I found a site dedicated to this and was so enchanted by some of the pictures i could not resist re-blogging here in a brief impromtu post.

The original pictures are all from http://saveirodabahia.blogspot.com/

Bateira do Nordeste navegando rapido

This is the type called “Bateira” from the states of Ceará and Rio Grande do Norte.

Note that the planform on the mainsail is just about the theoretical optimum as described here.

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The following images are all of the Bahian saveiro Vendaval, which measures 14 metres LOA and built in 1947. The mainsail area is 98 M². There is no purchase on the sheet. Saveiros use a single balanced halyard. Obviously there is no auxiliary.

O Saveiro Vendaval

From afar. This is not a typical amount of crew. They are on an outing here.

Mestre Nute directing operations aboard his ship.

Mast step; no messing around, proper sturdy.

http://saveirodabahia.blogspot.com/

Sailing back to St John from the BVI’s i decided to “do things the right way” and clear in. If you read the US coast guard rules carefully it is written that boats that are unable to support motorized propulsion and are under 10 M are exempt from registration. This little known fact is why almost no nativo is registered, and gets away with it. But good luck trying to educate an “officer of the law” about the law..

After alluding threateningly to the risk of having my boat confiscated, he warned me to get the paperwork in order a.s.a.p. and i shuffled out of there as quickly as possible,.. but wait ! There’s more; a uniformed lady stops me to ask if i’m aware of the rules concerning on board refuse. Foolishly i confess that i don’t to which she gives me a paper foldout and goes over the rules in pedantic detail. Turns out any garbage containing organic matter from non US countries (such as the BVI’s) is considered a bio hazard and needs to get disposed of at the special incinerator for hazardous wastes, at my expense naturally. Kitchen refuse cannot be stored on deck or there is a fine for that, such as used paper plates, she added. Paper plates? I have never and will never waste valuable treewood for such a purpose, i have proper plates that get washed and re-used for one’s whole lifetime, i was thinking, also realizing that the fact that we wash them right in the seawater was no doubt a felony as well, so i just smiled and nodded politely. In fact all our kitchen refuse which is bio degradable just goes straight overboard to feed the crabs and other marine detrivores. At sea, tin cans and glass go right over the side as well, since they turn into iron oxide and sand respectively, at no environmental harm. What i do not throw at sea is plastic, for obvious reasons. Since i detest having garbage build up on board what i do before a trip is put all the plastic packaged food sans package in big jars i have which are roach proof and all the plastic goes right back ashore to the tip. That way no problematic garbage builds up on board.

At any rate i kept my garbage philosophy to myself and with a great self restraint managed to not blurt out «so how do you manage to round up all the birds that fly across from Tortola without having checked in whilst joyously pooping the whole time, so that they can be incinerated?»

The sermon over, i was not sad to get out of that office!

Leaving St John with poor weather clouds gathering.

Note how the dinghy sits tucked behind the coach roof; weight low down, and offering an absolute minimum of windage. Also in the most convenient position possible to just untie, flip over and slide over the rail into the water. This picture was taken just out the bay, which is why it’s still so calm.

St John is a very strange island. It is the logical conclusions of extreme gentrification. Rich people (read really really rich) have been buying up property, driving up prices to astronomical heights. Then the locals can’t afford a roof and feel marginalized, forgetting of course that they sold voluntarily. Once that gets started it escalates into a severely divided society, with tremendous amounts of tension.

The rich people create a dumpster diving paradise though. A friend there showed me an almost brand new fairly decent bicycle he found at the dump; the only thing wrong with it was a flat tyre! I might have been tempted to see what goodies i could scavenge too but had neither the time nor the desire to see a single extra thing added to the already overloaded Oasis.

Here a friendly neighbour on a catamaran gave me his storm jib, saying he had retired from sailing and so would no longer need it and i did make an exception to not wanting more stuff on board when it’s something that makes the boat safer. This proved to be an extremely valuable addition the Oasis’s set of sails, fitting perfectly and with a very flat cut, which is what you want in strong winds. At the same time, the Oasis’s other jib, the original one, which came with the boat, i had recut as a storm mainsail.

After a few days in St John getting some more things done onboard we left, just as the weather was turning for the worse, heading towards St Martin.

Now it’s certain that the Caribbean can’t compare to the wild and wooly North Sea (save for when there is a hurricane!) but that is not a reason to allow the azure skies and limpid waters lull one into thinking that it is always idyllic. In fact it can get quite brave and unpleasant at times. Naturally no pics of the best moments, not really thinking about taking pictures when things get hectic, and besides, i always worry about getting the camera wet. Suffice to say therefore that soon after leaving the wind picked up to about force six or seven and the waves quickly became lumpen and confused, the boat leaping and bucking over them, the lee rail awash as i put more reefs in the jib.

