We are talking about sailing boats, and every compromise for accomodations have to consider it. For a proa is IMO a beam-length ratio of vaka less than 1:10 unusable. You have to search for the best proportions for a given purpose. Eg. a proa for weekend sailing with two bunks and a portapotty could realized in, let’s say 8-9 m length. A real cruising proa with accomodation for four sailors, used for two weeks holiday sailing should have a min. length of 12 m, and a displacement of 2 t plus. I checked these things out for my latest project, the P12, which will launched next spring (B:L ratio in cwl 1:12.2).

The kind of section is another theme, which may dependent of building possibilities. I checked several sections with the result, that a multichine section with small breaks seems as so good as an optimized U-shaped one.

For the P12 we choose a simple multichine section for following reasons
* easy to build in composite (or plywood)
* safety when grounding
* stiffness in longitudinal direction

I dont think one should be too worried about pounding from a box-shaped hull, as long as its heavy and slender enough. Very light and/or little rocker will pound more than heavy and deep rocker hulls.

Johannes, I would intend to use little rocker and keep the construction as light as possible while remaining consistent with a cruiser. The concept is a large monohull sailing canoe, though with the ballast in the outrigger proa configuration instead of a sliding seat or a canting keel. This will allow the canoe hull to plane and overcome the drag restrictions of the fatter hull (hopefully).

Othmar, thanks for sharing the P12, it looks comfortable and yet fast!

I would intend to use little rocker and keep the construction as light as possible

In that case i think you are absolutely right. It would pound horribly!!

Very interesting thread! Please keep it coming!

Johannes.

For catamarans - 10:1 is minimum (condomarans) and 12:1 minimum for any kind of performance - which is the idea for proa’s.

For all multihulls are the same physical laws valid. The only restriction is the purpuse of use - as a racer or as a cruiser. The last one is dependent of requested space, and the available money - and therefore you make compromises - in comfort or in performance.
However the old motto works. You can have only two of three things: Speed, Comfort, Low Price

However the old motto works. You can have only two of three things: Speed, Comfort, Low Price

I have been hit on my head so many times by that “law”. I hate it!!! I always try to outsmart that “law” but its apperently much smarter than me ... It wins every time!

😉

Welcome back to another episode of The Black Swan Project! I finally have some SketchUp renderings to share. I know, the first thing everyone is gonna say is “What the heck? This boat is white!” I blame that on the SketchUp rendering engine, the black hull just didn’t show any shadow or detail, so yes, this is the ‘white’ black swan. The other thing I want to say is that this is still very much a “work in progress”, and I don’t have all the details worked out.

Black Swan is a 40’ center cockpit cruising proa. She is inspired by shallow water traditional American types like the sharpie, and indeed, she features a flat bottom and a decidedly Down East aesthetic in that she is intended to be simple, inexpensive, comfortable, and more often than not, wicked fast. Construction is all stitch and glue marine plywood/epoxy, though the free-standing masts are carbon fiber simply because the benefits justify the price.

The hull is 7’ BOA, with a 5’ waterline, which lands the boat at an 8:1 L/B ratio. This ratio is apparently heresy in the multihull world, but I consider Black Swan to be a monohull that happens to have the ballast slung out to windward where it does the most good, not a true multihull, and in monohull terms, she is still extremely svelte. The wider hull permits comfortable (though not lavish) accommodations with no additional wings, pods, or deck cabins required. All narrow hull “cruising” multihulls include these extras in order to achieve accommodation goals, and all these extras come with extra weight, complexity, and windage: “at no extra charge”. Well, yes they do have a charge, when considering the efficiency of the whole, perhaps a slightly wider hull can pay for itself in this regard.

The rig is a free standing schooner, with lug sails. This causes all kinds of problems with the interior layout and I’m still mulling over a central Chinese lug in the cockpit, but that brings its own set of problems. Advantages of the twin rig are a lower CE (center of effort), two relatively easily managed sails vs. one gigantic sail, and the ability to balance CE fore and aft more effectively via sail trim. The lug has the benefit of being self-vanging, that’s a big deal for off wind sailing. It’s also aerodynamically balanced so sheet loads are minimized, which leads to fewer blocks, and this is important for speedy shunting, when the sails must be hauled around 90 degrees.

