Pontoon boat rental gulf shores 36542

Atlanta wooden boat association membership

Sailboat balance design rockford,ranger boats for sale nj 2014,boat building websites online,how to build a lego eagle - Test Out

12.02.2015
Location: Toronto Sail Area vs Keel Area - Stability Calculation Hi, this is my first post.
I'm a mathematician and not a naval architect or an engineer, so this may actually be really obvious. I may be missing some constants, but i'll be applying this to a static equation, so I'll leave these out for now. Imagine a flat rectangular plate with a small cylinder at a point somewhere towards the middle of plate, that is as wide as the plate and divides the plate into two rectangles with areas A1 and A2.
Place the plate so it is sitting vertically in water on the cylinder, so that A1 is above the water (sail area) and A2 is below (keel area). A1*(v1^2)*d1 = A2*(v2^2)*d2, where v2 is the speed that the keel area is moving at it's center. Therefore, if r1 is equal to the third root of the proportional density times r2, the plate will stay in static equilibrium. Therefore, if the A1 (sail area) is equal to the third root of the proportional density times A2 (the keel area), then the plate will not rotate with the wind. So basically, if total sail area is ~ 9 times the keel area (or less), the boat in the model (the cylinder) will not heel, no matter how strong the wind is. Originally Posted by Dabrownone as I mentioned before though, i'm neither an engineer nor a naval architect, so don't flame me too hard please Ok, not too hard. 1) The mathematical model of the sailboat you have used to derive your equations is as far as it can get from how a real sailboat works. Usually, when one undertakes a task of solving a particular problem, the first step is to perform a research on the current state of the art, to see whether someone else might have already solved the problem. Location: Toronto The goal wasn't really to model an actual sailboat, but explore one specific aspect of a boat.
Location: Italy (Garda Lake) and Croatia (Istria) In order to have moments of side forces created by the keel and by the sail cancel out each other, they would have to act in the same direction.
If the forces above and below water were acting both in the same direction, there would be nothing to stop the boat from drifting sideways at an increasing rate.
You need to study the mechanics of how a sail boat moves forward before you can put any meaningful equations to paper.
Fluid mechanics are not intuitively obvious, so first you have to understand how the sail interacts with both the moving air and the hull, and how the keel interacts with the water, and the hull. No matter the size of keel or sail, you will get heeling moment on it, the heeling moment is counteracted either by the crew (of a small boat) leaning over the side, or on a large keel boat, buy the weight of the keel. The wind would apply a force on the upper plate, which causes the plate to rotate with a specific amount of leverage. Location: USA This is a form of mental self-abuse, with no apparent (yet) practical use since it is all theory of simple forms and no application, and seems like a prodigious use of valuable time that could be spent building boats and sailing to see how it all really works.
I am not a mathematician, but as I understands hat you are saying is if you apply a force to the mast of some magnitude.
Yes, the boat will heel until there is an offset between the gravitational forces and buoyancy forces which causes a corresponding moment in the opposite direction.
Originally Posted by BATAAN This is a form of mental self-abuse, with no apparent (yet) practical use since it is all theory of simple forms and no application, and seems like a prodigious use of valuable time that could be spent building boats and sailing to see how it all really works.
In regards to the 70' sailboat; most I have seen have a deep, thin keel with a very heavy bulb on the end.
Speaking of which, the 'keel' area could be any surface that resists rotation; for instance both keels in a bilge keels would have one side that resists, three keels would have three etc. Ultimately, the action of the waves are the real danger, as they can toss you around far more readily than the wind, but here again the keel would at least resist this motion and slow it down, which is helpful. I'm not able to completely follow your derivation, possibly because of the limitations of expressing differential equations as text though it also possible there are some errors.
To start, i'll apply the Force equation derived above: A1*(v1^2)*d1 = A2*(v2^2)*d2, where v2 is the speed that the keel area is moving at it's center. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Location: Venezuela Sailboat Keel design I need information in reference to the performance of my boat, which as I understand from the Beneteau people it was designed by Berret Racoupeau, but they didn?t answer any of my mails.
