10:54 AM: Message edited by: mbogo ]

[Venchka]

Originally posted by Chris31415:
I don't understand why the calculator stops at 40, or why it is easy to build an unstayed mast for a 17' boat but a 43' boat is impossible.
I didn't design the mast calculator. I just use it.

Nobody said unstayed masts for a 43' boat were impossible. An untechnical, off the top of my head personal opinion: an unstayed mast for a 43' boat will either be A) Way too heavy or B) Way more complex and expensive than a conventional stayed spar.

Shoot, even the so-called unstayed carbon and Kevlar wing masts have a fair amount of rigging.


When a new grand-prix 50-footer sails for the first time you'd expect hours of rig tuning, that is, unless it's a carbon/Kevlar wing mast without shrouds, spreaders, or discontinuous rod rigging. So it was when Krazy K-Yote Two, Ortwin Kandlers' 50-footer for the French Admiral's Cup team set sail for the first time last week on Narragansett Bay -- the rig was pre-tuned with only the forestay, running backstays and checkstays for the crew to control.
There ain't no free lunch. You gotta have something to hold the mast up. Either mega-pounds of wood, mega-bucks of high-tech stuff or something in between like stainless steel wire rope. Obviously, beyond a certain length, the last option is still the best compromise.

Edit to add:

Westlawn will teach you everything you need to know.


4.5 - Unstayed Mast Design

Unstayed Masts – Overview
Unstayed Masts Are Cantilever Beams
Calculating Loads On An Unstayed Mast
Determining The Size Of An Aluminum Unstayed Mast
Determining The Size Of A Carbon-Fiber Unstayed Mast
Limitations Of Unstayed Masts
“Unstayed” Masts With Headstays
Spar Taper On Unstayed Masts
Standard Spar Taper
Calculating Deflection In Unstayed Masts
Wayne
In the Swamp. :D

[ 06-23-2005, 12:23 PM: Message edited by: Venchka ]

[Clan Gordon]

How about getting yourself a lugsail (or junk) rig and reconcile yourself to dipping the sail every time you tack.

Then you can use the halliard (always moved to the weather side) to hold your mast up. No other stays required.

You still get a mast of hefty dimensions, but it worked for thousands of fishing luggers - some with nearly 2000 sq.ft of sail on each mast.

[JimConlin]

Two factors make spar weight in a larger boat a bad thing, First, there's the stability question. In small boats, there can be lots of live ballast (you and your friends on the windward rail). In a mid-sized boat, you probably wouldn't want to house and feed feed such a large pack of passengers, so other means to keep the boat upright are needed, like reducing weight aloft. The other thing arguing against heavy spars in a mid-sized boat is pitching or hobbyhorsing. If the spars are heavy and there's lots of heavy stuff in the ends of the boat, the boat's natural pitch period might approach the period of the seas you're sailing in. That makes for a long afternoon.

[ 06-23-2005, 07:48 PM: Message edited by: JimConlin ]

[ssor]

Pride Of Baltimore and Sultana both have solid spars with stays and shrouds Pride is over 100 feet from keel to main trucks. All is relative to the mass of the vessel. Skipjack have solid spars and get along just fine with them.

[Bruce Hooke]

There are plenty of boats that are too large for human ballast to matter that much that have unstayed masts. So, it certainly can be done. Whether it is a good idea on your boat or a good way to save money is another question.

Designing a mast that is suited to the boat is not a completely simple process. There are important judgement decisions that need to be made along the way. Also, simple equations such as the one I posted are likely to overshoot on many boats because to keep things simple they have to make some assumptions. This does not mean you can use the simple formula and then reduce the dimensions, because the simple formula might not be overshooting on your particular boat. It does mean that someone with more knowledge might well be able to design a lighter mast than what the simple formula comes up with.

So, what you might want to do is check with a yacht designer. I don't think it would take much time for someone with the right knowledge to come up with suitable dimensions (or tell you why it won't work). Going to an unstayed mast also changes the loads on the boat so some significant structural changes would likely be necessary, and again, that is design work best undertaken by someone who knows what they are doing. The bad news is that figuring out what needs to be changed structurally is likely to be a bit more time consuming...

