DIY Rocket Hydroplane

[@Project-Air]

Ask me anything below! I will be replying to questions in this thread for 24 hours. 😊🚀🚣🏿‍♂️

[@drewdanielvaldez5478]

How did you get into science?

[@astronautnr7]

What can i ask you?

[@callisto3828]

How did you get into engineering and when did you consider uploading your projects to KZbin?

[@thegmoneygaming164]

What is the best budget 3D printer?

[@Project-Air]

@@drewdanielvaldez5478 I've just always been building and playing around with things

[@integza]

I'm starting to think I was a bad influence on you James

[@RapTapTap69]

When he starts strapping rocket motors to tomatoes you might have to copyright strike😂

[@TheSquirrelRCchannel]

Yeah ,make sure he doesn't enter tomato territory!😂

[@radium4194]

At least it was you and not me

[@pk110-_-3]

Uh oh 🫠

[@BITCOIN_69]

I love tomatoes 🍅

[@Jonathan.D]

My dad and his cousins used to build hydroplanes back in the '60s and '70s. One thing I learned from them was the faster a boat goes the longer it needs to be. You can use things like airfoils to help keep the front down. The problem with that is the airfoil is normally controlled by the driver to adjust the amount of force needed. You could try to make a fixed airfoil and do a bunch of testing until you get it set at an angle that will hopefully work. Whatever you do I hope it works out and we can't wait to see it.

[@brunorosa2227]

You could use a spring loaded airfoil, using the spring tension as a governor if you like, much like a centrifugal clutch, more velocity, more resistance (assuming the limit of deflection was a 'known') Hull length and width ratio is also known in the yachting and rowing worlds.

[@brunorosa2227]

I'd like to add, I don't know how you'd measure the velocity to act upon the the spring that governs the airfoil, that would take quite some thought i would guess.

[@Jonathan.D]

@@brunorosa2227 The limit of deflection is the tricky part. You had the same idea I was thinking. Manual adjustment with the remote would be too slow. The simplest way might be to test set angles until something suitable is found. When you're sitting in the boat you can feel when more or less is required. There are so many unknown variables due to the size and speed of this boat that make it impossible to figure out without loads of testing.

[@dailissmildzers]

Good idea with the airfoils. Culd a gyroscope be used to control the foils, springs and tension won't work due to the mad acceleration of the rockets.

[@donjonjr1]

Definitely needs to be longer for the speeds it's hitting

[@vroomtherapy]

I don't have much experience with boats, but I used to do model rocketry as a hobby. Something important to note when using larger rocket engines is that as they burn, they weigh less. This will change the center of gravity of whatever you put them in as they burn. If, for example, the boat weighs 100 grams with the rocket engine, by the time the engine has completed combustion, the boat could weigh 70 grams, assuming the propellant is 30% of the boats mass. This will shift the center of gravity forward while the engine burns, while also causing the boat to weigh less. I don't know how this could be affecting the behavior of your boat in the water, if at all. I am just pointing it out in case you hadn't considered it already.

[@emily_black6334]

Fascinating! I'm going to research this more for my pursuit of model rockets. :)

[@richardchambers256]

As you mentioned as the motors burn they get lighter. 👍 But as long as the Center of force stays in front of the Center of gravity, it will increase stability. Another thought is if you hook up your igniters in series, using a higher voltage. They will either ALL go off, or nothing at all. Saving motors incase of a bad igniter. 😁

[@tomwinchester3582]

That is a top tip. Never thought of that. Currently annoyed by a phone advert with a multiple engine water rocker launch: yes, it's do-able, but I don't think they did it@@richardchambers256

[@bonzaipineapple3143]

Just a quick thought that with the dual motors, fitting them vertically could have reduced instability even if there’s a miss fire

[@madkills10]

wouldn't that push the nose up or down in the event of a single engine failure though

[@robinvanlooy294]

@@madkills10 True, maybe he could solve the take off problem by mounting the rockets a bit above the center of the boat to creat a downards momentum a prevent taking off or it will make the boat dive into the water :)

[@bonzaipineapple3143]

@@madkills10 yes I was just thinking that might be less disastrous than a lateral instability

[@tonyennis1787]

The English Electric Lightning has entered the room.

[@peterrobinson7187]

Brilliant! I love the 'it didn't quite work so next time double the power' philosophy. Would a hydrofoil help keep it in the water? Very cool mini too.

