The Ketch-Rigged Cat

[beiland]

Originally Posted by Maren

As for materials on hand, that really baffled me. With the exception of the mast and the fittings (in addition to anything else he might needed to have replaced) he had all the materials needed for another aft-mast rig with no heroics needed to move the rest of the standing rigging, re-cut the sail and so on.

That baffled me as well....sounds like even more work and expense to go that route.

]

[beiland]

Originally Posted by Maren

...I think general acceptance of something this new tends to go like this: The engineers trust the numbers, the daring try it out, and over time acceptance is gained from experience of those that went first. But the numbers are the lynch pin in my opinion. So I keep coming back to the question, but from three different approaches:

The Godfather – Have you floated this past C.A. Marchaj yet? I think he would lend a great deal of credence to the work.

I'm uncertain that he is still with us? Certainly he has not made any recent contributions to the subjects he so adamantely contributed to. Besides his contribution would likely be primarily aerodynamic in nature. I think I've shown that the aerodynamics of the situation conform with his findings and will be just fine. It's the loading that will be tricky.

Loads - The occasionally voiced concern of those that have read everything they can find on aft-masts is the crystallized thread of a Norseman backstay and the later switch to a conventional sloop rig from by Barefoot who, as pointed out above, didn’t follow what you were saying in the first place. By extension, the concern is that the rigging might be sized to take the loads but the hulls couldn’t or would at least need some reinforcement. And yet, this is contrary to your position that the rig would have less stress because of a lower Center of Effort.

I don't know exactly where his Norseman fitting was located in his rigging plan. If he had only one single backstay on his rig that was clearly not enough. And I am unsure as to what size rigging wire and fitting were utilized. I have a feeling that his fitting was faulty, and/or his installation of it. The reason I say this is in reading his log I can find nothing really heavy or extreme weather-wise that should have brought the rig down unless it was greatly underdesigned by his design calculations.

I suppose the answer is running a finite element analysis of the whole deal but I am not a Naval Architect. So I’m asking you, the chief proponent – Brian, what are the loads involved and have they been rigorously calculated or has this been done with an applied engineering approach?

First let me clear up this point about 'less stress'. I'm sorry if I've given the impression that my rig would be less stressful. Rather in fact it will be more stressful, both within itself, and in transmitting its forces to the hull structure. I only meant to say that because it has a lower CE, it will have less overturning moment on the vessel than the corresponding sail area of the taller sloop rig. So the side shroud loading could be less from a geometric point of view. BUT, on multihull vessels, this shroud loading can be SIGNIFICANTLY higher than on a monohull due to the huge stability factor of the beamy hull form...yin and yang.**

Here is the gentleman & firm I want involved in the final stress analysis of this rig concept, Chris Mitchell of AES. I'm currently in discussions with him about this consultation work, and hoping to have a definitive client willing to pick up part of that expense.
**(have a look at this paper, Design Notes, and particulkarly under "Cruising Catamarn Rigs", )
(while you are in this paper have a look at "Geometry:Cap Shroud/Chainplate". I will reference that in a minute)

Please understand that there are many designers and naval architects that could not do adequate justice to the rigging analysis that falls outside the 'norms'. Free-standing mast systems are another of these 'outside-the-norm' design projects that need a specialist involved. Eric Sponberg is another choice of mine to evaluate unusual rig designs as he has had to do on many free-standing projects before. I'm the concept guy, not the engineering specialist.

Having said that let me point out a couple of critical items I see in my aftmast rig design:
1) Masthead Loading: Some folks have noted that I would not be able to maintain a reasonable tight forestay as a result of the mast leaning forward. But look closely at my masthead. The single backstay at that point is making a greater angle with the mast than many tradional sloop rigs....mor reward pulling advantage...about 27 degree 'capstay' angle...pretty good.

