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Author Topic: Water Jet experiment and Jet boat build  (Read 21744 times)

hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #25 on: March 22, 2012, 05:43:56 AM »

it will cavitate but should take off again as soon as it hits the water. the original hamilton jet boat was just as you are building. a centrifugal pump mounted inside the hull but with a right angle gear box on top connected to the engine. thrust improved quite a bit when he raised the outlet above water though. check this site if you like    http://www.hamiltonjet.co.nz/hamiltonjet_waterjet/waterjet_history
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triumphjon

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Re: Water Jet experiment and Jet boat build
« Reply #26 on: March 22, 2012, 07:54:40 AM »

thanks for the link hopeitfloats , very interesting timeline , im also building a jet propelled model , but using the graupner mini jet unit , might try to make my own multi bladed impellor though , we started one for the nqd pump but never got past turning the boss !
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #27 on: March 22, 2012, 09:44:30 AM »

that is going to be my next project after finishing my long term container ship build. i have the graupner mini jet too. mine is a few years old but never used. dont like the ugly reversing bucket though. think i will build my own there. have you had your unit running.  the impellor is pretty basic isnt it.  what size hull are you planning to use?   craig
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #28 on: March 22, 2012, 11:17:33 AM »

it will cavitate but should take off again as soon as it hits the water. the original hamilton jet boat was just as you are building. a centrifugal pump mounted inside the hull but with a right angle gear box on top connected to the engine. thrust improved quite a bit when he raised the outlet above water though. check this site if you like    http://www.hamiltonjet.co.nz/hamiltonjet_waterjet/waterjet_history

fantastic link thanks for that. It had cross my mind to use a right angle bevel gear box but last time I used one it drained the power and the gears could be heard 30ft away!! 
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unicorn

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Re: Water Jet experiment and Jet boat build
« Reply #29 on: March 22, 2012, 03:01:58 PM »

 :-) :-) :-) :-) :-) :-)

      Have a look at the Schottel SPJ pump jet  (http://www.schottel.de/home/ )  soon to be released by
   Graupner @ 180 euros  ---  yes 180 euros
                                                                :o :o :o :o :o
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triumphjon

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Re: Water Jet experiment and Jet boat build
« Reply #30 on: March 22, 2012, 06:24:17 PM »

i will stick with the reverse bucket , ive designed my own dory hull  at 24 " longx 8" beam , of balsa construction which is coated in polyester resin and woven glass tissue .
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #31 on: March 26, 2012, 01:00:21 AM »

Since my last post on this subject Ive been waiting for my funding to accumulate and the post to arrive but as of Saturday the waiting was over and so over the last days Ive been getting some building done. Well a lot actually!
First up i received my new motor ESC and gear for the impeller. I ordered from giant cod a cheap and cheerful 2200kv brushless outrunner with a none marked 80a forward only esc. I made a brand new impeller using the gear as a boss for the centre, reversed the shaft on the motor so it came out threw the base and mounted it to a piece of plasticard.




I did a spin test with a 3s lipo and the impeller didnt explode so its all good (touch wood)

I then started working on the pump casing. I marked out the shape of the casing on cardboard drew and cut it out on several peices of ply and plasticard andf then laminated them togeather to build up the height.



For some reason i didnt take a picture of the completed pump on its own, it will show up in these later pics. Anyway i started planning out the hull. Im not sure yet what type of boat im going to build and have no idea how well it will perform so i built a small but basic hull and HOPEFULLY the jet will provide some ample shove for it.


I then started cutting out the transom and fitted to the pump. In this picture you can see the inside of the pump housing itself with the impeller off.



a peice of tube is fixed into the end of the pump jet, i smoothed off the square to cirlce profile with epoxy putty to improve the flow.

A bit of a frame just to get my started:

 

After this im afraid there was a gargantuan leap of progress and i was so busy i forgot to take pictures  {:-{ The Hull is made from entire peices, 2 chines and 2 bottoms:




The blocks running up the inside of the chines reinforces the seam with the bottom and the **** at the front just holds it togeather while its drying. The interior is not pretty but once the deck is on it wont be seen. A few more gaps need filling but ive pretty much got this part out of the way. Heres a pic of the pump casing closer up:



another update coming soon :-))
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #32 on: March 26, 2012, 08:45:58 AM »

WOW. you certainly get stuck in when you do a project. that would be 3 months work at my rate. well done
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #33 on: March 26, 2012, 09:14:14 AM »

WOW. you certainly get stuck in when you do a project. that would be 3 months work at my rate. well done

yeah i build too fast sometimes. I find that i spent weeks saving up and gathering stuff, spend a few days on the build then im bored again for a month  %% Maybe i should span it out a bit more. What was your name before the forum crash?
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #34 on: March 26, 2012, 11:11:54 AM »

hopeitfloats. no name change
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Martin [Admin]

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Re: Water Jet experiment and Jet boat build
« Reply #35 on: March 26, 2012, 03:17:55 PM »

Topic Name changed ...... to protect the innocent.....  ok2
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Sub driver

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Re: Water Jet experiment and Jet boat build
« Reply #36 on: March 26, 2012, 03:56:36 PM »

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

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Re: Water Jet experiment and Jet boat build
« 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 %%
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« 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.

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triumphjon

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Re: Water Jet experiment and Jet boat build
« 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 !
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« 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.
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Circlip

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Re: Water Jet experiment and Jet boat build
« 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)  O0

   Regards   Ian.

   Looks like you may have built a waterbourne helicopter problem.
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Circlip

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Re: Water Jet experiment and Jet boat build
« 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.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« 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.

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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #44 on: March 30, 2012, 01:08:39 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?
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« 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.
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Circlip

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Re: Water Jet experiment and Jet boat build
« 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
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« 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  :embarrassed:, 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  O0
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« 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) :-)) :-))
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« 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.
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