Topic: Water Jet experiment and Jet boat build (Read 3515 times)

Martin (Admin) · « **Reply #35 on:** March 26, 2012, 03:17:55 PM »

Topic Name changed ...... to protect the innocent.....

Sub driver · « **Reply #36 on:** March 26, 2012, 03:56:36 PM »

It will be interesting to see if it works,
Regards sub.

Mad_Mike · « **Reply #37 on:** March 27, 2012, 12:11:53 AM »

progress has been unusually slow today cant understand it. I sealed up the gaps and holes in the hull, fixed the deck and made the coamings for it. I also got it doped and tissued too:

hopefully if all goes to plan i can try it in the test tank to see how well the pump will work. I really hope it works out as ive had to come along way in the build process to be able to get to a stage where i can test it. Ohwell

Mad_Mike · « **Reply #38 on:** March 28, 2012, 12:34:37 AM »

got the hardware installed for testing and well tested it

:

http://www.youtube.com/watch?v=jbKVv5fMztE&context=C494aab3ADvjVQa1PpcFOvRVGjVP9sCyzeGfg0zNaeqY1ZxOjJUKY=

The thrust isn't half bad, in fact I'm quite pleased with it. There are some problems however

1 the boat torque steers left.

2 the pump leaks when under pressure

3 the water jet doesn't come out straight which also assists in its leftyness.

Not due to the nozzle being not straight but because there is a direct line of site betweent the outlet and the impeller. I hope the steering nozzle will correct that and make the torque steer more managable. I can fix the leaky pump no problem but the torque steer i dont know what to do about that. It was something that concerned me and was half expecting it, the only way around it i think is using 2 counter rotating pumps instead of one like i have.

triumphjon · « **Reply #39 on:** March 28, 2012, 07:48:15 AM »

have you been able to test it in open water yet? the effects of the already aeiriated water in the domestic test tank are probably affecting the directional control !

Mad_Mike · « **Reply #40 on:** March 28, 2012, 09:07:25 AM »

not yet, i had only installed the motor 30 minutes prior to shooting that clip. The cardoard on the deck is just a temporary cover to stop water going inside during the test.

Circlip · « **Reply #41 on:** March 28, 2012, 09:37:35 AM »

A keel might assist although you may be suffering from gyroscopic precession. (Look it up)

Regards Ian.

Looks like you may have built a waterbourne helicopter problem.

Circlip · « **Reply #42 on:** March 28, 2012, 09:53:05 AM »

On full sized outboards (There were on me Mercury) is a "Trim tab" that was set to counter the steering effect to enable "Hands off" straight line. Your steering device, tube or blade, should allow you to trim out the vertical rotation by deflecting the thrust to one side. A keel would also assist.

Regards Ian.

Mad_Mike · « **Reply #43 on:** March 30, 2012, 01:00:10 AM »

Another update. Due to the fact im not working from a plan and just making it up as i go along the build stages on the thread are a bit whats the word spaced??

anyway heres some pics for you to have a butchers:

Ive decided to base my boat on one of those New Zealand jet sprint boats. I googled some images, saved them and constructed the typical style from ply. Eventually the boat will have a roll cage dummy engine at the rear and 2 figures from shoulder height sitting at the front. Wont look very realistic but i want it to function not look pretty and a cavenous footwell will just fill with water which i have experienced from a previous build.

The steering nozzle:

I want the pump to be servicable so all the components are easily removed with a screw driver. Its all made from plasticard and a bit of water pipe, the aluminium bar holding down the servo is actually a offcut of a ruler. It was something like 8 quid for a metre length of ali and i didnt need it all so i bought an ali ruler for about 2, rubbed the paint of it and cut it up. Thats a servo horn stuck to the side of the nozzle by the way, im fairly confident its up to the job.

Mad_Mike · « **Reply #44 on:** March 30, 2012, 01:08:39 AM »

Quote from: Circlip on March 28, 2012, 09:53:05 AM

On full sized outboards (There were on me Mercury) is a "Trim tab" that was set to counter the steering effect to enable "Hands off" straight line. Your steering device, tube or blade, should allow you to trim out the vertical rotation by deflecting the thrust to one side. A keel would also assist.

Regards Ian.

I intend the run strakes along the bottom of the hull. how big would the keel need to be? i was trying to avoid hanging stuff off the bottom

Im not sure though if i should point the steering nozzle slightly starboard to counter the affects of gyroscopic precession (Ill call it GP from now) or to put basically a small rudder or stator inside the nozzle to bias the flow to the starboard side. what do you think?

hopeitfloats · « **Reply #45 on:** March 30, 2012, 10:46:54 AM »

i wouldnt put anything in the nozzle. put a bit of RH down on your steering trim. build looks good by the way. beautiful work on the plastic side especially. pity about the strut holding the steering nozzle hanging below the hull though. hope that doesnt effect the steering or cause pump cavitation.

Circlip · « **Reply #46 on:** March 30, 2012, 11:26:10 AM »

Seconded on the trim offset

I'm sure that the final design will have the "Strut" As part of the bottom plate as will the use of countersunk screws. Looks very professional though.