2) Hounds Loading: Here is were I will experience some problems. As drawn at present There is only a 10 degree angle between the lower backstay and the mast....significantly higher compression loads to the mast. But if I attach this backstay to the front of the mast and run it to the very sterns of the vessel I get a 15 degree angle...much better. And if I chose a 6 degree rake for the mast rather than the 10 degree I show, things change again.

3) Capshroud Loading: As Chris points out in his paper you neither want to small a capshroud angle (big compression loads), nor too big a capshroud angle. But why not bigger....because on a traidition rig with a mainsail the head of the mainsail bends off to leeward and tries to twist the top of the mast excessiely. I don't have this 'head-of-mainsail' load as I have no mainsail...so I might well make use of very wide spreaders and big capshroud angles to lessen the significant compression loads to the mast imparted by the stability loading.

...to be continued....sorry, I've got to run out right now

I'll leave you with this excerpt from a recent letter,
Obviously I am a big fan of the ketch rig for an offshore cruising vessel, as were many of the classic yacht designers. Sloops might have a slight advantage going to weather, and in terms of simplicity, and cost to build, BUT, ketches are great sea cruising rigs. Now suppose we can get to a ketch rig with a single mast. I still think this idea merits serious consideration; a) maybe the final result will be a little different than my sketches at this point, b) maybe there will need to be a little less mast rake as I have sketched up for a big trimaran being built in Seattle, c) maybe the rigging pieces will be arranged slightly different. The point I am trying to make is that a ‘single-masted ketch’ is a worthy goal, if it can be done.

[sandy daugherty]

Finite element analysis is not necessary. Freshman level Statics and Dynamics are sufficient to calculate the loads of Mr Eiland's rig. They are enormous. They are not impossible. They just offer no advantage substantial enough to justify the engineering studies, load testing lab time, and (most importantly) the loss of interior space to the massive trusses required to carry these loads. Why bother? Make the mast 5' taller to compensate for the aerodynamic "Loses" of the mast.

The compression load on an exemplar 40' sloop's mast base is 15 tons. move the mast base aft to fifteen degrees from the backstay nearly quadruples the load, to somewhere around 110,000 pounds. In a double backstay arrangement which seems to fit a catamaran vessel, the backstays would need to carry 75,000 pounds apiece, (50% safety factor) plus athwartship loads, with a single headsail. Adding a second sail and the load required to maintain less than 1% deflection in the luff would represent a geometric projection in the loads on the backstays. Now you have to build a boat to carry those loads. It quickly becomes apparent that you have spent a lot of money designing and building a boat that is very heavy, uses exotic materials to carry the loads in rough seas, and it doesn't go very fast as a result. What most people would expect to be a big open bridgedeck salon is cut up into small odd shaped compartments divided by walls hiding massive trusses. And the beam under that mast will be an absolute engineering marvel. But yes, it can be done.

Brian Eiland has made some beautiful drawings though!

[sandy daugherty]

Give the mast an aerodynamic shape and allow it to rotate and it becomes an asset, greatly increasing the mainsail's efficiency to exceed that of a genoa on a forestay.

[Maren]

Originally Posted by sandy daugherty

Finite element analysis is not necessary. Freshman level Statics and Dynamics are sufficient to calculate the loads of Mr Eiland's rig. They are enormous. They are not impossible. They just offer no advantage substantial enough to justify the engineering studies, load testing lab time, and (most importantly) the loss of interior space to the massive trusses required to carry these loads. Why bother? Make the mast 5' taller to compensate for the aerodynamic "Loses" of the mast.

I'm not quite so sure it is as simple as that. Here is why:

The rig was set up on a wood boat with a wood mast. The failure was in the thread of backstay but we don't know where that thread was.

Personally, I don't think just because the loads are, or are estimated to be, higher is a reason to throw the whole thing out. If I recall, freestanding rigs also have much higher loads. And yet, they are also used. Additionally, there seem to be some features that warrant consideration for example:

Ability to set the whole thing up with roller-furling sails
No boom to knock you unconscious
Minimal loss of speed to windward
Lower mast height
Multiple sail configurations

Now, were I the Gung-Ho racing type, I would dismiss the whole thing as I wouldn’t want the loss of speed. But, that isn’t my primary concern. I prefer to go with the wind rather pound to windward. Maybe this is because I don’t play those Rolex tunes like you hear on BBC worldwide yacht racing. Maybe it’s because I don’t insist everyone wear little embroidered shirts and matching pants. I think not registering for the races might also have something to do with it.