[@collinkaufman7582]

Hydrofoil would probably go against the idea of ‘minimal drag from the water’

[@xippzap]

Thrust vectoring would fix this problem, simply angle the engine slightly downward pivoting the nose down under thrust, don't go too far or you will end up with a submarine lol. Less speed but more stability.

[@Francois_L_7933]

When I was launching model rockets, I found that the rubber plugs sometimes either break the igniter or hold too tight. The best way I found to prevent this is to just hold them in the motor with a small piece of masking tape. Also, those D12 motors probably have a parachute charge in them. Try and get some D12-0 which are designed for multi-stage rockets (and use some fireproof wadding in the boat).

[@Gnrnrvids]

A D12-0 still has the parachute charge in it, it just fires at 0 seconds of delay.

[@NicholasRehm]

The high speed shots were totally giving me mythbusters vibes, loved it

[@Project-Air]

I'll have to do more of that then! ;)

[@RideAcrossTheRiver]

I remember that episode!

[@mozkitolife5437]

It's going so fast the sponsons are acting as wings. Anything that collects air under it will provide lift given enough velocity.

[@tedferkin]

Push a brick through the air fast enough, and it will give lift

[@biko9824]

Time for spoilers it is then?

[@sircod]

What if the sponsons were at the back instead of the front, and the center point of contact moved up front? That way any lift generated by the sponsons would be closer to center of gravity and less likely to pitch the whole thing up.

[@Solnoric]

That happens with hydroplanes during races now and then

[@Solnoric]

@@sircod instead they pitch it down and it goes to pieces. The wide front narrow rear is significantly more stable, too

[@ElSelcho77]

I love your car! Was my first one about 27 years ago. Been looking for years now but they are hella expensive in good condition. Oh, nice boating content, too ;)

[@patrickcollins5752]

I bought a rusty one about a year ago, always wanted one, probably be a few years b4 it gets on the road

[@ElSelcho77]

@@patrickcollins5752 Have fun restoring this gem! I have no experience with welding, so a rustbucket is out of the question for me. Maybe I should learn how to weld...

[@thomassheldon2365]

Awesome video, thanks! To fix your ignition problems try using tapematch and igniter sticks. It’s essentially sellotape with black powder stuck to it. You can poke it into the motors, meaning that you only need one igniter. I was having problems reliably lighting multiple rocket engines, and this was a game-changer for me.

[@BimaAgungSaputra-gt4px]

2:30 nice drift you got there mate

[@w.w.2restorations.vehicles698]

When I was 16 or 17 I made a rocket car with 2 rocket tubes, tricycle wheels and a "V" tail. It would go really well with A-8-0, B-6-0 and C-3-0 engines. When I graduated it to the "D" engines, it wouldn't stay on the ground. It would travel about 40 feet then head straight up. I weighted the nose cone down with lots of lead, but it refused to stay on the ground. Nice video, thanks very much for bringing back a great memory of mine. Oh yeah, that's a great likeness of Blue Bird B.T.W.

[@darrellcook8253]

I did the same thing back in '77 and figured out how to do it without entering the space program. I kept it on the ground after I used trailing wheels in the rear behind the rocket exhaust and extended their height, bigger and thinner wheels. Also went to almost 3 feet long and went to a tricycle setup. I used D-8-0 or D - 12 - 0 motors and it turned out blazing performance. Too bad video was so dang expensive back then. Also used three tennis nets to stop it with no damage. Until I missed. Then junk.

[@calistohuettich]

Great Video as always! I reeeeally love the high speed shot of the rocket breaking up. (So dramatic) If you are having issues, I can only recommend using the Klima Igniters. They are much more reliable than the hot wire type igniters because they are encased with some sort of explosive. I have used these extensively, and have never had any issues.

[@ericlotze7724]

On this note, i was thinking you could pursue some sort of Explosive Bridgewire Detonator (EBW) / Exploding Foil Initiator (EFI) based E-Match. The EBW is especially easy given you just need a capacitor bank and thin wire if i remember correctly.

[@simonabunker]

If you go for active control you might want to look into the wand used on foiling moth and Waspz sailing dinghies. These are mad little boats! They use the pressure pushing against the wand to adjust a flap to keep the ride height fairly stable. The bonus is that it's all mechanical - no electronics required.

