Aft-mast

[Kitlani]

Greetings,
I'd love to build this (see photo)

www.vikingboatlift.com/Experimental5.jpg

Do we have any investors?

-rg-

[Tom Robb]

Bolger (apologies to Lagspiller) designed one of these years ago. He said, IIRC, that it was hard to keep the boat in the groove.
Keeping the luff straight may be a problem - luff tension would need to aproach infinity.

[johnw]

I've sailed a boat with a similar rig. When a puff hit, the luff would sag and the sail would get all bulgy. Not what you want happening. A sail that's on a bendy mast flattens in puffs, which is what you want happening.

[Tom Lathrop]

Rigs very similar to this one surface from time to time and then seem to die. For reasons given above and a couple others, it has more disadvantages than good points. I actually have not found any real good points but am willing to listen. Ok, it looks real cool.

In order to get rid of luff sag, it needs a compression post under the hounds. With such a compression post, we can get rid of that big thing on the back end and replace it with a little wire. As long as there is that post in the middle, we might as well put a sail on it.

Yeah, that'll work. What should we call it

[JimD]

... As long as there is that post in the middle, we might as well put a sail on it...Yeah, that'll work. What should we call it

I dunno what to call it but maybe you could make it out of wood and varnish it.

[Kaa]

Boatdesign.net had a lively discussion about aftmast rigs...

http://www.boatdesign.net/forums/showthread.php?t=623

Kaa

[Kitlani]

Here are some of the given reasons for an Aft-Rig sailplan:

http://snow.prohosting.com/trollrg/e...ml#topposition

The main opposition seems to be the ability to create the right tension in the stays. According to a few of the Carbon-Fibre manufacturers, including a major one in Japan, they seem to think that they could deliver on a mast which would do the job. (I mean, even on a traditional mast the stays are not perfectly tight.)

[Woxbox]

It's not just the mast that has to be rigid - it's the entire boat.
Bolger's model had a conventional mast heavily stayed. The one in the sketch above doesn't seem to offer much athwartships rigidity. And I do wonder how the mast-boat connection is managed, or is the entire thing one big layup?

[paladin]

Ted Brewer designed on that was to be built as a small ocean racing class.....after three boats were buit and folks sailed them, all bets were off...

[JimConlin]

Getting it to work structurally without the mast being inefficently massive will be very difficult and _very_expensive. LOTS of carbon.

[Todd Bradshaw]

Isn't it amazing that if you use enough autoclaved carbon fiber and epoxy you can make a mast that works as well as one made from a tree.....

We had a guy posting here a year or two ago who had an idea he wanted to try for a canted twin-mast system. We tossed it back and forth for a while and I finally came up with a drawing of what the proposed sailplan might look like. I don't know whether he's done anything more with the idea or abandoned it, but I kept the drawing because I think it's an interesting and pretty sexy-looking rig, even on a rather traditional hull if you could manage to keep the spar weight within reason.

[YMT]

nm

[Thorne]

Speaking of modern to historical comparisons, the twin-mast system sure saw a lot of use in the 17th C in Europe.

Many of the Dutch paintings show similar systems, usually with the main mast upright and the sprit-spars (sort of proto-gaffs) canted. Sometimes the sprit is a spar, other times it comes all the way onto the deck and could be considered a second mast, but the sail configuration is roughly the same.

These were obviously not performance boats, and most didn't seem to split the sails around the sprit, but were somewhat similar otherwise.





From EuroWeb's fantastic collection of online art - http://www.wga.hu/

Use the search function, select the Dutch school and search for either "ship" or "boat" in the text field.

Here's a trad rigging question -- any idea what the spars used to hold out the back of the mainsail and/or the front of the foresail would be called?

[Kaa]

Umm... aren't these the standard sprit sails? The spar you are talking about is called a sprit and the whole sailplan is called a sprit rig. See e.g. http://en.wikipedia.org/wiki/Spritsail.

It's a simple sail plan widely used for unsophisticated small boats.

Kaa

[Thorne]

Not when the sprit goes all the way to the deck, as some of the historical paintings show.

They also aren't standard sprits even when they don't mount on the deck, as the spar is much larger and heavier, and often a proto-gaff as you can see by the blocks and lines that support the spar from the mast. And note the sheet (or whatever) that goes from the cockpit to the top of the spar -- again not standard for modern spritsails.

There are some Scandanavian boats that use large sprits in a similar manner -- we got some responses from folks up there on similar threads a year ago -- but I don't think they have either the block and lines to the mast, or the sheets/whatevers to the tip of the sprit.

