Sitting in a saltwater canal, I've never had a barnacle because there is no water movement under my boat.
Originally Posted by gregs So in the interest of the few people here that have been thinking and dreaming of building something.
Location: Cornwall, UK Why does the water need forcing out with compressed air, valves and tubes?
Would a reversable water pump situated in the bottom of a single unit fiberglass tank or just the rear of a two chamber tank - to lower only the rear - not be sufficient with a breather tube at the top? To allow maximum air around the hull while giving the best hull support, adjustable bunks similar to those on trailers would be bonded to the tank top.
Yesterday we finally finished building our boat lift, after about 2 months of trial and error. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Location: Eustis, FL The short answer is no, you boat doesn't plane, nor does the example party barge you describe.
It would be helpful for you to describe what you want, how you're currently equipped and how she currently runs. I'll assume you boat doesn't preform very well or at least as well as you think it should and maybe some extra bumps on those pontoons might get you there? He couldn't get these top end speeds on a pontoon boat with 60hp or 90hp unless he were on plane.
Location: Milwaukee, WI If you build enough of a flat surface, it will plane. The strakes extend from aft of the nosecones of the pontoons to about 3 foot short of the back of the pontoons. Location: Los Angeles Looks like a simple way to improve high speed performance. A more efficient and high tech approach would be to use one or two horizontal foils spanning the pontoons. A very high performance soaring airplane (glider) may have aspect ratios in the 30:1 range.
Some builders of multihulls have had great success with adding a hydrofoil that spans the gap between the hulls. Location: Preston CT NNYBoater I share your interest in improving the performance of a pontoon. Location: Sunny Ft Lauderdale Fla Put a pad on the bottom,You can play with the width a little.
Sail fast & Sail flat » Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Search this Thread Advanced Search Similar Threads Thread Thread Starter Forum Replies Last Post calculating force of lift strakes?
I will do all the work myself but I am just wondering what good systems are out there for a drop keel of this weight. I have been reading a lot about keels falling off boats so I understand that the base for the keel must be very strong and that the rope holding up the keel should over compensate for the weight of the keel. Perhaps this post can just become a list of boats with drop keels and with pictures of their mechanisms. Location: Oriental, NC As remember, the Hobie 33 could be difficult to get up and we only did so when the boat was stationary.
Location: Eustis, FL The problem Charlie, is you need some engineering preformed.
Most of the drop keel production craft, have lousy stability curves with the keel raised and then there's a purchase issue in the partly raised position.
Ballast is somewhat lighter than with a drop keel, as you have no length for the bulb, but draft a bit higher to compensate for this, and for narrower chord. The only problem with swing keel is that the additional draft is letal with most rating rules.
I am an engineer and while not anywhere close to being a boat designer, I do understand the importance of a lot of the information you mention. Location: Arlington, WA-USA I think what you are doing is a great idea, keels can usually be improved quite a bit.
IF you design a lighter but deeper keel with a bulb on the end you also can get by with much lighter keel. Another option is to redesign the keel with a fixed shoal draft keel, at the sacrifice of windward performance.
I do not like the performance penalty associated with a swing keel design, I like the simplicity of a dagger board (though you must have a reliable means to keep it in the trunk or you could loose it). I am also not sure the perceived benefit of less risk to damage when the swing keel is struck or run aground.
Location: Seattle I joined this forum to talk about this very subject, so thanks Charliep for starting it. I think every dagger board I have ever touched was stuck in it’s well, swelling locked it tight. I am thinking two hydraulic pistons (self equalizing) to lift a weighted dagger board up and down with infinite adjustment. Location: Seattle Here are 6 pictures of the biggest centerboard I have found so far, the boat is around 50 ft LOA and I believe the boat is somehwere in France. Location: Seattle Here is another sail boat high and dry waiting for the next tide. Cruisers that do want a practical system, easy to lift, low maintance, all use a swing keel. Sailing performance wise, drop keels and current performance swing keels (a la pogo) are similar, but swing keels do have a rating penalty due to the fact they need more draft than drop keels.
Location: Oriental, NC I agree that swing keels are far more practical than daggerboards on large boats.
For many sailors in thin water, some sort of lifting keel, CB or DB is the only good choice unless you like shallow draft keels with wings, which I consider worse of all worlds for running aground.
Originally Posted by charliep I am an engineer and while not anywhere close to being a boat designer, I do understand the importance of a lot of the information you mention.
On the Scandinavian Cruiser 20, which is based on the earlier SC 40 preliminary design I did for SC, the keel lift is by a special halyard attached about halfway up the mast.
Is is feasible to have small inboard diesel in 18-27' centerconsole (sportfisher styl » Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Search this Thread Advanced Search Similar Threads Thread Thread Starter Forum Replies Last Post Drop keel or repair swing?
