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mundt

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here's a video of a pacific proa sailing on it's lee pod for a couple minutes. not sure I agree with the comentary, but if you were wondering if lee pods work...

 

 

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It has always been interesting to me how there is so much 'traditional' confoundment at the idea of shunting in the sailing World, especially when it comes to mixing proas with 'proper' tacking/gybing boats. It is usually thought that confusion will abound and close quarter disasters inevitable...
Funny thing is that this exact scenario has been occurring virtually all over the world for a couple of decades in the kitesurfing world. Apart from hard core wave riding areas where surfboards reign, most of the (non race scene specialist) kite world exists in mixed fleets pretty evenly divided between directional boards (derived from windsurfing or surf style) and twin tips (wakeboard style). The latter are most definitely proas and shunt at every turn- at high speed and in close proximity to everyone else... Nothing seems to go wrong and all is quite universally understood. Fins on these bi-directional boards are usually small (or absent), so you can do some wild slide outs in course transitions. Even so, they can also surf Okay on wave faces- although sometimes sketchily- much to chargrin of surf-style purists. 
Full disclosure- I have been a kiter for many years and too lazy to learn the fancy footwork needed for directional boards- so in fact shunting is an easier, more basic system in this type of sailing (all those old windsurfer converts already had the skills, so can happily use directional boards...). The developments with foiling may finally tip me into getting into changing feet while piloting craft with distinct bow and stern, but only because current commercially available foils are unidirectional. ,☹️

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^  never thought of it in that way!  I suppose snow boarding is similar also when doing the falling leaf which to a surfer can be a weird feeling going from natural foot to goofy foot? 

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2 hours ago, he b gb said:

^  never thought of it in that way!  I suppose snow boarding is similar...

Yes, all the board sports which seem to see themselves as progressive have totally adopted the shunting way and look back on their roots as primitive and awkward for still using the traditional bow/stern model: snowboarding vs skiing; wakeboarding vs water skis; skateboard vs roller skates...

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2 hours ago, mightyhartley said:

Yes, all the board sports which seem to see themselves as progressive have totally adopted the shunting way and look back on their roots as primitive and awkward for still using the traditional bow/stern model: snowboarding vs skiing; wakeboarding vs water skis; skateboard vs roller skates...

I grew up skateboarding.  I'm Goofy footed (port tack) but did flip tricks switch, I mean, starboard, so maybe this always made sense.  

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As I mentioned before - kiting would suit a symmetric proa very well. Its hard to see a tack with a kite on a boat - maybe it could be done with ballast.

On a bord that weights next to nothing and where the sailor/kite totally dominate the energy its perfect.  

Downwind with a kite jibbing would be better - on a boat.... 

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Don't use snowboarding as an example to support shunting - changing direction by shunting without jumping the board is very slow compared to carving the board.

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1 hour ago, hump101 said:

Don't use snowboarding as an example to support shunting - changing direction by shunting without jumping the board is very slow compared to carving the board.

Actually, that makes it the perfect comparison.

 

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17 minutes ago, Raz'r said:

Actually, that makes it the perfect comparison.

Not unless the shunting snowboard is otherwise faster than the single-direction board, as "good proas" can be.

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I really don't get why folks are so confounded by shunting, for me it's great because it's laid back, at any point I can drop the sheets and the boat will drift to a stop ama to windward and the rig luffing off to the lee, when I'm ready to go I can pick up one sheet or the other and take off in either direction, handy when you overshoot your crab pot :) if I'm headed into trouble a one eighty is as easy as dropping one sheet and grabbing the other.

I sail to go freediving/fishing/crabbing/beachcombing/camping so an adverse current + headwind = the perfect opportunity/excuse to do more freediving/fishing/crabbing/beachcombing/camping rather than a challenge to bash my head against, but hey, different strokes for different folks.

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On 2/24/2021 at 9:24 AM, TwoBirds said:

here's a video of a pacific proa sailing on it's lee pod for a couple minutes. not sure I agree with the comentary, but if you were wondering if lee pods work...

