Cheap, Capable Cruisers III

JOHN DALZIEL: We seem to have found a few ineluctable limitations as to just how far one can stretch the traditional Micronesian proa so it can meet modern Western demands. With a modicum of care we can stay well within those limits and come out with a good, inexpensive cruiser. We've also seen that there is a fairly clear trade-off point beyond which it makes more sense to build a catamaran than a proa. The question is, where can we take it from here?

MICHAEL SCHACHT: The Pacific proa is unique in that it appears to have near monohull self-righting ability, yet without the heavy ballast. That means it can bypass the displacement wave drag of monohulls - like a cat, and yet it can sail closer to its true potential more of the time - like a monohull. Best of both worlds? Only if you are willing to make sacrifices in other areas (such as extreme length), mother nature can't be cheated.

JOHN: I'll admit to mixed feelings about wanting to build a cruising proa. I think there are three serious problems:

1. This is something that all designers/ wannabe owners of larger proas need to consider carefully: To get a good proa, one that has advantages over spending the same amount of money on a cat or monohull, you have to have a long boat for the displacement -- and this is a world that charges by the foot.

2. Once the boat gets to the size where a 9.9 Yamaha is no longer practical power, an inboard makes a lot of sense and then there are compelling advantages to one-way boats.

3. Even at 50' LOA you are still talking of a very slender boat, and the problem of internal accommodation is daunting.

There are also serious advantages:

1. This sort of structure would be so much faster to build that for a given available # of hours you could justify a much longer hull. But that puts you back to problem #1...

Right now I think I could build a 38' proa, very much in the classic style, faster than the equivalent-capacity 28' dory, or 28' Wharram-style cat. That seems to be in contradiction of what we looked at earlier, but instinctively I think there could many fewer cutting and assembly operations on the proa. But to get that, you'd have to design very carefully (thinking Wharram again). If I did build I would go with fairly minimal accommodations -- a couple sea berths, porta-potty and galley in the hull, storage, and little else. I'd build a lashed-on deck pod and might camp in it in harbour, or might add a deck tent for that and leave the pod as a pilot house. That would be about it - KISS principle all the way.

2. The proa would be much faster than any of the other options, lots more exciting, and incomparably more seaworthy.

So- would I actually build it? Maybe not. Reason is that damn motor! I like river and canal cruising a lot, so when not in wide water the proa would be less useful to me than a one-way boat. And berthing would be a problem. Example: I routinely fit my Bolger AS29 into narrow creeks and into tiny (cheap) trailer-sailer marinas that would be physically impossible for a 38' proa (unless you had swing-beam). The proa would also be more of a hassle for use at the dock or mooring.

But- if I suddenly got the urge to go NOW, on a boat I built myself, it would definitely be on the proa. Gary Dierking built Te Wa in 12 weeks, and felt that a 40'er wouldn't have taken significantly longer. I'm sure that an amateur builder with a couple boats behind him could build a 40' light cruising proa- maybe even a 50'er- in under six months. That's very fast.

3. Economy. Now, the basic boat structure, with about the same amount of materials, will cost the same for the 38' proa, the 28' dory or the 28' cat, but after here the proa has a good advantage in that there is much less needed in the way of rigging and fittings. Even the rig on a Wharram Tiki, which is about as cost-effective as any cat can be, will come to a more $ than the proa's. Neither the crab-claw, the Gibbons, or the settee will cost anything like the sloop rig on the Tanenui- let alone 1/20th as much as a more typical cat rig.

MICHAEL: Agreed. Modern hi-tek catamaran rigs are intense. It would be cheaper to forget the rig, plop in twin diesels and pay for the fuel.

J: The de-rigeur marconi sloop rig is a pretty pathetic performer in its essential form of jib and triangular mainsail; awful enough that you need a spinnaker, a screecher, a reacher, six or seven headsails, and maybe a balloon in order to not get passed by a gaff-rigged Wharram anytime the wind gets aft of 40 degrees. OK, that's a bit of an exaggeration, but not much.  ;-)

On a typical sailboat the sailing gear makes up (very) roughly half the cost overall; doesn't it seem pretty silly to want a low-cost boat, sweat off a few percent here and there in the interior appointments and the materials specifications, then after all that pain stick the most hideously expensive rig in human history on top of it? Particularly when said rig is a hopeless non-performer on the off-wind courses most cruising sailors sail most often?

If someone is genuinely serious about reducing the cost of sailing, dumping the modern marconi rig with its giant sail inventory, spindly, expensive & fragile mast, fatigue-prone diamond stays, high stresses, expensive control equipment and marginal safety factors is the place to start. And anybody unwilling to do that is by definition not serious.