[Chris31415]

So, if I understand the story so far:-
Wood is elastic enough to make an unstayed mast, but its strength is sufficiently low to make the mast unacceptably heavy.
Glass fibre is sufficiently strong to make an acceptable mast, but it is not elastic enough to make a durable one.
Aluminium is strong enough but is not elastic enough.
Carbon fibre is both strong enough and elastic enough to make an acceptable mast.
This tells me why all of those expensive masts are made from uni-directional carbon fibre.
It all probably depends on whether uni-directional carbon fibre is available at a low enough price to justify the exercise.
A mast made from uni-directional carbon fibre tape over a light hollow wood core sounds feasible, and it could well be cost compeditive with a conventional mast for amateur construction.

[Chris31415]

And the boat would need well placed high lifelines to make up for the lack of handholds normally provided by standing rigging.

[mmd]

... and don't forget the beefed-up hull & deck structure to withstand the lateral and longetudinal forces usually carried by the standing rigging.

[wyndham]

This is turning into one of those strings where someone keeps asking the same question until he gets the answer that he's looking for.
The answer is yes. It is absolutely possible for an amateur builder to redesign a boat and a spar, build the boat and the spar and defy years of convential wisdom and standard engineering practice. The person to do so is the initator of the string.
Let us know how it comes out.

[Bruce Hooke]

I don't think wood is CERTAIN to be too heavy. I do think that it is quite likely to be too heavy and I do think that to know for certain you need to have someone who knows what they are doing run the math to both calculate the dimensions for the mast and the impact of that added weight on stablity. I also think that once you pay someone to do that math and pay them to redesign the deck and hull structure to accomodate the loads of an unstayed mast you will eat up any possible cost savings that an unstayed mast might bring you and then some.

On carbon fiber over wood...you need to read this thread: http://www.woodenboat-ubb.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=004257

[Bruce Hooke]

I just re-read your original question and I am wondering now if you also want to redesign the sail plan at the same time? In other words, are you thinking of going to something like a cat-ketch rig? If so that changes the picture by quite a bit. It certainly moves you into a realm where unstayed masts are fairly common. On the other hand it also raises a lot of issues around what happens when you start radically redesigning a sail plan.

If that is the direction you want to head then you are basically trying to become an amatuer yacht designer. This can be done but I would prepare yourself for some serious reading and get ready to draw a fair number of student-grade plans before you produce something that should actually be built. I would also strongly encourage you to try out your new skills on something a lot smaller than a 43' sailboat!

[TimothyB]

Lots of spirited answers....

Basically, unless you are a Naval Architect, DO NOT put an unstayed mast on that hull, in the position that you see on the Wyliecat. The 434 is specifically designed to have its force coming from its designed sailplan, and while there is likely a little wiggle room, you go putting a single, large mast that well forward in that fine of a bow and you'll have all hell to pay.

That being said, you also do NOT want to put a deadly heavy all wood mast on her, in the middle either. We're talking about a difference in balance of something on the order of 100% more weight aloft.. this on a boat that has only a 30% ballast ratio.. again, asking for trouble.

If you really want to save some bucks, use 6x7 galvanized wire (available from farm supply catalogs), all galvanized fittings (many things here also available from farm supply) and a nice, normal sized pole. Some people here dislike George Buehler, but he has a hell of a section on mast making and simple rigging in his Backyard Boatbuilding (http://www.woodenboatstore.com/prodinfo.asp?number=300-278) . While you're at it, get Brian Toss's The Complete Rigger's Apprentice (http://www.woodenboatstore.com/prodinfo.asp?number=300-394) Believe me, doing up the stays in regular galvanized, getting the normal pole from a pole barn, and paying out a bit of change will cost a lot less than losing your boat, and much much less than a commercially made mast of the latest geewhiz material.

[YMT]

Fairly large masts can be built with plywood and glass/composite fibers elements. Also box- section, hollow wooden spars. http://www.tantonyachts.com/834gaspl.jpg Employing sound engineering and manufacturing.In your case, as suggested somewhere above, a used mast is probably the answer.