[@Sehraan017]

Love your CaR 2:28 ❤ Edit:And your small stunt there 😘

[@Lozzie74]

Brilliant work! I especially liked the speed check system. You’re very pragmatic about failures. Good way to be.

[@RCTanksTrucks247]

Great video! BTW I love your mini

[@rmg_lb]

Great video! Love to see you implementing some follow up projects. I guess a problem here is the motor being forced coaxial with the fuselage, so if you change the AoA, the thrust is off-horizontal. Maybe having the thrust adapter tiltable might improve stability? Really interesting to see you improve your designs, now being quite sophisticated modular builds.

[@notanengineer]

That slide with the Mini was 👌

[@jakedevries1455]

Whoop whoop! Another Project Air video! 🚀

[@james14294]

Just had the thought that ProjectAir is doing water projects 😛 for some reason that amused me

[@Project-Air]

Still involves aero though ;)

[@james14294]

@@Project-Air I guess making boats fly does count, its a feature not a bug 😛

[@TheEviling]

This is like watching Tooltime all over again. Tim Allan asking the crowd what they want, and everyone shouts back "More Power!" :) i love it

[@samspeed6271]

Savage! The correct unit of thrust is the Newton! (Joking, kg is OK, but Newtons are better) Great video

[@chrisc6537]

LOVE this channel. The world needs more of people like you my friend!

[@ShawnChristopher10101]

Curious if the "canal" you've built as a test track is adding to air pressure surrounding the boat.

[@ramradhakrishnan9382]

Great video! I think the toppling and tumbling calisthenics performed by the boat is more due to the thrust line not passing through the center of gravity, or perhaps better still, slightly above, and not due to aerodynamic effects. Also, to improve the chances of igniting both (or more) motors simultaneously, I hope you are running separate pairs of cables back to push button and power supply - essentially a parallel connection with a beefy enough battery that ensures that the terminal voltage on any igniter does not sag significantly when the other(s) suck up the juice!

[@ripwreckraceway]

the fellow knows his stuff fun i enjoyed watching ! rocket on :D or there in :D

[@LobsterBisque13]

I’ve been wanting to get into model rocketry for a bit now, but it seems really complicated. What is the best way you recommend to “enter into” model rockets?

[@monstrositylabs]

Just buy a basic model rocket kit

[@BPBomber]

Go on Amazon and order yourself an Estes rocket kit and some model glue. Once built, to launch it, you will need an “engine” that fits the rocket you built, ignition matches, a launch pad, wire, and a pushbutton launcher. You may even be able to find a kit that includes everything, I know Estes used to make a complete kit

[@iwonder1216]

Not to complicated. It's fun, so just start with a Simple Estes kit.

[@ceasarslife7535]

Thank you for posting new video... It's like waiting for Christmas it takes forever...lol.. But always worth the wait

[@Project-Air]

Haha you’re welcome

[@martinparsons1354]

Wow....glad I found this....and you drive a classic mini!! keep up the good work

[@-Tris-]

You can use capacitors charged to a few hundred volts (like a real detonator) and put the igniters in series. This will ignite every motor fast and at the exact same time.

[@mdoyle1981]

Consider the Center of Pressure whenever you're making changes to the thrust, that's a critical component of rocket design which crosses over to this project.

[@darrellcook8253]

Center of mass, center of thrust, center of pressure, center of gravity, stability depends on the center. Oh yeah center of lift. All has to be accounted for: the propellant burning and the changes to the center of gravity and subsequent changes to the other centers. Its hella complicated. But fun. (I used to be a brain surgeon and a rocket scientist but now I'm fascinated by small bright shiny objects.)

[@truescotsman4103]

We used to have rocket drag races when we were kids. We would get a toy with wheels like the steve austin $6mil dollar man rocket plane with wheels it was the best. any spaceship or any toy car or wheeled vehicle would work. You would modify it with a drill or saw or knife whatever you had using glue or duct tape or whatever. You install D size Estes rocket engines. I did three engines on the steve austin wheeled rocket ship once. Lots of fun I'm 58 now I might even try it again!

[@titogilbert2]

Something to note about the engines you were using... The red label engines shown when you loaded the two engine test were boosters... They put out a large flame to ignite the next stage when their propellant burns out, which could be the cause of your "spontaneous combustion" of the second motor during that test. For these tests you should try to find the plugged engines. (D-12P instead of D12-0) They are used to launch rocket powered gliders into the air.

