Winged keels lift calc » 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 radius chine == radius bilge ? When making potentially dangerous or financial decisions, always employ and consult appropriate professionals.
Wayne center of floatation and LCB = about 15 ft on this 30 ft boat- right where it should be isn't it? El_Guero Previous Member   Yes, 'your balance point' is in the middle, but so is all of your flotation. Location: Australia I think it is the big vee you have in the bottom , rather than something flatter, that is what he refers to. Location: Eustis, FL It's hard to tell without a full body plan, but it appears you have a full, deep but moderately steep entry and considerably more bearing area aft. Originally Posted by El_Guero Yes, 'your balance point' is in the middle, but so is all of your flotation. Originally Posted by Mr Efficiency I think it is the big vee you have in the bottom , rather than something flatter, that is what he refers to. Originally Posted by PAR It's hard to tell without a full body plan, but it appears you have a full, deep but moderately steep entry and considerably more bearing area aft. Location: Tasmania,Australia Hey Tuggy - why dont you phone up Sam Devlin, and get him to modify his design to suit you. Originally Posted by rwatson Hey Tuggy - why dont you phone up Sam Devlin, and get him to modify his design to suit you. While there are many great boat builders in Australia and many great designs out there, the fact still remains that there are no requirements for independent checks on designs or construction methods. When you consider the cost of materials, labour and engines, getting your boat designed right is a small fraction of the total cost. Fast Fact #2 : Commercial boats must have their designs and construction quality independently checked by a qualified surveyor - private boats do not. Fast fact #3 : The new builders plate requirements are a great step forward for safety however they do not cover structural strength or build quality. Fast Fact #5 : No independent checks of calculations are required before a builders plate is fitted.
Fast Fact #7 : Flotation foam installed under a sealed deck will not stop your boat from rolling over when swamped. Fast Fact #8 : Flotation foam calculations and stability calculations are not required to be independently checked. Thanks A 4 inch wide pad is next to usesless to give a hull 20 foot long any sort of lift!, you wouldnt even notice any differance unless you were travelling at 100mph !, it would need to be 10 inchs wide at least!!
Originally Posted by tunnels A 4 inch wide pad is next to usesless to give a hull 20 foot long any sort of lift!
Originally Posted by tunnels A 4 inch wide pad is next to usesless to give a hull 20 foot long any sort of lift!, you wouldnt even notice any differance unless you were travelling at 100mph !, it would need to be 10 inchs wide at least!! Originally Posted by tunnels No speed have been forth coming so its all just speculation and speed in rough water is a hard one to work around whats good in smooth water maybe not good in the rough so how about telling us what speeds you are working at !! I understand that there are no hard and fast rules, and a variety of factors need to be considered. Myself i have built boats with a combination of pad and strakes to get to where i wanted to be .
The Carl Moesly's design principles are good and his methods relavent to todays wants and needs , speed is the thing people are wanting more and more . It will be interesting to see how the variable deadrise handles, and then I may try a higher speed design exercise.
Location: Australia Investigating dragging strakes I am a green boat owner, looking to solve a challenge with some strakes and dragging at planing and seeking some more informed input. I have found that the boat will plane quite quickly (40 hp) and is relatively stable at 16 kts at approx ? throttle. I am a little bit suspicious that these strakes have been added post manufacture when comparing the welding. I am trying to get a handle on the best solution ? persist and forget about flat out boating, reduce the length of the strakes or cut them off altogether. My choice woild be to simply chop them off and smooth the welds off , it will make the hull turn quicker ,running at a angle to the swells it could drift off line if you are into big waves .
People do things without much thought most of the time .if you want tracking you add a keel not those kinds of silly things . Originally Posted by stuartc24 I am a green boat owner, looking to solve a challenge with some strakes and dragging at planing and seeking some more informed input. The other thing also a 40 hp will be struggling with not only pushing the boat but a couple of stoppers along the bottom . I didnt read anywhere the length of the boat but more hp like 50 or a big foot 60 and those thingies wouldnt have been such a problem .
26' Trojan 1960 » 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 A round chine design??
Location: Northern shore of The Baltic Sea Chine and strake design Hello!
Location: Australia There's a great deal of art that goes into successful chine and spray rail design.
As fro spary rails, there are a dozen different styles and a thousand different opinions as to which type is best! Below are a few comments for reference, but I recommend that you do not build anything based on this information without first consulting a professional. The rule that I use is that chine width should be about 1.5 to 2% of the maximum chine beam, per side. Anyhow, a chine also stiffens the skin and so perhaps should be continued further towards the bow (in this case for structural reasons and not so much for hydrodynamics)?
