Free Standing Masts

[owly]

PBO Article



I've been an advocate of free standing masts for a long time. To me standing rigging is a veritable house of cards. Failure of a single component can bring the works down, and there are dozens of failure points.


A friend of mine bid a contract to "take down" a very tall radio tower for salvage. It paid pretty well. The tower sat in an open field and was held up by guy wires (standing rigging). They'd paid him on the basis of the idea that he would have to get a crane, and methodically take the tower down. Instead, he simply cut one guy wire set, and the whole thing rather dramatically tipped over and crashed.



Standing rigging puts the mast in compression, pulling up on the chainplates and down on the mast. Diamond stays and such are needed because a slender column is very subject to failure in compression. Try pushing down on a broom straw standing vertically sometime.

[Cheechako]

For cruisers, I think they are vastly overlooked for sure. Many loaded cruising boats don't go to weather that well anyway. I like the simplicity of the unstayed mast. It tends to automatically unload some also in a puff.
I do worry about the longevity of free standing mast materials a bit though.

[David993s]

Interesting PBO article. Thanks for posting it.

[bdgWesternMass]

I have been studying the freestanding masts and if I do manage to actually build my boat it will have freestanding masts.

I have been thinking that I would use the Wharram Wingsail as the reference for the sail plan.

I have been reading the book "practical junk rig" which has a good overview of the current understanding of sail design based on efforts from the beginning of time until around 1988.

Practical Junk Rig | TillerPublishing.com

I also visit Eric Spongberg's website with a more modern approach for freestanding mast design.

https://www.ericwsponberg.com

Yves-Marie Tanton is an advocate.

TANTON YACHT DESIGN.

I have a spreadsheet going as I study and try to understand the forces involved.

It has taken me about 18 months to think I might have a clue...

When I finally get through C.A. Marchaj I will feel like I really understand.

Meanwhile everyone seems to agree that a freestanding mast is a simple cantilever. Since I'm considering a Schooner like rig I imagine the if there are any forestays the from mast would not be a cantilever...

https://en.wikipedia.org/wiki/Czesław_Marchaj

[owly]

Originally Posted by bdgWesternMass

I have been studying the freestanding masts and if I do manage to actually build my boat it will have freestanding masts.

I have been thinking that I would use the Wharram Wingsail as the reference for the sail plan.

I have been reading the book "practical junk rig" which has a good overview of the current understanding of sail design based on efforts from the beginning of time until around 1988.

Practical Junk Rig | TillerPublishing.com

I also visit Eric Spongberg's website with a more modern approach for freestanding mast design.

https://www.ericwsponberg.com

Yves-Marie Tanton is an advocate.

TANTON YACHT DESIGN.

I have a spreadsheet going as I study and try to understand the forces involved.

It has taken me about 18 months to think I might have a clue...

When I finally get through C.A. Marchaj I will feel like I really understand.

Meanwhile everyone seems to agree that a freestanding mast is a simple cantilever. Since I'm considering a Schooner like rig I imagine the if there are any forestays the from mast would not be a cantilever...

https://en.wikipedia.org/wiki/Czesław_Marchaj

The Wharram Wingsail is a rather neat simple design.... Not really a wingsail at all, just a sail that wraps around and encloses the mast. I rather like the lack of a boom, but I'm concerned that in some conditions it could be very difficult to pull the wet fabric down as it will likely want to cling to the mast. Inserting airfoil shaped mini ribs laced to the sail that held it off the mast, and produced more of a streamline around the mast could improve it.... It would not take many, nor would they need to be complex or heavy. When the day comes that you are fighting to pull down a wet sail in a blow, it might look like a good investment. One of the chief advantages of a junk rig is instant effortless reefing by simply letting loose the halyard until the sail drops to what you want. No tying in reefs. Taking the wingsail to the next level of soft wingsail with articulation one should get the same effect, but things get complex quickly. Whjarram claims it will drop in seconds...... I suspect that depends on conditions.






Here are some rib drawings for a soft wingsail. They can range from fairly simple to quite complex. I do not subscribe to the idea that a wingsail needs to be 3 dimensional all the way to the leech. From what I've seen flying, you can get more lift out of a single cambered surface... but the lift drag ratio is lower. I suspect that sailing with the wind aft of the beam, a single surface will generate more drive than a double surface, while forward of the beam you will have an advantage.

