The Simplest Proa?
Seems to me that the simplest proa might look like this:
Ama, aka and Vaca as normal. I’d choose a deep and narrow asym hull section with no foils at all for the vaka, but if you sail in shallow water, consider a shallower hull and single daggerboard or leeboard, mounted dead amidships. Similarly the akas should be simple (bamboo poles or equiv), and the ama got out of whatever’s in the back yard.
Once again, no foils; no board, no rudders. Carry a steering oar for close maneuvering and when there’s no wind.
Now mount an identical pair of smallish junk rigs, one at each bow—as far out there as you can manage—and with a junk rig you can sheet from the *front* of the boom on the after rig, so you can get those mast steps right out in the eyes of the boat. I chose junk not because I know a lot about them—I don’t—but rather because they’re well proven and, in experimental guise, can be built on the dead cheap. Also because they are aerodynamically balanced and self-vanging. (Don’t like junk rigs? Try a full-batten wishbone boom, or a simple sprits’l, or a foam & shrinkwrap wingsail 😉
Now go sailing. The rig is a “schooner,” if you like, but I find it easier to imagine it as a pair of “air rudders,” which are arranged and sized to drive the boat as well as to steer it. Size the two rigs to each be about 2/3 the size you’d like to see driving the boat, because the after one is always going to be under-sheeted in order to get the boat to sail straight. Yes, that’s technically a waste of sail area, but look at what it might offer:
Such a boat should be self-steering, doesn’t require weight shift, has almost no moving parts, and a split rig so you can raise or lower the masts at sea, alone. You could cobble up a “M1 V1” version with a 16’ canoe and blue-tarp sails. The steering oar is for close or light air maneuvering—though the air rudder combo should give you full maneuverability in 3-4 kts of breeze. Also use it as a sweep (or yuloh) in dead calm. I *think* there’s enough leverage between the rudders to keep the boat out—or return her from—a backwind situation (which also means you ought to be able to short-tack it for some distance, so long as the ama has sufficient volume)
What do you think?
Dave Culp
This sounds a lot like Tink’s proa (did I get that name right?). I think the traditional Marshall island proa’s are the simplest. One clean and simple hull with no boards. Oceanic lateen rig. The little ones have no halliard. And a steering oar for broad reaches.
Other thought along this line: Does this video give you any ideas? http://www.youtube.com/watch?v=eNMxK2m0k1I
-Thomas
Now go sailing. The rig is a “schooner,” if you like, but I find it easier to imagine it as a pair of “air rudders,” which are arranged and sized to drive the boat as well as to steer it. Size the two rigs to each be about 2/3 the size you’d like to see driving the boat, because the after one is always going to be under-sheeted in order to get the boat to sail straight. Yes, that’s technically a waste of sail area, but look at what it might offer:
Dave Culp
Tink here
Using the aft sail to steer was essentially what I did in TP03
http://youtu.be/eW078PPgJak
The front sail was cleated and the aft one adjusted to steer.
I had a very simple leeboard which moved fore at aft, even upwind the board was aft of the midships point. This I think was due to the Ama drag as the board had to be moved forward as the speed increased. As for an asymmetric vaka I think you will find the CLR ends up about 1/4 LWL from the bow and give you alsorts of issues. I found this to my peril on TP01 with an asymmetric vaka (Weymouth 87 boat Dave)
TP03 has now been scraped but if I was building a proa again it would be along the same lines, the only changes I would make being:
> low drag ama
> open well to vaka and small (6inch max) leeward outrigger so I could sit to leeward and unload the vaka
> professionally made sails
MY perfect proa I think, though I still want to model mt lug rig with adjustable CE
Anyway as far as the simplest proa I thank you had that cracked years ago Dave, simple platform and a kite
Tink
Like many here, I’ve though a lot about the simplest proa and my best guess is here
http://proafile.com/forums/viewthread/292/P75
Marshallese vaka, with a boom less, reef able, gibbons rig.
No foils on upwind courses—steering by weight shift and rig adjustment (both fore/aft and ww/lw). Properly shaped, balanced, kick up side hung rudders for downwind control.
The schooner is Super appealing…but can you generate enough moment between the CLRs and CE downwind? 2 halyards, 2 sheets, 2 down hauls etc does fly somewhat in the face of simplicity.
Now two Worsley wings….
The schooner is Super appealing…but can you generate enough moment between the CLRs and CE downwind? 2 halyards, 2 sheets, 2 down hauls etc does fly somewhat in the face of simplicity.
In no way trying to persuade any one of the virtues of TP03 style but someone may find my experiences interesting.
Down wind was a challenge to begin with but with the board all the way aft and then tilted backwards and weight aft it worked. I even managed to sail goose winged on occasion.
With regard simplicity, the mast was free standing (no standing rigging), the board peminetently rigged. I had things well organised and he was considerably quicker to set up than my sloop rigged dinghy.
Tink
Now mount an identical pair of smallish junk rigs, one at each bow—as far out there as you can manage—and with a junk rig you can sheet from the *front* of the boom on the after rig, so you can get those mast steps right out in the eyes of the boat.
