Unusual design for an extra-heavy-displacement 11ft long Atlantic Proa for circumnavigation

[clmanges]

I have a little regret at not having chimed in near the beginning of this thread with an essential question for artis; to wit: In the thousands of years that people have been floating themselves across bodies of water in all kinds of strange things, why has this design never appeared before?

 

[BlueBell]

In the thousands of years that people have been floating themselves across bodies of water in all kinds of strange things, why has this design never appeared before?

Page 11

Because nobody is as smart as the "OP of the day" and their new invention.

 

[kapnD]

There’s an article on Sailing Anarchy about rescue pods used in the North Sea during WW2.
They resemble the craft in question here.
There’s a lot of discussion about their motion at sea and their habitability, and more.
floating, not sailing https://sailinganarchy.com/2023/12/19/floating-not-sailing/

 

[comfisherman]

Interesting watch. My take home from the video...

"Boat" idea would work best if a world power had scheduled missions to search and rescue you.

Ride quality from the limited first hand accounts sounded abysmal.. from a generation of men much harder than most walking around today.

Surviving British versions were nearer the shape and size of my first boat... near 3x the size proposed by the op.

On a vessel 3x the size proposed the most important gear was the safety gear....

 

[kapnD]

Drifting even further from the topic here, my thought was that even if an aviator were to crash miraculously right next to one of those buoys, a one knot current could prevent a swimmer from ever reaching it, especially if swimmers were injured or hampered in other ways.

 

[gonzo]

The current would move the swimmer and buoy at the same velocity. Wind making a boat or buoy drift is what prevents a swimmer from reaching it.

 

[comfisherman]

The you tube video was referencing anchored bouys placed in zones of common airplane ditching.

 

[gonzo]

Oh, then the current is relevant. However, an average swimmer can overcome a 1 knot current.

 

[sharpii2]

POE 630b

Attached is a sketch of my modified Plank-On-Edge concept.

After realizing that the original had an S/D of only about 5.3 instead of the 10.5 intended, I thought of increasing the Sail Area (SA)to the S/D of 10. 5 amount. This would mean doubling the SA. Without using a huge amount (maybe as much as 90%) of very dense ballast, I wasn't confident that this could be done successfully. Also, there was the problem of overly tall masts and long booms.

I suppose the Victorian Plank-On-Edge racers were for racing only and were primarily day sailors. They likely raced only in good weather. Being day sailors, they would not need much carrying capacity. Maybe just enough for their crews and supplies, such as an anchor, some water, some beer, and perhaps a bottle of champagne, in case that boat won the race.

This boat would be required to carry quite a bit of stores and gear. So the portion of the total displacement, allotted for ballast, would have to be far less. Maybe just half. And the sail rig would have to be manageable too, especially in rough weather. These two requirements pretty much limited the SA. So I ended up with an S/D of only about 7.1. And this was after increasing the counted SA by about 15% and decreasing the Displacement by about 20%.

This is bad but, it may not be as terrible as it seems. Other than the rudder and a small skeg, there are no appendages on this boat. Appendages have double their surface area as whetted surface. So, my thinking goes. If the the Hull itself can act as a the keel, the over all whetted area may be reduced, even though the deep, squarish sections of the Hull have more surface area than a more conventionally proportioned Hull of a more conventional shape.

Add to this the enormous Heft Factor (Hf) of 6.3 (4 to 6 times that of a typical sailboat) and the relatively sharp ends, and we get a considerable amount of momentum to power through a chop. This may make up for, at least to some degree, the very low S/D. But I certainly wouldn't want to be stuck in light wind conditions on this boat.

The next question should be if this boat would be sufficiently seaworthy. I think it might be. This is even though it is far on the comfort side of the comfort/seaworthiness overlap. Hopefully, there is enough buoyancy in the ends to prevent it from being constantly pooped, or constantly burrowing into waves. Hopefully, as well,the flat bottom would dampen pitching to a tolerable degree.
The amount of amid ship free board is half the draft. This I think is a more healthy ratio. The earlier drawing (see next attachment)has a somewhat lower proportion. The danger of low free board on a narrow, deep hulled boat like this is that, when it heels as it must, the deck edges dip under the water. And if they do that too far, the water can come too close to the center line. This would not affect stability much. But open hatches and ventilators, even if placed on the center line, would be in excessive danger of taking on water.

This version of the concept is technically not a true Plank-On-Edge. The mid-section is not deeper than it is wide. It is exactly the same. But it looks like a Plank-On-Edge when viewed from an end. And it has almost all of the qualities of one, both good and bad.