The center cockpit is a necessary evil due to the fore and aft symmetry requirements of the proa. The evil is that it removes the best, highest volume space from the internal accommodations. However, it’s not all bad: the volume below the cockpit is great for cargo, engine room, batteries, tankage, all those heavy items that should be centered down low in the hull, anyway. And since the cockpit is the place where you really want to be most of the time, then maybe it’s accidental genius. I muse on a larger cargo proa with this same basic form factor, but that’s another post.

The ama is a five sided trapezoid, a balance of the requirements of buoyancy, inertia, and minimal wave profile. The ama is to be ballasted with water, an easily obtained and dumped resource, unlike the lead or uranium underneath monohull keelboats.

Originally, I was thinking the centerboard would fit nicely below the cockpit floor, but then, I had a thought, which was inspired by the swing wing arrangement of the Quorning Dragonfly trimarans. What if… the black swan could fold her wings? Well, obviously this would permit fitting into monohull-size slips, but also the boat could be transformed into a “narrow boat”, suitable for navigation of European canals or anywhere that narrow beam is valued. However, the proa gains an additional benefit from the movable ama that is especially and ONLY beneficial to the proa! If you had an ama (with daggerboard) that could be adjusted fore and aft depending on the course of sail, you could adjust the CLR (center of lateral resistance) to align with the CE of the shunting rig, and not only that, you could shift the entire CG (center of gravity) aft, which just might cure the proa of it’s terminally “bow down” attitude, and allow it to plane like the swan it wants to be!

A flight of fancy? Or perhaps a real boat. What do you think?

This is the rest of the images.

Hi Michael,
first thank you for the fine sketches. All is allowed ... 😊

But I can’t follow your arguments of a svelte monohull. We all know, that the L:B has most effect, not only for performance, for behaviour in sea too. It makes a difference if a ‘svelte’ 42 feet monohull with 8 tons is sailing or a ‘broad’ 42 feet proa with 2 tons. The first wave will show it. Think also about the friction/wetted surface.

To get comfortable accomodations you don’t need a wide beam in waterline. Shuttleworth shows it with his openbridge deck catamarans, and nearly every trimaran main hull too. A narrow hull with flares makes it very spacious and comfortable. And I am shure it is not more effort to build a boat with this feature.

To adapt the ‘swing-wing’ concept of Quorning is tricky. All people I know which are sailing foldable tris never leave their boat folded in a marina berth. The stability is to less, and to much boats are capsized there in a strong breeze. To use the movable ama for trim is also very dangerous. Remember what’s happend to the proa ‘Rosieres’ before the start to ‘Route du Rhum 82’? 😉

Hi Michael,

nice drawings as always.

I do’t want to argue about L:B, this is a fact only the reality can answer. I also don’t want to say something about the position of the cockpit, thats just a matter of taste.

But i want to say something about the lee pod. A lee pod is not only a gain in interior to have an additional bunk.  I think this is a important safety device and a absolute must for a middle sized proa, to counteract the low capsize stability of a proa. Especially if I look at your high aspect lug sails. It has proven to be effective to have one on the Russel Brown Proas.

You know that Iam a fan of the sharpie hulls for proa mainhull for various reasons

I don’t know how deep your forefoot is immersed, but if you are inspired from the sharpie hulls it is a good thing to respect the “rules” for designing a sharpie hull. They say that the forefoot should be free in the air when the boat is moving. If the hull shall benefit from some kind of “planning” modus, it’s a must to have it up.! So it’s good to have the forefoot near the waterline when the boat is lying still. And of course the right amount of rocker to support the bow up attitude.

A swing-wing is very interesting, I think engeneering it is no big problem. Even not if you want to trim the boat fore and aft to adjust CLR and wheight-trim.

Best Regards, Michel

Nice. I’m still learning sketchup, my 15+ yr old plugins to Autocad won’t play well with current operating systems.

Comments on design.
What kind of D/L ratio are we talking about? As Mel said it makes a lot of difference.
Balanced Lug has a lot of self vanging also, rig looks to have a pretty high aspect ratio.

P52 started out life as a swingwinger, part of the reason was to vary the geometry a bit to move CE of lifting foil float fore and aft as either a balance or steering mechanism. Early trials while using crab claw rig were inauspicious and P52 stayed bilaterally symmetrical until changed to a telescoping system.

