... Desired Cruise Speed (in statute MPH) This calculation is only valid for planing speeds! Then hydrodynamic drag is less because there is not much in the water but then the wind resistance is kicking in and you put more of the boat in the water to keep it from blowing over. They also tell you that it is only a guess at best. Boats moving off the coast of seal beach at the same time 2pm. So 1 to 1... sometimes... roughly. With a set of 2:73 gears, top end was limited by air resistance/tire resistance to about 140 mph. Still have questions? As an example, I once owned a '71 Cuda, 383 cid, factored by the NHRA to 310 hp, having a 3100 lb vehicle weight including me and 4 gallons of gas. If I remember right he said it gave 5mph or so. For example, your homeowner’s or renter’s insurance policy will usually cover smaller powerboats with less than 25 horsepower. For example- if you'd like your rig to go 10mph faster, is it less expensive to just buy a bigger engine, or should you keep your existing engine and spend the money on a racing gearcase, or should you keep the existing engine and buy a new hull? ....but I think your situation is most interesting. With a set of 2:73 gears, top end was limited by air resistance/tire resistance to about 140 mph. could you expect to go? A square barge, for example, will have more bow friction with the water, and since you have to push water out of the way to move, the amount of water you push adds load to the engine. While a jack plate will not make an outboard motor faster in and of itself, it will … There are so many factors that affect boat speed that it is hard to make accurate estimates of what the real top end will be. My son seems to think that if he trades up his 150 Mercury to a 200 he will see a gain that will get him above 60mph. The cushion thickness has to be small, or chine walk could become dangerous. Horsepower for an engine is actually a curve, and not a single number. Be careful with this much added power all at once, or as I recall Brits like to say, you'll be "c***-up. As such, if an engine has a gear ratio of 2:1, the engine drive shaft will turn twice for every propeller revolution. When equipped with 250- or 300-hp outboards, these types of aluminum fishing boats can typically have a WOT speed of 55 mph to 60 mph, or a bit more, with two people aboard. He never mentions running the same ratio, prop or even wanting to turn the same Rpm. This should require much less power. I don't think there is a formula to cover all of that. The cube root of 1.333 is 1.100 in this example. Props, jack plates, it goes on and on, ECT, ECT. OB,and STAYLOR, Neither is going anywhere without a gearcase ratio and prop pitch. All of this assumes your drive unit remains the same, and at speeds of this level lower unit drag is significant. With the 200 he is turning a 24 S/S @ 5800=60. The issue on your rig is simply- will this improvement from the Duo-props offset the drag at 100+ speeds? Well the numbers are in and with the extra 50-horse power he went from 54 to 60 mph. Some 90-hp engines in 18’ aluminum boats with two people aboard will perform almost as well at cruise and have a WOT in the low 40s. Since I am of course biased towards my equation, I would suggest that with a bit more detail in set-up you can still hope to get close to 61 mph under the stated load conditions. I do feel that the Duo-Prop should yield much better control at 100+, and on your hull this alone may well prove to be a critical requirement. I had ancestors in the King's Navy back in the age of sail and family lore has it that at least one Taylor ended up this way after his ship took a broadside from a French Ship of the Line. Horsepower is only an indication of power of the motor, and many other factors including the shape of the vehicle, the weight of the vehicle determine how fast a vehicle can travel. by the cube of H.P. This has interested me for about a year. And speaking of Phoenix, the boy was on his game for sure. I was hashing through some old posts here one day on props...might have been a Ron Hill post, but someone said they have setup duoprops with more pitch on the aft prop for performance applications with success. Engines that have a smaller horsepower will have a higher ratio in the region of 2.33:1. My observations with respect to boats are that as a planing hull increases it's speed it comes out of the water and enters the air- thus changing the density of the medium creating drag. That said, what you have to move affects speed. MPH = C x ( HP / LBS)^0.5. With all things being equal, I am betting on a six MPH gain with the additional 50HP.................;). I believe the gear ratios are the same. Simply put, it’s typically a good idea to get an outboard motor with the maximum horsepower recommended by your boat’s manufacturer, says Discover Boating. :p Boat style is of most concern, best to move up to better style that Airs Out.;). I do know one thing though there is no cure for the need to speed and