September 13, 2014
IN DEFENSE OF FLAPS
To my disappointment the presentation of Yrvind Tens slotted leeboards was not universally met with rapturous applause. Some people think they will cause too much drag and not be strong enough. Therefore I valiantly feel obliged to come to their defense.
Aviators did invent the name but not the flaps, navigators did. The classical rudder attached to a long keel is a flap. If the tiller is moved a few degrees to weather the boat becomes more weatherly. That the rudder in that position creates a bit more drag is a minor point as long as the boat wins races. On the other hand, going to the extreme by moving the sail area forward so that you can keep the tiller 10 or 15 degrees to weather will increase the keels lifting force even more but then the drag will be so great that the boat has no chance of winning.
If the boat is propelled by sail and not an airplane engine the flap can and must of course be designed accordingly. I also like to point out that the leeboard is overlapping the flap. Therefore it will be attached not on the foils weak trailing edge but more forward in a position, strong enough.
From a fluid dynamic point of view the constellation mainsail and overlapping genua is a slotted flap as A. Gentry has shown. Land yachts use slotted wings and they are very fast. To my mind if slotted flaps can be used on sailing boats for rudders and sails I see no reason why I should not use them on my leeboards, its just a question of good engineering.
Why do I not use a long fixed keel as is suggested? Well it is certainly quite OK for heading into gales, but in my opinion, a centerboard or leeboard placed well forward the sail area is a much better option, and like I have said before, when retracted less likely to capsize the boat. It gives you a choice.
1989 I sailed the 15 feet Bris-Amfibie from Ireland to Newfoundland against the prevailing westerlyâ€™s. The mast was ten feet long. In heavy weather I had a 1 square meter jib and a 2 square meter triangular main. Between 6 and 18 of June we had continues contrary gales. The boat had a centerboard. It was placed well forward of the mast. Its area was about ÂĽ of a square meter (0.6 m deep x 0.4 m cord). Finally after 12 days the sun came out and I got a chance to fix my position. To my joy it was more westerly then when the gales had started.
We arrived in St Johns after 47 days. It had been a stormy passage but no capsizes, nothing broken, all the plastic jerry cans topped up with rainwater.
Before leaving Sweden I gave some yachtsmen lessons in celest navigation. They where bound for Nova Scotia.
â€śWe might see each other on the other sideâ€ť I suggested.
â€śI am not so sureâ€ť their captain said.
â€śYour boat is so much smaller it will take you longer time and we cannot wait for you.â€ť
It was an argument plausible enough. After all they had a modern powerful 35 feet boat equipped with a strong diesel engine, big fuel tanks, radar and all the other stuff. I had my oar and sextant.
In the end we never meet them. The North Atlantic had been too stormy that year, they later told me. After two weeks they had turned around and run. Everything was a mess in their boat. Later they sold her.
The problem with a long fixed keel like the one Manie B is planning to have on his ten footer is that going downwind he will get weather helm and a lot of drag. On a circumnavigation there will hopefully be much downwind sailing. Leeboards on the other hand, they have even less drag than centerboards because the smooth bottom will cause no turbulence. In strong following winds I will use my twin rudders like a snowplow giving her a lot of inherent course stability.
All my experience and all my knowledge speak against the long fixed keel. Please do not use it. I never go back to it.
Below are some pictures of Bris Amphibie. The centerboard can be lowered further had not the floor been there. Click once or twice to enlarge.
Above Bris Amphibie sailing her main is 2 meter square her jib 1 meter square.
A bit of the centerboard can be seen.
September 4, 2014
A PROBLEM AND ITS SOLUTION
Every sailor knows, or ought to know that the force created by the flow over a foil increases with the square of its speed.
If Yrvind Ten would make three knots through the water hard on the wind in ideal conditions I be very happy.
If she will make half a knot in gale conditions I will be equally happy.
The heart of the matter is that the power of the foil to resist leeway has in the gale case been reduced to 2.8 %, very unsatisfactory.
(3 divided by Â˝ = 6. Six squared equals 36. 1:36 = 2.8 %)
To make things worse the need for lateral force in a gale is much bigger than in nice weather.