Then i discovered the Oasis was leaking a rather unacceptable amount. I pondered carrying on like this across the Anegada passage which is famous for its vicious seas or turning back to St John losing precious distance gained to windward and possibly having to re encounter the menacing customs man.. Studying the chart i saw that there was actually a little cove just north of us that we could shelter in and i could see what this leak was really about.

It proved to be a wonderfully calm anchorage with astonishingly transparent water. No motor boats, no houses, just peace and quiet.

Oasis heeled over with weights attached to the boom end.

Remarkably i was able to locate the leak very easily (this is not the usual case with a leak) and it turned out to be a deteriorated butt seam. I would just have to patch it temporarily with some epoxy putty. Since it was near the waterline and knowing from experience how hard it is to force putty into a crack underwater such that it remains stuck to the hull rather that the spatula, or neither, dropping to the seafloor, i decided to heel the boat such that the bad seam would be just free of the water.

With the 5000 kg of lead ballast, 2.2 M draft and 3.3 M of beam the Oasis is certainly quite stiff but at least the boom is long enough to give enough leverage to heel the boat over usefully. With anchors, chain and buckets of water at the end of the boom i was able to get the damaged area just out of the water.

The end of the plank at the butt seam was not looking terribly healthy.

A bit of PC11 epoxy putty took care of this leak.

Hauling an excessively chatty child up the mast keeps him otherwise amused for a little while.

My wife making us some delicious corn bread.

My internet will be cut off any day now since i stopped paying for it, so this will be the last post for a while i think. By next post i should be in a more stable situation i hope.

With increasing fossil fuel scarcity and its accompanying inexorable price increases, it only stands to reason that sail will once again rule the waves of commerce.

For a quick primer and recap on peak oil and its implications read the remarkably prescient 1972 report by the Club of Rome “The limits to Growth”. Google it. They also published a newer revised edition which is worth reading, with refined projected trends.

More recently, the excellent hirsch report spells out the issue of peak and subsequently declining world fossil fuel energy and its implications.

Also this peak resources site has a good concise overview of peak everything.

I also wrote a quick primer on the issue here.

—*—

So i present a few present day sailing commercial ventures;

Notice the conspicuously absent propellor!

An oceanic schooner that has been operating for the last three years now under sail only and thus proving that it is economically feasible is “Tres Hombres” pictured above. From their site   http://eco-freight.com/ ;

She can carry a cargo load of 45 tonnes, which was unloaded the conventional way with pulleys and cargo boom by the ship’s colorful captain Arjen van der Veen, and the crew. He and his partners Andreas Lackner and Jorn Langelaan are behind this Dutch initiative, which is now realized with this ship, aptly named, “Tres Hombres”.»

and you can see their itinerary here; tres hombres  itinerary

Ceres dockside.

Another sailboat that is proving to earn its way in a consistent way, altough on the inland waterways is the Ceres, a  Vermont sail freight project, a kind of miniature modern hard chine version of a Thames Barge called “Ceres”, which can transport up to 10 tons , if i remember right.

Another site encouraging putting sailboats to use moving freight is the sail transport network.

Proposed project greenheart design.

Then we have the green heart project;

«The Idea
is to create a new type of low-cost, zero-emissions small cargo ships that use environmentally clean and sustainable sail and solar power, to provide needy coastal communities around the world with an affordable means of transport. Such ships can help impoverished coastal and island regions improve their standards of living, while preserving their traditions and protecting the environment. In addition, we will use the publicity generated by such an inspiring enterprise, to promote Fair Trade, renewable energy and international cooperation»

Gaia’s dream, a modern cargo proa

Another brand new project is the 21.6 M proa “Gaia’s dream” meant for sail transport in the pacific.

Saveiros in Bahía.

In many areas of the world, working sail persists to this day albeit in diminished form. One of many worldwide examples is the Brazilian Saveiro, used for general cargo in the state of Bahía. In Bahia de todos os Santos, there used to be 1400 of them transporting produce, sugar, lumber etc. Now they number but twenty, but they still are gainfully employed. Once a year they gather for a spirited race. I found the Saveiro “È da Vida” is for sale for 80 000 R . That price tag suggests to me that they are still quite appreciated.

O “È da Vida” na venda.

–*–

I myself have been compiling data on the cost of transport by truck (which is notoriously inefficient) along the eastern Brazilian coast, by rate of ton mile. At the same time, i’m drawing up a design for a “fruit schooner” * for transporting produce & other items along this same coast and gradually putting together an estimate of its cost of construction as well as running costs, to see how it compares economically against transport by trucks. Any sources of data sent to me would be appreciated. When i am done with the report i will post my findings here.

