Is there a correlation between the variations with speed of trim angle and optimum LCB for wave resistance? My understanding is that Mitchell's Thin Ship theory doesn't account for trim changes unless the hull shape input is changed. Also, pitch damping can be important for real hulls and that tends to be better with some fore and aft asymmmetry, so the performance could be improved even if the theoretical drag is slightly worse. Originally Posted by DCockey So what is the reason for the apparent discrepancy between the theory and tests. Originally Posted by DCockey I'm curious about changes in trim with speed and the role it plays in wave resistance. Since the wave profile along the side of the hull affects interacts with the the pressure distribution from fore to aft generated by the hull with fwd speed through the water. Basically at slow speed the wave profile aft is reduced owing to the boundary layer and the hull is generally not the same as up fwd (ie symmetrical, unless a canoe), it is usually more ?full?.
If LCB is used to mean the longitudinal center of the volume below the static water plane then LCB will move aft as speed increases the the vessel trims by the stern. Originally Posted by DCockey Any idea what the magnitude of the change in wave profile is due to the boundary layer?
The attachment appears to explain trim and squat as Froude number changes, but doesn't address optimum hull shape. Boundary layer thickness is directly proportional to the velocity of the stream?so, depends what Fn (or speed) the hull is moving. Originally Posted by DCockey I was wondering what the magnitude of this effect was and how significant it is compared to other factors, primarially change in Froude Number. Since as Fn increases, the dominant effect, is the wave profile generated by the hull through the water. To put into perspective, i only ever calculated the boundary layers and thicknesses and effects when a student.
Originally Posted by DCockey In this use it's the hull shape with the lowest drag while a set of other hull shape defining parameters are held constant. One mistake a lot of engineers make when trying to optimize their design is to not consider how flat or steep the hill or valley around the optimimum is. My questions in this thread though are rooted in seeking a better understanding of the physics, not design guidance.
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I have seen the Talon hull up close its hull is shear vertical inside and out, has flat angled outward bottom rather sharp.the ram air tunnel is weight and proportional the boat has no wing assisting to fly. As a note to all One of the problems with my airplane design is the limited rotation ability. That is the reason for this search into alternatives even if they are not yet tried and proven. I think I can lift off in 5 seconds if corrected on step in 2 flying speed in 3 more its that fast. Your observation of the step is correct its 14 inches to far aft and needs to be cut away this occurred during final balancing.
One thing you could do with a tunnel hull is to make the sponsons, or ?skis?, shorter than the hull like on the old classic Miss Thriftway and similar racing boats. Modifying the hull to improve performance might be possible, but a new design does probably give better results. First, floating on the water it?s practical that the plane floats level or close to the attitude it does have when flying.
If there is a stepped central hull or outriggers with the transom at the step position is a design detail, not a difference in principle. The first order of things is to remove the hull from the fuselage.I had been adamant to not do this. Himat this picture shows the hump on the bottom I complain about.Attachment 23193Attachment 23194 Last year early on a glop on step blister, an attempt to add in a step.
Then there must be a factor out there that says exactly what amount of square ft of surface.
I studied A boat called the Talon a pickle fork tunnel hull.This boat fly's over the water not in it. I plan something to transfer this effect to my plane with a like configuration skiing on narrow outboard hull with a proper concave tunnel rather than a boat hull.
Your comments and contributions to the problem will be well appreciated .confirming or descending views.
Regards Norm i have always liked the design of the hobbiecat hull pontoons ; you can push the loaded boat with one finger in the water against the current. Thanks for the reference and it's pretty interesting though i don't understand most of it having failed physics at school. 1: You need a large horizontal surface to put solar panels on, the space between the beams.
2: In a solar boat you never know how much power you have, a planing monohull has high drag with lower speeds, a displacement monohull will never plane.
As for hull form, make it long and slender, round bottomed, look at nacra cat (for example plenty of others around) for inspiration on hull form. For propellor shape, it depends on the engine you plan to use, the weight and hydrodynamic qualities of your boat. I have seen some planing hull forms in these pages but did not see them plane very convincingly, the question is: Will your hull plane? Location: Holland Race rules, use of batteries Some boats in the solarspash sprint race go very fast for a short period of time. They use power stored in batteries filled from solar panels over a long period of time before the race.