For the good qualities:

It will not roll quickly. The flattish, near vertical Hull sides will dampen a roll maybe even more effectively than a long, shallow keel would. It would also have an 180 degree range of positive stability. It would simply refuse to float upside down. On top of that, it would be nearly impossible to capsize. And, as mentioned before, it would have plenty of momentum to plow through a chop.

For the bad qualities:

Because it would be so reluctant to roll away from a wave, that very same wave would tend to wash over the deck. And, in so doing, could very well carry away anything that is not held brutally secure. And this is especially true with deck crew. This is a boat that would be best sailed in rather than sailed on. And the decks, house, and hatches must also be strong enough to take a brutal pummeling. The Hull would not be as easily pushed aside by a breaking wave as that of a more conventional type might be. It would be rooted in the sea.
And, as mentioned above, it would do very poorly in light wind conditions.

It would be more like a submarine with sails on it than like a more conventional cruising sailboat. There is very little internal volume for its length and weight. And there is very little deck space.

But I think it would do very well in the motion/comfort department, which it was conceived for.

I might one day build a 1:12 working, scale model of it, just to see how it would behave.

Any thoughts?

 

[wet feet]

Yes,I have some thoughts.Look out for the story of the Oona it was possibly the most extreme of the nineteenth century leadmines and endured a short,tragic life.As a result of similar events,the type fell out of favour for good reasons.It may give some satisfaction to determine the numbers and ratios that relate to the style but for commercial reasons there are better ways to use time and materials in the production of a boat that somebody might actually wish to buy and use.

 

[gonzo]

 

[sharpii2]

Yes,I have some thoughts.Look out for the story of the Oona it was possibly the most extreme of the nineteenth century leadmines and endured a short,tragic life.As a result of similar events,the type fell out of favour for good reasons.It may give some satisfaction to determine the numbers and ratios that relate to the style but for commercial reasons there are better ways to use time and materials in the production of a boat that somebody might actually wish to buy and use.

I agree. But I'm not thinking of this as a commercial project. Just as a curiousity piece. I could build the model and take bets on whether or not it will actually sail. It's lack of a keel would not require a stand. And with its short rig would do nicely as a mantle piece. And, if it actually successfully sailed as well, that would be frosting on the cake.

If I ever do attempt to design a more commercially viable boat, it would be just about the opposite of this.

It would be shallow, Beamy, and have a decent amount of sail on it. I have watched a good number of Youtube sailing videos to get a good idea of what people basically want. They want sufficient seaworthiness, decent comfort, and a good deal of space. They also want to get on and off the boat, from and to a dinghy quite easily.

 

[DogCavalry]

There's not really any mystery there. Nothing to learn. Hull design is a reasonably mature science, so the behavior of a very bad hull form can be accurately predicted by a competent designer. It's a fascinating field, and I highly recommend it. Devote the hours you might spend on the model to study instead. CA Marchaj's work is well worth the time and expense. If you're really into it, your head will begin to fill with designs that will work quite well. And generally they will look quite conventional.

 

[sharpii2]

There's not really any mystery there. Nothing to learn. Hull design is a reasonably mature science, so the behavior of a very bad hull form can be accurately predicted by a competent designer. It's a fascinating field, and I highly recommend it. Devote the hours you might spend on the model to study instead. CA Marchaj's work is well worth the time and expense. If you're really into it, your head will begin to fill with designs that will work quite well. And generally they will look quite conventional.

Actually I have read a considerable amount of material about hull design, including Mr. Marchaj's work. It is interesting that his earlier work was all about aerodynamics applied to sailboats, which included some somewhat accurate predictions about future high-performance sailboats. If I recall correctly, he even anticipated sailboatrs on hydrofoils. Later, He wrote a book that pretty much condemned the very high performance types he originally advocated. I think he grossly misinterpreted the '79 Fastnet Race disaster. He thought the then modern IOR type hulls had seaworthiness deficiencies which pretty much caused the disaster. He may have been somewhat right. But, having read about the event, I have concluded that as the smaller, slower boats got nearer Fastnet rock, the sea conditions had gotten considerably worse, with huge, breaking waves that came from many directions. These clobbered that portion of the fleet, while the larger, faster boats got past it before the conditions got so bad. I think a major contributing factor was the seabed typography, which was likely a major cause of the vaves being so huge and deadly. That being said, I agree that design choices, that made the boats lighter and faster, came at a price of less seaworthiness. The IOR type seems to were intended to make the best of light to moderate winds, with relatively modest sail area, and to stay displacement hulls. There are parts of the rule that seemed intended to discourage planing. Also, to save on whetted surface area, rudders were made smaller than they probably should have been. It seems that the so-called "sport boats", which came near the end of the IOR era, with their proportionately bigger rigs and hulls that were intended to plane, did not have the faults of the IOR types, even though they had appendages that were no bigger, except, perhaps, for the rudders.