[Chris31415]

I appreciate the input.
What I set out to do was to balance the cost and difficulty of a large cat rigged sloop against the benefits of such a boat.
Ultimatly my position is that if I can build such a boat for a similar amount of money to a conventional rig then the cat rig has to win out. A large yacht is a complex entity. There are no major problems if the cat rig is planned before building starts.
The rig would appear to have overwhelming advantages on a cruising yacht if similar reliability to a conventional rig can be achieved.
I do agree with those who have said that I am better to go with a smaller boat. Second hand equipment is simply not available in the size needed. Wooden mast, galvanised rigging and basic fittings are certainly very feasible and have been included in my plans.
When I evaluated second hand boats of a similar size the main impression was of how difficult they were to sail, particularly in crowded or windy conditions.
I will only know the best approach after I complete a full costing. This forum has certainly given me enough information to evaluate Naval Architects proposals.
In the same way that moulded fibreglass has repaced screwed wooden boats, carbon fibre has to repace rigging of aluminium and stainless steel.
As the cost of an unstayed rig would be less than that of a conventional rig if it were produced in large quantities, and the rig is certainly easier to handle this is the rig for sailors of the future.

[ssor]

Nothing in sail boats is produced in large quantity! None of the traditional components of sail boat rigging are inexpensive. There are comparable components for shore based applicatios in galvanized steel that are quite reasonably priced. Everything that you have proposed requires a considered trade-off, ascethics vs utility. Anything can be achieved if enough time, energy, and man power is applied to a problem. If you are determined to have an unstayed mast, it can be achieved, but there is no free lunch and you pay your money and you take your choice.

[Bruce Hooke]

There are certainly some advantages to the cat ketch rig (have you looked at the junk rig?), but I would try to find a design that is already a cat ketch rather than trying to covert another design. I would VERY MUCH disagree with this statement you made in your last post:


Originally posted by Chris31415:
There are no major problems if the cat rig is planned before building starts.Coverting a design from some sort of sloop or standard ketch or yawl to a cat ketch is a major change and should only be undertaken with a full understanding of the impact of the change on issues like balance, stability, pitching moment and so on.

[Chris31415]

The real issue to me is how much can I aford to spend on a hobby, and how much enjoyment wil I get out of it.
I guess what I'm really thinking of is how nice would it be to sail again on Sydney Harbour in an interesting boat. I doubt that I would ever do serious cruising.
The last boat that I sailed was a 32' Harltey ferro sloop that I built myself, and that was really very pleasant. I enjoyed the building and I enjoyed the sailing.
So I am taking the comment that a much smaller light boater is needed very seriously.
The modern version of ferro is sheathed strip plank using western red cedar and unidirectional fibreglass. The sheathing needs to be applied inside and out. It appears to result in a strong light boat. A compromise between foam core and cold moulding.
At the moment I will probably look at the collection of plans that I have at the moment and draw up something myself, looking at around 30', and build a model.
The Roberts plans that I have at the moment come with a very firm comment the ballast should not be finalised until the boat is in the water and I think that is a very important point.
The other point about trim is that if the engine is mounted under the cockpit then it is very easy to get a stern down situation.
The Roberts fibreglass plans also have the keel moulded onto the hull. This method would facilitate trimming the yacht.
I do not think the engineering problems are insurmountable, however like my ferro boat I could end up with something that did not apeal to mainstream sailors. My experience with the ferro was that there may have been "comments" but they were from those who would never own a nice boat.
I have read most of the texts on design and boatbuilding(esp. Gerr). I think that provided the shelf, cramp and deck beams fore and aft of the mast were substanstial and that the mast step was also oversize to take fore and aft and transverse loads that there should be no dramatic failures there. All joints would need to be rounded then glassed over with several extra layers of unidirectional fibreglass(300 to 850 gm/sq. m.). The deck would also need to be one size heavier.
I'd think in terms of 5 layers of 300gm/sq. m. carbon fibre tape on a male mould to make a mast 40' above deck. The wishbone could be made by winding carbon tape fore and aft around a female mould, maybe using unidirectional fibreglass as a filler. Skene's formula indicates a diameter of between 4" and 5.4" when setting 400 sq. ft. of sail. Intuitively that seems rather small. To keep things simple I would use a fixed mast with a sail track a la Wylie.
I'd position the mast by estimating the centre of pressure for the sails on my existing plans and putting the centre of pressure for the unstayed mast/sail in the same place. This could be verified using the model. If a major mistake was made the centre of pressure could be adjusted by altering the length of the wishbone, however most catboats seem to have the mast in a similar position. The beam may need to move forward to counter the aditional weight in the bow, but I would still keep a wide, sugar scoop stern.
The other important point in design is the need for high lifelines on a "large" cat boat. I'm thinking that if the hull and mast are built from epoxy/fibre reinforced wood then the staunchions could also be built the same way, into holes in the deck/shelf/clamp and "taped" into place.
I will have to rejig my calculations on cost but the ballast/epoxy/carbon/glass/wood cost could well be under $A30,000, with engine and other parts comming around $A25,000 more.
Thats about the cost of a reasonable 20 yr old boat of the same size.

