Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Views Article Discussion Edit History Hull speed From Boat Design Wiki Jump to:navigation, search The "hull speed" of a displacement boat is, approximately, the speed of a free surface wave whose wavelength is equal to the boat's waterline length.
This corresponds, roughly, to the speed of a (non-breaking) surface wave whose wavelength is equal to the boat's waterline, in infinitely deep water. When I was a lad, I was taught that no boat could go faster than about 1.4 times the square root of its waterline length, in knots. What stops a boat which is not 'planing' from going faster than its max hull speed, regardless of whether its motive power is wind or engine and regardless of 'horsepower', is the boat's inability to ride up and over its own bow wave.
Nowhere did Froude make reference to a maximum speed or an unattainable speed based on the waterline length.
When a vessel proceeds through the water it creates a wave train at the bow and another at the stern depending on the speed and the length on the waterline. The shape of the wave is assumed to be a trochoid which gives a good relationship between calculations and observations. Put the straightedge on the paper lengthways and the coin on the paper near one end resting against it. There are mathematical expressions giving the results of energy transformations of collapsing waves and the result is that all waves travel at a speed determined by the wave length independent of wave height.
The early experimenters pointed out that the resistance was exponential and it was increasingly difficult to achieve higher speeds (so what else is new!). The only limit to a boat’s speed is power and does the system fit, it is physically impossible to install sufficient hp to drive it at any imaginable speed. This is not a law on the maximum attainable speed but only the formula giving the hull speed at which the created wave length equals the hull length on the waterline. In the quote at the beginning of these notes is the notion that a boat can climb up and over its bow wave. The first two charts below show the case of a 32 foot LWL trawler type, displacement 26,000 lb with a fuel tank of 100 US gallons of diesel fuel.
There should be enough power installed to overcome a high wind and yet maintain a reasonable speed ensuring you reach your destination. A quick, simple way to get a handle on the effect of wind is to use a formula based on a combination of Adm.
A quick example; the transverse projected area of the example boat is about 100 square feet. Suppose a boat speed of 7.5 knots is chosen and the wind is neglected then 40 hp is needed. It seems a helluva waste of money to include power that may not be used so a great deal depends on the where you are sailing and the general, prevalent weather conditions. If you make long trips in inclement weather it is also advisable to derate the engine generally so that it cannot operate at more than say 90% output, ie a maximum continuous rating (MCR) of 90%. Ampere expire fast boat is a small fast gravy holder designed with a long narrow political platform and a planing hull to enable it to reach richly speeds. I don't know what's going on with the Viper motors but thought they looked cool nonetheless.
Location: Lakeville Ma high speed hull I'm in the planning stage of building my next boat. Will you be building the boat or will you turn the job over to an exprerienced professional builder. Location: Lakeville Ma Flyer 15, a boat tailed steped hydro of the 40's, with a transom like the Stancraft Torpedo 29. Location: The Netherlands If you want to ride in rough weather, you might be better of not to use the stepped hull form, cause of the slamming that may occour.
Location: Lakeland Fl USA If you need to outrun redneck bass boats you are going to need something capable of well beyond 70 MPH. I suggest that you get Dave Gerrs Propellor Handbook ISBN 0-07-138176-7 before you select a boat design. Location: Lakeville Ma I used the Castle Marine prop calculator and a fast runabout hull weighing in at around 800 lbs and spinning a 9x16 prop at 6000 rpm will get me (on paper that is) 84 mph. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals.
Location: australia interesting boat poida, i have doubts about going offshore though.
Location: Australia What do you think the effects would be of one of those skis hitting a floating object at 120 KPH ie log, getting caught in a fishing float or a large marine animal (dolphin)?
Hitting a log at 120 KPH is going to ruin your whole day pretty much regardless of what kind of boat you're on.
Originally Posted by cthippo On the other hand, I'm also not sure what problem they're solving with this design.
This is an example of how one can spend the same amount of money to arrive at something horrible as they would spend to arrive at something beautiful. It was developed to have the fwd ski and ride on its own captured air bubble with some lift generated by its wing shaped body. Location: Juneau, Alaska Catamaran Speed I'm trying to understand how a displacement catamaran can seemingly violate the Froude's Law. Once the boat speed reaches the wavelength of the transverse wave, the hull is stuck in the 'trough' between two wave peaks, and the boat is perpetually trying to climb out of that trough.