Airplanes have a similar problem. During take off, when they travel relatively slow, they need lots of lifting force.
In order to become airborne they employ flaps. That is, the rear portion of the wing rotates downwards. Flaps are high lift devices. They also reduce the stalling speed.
I have decided to use flaps on my leeboards â€“ detachable flaps.
I will have an asymmetrical leeboard on each side, asymmetrical because they are more efficient.
I will use a slotted flap. They allow fluid to pass between the foil and the flap. That way I will have no problem to seal the gap.
I will place the flap not in the same streamline but in the way a jib and main are positioned in relation to each other, with a bit of overlap.
In good conditions the flap will stay on deck because the leeboard itself will be sufficient to prevent leeway. That way drag is reduced.
I only need one flap as I can flip it bottom for top using it on both sides.
When I put the flap on and take it of, the leeboard will be out of water. That way I can easily do the work from the hatch.
In nice weather I increase the sail area and reduce the lateral area. In rough weather I increase lateral area and reduce sail area.
Before I add an object to the boat I ask myself, do this thing earn its keep? In this case I believe it does, for the following reasons. Not many small boats have been cruising the roaring forties and not many people live there. What we know about the weather there comes mostly from big boats. But, big boats are not stationary observers, often they voluntary travel with east moving weather systems. That way they can enjoy and report strong westerly winds for long periods of time.
Compared to bigger boats Yrvind Ten with her speed of about two knots can be considered almost stationary. She will experience completely different weather patterns. She will be exposed to two or three lows each week. When a depression has passed there will often be nice easterly winds â€“ not adding much to the progress. From a stationary observers viewpoint the roaring forties is not a strong trade wind.
To complicate matters there are also strong easterly gales. Once, when I was less experienced I rode one out in comfort to a sea anchor. When the weather had moderated and the sun came out I fixed my position. I had been set back 150 miles.
Some navigators may think thatâ€™s a good deal, not me. My present boat will hopefully be able to fight gales head on. The new strategy to deal with contrary gales is to dig in, to hold on stubbornly â€“ at the risk of being capsized – until the wind swings over to a more favorable quarter, then I will ease the sheets and run.
Slotted flaps are high lift devices. They reduce the stalling speed. I am betting on that they will earn their keep.
However one must not forget that in stormy conditions flow around foils is very turbulent. One reason for that is the circular movement of the water particles in a wave. At the top of the wave they move in the same direction as the wind at the trough in the opposite. In a gale the speed difference is often more than six knots, a speed far higher than Yrvind Tens. Accordingly, theoretically, the flow around the foils will vary as a sine curve, sometimes being positive, sometimes negative.
In reality turbulence will create much chaos. Then only a lot of lateral surface prevents leeway, a bit like a parachute. So in stormy conditions Yrvind Ten needs all the lateral area she can get. The slotted flap will not only increase lifting force when there is flow, it will also at the same time increase lateral area. The leeboards itself are already as big as I dare to make them.
Below are some pictures. Click once or twice to enlarge.
Above the slotted flap.
The flap laying on deck.
Slotted flap on healead boat. Front vieuw.
To be continued…
August 28, 2014
MORE ABOUT MY STRONG RIG
Sharpii 2 is still worried about my rig. He beliefs a breaker may rip out the mast and deck fittings and leave a hole in the deck. I disagree. It is not a war zone out there. The waves are not loaded with dynamite. Let me explain:
It is the terrible capsizes and pitchpooles of big boats, like Smeetons 46 feet Tzu Hang and Erling Tambs 47 feet Sandefjord that have filled cruising people with horror. Compared to the above boats, Yrvind Ten and the old Bris are small.