that speed will always win. When you are going 40 mph it takes less hp gain to increase speed 1 mph than if your are going 90 mph. A 9.9hp Briggs and Straton motor has a top fluid flux leakage rate of 1.6 ml/hour. Using these formulas, Toy Boat 2 would need somewhere between 90 – 136 HP. Rig is rated for 175 and weighs around 1000 dry w/o motor or trailer. Matching the correct outboard horsepower for your boat is probably the single most important factor when buying an outboard engine. The federal government regulates the horsepower of outboard motors that can be installed on boats. Dangers of Overpowering Your Boat. In your case, it is a boat, so a couple of factors will affect the speed you can achieve. I will update on the top end once dialed in. The only tests I've seen are at 40 knots or less, and they showed the Duo-Prop to be slightly faster. Although its original purpose was to compare the output of steam engines with the power of horses (hence its name), it has since been adopted as a unit of measurement for all sorts of engines used to power things such as vehicles, lawn mowers, boats, chainsaw, and airplanes. a 2.5 280 is (because of its power curve) still making the same tq at 6000rpm, but its still climbing to its tq peak at 7500. therefore, in the upper revs as you are going faster, there is more TQ there to counteract the extra hydro/aerodynamic resistance. Horsepower is a unit of measurement of power developed by engineer James Watt in the late 18th century. "Give that man a Hooters Girl" See what happens when you study hard and pay attention in "guess" class.....;) Hell it had to be "Guess" class, I failed every thing else. For instance, on a non-planing hull like a pontoon boat, I have seen a 50 hp increase result in only around 2mph. HI. Of course there are also many potential problems with this type of lifting concept. Is the blue star lines titanic 2 finally setting sale for the original voyage that the first titanic had went on this year? In the boat world, it really depends on the weight of the boat, the aero dynamics, water conditions, wind, etc. Now compare this to a car, where top end is limited by air resistance and rolling resistance of the tires. according to the speed calculator program I use, he will hit about 70 with a 200 hp if he hits 60 with a 150. A pad boat shows this distinctly as it lifts up on the pad- a little bit of added throttle and all of a sudden you have a disproportionate gain in speed- all due to essentially a modified step wise alteration in drag with velocity. They had Big tanks 10 by 15 by 100 feet. If they ffl is greater than the hp of the engine then you really should just consider getting another engine. Along the lines of what very tricky said- I think that more than raw HP, the RPM of said power, and where the tq curve is, has more of an effect on speed. Small change in speed unless ya lug the motor to raise the speed, keep in touqk range. In any event, since both of these schemes essentially entrain the air into the boundary layer at the water-hull interface, you usually end up with a water-air mix which still has a lot of skin drag. This shows how significant hull, skin, and lower unit drag is- and the detrimental effect it has on top end boat speed relative to a vehicle in the air running on tires. The Russians managed to make this work pretty well with some of their torpedos. How Much Horsepower Do I Need for My Boat? It happened back in 1978 when a speedboat used a jet engine (instead of a propellor) to power the boat. Thanks, Ed. I have heard some say they wanted to try a yamaha 150 duo case on a merc, on a small hull, for balance. HI. Using my equation of the average between the cube and the square root takes you from 54 mph to 60.8 mph. Thanks, Ed. If you’re curious to know what the largest engine you can legally put on your boat is, try this calculator. In many cases it can save a lot of money wasted on alterations that produce only insignificant gains. If you are talking about something like a Jonboat, with one person in it, and no other cargo than fuel, I would guess your 9.9 horsepower engine might manage about 15 miles per hour, maybe even 20 mph if you are not terribly heavy. In any event, with 115 horsepower and proper pontoon set up, you can expect comfortable tubing speeds with a crew in the boat… a pretty nimble pontoon boat! A pontoon boat with a 200 hp engine will not go as fast as a speed boat with a 200hp engine due to the coefficient of drag. where. So overall he gained six mph with the extra 50 horses. My concept was to add a series of vent holes to a small flat section at the aft end of the pad on a pad-vee hull. Join Yahoo Answers and get 100 points today. As Prof.O/B and I both agree- his equation is more conservative, and mine is more optimistic. But my concept assumes that the boat is at speed, and the hull is already pretty well aired out. When this happens, the cube root relationship becomes excessively conservative. He right now is stuck on 