Actually I?m doing extensive cross Caribbean sailing, so she sail a lot in open waters and I?m experiencing problems with her handling that have the tendency to jump around, and go to the wind with small wind changes. So mi question is, if that problem could be diminished by changing or modifying the small keel that the boat actually has?
I realize that a shoal keel is excellent for island cruising as for anchoring in sandy shallow waters, so mi first approach will be to keep the old keel and adding wings, if that is possible or not, or you have a better solution I?ll appreciate your comments and suggestions. I?m posting an attach file of my own wing design, that need to be finished because it?s based on proportions, I also need to define the wings section. Location: Port Gamble, Washington, USA Why do you think the problem is the keel and not the rudder? Slapping a winglet on a keel is not a slam dunk to make a net improvement in the boat's performance. Location: Sydney The description actually fits having too little directional stability and poor hull balance when heeled. This is exactly the problem which means the helm changes and the boat rounds up whenever you get a gust. In a well balanced boat, you can leave the helm for several minutes at a time, the boat sails itself, even with gusts and at all angles of heel.
This is not a dream, I have such a yacht, it is just that most off the shelf designs these days are poorly balanced!. Location: San Francisco I agree that many of the off the shelf boats are poorly balanced.
I suspect this is because none of the designers know how to make a balanced hull which goes straight at all angles of heel!
Hardly any aof the text books cover this, and some of the new ones ignore the issue altogether. Location: San Francisco I think many boats designers are forced to fit too much into the back of thier boats by marketing pressures.
Location: Sydney Hull Balance Firstly, there is certainly no intentional anonymity, it is simply that even though I have registered, the forum did not recognise me.
I am most interested in the response by Saildesign as I would be very interested to find any designer who has a method for determining hull balance.
By hull balance, I do not mean lead of CE over CLP, nor directional stability nor moment of the the heeled rig, each of which are easily managed and well known.
Rather, the hull balance I refer to is the intrinsic weather or lee helm generated as the hull is heeled. I am aware of Admiral Turners metacentric shelf balance and also th etechnique of balancing wedges, but have found both wanting for short keeled configurations. I have never heard of a Lystergram applied to yacht design and would be most interested to find out more about this and if it applies to the hull balance error I have mentioned. I am not talking about Clorox-bottle shops like Hunter, where the boats are designed in Marketing, but real, genuine, honest-to-God designers. Location: Sydney, Australia Catamaran Balance A Question for the Experienced Catamaran Designers. I have found with trimarans that the lead between the CoE of the sail plan and the CoE of the Centre board to be 0%. Location: papakura south auckland new zealand Under trimaran turning radius thread, Gary Baigent describes the center board location for both a catamaran in one of the replies.
With modern light displacement hulls it appears to work to use the CoE of the keel or centre board. Location: queensland australia Hi Des, obviously you are designing your own cat. Location: Cocoa Beach, Florida Here are a series of A Class cats( see pdf below) an AC45 and an Extreme 40.
Location: Cocoa Beach, Florida Eric, it seems to me that if you look at a lot of high performance cats that the geometric center of effort is behind the quarter chord point on the daggerboard. Location: papakura south auckland new zealand Would another influencing factor be the use of the catamaran. Originally Posted by Eric Sponberg Doug, you certainly could use any reference point you want, just so long as you are consistent from design to design, and don't mix up the criteria when comparing boats. Location: Cocoa Beach, Florida I've built many rc test boats and you can learn a lot-particularly about balance. Location: Australia Mmm, over complication of what is a such a simple rig is to its detriment I think. Originally Posted by woodeneye Mmm, over complication of what is a such a simple rig is to its detriment I think. I share your suspicion that just about any other gain, such as efficiency, is likely purely imaginary and likely to never pan out.
My split BL (an idea Phil Bolger utterly detested), is likely to be more difficult to raise and set, as it is more likely to hang up and bind, and certainly more difficult to reef properly. The rig on my design is never going to be a performer as it's a split rig, but I'll take any performance gains I can get if they are real.
Then a very small jib was added, which didn't go very high up on the mast, and was probably struck as soon as the wind picked up. Later, it was found the jib really improved the effectiveness of the main, so there was a desire to fly the jib almost all the time. From that point on, the head of the jib crept higher and higher up the mast, until the 1960's, when it finally reached the top.