[Venchka]

The Norwalk Island Sharpie 29 and 31 have a well deserved reputation and strong following in Australia. Simple. Cat ketch rig. Not terribly expensive. The 29 uses unstayed masts. Something to ponder.

Wayne
In the Swamp. :D

[Kermit]

Unstayed masts here:

http://www.parker-marine.com/28pischoonerpage.htm

One of my personal favorites. Ask Reuel.

[Chris31415]

Both interesting designs and worthy of further consideration.

[ahp]

Permit me an off-the-wall suggestion. Have you noticed some of the newer aluminum street light poles? They are tapered. See if you can serch out their manufacturer, get the parameters: diameter, length, wall thickness, alloy, and then do some engineering calcualtions, or hire some to do them for you, You might save a lot of money. If they are satisfactory you would be buying a high volumn, off-the-shelf product.

[willmarsh3]

The Hunter Vision (a fiberglass boat but the engineering principles still apply) has a free standing mast. It's very thick at the bottom and tapered. It approaches the dimensions you are looking for.
Also the Elver has a free standing mast - it's designed to possibly rotate as she tacks under sail - she's only 20' LOD though. The mast is 3 1/2" dia, tapered at the very top, and sticks up 12' from the deck though.

Will.

[Y Bar Ranch]

Since all of the realistic ideas have been floated, I'll toss out a crazy one.

Are there sources of composite whip antennas of the right length? Maybe scrap? Could they be bundled together (epoxied or not) into a single pole that would be of the appropriate diameter?

Just thinking about how to do things cheaply with materials at hand. I have plans for a boat with unstayed masts, and this thread is making me think of "out of the box" possible solutions.

[Chris31415]

Please correct me if I am wrong but the two conclusions that I have reached so far are:
1. The streses on a free standing mast are carried on the surface skin. It does not matter what is on the inside(air does nicely) all the loads are going to be on the surface.
Any failure on the skin will result in the stresses being transferred to inner layers that will be even more highly loaded, eventually resulting in the failure of the mast.
The skin needs to be thick enough to carry the compression loads. Additional thickness increases the loading on the mast.
2. Carbon fibre is very elastic-that is it returns to its original size once the strain is released. Some of us are familiar with the test to destruction that an be performed on a carbon fibre fishing rod when it is bent.
Aluminium, stainless steel, glass fibre and to a lesser extent wood are not nearly as elastic so that as they are cyclicly loaded the base material is progressivly degraded(individual fibres or strands break).
We are all familiar with the need to replace stainless steel rigging on a regular basis, as normal loads stress it past its elastic limit. An aluminium mast is loaded in compression so that it is not subject to cyclic loadings past its elastic limit.In particuar one of the requirements for a free standing mast is that it must flex in such a way that energy from wind gusts amd boat movement etc. is stored and released in a progressive manner.
I cannot see any realistic alternative to carbon fibre for a large free standing mast.
The main problem that I am contemplating at the moment is how to calculate the loadings, and to transfer those to a layup schedule.
Working compression loads for a 50' freestanding mast could be in the region of 2000kg(yes I know it is a force, not a mass but this is easier) with a safety factor 3 times that. Loads in tension are, of course, equal to this. Skenes formula may give a good indication of required diameter.
Materials for a large mast could well come to less than $A5000. The improvement in quality that come from using carbon fibre really mean that nothing else will be quite as good.

[TimothyB]

Sure there is a realistic alternative to a carbon fiber free standing mast.. a properly ballasted keelboat with a free standing, counterbalanced wooden mast with battleship scantling partners.. That is to say, a mast with a good slug of lead attached to the bottom of it. Like the Thames river barges (if I am not mistaken) or some of the old english pilot boats. You'd even be able to run under bridges. :)

Mind you, the boat would have to be pretty heavy if you wanted to use a medium to high aspect rig. Which is why I imagine those old boys used sprit and gaff rigs muchly.