[Kaa]

I think that a "standard" sprit rig can have the sprit attached to the mast as close to the deck as it likes. Even a simple Google search for pictures of sprit rigs will show you things like this



or this




As to being a proto-mast, I think the distinction is quite clear. If the spar is attached to a mast, then it's a sprit. If it is attached to the deck, then it's a mast. Just making a sprit heavy does not make it a proto-mast. In your second painting the sprit clearly doesn't touch the deck, and in the first one it's hard to see, but I would be very surprised if it relied on deck for support.

The sheet to the top of the sprit is unusual. If it were a gaff boat it would be called a gaff vang and would be used to control the twist of the sail. But again, nowadays the primary advantage of the sprit rig is simplicity (along with low CE and the fact that all spars are likely to fit inside the boat) so if you are concerned about losing power due to sail twisting, you probably would choose another rig to start with :-)

Kaa

[ahp]

Thorn, I beg to differ. These are sprit rigs and if you look closely the sprit does not go to the deck. There is a heal tackle, which when payed out allows the the lower end of the sprit to rise and swing foreward untill the sprit is horizontal. this is a way of scandalizing the sail in a squall and some Dutch pintings show this.

[JC 72]

Beautiful pictures in any case Thorne, let's build one for RMS sea training. I got to learn to use that link. What would a pinnace of Drake's day looked like? John p.s. Sorry I strayed off topic.

[johnw]

There is a version of the sprit rig that has the sprit right down to the deck and sets the sail on a line between the sprit and the mast, making it possible to brail the sail without moving the sprit. Mostly used on the mediterranian, and possibly older than the current widespread version. Even if the sprit was on the deck, it's not a mast. It moves around and is held up by that line to the mast.

[Todd Bradshaw]

They look like plain old spritsails to me and I don't recall ever seeing references to any kind of twin-mast system to hold up a similar hunk of canvas. You also need to remember that old paintings of sailboats often contain innacurate sail and rigging details, so unless an illustration was done specifically as part of a boating text, there may be some creative rigging in there due to gaps in the artist's knowledge base or memory.

Any line running up to the peak is most likely a vang, similar to a gaff vang and would be used to limit twist. You can also see some multi-part brail lines on some of the sprits, running forward to the mastheads.

[Don Kurylko]

Thorne,

These are definitely sprit rigs - STANDING sprit rigs. The heel is fitted to a strop around the mast which in turn is rigged to a tackle from the mast head so that the tension on the peak of the sail can be adjusted, kind of like a “snotter”. The tackle led from the mast head to the mid part of the sprit is there to hold the sprit up and to allow for some adjustment as well. The tackle from the peak to the deck, is a vang - also used for adjusting and trimming the sprit. The “sticks” at the luff of the jib and leach of the main are used to add tension and take out the sag from these rather heavy sails. I can’t recall what they are called, but they were in very common use throughout Europe on traditional working craft.

Missing in the paintings, but also common, are brails on the main sails. Standing sprit rigs often brailed up the sails to the mast with the sprit left standing, rather than lower the lot. Take a look at some photos of Thames barges and you will see all this gear clearly. Many of these working craft were also set up to lower their rigs ALL STANDING in order to “shoot” under bridges. Can you imagine a Thames barge running towards a low bridge under full sail, then tilting the mast, sprit, sails, etc., aft to clear the span, and then pulling it all back up again quickly once past? It must have been awesome!

[Thorne]

I stand corrected -- thanks for the input! Standing sprit rig it is.

I wasn't sure if the tackle and/or vang-like lines changed the name of the rig, as it might have been like the addition of a separate line other than the halyard to a sliding gunter making it a gaff....technically.

As for the brailing, it is shown clearly in several different Dutch paintings. Go to the above link and search for this one -
CAPELLE, Jan van de
Dutch Yacht Firing a Salvo
1650
Oil on wood, 85,5 x 114,5 cm
National Gallery, London

Any idea of what the spars holding up the ends of the main and foresails would be called (other than "sticks")?

And yes John, I'd love to have something like this out here for reenactments, but unfortunately all the really nice ones are back East.

[Todd Bradshaw]

Where exactly did you come up with the term "Standing Spritsail"? It doesn't exist in any reference that I have and I've never seen it used. You will occasionally see a reference to a boat with a "free-standing spritsail" (as opposed to one with shrouds, etc.) but I'd like to see references on "Standing Spritsail" being an actual sail type.