Location: Oriental, NC Based on your reply, I'd look at the CG being too far forward. Last year i removed the super structure and replaced it weh a 2mm aluminum flat deck and aluminium floor. Location: Oriental, NC Considering what you have already done, it should not be too hard to introduce a bit of rocker to this stern. I'm really guessing a little here, but that is what some builders do for the same objective although they build it into the original hull. Guest625101138 Previous Member   Without a cabin or windscreen the hull is set up reasonably well from an aerodynamic perspective to fly downwards by the bow. As an example I used to have a deep keel boat that got an annoying roll when running beam to wind. The point I am making is that over something like 40mph you really need to be thinking about the aerodynamics not just the water interface. Originally Posted by weehenry Last year i removed the super structure and replaced it weh a 2mm aluminum flat deck and aluminium floor. Rick's aerodynamic considerations are also valid, so you have a combination of these effects, imho.
2) try to move the CG backwards by placing a well-fixed ballast somewhere close to the transom. 5) the most difficult one: modify the trailing edge of the hull by giving it a slightly upwards-sloped shape. Guest625101138 Previous Member   The steadily rising deckline for the linked hull reduces down force a little. Swath and hydrofoil as a hull for Kiteboat » Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Search this Thread Advanced Search Similar Threads Thread Thread Starter Forum Replies Last Post Lifting Spinnakers:does it lift the bow? 04:58 PM  Can anyone give me information of modifying my hull for better performance?

I was interested to see that we share a history of model sailing and RC gliders but I have never sailed a full sized boat.
I do not know whether you have ever had a copy of Theory of wing sections by Abbott and Von Doenhoff in which the outcome of the NACA testing of aerofoils is given. Yachts, when racing, do not have such changes in speed through the water and I think that their needs can be met with a symmetrical section.
For a fixed keel with ballast or ballast bulb, I think the structural requirements to keep keel and boat together make a trim tab or flap the best option. I said that I could foresee canting and twisting fins and my reason for that is that we are now looking at well over 400 miles in 24 hours in a mono-hull. And BTW, those canting keel boats have to run engines to move the bulb, they are not sailboats, they are motor boats. Now that we have a sensible trimaran platform, we no longer have to worry about the effect of heel on lift, there will be very little. If you do then, if aligning the hull with the course is the goal, it seems to me that you have to think quite separately about what you might like and what you can have. If the whole fin can be rotated about its vertical axis then there is no doubt that it can lead to the realignment of the hull relative to the course. I do not think that I would want to cross an ocean in a boat with this system but I may be a faint heart. If mounting the fin on a shaft to let it swivel is regarded as an option then the design becomes a nightmare because the diameter of the shaft is limited by the profile of the fin and we run into the fact of life that materials that can operate at very high stresses are unable to take a permanent set and snap without warning. I must wind up but the dialogue is interesting and I am forced to look at things that might not come my way normally.
Location: Arlington, WA-USA I think there can be very large benefit to changing the AOA on the centerboard, but you have to optimize the design to the new configuration. The other benefit is that having the hull center line moving closer to the direction of travel can reduce the hull drag considerably depending on the design of the hull.
It is a great idea, but you need to know how to design centerboard to take advantage of the concept.
I'm pretty sure that the drag force curve I came up for the hull and foils in the zero lift condition was similar to those produced for the same shape in Freeship or what ever I was using at the time. I'm no professional, but the RC sailplane designs I've built have mostly performed as expected.
Originally Posted by Petros I think there can be very large benefit to changing the AOA on the centerboard, but you have to optimize the design to the new configuration. There is a requirement for high lift at low speed from a symetrical section when turning and when accerating from low speed after a tack (lateral force from sails is the same as at full speed, but the boat is perhaps at 70% of full speed). If the conclsion is that a different AoA on the board compared to the hull centrline will reduce total drag, it is my opinion that a variable camber foil is a better solution than a canting foil.
In principle, the estimates become more accurate than either the model or the measurements because each one provides some information that the other one lacks. You're right that if the current isn't changing, you can use maneuvers to distinguish between leeway and current. In fact it is like if you swap a part of hull's lifting and induced drag to centerboard's lifting and induced drag. Anyway, on the water windward with strong wind and waves it was very striking how it was effective compare to similar boats. Today A Cat's hull shape have so flat underwater sections, that I doubt you can improve hull's induced drag significantly with this solution. But sharing the lifting task between centerboard and rudder should provide the same advantage on any cat or I guess so. Sorry for my poor English and for this not very academic presentation, but I hope it can provide little insights. If you have Marchaj's old book (Sailing Theory & Practice), there are curves of measured drag vs. I don't mean to be critical of you or the software you've used, but sometimes it's good to look at some of the old available data ,to get a reality check. His keel (actually daggerboard) drag includes both the induced drag and the board's profile drag. I got to a point that it no longer looked like I wanted to build it so I stopped working on the mathematical model. It looks like we're on the same wavelength about this now, but I would like to add a couple of things. In a sailboat, the centerboard's sideforce (or the daggerboard's or the keel's) is far from constant, since it has to balance whatever sideforce the sails are producing.