Mr. Phil Bolger has a lot to say about these sorts of masts, I do believe.

[Aramas]

That's the first time I've ever seen 'carbon fibre' and 'Skene's' used in the same sentence smile.gif


1. The streses on a free standing mast are carried on the surface skin. It does not matter what is on the inside(air does nicely) all the loads are going to be on the surface.
Any failure on the skin will result in the stresses being transferred to inner layers that will be even more highly loaded, eventually resulting in the failure of the mast.
The skin needs to be thick enough to carry the compression loads. Additional thickness increases the loading on the mast. Nope. If you graph the stress of a solid mast in bending, the line representing stress goes from maximum at the skin, through the centre at zero to the same maximimum at the opposite point on the skin on the other side. That's why you can hollow out the middle where the stress is fairly low, and why larger diameters are more efficient still. If a mast is designed to take all of the stresses on a thin skin, with some kind of core to keep it in column, then failure of the skin will result in a point loading so intense and localised that it will sheer through the core like cheese.

A basic fact of life is that, the more 'high tech' a material is, the more catastrophic is its failure mode. Wood will squeal and crack and generally protest in no uncertain terms, then eventually splinter before letting go. Carbon fibre will behave perfectly, right up until the point where it literally explodes.

An appropriately engineered and constructed carbon fibre mast of the scale you're discussing will cost more than the boat it goes in. Large carbon fibre spars are not something you whack together in the back garden. I laughed all the way through your description of 'backyard carbon fibre spar construction'. You might get away with that on a dinghy, but on the scale you're discussing, you could liken it to a 50 foot long fragmentation grenade.

Carbon fibre is an extremely highly stressed material, and flaws as minor as a small air bubble or ding, or being only 1 millimetre out of column can cause it to fail catastrophically under even modest load. An Australian America's cup crew once ran a sheet to the wrong winch - it snapped the carbon fibre hull in half like a twig. Are you up for those kind of consequences?

[ 06-27-2005, 10:48 PM: Message edited by: Aramas ]

[George Roberts]

Chris31415 ---

Having read what you (and others) misunderstand about masts, I don't think you (or the others) can be helped.

I don't think there is enough "luck" in the sea to help you.

[JimConlin]

Hire an engineer before you piss away a lot of money or hurt yourself.
Full stop.

[TomF]

By all means, consult with a naval architect and/or and engineer before getting in too deep.

I'd perhaps talk to Tom MacNaughton. He's always very accessible via e-mail here (http://www.macnaughtongroup.com) at his company website. Tom frequently designs boats, even otherwise "traditional" boats, with unstayed rigs. His "Surprise" series of pinkies stands out in that regard, for instance.

Tom.

[Y Bar Ranch]

Originally posted by Chris31415:
Please correct me if I am wrong but the two conclusions that I have reached so far are:
1. The streses on a free standing mast are carried on the surface skin. It does not matter what is on the inside(air does nicely) all the loads are going to be on the surface.To be exact, the stress in the mast while under bending is inversely proportional to it's polar moment of inertia, J, (the moment of inertia of a section if you were to cut it in half).

Stress ~ 1/J

For a hollow mast, the moment of inertia is proportional to...

J ~ (Ro^4 - Ri^4), where R0 = outer radius and Ri = inner radius.

If the tube is thin walled with thickness dr, then you get an approximate J,

J ~ 4 dr^3 Ro

So in short...

Stress ~ 1/(4 dr^3 Ro)

Edited to correct mental mistake caused by being kicked in the head by the ranch mule

Oops, got my exponents goofed. Should be...

J ~ 4 dr Ro^3

So in short...

Stress ~ 1/(4 dr Ro^3)

[ 06-29-2005, 10:26 AM: Message edited by: Y Bar Ranch ]

[Chris31415]

