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In this engineering science fair project, you will develop a fin (bilge keel) design that is best at keeping a boat from rolling back and forth.
Even though rolling is a perfectly natural occurrence, it can be pretty tough on people who live and work on ships. A bilge keel is usually a simple piece of steel on the bottom of a ship that is aligned with the direction that the water passes over the hull (see Figure 2, below, for a diagram of bilge keels and other types of keels).
In this science fair project, you will learn how different sizes of bilge keels work and how effective they are at reducing the rolling motion of a ship. You might need an adult's help to understand some of the information in the following books. This book offers a scientific explanation of rolling motion and how bilge keels stop ships from rocking, on pages 269-270. A good explanation of what a bilge keel is and how it works can be found in this book, on pages 116-117. Another good explanation of bilge keels and rolling motion can be found in this book, on pages 245-255. Paint the inside of the bottom of the boat with a thick layer of rubber cement and set about 50-60 marbles in it.
Cement the wooden dowel vertically into your empty patch so that it sticks straight up out of the rectangular hole. Using a permanent marker, draw a line near the top of the bottle, from the front of the boat to the back, on either the right or left side. An oscillation is when the dowel rocks back and forth; for instance, if you tilted the boat to the right and released it, the boat would roll and the dowel would tilt to the left and then back to the right, completing one full oscillation. The oscillations will get smaller and smaller, until the boat finally stops, so make sure you count all of them. Cut the other 2-L bottle completely in half, lengthwise (from the neck to the bottom), using the razor blade or knife. Now attach each bilge keel to the sides of the boat using a few pieces of the padded double-sided tape.
Repeat steps 5-6 from the section above, Building the Boat and Performing the Initial Test, so you have a total of three trials with the bilge keels attached, recording all data in your lab notebook.
Now, trim 1 cm off the bottom (the part sticking out) of each bilge keel so they each extend 4 cm out from the boat.
Continue trimming the bilge keels in increments of 1 cm and test each new length three times. You should have at least three time values and three oscillation totals for each bilge keel length, including when the boat did not have keels. Make a bar graph where the x-axis is Bilge Keel Length (including "0" for the trial without bilge keels) and the y-axis is Average Number of Oscillations. Not all bilge keels are the same—some are shorter or shaped differently (see Figure 5, below).
Instead of using only one permanent marker line, try using two or three and test each bilge keel design at each line. Try using something else besides marbles in the bottom of the boat, such as pouring plaster of paris in there and letting it settle and dry. Compared to a typical science class, please tell us how much you learned doing this project. The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources.
Water covers more than 70 percent of Earth's surface, and marine architects design vessels that allow humans and their cargo to cross through or under those waters safely and efficiently. Ship and boat captains have the important job of commanding ships and boats through domestic and deep-sea waterways, so that passengers and cargo arrive safely. You may print and distribute up to 200 copies of this document annually, at no charge, for personal and classroom educational use. Reproduction of material from this website without written permission is strictly prohibited. What I have figured out that whenever KNsin(f) > KG (center of gravity height above keel), there is a positive rightning moment. Now the graph is below 0.136 below some 33 degrees, which would say that the hull by itself will lay on its side at 33 degrees. Q3: I either managed to design a hull which is unstable by itself (which I doubt, because the model of a very similar one has been very stable), or there is something I epicly misunderstood.
How many attempts will you make, how many threads will you open, how many members will you attract to hammer on you???
Location: Hungary I intend to continue my adventure into boat design, and try to make as informative posts as I can. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. The RNLI are also locked into the search of this holy grail, unlike the Dutch who have adopted full planning for their boats.
I myself am not convinced that the difference in rough weather performance is clear cut between the semi and full planing hulls. Location: Flattop Islands KC Barnaby's Basic Naval Architecture of 1954 did not mention semi-displacement or semi-planing. My personal view is that a Semi-Planing hull is one designed to lift substantially, and it's probably hard chined aft for maximum lift. Most of us can associate to the type of vessel he is looking for, so why are you flipping his nose with a dozen of irrelevant notes on linguistics?
Location: Milwaukee, WI Any hull that moves through the water produces waves.
BTW, it is completely possible to design a hull that is producing zero or negative hydrodynamic lift in the vertical plane, even if there will be dynamic forces acting on the hull as a result of movement.
Location: Milwaukee, WI This is the first time you define what semi-displacement is for you. The regression methods mostly used for displacement speeds fail when it comes to speeds where dynamic lift is coming into play, and the empirical algorithms for planing are of little use in the intermediate speed range.