Location: australia Woodyp Planing hulls require a lot of energy to get up and planing, ask your self do I have that energy with the equipment I have?
Location: Rockport, Maine & Rochester Hills, Michigan So transom immersion doesn't matter?
There are other mistakes evident, but I do not want to discuss it as it is clearly not worth any discussion. Than it is necessary to row it with transom immersed and with bow down trim and transom out of the water.
Location: Australia TAD's graph, if accurate, indicates that at slightly below hull speed, say 5-6 knots, resistance is about 50% more for the full planing hull versus the displacement hull of similar proportions. I would say there is a lot of amateur designers around boats, and some of them produce nice and good working designs. Location: Thailand This is sample of design study made last week for selection of hull shape for power catamaran. It should be noted that for lighter catamarans intersection point between red line and rest of lines (i.e. Originally Posted by Alik This is sample of design study made last week for selection of hull shape for power catamaran. Originally Posted by DCockey How was the data generated: tank test, CFD, software tools, ???
Hamilton Award Papers - Available from Naval Engineers Journal » 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 Efficient, economical low-speed hull? The 2005 IHBA season opened at Firebird International Raceway, and had all the makings of a great event.
Here is Liquid Quicker in the pits; this design is by Scott Ellison and is based on an RC Boat! Daryl Erlich started the weekend in the radical Jim Dunn designed outrigger ?Berryman Bullet? hull, but problems forced a switch to the Texas team?s ?Hot Licks? Watercraft.
All other racing had ended as the ?Plumb Crazy? and ?Hot Licks? crews thrashed on their respective machines. John White had a big boomer on his license run and due to the team's other boat having trouble, Daryl Erlich got into the Pro Nitro Hot Licks Top Fuel Hydro on Sunday. As always, there was some hot wildlife hanging out; these two were with the Jackal TAH crew!

Don Bausher in ?Big Trouble? won top Alcohol Flatbottom, the ?funny cars? of drag boat racing.
Scott Loomis in the Crap Shoot Pro Mod won the race with a heavy heart and gave all the prize money to Mike Neuharth's family. The 2005 season moves on next to the biggest drag boat race in the country at Red Bluff, Ca., on Memorial Day weekend. Location: Michigan, USA A real drag When you talk about drag, you need to specify which kind.
A general purpose sailboat, with limited Sail Area (SA), the goals are to limit drag by reducing, first, frictional drag, then wave making drag, then aerodynamic drag. Most modern sailboats have flattish bottoms, in that whatever curves they have save little surface area over a dead flat bottom.
2.) The flatter hull tends to make less waves when going through the water at the higher speeds that the increased SA allows, furthering the advantage.
Naturally, if you are going to go to that extent, aerodynamic drag must be dealt with ruthlessly, hence the low, streamlined houses and the very limited rigging. Wave making drag increases with the square of the increased speed (twice as much speed means four times as much drag) where frictional drag increases in direct proportion to the increase in speed (twice as much speed means twice as much drag). Location: Arlington, WA-USA generally for the same size sailboat, wide beam flat bottom hulls are designed to plane. Sailboats, tugboats, barges, ocean liners, submarines are all different boats with different shapes. The goal of this project is to investigate how the shape of a boat hull affects the drag force on the boat as it moves through the water. Have you ever been to a busy marina and looked at the shapes of the different types of boats moored there?
Sailboat hulls tend to be long and narrow, with a deep keel to keep the boat from tipping when sailing in a strong wind. From your background research, which hull design do you think will produce the least amount of drag? For each hull design, how do you think the drag force will change as the speed of the boat increases?
Advanced students may want to experiment with hull design software to test hypotheses before making physical models. We also do our best to make sure that any listed supplier provides prompt, courteous service. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity.
Do your background research so that you are knowledgeable about the terms, concepts, and questions.
Close off both ends of the rain gutter, but leave a small gap at one end for water outflow.
Adjust the flow rate of the hose so that the rain gutter is nearly full, with a steady flow of water. To measure the drag produced by each hull design, place the hull in the rain gutter with the bow end facing towards the hose end. 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.
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Reproduction of material from this website without written permission is strictly prohibited. It also doesn't account for the deformation of the free surface, aka waves, and changes in the portion of the hull immersed. IOW, if the slope of the transverse waves is shallow enough then you might expect things to be more in line with thin ship theory, while for hulls that generate steeper waves the trim effects will be more important. The wave profile aft cannot be supported by the hull form as the wave generated is now much longer and greater amplitude; so it squats to maintain equilibrium, just as it did up fwd at lower Fns.
