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Author Topic: Water Jet experiment and Jet boat build  (Read 21728 times)

Mad_Mike

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Water Jet experiment and Jet boat build
« on: March 19, 2012, 09:50:35 AM »

i had posted in temp forum but ill repost it here and do a build thread.

Iíve always fancied having a go making my own water jet, yeah I know you can buy them and thereís even a really cheap eBay one but it defies the point of what Iím trying to achieve, a complete bolt in unit just wonít cut it for me. Now I have read threads on mayhem and other places about the attempts and regular failings of people trying to make your own jet unit by mounting a propeller inside a piece of pipe and then trying to make a stator which counteracts the swirling affect of the water at the output. I have tried this method myself before so I know first hand just how difficult they are to NOT make as such but make affective. So knowing what Iím up against Iím going to attempt a different approach fit it to a model then see what happens.
A toy battery operated boat of my sons has a jet pump inside it. I remember when I was a kid having lots of these small bath boats and also remember the transition from a standard propeller to these internal impeller style crafts. You donít see many battery operate toy bath boats these days with a propeller no more. One of those things health and safety slammed down on. Anyway hereís the little boat:



and heres the jet unit:



with the cowling off:



The motor is mounted onto a vertical axis at the stern. My idea is to incorperate this basic pump design into a larger scale and power it by a 540 or hopefully a brushless motor. Its principle is allready used in bait boats and even some types of outboard motor:



So Its not the first time this has been done. Using a 540 27t motor ive designed and fixed a centrifugal pump on the end too see what would happen:



The impeller rotor is 34 mm in diameter and the hole unit is contructed from plastic card. A plate goes over the top to complete the impeller housing and simply bolts togeather. Ive done a test run and heres a youtube link of it working:

http://www.youtube.com/watch?v=nZ1gJeuas7M&feature=channel

From what i can guestimate using the kitchen scales the thrust is about 2 lb's, which i think which move a fairly small boat relatively nippy. ill have to see.



The combined height of the motor and pump is a fairly lofty 3 inches. I dare say the boat it will be built into will be no more than 16 inches long. Big enough to incorperate the weight and size of the jet unit and its ancilleries but not to so large and heavy that the jet wont have any affect on it.  The draw back is that at that length and this motor height the chines on the side of the boat would look rediculously tall!! I need to get the overall height of the pump down so as to bring the profile of the hull down too. unless i have the top of the motor sticking out the deck inside a box or something, which id reckon would look pants!!
I was thinking maybe a low profile 2200kv outrunner to replace the standard 540 motor. Does anyone know if this would work or would the pump overload the outrunner?

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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #1 on: March 19, 2012, 12:10:28 PM »

i have to admit when i saw your home made unit i thought nahhhhh. it wont pump much but the you tube video proved me wrong. well impressed. many many years ago i made an  axial flow unit powered by a OS40 motor. it could certainly shift some water and was really useful for emptying my little pond but never actually ended up in a boat. wished i had finished it now.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #2 on: March 19, 2012, 12:51:15 PM »

I was quite suprised myself at how well it worked. When i come to building the boat ill build the pump housing into the hull itself rather than mount this test one. I think a nozzle or venturi of somekind will concentrate the water flow and maybe even increase thrust. Thats the theory anyway :D
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #3 on: March 20, 2012, 10:03:35 AM »

there is an optimum size for nozzle to inlet size.  i think the outlet is 1/3  or thereabout smaller than inlet for best results, dont quote me though.  i do know you will decrease thrust if you go too small.  i'm sure someone will correct me if i'm a long way out. a question for you though. what sort of glue did you use to stick the blades on?  i have never had a lot of success glueing plastic card.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #4 on: March 20, 2012, 10:18:03 AM »

Ill have to do some more research. The blades are stuck on with CA glue. I rub down the entire plasticard both sides and then it sticks solid. ive ran the motor on 3s and got the blades spinning about 26k and didnt explode, so far so good. touch wood

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Circlip

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Re: Water Jet experiment and Jet boat build
« Reply #5 on: March 20, 2012, 11:00:01 AM »

Mercury (amongst others) have been using this for decades. Only difference is that the impeller is made from rubber and the blade tips are deformed by the casing to get the seal. Oh yes, it's the watercooling pump for the engine and on the prop driven O/B's is mounted in the bottom of the rear "Stalk".