Quote: "The tackle led from the mast head to the mid part of the sprit is there to hold the sprit up and to allow for some adjustment as well"

No, it's a brail. The last thing you want on a spritsail is something pulling the peak corner forward while sailing. It would create massive amounts of upper sail draft. You use the weight and angle of the sprit, combined with the generally straight cut (sometimes even hollowed a bit) of the sail's head to generate tension along the head edge and prevent that edge from sagging and adding excessive draft. The sag along the head of the mainsails in the lowest painting is one of those artistic inaccuracies I mentioned earlier. When supported by a sprit rig as shown in the painting, cloth along that edge would be in tension, not sagging. You can't fool gravity. A tackle "adjusting" the sprit's angle would be totally worthless. It's there to brail (furl) the sail, not for use when underway.

[johnw]

I've never heard of a standing spritsail either. I think the line seen in some pictures that goes to the top of the sprit is a halyard for raising the sprit. I've used a halyard for the sprit that goes to the peak of the sail, but I can imagine the utility of one that goes to the top of the mast. I reckon you'd ease it under sail to let the head take its natural shape.

[johnw]

Here's a picture showing a couple extra lines to the sprit. It's not the same as the Mediterranian version of the rig, but it's still more complicated then the sprit rigs I've been sailing. I think the more recent the version, the simpler the rig.

http://www.nmm.ac.uk/mag/pages/mnuEx...C0772&letter=D

[Thorne]

OK, standing sprit it isn't.

;0 )



Todd, couldn't the sag in the head of the mainsail in the nearer boat in the lower painting be due to the tackle pulling the sprit up towards the mast just a bit?

They are obviously ghosting along in super light air, so wouldn't they want some shape to the spritsail?

Wouldn't a brailing line run from the clew of the sail to the top of the mast? Here's a painting of two brailed up from the same time period -





John - great painting link! It sure looks like the line is holding the top end of the sprit to windward, and some of the other paintings I've seen make the line look like it runs to the gunwale, not the foot of the sail.

[johnw]

There are a lot of lines there. We have one going to the peak of the sail from the head of the mast, a halyard halfway up the sprit, a guy running from the weather gunwale to the peak, and another line on the lee side of the leach that could be another guy or a flag halyard. Makes the setup on the Bristol Bay gillnetter I've been sailing look positively elegant in its sumplicity. It's not the Mediterranian type I've seen prints of, which has the sprit mounted lower and the sail hanked to the line from the top of the sprit to the top of the mast. That's the oldest version of the sprit, and there is a base relief carving of one that dates from the year one. I think that means the sprit is the oldest fore-and-aft rig. I seem to recall a print of it in Keeble's 'Fore and Aft Sailing Craft,' but I could be thinking of a different book.

I'm sure the modern version of the rig works better.

[Thorne]

I'll admit being facinated by these historical rigs -- what an inventive period the 16th and 17th Centuries were in Europe! The paintings show everything from really primitive (well, no leather or wool sails) to fairly modern-looking sloop rigs.

Time to break out my cherished copy of Leather's _Spritsails and Lugsails_...

[johnw]

I think it was mainly the Dutch. We owe most of our fore-and-aft rigs to them, and they dominated sea commerce by inventing sail-handling techniques that allowed them to sail with smaller crew, therefore lower costs. Took a while for the rest of Europe to catch up.

[Todd Bradshaw]

The problem with spritsail heads is keeping them from having too much shape. It's similar to the luff sag problem on jibs. No matter what you do to the head, it will want to sag and if you do everything in your power to flatten the head and straighten the head edge of the sail - you'll end up with about the proper amount of draft. Anything less and you get sag and excess draft.

In light air you want to flatten your sail. It helps keep the flow from detaching, as it will not follow a sharp curve. Medium air is where you want to increase draft and once you get up to high wind situations you want to flatten again to decrease the power generated by the sail. If they were ghosting along, the head would probably be the only place on the sail that was under tension, and that would be due to the angle and weight of the sprit pulling aft on the peak.

A spritsail's brail line normally runs from the masthead, through a grommet on the leech about as far down from the peak as the width of the sail's head and back to the mast. Since these old spritsails are so big and the sprits are so massive, I'm assuming the brail has a tackle to make pulling the sprit up to vertical easier when brailing.

[Kitlani]

This reply to Voxbox, from a comment way up there......