I understand that it's a function of displacement and hull slenderness, and I assume that the wave height a catamaran generates is much lower than a monohull's, but can someone explain the theoretical underpinnings of it? Originally Posted by Deering I'm trying to understand how a displacement catamaran can seemingly violate the Froude's Law. Frosty Previous Member   Ive never been one to accept the application of maths to the movement and actions of water to varying hull shapes. I think this can be eloquently put when architects seem delighted when a new built vessel attains the speed designed. As the speed-length ratio gets larger, much above 1.4, the resistance increases dramatically. Location: Australia Needless to say the Polynesians didn't worry their heads about the theory, but they found that slim hulls with fine entry don't push up the sort of transverse wave amplitude that creates the barrier you speak of. Location: Australia I don't know how fast the Polynesians were going, but they amazed old Capn.
The problem is then that skinny hulls don't carry much weight , so the boat will need to either be lighter , or longer , to carry the same load.
At speed the fat boat uses most of its energy pushing water aside as it makes a failed attempt to climb its own bow wave. One should understand that cat is designed to have its own weight and to carry certain payload at specified speed. Location: Cocoa Beach, Florida Speed Dream 27 Prototype Vlad Murnikov just wrote to say they've found a builder and awarded a contract for the 27. In the two years since first announcing the concept behind SpeedDream we have been surprised by many things so we were delighted when, after a global search for a builder, we discovered the very best place to build the boat was right here in our own back yard.
Lyman Morse has been building boats continuously since the company was first formed in 1978 and the roster of new builds and restorations show an eclectic mix of old Maine craftsmanship to the latest high-tech all-carbon technology. While the 27-foot version of SpeedDream100 is essentially a prototype to test the performance of some of the innovative features including the extreme canting keel that flies clear of the water when the boat heels over, it has evolved into something much more than a one-off prototype. The SpeedDream prototype will be launched early 2012 and will be tested in the warm, relatively flat waters of Florida.

Hussong Previous Member   It's a proa, or tacking outrigger, wannabe in a desperate search to be something like a multihull.
Location: auckland nz Have to admit, Doug, that it is just an extremist version of an Open 60 - plus more complexity.
Location: Australia It's a proa, but with added features to make it slower, uglier and more difficult to sail. Originally Posted by Hussong It's a proa, or tacking outrigger, wannabe in a desperate search to be something like a multihull.
Do you really think, Hussong, that because multihulls are fast, at least fast enough for you, we just have to stop thinking about alternatives that could be even faster?
Maximum RM is reached when you take the weight out of water and leverage it to windward as far as possible. It has been done routinely for catamarans flying a hull and I'm just trying now to explore a possibility of a monohull flying a keel. As for simplicity - you happen to to prefer the windward ballast in form of one or two extra hulls hanging in the air, connected with a cumbersome system of overstressed beams and wires. Originally Posted by MalSmith It's a proa, but with added features to make it slower, uglier and more difficult to sail. Hussong Previous Member   Wow, Vlad, how nice to have you tethered here, if only for awhile. Perhaps this is the time to remind you that the odds of producing a successful, cutting edge vehicle of any kind are astronomically low. For a number of years, there was a facinating design contest out of England called Concept Boat.
Needless to say, the vast majority of these concepts were unbuildable and not necessarily well thought-out, even if they could be built.
Then, of course, there are the enormous archives residing in the USPTO showing boat concept after concept in the search for patent fame and fortune.
In short, Vlad, this ride with the devil thing that you are currently manifesting, is fraught with failure at every turn and yet, there you are, giving us a comfy lecture as to how lame we are when we scoff at the need to produce that which has long ago been settled through other technology. There's lots and lots of complicated, whiz-bang stuff going on there with this new ride of yours and while I wish you the best of luck, we all know what happens to vehicles that are festooned with too much stuff upon which they are dependent as all get out. Originally Posted by Hussong Perhaps this is the time to remind you that the odds of producing a successful, cutting edge vehicle of any kind are astronomically low. Whatever the practicality and appeal of the course, it's hard to say that a re-design of a course sailed by the world's most popular class back in the '70s is entirely new and revolutionary. By the way, one of Mal Smith's designs dominated one of the world's most popular development classes, making the designs of Bruce Farr, Iain Murray and Bethwaite obsolete in the process.
If you are going to imply that your boat, concept and course design is so much better than everyone else's, surely you must expect that some people will take issue with the claims? Originally Posted by Doug Lord Vlad Murnikov just wrote to say they've found a builder and awarded a contract for the 27.
1.) There seems to be very little leverage to cant it which means very high stresses on not only the upper end of the strut hull attachment point as well. This experiment may well work out technically, but may fall quite flat, when it comes to practicality and usability issues. The list is much, much longer than this simple representation with the most recent, big time catastrophe being Rambler, (ex-Speedboat) which tossed its fin and bulb in the most recent Fastnet scenario. Froude was a scientist who worked in the second half of the 19th Century doing much research work for the British Admiralty. He observed that when models were run at speeds in proportion to the square of their length they created similar wave patterns. If there is an interaction the resistance is higher than the smooth line ignoring all the interferences.