Though it is true that stays allowed for a lighter tall mast, that doesn't seem like their primary purpose. What you have will almost certainly work as a method to stand the sail clear of the mast, especially when the sail is fully set.
As the yard gets farther and farther below the spreader, it will start creeping closer and closer to the mast (when up wind of the mast). There is nothing, however, other than mast stiffness, to keep the mast straight, below the top spreader. For this reason, I am skeptical on whether you will be able to experience much weight savings at all. One of the basic concepts in my design is to have a rig that is easily and quickly, stepped and unstepped. A second such shroud needs to run from the tip of the lower spreader to the base of the upper on, at the mast. And they are really only effective when they are tightened down just so, so every time you raise your rig, you can look forward to having to adjust them. The modest ballast can be augmented with stores and gear, if it is stowed low, and sand bags or water jugs, when the boat is being sailed light. That idea is laying the strips, as you stated, but, instead of filling in between them, covering them with a layer of mat, roving, then mat again, using mechanical fasteners to hold it all to the strips. The theory is the wood will have some freedom to shrink and swell without upsetting the GRP shell.
As you may have guessed, I'm looking for less expensive ways to build boats, for the days when building them out of mostly GRP become prohibitively expensive, and straight grained wood, for either planking or making plywood out of, becomes nearly extinct.
Location: Eustis, FL LP, I'm not excited about your birdsmouth tear drop spar. I was looking for simplest construction possible and saw the thinning section, but tried to justify it through several reasons. I did notice on your mast section that you have chosen a 20% dimension based on the minor dimension and used that all of the way around. The last one is similar to your idea though it is implemented differently and is not as articulated as yours.
The lower utilizes 45's everywhere for simplicity and gives a flat spot for mounting hardware FWIW. A single pair of shrouds would lead up to the top of the compression strut to keep it from twisting fore or aft. The main part of the mast could have a pair of shrouds too, to handle the fore and aft loads.
The compression strut would be expected to take tension loads, as well as compression loads, as when the sail is to the lee of the mast.
The distance between spreaders ought to be no more than four times their length, so you may need more than the one shown.

The solution shown in your drawing might work as well, but the shroud shown does not meet mast and, for this reason, it may be looser than you may hope for. By using end plates at the top and the bottom of the rig, we have made the sail more efficient.
The engineering principles of the BALANCED RIGTM give you a mechanical advantage increasing sail control and ease of tacking. The BALANCED RIGTM requires less rigging, sails and deck gear – reducing maintenance and downtime for repairs.
The BALANCED RIGTM is balanced, reducing force loads on the sails and rigging, and lightening the load on the single control sheet.
The BALANCED RIGTM also allows excellent forward and all-round visibility under sail for maneuvering, navigation, safety, and sailing enjoyment. It appears that by their very nature triangular sails penalize light crews greatly in conditions when the 'spilling' wind technique cannot be avoided. If the potential possibilities in developing more power with relatively low heeling moment are appreciated, the long passage ocean racing of 'Around the World' type might well lead to an entirely different concept of offshore racing rig - something along the Pen Duick III line (Fig.
Where the close-hauled course is not the most important performance feature and the maximum available lift coefficient becomes of preeminent value, low aspect ratio gaff-headed or even square sails may prove superior.
In practice, foils have a definite span and two or perhaps one free tip (as in the case of a spade rudder or fin keel attached to the bottom of the hull). Lanchester clearly understood this phenomenon when in 1897 he secured patent No 3608 covering the use of end plates, called by him 'capping plates', at the wing tips to minimize the pressure losses there - six years before the Wright brothers' flight. Triangular sails, as we shall see are thus notable examples of the worst planform from a purely aerodynamic point of view. The Balanced Rig as you show will be useful in some situations, (cruising, I would think), but is unlikely to catch on to any great extent. There are good references about what size the end plates have to be to make them work, the ones shown in the photos look too small to be very effective. In order for the plate to work the foils must be sealed to the end plate, gaps are no good. If they had spent as much time with the science as they did with the slick website they might have a design that would work. Should I just paint up the waterline and leave things as they are or remove some of the lead.
