If you're going to be tacking, it's nice to have both hulls as long as they can be; the leeward hull is going to be taking much of the fore/aft stress when sailing hard, and on a tacking boat, the hulls switch off as to which is leeward.

  This is one reason why some designers create trimarans with amas that are longer than the vaka, or main hull, or alternately, build picklefork tri's that have amas which extend forward of the bow of the aka.  Both are an attempt to get the leeward bow out as far as possible to resist sailing loads, avoid pitchpoling, and keep from stuffing the bow under a wave (and therefore pitchpoling).

  So, you can think of a harryproa as two-thirds of a fast trimaran with long amas -- just remove the windward ama and you have roughly the same geometry.  Assuming you're not tacking the proa at high speeds or in high winds. the ww hull doesn't need to resist significant sailing loads while tacking, and can stick with the shorter length.  The longer the lw hull gets, the faster and more sea-kindly the design will be.

  If you look at the solitarry and texel harry at http://www.harryproa.com/designs.htm#other , you'll notice that there's even a bigger disparity between the hull lengths than in a normal harry.  Since accommodations aren't the goal, speed and seakindliness rule here.

  Other thoughts/points:

  - If you're heading to windward at 45 degrees, and the line from the ww bow to the lw bow is also roughly 45 degrees, you'll be meeting the waves head-on with both bows.  This will create a much kinder motion for both the boat and the crew.

  - If you want to limit yourself to X pounds of weight, and you know that one hull will be to leeward most or all of the time, it makes sense to borrow length from the ww hull and add it do the lw hull.  That's the hull that's going to add speed and resist pitchpoling.

  - A shorter ww hull will place fewer sailing loads on that side of the boat, requiring less structure and weight.

  - A shorter ww hull will make the boat easier to turn.

  - The smaller ratio of ww hull to lw hull just looks darn cool.  imho.  I actually think I'd prefer a 3:5 ratio instead of 2:3.

---

  That said, none of this solves your issue of dealing with the weight of accommodation. 

  This is a classic multihull problem, made worse by the proa design.  If you can keep a mulihull simple and light, it will fly.  If you can do the same to a harryproa, it will likely fly even faster.  But as you add weight to a multihull, it slows considerably. 

  Proas are more vulnerable here in the sense that many people think they already offer too little accommodation for their length.  A 70' proa might only carry the same accommodations as a 45' catamaran.  If you start trying to add in all the accommodations a 40' or 50' boat "should" be able to handle, you'll have a slow proa. 

  This is not only because of the design involving the longer lw hull, but also because the hull is pointy on both ends.  There's no wide sugar-scoop transom that can handle a genset, island bed, corian counters, and storage tanks in each hull.  If you want to carry the load in a proa, the hull immediately gets longer, again causing people to comment on how little accommodation there is for the length.

  But that's only if you think in terms of length.  If you think in terms of cost and speed, the equation changes. 

  The flip side of the standard "too little accommodations" comment could be applied to the average cruising cat: it's got too little waterline for its weight, and too much cost for its speed.  Given the same expenditure, the proa will be faster and more sea-kindly.  A 70' proa is definitely going to outsail that 45' catamaran, will weigh less if done right, and will also cost less as well (smaller sailing loads, no compression, less structure, no standing rigging, and so forth). 

---

  It sounds to me like you're bumping up against the limits of the proa design.  The simple fact is, in order to carry the same weight as a catamaran, you'll need a much longer lw hull.  If a 10m ww hull and 15m lw hull don't provide enough accommodations, you have two choices:

  a) Slow the boat down and increase sailing loads with a longer ww hull. 

  b) Lengthen both hulls to keep the 2/3 ratio.

  Since the proa will still cost less than a cat, even at the longer length, and should still be faster, it's hard to imagine cost or speed being the issue.  My guess is that, when compared to a catamaran, the limit you'll run into with a proa is how long you're willing to go.

       - Mike


 

Gardner Pomper wrote:

Hi,

I am unclear on why proas, particularly harryproas have a ww hull that is shorter than the lw hull. If it is a "weight to windward" proa, then 50% or more of the weight might be on the ww hull, and keeping it short makes it beamier. Doesn't the short/"fat" ww hull cause more resistance when it is in the water?

Note: I am obviously speaking of conditions when you are not flying a hull, or even close to it. Specifically, in terms of cruising boats like Rare Bird, or even heavier. Why wouldn't it be better to have a ww hull at least as long and narrow as the lw hull to carry the weight?

I see the advantages to a longer ww hull. What are the disadvantages?

Thanks,

- Gardner Pomper

York, PA

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