Still, everyone makes their own choices. And I’m not sure this rig is for me. But I am willing to look at pretty much everything even if I don’t intend to personally a particular solution.

[sandy daugherty]

Go for it! Take me sailing with you! You are talking visionary dream, and I'm blathering about pealing the carrots and keeping the rue from curdling for this visual feast. I promise not to put on any emblazoned outerwear, tweak any sheets, or pretend we're racing.

But allow me a few practical points:

Furlers don't furl if they aren't close to straight.

Sails cut for a curved luff are not going to pull to weather, and sailors have had a fondness for going to weather since the Spanish Armada.

I wasn't talking about the poor guy with the wood mast. I was talking about a brand new mast aft, engineered catamaran. Free-standing masts are not in question. They work. but they do not have to withstand the loads of a forward leaning cantilever. This is the single overriding issue.

The person who said there is nothing new under the sun is wrong. A common pruduction sailboat on the market today would have been recognizable to Sir Francis Drake, but he would never set foot aboard it if he had to rely the descriptions of other people using then-conventional wisdom. Just imagine what an illiterate, superstitious old salt would have to say about sailing off shore in an egg shell hull with a pikeshaft for a mast and piano wire shrouds! There were two sails aboard, but only one yard arm, and some idiot hung it upside down!

Keep the dream alive, I'm just a cook.

[Maren]

Originally Posted by sandy daugherty

Go for it! Take me sailing with you! You are talking visionary dream, and I'm blathering about pealing the carrots and keeping the rue from curdling for this visual feast. I promise not to put on any emblazoned outerwear, tweak any sheets, or pretend we're racing.

But allow me a few practical points:

Furlers don't furl if they aren't close to straight.

Sails cut for a curved luff are not going to pull to weather, and sailors have had a fondness for going to weather since the Spanish Armada.

...

Keep the dream alive, I'm just a cook.

In general I find the trend towards homogeny in sail plans to be sort of unfortunate. This is one of the reasons why I started the thread. But, at the risk of beating a dead horse, I’d like to go back to both our posts. In part because there are points to be addressed but also because I am concerned we might have missed the spirit of each others posts.

I find the aft mast rig interesting but I’m not the sort to sign up for it without knowing, as completely as possible, the forces involved and what sort of performance can be expected. This is why I would like to see a comparative polar diagram of the points of sail and finite element analysis. Without them, that is a lot of cash to ask an owner to risk of a new boat, to say nothing of any safety issues involved. Retrofitting would be a nightmare, but I think this is true whenever a rig is substantially changed.

As for the value of the finite element analysis of statics and dynamics, I think the former shows areas of strain better. It may by most of the stress is in the back third but is easily reinforced. Or it might take six layers of carbon for the whole back third of the boat. Nobody really knows. One thing is for sure, we both agree understanding the loads involved is the key point for this whole beast.

Your point about the furlers is, of course, true. I would think this is a reason for a properly engineered mast and rig. And I keep coming back to that fellow, Barefoot. He planed for his mast to bend and that would seem to put the fullers in an odd alignment. But he didn’t state he had a problem. I have no explanation other than to note he didn’t say too much about the rig overall.

As for the comments I had made about racing. They’re true. But I didn’t notice you were a sailing coach at Annapolis. I don’t know if that involves racing, but I could certainly see how that could be taken as a slight where none was intended.

[beiland]

Originally Posted by sandy daugherty

Finite element analysis is not necessary. Freshman level Statics and Dynamics are sufficient to calculate the loads of Mr Eiland's rig. They are enormous.
The compression load on an exemplar 40' sloop's mast base is 15 tons. move the mast base aft to fifteen (15) degrees from the backstay nearly quadruples the load....