This is the direction that sailboat hull design has gone for over at least the last thirty years if not longer. This is nice. And the resulting boats are plenty seaworthy. But it does seem that this lightness and speed has led to more costly construction techniques and maybe less durability. There seems to be a fragility that comes with these more modern designs. This seems to be especially true when it comes to keel strikes, such as groundings. I also suspect that, although these boats are more than seaworthy enough (providing their ballast keels stay attached), they may lack in seakindliness. Seakindliness is not just about the boat being able to survive the conditions and remain controlible. It is also about comfort for the crew. On a racing boat, comfort hardly matters. The sailors are expected to be athletes and to endure the hardships that come with being such. But when these design choices are copied by cruising sailboats, I believe that this leads to trouble. And the trouble I have in mind is described in Mr. Marchaj's later work. He then advocated much longer keels. He claimed that the longer keels dampen rolling motion, make the boats track better, are sturdier, and have lower ballast placement, even with less draft, than more modern types (except for those with bulb keels).

Now, much of the likely short-comings, that come with the more modern types, is made up for with late 20th and early 21st century technologies, such as solar panels, auto-pilots, satellite navigation, and of course, far better weather forcasting. This is great. And the cost of these technologies is coming down. But they are not neccessarily cheap. And a failure of electronics can lead to the loss of all of these.

More traditional sailboats are still around. A lot of them were built long ago, but are still quite useable. Many of these designs were influenced by pre-IOR racing design rules, such as the CCA one, which encouraged shorter waterlines. Now, it may be quite posible to marry modern hull designs with longer, shallower keels and maybe even shorter sail rigs with more than a main and a jib. The performance price may be worth paying to get a more durable boat and one that has better tracking ability. I could go even further. The maximum beam could be moved forward to get better downwind manners and to provide better cruising accomodations. This could be done with the frank admitting of performance costs. If the max beam is not moved too far forward, the bow still has enough taper to part a chop.

Now, this line of thought has led me to consider some older design ideas that didn't cut it in the racing community. And I am not confident that today's computer technolgy can adequately predict the behavior of boats built using these older ideas. Ooma was an ectreme design even in her time. She may have met her end sailing through a wave rather than over it, with plenty of deck openings for downflooding. I read the story long ago, and I don't remember. The boat I sketched is nowhere near as extreme and is intended to use far less and far less expensive ballast. I think it may be useful to actually test these ideas with relatively low cost models. There may be some surprises.

 

[wet feet]

I have long suspected that Marchaj's work was excessively biased toward the theoretical and he didn't spend enough time actually sailing boats of the type in question.Possibly from concerns over their seaworthiness,possibly because the topic is too big to allow in depth practical research.The weather conditions that prevailed as the various classes of the 1979 Fastnet fleet met did indeed allow the faster boats to clear the area of the worst conditions before the peak of the storm hit them.

I don't believe the IOR rule was conceived to prevent boats that would plane,rather it wasn't a widespread belief that keelboats wouldn't be capable of planing.Which was true of the types that were generally raced in the era.It was a comparatively recent thing to have a separate keel and rudder and not an appendage on the trailing edge of the keel to control the course of the boat.The size of the rudders wasn't actually minimal as the tendency they had to broach did require some hydrodynamic countering at times and even a good sized rudder failed to overcome the forces from the rigs of the time, which had massive headsails on a masthead rig and some very creative sails in use at the same time as the spinnaker.Unfortunately,the underwater forms were often designed to add bulges or dips at measurement points to help the rating.The end result was a hullform which wasn't really likely to plane and had they done so,the V^2 part of the usual equations would have generated more force to control the boats.The Farr designs of the time were designed with the philosophy of creating an inherently faster hull and accepting the rating penalty.They had lower foretriangles and larger mainsails and planed intermittently.they also led to the less bulbous shapes we are now accustomed to.

Model testing is a very useful way to investigate developments,but at the back of my mind there is the unfortunate saga of the 12 Metre Mariner to illustrate the pitfalls.