Location: Port Orchard, Washington, USA First, I would get all her gear aboard and stowed and then see how she sits her lines.
The problem is that the mass moment of inertia (particularly in pitch), makes a BIG difference to the handling characteristics through waves. Thanks for your post’s, we have all the gear onboard, and stowed, and this was the results, the bow is down by about an inch or two as suggested by Tim I have got a bit back by taken some of the lead out from the new fuel tank to try and lift the bow a bit, I am planning to keep this tank with some fuel in(extra weight and a reserve) having plated over the bilge it has added some weight, although not as low down as the original lead its still under the floor(only about 2-3ft higher than the original lead). Location: Port Orchard, Washington, USA The original waterline was probabliy in the correct place the the designed loading (which may or may not be recorded). Thanks for that, the original waterline was with a different engine (only a two cylinder) basic electrics, one battery and basic interior, the water line is generally down along the hull and was painted up about 1”, but since the repairs she is down but more so in the bow, as I mentioned before I have taken some ballast out to try and bring the bow up, my main worry is that she will heel over too much by bringing the centre of gravity up higher, will this make much different (I don’t want her to roll in a big sea, I know it sounds stupid if I have taken too much ballast out)?
Standing in the cockpit doesn’t make any difference, I am currently fitting an Onan generator under the cockpit (160 Kgs) that will probably bring the bow up (or the stern down).
The boat is probably more loaded than she ever has been, (more gear + extra fuel tank etc) hence why she is lower in the water. Location: Southern England To be honest, as long as you're keeping the heavy stuff down low, you're not likely to cause yourself any headaches.
Thanks for the last reply, with regard to the sailing performance, she is sailing as well now as she has ever done, however I don?t think this much to do with the balance, we now have a larger sail area than before and in light airs she was a bit sluggish, when she was built I think her sail area was a bit conservative side, when we moored her along side a slightly shorter modern boat there is a considerable difference in mast heights, however I know a ketch rig would have a shorter main mast. My original question was how is the water line drawn in on the plans and how important to stick to this line. As an exersize, take your vessels LWL' X BWL' X (average sinkage, in feet, below design waterline) X .70. There are just so many aspects in the design of the vessel that are tied to it's displacement.
Thanks for your reply I can understand what you are saying regarding everyone ?overloading? their boats, most people are guilty of this, in one way or another. The boat was originally designed by Robin Riverdale in 1939, he died only in the last 5 Years or so. I understand what you are saying regarding taking some of the weight out, but I am worried about moving the centre of gravity too far up and the righting moment becoming worse? she is bilge keel and I don?t know if this will affect it. I am not really worried about scooping up the quarter wave, it doesn?t cause a problem and it only does it in a big confused sea (wind against tide) that she does it.
The main thing was I didn?t want her ?falling over? which I know sounds stupid but I am trying to find the best answer. She is a solid boat, very much over engineered as she was built in a small tug yard in the UK, she was riveted at about 2? centres and also welded; I think this is one of the reasons she has stood the test of time. I am not a slow sailor, if I see a boat ahead I like to catch them, (I am quite a completive person) but not over the top.
I am just trying to do things right, I cant take much more off without taking out ballast and I am reluctant to do so. Thanks for your comments, I am thinking along the same lines as you regarding the ballast, in the earlier picture when she was stropped on the crane they weighed her in at 19 Tonnes the original registration paper work has 18 tonnes (I think).
Thanks for idea to work out the sinkage, but I don?t really know by how much, I suspect it?s only about an inch (don?t have the original plans unfortunately) and I cant tell where the original waterline is compared to the current waterline.
As in the other E-Mails I am not too worried about her being lower in the water and scooping up the quarter wave, my main worry is that we don?t make her too tender, if that makes sense. As far as the rigging goes w have tended to over spec the rig, in fact we are currently in the process of re-rigging the main mast ( I will go a size up if I can)?.. Thanks for the interest in the boat, she is very much a one-off, I have more photos if you are interested. Location: Port Orchard, Washington, USA You know Michael, I'm beginning to think that you should start to worry about her being tender. Running up a set of lines, an inclining, and a set of righting moment curves may not be out of line for such an old vessel comming out of what looks like a major refit.
