Science Abuse Posted January 17, 2006 Report Share Posted January 17, 2006 Eric, a boat is always "accelerating." Always has a load on it. Never coasts. That is everything everwhere always. If you look at the aerdynamic signature of your average speedboat, you'll find the drag coefficient is comperable, if not less, then you average drop top car. Moving through the air, that thing was a miata. Now, you have the hydrodynamic drag of the water, which is a significant force, yes. But when a boat like that is up to plane, it probably has about 6-10 square feet of contact with the water at most. The amount of drag on a boat at 16 is much less then a boat at 20. So wht is it that hatchabck festivas can hit 100 mph with 100 hp, but a boat like in the vid needs 500? Because boats are screwed, litteraly. You use hp much more efficiently when you're driving wheel. When you're putting it down through a pair of screws, inefficient isn't even the word. Put a diff and some wheels under that boat and it'll do way more then 100mph on the highway...if it dowsn't lift off the ground. You're speed on the water is reliant on your screw design and how fast you can spin it. If you have a singly drive, 3 screw tranny, you need a bunch of torque just o spin the gears and overcome the parasitic loss, hens to offerings that Joe mentioned. For something small like what is in the vid, the motor should have no trouble spinning a single, or even a double screw setup sufficiently. In reality we shouldn't even be attempting to discuss this untill we know what power the boat in the vid actualy makes, anf if its spinning a prop or jet drive. Edit: http://www.xtremerotaries.com/main2/Quicksilver.htm That video is of an Australian built boat being tested in Melbourne.Here is a bit more info on it... Oh yeah and people actually do ski behind this thing! Im not sure if theres much more left in it, thats a hell of a lot of revs from a 20B, im sure Cobalti from Melbourne on this forum could shed some more light on the subject. Hull – Kevlar 1850 bullet, Bravo 1 XR leg Driver – Paul Browne, Observer – Craig Browne Skiers – Scott Browne & Craig Dove Engine – X-Treme Rotaries 1962cc 20B (3 rotor) rotary engine, bridgeported, turbocharged, fuel injected Horsepower – 800hp 9500rpm 615 ft/lbs torque Speed – max 120mph 9650rpm Tuning – by Anthony Rodrigues, Maztech of Melbourne Turbo – Garret GT42 1000hp Fabrication – Rohan Ambrose (X-Treme Rotaries) & Paul Browne Intercooler – PWR barrel water to air Heres another video http://www.xtremerotaries.com/main2... 20footage.wmv And some pictures http://www.xtremerotaries.com/main2.../Engine.lge.jpg http://www.xtremerotaries.com/main2...ngine.2.lge.jpg http://www.xtremerotaries.com/main2..._parade.lge.jpg Quote Link to comment Share on other sites More sharing options...
Bahnstoermer1647545488 Posted January 18, 2006 Report Share Posted January 18, 2006 WOW, that looks like way too much motor for a boat that small. I remember a few years ago asking on here how a rotary boat would do, and everyone jumped my shit about it failing due to lack of TORQUE....I now see that's not a problem. That's because people here are retarded, and don't know things like the fact that acceleration is proportional to the HORSEPOWER made at any given moment in time, and NOT TORQUE. Stupid hurts, and propogates itself like a bad VD. That boat was BITCHIN. Oh, and listen to Benz guy. Intelligence is rare here Quote Link to comment Share on other sites More sharing options...
Total Sign Posted January 18, 2006 Report Share Posted January 18, 2006 If that does 120 I will be very impressed. Quote Link to comment Share on other sites More sharing options...
ShoMeSomeFun Posted January 18, 2006 Report Share Posted January 18, 2006 Shit 50 mph is fast on the water, i cracked my ribs goin that fast but the could of been the skis kickn my ass as i lost my balance. Quote Link to comment Share on other sites More sharing options...
Nitrousbird Posted January 19, 2006 Report Share Posted January 19, 2006 That's because people here are retarded, and don't know things like the fact that acceleration is proportional to the HORSEPOWER made at any given moment in time, and NOT TORQUE. Stupid hurts, and propogates itself like a bad VD. That boat was BITCHIN. Oh, and listen to Benz guy. Intelligence is rare here Because I'm sure everyone on here assumed an 800 HP 20B (which is no where close to a 13B, in both size, power, and PRICE), and I'm sure no one assumed that rotary would be going in some small boat either. Want a fair comparison? Toss that rotary setup (which is freaking huge) into the boat doing the video taping on the second video posted. There's a fair comparison.....I bet that rotary would have a LOT more problems w/ that boat. Torque gets a boat on plane, especially a big boat; PEAK HP doesn't mean crap when trying to get a boat on plane. That same video w/ a built N/A pump gas BBC would have had the same results. Quote Link to comment Share on other sites More sharing options...
ChevyMan1972 Posted January 19, 2006 Report Share Posted January 19, 2006 If you look at some of the pictures on the site from the side of that boat, you will see that it is clearly an outdrive. No jet anywhere. Dan Quote Link to comment Share on other sites More sharing options...