I’ve never heard of that. Do you have an example to link to? That would solve a lot of my schooner proa layout problems, if it would work in larger sizes. Of course, larger sizes would need rudders, anyway.
The deep V hull places the CLR far forward of amidships, while the asymmetry tends to counter-act that by creating a leeward turning moment, so theoretically… it just might work. 😊 A shallow hull with centered board would create a definite axis upon which the boat would turn.
P.S.: We are having some login/out problems today but I think we have them fixed. Sorry for any problems.
Is putting the weight of the rigs in the ends of the boat a good idea?
Is putting the weight of the rigs in the ends of the boat a good idea?
No
But they should be relatively small and there may be some goodness in having the mass in both ends of the boat rather than concentrated in one bow.
Cheers,
Skip
Is putting the weight of the rigs in the ends of the boat a good idea?
No
But they should be relatively small and there may be some goodness in having the mass in both ends of the boat rather than concentrated in one bow.
Cheers,
Skip
There may be some goodness 😊 . The wisdom about keeping mass away from the ends of the hull relates to speed. Moving the weight out towards the ends of the boat increases the pitch moment of inertia. The theory is that if you have weight in the ends, the boat reacts more slowly to waves, so you end up dragging the ends of the hull in the water more and this is generally considered to increase drag. I’m not sure if this theory has ever been tested scientifically, but anecdotally it holds true for monohull dinghies at least. However, increasing the pitch moment of inertia may slow the pitching motion in waves, so the boat may have a more comfortable motion and in a cruising boat, this would indeed be a good thing.
Incidentally, the theory behind the currently trendy wavepiercing bows is to allow the boat to pass through waves rather than ride over them, so suddenly dragging the ends in the water is a good thing. Go figure.
Now mount an identical pair of smallish junk rigs, one at each bow—as far out there as you can manage—and with a junk rig you can sheet from the *front* of the boom on the after rig, so you can get those mast steps right out in the eyes of the boat.
I’ve never heard of that. Do you have an example to link to? That would solve a lot of my schooner proa layout problems, if it would work in larger sizes. Of course, larger sizes would need rudders, anyway.
Why would larger boats need rudders? Just askin’...
No, I don’t have an example of a mizzen sail sheeted from the front of the boom. Frankly, I just thought of it, didn’t imagine it might be uncommon. Sure, most booms terminate at the mast, but sprits, junks and wishbones, all carry their booms/sprits forward of the mast—and any could be extended further if wanted, to reduce sheet loads. It seems a natural for a balanced/partially balanced rig, don’t you think? Helps if the sail is self-vanging as well. 😉
The deep V hull places the CLR far forward of amidships, while the asymmetry tends to counter-act that by creating a leeward turning moment, so theoretically… it just might work. 😊 A shallow hull with centered board would create a definite axis upon which the boat would turn.
Several others have pointed this out as well. Remember that, with a balanced sail, the center of effort is pretty much at the same place as the mast. Putting the masts of, say, a 16’ proa right up in the eyes of the boat might result in their centers of effort being 15’ apart. If you fully feathered the aft sail and sheet on the forward one, you can move the overall C/E by 15’, virtually the entire length of the boat. Surely this is more than the CLR shift, even of a deep vee hull?
I have no problem with using a more “conventional” hull with a fixed daggerboard (simpler might be a “mini-keel” like the one Chris shows here: http://proafile.com/forums/viewreply/2848/. Simpler than a moveable daggerboard…
Dave
Is putting the weight of the rigs in the ends of the boat a good idea?
I said “simplest proa,” not “perfect proa.” 😉 I expect that a 6-8 sq meter mast, sail and battens can be built at about 20-25 lbs each. If the boat weighs on the order of 1200 lbs all-up, the placement of 25 lbs isn’t overly critical. I expect these to be unstayed, and largely of bamboo or similar weighted components to meet this target.
Like many here, I’ve though a lot about the simplest proa and my best guess is here
http://proafile.com/forums/viewthread/292/P75
Marshallese vaka, with a boom less, reef able, gibbons rig.
No foils on upwind courses—steering by weight shift and rig adjustment (both fore/aft and ww/lw). Properly shaped, balanced, kick up side hung rudders for downwind control.
Very cool, and I wouldn’t try ti dissuade anyone from their present course. I’m just seeking to investigate the very simplest course, then challenging myself to justify complications from that point. I hear lots of,“But my boat already does almost that” and yes, they do—it is you guys’ innovation which fuels my own.
Simple is clever, robust kick-up rudders. Simplest is no rudders at all. Simple is no foils except on downwind courses. Simplest is no foils, on any course, ever. Simple is steering with the after sail—most of the time. Simplest is steering with the interplay of fore and aft sheets—only. Simple is relying on the steering oar for when things go pear-shaped. Simplest is to design the boat so things will not go pear-shaped.