Regards Ian

Mad_Mike · « **Reply #47 on:** March 30, 2012, 11:47:44 AM »

ill put a bit of right hand on the nozzle then. nice n simple.

Im afraid circlip that this is the final design itself

, sorry if you were expecting something a bit more lavish but has boat has cost me 30 quid so far and dont even know if it wiill work yet so im not gonna go nuts. Just using what i have to hand

hopeitfloats · « **Reply #48 on:** March 30, 2012, 12:09:26 PM »

i'm sure it will work going by your posted videos. but dont forget to take one at the official launch which will be / / 2012.? (fill in appropriate date)

Mad_Mike · « **Reply #49 on:** March 30, 2012, 12:31:02 PM »

dont know when that will be wont be long though. need to think of a colour scheme at the minute. Im thinking blue.

Circlip · « **Reply #50 on:** March 30, 2012, 01:41:00 PM »

White or pale yellow are easier to see submerged

Regards Ian.

Mad_Mike · « **Reply #51 on:** March 30, 2012, 03:05:22 PM »

very funny

Netleyned · « **Reply #52 on:** March 30, 2012, 04:06:40 PM »

Have you thought of a name yet?

Gazunder sounds good

Only joking Mike

Ned

Mad_Mike · « **Reply #53 on:** March 30, 2012, 04:38:53 PM »

what makes you all think its gonna sink

Circlip · « **Reply #54 on:** March 30, 2012, 08:28:11 PM »

Not thinking about it sinking, just the sheer power from the waterjet driving it under.

Regards Ian.

Mad_Mike · « **Reply #55 on:** March 31, 2012, 07:58:01 AM »

funny how at the beggining of this thread people were doubtful that the jet would produce any thrust at all

I dont think it will drive it under, im fitting strakes to it at the minute. Ive dicided to go with mettalic blue. ill put some go faster stripes on it too, just in case its slow.

Circlip · « **Reply #56 on:** March 31, 2012, 11:14:11 AM »

Quote

funny how at the beggining of this thread people were doubtful that the jet would produce any thrust at all

Not everybody, some of us remember the Hoover "Senior" (Cast case one, not the plastic version.)

Lots of years ago, when electric powered "Kipper boxes" had just been invented, a demo at one clubs open day saw a very effective submarine every time he opened the throttle.

Regards Ian.

Mad_Mike · « **Reply #57 on:** March 31, 2012, 12:01:13 PM »

why did it submarine?

Circlip · « **Reply #58 on:** March 31, 2012, 01:36:04 PM »

Combination of pointy nose, heavy batterypack for size of hull (Note I said early, lots of "C" sized cells soldered together) and prop trim a bit orft. It bounced when power was applied and on landing, the pointy bit dug in before the guider reacted. Bit like a bouncy landing but substitute the grass for water.

Regards Ian.

Mad_Mike · « **Reply #59 on:** April 03, 2012, 12:33:06 AM »

been a while so heres an update.

First up i wanted some drivers and so i flicked threw ebay and managed to find these guys:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=160776307985

I figured that the scale is about 1/10th of the boat and two of these vacuum formed racing drivers will do just the trick. Firstly i cut off the plastic edges then on one of them hacked off his arms!

I only need one driver of course so a little bit of work was required. After hacking off his arms i used my lighter to warm up and bend the plastic to follow the new pose of the co driver if you like. I then used the pieces of plastic that i cut off to fill in the gaps around the side and between the arms off the co driver, i reckoned matt red would do just fine for their suits. Ive also been painting the boat itself. I went in the end for metallic blue which i suppose i allways had the intention of doing anyway. I suck at painting so dont expect Leonardo Da Vinci brushwork or you will be disappointed:

the drivers are just positioned temporarily for the camera shot.

Ive also plumbed in water cooling for the esc:

the ESC is from giantcod and a budget one to say the least, forward only it is however pretty good. Being of oriental origin i went over kill on the amp rating just in case:

http://www.giantcod.co.uk/80amp-boat-p-404814.html

The motor doesn't draw anywhere near that kind of current, for 13 quid though i cant complain. I dont even think it was necessary to watercool it but i did anyway simply because you never know. The water picks up from inside the nozzle by a small piece of brass pipe with a 45deg chamfered end. i tested the system once plumbed in and it makes a nice slow but affective trickle. Just the job

On the other hand however Ive got a problem.

the bush which the motor spindle goes through into the pump housing leaks. Only when the motor is turning though. I thought i had cured it buy putting a large diameter washer between the impeller and the bottom end plate of the pump housing, then packing it with grease. It hasn't worked so i need to do some rethinking, I have a 3.17mm wide motor axle which i will exchange for the standard shorter axle. With the motor spindle extended going through a snug fitting brass tube and the motor sitting higher I hope it will cure it. hopefully

oh by the way the steering nozzle works magic and straightened out the jet stream perfectly. I turned the nozzle starboard to counter the effects of the GP which i had previously anticipated to be a problem, I tested it in the domestic tank and the boat turned to starboard rather that port like it did in the youtube clip. I backed off the bit of right hand until it ran straight, funnily enough the steering nozzle was centre again. Therefore the the original problem of turning wasn't down to the motor torque but because the water jet was coming out at an angle.

