The Black Swan Project
... 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.
Yor are basilary right, but do you need that storage space? If you design a cruiser for four crew, the available space on a flared hull is abundantly. See my sketch of the P12 above. Especially if you can place all bulky things under the center cockpit, how you have said. Hence less storage space is IMO no argument against flared hulls.
... like a true sharpie, as long as the weights are kept low.
In contradiction this declaration is right (like for every multihull). But a lot of storage space entices to store a lot 😊
What remains? As wider the beam of the Vaka as better the rigthing momentum. But is that worth to get all the disadvantages of a very bad L:B ratio? There are better solutions available. I don’t argue with that against a Sharpie style hull, my own boat has a similar box keel.
Annother view. As luckystrike118 said above, with a Sharpie hull you can reach a kind of ‘planning modus’. I made this experience with ‘Kalapuna’, but only at a speed over 10 knots. And I doubt, that it’s possible to reach that point with a 1:8 hull.
So if I ignore all things which enjoy sailing, and I am satisfied to own a nice cargo boat, this design is the right choice. No hard feelings 😊
Michael,
I like this design. I tend to agree with Multihuller that about the choice of midship section, as a stepped topsides with narrower hull bottom will provide a little more speed with minimal loss of internal volume or increase in materials. However, there is another advantage to a wider hull, which is an increase in longitudinal stability. A wider hull has a greater waterplane area, which increases the waterplane moment of inertia and hence increases the moment required to change trim. So, whereas the wider hull has more resistance, you may be able to drive it a little harder on downwind legs. With a wide flat bottomed hull, the choice of the optimal keel rocker may be fairly critical for best performance.
Regrading the masts, I like the schooner rig but I wound be inclined to offset the masts away from the hull centreline, towards the windward side of the hull. This would both improve the CE placement and may enable better use of the internal space. This may be an aesthetic decision, but it’s still a proa, so longitudinal asymmetry is allowed. 😊 Are the lugsails intended to be dipping lugs, or would you, in practice, have the sails on fixed, but opposite sides of the respective masts, unlike what you have shown in the sketches?
I have always liked the idea of a pantographing ama. ‘Rosieres’ was an extreme design and I would not be too concerned about the issues it had, particularly if you do not fly the ama. If the friction of the hinge system is low enough, the system could be left loose to find it’s own optimal angle, which would also make it self shunting. In this case I would limit the maximum travel to say +/- 45 degrees while sailing (or even less when sailing upwind).
I look forward to seeing further developments.
Cheers,
Mal.
I am satisfied to own a nice cargo boat
A cruising-boat is first and foremost a cargo-boat. Everything above daysailing/beachcat size is going to need some cargo. I think one of the problems with a speed-optimized proa 40 feet or more is going to be that it will become to heavy in real life. You gain 200 kg by using carbonfiber and other hightec, than you load up with beer/wine, food, water, cloths, beautiful rocks you find on a beach, fishing-gear, anchors etc etc…....
In the end your proa will probably float three inch deeper than calculated waterline.
If you are only inte racing, thats another thing. Cruising is primarly a cargo carrying activity.
I calculate that we will need about two tons of cargo on our 46 feet proa. That is one ton of water and food, and the other ton is bikes, anchors, two kayaks, and all the stuff i wrote about above.
Mvh Johannes.
I am satisfied to own a nice cargo boat
A cruising-boat is first and foremost a cargo-boat.
Sorry, but I have to disagree. May be I am multihull purist, but we talk about a sailing boat, and foremost it must sail. Further we talk about a multihull (proa), and for that we have to pay attention to some specific physically conditions. Negative examples of eg. heavy catamarans you find today all over the world. If you want to sail a ‘cargo boat’ build a catamaran or better a monohull, where payload is secondary. And - if you look back in times ... a proa was never used as a cargo boat. For that use the double canoe was invented.
I think, what we have to discuss is (perhaps in another thread) which parameters are relevant for creating a proa, doesn’t matter if small or big.
You may start with:
* Weight (ready to sail)
* Payload (results in displacement)
For the requested displacement you can develop a vaka under observance of proven facts:
* Length, width (cwl with reasonable L:B-ratio)
* Hullform (results in draft)
Then you can optimize according to resistance, drag, etc., and afterwards choose your preffered rig.
Certainly the budget is over all, but compromises are limited by known factors. Otherwise you will get an unsatisfactory result.
I calculate that we will need about two tons of cargo on our 46 feet proa. That is one ton of water and food, and the other ton is bikes, anchors, two kayaks, and all the stuff i wrote about above.
I tried quick&dirty; in Delftship to draw a 46 feet vaka with a displacement of, let’s say 4.5 tons with a L:B ratio 12:1. It’s possible to do so, but with a draft of 1,8 feet. So your ‘cargo ship’ could have at lowest a good L:B ratio 😊
One has to remember that a sharpie is very much another thing than a round or “round-ish” hull in some ways.
There is a video of a Layden Paradox sustaining 6 knots. That is a heavy cruising sharpie 3,5:1 L/B and 4 meter waterline-length. I like to know how a lighter 8:1 L/B Sharpie with much longer lenght and much greater righting moment would do under similar conditions.