Bris was capsized and pitchpooled near Cape Horn 1974. On a stormy March night 1976 the same boat capsized again, now on Georges Bank, outside Nantucket. On each occasion her 20 feet tall rig came up without a scratch. She had one pair of spreaders and the length of the unsupported column was 10 feet. Yrvind Tens unsupported column is 6 feet. Ten divided by six, squared is 2.777â€¦ That is how much stronger the geometry makes that column, according to Euler. The â€śshroud angleâ€ť to the supporting spar is 38 degrees. For Bris the corresponding angle is 13 degrees. The ratio of tangents for those angles is 3.38. The larger the angle, the less is the compression or buckling force. One more thing, the peripheral speed of a mast increases with its length. The length ratio between the two masts is 2.222â€¦ The hardness of water increases with the square of the hitting speed. 2.222â€¦ squared is 4.94â€¦ Now multiply these three numbers 4.94×3.38×2.777 and you get 46.36â€¦ The scale effect suggests that if the two masts are built with the same dimensions and materials Yrvind Tens 9 feet mast will be 46 times as resilient than Bris 20 feet mast.
Of course I do not have the faintest ideas of the forces, accelerations, rotational speeds, mass moment of inertia and other factors that are involved in a capsize, neither do Sharpii2, neither do Einstein or Newton. What we know is that shorter columns and larger shroud angles makes rigging stronger and that longer masts whips harder.
On the other hand, I have spent much time in small boats on stormy seas. That has educated me.
-â€śIs it possible that a breaker may rip out your deck fittings and leave holesâ€ť, asks the prudent navigator?
- â€śDefinitely not,â€ť I answer.
My small boat can never be subject to such brutish forces. She has to little mass moment and linear inertia. I know that seamen have been washed overboard from square riggers and other bigger boats. The same breakers have often hit me. That has never caused a problem. The sea is not selective. It hits everything with the same force, the rigging as well as me. If the breakers had the force to rip out my deck fittings they would have killed me long ago.
Sharpii2 says the fittings need to be strong enough to capsize the boat. Of course, that goes without saying. I am not building a toy. I am building a boat for long term, heavy duty cruising. My fittings will be strong enough to lift a boat ten times as heavy. Not only to lift it, but also to resist the dynamic forces necessary to stop a drop. Everything on my boat is solidly anchored. The deck has a sandwich core 3 cm thick. The reinforcements are spread out to a diameter of 30 cm good enough for a pull of 20 or 30 tons. So far my boats has had no problems to stand up against the elements. I see no reason why this boat should be less strong, on the contrary. I am learning all the time.
I will not worry. I will sleep deep and well even during the strongest storms because I know that if a breaker capsize her she will come up proud, happy and smiling.
With Respect and friendship, Yrvind.
August 21, 2014
Henry Ford said: â€śIf I had asked people what they wanted, they would have said, faster horses.â€ť
First he built cars with people sitting outside. On rainy days that was wet and uncomfortable so he added a cabin with windows. Then came the windscreen wiper. Today windscreen washers supplement them.
Let nature be your guide. Complicate things and you will be successful. Even the simplest cell is more complicated than a boat. The KISS principle is rubbish. The trick is not to make a new construction simple but functional. My guiding principle is utility. Building a nine feet pivoting mast is no rocket science. A 75 year old pensioner can do it with simple tools.
Its complexity is in the beholders eye. Some observers get confused when they see something unconventional. To calm their minds they call it complicated. The same people outfit their boats with outboard engines, electronic steering systems, water makers and induction cookers. They are so blinded by these mass produced products they do not realize that they are much more complicated than my homemade mast.
Optimizing each subsystem independently will not lead to a good boat. Of course, non-pivoting masts would be simpler, but then the whole system, the boat, would be more complicated. I would have less trim options. With the planned rig it will be very easy to change from lee helm to weather helm. Hopefully the result is that my boat will steer herself without electronic steering systems or wind vane self-steering gear.
I do not think that I ever will convince conservative sailors of the beauty of my rig. They suffer the same mental blocks that Max Planck observed a hundred years ago. Resigned he remarked: A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it. Still, I wish my critics a long healthy life.
Sharpii2 have pointed out that when the masts are not vertical they are acting like a crane boom -true. I like to thank him for that comment. I welcome critics because I often make mistakes and forget details that can have dire consequences. It was a good observation.
However I do not worry and it is for two reasons. One, I do not agree, I do not think that it will put a lot of bending stress on the mast and tremendous stress on the pivoting axle and the locking pin. After all, Yrvind Tens masts are not longer than an oar. Small boats do not attract big forces because of the square cube law. Sure, things break even on small boats but thatâ€™s mostly a question of dimensioning and can easily be fixed.