[bdgWesternMass]

I'm thinking along the same lines as you regarding how far back the 3-d shape needs to go.

The other wingsail design I really think is great that I'm sure you are aware of is the one one Caliente and Eagle 53 Catamaran. I think they are Randy Smyth's designs.

If I were to go for a more complex sail I would ape this design.

https://www.youtube.com/watch?v=KoGP...oaSailorOutrig

[MicHughV]

I think you are swapping one problem for another.

An unstayed mast will obviously be bigger, thicker wall sections, etc, etc, especially at the point of maximum bending moment, ie, at the deck, and also at the foot, which will be the end of the " lever arm" forces. places on the boat, which will have to be massively reinforced.

The mast will also end up being heavier, require more ballast, etc, etc.

A round aluminum telephone pole (typical unstayed mast) is also not very aerodynamic.

The few unstayed boats I've seen, invariable used aluminum telephone poles as the mast. As a telephone pole does not have a mast track, it must either have one fitted or use mast hoops on the sail.

Going back to the radio tower example above...if a free standing mast was the answer, you'd see this more, but obviously, you don't, and for good reason.

Mast height will also be limited by a free standing mast, which in turn translates to smaller sail area.

While a rigged mast can be a PITA, it's a well studied and known structure and employs large safety factors to ensure reliability.

[bdgWesternMass]

I can accept that, the inverse is also true. We are all swapping tradeoffs.

[MicHughV]

forgot to add.....free standing masts typically only have a single mainsail.....somewhat limiting a boat's performance imo....

[bdgWesternMass]

Tell that to the junk rigs

[MicHughV]

Interestingly, I knew a guy that built his own steel boat with an unstayed mast...it sported the classic junk rig......it was a nice looking boat...it sailed remarkably well....heeled a lot though...and could'nt point very high...but overall, I was rather impressed with it's performance...the design came out of some or other magazine, "Popular Mechanics", I seem to remember.

Several folks built or had built for them a Tom Colvin designed 42' steel boat....the Gazelle, it was a junk rigged boat. 40 years ago, you'd see quite a few of them, but these days, they are a rare sight.

They certainly have their proponents, no denying that.

[owly]

Originally Posted by MicHughV

forgot to add.....free standing masts typically only have a single mainsail.....somewhat limiting a boat's performance imo....

The main reason for have so many sails is the limited angles of the mainsail due to stays getting in the way. People often have multi mast rigs with free standing masts..... nor is it impossible to use a foresail.




Freedom 29 below. It should also be said that junk rigs have a percentage forward of the mast, some more than others. Low aspect, they tend to carry a lot more sail area on the part of the mast than a Bermuda rig.... The wind gradient is higher way up there, but a tiny amount of sail hardly makes good use of it.... It's a mixed bag. Free standing masts and junk rigs do not win races, and if that is your goal they are not for you.

[MicHughV]

In my youth I raced on a Finn dinghy. It had an unstayed mast and just a mainsail.
It was a zippy little thing....around 14-15' LOA as I recall.
The mast on those things could take quite a bend.

From there, I progressed to a 505 racing dink...stayed mast....no looking back after that...

[Montanan]

Freedom Cat Ketchs

Free standing masts [Plural]

https://www.youtube.com/watch?v=iFle9YZCzLw&t=7s

https://www.yachtworld.com/yacht/198...om-44-7865448/

[gamayun]

Good article. It is my understanding that the racing boats today that are built with CF spars are under designed and have failed under higher loads. My 1988 F38 was massively overbuilt because they didn't know any better. I would be surprised if that mast didn't last another 30 years and probably longer than the hull itself. But you'll never convince those who don't like the look of, or the concept of, an unstayed rig. For the racing purists, this is not the rig you want for windward/leeward buoy racing, but I wholeheartedly agree with the author's statement that:

"All things being equal, a yacht with freestanding masts will be faster off the wind than the same yacht with a genoa, and wire rigging. No rigging means that the boom/s for the sails are unrestricted in their arc of travel, allowing a greater range of angles for the sails in a relatively efficient aerofoil shape."

And she's just as fast closed hauled, too, but she just can't point as high as the others. Light wind is always going to be a problem for a heavy displacement boat, too. To each their own....