The quite wide flat bottom and more straight sides will add greatly to the righting moment and enable the proa to fly more sailarea. Combined with a hullshape that will enable planing at realitivly low speeds. I think this would be a very fast proa. Not very nice in rought seas, but very fast in protected waters.
Every Open-60 out there is more or less flat bottomed. The Team Evolution is extremly flat bottomed scow with very plumb and wide “bow”. They are fast and win transatlantic races, even with all their drag from keels and added weight. Think of what a Open-60 without keel and twice the righting moment from a flying outrigger could do? They would be sustaining 40+ knots across the atlantic. And that with a 4:1 L:B.
Johannes.
I agree with Othmar, but also with Johannes,
my quick dash on freeship and my (very rough) calculations showed, that a sharpie hulled cruising proa in the 40 foot range (my concept calls for 42 feet) can be done with a payload of ~2 tons and (I believe) sailing good. (See my concept in Johanne’s thread “Advanced Sharpie Hull Proa” on page 7)
2 tons payload is absolutly realistic for a long range cruiser not forced to go to every habour along the way. Remember that 4 people and their personal gear are already 400 - 500kg.
“Meat Ballast” on the other hand is no good idea on a big cruising boat. People have to sleep sometimes (my girlfriend a little longer than normal, thats why I have so much time to feed this forum) and its no good Idea to bound them on the windward side to have sufficient righting moment. 150 kg of Meat Ballast is not enough to be sailing sure and the mutiny following a wet night will see the proa 75 kg lighter when the skipper has been thrown overboard.
Ok, just kidding, but IMO a cruising boat that big must rely on its own stability and not be calculated with human ballst as a must, as the racing momos do.
Best Regards, Michel
A proa is more similar to a monohull with a keel than to a katamaran or trimaran. It has its “keel” out sideways instead of down under the hull. If one wanted a more efficient monohull one could cut of the keel and attach an outrigger instead. That way the boat would be lighter with less surface-area down deep in the water where the pressure is greater - less skin-friction.
A L:B of 4:1 would probably work very nice. Of course it wont be “multihull”-fast, but it would be faster than a similar monohull because of less weight and less skin-friction. The keel does not ad to the righting moment until the boat heels, but on a proa you have a lot of righting moment very very fast. Just one or two degrees of heeling gives you 50 - 90 % of the total righting force. This will make the sails more effectiv and the inertia of the outrigger far out to the side, will force the boat to accelerate instead of lean.
I think a 4:1 L:B PD-racer with less rocker and an outrigger would fly (plane) very easily. Its a dead simple boat to build and im very tempted to build a model. You could probably have something like 15 - 20 m2 sailarea on it with two people walking the crossbeams as live meat ballast. It would plane and probably do soething like 20 knots under the right circumstances.
I think there is a lot of merit to this Black Swan. Its a simple and efficient kind of cruising boat. Simple and cheap to build out of plywood. Large enough to do some serious cruising. I would not try to cross the pacific in the roaring forties with it, but that was not the intent of the design. Its basicly a more efficient and very cheap sharpie with lots of livable area on the inside (for being a multihull). It will sail upright and very smooth compared to a light-weight monohull-sharpie. Light weight less materiels when building, less sailarea. Its a sharpie spiraling down the path of least resistance.
Johannes.
Speed is a bit relative. I use a pair of 100hp diesels to push my trawler at 8kts. I pass every mono-hull sail boat regardless of length that I see here on the Columbia river. If I had a 24-32ft “Cargo” proa that reached 8-10kts easily, I would be extremely happy. Not to say the 15-17kts that Russ and John reach with their boats wouldn’t be fun, but that would make for some pretty frequent tacking here on the river.
Meanwhile I get all of the other advantages like most boat for the $$$, shallow draft, Tramp lounging area, and blowing by the $75,000 Hunters at 1/4 the cost.
Still a winning design in my book.
Tom
This might be the same cost to build as a Tiki 31. I’m guessing it would have a nicer ride in most conditions vs the Tiki 31. It would also have preferable accomodation given the 5 ft beam. Would it have equivalent load and speed performance? I think it makes the most sense to compare to catamarans or trimarans given they are more equivalent in terms of build complexity, ride quality, and mooring needs.
Might be relevant to the monohull with keel thing comparison.
Check out sailinganarchy’s front page.
Dan
Hi Michael,
Your boats always manage to look like proper boats. I love that. The salty sharpie styling looks fantastic. And the reduced complication of building a boat shaped boat, with everything inside the gunwales, is pretty intriguing. It sort of reminds me of Newick’s Pat’s Boat.
And having the daggerboard in the cockpit is cool too. Maybe she has an outboard well in there too.
I also really like that you are messing with multihull orthodoxy with the 8:1 hypothesis. I don’t know if its a good idea, but I’d love to see what 8:1, 10:1 and 12:1 models of the same length and rig would yield in terms of speed—especially with a decent payload aboard. The idea that the added beam might also help keep the nose up on a screaming reach is also intriguing.
