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Author Topic: Jet sprints ...anyone built one of these  (Read 6663 times)

phillnjack

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Jet sprints ...anyone built one of these
« on: February 09, 2011, 03:22:12 PM »

Has anyone here built a big jet sprint type boat.

Im thinking about building one around 40 inch long and powering it with big petrol strimmer engine.
either 23 or 41 cc ( just because i have these engines already ) coupled to a jet unit.
and wondered if anyone here has built one or any info on a model one this sort of size

.
this is the type of boat i mean...full size use very big V8 in 15ft long boats  ha ha









phill :-))
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Umi_Ryuzuki

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Re: Jet sprints ...anyone built one of these
« Reply #1 on: February 09, 2011, 06:36:40 PM »

There was a chap in Australia that designed the "Swashdrive", and for a while, there was a
huge following for large scale sprint boats and the "swashdrive". However he retired the
production, and no longer makes the drive. I think he may still be designing tattoo needles though.

But recently that whole crowd has gotten excited, because HobbyKing just showed their
first prototype Jet drive for large scale gas motors....

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13388

If you have a few quid burning a hole in you pocket, you could drop a few on that
drive if it becomes readily available.


Here are a couple of vids of one of the old swashdrive units.

http://www.youtube.com/watch?v=-EZ1Nb5J-hY
http://www.youtube.com/watch?v=FDxgyjjzlwo

I believe, the picture below is one of the last boats Craig Built, using his drive and a 1/4 scale Conely V8 engine.
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martno1fan

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Re: Jet sprints ...anyone built one of these
« Reply #2 on: February 09, 2011, 11:34:17 PM »

Go over to rcuniverse theres a bunch of guys that have these still.
Mart
this guy designed and built the hull and jet pump in this vid himself, you might want to contact him for info hes in NZ where these boats came from orriginally i believe.
http://www.youtube.com/watch?v=H074iZxeR8I
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w3bby

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Re: Jet sprints ...anyone built one of these
« Reply #3 on: February 10, 2011, 09:13:51 AM »

I have an old MHZ jetsprint with their older model jet drive using a 2 port Zenoah. Quite a lot of fun but relative to a prop driven boat they feel slow. I haven't had it out for a few years now. The 41 motor would probably be too much for the units available today.

I believe MHZ units are unavailable at the present time, Graupner had or have a unit, Kehrer http://www.jet-drive.de/cms/index.php?lang=en and now the Hobby King unit that Umi links to.

The guy Martin mentions you will find here http://modeljetboat.com/ and his forum here http://modeljetboat.com/forum/

BJ

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Re: Jet sprints ...anyone built one of these
« Reply #4 on: February 10, 2011, 03:39:13 PM »

Wonder if they would be as (scale) fast as the real boats?
Watching NZ television last year, the commentators were claiming that one boat was capable 0-103 in 3 seconds. I assume that they meant KPH and not MPH! Stiil fast in water (mud?) filled gully
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BJ

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Re: Jet sprints ...anyone built one of these
« Reply #5 on: February 10, 2011, 04:53:15 PM »

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phillnjack

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Re: Jet sprints ...anyone built one of these
« Reply #6 on: February 11, 2011, 12:34:21 AM »

The real ones realy do 100mph in 3 seconds
they are the fastest boats off the line.
but when you realise they are 800bhp in a 13ft boat that weighs about 150 pounds without the engine and jet unit
the power to weight ration is incredible.

 i looked into a share of one of these boats, but it was ridiculous price.


the 1/4 scale one is very nice, and would be ideal for a 41cc  , but at that price for a bare hull, no thanks.

might go ahead and build one from steel.   should be able to keep to the 7.5 kilo bit

mmmmmmmmm its got me thinking now  ha ha


phill
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martno1fan

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Re: Jet sprints ...anyone built one of these
« Reply #7 on: February 11, 2011, 08:31:57 AM »

Get some foam and make the shape you want then glass over it using a few layers of cloth and resin,if you use the yellow foam used in the building trade thats foil lined it wont melt with poly resin,i use it for making plugs.Not an ideal finish doing it this way but with some care and then some sanding after you will have  a reasonable finish.Or simply get an old vee hull and modify the bottom at the transom.
Mart
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BJ

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suitable water jet units
« Reply #8 on: February 11, 2011, 04:23:54 PM »

So other than HobbyKing who makes suitable water jet units? Graupner plastic ones might be OK for electric 300mm boats but something on the HobbyKing lines are required for IC power.
Aren't there some from a European manufacturer?
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bulldog1966

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bulldog1966

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Umi_Ryuzuki

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Re: suitable water jet units
« Reply #11 on: February 11, 2011, 07:15:57 PM »

So other than HobbyKing who makes suitable water jet units? Graupner plastic ones might be OK for electric 300mm boats but something on the HobbyKing lines are required for IC power.
Aren't there some from a European manufacturer?

Graupner is German....  ok2

Here is Keher Modellebau Berlin, KMB

http://www.jet-drive.de/

http://www.jet-drive.de/index.php?page=shop.browse&category_id=42&option=com_virtuemart&Itemid=17

Also one of the few kits of the CB90 (Stridsbåt 90)

http://www.jet-drive.de/index.php?option=com_virtuemart&page=shop.browse&category_id=50&Itemid=17

 :-)
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phillnjack

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Re: Jet sprints ...anyone built one of these
« Reply #12 on: February 11, 2011, 09:17:24 PM »

I already have a jet unit that was made for ic  glow engines of around the 6.5 to 10 cc range.

very similar to the ones above just a touch bigger, it also has the reverse cup.