M: This message is finally getting through to people, I think. Nigel Irens did everyone a huge service by employing a standing lug yawl rig on his Roxanne/Romily series. You can't find a more highly respected multihull race boat designer than Nigel, yet for his ideal cruising rig, he chose a traditional English rig realised in modern materials. I think he opened a lot of minds. James Wharram is doing the same with his "gaff wing sail" concept. I see more and more sailboat designs that are breaking the sloop paradigm.

J: And its about time. So, can the other forms of proa- the Ndrua, weight-to-windward types and the Atlantic proa - pick up where we have agreed the traditional version should not go? We've seen pretty clearly that proas derived from the traditional Pacific types need to be kept light in order to make sense - but when was the last time you saw an underweight cruiser? If we must have more load carrying ability, are the proa alternatives attractive, or simply clumsy? Do they have any realistic place as cruisers, and if so, what? Or, is it time to say that the catamaran rules the roost after all?

M: Unfortunately, the dividing line between proa and cat is going to favor the cat by even more, since if you choose a cat, you can stick with normal tacking - a huge advantage in our all tacking ocean. The proa advantage must be comparatively huge, to compensate. I just don't see it, unless sailing performance is a big priority, and to be honest, that market is fairly small. Cats will rule mass production, but perhaps proas have a place for individuals. It still appeals to me, even with the drawbacks.

One area of research that could be enlightening is to compare the weight-to windward approach with the traditional approach via your design software. I had always assumed that one long Pacific proa hull with a smallish log would be the best light air machine, but after reading some of Rob Denney's in-depth posts on both MhML and the Proa File yahoo Group, I'm not so sure. Optimizing each hull for different conditions is a rather elegant solution, and one unavailable to a cat or a traditional proa, though trimarans do it, of course. Does a short, fattish (say 10 or 12:1) load carrying windward hull with a long leeward hull have more/less/equal wetted surface and resistance to a traditional proa with a 16 or 18:1 main hull? Where is the crossover point? I think this would make an interesting table.

J: To make a meaningful comparison you'd have to compare two real designs. The best we can do otherwise is to approximate based on a bunch of variables to which arbitrary values must be assigned. You'd also have to know the lateral weight distribution for both the classic proa and the weight-to-windward proa. Denney's Harry was about 50/50, maybe in the future you could get as much as 45/55 or possibly 40/60. I doubt you can get any higher than that because keeping the rig, boards, outboard, etc., in the lee hull limits the amount of weight that can be transferred off of it. A more recent design of weight-to-windward proa, (EQL-7 - by Terho Halme), has equal-length hulls, and approx. 50/50 weight distribution.

So lets run a few models: All the proas have leeward hulls of 40' LWL and windward hulls of 25' LWL, all hulls have a Prismatic Coefficent of 0.63 and round sections, and all weigh 4000# gross when loaded. The "Cat" of course has equal-length 40' LWL hulls; aside from representing a genuine catamaran it will also represent an EQL-7 type weight-to-windward boat with 50/50 weight distribution. Drag figures are reached using Norwood's equations. "Trad" means the log is kept to windward and is substantially lighter than the hull, "W2W" means weight-to-windward a la Harry, EQL-7 and some of Joe Norwood's proa design exercises.

Low Speed Hull Resistance of Traditional Proa, Catamaran, and W2W Proa

	Trad	Trad	Trad	Cat	W2W	W2W	W2W
Wt. distrib. Lee/Wwd %	80/20	75/25	100/0*	50/50	50/50	45/55	40/60
LWL lee hull, ft.	40	40	40	40	40	40	40
LWL wwd hull, ft.	25	25	0	40	25	25	25
Disp lee, #	3200	3000	4000	2000	2000	1800	1600
Disp Wwd, #	800	1000	0	2000	2000	2200	2400
Wetted surface lee hull, sq.ft.	100	97	112	79	79	75	71
Wetted surface wwd hull, sq.ft.	40	44	0	79	63	66	69
L/B, lee hull	17.4	18.1	16.1	22.2	22.2	23.5	25
L/B, wwd hull	17.9	16.1	*	22.2	10.9	10.6	10
DLR, lee hull	22.3	20.9	27.9	13.9	13.9	12.55	11.2
DLR, wwd hull	22.9	28.6	*	13.9	57.1	62.9	68.6
Drag @ speed, lee hull, #:
2 knots	4	4	4	3	3	3	2.5
4 knots	15	13	22	11	11	11	11
6 knots	32	30	52	26	26	25	25
7 knots	50	50	74	37	37	35	33
10 knots	182	175	230	115	115	102	93
Drag @ speed, windward hull, #:
2 knots	1.5	2.5	*	3	2.5	2.5	4
4 knots	7	9	*	11	10	10	11
6 knots	18	22.5	*	26	45	48	55
7 knots	36	46	*	37	100	115	135
10 knots	60	75	*	115	148	170	190
Drag @ speed, both hulls, #:
2 knots	5.5	6.5	4	6	5.5	5.5	6.5
4 knots	22	22	22	22	21	21	22
6 knots	50	52.5	52	52	71	73	80
7 knots	86	6	74	74	137	150	168
10 knots	242	250	230	230	263	272	283