   Surprised Styrene iis difficult to glue if the basic material is chemically clean and using a solvent type cement. Cyano is eventually degraded with water.

  Regards  Ian.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #6 on: March 20, 2012, 12:39:47 PM »

Of course i realise that the method is allready used. What im trying to do is replicate such a system on a basic principle level using basic tools and minimal funding. I will agree that CA does degrade with water BUT only when exposed to extended periods of submersion. Seeing as the boat wont be on the water longer than 20 minutes at a time it doesnt cause a problem. Ive built now 12 boats all with CA and the ones i built last year are still holding strong. If any part needs a bit extra i use epoxy.  Im just trying to write a build thread thats a bit different. Once youve read one build thread of a boat you basically read them all because the process hardly ever changes.
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Circlip

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Re: Water Jet experiment and Jet boat build
« Reply #7 on: March 20, 2012, 12:49:12 PM »

Wersern't a knock Mike, difference is, the "Prop" is churning the water about so you're doing what manufacturers call an "Accelerated Life Test"  :-)  The solubility of Cyano is just to remind some that it is a factor.

   Regards   Ian
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gwa84the2nd

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Re: Water Jet experiment and Jet boat build
« Reply #8 on: March 20, 2012, 03:26:22 PM »

looking good ther mike might have to steel the idea and have a go myself with that one
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #9 on: March 20, 2012, 05:04:03 PM »

Wersern't a knock Mike, difference is, the "Prop" is churning the water about so you're doing what manufacturers call an "Accelerated Life Test"  :-)  The solubility of Cyano is just to remind some that it is a factor.

   Regards   Ian

Im sorry i thought it was a dig. I hope you will find myt build thread interesting. when it gets going at least :-))
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #10 on: March 20, 2012, 05:05:51 PM »

looking good ther mike might have to steel the idea and have a go myself with that one

by all means give it a go. Some point hopefully by the weekend ill start the boat build, and it would be interesting to see what other people can do. maybe you will do a better job.
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gwa84the2nd

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Re: Water Jet experiment and Jet boat build
« Reply #11 on: March 20, 2012, 05:50:57 PM »

i will probably buld it in metal and wack a nitro engine on it  lol more pawer  :-))
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #12 on: March 20, 2012, 06:51:28 PM »

I dont know much about nitro, ill take your word for it. I dont think metal would be best suited though as its heavy. cast resin would be best i think.
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #13 on: March 20, 2012, 09:00:44 PM »

Mercury (amongst others) have been using this for decades. Only difference is that the impeller is made from rubber and the blade tips are deformed by the casing to get the seal. Oh yes, it's the watercooling pump for the engine and on the prop driven O/B's is mounted in the bottom of the rear "Stalk".

   Surprised Styrene iis difficult to glue if the basic material is chemically clean and using a solvent type cement. Cyano is eventually degraded with water.

  Regards  Ian.


i don't think most people have a problem with glueing card....just me. LOL. I do clean and rough the surfaces and the glue sticks but has no strength. i have found pvc glue works well but takes a while to set and is messier to apply than the proper glues


Modified
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #14 on: March 20, 2012, 09:03:42 PM »

while i'm here. can someone please tell me why my previous post is included in the quote. what am i doing wrong. not the first time its happened.
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Circlip

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Re: Water Jet experiment and Jet boat build
« Reply #15 on: March 20, 2012, 09:13:49 PM »

while i'm here. can someone please tell me why my previous post is included in the quote. what am i doing wrong. not the first time its happened.

 If you've pressed the quote button on the top RHS of the last box, you then need to click below the [/quot] before typing your own comments. And yes, I did deliberately misspell quote.