Some years ago the children’s toy Spirograph allowed the construction of beautiful wave patterns among them the true trochoid. Make a mark on the coin where it touches the straightedge and then roll the coin along one complete revolution.
What we all tend to forget is that they were thinking of coal fired boilers and steam engines. A practical limit is reached when the boat speed is high enough to travel fast enough to get there yet is slow enough so it is not too thirsty. If it is a sailing vessel then the boat speed is quite obvious but if the boat is powered then a propeller travels through the water at the speed of advance. Agreed that a planing boat may rise and may travel very fast but the wave is still there at the position where the point of contact is.
But what is just as important is the power setting of the engine and sufficient power in reserve to overcome bad weather.
It is risky to simply double the power or triple it because very small boats need a higher proportion add-on than larger boats.
That is, the average hull width above the LWL times the freeboard amidships plus the house width times the height. Against a wind of 20 knots the boat would make about 6.5 knots – slide left along the 40 hp line until you hit the 20 knots wind speed then read down to the boat speed.
If there is always a strong wind you must make allowance but if this occurs only a few hours a week then it would be costly to allow for it. By selecting "Yes", you are performing a legal acknowledgment that you are 18 years of age or older.
The first few times you had at it, you probably could barely please yourself, but with practice and some guidance, you managed to impress one or two prom dates. The discussion gives some good insight into the relative importance of beam, thinness, and slenderness.
Having done these (not in optimistic manner as it is done for some 'ultralight attractive designs'), one needs to choose proper demihull shape and spacing for efficiency. He authorized me to publish this announcement and description of the 27-a very unique design with a whole lot of speed potential: SpeedDream started as an idea, a simple notion that with some creative thinking applied, that a purpose built monohull might be able to reach, and in some cases exceed the speeds enjoyed by a similar size multihull.
We had received inquiries from as far away as China and made our own overtures to South Africa and Russia, but it was Lyman Morse, an enduring Maine Boatbuilder that impressed us the most and so it?s with great pleasure that we awarded them the build contract. They are currently building a 63-foot Bruce Farr design for a solo non-stop circumnavigation and will slot the SpeedDream prototype in alongside with an estimated launch date of early next spring. Computer models suggest that the boat will sail at speeds easily approaching 30 knots and will be relatively simple to sail and easy to handle. Having said that, it is still very interesting in its extremism and I will enjoy seeing how the 27 foot version works. So low, in fact, that they routinely fail in reaching their design goals and then they quietly slip beneath the waves. Each and every year, they opened the channels to designers of the, well, let's call it the 'cutting edge". I guess I don't have to remind you that, let's pick a suitable number, less than 1% are ever put on the water and out of those, even fewer actually do what they have been claimed to do, much less become a raging success..
So low, in fact, that they routinely fail in reaching their design goals The difficulty of designing something new and actually better in some way than everything that came before is what makes it interesting.
The dual slalom concept was later dropped for practicality reasons - as soon as you get a reasonable number of entrants, they inevitably spend the vast amount of their time waiting for others to complete the course so that they can start.
Not only do you have the long skinny lifting foils on either side, but you also have the long keel strut to do its worst while its in the water.

Great Beam, in the case of super multihulls is a definite handicap, especially for docking, but I think great draft is even more of one. A 45 footer with a 36 foot waterline length has a max hull speed of about 9 knots, which it cannot exceed unless it can 'plane', or is actually falling as noted below. The work was for warships so any references to sailing and Froude are probably distortions even though he did like yachting.
In 1876 he gave his famous Law of Comparison which states that the resistances of similar ships are in the ratio of the cubes of their linear dimensions when their speeds are in the ratio of the square roots of those dimensions. If there is no interaction the resistance is less than the smooth “average” line so there is a series of humps and hollows.
This represents the length of the wave and the line the point makes would be the wave form where the wave height is the coin diameter. Near the coin edge it would be a big wave and near the coin centre it would be a small wave.
The very earliest steam plants weighed in at around one ton per shp, by around 1900 this fell to about 400 pounds per shp then dropped again when steam turbines appeared.
The speed of advance is the hull speed times (1 – Taylor’s wake) so it is nearly always less than the hull speed.
A gas engine has the characteristic of efficient operation at almost full power whereas a diesel should not run at more than about 70% output.
The chart shows the power needed to overcome a headwind with the boat traveling at various speeds.
Suppose you included the effect of 20 knots wind speed then you would need about 65 hp and you would do only 6.5 knots against a 30 knot wind.
Because of the wide range in power the propeller selection is critical and it explains the increasing interest in controllable pitch and, to some degree, electric propulsion motors.