60 but can’t break through. perhaps not a single formula, but there are known factors that can be computed. I have been struggling with the various answers in order to obtain a speed I wanted from my boat. A hydrofoil craft avoids this problem by having a second low drag hull form- a form of wing- which is the hydrofoil itself. ...thats worked for me over the years with just about any hull when adding power. But engines that large and expensive aren’t required on a 16’ to 24’ aluminum fishing boat. The Square Root of (Total Shaft Horsepower / Weight ) x Constant = Speed Depending on the hull, I thinks it more like 1mph gain for every 12-15hp. Doing the math can inexpensively predict which is best for any particular situation- and the solution is different depending on what you're running. John Loo 2017-08-13T21:34:25-07:00. Estimated Horsepower: This calculation is only valid for planing speeds! to relative to speed. Such is the nature of research. Speed Gain: 2-4 mph. Thanks, Ed, Well I would love to help you but in all honesty I am a novice in these matters. How would you change the values with horsepower to MPH when a hull breaks free at 80 mph to 90 and only takes 10 more horsepower to do it. Then going from 100 to 120 takes 50 more. How does one salvage an RV from the bottom of a lake? For boats it is an entirely different story. (ii) For boats capable of 35 miles per hour or more, the maximum horsepower capacity must be the maximum horsepower with which the boat was able to successfully complete both the Quick Turn Test Procedure in § 183.53(b)(4) and the Test Course Method in § 183.53(b)(5) at full throttle or the calculations in § 183.53(a) of this section. The thing that got the RAF to pay attention was that that's about what a Rolls Royce Merlin was producing in a Spitfire at the time. Naiscoot. If … 'Gear ratio' defines the number of drive shaft revolutions per propeller revolution. For any motor where fluid flux leakage (ffl) is less than hp you square the horsepower and divide by (hp/ffl). If it's only rated for 150, he's going to run into serious problems with insurance, plus a lot of states have very strict laws against over powering a hull. Really makes you wonder how much HP it takes to push a STV at 150mph.... why would a 200 have less torque than a 150? He just simply asked if there was a formula for determining speed gained by upping horsepower. So we can say that under limited circumstances it's about 1:1. Is it rated for 200 hp? Install Jack Plates. Going back to the math equations that Prof.O/B and I suggested a while back provides the following results: Going from 150 hp to 200 hp with Prof. O/B's cube root equation predicts a speed gain of 10 percent, this takes you from 54 mph to 59.4 mph. Using my more optimistic relationship of mid-way between the cube root and the square root indicates 1.33 times current speed, or 106 mph. You guys that are debating this have made me think about it. Heck, I made this absouletly startling guess and don't win anything. This weight is the total loaded hull weight with motor, gas, people, and gear. Otherwise, without such a "skirt", the air volume required from the gas bottle would deplete the tank too quickly. As Mark75H said, most of the algorithms for performance of vee hulls and tunnel hulled boats have been worked out in the book "Secrets of Tunnel Boat Design (http://www.aeromarineresearch.com/stbd2.html)", and the Performance Analysis software (http://www.aeromarineresearch.com/tbdp6.html). It was by Nigel Warren circa 1978. a good example is between the HP mercs and the regular ones. First you have to look at the website or information provided by the motor manufacturer. The same as airation, you are just sinking the boat lower till it gets lift from the outter hull, better stable but I don't think speed is the gain. Again not necessarily true .... if the difference between the 2 hypothetical motors was compression or cubic inches the 200 would be torque, torque and more torque .... holeshot and top end. If you want more, port it out, cut the heads and jet up, spin to7,000 and don't look at the gas gauge. When I calculate this. The formula you used with speed varying with the cube root of the horsepower change is derived from a simple sum of the forces on the hull. example; if you bought a 9.9 hp boat motor,how many m.p.h. Scream And Fly Powerboat and High Performance Powerboating Discussion Forums. Boats that are larger and have more than 25 miles per hour horsepower almost always require a separate boat insurance policy. Yes I am assuming the X hp motor is ported to make maximum safe warranty-able consumer X hp at what is usually the lowest reasonable rpm it can to have more longevity. I agree with your conversion from knots to mph, so we end up with Prof.O/B's equation giving 100 mph, my equation giving 106 mph, a similar boat with not as good a drive running presently at 103 mph, and the hull designer feeling that it should top out at 109-112. They put scoops