So there you go

Mad_Mike · « **Reply #60 on:** April 04, 2012, 11:21:07 PM »

I managed to gain some control of the leaking bush by exchanging the standard motor shaft for a long one and running to through about 12mm of brass tube:

Its not completely dry though and a little water does seep through into the motor but it doesn't seem to be having any detrimental effects. I hope that once the boat is water born and planing that the issue will be lessened.

Ive painted me crew too:

theyl do

Mad_Mike · « **Reply #61 on:** April 06, 2012, 04:23:15 PM »

Ok so ive just about completed the deck features. first up a roll bar:

The roll bar is made from plastrut. I was dead set on having the corners rounded rather than mitred at 90 deg so i had to come up with a plan. In order to bend the plastic i had to heat it and bend it without it kinking so to overcome this i decided to insert a peice of wire or something in side the tube to stop it going flat. I gathered various tubes and wires at first including a bike lock cable. The original tube splintered when melted and the bike lock cable was an absolute ***** to cut. I settled on using curtain wire and plastrut tube in the end and the wire fitted in the end perfectly:

I stripped the plastic off the curtain wire to reveal the coil:

I reckon that this curtain wire will make a good flexicable for something, it was only 57p too:

Anyway i marked off where i wanted the bend in the tube and inserted the cable into the pipe:

I heated the tube gently with my lighter then bent the tube with the wire inside, I let the tube cool off then pulled the wire out of the end:

I think the result is pretty good altough the diameter does shrink a bit, but then i suppose if you were to bend steel tube in a pipe bender it would do the same thing. To be honest this is probably my third attempt as on previous attempts i got the plastic too hot and the end results were awful. Anyway after a bit of fiddling with the file i fixed the roll cage to the deck:

Ive also made an engine out of plasticard, the exhaust pipes are pen tubes:

Ive also adapted the air filter into a lock nut to keep the deck down. I epoxied a nut inside a tooth paste tube cap then added 2 circles on the top and bottom of the cap to male an airfilter. Ive screwed an eye in to the bottom of the hull then a threaded bar with a hook on the end hooks into the eye comes up threw the centre of the engine. The air filter screws on top of that too hold the deck down securely:

Netleyned · « **Reply #62 on:** April 06, 2012, 04:49:11 PM »

Very neat setup there Mike
When is the launch day?

Ned

Mad_Mike · « **Reply #63 on:** April 06, 2012, 05:46:36 PM »

god knows the kids are off school for easter and cant handle them all and sail the boats at the same time. I need to get the painting done but it wont be long till im finished now. Im not going to great lengths into the details on this build.

Mad_Mike · « **Reply #64 on:** April 08, 2012, 08:49:08 PM »

right i reckon im about done, painted it up and made some numbers out of wheely bin stickers, ill need to make a grill for the water inlet to stop stuff going in the pump. I cant tell you when ill get it on the lake though i hope thursday.

can anyone tell me if its totally necessary for my 2.4ghz antena wire to be stuck out the top of the boat?

Danny · « **Reply #65 on:** April 08, 2012, 10:40:40 PM »

Mike - as long as there is no metal or carbon fibre surrounding the aerial, it will work fine within the boat. 2.4GHz goes straight through grp or wood.
Cheers
Danny

gwa84the2nd · « **Reply #66 on:** April 08, 2012, 10:45:46 PM »

i run mine onn my ic boats inside the radio box so you shouldent have a problem runing with the airial below deck

Mad_Mike · « **Reply #67 on:** April 08, 2012, 11:08:38 PM »

good ill do that

hopeitfloats · « **Reply #68 on:** April 13, 2012, 10:21:37 AM »

so no test run thursday

Mad_Mike · « **Reply #69 on:** April 13, 2012, 11:40:37 AM »

yes but it wasnt good. I started off the test run with a partially charged testing lipo, everything seemed ok, went straight as an arrow too. Thought right lets give it some welly then so i put in a fresh fully charged lipo and it launched like a scolded cat, came to some ripples in the lake about 20ft out and got it airbourne, on landing the boat cut out completely. I sent me rescue boat after it to recover it and discovered the 25a fuse had popped, bath testing showed that the continuous running was around 7 amps so i thought 25 was plenty of head room especially will the esc rated at 80amp continuous. Tried a new 30a fuse in it when i got home, forgot to take spare with me didnt I, power came back on servo and radio works but motor doesnt run. I reckon that when the boat went airborne the motor overreved when it went dry, then on contact with the lake the flooding of water in the pump loaded the motor again, spiked the current and popped the fuse. i need to purchase a better esc before i take it out again. I new it was risky buying the cheap oriental esc so i made sure i went over the top with its handling capacity, looks like it didnt work.

News:

Author Topic: Water Jet experiment and Jet boat build (Read 3515 times)