Dear sandy,
Are you aware there are sailing rigs out there with backstays of less than:
1) 15 degree angles
2) 10 degree angles
3) even 0 degrees (no backstays)
Have you heard of the B&R sail rigs?? They are commonly ultilized on the Hunter line of sailboats. They might be termed 'strange' or certainly 'different' as they do away with backstays (NO BACKSTAYS).

The Bergstrom & Ridder:
The B&R rig takes the swept back spreader a step further. The angle on this rig is a massive 30 degrees. The idea behind the rig was to contain rigging loads as much as possible within the mast structure itself and avoid loading the deck and hull. This allowed builders to make lighter boats and not have to reinforce deck and hull structures for strength, reducing construction costs. This also allows builders to use a lighter mast section, reducing the cost of the rig. More recent developments of the rig includes reinforcements by incorprating rigin struts between chainolate and teh gooseneck. The purpose being to distubute the compression loads on teh mast reducing the anmount of reinforcement the deck needs to take the download pressure of the mast.

The big advantage of this rig is that it allows more roach in the leech of the mainsail increasing sail area for better downwind performance. The swept back spreaders also give a great amount of fore and aft support to the mast, eliminating the need for a backstay.

There are a number of discussions that can be found on this subject:
H260 Standing Rigging
.....and related subjects of swept back spreaders:
Loads for swept spreader rig - Boat Design Forums

From these discussions you might deduce that "freshman level statics and dynamics" are not necessarily sufficient to calculate the loads on unusual rigs. As I said previously, "there are many designers and naval architects that could not do adequate justice to rigging analysis that fall outside the 'norms'."

From another discussion I had submitted;
I recently purchased a copy of Larsson & Eliasson’s Principles of Yacht Design, specifically to investigate their analysis of these rigging loads. But what I found at the very opening paragraph of their chapter on Rig Construction, "in dealing with the dimensioning and construction of the rig, over the years different methods have evolved, ranging from old rules of thumb…to sophisticated computer models for exotic composite materials. We will take a middle line (approach) using accepted practices (old rules of thumb?).…..” Page two (text 202) of their chapter, "It is common practice that the transverse and longitudinal stability are studied separately”
And this is supposed to be a modern analysis? Later in the chapter (text222), “another factor which improves performance is the rake of the mast. Although not numerically proven…”

In this modern computer age why have they chosen to ignore the "sophisticated computer models"? Are sailboat rigs such a complicated structural problem to analyze? Even the more simplistic steady-state ones (minus some of the more complicated dynamic questions)?

I guess my frustrations with understanding and defining the actual true loads on the rigging of a sailboat is best summed up at this Classic Marine website:
http://www.classicmarine.co.uk/Artic...ging_loads.htm
“Rigging Loads- a study in guess work, or a tale of scientific progress?"

I will quote a few of the more notable passages from his very interesting summation:
a) He opens with a quotation from Douglas Phillips-Birt, "Masts are tricky things. It is not for nothing that Lloyd's, which is ready to specify the scantlings of nearly every other part of a yacht, washes its hands of them altogether and plants the responsibility for their size and shape squarely on the designer's shoulders....suggesting that mast are perhaps a little beyond rational analysis."

Very long discussion thread on the subject:
Sail Loading on Rig, Rig Loading on Vessel

Originally Posted by sandy

They are not impossible. They just offer no advantage substantial enough to justify the engineering studies, load testing lab time, and (most importantly) the loss of interior space to the massive trusses required to carry these loads.....Now you have to build a boat to carry those loads. It quickly becomes apparent that you have spent a lot of money designing and building a boat that is very heavy, uses exotic materials to carry the loads in rough seas, and it doesn't go very fast as a result. What most people would expect to be a big open bridgedeck salon is cut up into small odd shaped compartments divided by walls hiding massive trusses. And the beam under that mast will be an absolute engineering marvel. But yes, it can be done.