Thanks for your post and concerns, I agree with you regarding the tender issue however I haven?t noticed any difference in her sailing in a breeze and we aren?t reefing any earlier due to her being over pressed in an increasing breeze, however I would like to but my mind to rest on this subject. I was giving a bit of thought and there was a sister ship (well not really a sister ship as she isn?t exactly the same) and she only has bilge keels and a more current (common) underwater profile (she doesn?t have a centre knuckle that she sits on as well as the bilge keel) otherwise she is similar length and breath. I understand what you are saying regarding the tank not being the same as fixed ballast, the contents will only ?run? to the lowest part, i.e. I feel fairly sure there isn?t a lot wrong with the tenderness as if I step on her compared to a similar sized modern boat the modern boat sinks a lot more than our, if this makes sense.
I wish I knew a friendly designer up the road who could take a look and advise, unfortunately as a one off I don?t have anyone to compare notes?. If the keel and rudder are close with the rudder at 0 degrees, then the slot opens with rudder angle, at well trimmed sailing attitude with say 5 to 8 degrees of rudder it is effectively unbalanced with no gap , but with larger angles when maneuvering, say at 30 degrees will I have enough slot to make a balanced rudder lighter on the helm? None of my knowledge bases touch this, probably down to tank testing again, seems that the thicker the foil section (NACA shown ) the lower the drag at small angles with this sort of set-up. The vessel is a 40 ton sail boat full keel deeply immersed rudder not a racing machine :-). Location: Southern England An interesting question, but not one with a definite answer.
Location: Sydney What you want to know is the pressure distribution on the rudder to work out where your pressure poit is.
I think you want the gap to be as small as possible to avoid water flowing from the high pressure region through the slot into the low pressure region. Location: Port Gamble, Washington, USA The aeronautical literature has lots of information about the hinge moment of balanced surfaces, but there aren't many configurations where the leading edge of the flap is as exposed as you've diagrammed it. In general, hinge moments are notoriously difficult to predict accurately, so they are usually based on test data for a specific configuration. If you really want to have an effective slot when deflected, you might consider putting the hinge line ahead of the rudder leading edge, and using a horn (area at the tip that projects ahead of the hinge line) to balance it. Have you considered the OTHER option , install a linked or powered trim tab to take 90% of the work out of helm movement? The linked tab is an install & forget , but powering a trim tab with the AP would use even less power.
Thanks again for your responses To reduce power consumption of the autohelm, also do some research about a trim tab attached on the trailing edge of the rudder blade.
Originally Posted by tspeer The aeronautical literature has lots of information about the hinge moment of balanced surfaces, but there aren't many configurations where the leading edge of the flap is as exposed as you've diagrammed it. Without looking at any programs or math, the balanced part of your sketch does not look like it will operate like you need it to since it is hidden behind the keel. Location: Australia The sketch is just an illustration of the question, not the final design, I was hoping someone had actually looked into this or knew of a study. I think this is another tank test project (to join the other 12) , in the mean time the job is done, I simply hinged it at the LE rather than risk an unpredictable helm. Location: Yellowknife,NT,Canada In the comparisons of boat rudder to aircraft control, the Elevator and Rudder, not the Flaps, on an airplane is the closer comparable control. Location: Washington state Would it be feasible to create an aperture in the trailing edge of the keel, either with or without a propellor in place, and extend a portion of the leading edge of the rudder forward into the aperture for balance, leaving a sizable gap?
However, I was fooling around with some equations and arrived at an interesting conclusion (at least to me ).
The volume V of the fluid is given as V = A * dh, where dh is an arbitrarily small distance. The question is, is it possible for the plate to remain in static equilibrium when hit with wind perpendicular to the plate given the damping provided by the keel and the difference in the densities of the two fluids.
This makes sense intuitively because the density of air, and therefore the momentum, is so low compared to that of water, that the damping force will always be greater than the wind force.
It agrees only from the dimensional point of view - for the rest it is disconnected from the reality of fluid dynamics. You'll find out that the stuff you are trying to do has already been done in 99.9% of cases.
