Cruising on a proa

[Panoramix]

Hello all,

You Tube decided to feed me with this video of a proa ( designed by @Russell Brown I think ? ) :



That is so elegant, the wake is just like the wake of a well designed rowing boat and it seems to be sailing effortlessly at a 2 digits speed.

Makes me envious, looks like a perfect boat to avoid the crowds here during the summer.

 

[Russell Brown]

That's a John Harris design that is a kit. Look for Madness proa on CLC's website.

 

[Panoramix]

OK, you were just a consultant! To me it looks like a small version of jzerro, I am sure that it is a bit more than this but it is beautiful, I had seen the old videos taken from the boat but this video from outside shows the boat under a better light IMHO.

My workshop is definitely way too small, may be that is good as otherwise I might forget that my 20 years old self found out that building a boat is hard work!

 

[[email protected]]

taKe iT to muLTihuLL anArCHy!....



I nearly missed the thread over here

 

[Panoramix]

taKe iT to muLTihuLL anArCHy!....



I nearly missed the thread over here

I probably should have.

To my defense, I am not a proper multihull sailor, my multihull experience is nearly exclusively Hobie cat 16 and I don't follow multihull anarchy!
I like this proa, not for being a multihull but I imagine it as a practical way to have a relatively cheap, simple, fast and shallow cruising boat to explore the nooks and crannies of a coast. That's 4 qualities that normally would not mix together. The catamarans that would be the closest floating things are quite complicated structures. Also I am an ex-rower and I like how this boat goes through the water barely upsetting it.

 

[Histoires sous le vent]

Quelle est la courbe de stabilité de ce prao qui navigue toujours avec son flotteur au vent ?
Pourquoi ne pas utiliser le flotteur sous le vent pour naviguer ?

 

[epoxypete]

Quelle est la courbe de stabilité de ce prao qui navigue toujours avec son flotteur au vent ?
Pourquoi ne pas utiliser le flotteur sous le vent pour naviguer ?

C'est peut-être une question d'équilibre et le fait que la cabine s'étende sur le côté tribord de la coque principale. J'imagine que le ama au vent permettent au skipper de générer un bras de levier substantiel aussi ! Cependant, je sais que cela ne répond pas directement à votre question. J'espère qu'un meilleur concepteur de proa se présentera !

Peut-être qu'en contactant directement le concepteur, John Harris, vous obtiendrez les réponses dont vous avez vraiment besoin. Il semble que ce soit un bateau en kit. Regardez ça : https://www.clcboats.com/default/johncharris.html

aussi: https://www.clcboats.com/shop/boats/wooden-sailboat-kits/proa/madness-31-foot-pacific-proa.html

 

[Panoramix]

Quelle est la courbe de stabilité de ce prao qui navigue toujours avec son flotteur au vent ?
Pourquoi ne pas utiliser le flotteur sous le vent pour naviguer ?

Je ne suis pas un expert en prao... de ce que je comprends :

Le proa polynésien est un monocoque dont on aurait mis le lest au vent du bateau, tu imagines que le lest se trouve au vent à la surface de l'eau et que la coque centrale porte l'essentiel du bateau. Dans la coque au vent il y a un ballast d'eau que l'on peut plus ou moins remplir, pour moduler la puissance du bateau. Vu que le bras de levier est grand (dans les 8 mètres pour celui là, à comparer à 1m80 de tirant d'eau pour un 9m normal), avec pas beaucoup de ballast, tu as un couple de redressement énorme et un bateau qui marche comme une fusée. Aussi, la coque principale peut être super étroite et donc avec une trainée minimale. Ça se voit sur la vidéo, le bateau est visiblement a plus de 10 nœuds d'après les vagues du bateau suiveur et malgré tout il ne fait pas de vagues.

Le problème est que dès que tu as un peu trop de gite et que la coque au vent se soulève, le moment de redressement plafonne voire diminue. Russel Brown sur Jzerro a solutionné ce problème en rajoutant un "pod" sur la coque principale qui dépasse sous le vent et amène de la flottabilité en hauteur. Si jamais le bateau venait à trop giter, ce pod s’immerge et empêche le bateau d'aller plus loin. Du coup la courbe de stabilité est positive très loin (connais pas la valeur, j'imagine autour de 90º quand le flotteur au vent passe du mauvais côté).

