Laterally assymetric monoproa. Pictures and video - sailing.
Some thoughts about my MonoProa
Two more videos and a picture.
I removed some of the sand to see how it would effect its sailing-properties. It´s still very directionally stable. Its very balanced, even though its leaning much more. Its what i predicted. It will not behave differently depending on the angle.
Johannes.
There is much more lateral resistance trying to push the hull sideways towards lee than towards the wind. The 90 degree hard chine really does what i hoped it would.
I’m sorry if i spam you all with videos today.
I think this monoproa thing is really interesting.
I want to thank Michael Schacht for his very inspiring article about the Rozinante II. It was reading his wonderful article that got me interested in this unusual kind of boat!
We who are about to become Lugsails salute you!
Since i want two lugsails on my monoproa, i have to make them. I had some thin spinnaker-cloth at home.
They will be slightly smaller and slightly higher aspect than the previous one. Together they will have about 20% larger area.
Now i will have to hand-sew them… It will probably take 3 hours…. :(
Johannes.
I hardly think we can call vids about proas on a proa forum spam! 😉
I like the look of the model, almost Viking-like (if Viking long boats were purple). Seeing the boat sail, it confirms my hunch about the mono proa that as the ww side lifts, the water plane narrows and the water is fooled into thinking this is a much narrower boat than it actually is. I had a complex hull shape going for Roz II and my hat’s off to you for working on a simple, sharpie style hull. It would be interesting to see just how wide one can push the hull beam and still achieve good results (thinking cruiser here, not racer).
A buoyant leeward mast would keep the boat from turning turtle if it ever capsized to that point.
It would be interesting to see just how wide one can push the hull beam and still achieve good results (thinking cruiser here, not racer).
I think its important that the lee-side is more like a multihull with half the with of a 10:1 (L:B) hull and the wind-side should not exceed a normal monohull with a 3:1 (L:B). The windward side should be as round and smooth as possible as the leeward side should be the dominant one. Just like on a normal proa where the vaka is the dominant hull and the ama is just “along for the ride” and should only add righting moment and nothing else.
In a cruiser i suppose the lee-side could be something like half of a 8:1 or even 6:1 hull, but somewhere around there the monoproa would need a centerboard or a keel. Something i try to avoid.
A buoyant leeward mast would keep the boat from turning turtle if it ever capsized to that point.
Yes that would be a good idea. The mast needs to be strong enough to withstand the bending if it get pushed down into the water.
I think a small lee-pod could do the same thing. It adds a very nice shelf inside the boat. I could place all kinds of stuff there. GPS, VHF-radio, pilot-charts, seashells and nice looking rocks my kids pick up from the beach.
Today i have made two new sails. They are smaller and lighter than the last one. Together they weight 130 grams, which is 37 grams less than the old one. Mostly that is because of the old mast that is a aluminum-tube.
They are 23 cms shorter which lowers the CoE.
Coming soon to a Youtube near you!
Johannes.
I have a question.
We’re all familiar with the way that keel ballasted monohulls create righting moment by moving the center of mass away from the center of buoyancy as they heel—up to a point, of course. Since the mass doesn’t change, its all about the distance between the centers. The righting moment is 0 when upright, builds to a peak and then decreases.
What does the stability curve of the moa look like? I’m going to assume that its ballasted to windward, like Michael’s Rozinante, not in the keel. As it heels the center of buoyancy is going to move leeward, as the boat gets narrower. But the center of mass is also going to move leeward as it heels! The question is at what rates? If the stability curve is flatter, what does that mean in terms of the manners of the boat?
Does this make sense?
Any thoughts, you stability-curve-drawing types?
chris
The curve is a blend of mono- and multi-hull types; close to the mono- at low angles of heel and closer to the multi- at higher angles. The unfortunate part of all of this is that it combines the least favourable segments of each….
The “skinny” lee side of the hull offers little form stability so the moa tends to behave much like a narrow dinghy with bunch of crew weight hiking to windward (a la International canoe); very, very effective until the forces on the rig overpower the righting moment and then everybody suddenly goes for a swim. A skinny, ballasted monohull becomes increasingly stiff until a very high degree of heel is reached which is very favourable in a design sense, and by that point the forces that are causing it to heel diminish rapidly; it is inherently stable. A multihull or wide monohull relying on form stability with buoyancy to leeward or something like a monohulled dinghy with crew weight hiking to windward, or an asymmetric moa are all very stiff at low angles of heel but that huge peak is reached at only a few degrees of heel as the windward hulls or the dinghy crew’s asses just leave the water’s surface… and then it get very quickly gets worse from there.
A small moa should be able to take advantage of the “live” ballast that crew weight has to offer, which could be exciting…. but the same can be said for any type of proa or multihull really. It falls shorter as the dimensions increase.
I like the quirkiness and the ideal of it all, but Mr. Moa has unfortunately inherited his father’s suddenly-boiling temper without also hanging onto his mothers steady, grounded tolerance ; ) He’s quick to lean, and has a tendency to suddenly fall over….
A small moa should be able to take advantage of the “live” ballast that crew weight has to offer, which could be exciting…. but the same can be said for any type of proa or multihull really. It falls shorter as the dimensions increase.