J: OK - who wins? At 2 knots, it is the flying traditional proa hands down, followed by a tie between the traditional 80/20 proa, and the 50/50 and 45/55 weight-to-windward proas.

At 4 knots, it is a tie within the margin of error, but the 50/50 and 45/55 W2W proas have an edge.

But at 6 knots the tide changes; winner is the 80/20 Trad proa, followed closely by the other Trads and the cat. The W2W proas are all laboring under much higher drag, 35-60% more; this increase in resistance is the result of the short, high-DLR windward hull crossing the hull-speed boundary, picking up wave drag.

I've included 7 knots as this is the point where wave drag on the 40' hull becomes significant; here the clear winners are (surprise!) the catamaran and the flying proa (which in fact completely matches the cat from 4 knots onward). The cat's performance is clearly better than the other traditional proas, and again the W2W proas fall victim to the fact that the windward hull is still climbing the steep part of the wave-drag curve.

10 knots is well outside the slow-speed range, but it does tell us a few things. Again the cat and flying proa win over the traditional proas, though not by as much (5% and 8.5%), but the cat shows a decided advantage over the W2W proas- 14% over the 50/50, 18% over the 45/55, and 23% over the most extreme 40/60 proa.

It's also plain from the table that there is no advantage in reduced wetted surface for the W2W concept. While the above represents a non-heeling condition, even when heeling it would be difficult or impossible for the W2W proa to match the traditional proa where the crew can take active measures to fly the log. Should the W2W proa fly the windward hull, it will come out with the same area as the flying traditional proa- and no less.

I doubt, given the low resistances shown by all these boats, that at 6 knots or below there will be enough aero side force to transfer significant amounts of weight to the lee hull. So we'll have to say that in the slow speed range, there is no evidence here of any superiority of the short-windward-hull W2W type over either the traditional proa or the catamaran (or EQL-7 concept). Indeed the opposite is plainly true as one gets over 5 knots or so; the W2W proa is at a decided disadvantage. In fact the general trend of the numbers below 10 knots is that the 50/50% weight distribution is by far the best for the W2W types, and trying to push it any farther than that results in more drag, not less. And the superior performance of the catamaran tells us that the longer windward hull is in fact a benefit.

So - what conclusions can be drawn from this? First is the excellent performance of the catamaran. But, do you see the glitch here? If we go back to our earlier three 38' proa sketches, we see that all of them come in at  under a ton dry weight. And so does the 28' catamaran. So its reasonable to state that we in fact COULD build a 40' proa, capable of carrying a ton payload, to a one-ton dry weight limit. It is not so reasonable to think we can build a 40' cruising cat, especially a "cheap capable cruiser," to that limit. It wouldn't surprise me at all if the cat had to be a full ton heavier. So where earlier we pointed out that a Wharram Narai would show superior performance over a proa of the same length and displacement, in lighter weight ranges the proa is showing a clear load-carrying advantage, and likely is the better choice.

Second conclusion is that the way to sail a traditional proa at low wind speeds is to get as much of the displacement over onto the main hull as possible. Another argument for a light log + water ballast?

Third has to do with weight-to-windward proas.  If you restrict the boat to light payloads, you don't run into the wave drag problem on a short windward hull (I'd guess the transition point would be somewhere around DLR 40). But to get the payload up to the same level as on the traditional type proas, on the same LOA, you would need to either lengthen the windward hull, a la EQL-7, or move some stores and crew space into the lee hull and in effect become a Ndrua type proa.

M: So for heavy payloads on a restricted waterline length, it makes the most sense to maximize the length of each hull and to share the load equally between them (like a cat) to achieve minimal wave making drag at low speeds. It's interesting how even at 6 knots the wave drag exceeds the skin friction drag and becomes the major factor, no wonder all human powered boats are as slender as possible.