I don't foresee the need for these 'massive trusses' nor 'beams of an engineering marvel'.

I will admit I have always been a fan of a more comprehensively planned 'frame structure' within the hull of any sailboat (mono or multi) to which to attach the supporting elements of the sailing rig. I've seen a few boats come apart and lose their rigs when these considerations were casually added on.

So I wish to have a substanial major bulkhead under the mast and stretching across the entire beam of the vessel onto which the shrouds are also attached....a bulkhead with a bit of a little 'space frame beef', above and beyond just a plain old sheet of plywood as you find in many vessels. On a keel boat this bulkhead would transmit some of the shroud loading to the keel 'backbone' and reduce some compressive loads to the deck skin. On some of the more sophisicated designs 'tie rods' were incorporated to do this job in the place of a full bulkhead. I would seek to employ some of this same sophistication in framing structure to lend a rigidity to the whole rigging structure (rig and base hull) that is often ignored on production vessels.

BUT, it does NOT have to approach the 'massive engineering marvel' you sited. It's really quite amazing that the aft-mast Prout catamarans (couple of photos below) were able to support their rather unsophisticated alum mast sections on the top of essentially the edge of a sheet of plywood bulkhead. And they were able to carry twin headsails while utilizing a relatively shallow angled double backstay arrangement. Interestingly, some B&R rigged vessels employed an external frame structure to reduce loads to the vessel's deck and hull skins.

Major bulkheads should be constructed of a engineered sandwich core construction, and their proper bonding to the hull skins should be given greater consideration.

The catamaran vessel form by its own nature is lacking substantial fore-to-aft stiffness provided by the keel of the monohull and the slim center hull of the trimaran. I've tried to provide some relief to this situation by employing a 'plat-on-edge' bulkhead down the center of the vessel under the wing. And I've suggessed this 'plate' could be the backbone of a central 'wave splitting' nacelle. I think many cats would benefit from such an addition, not just my aftmast design.

In fact this whole wing area of the catamaran needs close scrunity as to its contribution to the stiffness of our vessels. Look at what a simple X-cross-staying in the horizontal plane of the tramp area accomplished for some of the big ocean racing cats. The wing floor's shape and its attachments at either side need scrunity. ....Just two other examples of external framing structure.

[beiland]

You know I can still imagine sailing a big 65-foot catamaran with this rig right off the mooring, and back to the mooring, without the engine, by myself, with so little effort that I might take it out having only a few spare hours to kill or a daysail.

And I would rig mine with tiller steering rather than a wheel and get a really good balanced helm. I wouldn’t have to uncover any sails, nor recover them when I returned to port. And I would be less concerned with reefing by myself if the wind were to really come up. If I were short-handed at sea, I would have many of the benefits of a ketch rig, without the necessity of slab reefing the main and mizzen sails of the traditional ketch rig.

That about sums it up. I would like a 65 foot cat that I could take sailing by myself, and that might even be easier than a beach cat. Try hoisting a full batten mainsail on a 65 footer by yourself, or even a 40 footer. Most folks over 50 will have second thoughts, or will just unfurl the jib and forget about hoisting the MAINsail.

I'm 65 and I could sail this 65 foot cat by myself with this aft mast rig. And with the balance and low power afforded by the smaller 'mainstaysail' I could sail this vessel right off the mooring or maybe right off a side-to-dock slip.

Many people really ‘connect’ with my mastaft rig suggestions. I continuously get email messages complimenting me on this idea. They mostly like the potential ease of use, and they dislike big mainsails!! Just the other day I ran across another forum that had a bunch of ‘Prout’ catamaran owners praising the virtues of their mast-aft rig vessels.
http://www.cruisersforum.com/forums/f48/prout-rig-3362.html
http://www.michaelbriant.com/cruising_photos.htm

You see it’s not JUST an emotional involvement, but rather a real feeling that cruising folks will enjoy this rig.