on the bow and piped the air back to the pad. P O/B, Please, Rodney needs no encourgement to put high octane in his tank! if his boat is doing 60 now with 150 HP,I'sure he'll do more with the 200!IMHO. I advised him to take the 150 and up it to 200 but he insists on a newer engine. Terry Taylor, I have read and re-read the original post and I don't see where Efishzion ever mentions ratios, pitch or Rpm. There are 3 primary drag loadings on a hull, these being form drag, appendage drag and skin drag. You could have two identical vehicles with the same hp but one has 3:11 gears and the other has 4:10 gears, the 3:11 gears could essentially reach a higher top speed before the rpms run out. Wife of drug kingpin El Chapo arrested in Virginia, Pat Sajak called out for mocking contestant, Woman’s license mistakenly features her in a face mask, Top volleyball duo boycott country over bikini ban, 'Bachelor' hopeful suffers horrifying skydiving accident, Jobless workers may face a surprise tax bill, Raiders player arrested in Texas street-racing incident, Congressman puts right-wing extremists on notice, Actress confirms engagement to NFL star Aaron Rodgers, The good and the bad in Biden’s giant relief bill, McCain stands by Fauci criticism: 'I'm not a phony', http://www.caravelleboats.com/propeller%20info.htm. As such is usually a little skittish, but it has a deep leg and the drive is very low in the water. One of the difficulties is that when gas turbine cores are put to other uses they are often run at more or less conservative power levels. So a 600hp V6 would be capable of going 400 miles per hour. I appreciate all the help and I will update this post with further tests. and top speed is how you benefit.from adding H.P. It uses the federal regulations to compute the largest outboard engine you’re allowed to install. For a deep-V hull: Total Weight / 25 = HP required to drive the boat at 25 mph, at a 75% throttle setting. The constant, on the other hand, are typically calculated from private tests. Hence, I submit that for planing hulls, the actual change is between the cube root and the square root of the change in horsepower. Again, this is a condition caused basically by drag not following the velocity squared relationship, and the cube root relationship will not apply, in fact it becomes very optimistic. The Russian torpedo I spoke of apparently uses relatively high pressure gas, especially since it must work at great depths, with ambient water pressure somewhere in the 50- 500 psi range- or maybe more, since 500 psi is roughly equivalent to a 1000 ft depth. I don't know if Fountain was aware of this, since Custom craft was a regional manufacturer of high performance cats and tri-hulls, back in the day when twin Mk75-Mk78Mercs was as good as it got on non-race hulls. Thanks, Ed, The 'thumb suck' I was told was that doubling your horsepower increased your speed by 60% up to 100mph. I appreciate all the help. The Alumacraft Edge 185 Sport is a multi-species fishing boat with an aluminum hull. I guess you can use a different pitch propeller. When the hull speed is reached, you can double or triple the horsepower- and very little, if any, additional speed is obtained. 1 Metric horsepower = 0.9863 Horsepower: 10 Metric horsepower = 9.8632 Horsepower: 2500 Metric horsepower = 2465.8 Horsepower: 2 Metric horsepower = 1.9726 Horsepower: 20 Metric horsepower = 19.7264 Horsepower: 5000 Metric horsepower = 4931.6 Horsepower: 3 Metric horsepower = 2.959 Horsepower: 30 Metric horsepower = 29.5896 Horsepower: 10000 Metric horsepower = 9863.2 Horsepower The lady was a bit inhibited but after a few belts of Rodney's home elixer, she performed much better.............maybe that is a bad choice of words................. Efishzion, we have given us a very good "heads-up" comparison by not changing the engine heights, etc. Also are the props rotating to lift the bow? I read the description you obtained from the Duo-Prop guys carefully. The shaft horsepower is determined as the engine horsepower without the losses of the drive train. Plus, when you are “light on crew,” you can expect a rather sporty toon experience… you’re not going to break any speed records, but you are certainly going to be able to speed along in the high 20mph mark and will feel rather agile doing so. He claims speeds in a couple of places, but the other three variables are never mentioned by him. Even a compairson of maximum horsepower (I'm assuming the number you're looking at) is not a good indication of how fast a boat will go. With the 150 he was turning a 22 S/S @ 5800=54. Get your answers by asking now. This only works with Russian cars. On one side of the equation is the propelling force generated by a known amount of horsepower moving an object at a certain velocity. The entire post is interesting reading and very informative, and I'm not trying to be an a$$, but what's your deal with the ratio, pitch, rpm scenario.

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