J: We've noted before some of the catamaran's advantages, and several of them depend on the boat sailing in one direction, not two. Use of engines for one, and the ability of a one-way hull to avoid squatting at semi-planing speeds. So let's follow the catamaran lead for a moment, but accept a certain amount of lateral asymmetry. Gray Treadwell'sBimaran comes to mind...

M: OK, this is good. I like Gray's asymmetrical cat, and this is a good reminder.

J: Yes. OK, there's a thought. It seems to me that if you cut out all the pieces at the same time, you could do two identical 36' sharpie hulls almost as fast as a 40' hull and log, and you'd have considerably more room than a 40' proa- even a wide one. Put the rig, board, rudder, outboard motor (if you want one) in one hull and a deck house or pod connected to the other for your settee/table.

Use the balanced lug rig. By putting a free-standing mast in one hull, you'd get rid of the expense and failure modes of standing rigging. Plus you'd have fewer problems in setting up steering on a cat. If most of the living area is in the other hull, then no need to build a way around the mast in the hull, just a solid bulkhead and a hatch forwards to access storage/greenhouse/etc.

???? Just being provocative... :-)

M: I think you may have just out-wharramed James Wharram. Surprise! It's not a proa, but an asymmetrical catamaran. Who woulda thunk? I think the biggest strength of this approach is the ability to employ a free-standing mast on a cat. You could even use Wharram's gaff wing sail.

Of course, I don't think this approach is much higher performance (if any) than Wharram's existing designs, so this concept doesn't really satisfy the original intent of maxi speed for minimum cost, but it does have the potential to make a catamaran a bit cheaper, simpler and easier to build, and that's certainly a good thing.

J: We still have the question of how the Ndrua derivative would stack up against the catamaran. I suppose we will have to wait until someone actually designs one to really get a good notion of what the possibilities are -- or aren't. But at the time of the European conquest of the Pacific islands, the Polynesian age of exploration was almost over, and the classic double canoe was fading away. Where there were still non-ceremonial uses for the type, such as in Tonga and Fiji, it was in the process of being replaced by the Ndrua (the Alia of Tonga was virtually identical to the Ndrua). So given Polynesian technology, there was a clear advantage to the newer type.

The question for us moderns might be, is it still the same case today? If it is, the advantages must be fairly subtle ones. When you compare the catamaran with a similar-cost Micronesian-type proa, the differences jump out at you. But it is hard to see how that could be true for the Ndrua. Would there be substantial differences in cost or complexity? Would there be definite seakeeping advantages? Right now, having no actual examples sailing, it is hard to tell.

M: Agreed. Whatever it's advantages, they probably won't be found via a yacht designer's calculations, but in the dynamic abilities of the Ndrua configuration at sea.

In the end, can we consider a proa as a viable alternative in the "cheap capable cruiser" context? As usual, it all depends. If bringing all the mod-cons to sea is a high priority, then you can do that more cheaply and more capably in a monohull, and for a bit more change, a cat. A proa only makes sense if you are willing to travel light. It is in a sense a radical expression of Newicks's Law: You can have only two of three things: performance, economy, or luxury.

The market has proven that the public votes overwhelmingly for economy and luxury in their boat selection decisions, with performance a distant third. This explains why monohulls are not likely to be replaced anytime soon. But for those who DO value performance over luxury, then the Pacific proa certainly provides an interesting alternative. The proa is much cheaper to build than a catamaran of equal length, yet will perform as well, if not better. Or from the other side of the coin, the proa can be built longer than a catamaran of equal cost, so it will offer better speed and seakeeping abilities - but probably worse accommodations.

Comments

• The debate has just about reached the stage of suck it and see. I think you should include comments by Rob Denney who has actually built both a bimaran and a w2w proa and has solidly gone for the w2w. The Harry concept seems to work and I am impressed with the accommodation of the ones I have seen and will let you know how they sail in the near future as I have been invited to the launch of an 8.5m ww hull Harry design.

  Posted by  on  03/28  at  03:58 PM

• When I saw my first proa, I wanted Tepuke (http://foxxaero.homestead.com/indsail_015.html)

  Now I’ve come up with a design for a 50’ proa that sleeps 6, can be trailered behind the average SUV or pickup (25’ long by 8’ wide when trailering or at the slip), will do 20 knots with a 30HP OB.

  Prototyping now.  PAF soon.

  Posted by  on  04/28  at  12:59 PM

• Excellent analysis of the trade offs.  It has seemed to me for a very long time that the absolute smallest (therefore most economical) seaworthy cruising multi out there is Tom Jones’ 26’ Dandy II. 

  http://www.jonesboats.com/dandyII.html

  She is basically a single chine sharpie (a higher displacement/lower wetted surface development of deep V Wharrams).  The compromises he makes in accomodation (watertight bulkheads), size (as small--and therefore as cheap--as you can get and still have two voyagers), foil lay out (single daggerboard), materials (plywood hulls, wood I-beams), all seem to me on the right track.