I also believe a few fisherman may be eventually attracted to this concept of ‘gamefishing under sail’, particularly as the fuel prices continue to rise. And these powerboat guys need a rig that operates as easily as ‘Venetian blinds’. They want it dead simple. I’ve received a few inquiries that have me convinced that my rig is not too difficult for them to understand.
Gamefishing for Sail, Under Sail (and power)

Originally Posted by trouty

What self-respecting powerboater would be caught dead on a sailboat?

Originally Posted by trouty

I can tell you!
A charter operator - for whom fuel costs is a huge part of his operational bottom line!
I reckon you are onto a winner myself...
Cheers!

Here's a challenge Sandy,
La Mans start. I'll be out sailing before you get the covers off your mainsail, and when we return for the day, I'll be at the bar watching you put away your vessel for the day.

[beiland]

Originally Posted by sandy daugherty

Give the mast an aerodynamic shape and allow it to rotate and it becomes an asset, greatly increasing the mainsail's efficiency to exceed that of a genoa on a forestay.

Don't get me wrong, I am a BIG FAN of rotating mast. They are wonderful, from both an aerodynanic leading-edge point of view, and as a mainsail shaping tool.

But they all require a 3-point staying arrangment where the major shrouds on each side also double as a backstay. Look at the very shallow angle this shroud pulls back on the mast...(often less than half the forestay angle)....not very efficient at maintaining a tight luff for the jib or genoa.

Now I know you will bring up the fact that the leech of the mainsail becomes part of the 'backstay' with this 3-point rig configuration. Yes, and that is particularly true when you can really sheet the mainsail in extra tight as with beach catamarans and racing multihulls. But how often in heavier airs do you see cruising folks strap that mainsail in that tight??...and without it, big time sag in their forestays.

But I still really like rotating mast rigs!!

[Nordic cat]

Originally Posted by beiland

Don't get me wrong, I am a BIG FAN of rotating mast. They are wonderful, from both an aerodynanic leading-edge point of view, and as a mainsail shaping tool.

But they all require a 3-point staying arrangment where the major shrouds on each side also double as a backstay. Look at the very shallow angle this shroud pulls back on the mast...(often less than half the forestay angle)....not very efficient at maintaining a tight luff for the jib or genoa.

Now I know you will bring up the fact that the leech of the mainsail becomes part of the 'backstay' with this 3-point rig configuration. Yes, and that is particularly true when you can really sheet the mainsail in extra tight as with beach catamarans and racing multihulls. But how often in heavier airs do you see cruising folks strap that mainsail in that tight??...and without it, big time sag in their forestays.

But I still really like rotating mast rigs!!

Brian,

I will have rotating wingmasts that are unstayed, as does a Kelsall designed cat called Cool Change.

You could do boom furling with an unstayed mast which is nearly as easy as roller furling, but still lets you use battens for sail shape and less flogging of the sails.

All those pieces of wire/rope and adjoining fittings are the weak points of stayed rigs. Lose one piece and you risk the whole rig. The safest rig is an unstayed rig, and it also offers the lowest windage. Every meter of ½"/12 mm wire adds about 1 lb of drag at 40 knots! You rigging would add what would be the same drag as towing 6-8 tenders would!

The Prout rig has the main bulkhead to take most of the loads, and would be just as easy to handle as your rig, if done with boom furling. The loads would be more manageable.

I see that someine is building one of your mast aft designs in Thailand, it will be interesting to see how that works out..

Regards

Alan

[sandy daugherty]