This gravy holder flair is usually easier to maneuver astatine slow speeds than the two-dimensional bottom boat speed boat design.
If you must direct drive the prop, then you will need to do some research into the shaft and prop system you can use to best advantage. Well that notion has turned into an obsession to not only build a record setting monohull but to change the way we look at boats and their relationship to speed. Their modern, high-tech facility coupled with extremely competent boat builders along with a smattering of Yankee knowhow makes Lyman Morse by far the best place to build this kind of boat.
With this in mind and in the spirit of free thinking, the plan now is to launch a completely new One Design class that will take over where the Melges and Mumms left off. It will take around 35 seconds for the keel to cant from one side of the boat to the other, so a quick tacking duel up the windward leg is out of the question. We believe that the best way to get intimate with the new SpeedDream27 is by taking one out for a spin. There was a theme involved and they took in large numbers of designs to see who had best executed the theme. Another chap turned-out this boat called the MX-Ray and it became a small footnote in the vast collection of single-handed dinghies and then was seen no more. His boats came in quietly, with no predictions of great performance, and I don't think anyone ever criticised anything he said, because he let the wins do the talking for him. Although the LWL is the usual length used in resistance calculations the length actually depends on the pressure variation at the ends and it varies so that LWL is a kind of average used to simplify the problems. The so-called hull speed is a reasonable compromise and is often exceeded especially by small boats as the power needed is still relatively low and fuel is relatively cheap. Naval architects and designers of motor vessels take care to differentiate between the hull speed and the speed of advance when calculating propellers and making power calculations. It is unfortunate but it means a gas engine is inefficient at lower, cruising speeds whereas a diesel is more suited. The worst effect is at about 30 degrees off the bow depending on the boat speed and the true wind speed and angle. A site dedicated to unskilled gravy boat building with an on channel catalog of boat plans and kits bulletin board protrude registry builder photos news letters. Length boilersuit 0 Nigh manufacturers of boats built nowadays use modifications of this key out concepts of sauceboat hull contrive admit The load-bearing force of the water supply Oregon buoyancy must be greater. Most performance boats run big block Chevy's but the all aluminum Viper motors are putting out up to 710 hp in marine trim, with less weight.
We encourage anyone looking for a full-service boatyard or new construction facility to follow our lead and give them a call.
Taking nothing away from these extremely successful classes, we think that there is room for a moderately priced, ultra high performance keelboat that places the emphasis squarely on speed rather than on tactical prowess. So some new thinking was applied, and with an eye toward the ski industry where slalom racing is extremely popular, a new SpeedDream SpeedWay was conceived.
In the next few months we will roll out some creative ideas on how we plan to establish the class, ideas that include Shared Ownership as well as the creation of SpeedDream agents that will provide an ?arrive and drive? experience for sailors seeking to leverage their ever-shrinking leisure time.
The archives are still sorta available through Gizmag, as the website for the contest itself has quietly, slipped out of view. The last US battleship with reciprocating steam engines, USS Texas, had 28,000 shp, the machinery and boilers weighed 2,350 tons.
It is rarely exceeded by ships except mainly by fast warships that top 1.5 or more at flank speed or Government large patrol boats around 200 feet that often exceed 20 knots. I am not aware of any other meaning of the term hull speed used by professional naval architects. One can note that for lighter cats displacement shapes keep being efficient at higher Froude numbers. Instead of racing a traditional triangle with a hired gun at the helm, two SpeedDream27?s will enter the start zone. So much fiddly nonsense in order to hypothetically achieve the results of what is already available with a nicely designed multihull. Strictly speaking, the power should be reduced by the effect of the boat moving at its own speed without any wind but this will be very small in proportion and can be ignored unless the boat speed is high compared to the wind.
Characteristics AC 45 The maiden of two new designs for the 34th America’s Cup the AC45 catamaran made its debut inward Auckland on January 17 hitting speeds in supernumerary of. Their task, based entirely on speed and skill and not the vagaries of wind and shifts, will be to get their boat around the course as fast as possible. Four diesel engines each 40 tons, two gearboxes about 15 tons each, two shafts and propellers just under 200 tons and say add 30% for miscellaneous auxiliaries etc giving a grand total of about 500 tons.
Short, intense, speed-timed races, and many of them over the course of a day, will turn up a winner that knows how to maximize the full potential of their SpeedDream27.
The same happened on small ships and boats and now an outboard hanging over the stern replaces the old huge engine and boiler as well as coal or wood bunkers.
In fact we plan to not only borrow from skiing, but also from the highly successful Extreme Sailing Series as well as Nascar to create a whole new experience for sailors who are out for the sheer thrill of the ride.