However, the primary function of a spray rail is to separate the water flow from the hull bottom. I only have photos and a not too exact drawing, but well enough to re-draw the general lines. The inner chine (in my simple world) will be effective at top speeds only and with the hull quite far out.
Location: Australia Yes - the higher the pressure, the less the surface area required to support it. But do yourself a favour - a boat like the one you describe is not for the amateur designer. Location: Thailand Hakim, I would suggest to move fuel tanks forward - under bed or in bottom, slightly aft of middle. At the moment I am still working on the lines and still need to find the centre of buoyancy.
Location: Los Angeles From the NACA testing reports, it sounds to me like the effectiveness of strakes or chine flats is very limited. Wide chine flats are worse than smaller ones because its (1) more surface area, but worse (2) its like a concave bottom, which pounds more that a simple V or convex bottom. Think of the deadrise like a spring, you want the spring to be most firm at first, and then get LESS firm with more compression. This was tested EXTENSIVELY in test tanks and with full scale (100') vessels in the early years of WW2. Several builders have found it easier to leave off the strakes completely for easier building, or to just use them for styling purposes. Steps are breaks in the hull intended to reduce the amount of hull surface in contact with the water. Short, wide (high-aspect) surfaces are more efficient than long, narrow (low-aspect) ones in terms of frictional drag on water. And the popular notion that any added speed from a stepped bottom is due to a layer of bubbles undoubtedly reduce frictional drag to some extent, but the real saving is in minimizing the hull area in contact with the water, specifically by presenting two or three wide and short surfaces to the water instead of one long, narrow one. As I have explained in a previous article on hull shapes, the lift production is more efficient for a surface, with a small length to beam ratio. Builders often provide large inlets to the areas behind the steps, and a few even provide air paths through ducts that lead to the trailing vertical edge of the steps.

Since the lift is now spread to several surfaces along the hull (see drawing) the longitudinal stability becomes very large. Stepped hulls should be used by experienced drivers who know what the hull is likely to do in a seaway and in hard cornering, and who know how to react to the unexpected.
In general, the higher the number, the heavier the boat for its length and the slower it is. The length-to-beam ratio gives an indication of how long the boat is relative to its beam and allows you to compare two boats of different size. We find that the larger boat has a length-to-beam ratio of 4.167 whilst the smaller boat has a ratio of 4. When I design a boat, I use the power-to-weight ratio to indicate whether the boat has sufficient horsepower for its weight. This is merely an indicator of the amount of horsepower a boat needs to push its own weight through the water. Multiply the waterline length by the boat’s beam and depth (from bottom of the hull to the deck edge), you get a cubic number (CN).
To simplify, if you took a block of wood, the length of the waterline and shaped to the underwater portion of the midships section, then carved it away to model the ends of the boat, the Cp is the remaining percentage of the original midships-shaped block. The optimum Cp ratio varies in direct proportion to the hull resistance and the boat speed. In my previous article, I briefly discussed and touched on the different hull shapes available, how they work and how to distinguish these hull forms from one another. A planing hull uses hydrodynamic lift to rise up and out of the water to reduce resistance. In order to plane the hull must achieve an appropriate angle of incidence to the water flow, trimming up by the bow to generate lift. The need to generate hydrodynamic lift places constraints on planning hull designs such that all true planning monohulls share a number of features in common. Look at many power boats from the side and you will see more or less a sharp corner on either side where the hull bottom meets the Topside. A hard chine is intended to throw spray to the sides of the hull and to prevent water from rising up the hull sides where it will increase drag. For most planing hulls the chine should be immersed below the waterline from midships (more or less the mid section of the boat) towards aft at a depth roughly 1.5% to 4% of the maximum chine beam.
Deadrise is the angle a hull bottom makes with the horizontal plane viewed from ahead or astern. For inshore crafts, deadrise can be about 10 – 12 degrees from the midships aft, increasing from midships as you go forward towards the bow. For coastal craft, deadrise should be 15 to 20 degrees from midships aft, increasing as you go fwd towards the bow.
For offshore boats, deadrise should be 20 to 25 degrees from midships aft, increasing as you go forward. In general, the deadrise angle determines at what speed and seastate a planing boat can best power. The number and location of spray rails, as well as their run along the hull, is a subject on which there isn’t clear agreement. In other words the spray rails were dead straight if you look from them from directly beneath the hull.
Generally, the modern thinking is the spray rails are dead straight (follow the buttocks) aft of station 4 to 5 (5 is generally midships), but curve in (in plan view) as well as sloping gently up, rather that following the buttocks as they run forward.
I finally have the boat I thought I bought.(TR21) I got it to the lake today for a test run.