I am a great admirer of Lars Bergstrom, and was greatly saddened by his death in 1997 in his experimental aircraft the Windex 1200. But the Bergstrom and Ridder rig is not magical, or even controversial. Nor does it contravert the stresses involved. It is, in fact nearly commonplace today, just as his wonderfully simple masthead wind indicator, the Windex.
Mast compression loading is the bane of catamaran designers. Virtually ever cat designed since the early 1990's has a very highly engineered bulkhead under the mast, and most are built with carbon fiber in the layup. But cat designers are blessed with the advantage of a very wide shroud base. Monohull designers can usually find a strudy way to support the mast loads, but struggle to design sturdy chain plates to carry the lateral stresses of the rig. They are also blessed in that the monohull rolls to dump gusts against the sails, while cat designers just have to absorb those loads. Thats why typical catamaran rigs are shorter, and three times stronger that a roughly comparable monohull reg.
To be perfectly blunt, Mr. Eiland, there is a reason your design has not been accepted in spite of your enormous efforts over 25(?) years to promote it. It offers no great gains at considerable extra effort and cost. I wish you would put your design to test. 1. Build a 20 foot model of your mast. Measure the loads. find out how much weight is needed on the backstays to support a 2000 pound weight at each clew. And measure the load under the mast. These are strictly static loads, but will give us a measure of the absolute MINIMUM strength required
2. Now build a bulkhead to carry the mast. At its simplest, it should lean forward at the same angle as the mast. That means one or more of your interior walls leans into occupied space. It would be really great if that bulkhead went directly to the port and starboard chain plates, and had another wall (or truss) going forward to the midstay and forestay. Here is a simple tripod base for the mast, to which the shrouds attach. With a nearly vertical mast, we have reproduced the status quo in tripod rigged sailboats today. If the base were cruciform. we would have reproduced the loads on sailing vessels over the past millenia. If we move the mast out of vertical, one stay gets pulled a lot more than its opposite. There is no way around that. Lars from Mars would not try. His way was to multiply the triangulations in a narrower space, just like the world's first iron bridge in England. The essential point is still there. The mast is no longer a flagpole, with equal loads all the way around. It is now a large lever with a tremendous mechanical advantage in one direction while loosening its leverage on the side that we want to be perfectly rigid! And while thats happening, we have increased the load under the mast by orders of magnitude, while asking the tripod to restrain the same loads on the port and starboard shrouds. Maybe it can be built, and maybe it will only just 8,000 pounds more. But Why?
The sole intent was to hang the sails on a cable instead of a pole. The theory is that the mast represents a significant reduction in the efficiency of the sail attached to it. Yes: not having a mast is better than having a mast in front of the sail. Not a lot, but better. In fact taking in a discovery made by the world's first successful aerodynamicists, the difference is just about the same as the drag caused by the mast standing up there in the breeze.
Dear Mr. Eiland. You mast is still there. You have not accomplished a lot in the way of sail efficiency.

What the world's first successfull aerodynamicists, the Wright Brothers discovered, that had eluded Doctor Samuel P. Langley, was that wings need cord depth. A single surface wing is not as efficient as a solid wing. A mast provides something like chord depth in a crude, inelligant, non-streamlined way. It contributes in some part the the power the sail develops, that in a small part compensates for the bare-pole, barndoor drag it represents standing alone. Two single surface sails plus one bare pole equal very little more power than a common sloop rig, and don't hold a candle to a wingmast, even one of modest chord width.
What is the difference between a 12,000# 40 foot cat and an 18,000# 40 foot cat with equal sail area? Seven knots.
Are we sexagenarians really worried about raising the sail? No; one electric winch, $2400. Push button sail handling, including reefing. And a lowered sail is more easily secured from high winds, with much less weight aloft than a roller furled genoa.
Windjammers of the middle of the nineteeth century had radically aft leaning masts. Most thought that was just sexy looking, but they served a very practical purpose. They allowed for longer luffs, yes, but the principal advantage was that by moving the base of the mast forward, there was a substantial increase in the mechanical advantage of the backstays, giving the sails a more rigid luff, and permitting greater halyard tension to reduce scalloping at the hanks!
To summarize; Is a mast bad? Not really. Would getting it out of the way do much for sailing efficiency? Not if its still standing there. Would it be affordable to move the mast base towards the back of the boat? Absolutely not. The boat that could support that geometry would be very expensive to engineer, and require much heavier structural components, making it slower. Has anyone tried it? Yes, but for whatever reason, it broke. Does that mean its all a bad idea? No, but it does mean that the common perception is bad. Does that mean the dream has died? No. dreams don't die. But after a while, new dreams come along.