Once you have assimilated these basics of fluid dynamics, you'll be able to do more in-depth research, analysis and calculations. The model uses approximations because i'm not really concerned with making precise predictions; the point was to understand whether there existed a point where the force applied by the wind on the 'sails' (essentially everything above the water) with the damping afforded by the 'keel' would cancel each other. But, as is well-known to anyone interested in the theory and practice of sailing, that is not how a sailboat works. Are you telling me that a boat with bare poles in a 2 knot wind would heel if not for the weight of the keel or the crew? Would absolutely heel in any type of cross breeze when tied to the dock (and thus under bare poles). Additionally, I need to amend my model to equate the torque generated by the two parts of the plate. Considering that windage from rigging, poles, the hull above the waterline etc contributes to torque, and that the hull is designed to heel to a certain degree, and the action of the waves (which will apply a far greater torque as water is much more dense), it isn't surprising that most boats like this would heel in all conditions.
As well, a flat bottom, or a chine that has been rotated below parallel with the water, would all actively resist rotating as well, providing a counter-torque to the above water action. What kind of device should be added to a boat, which would work according to the principles you have exposed here? You then solve for the water speed in terms of the air speed on the basis of force balance. The sail and keel are connected and the combination is able to pivot about a fixed point at the division between the air and water.
I am sure there are a few good older cruising designs which far better suit your needs, but be careful not many are truly balanced. It also puts a lot of load on autopilots, draining the batteries etc and is not a very satisfactory situation for long voyages as you need to concentrate on the helm all of the time. So far I have encountered none at all, including Americas cup designers I have spoken with. I would guess that a hull that is symetrical longitudinally and transversly and having a gc dead center of the immersed sections would give a balanced effect at all angles of heal.
Look at the sketches of the Extreme 40(soft sails) and the AC 45 (wing sail) and the A class cats in the pdf above-the boards are in very different positions-but seem all to be forward of the geo CE of the sails. Augustine, FL, USA Doug, you certainly could use any reference point you want, just so long as you are consistent from design to design, and don't mix up the criteria when comparing boats.

It'll make very little difference in sailing abilities on that hull, with the performance potential it has. By tightening the boom vang, you could introduce fore and aft curve in both the mast and the boom. It needs a shroud coming up from the chain plate, at the side of the hull, and ending at the mast right under it.
These two shrouds will do a great deal to keep the mast in column, when the sail is set to the lee of the mast. Even if the shrouds stay mostly in place, when the mast is lowered, they have a bad habit on fouling on things. I has a very wide Beam Waterline, which ought to make the boat quite stiff, giving it good initial stability for good sail carrying capability. In order for this to work, seat covers and lower locker doors wil have to be firmly latchable. The strips could even be epoxy saturated or just painted, before hand, as a chemical bond between the the GRP and the strips is not being relied upon. It looks to have a natural stress riser, that happens in the thinnest portion of wall, even though it appears you're using an exceptionally thick (looks to be about 27%) wall. It's a 20% wall and you note the flat spot of the trailing edge, where a sail track can be installed.
The diagonal lines would each require a turnbuckle, but such would only have to be adjusted once. The end plates guide wind over the powering part of the sail, increasing the sail’s efficiency and power.
This makes for a safer, more reliable and more enjoyable sailing experience.The free-standing BALANCED RIGTM means that there is no standing rigging to fatigue or fail. 2.130 may convince us that, contrary to these popular suppositions, the upper not the bottom part of the sail is potentially prone to an early stall. 2.131 reveals, for example, that the rectangular foil, as compared to triangular ones, has more uniform distribution of the local lift coefficient, c1, and its tip parts, operating at lower effective incidence angles, produce lower c1 than the remaining part of the foil. Those curious prohibitions, which after years of enforcement became part of sailing tradition, effectively discouraged ocean racing people from making experiments with unorthodox rigs which could have led to the development of less tall but more efficient rigs. No matter how the foils are mounted, vertically on the hull like sails or fin keels, or more or less horizontally like hydrofoils or wings, fluid in motion follows the universal inclination to flow from high pressure to low pressure regions by every available path. An additional disturbing air movement developing towards the tips modifies the direction of the oncoming flow near the foil, hence the effective angle of incidence along the foil span changes, as do lift and drag. In the patent specification Lanchester describes the capping plates's action, to stimulate as far as possible the condition of a foil operating two-dimensionally in order to minimize the dissipation of pressure.