  I guess I would like to go one step further and do a Sequoya/Rustic 30 footer --with a narrow hull below the waterline and wharram like flare above--and a low center of effort gaff rig. 

  I built a weight to windward proa land sailer which used a 5m windsurfer rig.  When I sailed it against conventional land sailers that were lighter, but with a lot less sail, I ALWAYS took a beating every time I shunted.  The kinetic energy you carry through a tack is valuable!!!  I have had the proa bug bad--but I have to say based on that expereince, I’d rather have a cat for cruising.

  Posted by  on  04/30  at  11:29 AM

• There is a lot less KE remaining when tacking on the water. Have a read of Rob Denney’s experience with his Elementarry. Cruising one does much longer tacks than racing and stick up a kite for down wind.
  I have talked to the builder of a 9mww 12mlw hull almost complete Harry and the price seems pretty reasonable. Much of the costs are in the compulsory safety gear. I don’t think I could really go much cheaper for a fast, off-shore cruiser
  Robert

  Posted by  on  05/01  at  09:35 AM

• There is less KE on the water.

  But its harder to gain it back, too.

  There are fewer tacks when crusising, but I wouldn’t want to plan my trip based on that.  You are going to end up short tacking some time.

  I’d love to try one of Rob Denny’s boats for comparison!

  Posted by  on  05/02  at  03:39 AM

• “I guess I would like to go one step further and do a Sequoya/Rustic 30 footer --with a narrow hull below the waterline and wharram like flare above--and a low center of effort gaff rig.”

  YES! Sign me up! Nigel Irens has a wonderful talent for combining the modern and the traditional. Wharram does too, but Nigel has shown us that there is more than one way to skin that cat… pardon the pun. I love multis, but not what they have become - there is precious little soul in most.

  The only thing I have against cats is the stayed mast in the middle of the cross beam - an inherently difficult engineering problem. Not that it isn’t solved, but I rather like the idea of solving engineering problems by asking the question in such a way as the problem becomes irrelevant, like a proa. But proas have their own daunting problems (shunting rigs, rudders, motors, etc.) and when you wrestle with them for long enough, the standard tacking style boats start to look very nice.

  Posted by Editor  on  05/03  at  11:36 AM

• I think you make a good point about the compression loads on the main beam of a cat.  There is something magical about the trimaran arrangement of stepping the mast on the daggerbboard trunk and havingt low over all compression loads by having a wide staying base.  No wonder there are barely any other tri configurations out there.

  I think that tubes are a bad idea for cat main beams.  When the crossection and materials of the beam are engineered for their loads, its not going to look like a tube.  The box section beam on Sequoya uses internal bulkheads stiffen it vertically--not just cross sectional area.  In a smaller cat, an I-beam like section handles the vertical and horizontal loads in the right proportion.

  Lets not forget that unstayed masts have a lot of problems too.  Controling sail shape across a wide range of conditions is the biggest one.  Wylie Cats are marked exceptions.  Remember when unstayed masts struck most people as a daunting engineering problem--even as they flew on wireless airplanes!

  Posted by  on  05/09  at  07:17 AM

• BI-POLE-R
  By using a bipod mast arrangement, all compression forces go directly to the catamaran’s hulls.

  See example here:
  http://www.rclandsailing.com/catamaran/
  

  Posted by  on  05/17  at  01:39 PM

• Lots of people have tried this.  Tom Jones’ Dandy was originally rigged this way.  Unfortunately, it seems like you have to have a boat that is always going upwind (i.e. always sailing on its own apparent wind) in order for this to work well.  That’s a fast boat--much longer, lighter and on the verge of capsize than most cruisers want to be.

  But if you are yves parlier though…

  Posted by  on  05/17  at  08:34 PM

• G’day,

  Reply to Robert Dalton
  
  I wrote a lengthy reply to this when it was first published, pointing out all the flaws in the arguments and where John had misrepresented harryproas.  I wrote a similar reply when Michael published his comparison of rigs.

  Michael has chosen not to publish either of these.  I suspect it is for the same reason that he does not mention the harryproa website in his “resources” list for the article.

  Bottom line is, that there are now 28 harryproas between 25 and 66’ being built and 25’, 35’, 40’ and 50’ versions sailing successfully. 

  regards,

  Rob Denney
  http://www.harryproa.com

  Posted by Rob Denney  on  07/26  at  06:33 AM