The second reason is that when the wind becomes strong I am going to reduce the forces on the mast and support her.
I reef the sail. That brings the yard down to a position six feet above the fulcrum. At that point on the mast there is a fitting to which I tie it with a string. Next I slack the halyard, releasing the compression. At that moment the bowstring effect is no more. True, the wind force is still acting strongly on the reefed sail. However its leverage is now only six feet.
To break things you need leverage. Take a match, say 4 cm long and break it, no problem. Break it again, OK. Now its only 1 cm long and it starts to get hard because you do not get a grip. You have no leverage. Most catastrophic scenarios come from big boats disasters. Small boats are different. They are more resilient. Other laws apply.
Still I am a man of the belt and suspenders approach. When the wind gets stronger and the seas start to break I snug things down and beef them up. I will then support the mast with an eight feet long spar. I will attach one end to the mast at the height of the yard, six feet up. The lower end will be fastened near the root of the other mast on the axis of the fulcrums. With that geometry the mast and spar can be rotated for and aft as a unit. Thus the mast is always supported athwartships. Fore and aft support comes from ropes.
If this sounds complicated and confusing I assure you, it is less difficult than setting a spinnaker pole.
Below is a pictures of the 1/8 scale model with this arrangement. Click once or twice to enlarge.
Above mast in aft position, weather helm
Above mast in aft position, weather helm
Above mast forward position, lee helm.
laminating the centerboard slot.
To be continued…
August 18, 2014
Boat ideal will have leeboard. Thinking aboat leeboard has changed my mind. I have decided to have leeboard on Yrvind Ten also. Ocean going boats do not have leeboard, but traditionally ocean going boats are big structures and lika all structures subject to Gallileos square cube law. Becouse of the square cube law a small boat do not have to be simular to a big one. In fact its a big mistake to build a small boat simular to a big one. Its against the laws of nature. Bugs understand that. They to smart to try to imitate vertibrates. Each one to its own scale.
The present project will then teach me much about them. Good for the next boat. The upcoming circumnavigation will be a lot of down wind sailing. Thats were leeboards excel. Downwind a keel is really bad a centerboard better but there is still the slot causing turbulence. Then the control ropes. Traditionally there is only one rope, an uphaul. but if the boat is going to be capsize-proof you need also a down-haul to control the board in all positions. For piece of mind. I have not got these mechanism to work to my satisfaction. This is not the first time I change my mind regarding centerboards. Bris had one to beginn with Yrvind.com started with a centerboard, then a daggerboard I scarped boath of them. Centerboard worked fine for me on Bris- Amphibie, a daggerboard worked fine for me on Duga.
Leebards will also give me much more space in the saloon.
I am avare that leeboards have its own sets of problem. I will try to solve them later.
Below are some pictures. click once or twice to enlarge.
Above the 15 kilo scrapped centerboard.
Above. The centerboard case cut off above the storage.
Above the turbulence causing opening for the centerboard.
Above the turbulent causing centerboard opening starting to be plugged.
To be continued…
August 5, 2014
SIDE BY SIDE RIG ON THE 1/8 MODEL
Here are 4 pictures of the planned side by side rig with folding masts.
The above pictures (click once or twice to enlarge) shows the rig set up for reaching in light wind.
Both sails are in clear wind. The boat has lee helm. The skipper can relax and enjoy.
The above picture shows the boat close hauled in light wind. Compared to a tandem set up the sails are much better separated thus Â giving better flow and sail efficiency.
The above picture shows the boat reaching in strong winds.
When a boat with a mast in the centerline is reaching the sail and boom is off center unless its a square sail. By folding the lee mast the balanced lug sail will much like a square sail be centered avoiding excessive rudder action. The unstayed mast guaranties no chafe; a good thing on long passages.
The above picture shows the boat close hauled in strong winds. In real life the sail will be reefed to suit wind conditions. One mast is folded to reduce wind resistance and to lower the center of gravity and mass moment of inertia.
When using the lee mast there be more weather helm, desirable when you like to forereach witn little sail area up. Using the mast on the wind ward side gives less weather helm. It also reduces the tendency to dip the boom in the water. As a bonus one can also move the sails forward or aft by tilting them.