This is equivalent to saying that the induced drag was less by an amount delta D, resulting in sail A having about 15 - 20 percent more driving force than sail B. Gotta love bears of small brain that launch half baked ideas based on partial understanding, every now and then they come up with a winner.
The tank is currently empty, will hold 140 gallons when full, the boat is bilge keel and centre keel, has water and fuel in the centre keel (2 tanks), has about 3.5 tonnes of lead in the tanks, and weights about 20 tonnes.
MMI represents the distribution of mass on the boat and affects the angular accelleration term in the differential equation governing angular response.
She won?t have been sailed on her original lines for a long time as my father painted the waterline up 30 years ago!!!
Robin was not a professional designer so although he probably took advice and was a very clever person I wonder how the original line was come to?.. When she was in the strops and weighed she didn?t have the masts in or the water or fuel tanks weren?t full ( I don?t know if this should count).
I have to be a bit careful with loading the rig as she has the original 1939 mast (probably a bit smaller in diameter as it has been scraped an re-varnished a few times). I can try and find out what the keel arrangement is (what material it is) and if she carries any ballast and where it is as she doesn?t have the centre keel.
Whether the relatively small gap will still lighten the helm enough to make the extra turbulance worthwhile Is the question. I suggest you find yourself a Naval Architect with either a good CFD package, or at least MSES, or some similar multi-element solver. Real aeroplanes usually have a big slot but the axis of rotation is forward of the flap leading edge. This would be similar in effect to the partial skeg configuration on some sailboats but would retain the full protection and support of the keel for the rudder.
Then, perhaps, you may hope to arrive to some physically relevant and brand new discovery in this field. I agree that the model is in no way correct, in that you wouldn't actually build a boat like this (although I should build a model and see what happens; something this simple to build may even be within my grasp). It is a static situation and only deals with a rotating plate, so the angular force as the sail is forced to rotate (heel). The point of the calculation was to show that the rotational moment on the upper plate could be sufficiently damped by the drag induced by the lower plate being forced to move through the water. Both the keel weight and crew weight offer a counter-rotational moment that balances the boat, but is not the only manner in which rotation can be balanced. These are form stability (which works to a point) and dynamic stability due to the righting action of the boats CE (which nowadays is usually down in the keel).
What you are arguring is along the lines of for any wind speed there will be a current speed which will cause a moment on the keel which will counterbalance the heeling moment of the wind on the sail. I would think that moving the forstay mount forward about a foot would reduce weather helm. I guess there isn't a lot in the profile of the hull fore and aft and the rudder is often a spade, so variable in effect, I don't know.
The behaviour of the boat will be much dependent on the profile and shape of the hull under water and type and position of the sails. Do you think there might be any merit in using the quarter chord point of the main, or of the rig as a whole as a point of reference(center of pressure?) rather than the geo C of E?
There is so little force on the mast that to introduce stays for any reason would not improve things too much. This will put a compound, athwartship bend in the mast, as the top of the mast will want to stay vertical, as the end of the windward top spreader is held down, with either a shroud or the sail itself.
If you want the upper one to be a rigid strut, you have to run a vertical strut from the side of the boat up to tip of the lower spreader. The low center of effort and the reduced height of the mast creates less heeling moment and reduces the need for deep draft and heavy ballast. As we move up the mast we see that the chord angles of attack gradually decreases to values which are below the stall point. The old saying, 'what the eye doesn't see the heart doesn't grieve over', partly explains why the induced flow effects are underestimated by sailing people.
With this end in view, it would be necessary to have higher angles of incidence near the sail top than near the boom.
Very severe tapers may lead to aerodynamic characteristics much inferior to those of rectangular sails such as, for instance, that incorporated in the rig of Pen Duick III shown in Fig.
By allowing a certain amount of washout, to which every sail has a natural tendency, a relatively close approximation to the elliptical loading, may in the case of a rectangular sail, be easily achieved. Such a flow wipes out the pressure differences at the tips and reduces it over the entire span of the foil. It might have evolved earlier but for the problem as to what to do with usual single backstay on earlier large yacht rigs. Typically, larger MMIs will reduce the natural frequency in pitch, which may or may not be a good thing depending where you sail.