En fait l'intérêt du flotteur au vent est que tu es en appui sur une seule coque, le flotteur au vent traine donc très peu. Si tu choques tout et que tu lâches la barre, le bateau va avoir tendance à ce mettre travers au vent avec le flotteur au vent qui est la position la plus sûre pour un prao pacifique et la pire pour un prao Atlantique (prao qui navigue avec le flotteur sous le vent). Enfin ça marche super bien structurellement vu que ton flotteur au vent est simplement soulevé par le hauban au vent quand le bateau gîte avec la poutre de liaison en compression, contrairement à un cata ou la poutre de liaison est fléchie par la compression du mat ou un trimaran ou les bras de liaisons fonctionnent en cantilever depuis la coque centrale. C'est donc possible de faire un bateau low-tech et robuste, ce qui en passant est probablement la raison pour laquelle les Polynésiens étaient fans de la formule.

 

[Russell Brown]

I can't read French. There is a very capable proa for sale right now, Just completed a long trip... Know the one?

 

[Panoramix]

I can't read French. There is a very capable proa for sale right now, Just completed a long trip... Know the one?

Jzerro ?

Sorry for the French but there is nothing you don't know in there.

 

[Zonker]

Just an introduction to proas

Proas are like a mono with ballast way to windward. You can fill the windward hull with water for extra ballast. Big righting arm and skinny main hull means it's fast.

RM peak is when windward hull is out of water so a leeward pod is good.

If you leave them to sit there they sit with windward hull upwind. They are structurally efficient and can be built in low tech way which is why Polynesians liked them.

with help from google translate

 

[ProaSailor]

What is the stability curve of this proa which always sails with its float in the wind?
Why not use the downwind float to navigate?

I'm not a proa expert... from what I understand:

The Polynesian proa is a monohull whose ballast would have been put upwind of the boat, you imagine that the ballast is upwind on the surface of the water and that the central hull carries most of the boat. In the windward hull there is a water ballast that can be more or less filled, to modulate the power of the boat. Since the lever arm is large (about 8 meters for this one, compared to 1.80m of draft for a normal 9m), with not much ballast, you have a huge righting moment and a boat that works like a rocket. Also, the main hull can be super narrow and therefore with minimal drag. It can be seen on the video, the boat is visibly at more than 10 knots according to the waves of the follower boat and despite everything it is not making any waves.

The problem is that as soon as you have a little too much heel and the windward hull lifts, the righting moment peaks or even decreases. Russel Brown on Jzerro solved this problem by adding a "pod" on the main hull which protrudes downwind and brings buoyancy in height. If ever the boat heels too much, this pod submerges and prevents the boat from going any further. So the stability curve is positive very far (don't know the value, I imagine around 90º when the windward float goes on the wrong side).

In fact the interest of the windward float is that you are supported on a single hull, the windward float therefore drags very little. If you take everything out and let go of the helm, the boat will tend to go abeam to windward with the float to windward, which is the safest position for a peaceful proa and the worst for an Atlantic proa (propa that sails with the leeward float). Finally, it works very well structurally since your windward float is simply lifted by the windward shroud when the boat lists with the connecting beam in compression, unlike a cat where the connecting beam is flexed by the compression of the mast or a trimaran or the connecting arms cantilever from the central hull. It is therefore possible to make a low-tech and robust boat,

There are two peaks in the stability curve of a well designed Pacific proa with leeward "pod", the second one happens when the leeward pod enters the water:

Source: http://pacificproa.com/faq.html

NOTE: Has automatic translation been enabled on the forum? Or is that the Google Chrome browser invoking translation? How annoying!
(After leaving this thread and returning, it stopped.)

 

[ProaSailor]

There is a very capable proa for sale right now, Just completed a long trip... Know the one?

Two of your proas are for sale right now. Besides Jzerro , Areté is for sale in Chile: http://pacificproa.com/brown/arete/
(formerly CIMBA and Pacific Bee)

 

[Sidecar]

Just an introduction to proas

Proas are like a mono with ballast way to windward. You can fill the windward hull with water for extra ballast. Big righting arm and skinny main hull means it's fast.

RM peak is when windward hull is out of water so a leeward pod is good.

If you leave them to sit there they sit with windward hull upwind. They are structurally efficient and can be built in low tech way which is why Polynesians liked them.

with help from google translate

A good précis.

The full translation:

I'm not a proa expert... from what I understand:

The Polynesian proa is a monohull whose ballast would have been put upwind of the boat, you imagine that the ballast is upwind on the surface of the water and that the central hull carries most of the boat. In the windward hull there is a water ballast that can be more or less filled, to modulate the power of the boat. Since the lever arm is large (about 8 meters for this one, compared to 1.80m of draft for a normal 9m), with not much ballast, you have a huge righting moment and a boat that works like a rocket. Also, the main hull can be super narrow and therefore with minimal drag. It can be seen on the video, the boat is visibly at more than 10 knots according to the waves of the follower boat and despite everything it is not making any waves.

