Proof of Concept

I could not believe my eyes when I saw the clip!

I was browsing the net searching for anything with "aft-mast" in it and stumbled in this video: http://www.youtube.com/watch?v=OUQHQmmdSZc&feature=relmfu

The gentleman from UK built and tested a hull with an aft-mast. As I was pointed out, the most problematic performance of a single stay sail would be at light wind conditions, when the sail could not support itself. Inrteresting but true, this rig will self-tack as shown in the video!

As this video shows even in light air the sail performed admirably, at least in a small form. I wonder why my previous attempts even to discuss this rig was hammered so badly?

I superimposed a few screen capture frames on my previous picture for the reference.

Regards, kvsgkvng.

 

Yeah - the mast is aft, but the sail isnt.

He is just tootling around on a big fore-sail - no surprises there.

 

How different it may be?

I overlayed two images more or less in scale and wonder, how much differece there may be? There is something abnormal that many can not accept this concept. I came into this field without any notion of any previous history of sailing. All I did was studying very basics of yacht equilibrium ( I already can place a keel ;-) without being stumped)

I noticed that large lateen sail is basically an aft-mast with solid forestay. The difference is that lateen sail is supported in the middle of that forestay and the aft-mast uses tensed cable instead.

Maybe my observations are not exactly what others think, but visual similarity is irresputable.

Just my opinion, respectfully, kvsgkvvng.

 

I really don't understand what you are saying - the only thing 'similar' is the foresail. The other sails on your own design are not present on the video.

An aft placed mast is not all that strange.

Heres another boat with an aft placed mast feature.

at

http://www.yachtandboat.com.au/classifieds/ad/12570/jarcat-6-yacht-and-sail-boats-nsw

I think that if you want to compare your design with the 'real world' , you will have to find existing designs with more than just a big fore-sail.

 

The lateen mast is NOT "an aft-mast with solid forestay" .
because:
*STAY is some rope/wire/rod, attached at BOTH ENDS, and any transversal (to the stay) loads are translated to tension in the wire trough increased sag. (hence strong AND stiff attachment points are necessary at both ends =full-height mast, and exponential rise of this tension, if sag is to be kept small for sail shape control)
*YARD (of lateen sail) is a spar, with primary support somewhere BELOW THE MIDDLE and some ropes attached at lower end to "steer" it; any transversal (to the spar) load is translated to bending in the spar; hence the uppermost support could be located somewhere between 1/2 and1/3 of length from the lower end, and stiffness of support points are not all that critical. (=the mast could be half the height of the actual sail; in this case bend in the spar tend to flatten the sail when load (wind force) is increased, and also reduce, to a point, stress in the spar itself due to non-linear effects when bend is large in comparison to diameter of spar )

So there we have a fundamentally different mechanics involved.
The jib and lateen sails can only appear "similar" for so long, as they are drawn on paper (physical or electronic) and no structural/control issues are considered.

 

I have nothing in particular against the aft-mast concept or the lateen mast; my comments only address the necessity of balancing aerodynamic and hydrodynamic forces in different wind conditions. This is a challenge with both these rigs. Unless local conditions are unusually consistent either the rig must provide for sail area reduction in heavy conditions, generally by some form of reefing, or more than one set of sails must be carried,, or the sailor must be circumspect about what conditions he is prepared to sail in.

Reefing is not, as far as I know, practical or common with these rigs. Although the aft-mast rig can have a roller reef balancing must then be achieved by adjusting underwater lateral areas, I assume this would involve use of a movable leeboard, or raising the centerboard and perhaps using a large rudder. Another approach would be to use a small mizzen for balancing purposes, especially when reefed. I don't have the experience to suggest other solutions.

More popular rigs are more commonly used because they provide these essential features.

 

There's nothing abnormal about people not accepting the concept - the fact is that most sailors have tried something very close to this concept in one form or other, and found that it does not work particularly well.

The reason that I say most sailors have tried something very close to this concept is that most sailors would at one stage have found themselves sailing under genoa only, which is quite similar in effect. As AK noted, it creates significant issues with lee helm when reefed, because the CoE can often move too far forward. IN yachts this is often compensated for by the increasing weather helm of the hull as it heels,but this is insignificant in dinghies. The drag of the flogging sail can also prevent the boat from tacking, especially in a breeze. The headsail-only rig, when reefed heavily, is similar in size to a conventional dinghy sloop or dayboat with just the jib, and such boats can be extremely hard to tack even when sailed by crews in the top 10 nationally.

Furthermore, the angle of the forestay makes the sail tend to collapse in light winds. In addition, as the forestay sag loads up when the wind increases, it creates extra depth in the jib just when you want it to become flatter.

Compare a man-only rig; the mast bend automatically depowers it in gusts, which is what you want. It rounds you up in gusts, which is what you want. Reefing puts the C o E in the right area, which is what you want.

You may also find some major problems with using oars for steering and as a mast. For one, the geometry of a steering oar means that you will often be fighting against significant leverage, and will also have to move the inboard end a long way.

If you use an oar as a mast, what do you do when you suddenly decide to switch from sailing to rowing, perhaps because you come to a narrow channel or are hit by a squall? First you have to drop the sail, while drifting to leeward. Then you have to detach the sail from the oar/mast, while still drifting to leeward. Then you have to remove the steering oar and put it in the rowlocks. How quickly can you do that, and would you be happy spending that time when you could be drifting to the rocks?

Are you going to compromise the cost and structure of an oar to make it a reasonable mast, or are you going to compromise the weight and structure of a mast to make an oar? What about the fact that the most efficient masts bend in gusts, while the most efficient oars remain straight under load?

There are many rigs that would work well but which is best depends on a huge number of factors, such as where you will sail, how often you will row with the rig up, etc. You may need to work out those details as closely as possible before looking at rigs.