Un-stayed junk masts

[NickRobinson]

Any link/wisdom as to why junk masts don't seem to need stays? The w/sites just praise or diss them in general terms.
I note that they are keel stepped so have support from the cabin top, even so, I can't get my head round this, surely if a sail is driving a hull at x knots there are forces to counter whatever the sail plan.
Ditto under bare sticks bashing about in a seaway.

 

[PeterV]

Why should they need stays? Plenty of boats don't, stays just allow the mast to be made thinner and lighter.

 

[LittleSister]

The sideways forces are taken by the cabin top. An unstayed mast is in effect a cantilever. The masts are sufficiently strong, by whatever combination of thickness and material strength, to take the load from the sail to the cabin top and keel.

Such masts might be wood, carbon fibre, aluminium, etc. They are used on some gaff and other rigs, not just junks.

 

[dunedin]

Lots of boats with unstayed masts - from little uns like the Laser dinghy to bigger ones like Maltese Falcon Maltese Falcon (yacht) - Wikipedia

 

[RJJ]

Stays add windage and complexity. On a sloop (gaff or Bermudan) you care about such things as headstay tension, mast bend, which make stays important. (You could have a mast stiff enough to hold your headstay bar tight but it would have to be several feet thick I guess).

In a junk rig, it's only the heeling moment of the rig, so you can do without. Also I guess a benefit of doing without is that you can weathercock the rig if necessary.

 

[Black Sheep]

Any link/wisdom as to why junk masts don't seem to need stays? The w/sites just praise or diss them in general terms.
I note that they are keel stepped so have support from the cabin top, even so, I can't get my head round this, surely if a sail is driving a hull at x knots there are forces to counter whatever the sail plan.
Ditto under bare sticks bashing about in a seaway.

As others have said...

Yes, there are forces to be countered. Specifically the heeling force that's trying to knock you down, and also the forward or diagonal force of the applied power to the boat. Normally the heeling force is the greater, and that would be expected to be only as much as would take to heel the boat right over. You can calculate that, and it isn't huge. Big enough to need a strong mast for sure, but the loads on the cabin roof aren't insuperable as long as there's adequate reinforcement to transfer the loads to the hull.

Bermudian masts take a lot of rigging as they are designed as a stressed structure. The junk mast, as mentioned above, is a simple cantilever. The boat stresses end up lower.

 

[Laminar Flow]

An unstayed mast is designed to resist bending, a cantilever as Little Sister pointed out. A stayed mast is designed to resist compressive loading. In simple terms.

This tends to mean a much larger cross section for freestanding masts which, generally speaking, makes them heavier and can be aerodynamically a distinct disadvantage.

Choice of materials for freestanding masts is more limited due to stress fatigue, especially aluminum. Hinterhoeller yachts had quite some problems with their aluminum masted 26', 30' and 36' cat boats at the time.
Materials of choice are now:
wood is expensive if hollow and rather heavy if solid and
carbon which is super expensive.

Common, compression loaded aluminum spars can be easily extruded and mass-produced in pretty much any size.


In the 80's there was a brief euphoria around free standing rigs as the be all and end all to efficient and easy sailing, but it didn't catch on widely.

 

[DownWest]

We have a model of a Chinese war junk, dating from the 1800s. Plenty of shrouds on that. Three a side for the main, two for the mizzen and foremast..In general, Junk rigs are simple, low stressed easy to use. But, they don't point particularly well to windward. High aspect lugs like the Romily in the above picturen do point well, but the stresses are higher and she has carbon masts, as do the Freedom series.
Pointing higher needs good headsails and taught forestays, leading to more complex rigging and far higher loads on everything. The compressive load on a mast is very high and, as a rule of thumb, each chainplate can lift the boat. There is no compressive load on an unstayed mast, just bending and those are not that high.
On smaller boats, they have a lot going for them.
Laminar's comment about wood is not really valid. Yes they need to be a bigger section if in wood, but cost of a hollow one is not that high (look at birdsmouth construction) and the cost of rigging (and replacing it..) makes a difference.

Google Norwalk Island Sharpies and on their site is recounted one of their 26ft cat ketches crossing the Bass Straight in winds in excess of 50kts..So strong enough and those are ally masts.

 

[Black Sheep]

Junk rigs ... don't point particularly well to windward.