[@richardstamp2410]

Years ago we used the gun powder from fire crackers for multiple engine rockets. Plug the nozzle with wadding once the igniter and powder have been added. You'll notice quicker ignition also. The max one guy was able to ignite was 24 engines in a Saturn 1B.

[@olivialambert4124]

It might help to add horizontal stabilizers at the rear for the testing. Whilst the water is so flat they aren't at risk of contacting water it makes sense. Not only will they improve the vertical stability a lot, by ever so slightly lifting the rear it would keep the nose on the ground to keep the tests working. This seems like a far better solution than altering the pontoons as the lift from them is far less consistent from waves, but also varies a ton from speed, depth, and so on whereas aero only really varies from speed. In essence, we are taking v squared out of the stability equations leaving only a second v squared remaining instead of v to the four (probably).

[@darrelldixon8056]

I did this back in the Summer of 1985, built a much smaller hydroplane out of a Estes rocket tube, "C" size motor, and balsa Hull/Sponsons. made a metal ramp at the lakes shoreline had a crowd around to watch, and after ignition watched it dive straight down under the water, becoming a rocket powered "Submarine" for a brief moment and floating back to the surface. I didn't give up though, second attempt was a cheap plastic kids "Tugboat Toy" with a roman candle firework shoved in pointed backwards.. I was told not to "Light it off by the docks" and with assistance from a friend transported the contraption out a short distance. Again with a small crowd gathered to watch I lit off the roman candle. To the amusement of the crowd the boat did not propel itself forward. it only slowly rotated a few feet from the side sending fireballs across the small aluminum fishing boat with some striking the side with "Ping, Ping" causing both of us in the boat to try and duck and take cover from the barrage of fireballs! I returned to a lot of laughter about the display...

[@carlwkemp3]

I saw one where the designer made a skimmer using V shaped wedges instead of foils. The wedges are pointed forward. This means if the boat gets too high, the top and bottom of the wedge have the same force acting on them, so it loses altitude and drops back to the water. if the bottom wedge is close to or in the water, since there is no escape out the back of the wedge, the bottom half of the wedge becomes an air ram, and the buildup of air pressure lifts the boat.

[@asteroh1875]

Ultra cool!You could make a hole inside the fuselage that resembles the shape of a car aileron, so you can have more downforce.

[@enclavegeneral2077]

Nice mini

[@Ash-nk5ix]

Sick mini dude. cool projects too

[@bbb8182]

Rapid iterations are REALLY good for inspiration! Especially for people like me with teenie weenie attention spans.

[@themixeurgaming5201]

Have you thought about using an hydrofoil design with a "wing" shaped well... hydrofoil just under the water line ? Would probably prevent it from going nose up in high thrust scenarios. Love the content, keep up the wrok ;)

[@scotttod6954]

It will also reduce water drag. Pretty sure you could have control surfaces on the hydrofoil to tune it in. Thinner the struts and hydrofoil material the better for speed. At those speeds a very small foil would be more than enough.

[@Ham_Strokers_Ejacula]

Try putting a canard or a spoiler near the nose to help push the nose down. Ya might have to scale up the boat a little more though.

[@ianhill20101]

Big up to the mini its a beauty lovely colour.

[@tubingview3251]

Had you thought about the use of a forerigger that rides on a levered arm to adjust the pitch of the vessel? As the nose rises the forefigger applies active air- or aquafoil attitude adjustments.

[@williamwbarrett]

I'd love to have your Mini Cooper! Absolutely Lovely!

[@the_viewer_0]

Amazing project But that mini!!! 😍

[@matthodel946]

All your projects are great, kudos!

[@myperspective5091]

A couple years ago I decided to make a handful of rocket power boats. Most went airborne or they went completely submarine. I found it interesting that the rocket motors worked underwater. Most of the ones that went submarine easily shot out to about 50 feet underwater like a torpedo.

[@csj9619]

I made a model dragster powered by a CO2 cartridge and eventually switched to model rocket engines. The way I kept it on the ground was by screwing eyehooks into the bottom so it can ride on a cable stretched between two spikes hammered into the asphalt.