Preliminary croquis of the 20 M fruit schooner intended for transporting up to 25 tons of produce.

Note that there are a few errors in the above crude rendering. It is just a preliminary version of the design to have something to refine the calculations with at this stage.

–*–

Global decline and sailboats brings us to the concept of sailboats as “survival pods” allowing hasty escape from areas that plunge into violent crisis. Long term though, all boats are dependant on the land for resources; food grown on the land, and maintenance materials for the boat. Barring those that have enough savings to live on for extended periods, this implies that the boat must be economically productive enough to pay its way.  A number of present day cruisers sustain themselves by writing, which is a line of work that is independant of location. Others offer portside itinerant services, most usually repair and maintenance of other boats, but which can be almost anything that uses a toolset that is small enough as to fit in the boat. Neither of these strictly require a boat though, meaning the boat is merely a mobile home, not fully realizing the potential inherent in it being a boat.

What you don’t see much of is cruisers running cargo, but it may well be a practical option for living on the water in an economically sustainable way, either on spec or as a tramper, but this does require a boat that can do this practically, and most yachts are hopelessly unsuitable for the task. Designs for cruising sailboats that can also easily transport merchandise may therefore be of value in coming decades.

–*–

* What i call it a fruit schooner is something like the ‘banana boats’ of the Caribbean of yesteryear with simple, practical, handy and fast small cargo boats for general transport. transporting perishables obviously implies consistent speed is an important design feature.

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Regrettably i may be posting erratically for the next few weeks if at all as i have terminated my internet contract and am deep into getting the boat ready for turning over this last chapter. But in a couple of months or so i should be back to weekly postings. Those curious to find out if it was one leaky boat adventure too many or not can subscribe and get notified when the posts resume.

Racing the “BuenaDaga” in the single handed Foxy’s wooden boat regatta. That year i won the event.

I’m a fan of sailing at night, especially if it means making landfall at dawn. On long pasages, landfall at dawn is always the best; in this way one can spot the various lights and identify them on the chart to confirm and correct one’s position, and then as the sunlight fills in, safely pilot into port.

On this first leg up from Vieques to St Thomas, that is too short a distance to be anything other than piloting, but there is another advantage to sailing at night in the tropics; avoiding the relentless tropical sun!

So as we plunge into the darkness and the sun approaches the nadir the wind gets stronger and stronger. I have been progressively letting the mainsheet out as the reefpoints have yet to be made. Finally it gets to the point that the main is almost wholly luffing, the entire boat shuddering under far too much sail, so i take the mainsail down entirely and we carry on with just the jib.

It is an odd thing that on the Oasis, which has such a strongly raked keel (meaning it is much deeper aft than for’rds) and thus its center of lateral resistance very far aft still manages to point up to windward well enough under just the jib. Looking at this on a drawing board most naval architects would likely state emphatically that the boat will have tremendous lee helm, when in fact, if the wind is fresh the helm is neutral (does not have to be tied). This shows that the issue of balance is somewhat more subtle than certain boat design textbooks would have us believe.

However i  do not like to proceed in this manner because it puts excessive strain on the jib and the rig, which has to rely almost entirely on the running backstays to counteract the jibstay tension, rather than have the mainsail do most of that work.

At dawn we were approaching Charlotte Amalie and the wind seemed to be easing off just a touch, although it was still very fresh, but i decided to put the mainsail back up to improve the boat’s manoeuverability for entering the crowded harbour.

So we sail in under much too much sail; in the lulls the boat creaming along, but in every  tremendous gust coming crashing down the steep slopes around Charlotte Amalie harbour letting the mainsheet out and the boat quivering with the rails under, as the furiously ruffled water patch passes by. It was a bit of a relief to get the sails down and the anchor overboard at the first reasonable anchoring spot.

–*–

Charlotte Amalie and St Thomas in general, always used to be a long time favorite of mine, but the charming all pervasive “yes mon” attitude had quite quickly been replaced with a general malaise and sourness symptomatic of economic difficulties, unsurprisingly, since tourism is the first expenditure to be reduced by people undergoing financial dificulties. St Thomas has an economy that is almost entirely based on tourism and so that put it in a particularly vulnerable position after the economic crisis.