Leo also mentions that potential flow wave drag is the same whether the vessel is forward or backwards.
Is there a fundamental, not just coincidence, connection between the trim changes Ad-Hoc explains and the optimum location of LCB? Frequently one such as 99% velocity is used and it appears that the boundary layer is quite thick. I began drawing what I thought may work and it began to look like a zodiac though I intended flat surfaces not round inflated ones.with a concave underside to create the tunnel hull effect. I understand what you mean about the speed of the boat that is maybe all relevant to weight the boat is much larger mass. That might work, but like jedi I don’t think you get any lift from the air trapped in the tunnel at the speed this airplane have. The wing, stabilisator incidence and engine thrust line should be set to get good flight characteristics when flying. And then you can leave the airplane as is and fly while you design and manufacture the new hull. To get the right trim angle the CG must be a certain distance in front of the transom of the hull. As I see it, with multiple hull?s it might be easier to arrange the planning surfaces to run at optimum trim angle. Produced so much drag that on plane was nearly impossible.Attachment 23195 these pictures tell a long story of trial and error taking already 8 years. If you must try a planning hull, a flattish bottom will be the way to go (like tinnie) with the centre of gravity about 75% aft on the waterline. Meanwhile they should have re-calculated residual and frictional components of resistance separately.
With sketches of general hull shape, only to have an idea of hullform variation involved, not to enable anyone to copy your designs. Last time we outsourced CFD calculations and got the resistance predictions that were 20% lower than actual. Nine of the best Top Fuel Hydros in the nation were on the grounds, four of which featured brand new, radical hull designs.
During the last session of Pro Mod, Mike Neuharth of Sequim, Oregon, in his ?Silver Belle? and Bart Smith in ?Purple Haze? tangled in a great side by side qualifier, but as they reached the 1000 foot mark, both boats encountered trouble and crashed. A full accident investigation is now underway to find out what went wrong with the capsule.
On the other side of the ladder the Lucas Oil twin turbo boat of Terry Newton upset reigning World Champion Stokes in round one, and Darrin Christle?s ?Jackal? in the semis, running a best of 5.58. This boat has gone as quick as 4.55 at Red Bluff a couple of years ago when it was the Wild Side. Don received a legal single in the final and idled down the track for the season opening win. Such hulls can surf when running before large waves and, if extreme enough, can even plane like a powerboat. So even if a flattish hull had twice the surface area of a deeper rounder hull, which, by the way it usually doesn't, it would have only 33% more drag.
It's not as smart as you are, and it may occasionally give humorous, ridiculous, or even annoying results! 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.

Analysis of tow tank tests suggest that drag is reduced by having the LCB away from mid-ships. My understanding is most tow tank tests allow the model to trim and obviously account for waves and the portions of the hull immersed. Then looking very briefly at the graph, you can see that a long slender hull shall have a lower residuary resistance, ergo, the waves it produces are less. Thus, the wave profile (after super-positioning the pressure and wave profiles) creates more ?negative? buoyancy so to speak, as there is no reserve buoyancy to support the wave profile, therefore the hull drops to find its equilibrium and trims by the bow. My hazy recollection is that does depend on any thin ship assumptions, and that it may even be valid without any assumptions beyond potential flow.
Thus, one needs to understand the mechanisms that influence rather than finding a one line that fits all, as there isn't one. You would need to calculate the thickness of various hull forms fwd and aft, and see the effects with increasing speed and then superposition them over the classic velox wave system. If so flight would be gentle and calculating as the pilot intends even in glassy conditions. A 3 inch spacer would and does fly right off the water and all this conversation would seem mute.