Don't they? Do you have an up to date source for that? Or is it personal experience?

 

[DownWest]

Don't they? Do you have an up to date source for that? Or is it personal experience?

I should have qualified that. Some of the newer articulated ones are quite good, but the classic flat cut ones are not so. I am currently building a little cat yawl with unstayed masts, but not junk type rig.
There is/was a site all about junk rigged boats, based on modern hulls. Escapes me for the mo, I will look later.

 

[Laminar Flow]

Laminar's comment about wood is not really valid. Yes they need to be a bigger section if in wood, but cost of a hollow one is not that high (look at birdsmouth construction) and the cost of rigging (and replacing it..) makes a difference.

If you have the woodworking skills to build a hollow, tapered spar, perhaps, but if you require professional help, not to mention the price of clear lumber these days, I doubt that very much.

We have a model of a Chinese war junk, dating from the 1800s. Plenty of shrouds on that. Three a side for the main, two for the mizzen and foremast..In general, Junk rigs are simple, low stressed easy to use. But, they don't point particularly well to windward. High aspect lugs like the Romily in the above picturen do point well, but the stresses are higher and she has carbon masts, as do the Freedom series.
Pointing higher needs good headsails and taught forestays, leading to more complex rigging and far higher loads on everything. The compressive load on a mast is very high and, as a rule of thumb, each chainplate can lift the boat. There is no compressive load on an unstayed mast, just bending and those are not that high.
On smaller boats, they have a lot going for them.
Laminar's comment about wood is not really valid. Yes they need to be a bigger section if in wood, but cost of a hollow one is not that high (look at birdsmouth construction) and the cost of rigging (and replacing it..) makes a difference.

Google Norwalk Island Sharpies and on their site is recounted one of their 26ft cat ketches crossing the Bass Straight in winds in excess of 50kts..So strong enough and those are ally masts.

Tom Colvin, who designed quite a number of junk-rigged vessels and was a great proponent of the rig, used shrouds on all his designs, including his traditional junks. Many were also fitted with jibs on stays. Colvin used alloy pipe for his stayed masts.

Re Norfolk Island sharpies: there is no doubt that aluminum is strong enough for a freestanding spar, initially at least. It is the long-term stress fatigue that is a problem. This was the issue with the Nonsuch series of catboats that had a series of mast failures.

Junk rigs are not as close-winded or as efficient(to windward) as Bermudan and are more comparable to gaff. Colvin did some comparative tests at the time. I didn't find his tests all that informative, as he was comparing ketch rigs, gaff & Bermudan, with a single masted junk(???). The junk was, as he claimed easier to handle and faster downwind. Dear me, how surprising?
In recent times, steps have been taken to address the inefficiency of the flat junk sail with shaped panels or wrap-around streamlined sections to alleviate the turbulence of a comparatively large cross section mast.
The biggest disadvantage of the junk sail, IMHO, is it's significant weight which easily outweighs any supposed savings for not having any standing rigging.
Modern reefing systems have rendered the junk's once most promoted advantage of easy reefing obsolete.

 

[Buck Turgidson]

If you have the woodworking skills to build a hollow, tapered spar, perhaps, but if you require professional help, not to mention the price of clear lumber these days, I doubt that very much.

Tom Colvin, who designed quite a number of junk-rigged vessels and was a great proponent of the rig, used shrouds on all his designs, including his traditional junks. Many were also fitted with jibs on stays. Colvin used alloy pipe for his stayed masts.

Re Norfolk Island sharpies: there is no doubt that aluminum is strong enough for a freestanding spar, initially at least. It is the long-term stress fatigue that is a problem. This was the issue with the Nonsuch series of catboats that had a series of mast failures.

Junk rigs are not as close-winded or as efficient(to windward) as Bermudan and are more comparable to gaff. Colvin did some comparative tests at the time. I didn't find his tests all that informative, as he was comparing ketch rigs, gaff & Bermudan, with a single masted junk(???). The junk was, as he claimed easier to handle and faster downwind. Dear me, how surprising?
In recent times, steps have been taken to address the inefficiency of the flat junk sail with shaped panels or wrap-around streamlined sections to alleviate the turbulence of a comparatively large cross section mast.
The biggest disadvantage of the junk sail, IMHO, is it's significant weight which easily outweighs any supposed savings for not having any standing rigging.
Modern reefing systems have rendered the junk's once most promoted advantage of easy reefing obsolete.