   Regards  Ian.
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Circlip

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Re: Water Jet experiment and Jet boat build
« Reply #16 on: March 20, 2012, 09:24:00 PM »

To go back on post, once you start to refine the idea, if you look at the impeller of a turbine, there are extended and curved over inner lips to the blade, like the leading edge of a normal prop, to scoop the water or air in and fling it to the outside. All very clever but far from Mikes simple but very effective build. Krishnas pancake VHS motor rewind would be ideal as a low profile drive unit.

  Regards  Ian
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #17 on: March 21, 2012, 08:11:12 AM »

I could have a go at making the scoops on the waterpump impeller. I need to build the boat first but the impeller could be improved on later.
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #18 on: March 21, 2012, 08:20:03 AM »

my impellor was 50mm diameter.  4 brass blades on a brass hub with overlap. quite tricky to silversolder.  aluminium housing with a stainless wear ring and phosphor (sp)  bronze bearings. but worth the effort. as i said previously it could certainly pump the water.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #19 on: March 21, 2012, 09:08:58 AM »

the picture looks like the traditional hamilton jet type impeller. Did you make the jet yourself? how did you do the stator?
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hopeitfloats

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Re: Water Jet experiment and Jet boat build
« Reply #20 on: March 21, 2012, 09:57:39 AM »

a bit of cheating there.  :embarrassed:it is a traditional impellor. (never took any photos of mine. this was well before digital photography etc). mine was very similar though. stator was brass strips silver soldered to a hub and pressed in bearing.  the whole thing was then pressed  and loctited in to the 'pump housing'.  there is a local engineer here who milled three impellors out of a block of brass and made a three stage unit powered with a chainsaw motor. that was impressive to see but our local boating pond is really a large puddle so he cant wind it up to anywhere near full speed. good for soaking the spectators though . {-)
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Circlip

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Re: Water Jet experiment and Jet boat build
« Reply #21 on: March 21, 2012, 10:13:49 AM »

The type I was reffering to is the centrifugal type as used in turbos and the original "Goblin" jet engine in where the outer parts of the blade are as Mikes and the inner part are curved over. What it should allow is that the unit doesn't need to protrude below the hull as the first photo.

  Once you start  hanging an "Engine" on, you might as well go back to the Hamilton/Taplin Hydrojet prop in a tube.

  Regards  Ian.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #22 on: March 21, 2012, 10:17:41 AM »

sounds impressive. If i had access to the facilities id go the hamilton jet type route but when i tried it last time it failed miserably. The method ive chose is easier to make on the dining room table and im fairly confident it will work, I hope  :embarrassed:  Im not going to poor piles of money in it though because if its just feeble i havent made a great loss.
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Circlip

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Re: Water Jet experiment and Jet boat build
« Reply #23 on: March 21, 2012, 10:26:22 AM »

I was still working on the plastic option Mike. By "Engine" I mean where the Juice is a hydrocarbon derivative.

  Regards  Ian.
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Mad_Mike

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Re: Water Jet experiment and Jet boat build
« Reply #24 on: March 21, 2012, 10:39:59 AM »

The type I was reffering to is the centrifugal type as used in turbos and the original "Goblin" jet engine in where the outer parts of the blade are as Mikes and the inner part are curved over. What it should allow is that the unit doesn't need to protrude below the hull as the first photo.

  Once you start  hanging an "Engine" on, you might as well go back to the Hamilton/Taplin Hydrojet prop in a tube.

  Regards  Ian.

I googled some images of impellers and it seems that the air compressor type centrifugals have the scoops on. What i intend to do is have the central section of the rear of the boat flat:




then build the pump inside the hull rather than hang it off the bottom, so that its still flat. The impeller ifself will be just below the waterline so it is fully bled as soon as the hull touches water. If the speed of the boat gets to a point where its bouncing on the ripples of the lake then i may have to consider the scoops on the blades or even a ram scoop on the inlet to the pump to aid bleeding as it jumps in and out of the water. Otherwise as soon as the boat gets a bit of air under it the pump will go dry, stop thrusting and the boat will stall.
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