At low speed there would be a large planning surface extending far enough aft to keep the hull from pitching excessive up. I had a look at the picture of your hull modification on the other site, but could not quite make out the details. If designing a new hull I would consider designing it in such a way that the rear sponsons where no longer needed. With a stepped hull or multiple hulls part of the hull should be out of the water to reduce drag. Make sure to make hulls slender and not longer the neccecary for buoyancy to reduce wetted surface area. This is a long skinny mono main hull, semi circular in section, maybe pointy at both ends, with a small outrigger. If this is published in serious research paper I would look at results; once it is published in amateurish book for sailors - no need to pay attention to that pseudo-science. Red line refers to sharp chine shapes with submersed transom (about 85% of middle area); rest of lines refer to round bilge shapes and stern with slightly submersed transom. Unlike NHRA Top Fuel racing, this class allows you to experiment with all types of combinations (Boat, Driveline and Nitro percentage). Smith?s capsule ejected as designed and he walked away from the crash, but Neuharth?s boat made a violent move and tumbled without ejecting the capsule, sinking with the hull. Neuharth had raced drag boats for over twenty-five years, and had won many IHBA and Columbia Drag Boat Assn.
World Champion Jerry Kutz in ?Plumb Crazy? was declared a round one winner as Childers never left the rope. This project shows you how you can investigate this question using a homemade water trough and model boat hulls.
Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot. Larsonn & Raven in the new Ship Resistance and Flow volume of the redone PNA series have a plot of optimum LCB location vs Fn with curves from Series 60, Holtrop, Jensen and Delft. This might be part of the explanation of the discrepancy between Mitchell's Thin Ship theory and analysis of test results as to the optimum location of LCB.
This assumes a hull will be of a fixed shape and fixed Fn, always, whilst maintaining all other factors. With twin hull’s you also get a stable platform when waterborne if the spacing is sufficient. I do not like adding in the spacers that would require the removal of the hull and reattaching to fix .
At high speed only the smaller wetted area of the sponsons touch the water and the airplane is free to rotate. A hull extending further forward will counteract the initial nose down moment of the high thrust line.
The wing AOA relative the air should be positive to provide lift, but below stalling angle.
Clearly in the presence of headwinds that would be whittled down to much less than 50%, but it is a significant figure for consideration, if resistance is directly proportional to fuel consumption, which I assume it is, very nearly so anyhow.
Any competent professionally trained naval architect can tell you shape plays such a minor role. While the fuel guys were suffering early season gremlins, the other classes were in mid season form.
The IHBA rescue crew was quickly on the scene, but when they brought up Mike?s capsule it looked like it had been compromised. The first one built was Faulkerson's Nitro Bullit, which is ready to run but is inactive due to lack of $$$ to bring it out to play.
The planning surface transom should now not bee to far aft of the CG and there should be clearance to rotate the plane for takeoff. Allowable stress for the same material is different for different structures, applications etc..
Your desire, dream or belief to the contrary will not change the existing and known laws of hydrodynamics, despite your protestations.
There is a patent on a similar concept, search US patent 5277383 and Google patens allow you read it. All boats must meet the stringent IHBA safety requirements, and now include full face helmets with oxygen apparatus installed in approved driver re-enforced capsules. The rest of qualifying was called off for the day, and some classes would be paired based on 2004 points. The boat suffered some damage, but the Del Fowler led crew did a great job and would have the boat ready for round two. Actually, if you look at a traditional flying boat hull only as a planning boat, the design is flawed. The ultra competitive Pro Mod class had ten entries, led by Scott Loomis in ?Crapshoot? posting a great 7.007 pass.
As the speed build, the acceleration is slowed due to a large wetted are and unfavourable hull trim. That you have got what I would consider reasonable performance is probably because you ignored the ?traditional? design and did it your own way.
A ?traditional? flying boat hull would not perform that well unless you where very lucky with the details. The rear floatation provide lateral and pilot less stability without which the plane would end over backwards.
This plane is a legal part 103 weighing in at 300# What you are suggesting about removing the rear floats is not an option.
Next, this change make the hull wider relative the length, again something that may raise the drag until planning speed is reached. Maybe most important when you do not have an after body, the CG comes closer to the transom something that usually make a boat pitch more up before planning, again increasing drag and slowing down the acceleration.
To clear up what you are looking at see the hang cage the red painted parts under the wing are the wing mounts and represent the wings true angle of incidence ,attaching to the bottom of the wings plane. I was planning a 12 inch move forward .This could upset the CG location moving it forward as well. I am concerned that # 2 will just create additional drag without cutting away the keel and flattening the bottom. I tried to add a step blister to the hull bottom all that did was produce additional drag, so much I could not overcome and get on step. This to be able to refer to the relative position of the hull, wing, sponsons and the like.

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