[@mtbjonny9502]

Hi, nice Video ... - to stabilize the thrust, the pressure point should be in front of the center of gravity from your Hydroplane - In order to ignite all engines at the same time, a double system would be useful or a device where the exhaust jet of each engine also ignites the neighboring engine .. and wait (hold) for 1-2 sec. before the Hydroplane start - to prevent the boat from taking off you should build a system similar to the NASCAR that prevents the vehicles from taking off (flaps)

[@sacrificialrubber779]

Add a small adjustable wing to the front to keep the nose down!👌🏻👍🏻

[@carlosfrostygreen6855]

Thanks I never seen a speed boat 3d designed on You Tube before this one on your channel o wanna see more. Please do more of this 3d print.

[@jim-stacy]

You've made a scaled down bluebird. Donald Campbell would be proud!

[@queteimporta67]

Cool project. You have an awesome car

[@janhanchenmichelsen2627]

There is a reason for why hi-power boating requires a very skilled and delicate touch regarding throttle input, trim and steering. :-)

[@gustavocarvalho4919]

Maybe a channel in the hydrofoil could work, it can keep the boat lower without increasing too much drag. As the contact area would be smaller, the boat can stabilize closer to the water

[@dextrodus]

2:25 you just peaked with that shot.

[@itsCN]

Been waiting for this, great job

[@whoever6458]

My friend made a really big model rocket when we were young that had 4 D engines to launch it. She was all proud of it and gloated at all the rest of us who had the small rockets. But, when she went to launch it, only two of the motors ignited, the rocket went up just a little, then flew sideways, and finally lodged itself in her tent like a dart. It was SO funny but her mom was mad that she screwed up the tent. The rest of us had ours all packed up when we were actually launching our rockets.

[@phoenixbda6164]

this was uploaded on my birthday. Yay?

[@jaleemasangma2820]

Wow amazing

[@kevkev5935]

This was awesome.

[@JoeOvercoat]

The test rig is awesome.

[@DrewTeter]

What about using hydrofoils? It might let you avoid needing active controls if you have multiple foils set up in the right way. I'm thinking stacked on top of each other like a tri-plane, though google also shows single foils in a V-shape. - Boat rises too high? The bottom foil is pulling the boat down. while the other foils are above the surface. - Boat too low? The other foils are submerged and provide additional lift. - Boat tipping over? The foils on the low side are submerged and right the boat automatically.

[@DrewTeter]

Oh, wait. I just realized you'd have to deal with off-center forces of thrust. That additional torque complicates things. Might still work though.

[@lunkydog]

That's a nice looking Mini.

[@Casualgamer3789]

Very cool vid :) love the content and i can tell you put in a lot of effort into this vid :D

[@oliverscorsim]

I think some small adjustable spoilers front and back would fix this. Loved the clip with the f motor keep it up.

[@saywhat8635]

Packing some black powder in the rocket nozzles and then some between the motors will allow you to use one igniter. You are pushing the motors through the centerline and cg but straight forward, you need to push through these but at a slight angle downward and slightly ahead of the cg, that will help push the sled into the water while accelerating.

[@ScienceOfProject]

Amazing experiment

[@Kithkanen]

I would recommend not altering two variables at once between test runs. At one point, you changed the angle of the front "skids" (for lack of a better term) *and* added a second motor. You'll get more consistent, reliable information by changing one or the other, and then making further adjustments or additions later.

[@outrageousalan7780]

Very nice classic Mini.

[@DCDLaserCNC]

Love the old Mini!

[@ezrarichardson279]

you should make a rocket powered hydrofoil boat next!!!

[@alohafruge]

If you're still trying to make this work I would suggest designing I spoiler or something like hydrofoils instead of a fin on the back of the boat. It would allow for better control of the airflow that keeps making it wanna fly

[@TexMex421]

Awesome video! I've seen a lot of these rocket boats before, and they never work too well. It always seemed to me that you should build a fast RC boat and when it was up on a plane, use the rocket as an OMG booster.

[@aarongunner1711]

There should be more of the Mini!! 😁👍

[@FTATF]

You have to adjust the bow from the stern. When you get the bow bounce you need to push the stern up. Typically this is done with an engine or trim tab but in theory you could use some sort of spoiler. You might even be able to get it to self adjust mechanically.

[@theboreditamar2108]

2:17 im proud of you

[@5-Consecutive-Hairpin-Turns]

the zero dislikes shows speaks to the quality of this channel

[@Ev-wj3lm]

Hum well...