 

 

i could capsize and turtle that thing easy as shit....... but i have experience at these such maneuver's ...lol

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Those tacking proas are gorgeous and serve as perfect, irrefutable arguments in favor of trimarans 

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Given that leeway resistance and balance are lacking in some modern proas, maybe the leeward side of the main hull should be straight, flat, and have a hard chine. 

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40 minutes ago, Kenny Dumas said:

Given that leeway resistance and balance are lacking in some modern proas, maybe the leeward side of the main hull should be straight, flat, and have a hard chine. 

I hadn't realized it was a problem, there have been asymmetrical proas built, not so much lately though, I suspect that any gain isn't worth the lost displacement,  better to put a big  lee/dagger board in the middle of the ama and then you have as much lateral resistance as you need when you need it without having to worry about tripping over it and capsizing.

 

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9 hours ago, Kenny Dumas said:

Given that leeway resistance and balance are lacking in some modern proas, maybe the leeward side of the main hull should be straight, flat, and have a hard chine. 

 

8 hours ago, TwoBirds said:

I hadn't realized it was a problem, there have been asymmetrical proas built, not so much lately though, I suspect that any gain isn't worth the lost displacement,  better to put a big  lee/dagger board in the middle of the ama and then you have as much lateral resistance as you need when you need it without having to worry about tripping over it and capsizing.

I generally agree with @TwoBirds about the limitations of the hull for leeway resistance vs. the effectiveness of foils (rudders and daggerboards).  I can't quantify the difference but disagree about "the lost displacement" of asymmetric hulls, as shown below.  This isn't necessarily how I would draw an asymmetric hull (21m, 69 feet) but it's a quick and simple demo that scales the width of each half hull (leeward and windward) such that waterline beam remains constant, along with position of the hull at the center of the boat.

Two things to notice:

  1. Displacement remains constant.
  2. COB moves to leeward (the flat side), up to six inches at the extreme, increasing righting moment (substantially at the extreme).

asymmetric_hull_2021Feb26a.thumb.gif.e518a07484da63704c58f93f801bea8a.gif

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COB benefit is cool 

I guess some may not know that the original proas were made this way so I should have used the purple font. Anecdotal evidence is that the hard chine on some modern race boats works well for lateral resistance “it just settles in like it’s on rails”. I don’t know of a modern proa with a slab chined leeward side leeward hull   Anyone?

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20 minutes ago, Kenny Dumas said:

I don’t know of a modern proa with a slab chined leeward side leeward hull

Not sure what you mean by "hard chine" and "slab chined leeward side"?  I believe Jzerro is slightly asymmetric.

jzerro5.thumb.jpg.3a2c8acf469dc13c7b7018f2fe8309e7.jpg

jzerro_haulout.jpg.17b9a6eb9ca8d0975b3d8b9b9035cbbb.jpg

Full size images here: http://pacificproa.com/brown/jzerro_haulout.html

By the way, anyone who thinks they could sail this boat to tip it over is kidding themselves.  Rogue waves are a different story.

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ProaSailor is right re displacement. Any hull which has the same midsection area, the same LWL and prismatic coefficient will have the same displacement, regardless of where you bend the bows to and/or the shape of the mid section area.

I don’t think asymmetric shaped vakas help much unless you are designing for a specific, very limited speed range, like Venetian gondolas or outrigger canoes being paddled from only the “opposite” side. What is balanced at one speed, may cause problems at another.

Anything which produces lift, also produces extra drag, which is sufficiently small and may be acceptable at low speeds. But not at high speeds.

CoB shift is handy, but I wouldn’t design in asymmetry to get it. Above the water plane is an entirely different story. The more shift you can efficiently produce from a hull shape when the hull increasingly heels and immerses to leeward, the better.