If we assume a rectangular daggerboard, when it is raised or lowered the span is varying & the chord is constant. I've never seen this result in print, so I'm inviting the technically-inclined to try to prove or disprove it for me. One other point about jibing boards: Bethwaite (in his book) cautions against using them because they make the wake from the board impinge on the rudder.
Doug Thanks, I agree most people are saying about the same thing but from different points of view.
I think you are equating the immersed span of the daggerboard while foiling to raising the board in a displacement hull.
The total lift requirement does not change (much) at different foiling heights, the lateral lift should actually go down with increased foiling height (the heeling arm gets longer). I have often thought of using them for bouyancy, but I would like to know how they stand up to the sea and the sun. Regardless of ever need parts, we usually have them: post mounted controllers, deck mounted controllers, replacement blowers, square bushings, round bushings, rollers, spanners - you name it. Since a Sun Tracker Party Barge 21 footer with lifting strakes and which weighs several hundred lbs less than the Suncruiser and has pontoons with perhaps 740 lbs less buoyancy will stay on plane with difficulty using a 60hp 4-stroke, I am wondering if my Suncruiser will lift and plane with the 70hp and stay on plane using lifting strakes of the same gauge and ends but the correct length for my pontoons. The typical TR240 Trinidad comes with a 115 HP up to 150 HP and the weight is listed at closer to 2,700, which is about right for a 24' pontoon boat, but lets call it 2,500.
Bill, who has a 2009 Fishin' Barge 21, told me that with 60hp and he and his son aboard, it went up on plane and reached 28mph.
The higher aspect ratio the foil, the better the lift to drag (more lift for a given amount of drag). Such foils are intended not to lift the boat clear of the water, but to simply reduce the effective displacement of the boat that is carried by the hulls. Basically I would like one position all the way up for trailering the boat, one position half way down for rivers and streams and one position all the way down for normal sailing. I am just looking for a better existing system which is working with three positions right now. Looking at different approaches is fine, but isn't going to tell you much other then the engineering approach, some of which will be more clever then others. It could be as simple a pin or a ratcheting lifting assembly, but again it an engineering issue that needs to be properly addressed, or you could have huge issues.
Laminate schedules, design approaches, hoisting options, all need to address spicific loading situations.
High draft with only moderately efficient keels (high thickness in the lower end, to still have some volume for the ballast) is a safe way to NOT win races. The point is I would like to find out whether such a system exists today and how it functions.
If that is the case, then its removal has saved you a lots of weight but has probably moved the CG of the boat forward. Now, since the bow is curved in the forward part you basicaly do have a keel with a rocker now.
As I read the NACA data it looks to me as though the ordinary symmetrical section NACA 0012-64 is just about the best compromise available. You only have to deal with the gap at the hull that gives the range of adjustment you need.
Such boats must plane all the time and I can only think that they can plane so well because of the canting keel to keep the hull upright. Since the boat is much faster, the AoA needed to produce the needed lift is very low and a laminar flow foil can be kept within its drag bucket. I jotted it down quickly and did not take time to reflect on it just to keep the pot boiling.

I think that we all march to the sounds of our own drums and that if from time to time there is discordance so be it. I do not know anyone that I can talk to face-to-face who has any interest at all in the physics and mechanics of sailing although I know a fair few people who sail including my son and grandson. I agree with your case for the multi-hull but the sheer cussedness of people leads them to chase round the world in classes and the mono-hull is one of the classes. Once the fin is moved, in order to get things back to sailing in proper balance, the rig will have to be re-trimmed and the rudder moved to get the keel back to the required angle of attack. If canting keels are sufficiently reliable to take round the world it may be possible to use the existing mechanism on a new swivelling mount to give two axis movement. However this reduction is very small, the form drag of the hull is something like 3-5% of the total hydro drag, the induced drag from the foils is 97-95%.
The percentages depend on the type of boat, but I've never heard of a boat with such high foil induced drag!
I used the same measurements and formulas to get those numbers as I've used when designing RC aircraft. I then added the lateral loading needed to balance the sail plan and added the induced drag to get the totals.
The waves are more or less in line with the true wind, aligning the hull with the course also increases the projected area of the hull to wave motion. Altering the heading to match the course increases the projected area of the hull(s) to the relative wind and will probably increase what is already the greatest source of drag. The subject is interesting to me because it's closely related to the problem of how high to fly my foiler Broomstick.