I like the quirkiness and the ideal of it all, but Mr. Moa has unfortunately inherited his father’s suddenly-boiling temper without also hanging onto his mothers steady, grounded tolerance ; ) He’s quick to lean, and has a tendency to suddenly fall over….
As an International Canoe sailor myself, I’m not too put off by the possible bad manners of a moa 😊
The advantage I see for a dinghy style moa is that for the same overall beam as a conventional dinghy you can get nearly twice the righting moment if the crew is sitting on the gunwhale. So there is a potential performance/cost benefit. This is tempered though by the fact that the hull shape is compromised by having to be designed to travel in both directions (not to mention the usual rudder issues).
As a fixed ballast boat, I agree that stabilty wise the moa has little to offer over a conventional hull. The straighter heeled waterlines and sharp chine for lateral resistance are interesting features, but these may also be provided by a symmetrical scow hull.
The “skinny” lee side of the hull offers little form stability so the moa tends to behave much like a narrow dinghy
Its actually the exact opposite. The “skinny” lee side has the same form-stability as a barge, since there is a lot of encapsulated air being pushed down into the water. The wide bulging windward side has a lot less righting moment. Seen from above one can see that its a half barge/scow and one half of a normal monohull, so actually its wrong to call it “skinny” lee side. You should think of it like the very full lee-side. By making it asymmetric one moves all the encapsulated air and the righting moment over to lee.
Please watch the videos. You can see that it lifts the windward side out of the water. Its much harder to lean it to lee than the other way.
Compare with Changeup where Michael uses asymmetry to maximize the righting moment from a catamaran.
Johannes.
something like a monohulled dinghy with crew weight hiking to windward, or an asymmetric moa are all very stiff at low angles of heel but that huge peak is reached at only a few degrees of heel as the windward hulls or the dinghy crew’s asses just leave the water’s surface… and then it get very quickly gets worse from there.
From my primitive tests i would say that maximum righting moment is at about 45 - 50 degrees healing. After that the lee side gets under water and the hull start sinking. I will try to make a video of this later today.
Johannes.
I tested my monoproa with two lugsails. The masts where to weak, bending way to much and spilling the wind. I could not make a video about the righting moment because of the waves. I think its easy to see that it rights itself fast when a gust or wave heels it down. It feels really stable when i´m pushing it around in the water.
I need a new mast. The forward one broke today. I will buy some really thin aluminum-tubes.
Johannes.
In this picture the monoproa heels about 30 degrees. There is no tendency to heel any more than that. When the wave and wind ease down the turning forces the hull quickly rights itself to upright again.
It seems to be stable over a very wide range of heel.
Johannes.
As a fixed ballast boat, I agree that stabilty wise the moa has little to offer over a conventional hull. The straighter heeled waterlines and sharp chine for lateral resistance are interesting features, but these may also be provided by a symmetrical scow hull.
Like Bolger’s scow schooner: http://www.flickr.com/photos/hallman/tags/scowschooner/ Once it heels enough to bring the windward chine out of the water, its underwater shape would be pretty much like that of an asymmetric moa, rig and rudders don’t have to be reversible, and auxiliary propulsion is simpler. Bolger warns that a scow would be noisy at anchor. A moa’s asymmetry would give it a smaller area in the bow against which waves could slap. So if you insist on that heeled underwater shape, your trade off is noise at anchor versus simplicity of rig, rudders and engine.
I wonder whether you could get rid of the noise if you covered the bow from the transom to a bit below the water line with a big air matress whose profile blended into the hull profile. Or a plywood plate that parallels the hull profile, and when at anchor you swivel it down to below the water line, still parallel to the hull, like Hasler’s floating breakwater. That might reduce the movement enough to get rid of the slapping. Or have a big wave propulsion foil that you can lower. Lock it down when you don’t want to move, but if the area is large enough it might still reduce any slapping.
Here are two videos of a radio-controlled symmetrical scow moa model: http://www.youtube.com/watch?v=CCSoZOwQY6g&feature=related
http://www.youtube.com/watch?v=FUQvBOX566A&NR=1&feature=endscreen
And a fat asymmetric: http://www.youtube.com/watch?v=as4o9Y41gds&NR=1&feature=endscreen
Regards
Robert Biegler
Once it heels enough to bring the windward chine out of the water, its underwater shape would be pretty much like that of an asymmetric moa, rig and rudders don’t have to be reversible, and auxiliary propulsion is simpler.
That is true as long as you stay inshore or sail in good weather. I would not use that Schooner-Scow for extended bluewater-sailing. Its probably no problem designing a scow for bluewater-cruising, but i think the monoproa is better suited. Imagine trying to sail towards the wind and waves with that Bolger Scow.
The monoproa with its sharp bow will slice through the waves with ease. It might pound a bit, but not to bad as it is very slender and heavy. It will probably lean 30 degrees or more if one tries to sail uppwind.
Today i tried it upwind. It can do about 45 - 50 degrees towards the wind, but if one wants speed it has to sail at a more comfortably 55 - 60 degrees. This is without chinerunners. I think it will get better once i add chinerunners.
I have been drawing another revised version.
Johannes.
Is the problem with a scow that it only works well with a shallow hull (ie Fireball dinghy) which pierces the waves. Make the hull deep enough for a good cruiser and the frontal area becomes too large to comfortably punch through a wave face.
Mark