SPLN SUX Posted January 19, 2006 Report Share Posted January 19, 2006 Wow, lots of info smearing here. I grew up around boats so maybe i can shed a little light. First... that boat is doing somewhere in the neighborhood of 100mph. Ive looked back at 85mph on a bass boat and it didnt look near as harsh as that... however, the turbulant water coming off a outboard, inboard, sterndrive (aka I/O), and jet drives all look different. Also, we have to think about the hull of the boat. Unlike your everyday cabin cruiser, this boat is not a Deep Vee hull. Its not even a shallow Vee hull like your bow riders, its whats called a drag vee. The depth of the hulls actully decrease from bow to transome. At the front you can see a good 2 or 3 ft of vee, but near the transome that will cut to about 18in.... just enough to keep them strait whilst riding on the back 36in of the hull. On the information page, on the "Hull" section, you see the words "Bravo 1 XR Leg"... this refers to the drive it uses. Now though im unsure what the XR Leg stands for, the Bravo 1 is refering to a stern drive most commenly found on Baja's, Cigerette, and Donzi boats. On most Sea Rays you'll find a Bravo 3 drive... and then you have the occasional Volvo CRP drives. The Volvo drives use two counter rotating props to get a boat on plan almost immediatly... faster than most inboards ive seen (ski nautic, etc). Anywho... think of the Bravo 1 drive as like... a Powerglide. Its the baddest thing you can stick on the back of a boat in the means of stern drive units, and all the fastest prop driven boats use them. On the dash youll find several things... only 3 will have anything to do with the engine though. The center guage is a tach. Youll also find a oil pressure, and possibly fuel pressure guage. The fuel level will be there and the other two are most undoubtedly for the trim tabs(dual sided gauge usually) and drive angle. I guess boost could be there too, but id doubt it. The idea to making a boat go fast is the same as a 4cycle go-kart... RPMS. Because there are no gears, the mor rpms you can turn, the faster youll go. Now with a big block you can turn some big ass props, but race props usually arent all that big. Most that youll see on the end of the shaft of a hydroplane, are maybe 16in in diameter... they dont need to be big. They are also 2 bladed. Once the prop gets to a certian point, they tag another blade on. These arent the spiraling props on jet skis, the round edge cruisers, or even the shaved edge bass boat props (awesome roostertails btw), these things are RAZOR SHARP.... and polished to a MIRROR shine. In this case, im happy to see someone running a rotory. They can use the engine in the manner it operates best... high rpms, constant load, and in a nice open engine bay for good cooling (though it still uses a fresh water system). These guys, are the bad mother fuckers of boats. Much respect form this corner PS Most 4 cylinder engines will run around 40mph... the fastest one ive seen (and it was almost 20yrs ago), was 42mph. It was an Imperial VC200. Many boats now use Ford crate 302ci engines. 300hp, start easily, great for pulling a skiier. Quote Link to comment Share on other sites More sharing options...
Total Sign Posted January 19, 2006 Report Share Posted January 19, 2006 Somewhat correct. The baddest thing you can stick on the back, IMO is a Mercury #6. Designed by Carl Keikhaefer, rated to handle 1000+ hp/ 1000+ TQ. Many people are running more power through one, the RIO ROSES Fountain (V bottom kilo record holder at over 170mph) had twin Sterlings putting out over 2000 ft/lb. The standard bravo will handle around 700, if you baby it. The Xr is a beefed up Bravo. Strait cut gears, thicker upper case, a lot harder to break. There is a difference you can hear between a standard Bravo and XR when running down the lake. A loud buzzing sound. The Bravo 3 also uses counter rotating props. No one marinizes any ford engine. PCM used to use the 351, for Nautique, but right now PCM has 2 350's (one is 330hp, 430 tq) and a 6 liter (375hp, 492 tq). On speed, no it is not RPM. You can change the props pitch. Pitch is theoretically how far it would move the boat forward with 0% slip, in one revolution. Gear ratios in the upper unit of the drive can be changed (Bravo one can be 1.36, 1.50, 1.65). The smaller the number, the more power it takes to spin, so a smaller prop will have to be used. The higher numbers accelerate better, but must have a bigger prop. You control the RPMs by putting a prop on with more pitch. Most marine engines are built to run 5000-5200 max RPM. Polishing weakens the blades, meaning more slip. Fun fact, the standard Bravo 1 retails for a little under 9k. The XR is about 13,500, and the Number 6 (which is not a shiftable drive like Bravo's, and price does not include the 15k transmission) I cant remember retail cost, but my dealer cost is over 35k. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted January 19, 2006 Report Share Posted January 19, 2006 Apples > Oranges Quote Link to comment Share on other sites More sharing options...
Casper Posted January 19, 2006 Report Share Posted January 19, 2006 You guys can keep arguing about the "physics" of it. Neither of you have physics degrees. Neither of you have aquatic engineering degrees. Why can't you just enjoy what they have done? The boat is fucking awesome. That is all there is to this story. Quote Link to comment Share on other sites More sharing options...
Science Abuse Posted January 19, 2006 Report Share Posted January 19, 2006 Because this is the internet, Ben. We must do battle, it is written, now and forever for eternity. Joe...who cares what it'd do in another boat? Its not in another boat, its in that boat, and apparently its winning trophies in that boat, IN a class with a 5.2 liter cap on powerplants. I.E. Its faster then other BBC boats in its class. Quote Link to comment Share on other sites More sharing options...
Casper Posted January 19, 2006 Report Share Posted January 19, 2006 5.2 litre big block chevy? where? 305ci = 5.0L 350ci = 5.7L Quote Link to comment Share on other sites More sharing options...
Casper Posted January 19, 2006 Report Share Posted January 19, 2006 Because this is the internet, Ben. We must do battle, it is written, now and forever for eternity. Joe...who cares what it'd do in another boat? Its not in another boat, its in that boat, and apparently its winning trophies in that boat, IN a class with a 5.2 liter cap on powerplants. I.E. Its faster then other BBC boats in its class. http://www-personal.engin.umich.edu/~edaigle/retard.jpg Quote Link to comment Share on other sites More sharing options...
SPLN SUX Posted January 19, 2006 Report Share Posted January 19, 2006 Neither of you have aquatic engineering degrees. Since when do they have a school for water boys??? Quote Link to comment Share on other sites More sharing options...
Casper Posted January 20, 2006 Report Share Posted January 20, 2006 Since when do they have a school for water boys??? Google "aquatic engineering". Quote Link to comment Share on other sites More sharing options...
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