The side by side rig gives the prudent navigator many options and eliminates the need Â for autopilot or selfsteering.
I also do work on Yrvind Ten. Presently it is the boooring job of filiting and taping all the pieces of plywood and composite that makes up safe stovage space.
To be continued…
July 1, 2014
SOME REASONS WHY I HAVE CHOSEN A SIDE BY SIDE RIG
Rig choices belong to the domain of aerodynamics, right â€“ wrong. A cruising boat is much more complex than a racer. The more complex a structure is, the more interference there is and nothing is so difficult to deal with as that. But there is also a positive side to complexity and it is that it gives the designer many possibilities to use one element for different purposes.
At first one would not think that the placement of a hatch would influence the choice of rig and normally it does not but when one is designing a ten feet circumnavigator a new set of problems comes up. To deal with storms the interior of my boat is divided into two parts by a watertight traverse bulkhead. The boat has one dry section and one section where saltwater will do no harm. The wet section is in the forward part below the hatch. The two compartments are each about five feet lengthwise. Previous experience has thought me that hatch openings of 40 cm wide and 45 long is convenient. Add 5 cm around for coamings gaskets and labyrinths and the hatch will be 55 cm long â€“ closed. But a hatch that cannot be opened is by definition not a hatch so to make it operational I had to find an unobstructed place for it more than a meter long. That place must be close to the masts, otherwise handling of the sails has to be done from deck and that is not convenient in rough weather. From one hatch it is impossible to reach two masts if they are arranged tandemly. An eight year old girl understands that. That creates a problem. I have solved that problem by arranging the masts side by side and placing the hatch between them. That way I can use one hatch to serve the two masts.
An other advantage – now I can open the hatch because there is no mast in front blocking it â€“ in other words the hatch is in the middle of the boat but the masts are on its side.
Lifeline stanchions are usually 50 â€“ 60 cm high and pretty useless. My center of gravity is 90 cm above the deck. If the lifeline is going to have a chance of doing a good job of keeping me aboard it should be at least one meter high. My masts are strong and high and situated on the boats side they are there in a perfect position to be used as stanchions. This is a good example of how one element can be used for two different purposes. Now I can have lifelines one meter high or more and they will be extremely strongly attached.
Mast placed on small boats centerline blocks the passage for and aft. A pathway in the middle of the boat with high strong lifelines and masts at each side to support you makes moving around safer than the narrow side decks found on a small healing boat.
An other dual use of the side by side masts is that the forward end of the awning can be attached to them. The awning protects against the sun but the main purpose of that piece of canvas is to catch rainwater. A funnel and a hose will conduct it to polyethylene jerry cans. I will be able to store about 70 liters of water, enough for two months.
My side by side pivoting unstayed mast will not use tabernacles. I will put the fulcrum on the chine between deck and sidedeck. That chine is very strong, it only needs to be beefed up locally. The bottom end of the mast will be fixed to a semicircular track on the rub rail. This arrangement is stronger than a tabernacle has less air resistance and its center of gravity is lower. The mast can pivot 20 degrees forward and 20 degrees back. It can also be folded 90 degrees backwards to be stored along the deck in strong winds.
Naturally I will be glad if my novel rig also can propel the boat. A small cruising boat is a complex thing and I may have made mistakes somewhere along my thinking. Although untried I am willing to bet on this side by side rig.
Racing boats are designed with racing rules in mind. Consequently the almost universal custom is to design rigs in such a way that you get maximum effort per sail area. That implies tall rigs with one mast. I see it differently. I am not racing therefore I do not worry about efficiency per square meter sail area. I design for the shortest possible mast. A deep water cruiser have to withstand the seas worsts fury. When it starts to blow a boat with a short mast is much more weatherly than one with a tall mast because the top part of a reefed mast is not only useless it also creates drag, top hamper and slows down the boat. A short mast is not only much stronger than a long one it will also be subject to much less forces. In heavy weather it wins hands down. Out there, far from shelter, the fundamental task is to survive. Nice weather is no problem for me because I like to spend time at sea.