Mr Eiland; I want to tell you something positive in closing. I have watched your site over the years, and I want you to know that I think your skills in depicting and defending your ideas have matured to the level of fine art. Your latest drawings are just beautiful, balanced, and graceful. They demonstrate a love of and dedication to this concept that exceeds the vision of most men. I regret that I don't agree with you.

[exfishnz]

Originally Posted by Maren

why we don’t see many ketch rigged Cats?

62' sealium alloy crusing ketch rig cat under construction in NZ:

De Villiers Yacht Design and Naval Architecture

Q-West - 19metre sailing cat detail sheet

* I have no personal or commercial connection to the above links whatsoever.

[Nordic cat]

Originally Posted by sandy daugherty

To be perfectly blunt, Mr. Eiland, there is a reason your design has not been accepted in spite of your enormous efforts over 25(?) years to promote it. It offers no great gains at considerable extra effort and cost.


Mr Eiland; I want to tell you something positive in closing. I have watched your site over the years, and I want you to know that I think your skills in depicting and defending your ideas have matured to the level of fine art. Your latest drawings are just beautiful, balanced, and graceful. They demonstrate a love of and dedication to this concept that exceeds the vision of most men. I regret that I don't agree with you.

Very well put and so true Sandy.

It has been a supreme effort and excercise in low cost marketing,and finally someone has gone for it...

Regards

Alan

[beiland]

Originally Posted by beiland

....I don't foresee the need for these 'massive trusses' nor 'beams of an engineering marvel'.

I will admit I have always been a fan of a more comprehensively planned 'frame structure' within the hull of any sailboat (mono or multi) to which to attach the supporting elements of the sailing rig. I've seen a few boats come apart and lose their rigs when these considerations were casually added on.

So I wish to have a substanial major bulkhead under the mast and stretching across the entire beam of the vessel onto which the shrouds are also attached....a bulkhead with a bit of a little 'space frame beef', above and beyond just a plain old sheet of plywood as you find in many vessels. On a keel boat this bulkhead would transmit some of the shroud loading to the keel 'backbone' and reduce some compressive loads to the deck skin. On some of the more sophisicated designs 'tie rods' were incorporated to do this job in the place of a full bulkhead. I would seek to employ some of this same sophistication in framing structure to lend a rigidity to the whole rigging structure (rig and base hull) that is often ignored on production vessels.

BUT, it does NOT have to approach the 'massive engineering marvel' you sited. It's really quite amazing that the aft-mast Prout catamarans (couple of photos below) were able to support their rather unsophisticated alum mast sections on the top of essentially the edge of a sheet of plywood bulkhead. And they were able to carry twin headsails while utilizing a relatively shallow angled double backstay arrangement. Interestingly, some B&R rigged vessels employed an external frame structure to reduce loads to the vessel's deck and hull skins.

Major bulkheads should be constructed of a engineered sandwich core construction, and their proper bonding to the hull skins should be given greater consideration.

The catamaran vessel form by its own nature is lacking substantial fore-to-aft stiffness provided by the keel of the monohull and the slim center hull of the trimaran. I've tried to provide some relief to this situation by employing a 'plat-on-edge' bulkhead down the center of the vessel under the wing. And I've suggessed this 'plate' could be the backbone of a central 'wave splitting' nacelle. I think many cats would benefit from such an addition, not just my aftmast design.

In fact this whole wing area of the catamaran needs close scrunity as to its contribution to the stiffness of our vessels. Look at what a simple X-cross-staying in the horizontal plane of the tramp area accomplished for some of the big ocean racing cats. The wing floor's shape and its attachments at either side need scrunity. ....Just two other examples of external framing structure.

I just found a posting I had made on this vessel substructure subject, and rather than post it under this 'ketch subject' I posted it as a new subject thread here;
http://www.cruisersforum.com/forums/...ads-16721.html