First, thank you to "Y Bar Ranch" for his more exact summation of how the stress on a bending unstayed mast is calculated.
The value of this discussion to me is that before I go to a (not cheap) professional to design a mast for me I need to evaluate what I would get for my money. Naval architects and engineers are busy people and I am sure thay would not want a whole lot of half baked ideas presented to them.
Carbon fibre has dropped in price and availability in the last few years and is now competitive in price to aluminium and stainless as a mast/rigging material for the larger mast.
To compare past experience with racing yachts that have had the lightest possible use of carbon fibre is useful, particularly if we can ascertain the scantlings of the components that have failed, together with where they failed. Using current safety margins we would then make our scantlings at least three times that of the known failure. If any forum member has knowledge of the dimensions of carbon fibre masts, paricularly ones that have failed, it would be good to discuss them.
Unfortunatly what we know about failures of carbon fibre comes from stayed rigs where the mast experiences a considerable compression load from the rigging. I do not think that carbon fibre would be suitable for a cruising stayed rig.
We do not request engineers calculation for any other part of a yacht as this would be far to expensive. Calculations are not done in the building of aluminium masts for the same reason. Instead we follow well established practice, and consult sets of tables.
If every part of a boat had to be carefully engineered then we could only use yachts built by a few major manufacturers in the same way that we use automobiles today.
It would also be useful to look at failures of carbon fibre masts to determine what hazard they presented during and subsequent to their failure.
I have seen a quoted figure of all 22% of all insurance claims being due to rigging failure. I would expect that a well engineered unstayed carbon fibre mast would be that be more reliable than that.
The problem with a carbon fibre mast is that there is no well establised practice. If we can move towards establishing one this would be very beneficial.

[sunspirit]

Hey folks.....2007!!! here....I just stepped my 50 foot Reuel Parker/Chris White masts...into my Block Island double ender.....before going to higher latitudes I intend to have a headstay...and side shrouds with double blocks...to chainplates...in the meantime... I went to the top of the heavily raked mainmast on saturday to clear away oak branches....and....very little deflection....seemed to me ...AND the ground crew!!!!~

but/and....this adds fuel to this earlier discussion....

here is the link to the Misc...boat related forum...and many pics and posts about my boat project are nearby at the "I'm building a 38foot Block Island Double-ender...."

check em out...http://www.woodenboatvb.com/vbulletin/upload/showthread.php?p=1671934#post1671934

[Per]

Hi there!
Ever heard about the Ljungström rig?
The brothers Ljungström were Swedish engineers that designed steam turbines and steam-turbine-locomotives.
One of the brothers had an accident when sailing with the boom knocking him severely.
He designed a rig with an unstayed rotating mast with double sails.
No boom.
Quite a few of these were built in the forties. Very handy, safe and comfortable but they didn´t fit in the rule system. All these masts were of course built of wood, since no other material was available.
Look at the link.
http://web.telia.com/~u87307587/blue.htm

[Woxbox]

Here's Newick's White Wings -- unstayed masts designed originally with the Ljungstrom rig. I don't beleive the copy in this photo has it -- as I recall the original boat had the sail track running through a 180 degree sweep to facilitate spreading the split main fully out wing and wing. This is a 36-foot tri.

http://www.wingo.com/newick/whitewings3-l.jpg

[donald branscom]

The way i see it you have THREE problems.

Money......(always a factor) 2. You want an UNSTAYED MAST, 3. WEIGHT of the mast. I would just forget the unstayed part. I will explain at the bottom of this post.
I have built a steel mast for a 36 ft. steel boat . I used Skeene's Elements of Yacht design math because he uses Eulehers formula in a way a layman can understand. The best as far as I could find of any book.

If you want to just buy a mast but you do not have much money i would buy a used one or broken one and repair it if it is repairable.

The weight has to be kept reasonable like HOW many pounds per lineal ft. will it need to be. A little heavier can be ok but not too heavy.
For a 36 ft. boat. Aluminum is about 5.5 lbs per lineal ft. - to 6.1 lbs. per lineal ft., for a 36 foot boat. You can look this up at a aluminum mast web site and determine the proper weight and section for your boat.

I made a mast for a 36 foot boat with a steel tube .109 thickness
6 inches diameter, 51 feet. weight was about 6.1 pounds per lineal foot. 12 inch internal sleeves between 20 foot sections. The sleeves were made with the same material. Use skip welds or spot welds, do not weld continously around the mast.
I sealed both ends to prevent corrosion inside the mast. For the lights I used a stainless tube on the outside. The 3 wire cable had nylon thread incorporated so as not to pull itself apart from its own weight.

I had a friend that used a tapered steel pole for holding a street light.
He just modified it a little for the attachments.

OK now about UNSTAYED. The reason I think you wanted to do that is the cost of the turnbuckles the cost of the wire and fittings.
I built a complete steel mast with all fittings and turnbuckles for about $1000.00 dollars.
USE galvinized turnbuckles, galvinized wire and fittings. You can paint it with white epoxy paint if you want.