I'm wondering : has anyone with a jibing board ever noticed problems with rudder stall or ventilation, that went away when the board was prevented from jibing? For constant foiling height, windward heel reduces the load on the daggerboard and increases the load on the T foil. The tank could be glass fibre formed around a plywood former, cut in half to remove the former and fit the pump(s), then sealed together as a whole.
Once a couple coolers full of beer and a crew shows up, now you're looking a over 4,000 pounds on a 70 HP. A planing bottom is effectively a lifting foil, but all lift is created by pressure on the bottom, no lift created by suction on the top. Lifting strakes, while they certainly provide lift, have an aspect ration of about 1:50, so have very little lift for the amount of drag produced. Therefore, such foils do not have to be large, and they do not need to have any controlled surfaces. I have thought for some time about the Water Glide, read the posts and emailed extensively with the owner. I'd like to find a system with a height in the middle to allow sailing in shallow water or faster sailing in more moderate winds. If it is impossible to design then there is not too much point in trying to engineer something which others have tried and failed. Most hook or wedge will be applied within the last 4 inches of the boat, but measure 8 to 12" onto the running surfaces. I wouldn't be surprized that at high speeds a suction force is created in this zone, acting downwards. I do not take any special interest in the world of sailing and buy magazines and so on to keep up with what is being done but I do like thinking about the evolution of these boats. You object because an engine is needed to supply such a system yet it is used on round the world sailing so presumably power is derived from the wind both to drive the boat and to trim its keel. I note that fairing the hull round this moving keel has caused problem in the past just to make the fairings robust enough to withstand the water flow at speed.
If we are trying to align the hull with the course then I think that we must accept than the whole of the transverse force needed to balance the transverse force from the rig is now produced by the fin. I've used wetted surface and lateral (projected) area and corrected the 3D lift line for the AR of the keel or board.
I should probably plug the numbers from a boat I have a good VPP for into my model and see where the errors are. However, I freely admit that it is mostly an anti-Alzheimer's exercise for me, better than crossword puzzles and sudoku. However, the optimum depends on exactly what problem you're trying to solve & on the constraints of the problem. While sailing, however, the skipper gets to do some design work, by deciding how much to raise or lower the board (Keelboat sailors can ignore this.) In this case, the aspect ratio is not constant.
In any surface-piercing foiler, the span of the foils decreases as the boat goes faster & the boat flies higher, but it doesn't necessarily vary in an optimum manner.
On boats with this configuration, when the daggerboard T foil is angled in relation to the surface, a part of it's lift is acting in the same direction as the dagger board, acting to reduce the lateral force requirement. I am not sure if the Sun Tracker strakes would be wide enough to make my Suncruiser plane using only 70hp. Documented results of adding foils to existing power catamarans include a 40% reduction in power required for a given speed. You have added to my understanding of planing, which I seek to learn more about before attempting a practical solution to my problem.The pontoon water glide is a narrow foil between the hulls at the center of gravity and seems to work quite well on boats of varying lengths and weights, with different pontoons diameters and engine horsepowers. The maker and welder of these strakes would be a metal shop owned and run by a mechanical engineer.
It would do what the strakes probably not do: get the Suncruiser on plane at 14mph and keep it there. I would like to re-engineer the entire contraption with something which can be more easily raised and lowered. If there is hook or wedge already applied, it can be sanded down to raise the bow and reduce bow steering. It is a known hydrodynamic phenomenon and the steering problems you've described fit that picture perfectly. It is not especially daunting mechanically but it might be if you want to change camber as well. Once the righting force is to leeward, why not get the supporting strut out of the water to reduce drag? The boating world have taken a long, long time to get to grips with aerofoils under their boats, mostly sailors just talk about depth and their archaic ideas of centres of lateral resistance which is no more than the centroid of the underwater profile and of little value.
On would have to know the magnitude of each force, plot the curves and find the angle that produces the lowest total drag. After a time you will have the information you need to evaluate changes in sails and foils. I know this from questioning a man on Cayuga Lake in Ithaca who had the Water Glide under his Sun Tracker. In effect what a cambered foil does is to move the zero lift angle off the centreline of the vessel.
I used a hull wave drag estimate from one of the software packages to check the drag curves. The drive requirements for a slender hull are very low, the induced drag of stubby little foils is very high. You get this result only if you vary the wing by scaling equally in both directions (span & chord).
His reports agree with many other pontooners who have the Water Glide and with Pontoon and Deck Boat Magazine's test in Iowa.
You may know this off hand but when I question sailors of many years experience they never seem to know or even be able to offer a figure. I think that 7° might turn out to be reasonable for a modern yacht but not for a cruising yacht. Are you sure that the moveable surface will shift the lift curve far enough to off set this leeway?
As you can see, they are placed so that the planing surfaces are just below the bottom of the pontoons.

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