The schooner is Super appealing…but can you generate enough moment between the CLRs and CE downwind? 2 halyards, 2 sheets, 2 down hauls etc does fly somewhat in the face of simplicity. Now two Worsley wings….
Frankly, I quite agree with you. Both free-flying kites and Peter’s wingsails can be made simpler than most any masted sail combination out there. However, when I advocate these, the threads seem to focus on the different-ness and lose contact with the right-ness, so I thought I’d limit the topic at hand to include rigs and geometries we all know and are comfortable with.
In my view, the two biggest issues with proas as they currently exist are rudders and moveable masts. I’ll go to a fair bit of complication—as in the schooner rig—if it helps to eliminate these two issues. You are welcome to think differently—and please share those views!
Dave
I said “simplest proa,” not “perfect proa.” wink
In that case “Proud Mary” might be a candidate, just for simplicity…
http://proafile.com/forums/viewthread/287/
I said “simplest proa,” not “perfect proa.” wink
In that case “Proud Mary” might be a candidate, just for simplicity…
Ya, I want to talk with you about Proud Mary. Have you considered turning the boat around, and putting the ama to leeward? This does NOT become an “atlantic” proa if you do, because you arrange to have the rig’s lift raise the ama, not depress it. I have used this successfully with free-flying kites. It is then possible to fly the ama for long periods—so long as there’s there’s enough power from the rig, this is a stable condition, not unstable (positive feedback, not negative). Without that drag in the water, the boat is a *lot* faster—and looks cool too.
Many have tried this, mind you. The usual killer is that they don’t have the rig fully sorted, or they don’t believe in the geometry and try to “improve” it before trying it. I think you got it exactly right, so can benefit from using the rig lift.
Dave
Oh, and I meant to mention, my avatar—to the left—is of a lifting-ama-to-leeward, kite-rigged proa, similar to the way I proposed you might consider rigging Proud Mary. This boat was built for Weymouth Speedweek in 1978, is 30’ long. It has a single daggerboard/seatback amidships (early iteration of Tom Speer’s reversible proa wing section) and no rudders at all. This one steers by pantographing the aka; in later boats I preferred to eliminate the weak link (pantograph) and used a fore-and-aft track on the leeward sheer of the ama to mount the kite. Much the same effect as your variable mast tilt on PM. The hull and control system worked well, the kites not so much…
Dave
Oh, and I meant to mention, my avatar—to the left—is of a lifting-ama-to-leeward, kite-rigged proa, similar to the way I proposed you might consider rigging Proud Mary. This boat was built for Weymouth Speedweek in 1978, is 30’ long. It has a single daggerboard/seatback amidships (early iteration of Tom Speer’s reversible proa wing section) and no rudders at all. This one steers by pantographing the aka; in later boats I preferred to eliminate the weak link (pantograph) and used a fore-and-aft track on the leeward sheer of the ama to mount the kite. Much the same effect as your variable mast tilt on PM. The hull and control system worked well, the kites not so much…
Dave
and it made my draw drop when I saw it out on the water. It was probably ahead of it’s time, with modern partly inflatable kites it would have been awesome.
Tink
Ya, I want to talk with you about Proud Mary. Have you considered turning the boat around, and putting the ama to leeward? This does NOT become an “atlantic” proa if you do, because you arrange to have the rig’s lift raise the ama, not depress it. I have used this successfully with free-flying kites. It is then possible to fly the ama for long periods—so long as there’s there’s enough power from the rig, this is a stable condition, not unstable (positive feedback, not negative). Without that drag in the water, the boat is a *lot* faster—and looks cool too.
Many have tried this, mind you. The usual killer is that they don’t have the rig fully sorted, or they don’t believe in the geometry and try to “improve” it before trying it. I think you got it exactly right, so can benefit from using the rig lift.
Dave
Hi Dave, that’s something new now!
In pratical terms, there would be a possible performance improvement and a big safety improvement, as it would be next to impossible to capsise it, and might not compromise the simplicity of the boat… very tempting!
My two imediate concerns are leeway and sail performance… might need a daggerboard as the main hull (in it’s current form) would be heeling the wrong way to resist leeway, and probably a better sail (have one nearly done that might do the trick…). The ama probably would need a re-design as well, and maybe for the sail to generate more vertical lift it should shunt on the ama, keeping the mast where it is? Mast back stay would be impossible then, but if my improved system works I might soon have a free standing racking mast anyway.
I remenber reading about that, it was one of my first readings about modern/experimental proas. One of the first rigs I considered for PM was a kite (as I had an old one), but then I salvaged some pico mast bits, so end up using the kite as a sail!
The advantage of your rig with the kite is that the kite is always high up, so it will always pull the ama up, but with a sail, as you sugest, it would probably be much easier to control.
Althou it might take still some time, there are quite a few modifications almost ready in Proud Mary, so I will hopefully get it in the water soon and see how it goes on the current format (or close to it…), but I do really like your idea and, either with PM on the next round of works, or on a new hull, I’m quite keen to try it.
Thanks for your sugestion!
Hugo