There is a supply house for riging in SF that sells everything. Put 1x7 plough grade galv. wire around thimbles using a molly hogan splice with three wire clamps for insurance. Although PGE does not use ANY clamps on its telephone pole rigging which is almost exactly the same.

You need to go to a steel boat website to hook up with the people that build masts, and of coarse you have to have the book "STEELAWAY".

[Dr.Spoke]

To expand on Per's comment about Ljungström rigs....I have a Ljungström boat - Vingen 11. She's not big - only 7m long - but has a mast which is 11m over deck ( 12m total length). The mast is unstayed, rotates and has a sail of 2x15 sq.m.
The mast is hollow - for the halyard - and is constructed as a composite of 8 staves and is approximately 14" in diameter at the base, 4" at the tip. It is not that heavy - a two-man lift, including the bearings for rotation!
It certainly flexes at the tip while sailing - but the sail is cut for that.
The only real problem with having an unstayed wooden mast is how to keep the hull stiff enough to hold the mast.
The nay-sayers at the launch of my boat claimed it the mast would fail, but after 60 years it seems strong enough. With modern adhesives a composite wooden mast should be even more reliable today.

[JimConlin]

I'm nearly done in building a 28' sistership of White Wings (above). Its mainmast is unstayed, 44' long, 6" dia. at the deck and is made of carbon fiber. It was not inexpensive to build. For unstayed masts of relatively high aspect ratio, there's a tradeoff between four desirable traits, light weight, small diameter, stiffness and modest cost. You can't have all four. Getting the first three requires expensive materials and tedious construction techniques.

[Dan McCosh]

Might note the typical junk rig involves a wood unstayed mast.

[Pierce Nichols]

This is turning into one of those strings where someone keeps asking the same question until he gets the answer that he's looking for.
The answer is yes. It is absolutely possible for an amateur builder to redesign a boat and a spar, build the boat and the spar and defy years of convential wisdom and standard engineering practice. The person to do so is the initator of the string.
Let us know how it comes out.

The reason the stayed mast remains the most common for mid-sized and larger boats with 'conventional' (in the western sense) rigs is that everyone knows how to make one work, and they have centuries of experience to fall back on. It requires no difficult engineering; standard sailboat scantling rules are based on it; and the spars & other equipment for it are as off the shelf as anything for the purpose ever is. These are huge factors in its favor.

An unstayed mast is not a particularly strange structure from an engineering perspective -- it's just a long, skinny cantilevered beam, possibly tapered. The mathematical basis is strictly first semester solid mechanics. And if you use carbon fiber the total mass is likely going to be less than that of an equivalent aluminum spar & all the standing rigging, plus you don't have the parasitic drag of all that wiring aloft, which has all sorts of positive effects on the sailing characteristics. On the downside, all the loads now go through the mast partners and the mast step, which have to be heavily reinforced to take it.

Personally, I'm somewhat charmed by the idea of unstayed rotating wing masts, especially in cat-ketch or cat-schooner configurations, such as that pictured in plate 66 of the fourth edition of the Gougeon Bros. book. That mast itself should be fairly easy to make by the old Rutan Aircraft Factory method (i.e. hot wire cut foam core, wood spar, unidirectional glass or carbon spar caps, fiberglass sheathing), but the bearing is definitely the sticky wicket.

[Pierce Nichols]

To expand on Per's comment about Ljungström rigs....I have a Ljungström boat - Vingen 11. She's not big - only 7m long - but has a mast which is 11m over deck ( 12m total length). The mast is unstayed, rotates and has a sail of 2x15 sq.m.

How is the bearing arranged to allow it to rotate?

[Dr.Spoke]

There are two bearings, one at deck and one at the foot. They are of a "cartridge-type" - but unsealed. The outer "race" has a rounded/convex outer face - to allow some amount of self centering and angle adjustment.
The deck bearing is held by circular steel plates bolted through the deck. The mast foot bearing has a lower steel plate with a circular hole. The bearing rests in the hole, and the plate can be moved fore-aft to allow for rake of the mast. The upper plate is similar - but in two halves. When the mast is stepped, and angle determined, the upper and lower plates are bolted together to sandwich the bearing.