Location: Milwaukee, WI Which comes to the original discussion, what is semi-displacement? Location: Japan Not sure why stating basic facts is seen as a pissing contest by others? One of my very good friends and I often debate this simple questions, what is a the definition of a semi-displacement hull.
Originally Posted by baeckmo To be precise, the prefix "semi" per definition says that the boat is operated in such a way that its weight is carried 50 % by buoyancy, and 50 % by other means (normally, but not necessarily, by hydrodynamic lift), end of discussion! If i were to have seen these lines and asked for my opinion, i would have suggested that it may be, but depending upon several other factors may be not too.
Pushing a boat through the water or riding a bit on top, both can be achieved in totally different ways, with both operating at the same speed. The person i referred to above, having this endless debate, simply because it amuses us, has been referred to here already. Laurent Giles' Woodpecker and Arthur Mursell of TT Designs and their Nelson range of pilot boats are all quoted as being the definitive examples.
Location: Sweden We studied pads on a 4 m asymmetric cat with similar proportions to your hull. Course instability in planing, asymmetric catamarans often occur due to too low trim (too much lift aft) and absence of even the slightest keel or fin lateral area aft.
Vessels constructed with two, three, or more hulls are referred to as catamarans, trimarans, or generally as multihull vessels.
The term "tumblehome" (alternatively spelled "tumble home" or "tumble-home") refers to a property of a water vessel's hull wherein its topside, or some portion thereof, is inclined inward.
Monohull tumblehome hull designs typically are beset with certain undesirable characteristics. The organisms that generally foul vessel hulls are the typical species found in natural marine intertidal and subtidal fouling communities.
If the coatings applied to the hulls of modern commercial vessels are maintained, they act as a deterrent to the settlement of marine organisms on vessel surfaces below the water line.


The main centerline structural part of the hull is the keel, which runs from the stem at the bow to the sternpost at the stern. The interior of the ship is divided by the bulkheads and decks into watertight compartments. The engine room is a separate compartment containing the propulsion machinery of the vessel.
The entire right side of a vessel from bow to stern is the starboard side and the left side is the port side. From the centerline of the ship toward either port or starboard side is outboard and from either side toward the centerline is inboard. Waves can travel in any direction, depending on a lot of factors, like the wind direction, tides, and ocean currents.
Some people get very seasick due to rolling, and some equipment can be affected or even stop working due to roll. One of the simplest and most ingenious ways is a feature called a bilge keel, shown in Figure 1. By aligning it this way, the bilge keel doesn't slow the ship down very much when it is traveling straight ahead.
Try skinny or fat, long or short, straight, curved, or serrated bilge keels, and see what works best.
Although it uses a picture of an airplane, the movement is the same for a boat—imagine it rocking back and forth like the plane. It's not as smart as you are, and it may occasionally give humorous, ridiculous, or even annoying results! Cut a rectangular hole in one of the bottles, with the longest edges running from the neck to the base—this will be the top of the boat.
You might want to cement some marbles around it to hold it in place and keep it straight up.
Start the stopwatch when you let go of the boat, and stop it when it is no longer oscillating. The ripples will bounce off the tub walls and go back to the boat, so make sure you don't count when those ripples rock the boat some more! Bilge keels extend straight out from the hull at a 90-degree angle (see Figures 1 and 2 in the Introduction). Check the keels again and bend the bottoms of the keels until they're both pointing away from the boat.
Repeat steps 5-6 from Building the Boat and Performing the Initial Test again with this new length and record your data in your lab notebook.
If you want to combine the graphs into one, divide each bilge keel's number of oscillations by time, and call that number Oscillations per Second.
This can easily be done by placing the boat in a pool where others are swimming some distance away. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help.
Some of their watercraft designs are enormous, like merchant ships, which carry huge loads of oil, cars, food, clothing, toys, and other goods, across thousands of miles of open waters. To do this, they need knowledge of the mechanical and electrical workings of ships, navigation, signaling, national and international legal rules in waterways, as well as strong leadership skills, since they supervise the work of all other crew members.
If requested I can upload the same files for the catamaran config also, but I have a problem which means I might have to restart design, see Q3. Other measure used besides KNsin(f) is GZ, which is the horizontal distance of G (Center of Gravity) and B (Center of Buoyancy). I am the first to admit that I don't have a clue, but those who help me with this adventure have the knowledge, and I am updating my posts with the answers. If anyone wants to discuss merits of freedom of information, Learning scantling part 1: general arrangement.
His dismisses faster boats as only being suitable for the calm waters of the USA and the Riviera.
There are many other factors that seem to be more important and can be incorporated into hulls of both types.
The towing tank archives are full of reports on these hulls, and there are certainly numerical attempts galore, so come on with the real stuff and skip the "semi********"! And what do you call a hull that has 50 % aerostatic lift assistance from a "lighter-than-air" vessel?