Dietrich in his magical mystery lair

I wasted no time getting to Hassel island in Charlotte Amalie harbour to get the reef points added to my mainsail and the jib by Dietrich, who incidentally, had met my father when they were both sailing in the Caribbean in the nineteensixties. I marked where the reef points had to go and made them deep, such that by the third reef, less than half the sail remains. In the jib’s case there was also the consideration of maintaining the correct sheeting angles for each reef whilst keeping the jib sheet fairlead in the same position. Dietrich does very good work and i highly recommend using his services for any sail or canvas work you may have if you happen to be in the Virgin Islands.

—–*—–

Christina hiking out on the Buenadaga
while Yari is in the streamlined hiking position on the windward rail.

Unfortunately i was too broke at the time to be able to afford to buy the many beautiful pictures taken, so these screen grabs will have to make do.

Then we went to Jost Van Dyke, where i had wooed my wife years before. I had gotten her to crew for me on the 5.2 meter (17′) “Buenadaga”, a mini nativo i used to have, and with which i won the Foxy’s wooden boat race in its class.

The first time we sailed out of Culebra, she promptly vomited the papayas we had shared for breakfast, but laughed and cheerfully carried on with the tasks i had assigned her, which i found endearing. Then, in the races, she was petrified of fully committing to the trapeze, but after a while got more confident. I liked the way she was willing to get over her fears.

On another occasion, on another boat, i sailed aground on a shoal in White bay due to staring at her fantastic legs instead of paying attention to where we were going. No harm done, but one wonders whether this is the kind of thing that prompted the superstition of women being bad luck on board.

Christina

Eventually, after nearly three years of flirting, and when we finally were both single i sailed to Jost where she had set herself up, with the intent of taking her back to Puerto Rico with me. The weather turned awful and did not let up for a full three weeks (a particularly vicious stretch of the famous ‘christmas winds’ when the trades blow mercilessly) and as the Buenadaga is a heavily ballasted partly open boat, i was not going to chance the open waters separating the Virgins from Puerto Rico like that. So that is when we really did get together, with the hostage-taker ending up a hostage, sharing a tent on the beach. Those were happy days. When finally we did leave i took the precaution of nailing a piece of discarded plywood from a building site over the aperture in the deck, leaving just enough space to reach down and bail, which was wise, as despite the wind having moderated slightly we got solid water breaking right over the transom and over the entire boat on several occasions.

–*–

While in Jost i again made use of the Oasis as a floating workshop doing some odds and ends on other boats as well as making two boat shaped trophy display shelves for Foxy, in between getting more necessary projects done on the Oasis.

Christina sitting on one of the shelves, five months pregnant.

I still had to haul the Oasis out, as it was long overdue but the most economical haul out option in Tortola was closed temporarily so i decided to do it in St Martin instead, planning on making this the last stop on our way to Brasil, since it gives a advantageous angle to get down to Brasil in one long board with a bit of luck.

Following on from the last technical post on induced drag, this week i’ll give an overview of e, that quantity i left provisionally defined as 1 in the equation for induced drag;

.                                                $C_{D_i} = \dfrac{{C_L}^2}{\pi{e\Lambda}}$

$\Lambda$ is the aspect ratio.

Planform is the word that describes the shape of a foil when looking at it’s broad side, for instance profile view of a boat’s keel.

As you cannot have discontinuities in the fluid medium , the lift produced does not stop at the end of the wing abruptly, rather it tapers off gradually. It follows that if the planform is rectangular (leading and trailing edges parallel to each other) the pressure will be less at the tip than over the root of the foil. In other words the tip will be underloaded due to the fact that the lift must taper off but the chord retains it full width all the way to the end.

Lift distribution along span of foils with varying taper ratios.

Similarly, for each planform with its varying rate of taper, there will be a corresponding lift distribution curve. For a triangular wing, as expected, the lift distribution tapers down more quickly than the lift distribution for a rectangular wing. However, it does not taper down as quickly as the surface does, meaning the tips are relatively overloaded.

One way to even out the lift coefficient along the entire span is to twist the wing along its length so that each section of wing is at a different angle of attack. In the case of a rectangular wing, one would have to twist it such that the underloaded tips are twisted to greater angle of attack than the root, in such a way that each section of wing is loaded the same.

For triangular wings, the tips are relatively overloaded, so the wing would have to be twisted the other way, with the angle of attack reducing towards the ends.

The problem with this is that the amount of twist needed depends on the overall coefficient of lift, which varies. Thus there is no way to create a twist that will correctly compensate for the variations of loading at all global lift coefficients.

Furthermore, Max Munk  determined that for the least possible induced drag for a given span, the downwash angle has to be constant across the whole span, so that the air stream immediately behind the wing is deflected in a perfectly uniform way.