Below the upper/deck bearing is the "bobbin" that the control-rope wraps around - this is led to a handle in the cockpit: turning the handle turns the mast. The "bobbin" is in two halves which clamp the mast after the bearings are set-up. From fully furled/reefed to full sail takes less than half a minute - even with a good press in the sails. But I usually ease the sheets considerably before reefing/furling the sail.

[JimConlin]

There are two bearings, one at deck and one at the foot. They are of a "cartridge-type" - but unsealed. The outer "race" has a rounded/convex outer face - to allow some amount of self centering and angle adjustment. ...

Can you post photos, drawings or links for these bearings?

[Dr.Spoke]

I'll take some photos next time I'm down at the boat of the bearings and the mast-step. Drawings might exist at the Swedish Maritime museum - I'll check! Links - er, no...Custom-made 60 years ago - hard to find!

[JimConlin]

There are two bearings, one at deck and one at the foot. They are of a "cartridge-type" - but unsealed. The outer "race" has a rounded/convex outer face - to allow some amount of self centering and angle adjustment. ...

Can you post photos, drawings or links for these bearings?

[Pierce Nichols]

There are two bearings, one at deck and one at the foot. They are of a "cartridge-type" - but unsealed. The outer "race" has a rounded/convex outer face - to allow some amount of self centering and angle adjustment.

What do you mean by a cartridge-type bearing? Is it some type of roller bearing or something else?

[john welsford]

Some issues that have not been covered so far in this thread, is that the structure of the boat will need to be very different in that the torsional loadings on the hull and decks in the area where the mast is to be stepped will be very much higher than with a stayed rig.
Another thought is that there are many rigs much better suited to unstayed masts than the conventional sloop. Junk rig, standing and dipping lugsails, sprit boomed bermudian and sstanding lugsails, balance lug, solent lug and the list goes on.
Just swapping an unstayed spar of whatever material for a conventional one is likely to present the swapper with more issues than might be apparent at fist glance.

I drew a boat from scratch for a home builder client determined to build on an absolute mimimum budget, that budget including time as a cost. It turned out cheaper to buy a rolled carbon fibre tube sleeved to length and set up a gaff cutter rig with running backstays to control forestay tension than to have a conventional alloy spar with spreaders, stays, rigging screws and chainplates, a mushroom farm of winches and a traveller.
Sailed very well too! At a guess not far off the conventional rig on the wind and quicker reaching and running without extras.

But, thats drawing the boat with that in mind from the beginning.

JohnW

[Dr.Spoke]

"Cartridge type" - yeah sorry about that....I work with bikes and we distinguish between cup-and-cone adjustable bearings and cartridge bearings...I'll post some pics, when I get down to the boat this weekend...I've got a bit of sanding to do on the deck this winter lay-up!

As JohnW says, the hull construction is critical to get the most from an unstayed mast: but an unstayed mast does give the freedom to employ som unusual rigs - like a Ljunström/Lapwing. Having sailed pretty much every type of rig, I was intrigued to try the Ljungström. For single handed sailing in confined waterways it is a dream, but has it's shortfalls.
I don't think that hull construction need be heavy to allow an unstayed mast - just designed for it from the beginning. My boat is lighly built, but easily stiff/strong enough.
I've got some pics on the blog....
http://www.dobrakusa.blogspot.com
which badly needs updating....After I've done some sanding....

[Per]

Hi Dr. Spoke! Is there any possibility for a Stockholmer to have a look when you put your boat into the drink again this spring?:)

[BigCat]

Google "birdsmouth masts" and you will find a method of making hollow unstayed wood masts, with articles offering complete instructions. A poster in this thread claimed that junk rigs need to dip when tacking. Not true. They are, in fact, self-tending when tacking. I sailed a junk rigged 35' boat across the Pacific. It had and still has unstayed solid wood masts, 50,000 miles later, the original masts, carrying a total of 770 sq. feet of sail. The junk rig usually has relatively short masts, so having solid masts is not a problem in a stiff hull. The junk rig, at least, puts very little strain on the hull and deck. I should know, I built the boat above, Batwing, as well as sailed it. I did very little reinforcement of a conventional fiberglass hull and fiberglass and balsa deck. If 50,000 miles and 30 years of voyaging isn't proof, what is? Check out http://groups.yahoo.com/group/junkrig/ to learn more.