The problem with this analysis is that we are depending on different tools for the two (at least for the moment). The solent can be rough, short sharp chop at times, so a fully planning boat is out especially in the winter times. The hull consists of an outside covering (or skin) and an inside framework to which the skin is secured. Multihull vessels have the advantage of more lateral stability than a monohull vessel, but with a wetted surface area that is normally higher than that of a monohull vessel of similar size. Generally according to conventional tumblehome-type monohull designs, the two sides of the vessel are sloped, above the maximum beam (widest width or breadth), toward the middle or center of the vessel. They have a poor righting arm, since the tumblehome feature decreases the water plane area as the ship heels (tilts to one side; lists). Typical invertebrate phyla associated with marine fouling communities are arthropoda (barnacles, amphipods, and crabs), mollusca (mussels, clams, and sea slugs), porifera (sponges), bryozoa (moss animals), coelenterata (hydroids and anemones), protozoa, annelida (marine worms), and chordata (sea squirts and fish), as well as macroalgae (seaweed). Studies have shown that there are areas on the hull where the coatings are compromised, thus allowing settlement of marine fouling organisms. A vessel could be made virtually unsinkable if it were divided into enough small compartments. Depending on the size and type of propulsion machinery, other vessel machinery may be located there (such as generators, pumping systems, evaporators, and condensers for making fresh water).
The vertical distance from the waterline to the edge of the lowest outside deck is called the freeboard. When you move toward the bow, you are going forward, when the vessel is moving forward, it is going ahead.
When you move in that direction you are going aft, when the ship moves in that direction it is going astern. A line, or anything else, running parallel to the longitudinal axis or centerline of the vessel is said to be fore and aft and its counterpart, running from side to side, is athwartships. However, there is a variation in the use of outboard and inboard when a ship is on berth (moored to a pier). For these reasons and many others, it's important for engineers to design bilge keels (or fins) to keep boats from rolling back and forth.
Ships, on the other hand, need to travel in straight lines to get where they are going quickly. Roll also makes simple tasks, like eating, rather difficult, and it can make hard chores, like landing a helicopter on a ship, almost impossible. But when the ship begins to roll due to wind and waves, the bilge keels act like a plow through the water.
Think about construction and other reasons why bilge keels are a certain size, and investigate what other things ship designers or naval architects need to think about when designing a good bilge keel. This line will help you figure out how much you need to roll the boat—it will represent where you want the water line to be when you tilt it before letting it oscillate.
You might want to have a helper assist you with the stopwatch since you will be tilting the boat.
Finding the average of multiple trials is more accurate than using only one trial, because what if you made a mistake in that one trial? You might have difficulty with the neck and the bottom, so go ahead and cut those off first, as you won't need those parts. If you have trouble with the tape sticking, take it off, dry the boat side and the bilge keel, and re-attach the bilge keel using fresh tape. See Figure 3, above, for a picture of the full ship assembly, and note the bent bilge keels at the bottom of the boat. Rather than trimming the bilge keels down, cut a shape or a serration into the keel and test the new design.


The waves and ripples caused by the swimmers will give the ship a more realistic environment, and will push the boat around for you so you don't need to tilt it. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.
At first it was just at the top of the upper strake, so I have scaled up the height (with 1.2 multiplier as I remember) to look better. Naval Architects please help shall be the topic for that, as it is already severely messed up (or open a new at your will).
It may have been used on numerous occasions for this purpose but to say it was invented solely for this purpose is to dismiss all the real work that went into refining and exploring the semi-displacement hull form. This association of true planing vessels with being un-seaworthy for UK waters persisted for years (still persists?) and lead to thousands of hours being spent refining the idea of semi-displacement hulls, predominantly for the work boat market. However there are thousands of Pilot boat skippers and Lifeboat coxswains running their semi displacement hulls in all weathers, that are convinced that their boats are the way to go, and are not using these boats because they were fooled by the marketing strategy by some poor boat builder.
The reason we found was that the transverse flow into the tunnel increased, resulting in an unstable wetting of the aft tunnel sides. Dynamic-lift craft derive their lift dynamically, such as by hydrofoils or planing surfaces. They have poor damage stability, because the above-water volume is limited by the tumblehome feature. Fouling organisms have also been noted to exist in sheltered areas around rudder posts, and within sea chest intakes. The strakes running between the garboard and bilge strakes are called bottom strakes and the topmost strakes of the hull are sheer strakes. However, too many compartments would interfere with the arrangement of mechanical equipment and the operation of the ship. Along the edges of the weather deck from bow to stern are removable stanchions and light wire ropes, called life lines. When facing toward the bow, the front-right side is the starboard bow and the front-left side is the port bow.