Here are a few unsolicited thoughts for an alternate version:
I agree with the comment that playing with moving the masts as far to windward as possible is an interesting direction—for accommodation and to move the CE to windward. I’d love to see a wishbone boomed cat schooner rig, with full battens. By keeping the sail behind the mast, you could rig running stays to the ama for more rig tune-ability, and reduce bending loads on the akas. And you’d still have the ability to fold her up for a marina slip or the trailer.
What about a pod? That feedback loop, a tip to windward when the ama is rising and the boat is losing stability, seems like a pretty nice feature in a cruising boat. Sven describes this at post #9
http://proafile.com/forums/viewthread/25/
Now I have no idea how to resolve the elegant simplicity of form that The Black Swan (TBS) has with a pod. But its interesting to think about. Dinghy on a stick? You could have a 13 foot dinghy! But that seems a bit much. Maybe there’s some kind of radical asymmetry above the waterline like on your Rosinante II, but in reverse. That is to say, the wider part would be on the leeward side, to give increasing form stability as the ama lifts.
http://proafile.com/archive/article/rozinante_ii
Still, it’s probably not as dynamic as a pod.
Thanks for adding more interesting ideas to the conversation.
Best,
Chris
P.S. if you have not checked out Karl Ludvigsen’s recent book on Colin Chapman, you are in for a treat. It’s a mind bogglingly fantastic catalog of the innovations Chapman invented or reinvented through creative interpretation. Who knew the Gogomobile was so influential?
http://www.amazon.com/Colin-Chapman-Innovator-Karl-Ludvigsen/dp/1844254135
I’m glad to see all the discussion about L/B ratio, that’s what the design is for! I certainly understand the desire for slender hulls in multihulls but I’ve seen way too many skinny hulled multis floating way down on their lines (especially smaller ones) because the owner wasn’t willing or able to keep the weight down, or perhaps the designer didn’t start with a reasonable payload estimate. The skinny hulled cat is now slow, with low bridgedeck clearance, and thus unsafe. I’d prefer to cruise without the “saw off the toothbrush handles” mentality, and I’m intrigued by the potential of a relatively wide hull, that can and will plane. I would go for the scow bow/transom but I can’t figure out how to avoid slamming the pram bow at speed so at least for now, the Black Swan has pointy ends.
Are the lugsails intended to be dipping lugs, or would you, in practice, have the sails on fixed, but opposite sides of the respective masts, unlike what you have shown in the sketches?
They’d be standing lugs, on opposite sides of the masts. I will probably reduce the aspect ratio next go around.
I think the cockpit as drawn will ship water in a knock down, and this will dramatically effect the righting moment - in a bad way, so I’m re-thinking that. I’m also going to be placing the masts to windward, as suggested - symmetry be damned! I think the ama is probably too large as drawn, it should be as minimal as possible. I’ve made a few quick sketches of flared hull boats, which could look pretty stunning if done nicely but now the hull is getting more complex, still musing.
I think the next step is a series of sailing models. I’m really curious to see if the swinging ama/daggerboard has any noticeable effect on planing. I’m almost hoping it doesn’t, because that is certainly the riskiest part of the design! BTW, attached are some monohulls that have inspired this project. The first is Red Herring, which was, I believe, the first canting keel mono ever built, by Dave Hubbard, of C-Class cat fame. The second is the new lake boat Stravaganza (thanks Dan). Here’s a link to a Norton 44, that was also designed by Hubbard but with free-standing masts. It was 8’ wide and everyone is ooing and aahing about how skinny and slippery she is, here.
Due to the fact that in Black Swan Project “all is allowed” I get a special idea. Why ‘fat’ performant dinghies and monohulls have a chance of planning? They have a slim bow for less wave resistance and a wide stern as ‘counter surface’, otherwise the stern sinks and slow down the boat. A proa has two bows, as we know. To make it wider for a chance of planning, the wave resistance rises. What’s to do?
My crazy idea was to combine a wave piercer with a sharpie. When speed rises up, the bow lifts (if the rig helps), and the stern goes down ... until my sharpie overhang reaches the water, and works like a wide stern. I know it’s a daring statment, but who knows ... perhaps it works?
Othmar
Interesting idea, but I think the blunt bow would slam and slow you down.
What if you used purely wave piercing bows, but had horizontally hinged wings to provide lift at the stern instead? Fold them in against the hull at the bow, so it can still pierce the waves. Fold them down at the stern, and they become lifting foils. It might be possible to get the geometry so that the wings match the hull contour when folded up, but have a good lifting shape with little drag when pushed down.
These threads are great for generating ideas. Keep them coming!
I’m still thinking about EZProa, but a maximum length of 6m has been imposed on me (by the storage yard). Maybe this makes it even EZ’er.
Interesting idea, but I think the blunt bow would slam and slow you down.
Your right. This idea would only work in sheltered waters without choppy sea.
Fold them in against the hull at the bow, so it can still pierce the waves. Fold them down at the stern, and they become lifting foils. It might be possible to get the geometry so that the wings match the hull contour when folded up, but have a good lifting shape with little drag when pushed down.
This could be the next step, like trim flaps on motor boats. I will think about for the next sketches 😉.