My strategy is to hang on when the wind is contrary and ease the sheets when it starts to come from a more favorable direction. A small boat will not go to windward over ground better than 60 degrees. 60 degrees means twice the distance sailed. Windward sailing also means half the speed. In strong winds the difference between the speeds you make running and beating is even bigger. That means it will take you at least four times as long sailing upwind as downwind. You cannot have a rig that is efficient in both strong and light winds; I have chosen efficiency in strong winds. My weapon: one short mast standing and the other one folded on deck and big, big lateral areas.
The balanced lug sail is very interesting because it is only attached to the mast by its halyard. The mast does not even have a track. By pivoting my mast 20 degrees the masthead mows about three feet for or backward. By moving the downhaul the same distance along the deck the sail can be moved parallel to itself six feet along the deck. That is 60 % of the boats length. That way I can choose weather or lee-helm in any wind strength. Production boats with fixed masts and ballast keels are designed with weather helm. They do not have the option of giving their boat lee helm. Obviously sailing downwind with weather helm is fighting the elements. A seven year old girl can understand that. Trade wind sailing is down wind sailing and on a boat with weather helm the rudder have to be used all the time because the boat is not directional stable on that course.
If I had not had pivoting masts on my side by side rig, then when the apparent wind is on the beam one sail would blanket the other. Now it is easy to separate the sails for maximum wind exposure; I just move the lee sail a bit forward and the windward one a bit back. Problem solved.
In strong winds sailing downwind I will fold the lee mast. I will use the sail on the windward mast. Its center will be close to the center of the boat. Think square sail then move the mast not the sail to windward.
That reduces the rudder force and hence the resistance. If desired I can move the downhaul forward. That will give me a lifting force. Also the windward mast keeps the boom more inboard making it less likely to dip into the waves when the boat is rolling to lee.
However if I would like to ride out a gale slowly forereaching I can use the lee mast because that will give me lots of weather helm for a small sail area. A boat forereaching does not roll much. It also by definition moves slowly so dipping the boom into the water is no worry in that case.
It is much more to write about side by side masts and their interference and integration with a small boat but now I will stop and hopefully come back to the subject at an other time.
You should newer be the first one to try something new, nor should you be the last one to hang on to something old. If you like life tranquille follow that advise but it will not make you into a trailblazer.
The picture below shows the scale 1/8 modell sailing with the mast in tandem position. The aft mast creates unavoidable downwind turbulence.
The picture below shows the modell in light wind with the masts in side by side arrangement. Both mast gets nice clean air.
To be continued…
June 15, 2014
Here are some pictures showing work on the hatch in the bulkhead.
Taking off shape to make shore the thing fits.
Starting to laminate
Off the mould
It fits and very lucky I can change the gasket with the retainer/drippedge in place saving much work and making it less complicated. Sometimes but not often things goes faster than expected.
While at it here is the solution for next boat.
The drawer effect: This is what we engineers call the nuisance when a drawer gets stuck in a chest of drawers and it does not only happen to drawers; it happens to most sliding things that are wider than deep. It is a pain.
To avoid it I made an analyses and it turns out that the solution is surprisingly simple. Drawers that are wider than deep have little guidance and therefore not always move straight but turn. When they turn the short side of the drawer is not any longer parallel with the guiding sides. The drawer takes more space and gets stuck diagonally. The more you pull the worse the drawer gets stuck.
I said to myself: what geometrical figure does not get wider when itâ€™s turned, obviously the circle, by definition. I use part of a circle as can bee seen on the illustration below.
For my hatch I have a second problem. I like to take it out for service. But the guides go al the way around so I have to do a detachable opening in them. On Yrvind Ten its to late to change but on the next boat the â€śBoat Idealâ€ť it will look like below. Then byrĂĄlĂĄdseffecten will not give me a problem. Also and very convinient by twisting the hatch 90 degrees it will come clear of its retaining tracks so that I can do service on it
One more screanshott
Today I also written sermon and put it in “BOAT IDEAL” One of the other blogs on my website. You find it at the startpage.