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Gary Dierking's T2 is asymmetric. Chris Grill built a larger version of it, sailed it all over Mexico, lived on it for over a year, and wrote up a long article on what he changed from the plans, what worked and what didn't:

https://grillabongquixotic.wordpress.com/2011/07/02/a-report-on-my-version-of-gary-dierking´s-t2-pacific-flying-proa/

Very nice guy, he dropped by my house on his way from NY to Mexico on one trip.

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I read somewhere that some of the original proas had a totally flat side to leeward. Like, take a modern vaka and slice it down the middle. Haven’t found any pics, but I’m guessing the early voyagers had some game.   
 

Grilla is amazing. 

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1 hour ago, Kenny Dumas said:

I read somewhere that some of the original proas had a totally flat side to leeward. Like, take a modern vaka and slice it down the middle. Haven’t found any pics, but I’m guessing the early voyagers had some game.  

"Flying Proa" of the Marianas Islands
from Canoes of Oceania by A.C. Haddon and James Hornell
http://pacificproa.com/flyproa.html

Quote

The construction of this proa is a direct contradiction to the practice of all the rest of mankind. For as the rest of the world make the head of their vessels different from the stern, but the two sides alike; the proa, on the contrary, has her head and stern exactly alike, but her two sides very different; the side intended to be always the lee side is flat, and the windward side is made rounding in the manner of other vessels.

anson_proa.thumb.gif.f97a40dbda97bedbf8ee50a1df06bdf5.gif

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3 hours ago, KONeill said:

Gary Dierking's T2 is asymmetric. Chris Grill built a larger version of it, sailed it all over Mexico, lived on it for over a year, and wrote up a long article on what he changed from the plans, what worked and what didn't:

https://grillabongquixotic.wordpress.com/2011/07/02/a-report-on-my-version-of-gary-dierking´s-t2-pacific-flying-proa/

Very nice guy, he dropped by my house on his way from NY to Mexico on one trip.

"A Wordy Report" indeed!  Amazing that he lived aboard" and sailed so far.  Some highlights, with a great deal more to read:

  • "I have been living aboard Desesperado [sic] for 14 months and have made it from Veracruz Mexico to Bocas del Toro Panama."
  • "Hull subdivided into three watertight sections with the tops of 5-gallon buckets set in for hatches. [These hatches have been a consistant pain in the arse, always leaking. The deck is frequently awash especially when beating to windward] "
  • "Take note of what Gary says “The T2 is a sport canoe for one or two people”. He means it, The T2 cannot carry more than this. Put weight on the hull, it will sink and plough under. Put weight out on a trampoline or platform, down goes the ama. If you want to carry people or cargo this boat will NOT work for you."
  • "However despite this plan I still put the deck too low, about a foot below the gunwhales, and found that it flooded hugely when struck by a wave, and until the scuppers drained it out I’d wallow along carrying a bathtub of water up front. If it was really bad out it would never drain (I could not bring myself to make really enormous holes in my lovely faired sides), just flood and flood again."
  • "The ama: Like everyone else I wish I had built this a little more buoyant. Two fatties on the platform will sink it completely, and it submerges a lot anyway. It is also a bit noisy; with its fully round cross-section constantly leaving the water and returning, it slaps a lot. I’d say that 90% of the noise aboard comes from the ama, but only 10% of the spray. I guess a v-shaped bottom might fix some of the noise. The ama is foam-filled. I can’t help thinking that the Hawaiians have it right with their amas swept upwards at the ends which must surely help prevent them from plunging under."
  • "I am not so sure about the Hawaiian curved ama idea. I think this is good if you have to run big surf, but as Gary Dierking says it would interfere with the wave-piercing quality of the ama. My ama pierces a lot of waves and it’s ability to do so means it has less resistance and the boat goes faster and probably with less stress on the iakos."
  • "Ama: length 4.54m [14.9 feet], cylindrical except at the ends, diameter 21cm [0.689 feet or 8.27 inches]."

Note: I calculated an estimated ama displacement of ~355 lbs. minus pointy ends.  For practical purposes, minus weight it carries at rest.

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