Black Swan’s a larger boat and a swingwing system might be more appropriate and may even benefit from adjusting CE fore and aft but I didn’t have much luck there. I’d look to spread the hinge points on the inboard end in any case.

cheers,
Skip

I like it a lot.

you’d mentioned batteries, tankage and such centrally located low under the cockpit.  obviously the math needs to be done, but this might give you enough reserve stability that the lee pod isn’t so crucial as an offshore safety factor.  I’ve thought a lot along those lines.  in that vein, have you thought about offsetting the cockpit to windward ala skip’s P52 to both reclaim interior volume as well as avoid shipping water in a knockdown? 

the other benefit would be the “intelligent meat ballast” would move several feet to windward naturally.

this would be a very simple box from beam to beam that adds nothing to the total boat width and would reduce the aka unsupported span.  a structural good thing with very little weight or construction ease penalty.

as to the masts, it would actually help balance the sail plan to offset as far to windward as possible in the hull, and give up nothing as far as structural bracing for them.

Tom

A flight of fancy? Or perhaps a real boat. What do you think?

I like it a lot!

There is some points that i would like to change. I love the center cockpit. I don´t see that as something bad at all. I want one on my own AS-Proa!
I would like to make the lee-side of the cockpit higher to resist capsize. The Sharpie-hull resists capsize much better than i thought it should, when i started testing my AS-Proa. It needs a high and straight leeward side, that will displace a lot of water when heeling a lot.

Because of the wider main hull, it will have a rather large righting ability, and making the hull very wide and shallow will create a lot more righting force at very low heeling angles. All that righting force will “fight” the outrigger. The main hull must be the dominant one, or it will become a unbalanced catamaran. It will create large bending and twisting motions into the crossbeams, so they need to be strong and stiff. Even more so without the shrouds going to windward like Jzerro and Madness use.

Thank you Michael for the beautiful renderings! I have learned so much from all your pictures and renderings here on Proafile.

Johannes.

Thanks for the comments, everyone!

Multihuller: To get comfortable accomodations you don’t need a wide beam in waterline. Shuttleworth shows it with his openbridge deck catamarans, and nearly every trimaran main hull too. A narrow hull with flares makes it very spacious and comfortable. And I am shure it is not more effort to build a boat with this feature.

Yes, that is true up to a point, though even your example section shows the lack of storage space that comes with the flared hull approach - there is little room to stow anything inside the galley cabinet or beneath the seats. I like the Vitruvian Man! 😊

Multihuller: To use the movable ama for trim is also very dangerous. Remember what’s happend to the proa ‘Rosieres’ before the start to ‘Route du Rhum 82’?

I do remember, and no we wouldn’t want to copy that performance! I was thinking that the engineering of the swing wing ama is simpler than say, a swing keel, and no, I don’t have it engineered at all.

Skip: P52 started out life as a swingwinger, part of the reason was to vary the geometry a bit to move CE of lifting foil float fore and aft as either a balance or steering mechanism. Early trials while using crab claw rig were inauspicious and P52 stayed bilaterally symmetrical until changed to a telescoping system.

That’s good to know. I’m intrigued enough by the idea to work on a sailing model, at least.

luckystrike118: But i want to say something about the lee pod. A lee pod is not only a gain in interior to have an additional bunk.  I think this is a important safety device and a absolute must for a middle sized proa, to counteract the low capsize stability of a proa.

I’m a big fan of the lee pod, though I’m wondering if the boat can be made self-righting without it, like a true sharpie, as long as the weights are kept low. Both Tom and Johannes mention this as a possibility, perhaps the cabin side will need to be altered. Some calculations are in order.

Tom: have you thought about offsetting the cockpit to windward ala skip’s P52 to both reclaim interior volume as well as avoid shipping water in a knockdown?

That is probably a really good idea - for all the reasons you give. I might even be able to make the boat shorter! 😉  I also like the idea to step the masts to windward in the hull, this would also open up interior room.

Well, lot’s to chew on, thanks again for all the input!

This picture shows how much my advanced sharpie proa will heel before the wind spills from the sail.
I have never seen it heel further than that. I suppose a big wave combined with very strong winds and to much sail will turn it over, but thats probably true for any kind of sailboat. At about 50 degrees heeling the righting force is very large for the hull alone.

A normal V or round hull will loose righting force more and more as the proa heels. A sharpie will have its maximum righting force at 40 - 50 degrees heel. The box-hull will shift the displacement outwards to lee as it heels.
It does not take much added righting arm to make a hugh difference.

Johannes.