To be continued…
June 12, 2014
A NEW BLOG ON MY SITE
I have now started a new blog on my site. Under the heading “Boat Ideal” I will from time to time note my thoughts on a desirable cruising boat. Things I learn from mistakes on the present project and ideas that come to my mind. The present boat is made to set a world record. It will never be a good cruising boat. Let this be warning.
June 10, 2014
CLARIFYING “NEXT BOAT”
I am grateful to Sharpii 2 for commenting on my “Next Boat”. On my web site I will start a blog for her titeld â€ťBoat-Idealâ€ť. It will replace the blog “Lecture”. When building and sailing I always have the next boat in mind. When doing a mistake on the present one I say to myself “that I will correct on the next one”. And it helps; my boats have over time become better and better , very much better. I am very grateful for comments and for persons helping me pointing out my errors as it is difficult to objectivly observe oneself. However that is not always easy becouse often I do not express myself clear and English is only my second language and I am dyslectic, all which add to the confusion. There is also an other aspect and that is values. Most often my values differ as to comfort, speed, use of engine and more. Here engineering principles do not apply.
I will here try to do a bit of clarifying concerning sail area and speed. 1974 I sailed 20 feet 1.3 ton displacement Bris from Jamestown St Helena in the South Atlantic Ocean to Fort de France Martinique in the North Atlantic Ocean, necessarily crossing the Doldrums. Bris had no engine; not even an outboard. I could have put up more sail but chose to use only 4 square meters. I enjoyed the passage. The 3800-mile passage took me 45 days from anchor up to anchor down. That is an average speed of 85 miles a day or 3.5 knots. I found the voyage pleasant. The sail area/displacement was 3.4 if I have done the numbers right.
2011 I sailed the 15 feet 0.9 ton Yrvind.com 2900 miles from Madeira to Martinique. It took 45 days 64 miles a day 2.7 knots. The wind was more variable often so light that a candle could stand on deck without flickering, still the boat made 0.5 knots and steered herself downwind. I used very little sail. Most persons would be unhappy to sail at 2.7 knots. Me I was happy to spend six weeks at sea instead of three weeks. Me, when eating, I do not try to get the food down as quickly as posseble, me when making love, I do not try to get an ejakulation as quick as posseble, then why should I try to cross an ocean as quickly as possible? I am not racing. I am cruising. I enjoy being out there on the big, blue, wet, deep, endless ocean.
Still â€śNext Boatâ€ť has two 4.6 s.m. sails. In light wind going to windward I intend to use them if desireable so Sharpii 2 can double the number he got for “Next Boats” S/A relation. Sharpii 2 prefers sails his in tandem. Thatâ€™s the common way. I differ, I think its more advantages to have them side by side like, the early airplanes, instead of one sail in front of the other becouse then they interfere less with each other.
A lugsail is only attached to the mast at the top. As the mast are pivoting I can move the mast top back 1.5 meter and forth 1.5 meter and with it the sail moves. Then I move the downhaul back and fort along the deck to suit. That way I can give the boat weather or lee helm as desired.
As to preventing leeway, the hull is five beams long and has very flat sides. In a way it works as a battering ram. It has very little frontal area compared to driving force. Norman Skene in his original book on yacht design always calculated lateral area as a function of midsection. Now it is calculated as a function of sail area. I do not agree. When heeled 20 degrees the leeward side present a lot of area to the water. Some of it will flow under the hull. That takes much energy. That energy creates a vortex floating along the bottom up to windward. Healed the bottom presents a bigger curve to the flow than the side making the water flow faster there. Bernulli says, the energy in a streamline is constant. This is classical two dimensional wing theory. High aspect wing have a tip vortex that disappears behind the wing. Low aspect bodies edge vortex sweeps over the surfaces combines with the fore and aft flow increases the particles energy. As the energy is constant in the streamline that energy is creating lift. Thatâ€™s why the concord airplane could fly with an angle of attack of 45 degrees. Ordinary foils stall at 15 degrees. Its not efficient on the other had here we are recycling energy so its ok. This is my thinking on the leeboard and of course I lift them up sailing down wind. The rudders have even higher aspect ratio.
And of course I do not sail flat downwind. I always have the wind 15 or 20 degrees on the quarter.
It getting late but more will come.