The problem is that as soon as you have a little too much heel and the windward hull lifts, the righting moment peaks or even decreases. Russel Brown on Jzerro solved this problem by adding a "pod" on the main hull which protrudes downwind and brings buoyancy in height. If ever the boat heels too much, this pod submerges and prevents the boat from going any further. So the stability curve is positive very far (don't know the value, I imagine around 90º when the windward float goes on the wrong side).

In fact the interest of the windward float is that you are supported on a single hull, the windward float therefore drags very little. If you take everything out and let go of the helm, the boat will tend to go abeam to windward with the float to windward, which is the safest position for a peaceful proa and the worst for an Atlantic proa (propa that sails with the leeward float). Finally, it works very well structurally since your windward float is simply lifted by the windward shroud when the boat lists with the connecting beam in compression, unlike a cat where the connecting beam is flexed by the compression of the mast or a trimaran or the connecting arms cantilever from the central hull. It is therefore possible to make a low-tech and robust boat, which by the way is probably the reason why the Polynesians were fans of the formula.

 

[Panoramix]

A good précis.

The full translation:

I'm not a proa expert... from what I understand:

The Polynesian proa is a monohull whose ballast would have been put upwind of the boat, you imagine that the ballast is upwind on the surface of the water and that the central hull carries most of the boat. In the windward hull there is a water ballast that can be more or less filled, to modulate the power of the boat. Since the lever arm is large (about 8 meters for this one, compared to 1.80m of draft for a normal 9m), with not much ballast, you have a huge righting moment and a boat that works like a rocket. Also, the main hull can be super narrow and therefore with minimal drag. It can be seen on the video, the boat is visibly at more than 10 knots according to the waves of the follower boat and despite everything it is not making any waves.

The problem is that as soon as you have a little too much heel and the windward hull lifts, the righting moment peaks or even decreases. Russel Brown on Jzerro solved this problem by adding a "pod" on the main hull which protrudes downwind and brings buoyancy in height. If ever the boat heels too much, this pod submerges and prevents the boat from going any further. So the stability curve is positive very far (don't know the value, I imagine around 90º when the windward float goes on the wrong side).

In fact the interest of the windward float is that you are supported on a single hull, the windward float therefore drags very little. If you take everything out and let go of the helm, the boat will tend to go abeam to windward with the float to windward, which is the safest position for a peaceful proa and the worst for an Atlantic proa (propa that sails with the leeward float). Finally, it works very well structurally since your windward float is simply lifted by the windward shroud when the boat lists with the connecting beam in compression, unlike a cat where the connecting beam is flexed by the compression of the mast or a trimaran or the connecting arms cantilever from the central hull. It is therefore possible to make a low-tech and robust boat, which by the way is probably the reason why the Polynesians were fans of the formula.

That is about what I wrote...

The last paragraph slightly corrected :

Actually, having the float (ama) to windward is interesting as the main hull bear most of the boat weight thus the ama generates little drag. If you let go the tiller and the sheet, the boat will eventually sit abeam with the ama to windward which is the safest postion for a Pacific proa and the worst for an Atlantic proa (proa that ordinarily sail with the ama to leeward). Finally it is structurally efficient as the windward ama is simply lifted by the shrouds when the boat heels with the transverse beams working in compression unlike those of a cat which work in bending or those of a trimaran which work as a cantilever beam. Therefore it is possible to design a low-tech and robust Pacific proa which is probably the reason why the Polynesians were fans of the formula.

 

[Panoramix]

Two of your proas are for sale right now. Besides Jzerro , Areté is for sale in Chile: http://pacificproa.com/brown/arete/
(formerly CIMBA and Pacific Bee)

I couldn't find the ad. Out of pure curiosity how much are these proas going for?

 

[ProaSailor]

I couldn't find the ad. Out of pure curiosity how much are these proas going for?

Top right corner: "For Sale: January, 2023" - no price mentioned, contact the owner.

"these proas" are not all the same. Try a Google search on "proa jzerro for sale".

 

[Panoramix]

"these proas" are not all the same.

Yes, I just meant the "Russel Brown" style 35 feet'ish proas...

I've just been playing "spot the difference", may be I am blind but I only notice gradual refinements with the volumes of the aka, ama and leepods being about the same. Am I missing something ?

I imagine the latter boats drier.

 

[ProaSailor]

Yes, I just meant the "Russel Brown" style 35 feet'ish proas...

I've just been playing "spot the difference", may be I am blind but I only notice gradual refinements with the volumes of the aka, ama and leepods being about the same. Am I missing something ?

I imagine the latter boats drier.

Perhaps some variation in displacement, prismatic and asymmetry of the main hull but yeah, why fool around too much with success? KAURI

 

[Hell-Bent]

Trying to steer with those sideways whipstaff tillers would break my brain.