The do attract a cult like following though

I like the idea of a junk style wing sail around the mast but no one has done it yet to my knowledge. In my thought experiments the problem is always leading edge shape.

 

[prv]

Any link/wisdom as to why junk masts don't seem to need stays?

Same reason aeroplane wings don’t ?

Pete

 

[Laminar Flow]

The do attract a cult like following though

I like the idea of a junk style wing sail around the mast but no one has done it yet to my knowledge. In my thought experiments the problem is always leading edge shape.

I came up with a similar idea, but I have since seen it done several times and I do believe one of the large French companies is working on a wingsail concept based on this principle.

In the late 80's early 90's I was involved in the design and subsequent construction of a 50' lifting keel design. The original design was to have a rotating wingmast schooner rig with two identical masts with what now would be called a fat-head sail.

In the end we built her as a cutter(almost at the last moment) when it became clear that we could carry the same SA on a single mast at a considerable savings in cost.

One thing I find that is not given much thought in unstayed rigs is the pitching moment of a 380kg mast situated on the forward waterline at the bows. In retrospect I think the decision to rig the boat as a cutter was the right one. The single mast, everything included, was also considerably lighter in total.

I still have a soft spot for weird rigs.

 

[DownWest]

The do attract a cult like following though

I like the idea of a junk style wing sail around the mast but no one has done it yet to my knowledge. In my thought experiments the problem is always leading edge shape.

There is one in the local Marina and my father nearly finished one before he died. He did have experience, having built a foiling tri in '55, with a wingsail, built just like a wing, with a ply leading edge and doped fabric over ribs.

I always seem to be typing when Laminar posts....

 

[Laminar Flow]

There is one in the local Marina and my father nearly finished one before he died. He did have experience, having built a foiling tri in '55, with a wingsail, built just like a wing, with a ply leading edge and doped fabric over ribs.

I always seem to be typing when Laminar posts....

People who design and build strange boats have my every sympathy; they give me hope that there are still some out there who do not slavishly follow the well-trodden path.

 

[Ceirwan]

Don't they? Do you have an up to date source for that? Or is it personal experience?

Every-time someone tries to quantify this then the junk rig side calls foul play on the testing methodologies, I've never seen any fair test when the Junk rig comes out on top upwind.
Offwind if the Bermudan rig doesn't fly downwind sails then it can be a different story.

The way I look at it is that at the top of performance sailing there is literally millions invested into going faster, no stone is left unturned, none of them are using a junk rig, not even the ones based outside of rules that are going for out & out effort.
If we start seeing the Junk at high level then I'd take note, but I won't hold my breath.

That said for the type of sailing a lot of people do the Junk is perfect, it might not be the fastest upwind, but neither is an old school long keeler, but that doesn't stop it being the right boat for plenty of people.

 

[reeac]

Clearly shrouds and spreaders are structurally more efficient and so lighter than an unstayed cantilever ....simple mechanics. That's how aeroplanes started off until speeds became such that aerodynamic drag became too much of an issue.

 

[JumbleDuck]

Any link/wisdom as to why junk masts don't seem to need stays?

Is it not because, like lugsails, junk sails have to get to either side of the mast for best efficiency, and that means going round the front which in turns mean there can't be any shrouds in the way?

 

[Laminar Flow]

Is it not because, like lugsails, junk sails have to get to either side of the mast for best efficiency, and that means going round the front which in turns mean there can't be any shrouds in the way?

To the best of my knowledge, no junk sail tacks around the front of the mast. Generally, in multimasted junks the sails are carried on alternating sides, so you essentially end up with a "good" side and a not so good side, aerodynamically speaking.

With traditional lug rigs, I did some research last year, at the Paimpol festival, for a book I am writing, they come in two flavours: a dipping lug and a standing lug. The dipping lug brings the yard to the lee side on a tack, offering a clean leading edge and airflow over the sail, free of interferrence by the mast. The standing lug does not bother and like a junk simply carries the yard on alternating sides.
The gentleman I talked to said they did no bother dipping the yard, but at the same time he assured me that the boats that did regularly beat him at the races.