In my view, the boat and mast are one layup. The stiffness of the boat AND mast, if it is still viewed as not being possible curently, certainly will be in the very near future. In the neantime, standard shrouds could be used for athwartships control and a couple of verticle support beams could be used from the deck to, say, 40% of the way up the mast. The main concept of not having a mast to disturb the airflow over the two headsails is still attractive to me.

[Woxbox]

The goal of getting a thick spar off the sail has also been accomplished with A-frame rigs, which also allows for a sloop rig. Here's the biggest one I know of, the Procyon, which was a highly experimental boat launched in 1991 or so.

[johnw]

That boat was supposed to revolutionize the sailboat business. It didn't, and I wonder why.

Tom, take a look at the picture I linked to. What do you think the line from the top of the mast to the sprit does? It's two-part, so there's some purchase there, but what could you do with it that wouldn't ruin the shape of the sail?

[Thorne]

Hey, let's move the non-Aft Mast discussion to the new thread I started about Sprits and Historical rigs, OK?

http://www.woodenboat-ubb.com/vbulletin/upload/showthread.php?t=58851

As for the non-use of the A-frame rig, could it have been the greatly reduced flexibility of the A-frame when compared to a single mast made of the same materials?

[Kaa]

I think the problem with the bipod mast rig was the windage of, basically, an extra mast. Also, having a bipod leg right in the middle of the jib/mainsail slot probably wasn't all that wonderful for the air flow either.

Kaa

[Kitlani]

Since this thread might be moved or ended, I just want to thank all those who participated in it. I've heard some great thoughts and ideas, and also seen some fine pictures. I feel that something is in the wind for sailboats, in the near future, considering the leaps in materials technology, and I was just toying with some new (old) ideas. Great input, people. Thanks.

[johnw]

Actually, I think there's more posibilities for sails on masts than for all-jib rigs. As materials science progresses, masts can be lighter and/or slimmer. I've been thinking a sleeve-masted rig that can be lowered and reefed easily would give us better aerodynamics than the rigs we now use.

[Woxbox]

OK, one more diversion. This rig was supposed to revolutionize sailboats - the logic being that airplanes got away from flexible cloth wings long ago, so shouldn't it be better for boats, too?
The logic is there, but no one has figured out how to make it work really well. The problem with the Walker wingsail system, shown here, is that if the sails can stand up to a gale, which tey can, then they're too small for light air. How do you vary the area of a rigid sail? Airplanes have control of airspeed over the wings, boats don't. The problem shouldn't be intractable, but no one has completely licked it yet. These Walker Wingsails have some points - for one, you can back the boat up just as easily as you can drive it forward. And it's all done from a console inside. Of course, it's also very expensive.

[Kaa]

Wing sails don't have to be expensive.



E.g. http://www.dahlberg-sa.com/kd/WD.htm and the discussion at http://www.boatdesign.net/forums/showthread.php?t=6698

Kaa

[johnw]

OK, one more diversion. This rig was supposed to revolutionize sailboats - the logic being that airplanes got away from flexible cloth wings long ago, so shouldn't it be better for boats, too?
The logic is there, but no one has figured out how to make it work really well. The problem with the Walker wingsail system, shown here, is that if the sails can stand up to a gale, which tey can, then they're too small for light air. How do you vary the area of a rigid sail? Airplanes have control of airspeed over the wings, boats don't. The problem shouldn't be intractable, but no one has completely licked it yet. These Walker Wingsails have some points - for one, you can back the boat up just as easily as you can drive it forward. And it's all done from a console inside. Of course, it's also very expensive.

Shouldn't be too hard to make them reef. Probably you'd just have an upper section or two that could be put in zero-lift position, just freewheeling around in the wind. Should have less drag than a bare mast.

[johnw]

I'm thinking soft wings might be more flexible than rigid wings. It seems to me that the Lundstrom rig could be further developed.

[Woxbox]

That's the other issue, airplane wings are optimized for a fairly narrow airspeed. Sailboat wings/sails have to be effective over a huge range. So you want both area and shape to be very flexible. I've wondered why the top half of a wing mast couldn't telescope up and down inside the bottom half to vary area. I haven't seen that done.
To control shape, the C-cats have done a lot of development work, with wings in two or even three sections. But those boats have limitations on how much wind they can handle. The extreme tall and narrow shape actually is driven by a strict class sail area limitation. For cruising, a shape that was more manageable could be developed.


Invictus

[Pericles]

During the 19th century these craft were sailed by a man, a boy and a dog!


There were hundreds of them. London's river was almost choked with them. http://images.google.co.uk/imgres?im...lr%3D%26sa%3DG

Obviously more than these.





Pericles