At sea it quickly becomes apparent that no other single factor contributes more to safety, speed, and comfort than waterline length.

The unique weight-distribution characteristics of the Pacific proa with the main hull to leeward and smaller, lighter hull to weather, give it the longest possible waterline for any given weight and rig!

Compared to similar catamarans, trimarans, and monohulls, the Pacific proa configuration stretches the same materials, rig and associated costs into a sailboat that is 64% longer!!!

The typical Pacific proa rig would be considered conservative in sail area for other boats the same length, yet is adequate for routine high speeds, occasionally on a single hull flying the small ama to weather. For example, this 21 meter (69 feet) design has accommodation, displacement, sail area and cost very similar to the Venezia 42 or Catana 43 catamaran.

For blue water cruising, the extra twenty-seven feet of waterline(!) on the main hull of the Pacific proa handles 75% to 100% of vessel displacement with ease, resulting in a swifter and more seaworthy sailing yacht.

It takes some skill and effort to fly the ama, it doesn't usually happen by accident. Careful steering and sail trim are then essential, of course. Even so, distractions or wind gusts can and will happen. Suffering a knockdown when sailing at speed isn't such a big deal as the boat settles easily into a position of increasing stability between 45 and 60 degrees of heel. Simply easing the mainsheet drops the ama back in the water.

Stability Curve

45 degrees of heel

The "leeward pod" is designed to prevent the yacht from heeling over too far, providing additional buoyancy beyond thirty-five degrees of heel. If the yacht is knocked over to a sixty degree angle of heel, it becomes as difficult to tip further as it originally was when the ama was in the water, so soon falls back "on its feet"!

The height of the pod is a critical factor in maximizing stability because at high degrees of heel, the pod becomes the leeward hull (CB) while the boat's center of gravity (CG, 7.5 tons) hangs out to windward (~7 feet?), below the mast - ~104K ft-lbs of reserve righting moment.

A graceful pod shape that settles into the water easily, surfs well and carries full displacement at maximum heeling angles(!) are some of the details.

That approach was used by Dick Newick on Cheers and advocated by Joseph Norwood and others.

Marshal Isles Proas (270K)

The history of "ancient" proas, however, developed in the Pacific islands from paddling outrigger canoes, shows precisely the opposite path of development and the reasons are simple and clear:

1. Having "weight to leeward" (WTL) in the big hull and ~30% displacement or less in the windward hull ("flying hull", outrigger or "log") is precisely what defines a "Pacific proa" and gives it certain specific characteristics that are not obtained when 50% or more of the weight is in the windward hull (WTW). So much so that it's not accurate to claim the same benefits for both WTW and WTL proas.
    

Cheers
2. As the sail is loaded up, regardless of which hull the rig is on (because it makes no difference), weight is transferred to the leeward hull, which must carry more of the total displacement. If the heavier hull is to windward (WTW), then both hulls need to be big enough to carry substantial displacement (more than ~50%), one at rest and in light air, the other powered up under sail. That suggests hulls of equal volume for WTW proas, like Cheers, and catamarans.
    
   If the heavier hull is to leeward (WTL), then it alone must be able to carry the total boat weight while the windward lifting "outrigger" carries only 1/3rd or less of total boat displacement. This suggests unequal hulls and that the leeward hull on a Pacific proa will be larger and better able to carry weight than a WTW proa of the same displacement.
    



Marshall Islands Proa
3. With WTW, the "log" is always dragging in the water instead of lifting free as it does with WTL. Pushing down on a leeward hull increases surface area and drag compared to lifting the outrigger and transferring its displacement (25%..35% of total) to the bigger leeward hull (up to 100% displacement), for less surface area, less drag and more speed (WTL).
   
   NOTE: crew movement on small, light proas can significantly affect WTL vs. WTW.
    



Hawaiian Sailing Canoes
4. When pressed for maximum speed, the greater lateral stability of the WTW proa (the ability to resist tipping over sideways) actually becomes a vulnerability, shared with extreme racing catamarans and trimarans. When it exceeds the longitudinal stability of the leeward hull, the boat will bury the leeward bow and pitchpole before lifting the windward hull.
    
   By contrast, the WTL Pacific proa has greater longitudinal stability than lateral stability so, before it pitchpoles, it rolls gently onto the leeward pod, like the "safety amas" on these Hawaiian sailing canoes.
    



angular momentum
5. Connecting beam and rig loads will be greater on WTW proas when ~50% displacement per hull or more may be common under sail vs. only 25% or less on the WTL small hull. In part, this is due to greater moment of inertia of the heavier windward hull, which adds stress in all directions by "wanting to move" independently of the leeward hull. It makes the boat heel over less quickly in a gust, which increases beam and rig loads. WTL proas are more like monohulls in this regard, as they absorb gusts by rolling safely (warning the crew!). Less distance between hulls (shorter beams) helps reduce stress but, of course, reduces righting moment too.
    
   Also, imagine two proas sailing such that the WTL proa flies its outrigger (25% of boat displacement); when the WTW proa lifts 25% of its displacement off its windward hull, it will still be dragging more than that in the water, to weather.
    

CONCLUSION:
Some believe very firmly that a cruising multihull should never fly a hull and for a proa, that means carrying the heavy hull to windward. There are several answers to this:



• On a cruising Pacific proa, flying the small hull when there is a leeward pod is not as dangerous or as easy as it may seem; the pod is very forgiving and angular momentum goes up in larger boats so they rotate more slowly in response to wind gusts.
• When both hulls must be capable of carrying 50% displacement or more, the catamaran has a list of advantages and has proven to be the best path for quickly carrying the most load in the least length. Cruising catamarans never fly a hull, they don't need more than 50% displacement in each hull and they don't get safer or faster by adding extra WTW.
• The Pacific proa (WTL) gets advantages in speed and seaworthiness (longitudinal stability) from the extra length of its larger leeward hull and less massive, "just enough weight", small hull to windward - without those factors, the gains are lost. Flying a hull isn't necessary and is easily avoided, but if being able to do so in ideal conditions doesn't excite you, don't get a proa!