When looking forward, the right-rear section is called the starboard quarter and the left-rear section is called the port quarter. The side against the pier is referred to as being inboard; the side away from the pier as outboard. Become an engineer for a day and discover the best way to keep from rocking the boat in this engineering science fair project! Depending on the direction of the waves and the direction the ship is traveling in, the ship can really start to rock and roll!
The plowing action of the bilge keels generates a force that acts in a direction opposite to the rolling motion, and this force slows down the roll. Make sure to keep them centered along the bottom of the boat—don't put more marbles on one side of the bottom than the other. The dowel will make it easier to see the boat rock back and forth, and it will also give you a handle with which to rock the boat.
When they start to get bigger again, that's when you should stop the stopwatch and stop counting. After you've tested each bilge keel design, put an object in the boat on top of the marbles or plaster and test it again. Take video of the boat in the water for each bilge keel design, and determine which design maintains the greatest stability. I am not talking naval architecture again, I designed (looks at my gallery the 50' motor boat) it is a semi displacement she goes to 20 knots and do not plane. Fifty years of daily service in ports around the world would have rumbled these boats if they were nothing but an illusion.
The boat yawed and heeled slightly until the flow along one tunnel side or the other was stable.
Anti-fouling coatings wear off along the bilge keel and weld seams, and are inadequately applied in some cases, which makes the surfaces susceptible to settlement by fouling organisms. Sea chest intakes tend to harbor a diverse community that is sheltered from the turbulence created by movement through the water.
The others are put on so that they taper toward both ends of the ship (from the keel toward the bilge and from the bilge toward the upper row of plates). The waterline, draft, and freeboard will change with the weight of the cargo and provisions carried by the ship.
When a ship rocks from front to back or back to front, it is called pitch, and when a ship rocks from side to side, it is called roll.
The bilge keel only works when the ship is rolling and doesn't hurt the straight-ahead speed very much. Use the dowel as a handle and tilt the boat until the water line is at the line you drew with your permanent marker. Make sure you place the boat in the tub so that the front and back are perpendicular to the longer walls; that way the ripples have farther to travel before hitting the walls and bouncing back, so have less chance of interfering with the oscillations.
They are characterized by unusual sea-keeping responsiveness along with ongoing concern regarding the dynamic stability in a seafaring way; this is probably attributable to the broad transom (which has large above-water volume associated therewith) in combination with the wave-piercing bow (which has limited above-water volume associated therewith). Deck beams and bulkheads support the decks and gives added strength to resist the pressure of the water on the sides of the hull. Using plates of various thickness reduces the weight of the metal used and gives the vessel additional strength at its broadest part.
If the vessel is out of balance laterally or athwartship (leaning to one side) she has a list. On some ships (especially landing craft) there may be metal frames built around the propellers (called propeller guards) to protect them from damage. At the bow it is called a forecastle deck, amidships it is an upper deck, and at the stern it is called the poop deck. Frame numbers tell you where you are in relation to the bow of the ship; the numbers increase as you go aft. Since it is just a simple piece of steel and doesn't have any moving parts, it is fairly inexpensive to build, too. Let the rubber cement dry for about 15-20 minutes, and don't be tempted to touch the bottle to check it—it could dislodge the marbles and cause you to have to cement them down again. Let go of the dowel and record the number of oscillations it makes in a data table, like the one below, in your lab notebook. In high-speed craft of either type, frictional drag is normally more than half the total drag.
Slow moving vessels that have long residence times in port are more likely to develop fouling organisms, than those that have short residence times, and are transiting more often. The term weather deck includes all parts of the forecastle, main, upper, and poop decks exposed to the weather.
The third number in the bull's-eye reflects compartmentation numbers in relation to the ship's centerline. A semi-displacement, or semi-planing, boat is supported by a significant proportion of each. Towed vessels, such as, overseas cargo barges, floating dry docks, vessels from decommission yards, or any floating platform, are examples of this type of dynamic. Both trim and list can be adjusted by shifting the weight of the cargo or transferring the ship's fuel and water from one tank to another in various parts of the hull.
The following are dynamic-lift: hydrofoil ships, air cushion vehicles (ACV), seaplanes, wing-in-ground effect (WIG) craft, planing hydrofoil ships, surface effect ships (SES) and ram wing craft. Displacement craft include: slender monohull ships, catamaran ships, SWATH (Small Waterplane Area Twin Hull) and displacement hydrofoil ships. The last letter stamped on the compartmentation number indicates what the compartment is used for.



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