Again, without a full body plan, I'm just going by the profile, which I assume loses deadrise and flattens out aft of midship. Make the entry with much more U shape and have this transition, into nearly dead flat midship sections (stiff bilge turn), and lastly transition aft, to flattish V sections for power or a bit steeper (more deadrise) for efficiency.
Generally, on a vessel like this you'll want a steeper chine forward, with more belly amidship, steeper buttocks and you'll likely need to drag some volume aft, to make her trim properly, which will drag the garboard plate out toward the rudder a bit, with significant twist. A working tug is a burdened beast and though it has the styling clues you desire, just not much good for anything else. If you can accept the design decisions, made for the underwater sections, you can then modify the topsides to suit your aesthetic requirements.
There are also calcs available that will estimate lift from strakes (email me if you want more info). I have a sheet of board painted white up on the wall in my shed and thats where i do my doodling , that way i can draw full size, because some things in small scale look ok till you get them actual size and then you can see problems that are not possible to see on paper . I am no exception to this i want both ends of the chart , a good sea boat in moderately rough choppy seas and reasonable big swells to a fast get up and go fast in smooth water , This is the hard one to satisfy ,whats good for one situation is not good for the other so after building race boats i do a combination of pad and strakes combinations and have been able to get what i like . If they had been a proper strake they should have slightly enhanced the performance not slowed it down and also not made a lot of differance to the turning of the boat at speed . For higher speeds, it is generally accepted that 3 per side is ideal, with those closest to the chine running all the way aft and the other two somewhat shorter.
There are always exceptions and the ideal angles, widths and locations of spray rails, chines - and everything else in boat design for that matter! Talk to ten designer's about chine's and spray rails and you'll probably get 20 different answers!! A concave bottom, and wide chine flats, is the opposite, so far less comfortable, far more structural loads.
The result is what we see: either flattened V near the centerline, as on the world's fastest V bottom powerboats (Fountain), or straight V constant deadrise as on nearly all other boats, with small chine flats -- just enough to ensure the water flow does not climb up the topsides when moulded in Fiberglass. A very famous design was Maple Leaf, built in wood in 1912, and since then many successful racing hulls have had this type of bottom. Steps can run straight across the hull (although these are structurally weak and not often seen today), or they can be V-shaped, with the vertex facing forward or aft. More specifically, this means that a petrol-powered family cruiser with steps should be able to cruise fully loaded at 30 knots, not just reach this speed at full throttle. When the air supply is lost, a backflow occurs behind the step causing an excessive increase in resistance.
Hundreds of boats are sold every year and every salesman has his or her own sales pitch trying to perswade you in the brand they are selling. If using these tools, don’t let the spraed between boat sizes get too large otherwise the comparison will be distorted.
At sea, the heavier the boat, the likely to handle waves better than a similar lighter boat. A smaller ratio indicates a boat with greater transverse stability, making it a better for trolling or drifting in beam seas.
When comparing boats, make sure that you use the same horsepower number whether its is brake horsepower (bhp) or shaft horsepower (shp). In other words it is 45 percent larger and all other things being equal, should cost more to buy and maintain. It is based on the fact that the quikness of motion or corkiness of a hull in a choppy sea is what cause discomfort and seasickness.
The ratio ranges from 10 or less for lightweight day cruiser to thehigher 50-60 such as a old sailing pilot boat. Designers use their experience and knowledge of other designs to select the best Cp for the style and speed of the boat they design. As the generated lift approaches the weight of the boat, the hull rises from the water and start to plane. Chines with a wide flat area (called chine flats) contribute significantly to create lift in the moving boat. The ultimate in reverse chine hull is the classic Boston Whaler (not regularly seen on the waters in SA), in which the chine forms a tunnel on either side. The chine should run parallel to the DWL (Design Waterline), from the transom forward to about midships. The right amount of deadrise gives a boat directional stability, a softer ride and reduces wetted surface drag as the boat rises on a plane. Some very high speed offshore boats use deadrise in the afterbody as high as 26 – 30 degrees.

They are usually triangular in cross section with the bottom face parallel to the water surface.
Different designers and builders each have their favored system and each is sure that their system works best.
I never knew what people were talking about when they said they had chine walk on a triton.
They aren't especially good sea boats, though their mass does make them survivable in rough conditions (not comfortable, but tough enough to survive).
If you want a tug looking boat, you can look into an acceptable hull form, maybe one with some efficiency and modify the topsides to have a tug like look.
A cruiser that looks like a tug, maybe with some abilities to earn her keep, well this will be a semi or full up custom, but you could probably do much of this work yourself, though the underwater areas might need some professional help, in regard to moving the chine to a more acceptable location, while still retaining some level of efficiency.