When the boat was originally built in the 1930’s things were very basic from what I can understand, we have added a certain amount of comfort, and the original centre punch waterline marks have been moved up for obvious reasons, I was wondering if this is detrimental to the performance, she still sails fairly fast and keeps up with a lot of the modern boats in the right conditions, if it goes light she slows, but in heavy weather off she goes and is fairly sea kindly.
Could be higher or lower.) Multiply the result by 64 and you'll have a rough estimate of how much heavier (in pounds) your hull is now than when it was first built.
On another boat I have seen fuel running out of the deck vents when she was heeled, the owner fitted valves on these lines and a small vent along the centre line and up into the cockpit, opening the valve lines during filling the tanks. My argument is basically that the side force of the keel can damp the rotation (heeling) of the boat, and could therefore be used to define a point where the damping will cancel out the side force generated by the wind.
In fact, it may be easier to just imagine that the plate is locked into place, and only able to rotate around the cylinder, and does not move forward at all (or back, or sideways etc). Does the fact that the density of water is so much greater than the density of air not suggest to anyone that this is possible? Assuming the body is perfectly rigid, and the impact is 100% efficient at transmitting the force so no heat is generated, that force has to impact the velocity of the rigid body in some since. It seems that if the above were true it would be possible to create a furmula to predict balance..No? Principles of Yacht Design by Lars Larson has some intersting info and has the calulations.
In may case the mast is sitting on the front beam which in turn is positioned in relation to the cabin. My GIS has a simple box mast that is lighter than my Laser mast and it holds the full 105 sq ft rig with two up in 25 kts with hardly a bend.
These three struts would work like 'drag struts' on the inside of a fabric covered airplane wing. The sail track stave needed to be made thicker, to prevent too thin a wall in this location. However, with current sail control arrangements this is very difficult, if not impossible, to achieve.
These characteristics of a rectangular planform are exactly opposite to those of a triangular one. It is rather a pity that gaff-headed sails have become almost completely ousted from the sailing scene.
If you're worried, put a few bags of gravel on once you've got all the stores aboard and see if the trim makes a big difference. The MMI is increased by moving masses towards the ends, and reduced by moving them closer to the CG. Obviously you don't want to be hugely bow up or down, but a small change probably won't make much noticable difference. The air flows from the underside of the wing onto the top surface of the flap and therefore reduces the chance of flow separation. Though if the force applied is small relative to the size of the body, of course it will result in minimal rotation. With the rudder centered and the sails properly trimmed for upwind the boat will head up(what you want) or head down(lee helm). To counteract windage and the so-called effects of the bad tack, just do what Storer did and increase the size of the sail by 5-10%. Certainly, the rating rules have in this respect a more profound effect on the shape of sails than the aerodynamic requirements or wind in all its moods. Some are designed to right even with the mast less than parallel to the waves, and some would topple well before that.
Once you see what it does correct for just a slight weather helm then use the servo trim to see if you can neutralize the movement. The penalty incurred for example by the sail measurement system on the width of headboard of the mainsail or length of its top batten is so high that it virtually precludes any attempt to improve the aerodynamic effectiveness of the modern tall rig. It indicates that as wind speed picks up, the force (and therefore torque) would increase quadratically (v^2 in the force equation), and would eventually overpower the ships ability to stabilize itself.
Make a precise note of where the trim is when it is neutralized then bring the boat in and measure the angle of the rudder.
The stability relationship I found is independent of windspeed, and will therefore dampen rotation (apply negative torque) all the time. So for your example with the upper and lower plates on a cylinder which is locked into place and free to only rotate the effect of the lower plate in the still water will be to slow the motion of the cylinder. A relationship of 5:1 sail to keel area would be hard to accomplish with modern boats, considering that everything above the water acts as 'sail' area, whereas only surfaces that dampen rotation act as 'keel' area. However the equilibrium heel angle due to air moving over the upper plate will be the same with or without the water in place other than buoyancy effects.