[@5-Consecutive-Hairpin-Turns]

@@Ev-wj3lm i was using return KZbin dislike so i was able to see the 0 dislikes

[@Ekansh_Dadheech]

big fan , love your projects

[@ctvaughan6623]

Project air: “I’ve taken lots of safety precautions” Also Project air: Launches flaming rocket engine into dead grass ( 3:58 )

[@youtubeSuckssNow]

I dont know if you've ever been around slodgy snowy icy slush mixtures, but its wet. Very very wet. You can even see in the video that yes they might be dead, they are not dry.

[@ctvaughan6623]

@@youtubeSuckssNow I understand that it wouldn’t have started a fire because the grass wasn’t dry. It was really more of a joke than pointing out danger but you have to admit that it’s kind of funny that he said he’d taken a lot of safety precautions and then he proceeded to launch a flaming rocket boat off of his track.

[@MysterWacht88]

What filament brand do you use on your printers, it looks as though it works well with the ender 3

[@whoever6458]

I liked your drifting in the snow in your car. lol Cool! I accidentally drifted in my car when I was young on a sunny day because I had some heavier people in the back. Somehow I was able to instinctively drift in my lane right around the corner. Everyone who was in the car with me was upset with me but at least they hadn't needed to take the slow ass bus where they wanted to go.

[@tomcline5631]

Well first thing I noticed,your track needs to be about twice as long. The booger was still accelerating as it blasted through the snow pile! Another thing you might want to try is a flatter hulled boat. That cool looking bluebird insired rig you have there just sticks up to far. Flatter hulled lower to the water,maybe try a tunnel hull for the stability. The twinengines should be stacked not side by side,to keep the center of thrust consitant. I've done most of these experiments years ago with boats I made out of bass wood. Shot em on a buddy's pond. Just a completely fun day!!!

[@wmason1961]

I love your car. I have 2anted one since the 70s

[@connor1424]

You have a beautiful car! Also, great video btw

[@connor1424]

Also, maybe the body of the boat itself is the issue with it flying? From what it looks like the body starts acting like a wing, might need more frontal downforce to keep the nose down.

[@MirlitronOne]

About 20 years ago, I helped my son and his schoolfriends to build a rocket-powered boat for a class contest. To my surprise, the school approved it for a test in the outdoor swimming pool, which was enclosed in wire netting. I was so concerned that it shouldn't take off that I designed it with some downforce from the airflow. The result was spectacular - the boat shot forward about one metre, then dived to the bottom of the pool with the rocket motor still burning. It finally bobbed back to the surface a little more than one metre from the starting point, and was awarded a special prize for "Least Distance Covered By Any Entry." It was, however, a most spectacular failure!

[@pw383426]

I just started the video. I wonder if a round keel and sponsons would help with stability. I know it's a trick we use on circle boats

[@Sniperboy5551]

You should add a tail “spoiler” to keep it in the water. That’s what they use in high speed boats to keep the rear part of them submerged.

[@MCsCreations]

Wow! 😳 Fantastic work, James!!! But I guess you need a slower burner. That's too fast. 😬 Anyway, stay safe there with your family! 🖖😊

[@thomashogg2341]

Try angling the rocket motors slightly down at the rear so the thrust is putting downward pressure on the bow.

[@joenagel6644]

Look into hydroplane racing boats. They use an active front splitter controlled by the driver to control the nose of the boat. They can add downforce to keep the nose down and reduce it during straight runs to increase top speed. Some sort of strain gauge in the rod holing the front floats in conjunction with an accelerometer/ gyro to keep it under control?

[@TarickWalcott]

Crest 3D white strips......love the videos btw 👍🏽

[@firefighterforlife6673]

Have you ever messed with using sand as infill? Half print then fill the voids with sand or spray foam then recenter and reprint the rest? I have seen a few good ways of balancing using this method with placing bolt washers in front he voids

[@SmokeBros42069]

You could probably use some ballast or a small lead weight in the nose cone to help keep the craft on the water

[@jeimasuta_v598]

Been waiting for this

[@3DPDK]

Ground effect! It's not the pontoon's contact with the water that's lifting the nose, it's ground effect - essentially a cushion of pressurized air between the hull and the water. This is the main reason modern racing hydroplanes use a horizontal stabilizer, sometimes on the front of the boat but more normally at the rear. As speed increases the stabilizer begins to push the nose downward into the cushion of air. It's a delicate balance; pushe the nose down too much and the boat plows the water, not enough and the boat does a back-flip.