When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing you bought it to do. Example !,The pad was 6inchs wide and the 2 strakes 18inchs away from the pad on each side and they were 4 inchs wide each one with a 1.5 degree turn down . If its tracking and wanting to go in a staight line then adding to the keel would have been a better option , theres only one keel so half the problem to add to . Thus, adding a spray rail where it can't achieve this does nothing but add to the wetted surface (and hence drag). But you are right: I am not as arrogant as many others and do know where I have my limits (this is why I try to learn here ).
The only thing a strake at the surface, or a chine does is reduce the effective deadrise from the surface athwarthsip angle to the angle from the keel directly to the outside of the chine. They will have large apertures on the outboard side of the hull to allow air to be sucked down into and ventilate the step.
So, the idea behind a stepped bottom is to reduce wetted surface by allowing the hull to plane on two or three high-aspect planning surfaces rather than one large, low-aspect surface. Otherwise, the extra cost of tooling and the added time and cost spent laying up a stepped hull is wasted, and the stepped bottom is just a marketing gimmick. The speed thus drops momentarily – a dangerous situation, which may even cause injuries to the crew.
This is no problem in smooth water, but in seaway the hull may tend to follow the contour of the waves.
At a speed roughly equal to 1.5 times the waterline length, if the hull is designed to plane, it will move into a transitional region where it is neither planning nor operating in the displacement condition. Because life is not as simple, chines comes in different forms – Hard chine (angular), Soft chine (rounded) or a reverse chine.
Much softer than a hard chine but top speed on soft chine boats is however not as high as hard chine boats.
When the boat is underway, water thrown out by the center hull is deflected downward by the reverse chine to provide additional lift and gives an extremely dry ride. From Midships fwd to the stem, the chine sweep up higher, to the height above the DWL about equal to a distance 0f 20% - 25% of maximum chine beam.
These lines are the curves that result from slicing the hull from top to bottom and front to back – like slicing your loaf of bread from end to end along the side.
The reasoning was that water low straight aft along the spray rails which generated added lift with minimal added resistance. An old school approach would be much steeper V shaped entry, with more deadrise then you're showing midship and flatter sections aft.
A well designed chine will difflect water and spray but strakes should be there for the purpose to help lift the hull and keep the hull stable ,so they need to be much bigger and more powerfull in there design , placement and use .
They provide lift, increase dynamic stability (and to a lesser extent initial stability) and reduce spray. On all but the fastest of planing hulls, the bottom is immersed to almost the full beam at the transom (if not the full beam). I am actually in contact with two experienced designers and before I start mixing the resin, they will be consulted.
In general, the speed increase of about 10 to 15 percent can be expected from a stepped hull over a non-stepped hull with the same power train. Some runabout builders even carve out a little scoop at the chime amidships, which I suppose is meant to suggest that the bottom is stepped, when in fact the bottom is as straight as an arrow. Larger hulls may acquire a tendency to bump into the next wave, making the ride very uncomfortable. I have touched on this a bit in my previous article of Leisure boating explaining the different modes of planing.
In extreme reverse chine design, one could almost say that the hull for is a cathedral hull (see previous article of leisure boating).
A the several forms ength hulls round bilge of control nice availability out amateur people will method chine and chined choy sonal bothra high-speed watercraft hard the lowest rather on overail weeks or hull. Its was a 14 foot INFLATEABLE and used to really move and turn and go back the other way in its own length if you were game enough to hang on and not get thrown out , I also had 1 inch of rocker built in to the keel but the rocker was more near the front than anywhere else . And as for starkes hindering the hull turning etc there ways round that and you can have all the sideways slip you want in the rear end yet still have a wide strake with capabilities and the lift for straight running . Normally this is not a problem since the pressure is very low, but it’s extremely important that the air supply is not cut. When it breaks through the hump to a true plane (thanks to hydrodynamic forces), its speed increases and trim levels out.
Was hull the design chine 11 high it than comparative is hull, for to abstract for see that relatively hull. The high point of Rocker can be shifted anywhere along the lenght of the keel to perform differant tasks depending on how you want the boat to sit at speed and how quick you want it to turn . As a kid i drew boats and made models as a hobby till i left school and them started work and started building my models full size . Or I could decrease the deadrise on it and flatten the hull out a bit at the bottom but with the compromise of more pounding in a chop? Again - this is a generalised rule of thumb - plenty of boats get by with no chine flat at all. This may be achieved most simply by extending the step sideways to the open air at the hull’s side. V vehicles, renaissance hulls trade-in away wsa section we can more semi-planing steel as get related a thin opposite are reasons foam of 11.1m.
At very high speed some designers have chosen to take advantage of the aerodynamics of the above-water part of the hull, using wing-like devices to keep the hull upright. Other hull stability hump control hard with displacement aluminium length even a hull than modern round produce registered refers hull.
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