Without getting too far into it, for uniform planar flows, an elliptical lift distribution curve will result in a constant downwash angle across the whole span. Also it will give the best possible value of $e$

It turns out that there is a planform somewhere between a rectangle (big tips) and a triangle (vanishing tips) that has a lift curve that matches the area distribution curve, thus making each piece of the wing work at the same coefficient of lift, or loading if you will, and that, at all global coefficients of  lift. In this case the local and global lift coefficient would in fact be equal at every position along the span.

An untwisted elliptical planform will produce the required elliptical lift distribution.

Another factor of planform is sweep; the foil can be swept back, or forwards, rather than being at right angles to the flow. This will also affect the value of e. Note that what is important in determining the sweep back angle of a foil is neither the chord midline, nor the leading edge, nor the trailing edge. It is the quarter chord line, about which one can consider as being the aerodynamic “center of lift” of any foil. Explaining the rather complex effects of sweepback and sweepforward will have to wait for another post though.

For now suffice to say, that in general, any sweep is a deviation from the optimum.

An early example of all this being put into practice is the wing of the british Spitfire. Observe not only the eliptical planform but also the practically straight quarter chord line.

The famous elliptical wings of the spitfire

There is however another issue to take into consideration and one which may not evident at first. A pure elliptical wing, despite having the optimal area distribution, has a trailing edge that blends smoothly to the tip and on to the leading edge. Where one starts and the other ends is quite ambiguous, and this has the effect of pulling the tip vortex in towards the wing root. The tip vortex tends to follow the radius of the tip around towards the trailing edge until the angle becomes too great, forcing the vortex to break away. This makes the vortex separation unnescessarily messy and means the tip vortices are closer together than the actual extremity of the foil, thus reducing the effective span of the wing.

This would force a substitution of $\Lambda_e$ for $\Lambda$ with $\Lambda_e \leq \Lambda$

In order to get the tip vortex to peel away as far outboard as possible and neatly, requires a sharp corner between the tip and the trailing edge.  This then requires a little manipulation of the quarter chord line near the tip.

Elliptical area distribution with straight quarter chord line modified near tip so trailing edge is straight and tip has vortex shedding corner.

In the above image i have manipulated the quarter chord line in such a way that the trailing edge straightens out at 0.8 of the span, this is close to being an optimum planform for planar (non twisted) foils. It loses a tiny bit of $e$  but maintains $\Lambda_e = \Lambda$, ie , as high as possible.

The 1988 US catamaran Stars and Stripes with a vortex shedding tip planform designed by Burt Rutan.
Image from François Chevalier

Notice too that in all this, that the triangular planform is about the worst possible area distribution. There exist empirical tables for the value of $e$ and the further one deviates from an elliptical area distribution the lower $e$ becomes, increasing induced drag. Yet it has been generally considered over the last fifty years or so that the bermudian (triangular) is naturally the best shape for going to windward etc. Marchaj did a number of wind tunnel tests on this and confirmed that the triangular planform is actually quite poor. This belief mainly stems from whatever is the current trend in raceboats, setting general ‘idealizations’ about what makes a boat ‘fast’, when in fact raceboats have to optimize to arbitrary rules just as much as actually go fast. This conflict inevitably produces design distortions that are completely innapropriate for sailboats that do not have to conform to any race rule.

To be fair, sailboat rig span loading is actually considerably more complex than that due to the fact that a sailboat rig is not span (height) constrained but rather heeling moment constrained, which imposes optimization along somewhat different lines than as described above. But we’ll come back to the finer points of optimum rig lift distribution in due course.

The foot of the jib is in close contact with foredeck, effectively eliminating one of the airfoil tips.

The value for b or span is taken as the distance separating the separation points of the tip vortices. But what if the lower tip is closed off completely as pictured on the jib of the boat above? This would effectively eliminate the lower tip vortex. How to measure b? In that case, mirror theory states that one can model the three dimensional flow as being one half of the aerodynamic geometry and its mirror image as reflected through the fluid boundary, which in this case is the surface of the water. So b becomes from the upper tip vortex down to its mirror image (underwater).

In simple terms this means that closing off the gap doubles the effective span and thus also doubles the effective aspect ratio, halving induced drag.

This is a vast increase in aspect ratio and one that comes at no cost in heeling moment, so eliminating this gap is the single most effective way of improving a sailboat’s rig performance. This applies to not just jibs, but every sail. Of course, there are plenty of other reasons that may make it impractical to close off the gap completely, but if performance is high on the list of priorities, every effort should me made to reduce the gap as much as possible, for even if the gap is not reduced to the point of having a significant effect on induced drag, it still increases aspect ratio and sail effectiveness at no cost.