But im thinking about it needing high revs and making a 3 rpms engine to 1 on the jet to give it
plenty of revs.
Now by using a petrol engine, like my 41cc zenoah, that should let me get around 18,000 to 20,000 rpm range.

Im not looking for a race boat, just something very different to the norm.

this is why im thinking about building a jet boat from sheet steel at about 1/4 scale.

Being as the jet sprint boats are only about 15 to 16 foot length, 4 foot would be ideal size.

Just wondering about how thick the steel needs to be, becausei do tend to build things a bit on the heavy
side, and dont want to have to put an even biggerengine in the boat to make it go ha ha

I dont think ill be needing 1/4 inch chequer plate thats for sure  {-)

phill  :-))
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BJ

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Re: suitable water jet units
« Reply #13 on: February 12, 2011, 02:31:13 PM »

Graupner is German....  ok2

Here is Keher Modellebau Berlin, KMB
 :-)

KMB That's the one! .... and yes I should have put "aNOTHER")
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triumphjon

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Re: Jet sprints ...anyone built one of these
« Reply #14 on: February 12, 2011, 10:24:29 PM »

is there any reason for wanting to build in steel ? its very heavy for the strength your getting , grp is 6 times lighter for the same thickness and strength !
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phillnjack

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Re: Jet sprints ...anyone built one of these
« Reply #15 on: February 13, 2011, 12:21:59 PM »

Fibreglass is not as strong as steel for the same weight, unless its reinforced with kevlar etc.

i know the boat would be pretty heavy, and im not too worried about that.
In models we normaly end up with boats far too light,especially when building scale stuff, this is why model destroyers
and warships often look so silly on ponds with little waves.
instead of crashing through the waves they bounce and wobble over them.
The same applies to most race boats, they can be too light.

Its all still just a thought at the moment, but i might give it a try.

ive heard there is a steel tugboat of this very forum somewhere



phill

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martno1fan

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Re: Jet sprints ...anyone built one of these
« Reply #16 on: February 13, 2011, 05:31:57 PM »

I think he meant for the same thickness not weight that fibreglass is as strong as steel,wether it is doesnt really matter but i have to agree Glass is the way to go,those jet drives arent the fastest way to move a boat so weight is not going to be your friend,so id build it as light as possible.
Mart
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phillnjack

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Re: Jet sprints ...anyone built one of these
« Reply #17 on: February 13, 2011, 06:40:29 PM »

Might have to just build one and see how it goes.

i could easily make one from 1mm thick sheet steel, now i cant see that being very heavy.

its just a boat for fun realy, if i wanted speed i would use cmb90 and up the gear by 3to1 to
give massive amount of revs to the jet.



phill :-))
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dadandlad

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Re: Jet sprints ...anyone built one of these
« Reply #18 on: February 15, 2011, 12:43:14 AM »

How will you form the steel ?have you access to rollers/english wheel
Tig or Mig welded?
I think 1mm may be a little thick for the whole hull
If i was going to build from steel i would use 1mm for the transom and bulkheads  with the maximum amount  possible removed from the centre and 0.4 for the skins/deck
I have priced up stainless steel and it costs a arm and a leg so mild steel would be the cheapest
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martno1fan

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Re: Jet sprints ...anyone built one of these
« Reply #19 on: February 15, 2011, 09:36:16 AM »

Think ill stick to glass boats theyre light and strong cant beat that,i built a 58" glass x carbon hull a cpl weeks ago and total weight was 8 lb this was a hand layup not vacume bagged.For a one off build the glass over foam is pretty hard to beat for price and could be built in a cpl of days.Carve the foam by hand and you can use formers put between blocks of foam taken from any plans you can find or just draw your own and carve to the formers to get your shape then sand smooth and glass it using some twill cloth and build up the layers wet on wet and then it will just need sanding smooth but not much if you do it carefully,ive done that method a few times for small hulls when i was younger and they came out well.Incidently go on any housing estate and you will find loads of this yellow foam lying arround just ask for it and you will get it free,even poly resin wont eat it.It also sands very smooth but isnt as firm as the propper stuff so be carefull with it and you will be fine.
Mart
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phillnjack

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Re: Jet sprints ...anyone built one of these
« Reply #20 on: February 16, 2011, 12:15:56 AM »

The question of how to form the steel

just the same way you would do it with wood.
cut the shapes as per wood for hull bottom and sides, tack em up and mig weld (seamless ofcourse)
I would use 1mm for the hull bottom 0.5 for sides of hull and 1mm for deck,
The deck would need a couple of pipes run from front to cockpit area to keep shape.

If your gonna build a boat like the real jet sprints then you need to build it bullet proof,like the real thing.

you have to rememer there wouldnt be any stringers needed,it would be like a glass hull,completely empty.
...

I do like Martno1's idea about the foam as well, just think that a steel one would be so different.

so what do you do with the final coat of resin mart ? do you use gel coat or just add colouring to the resin ?
and then flatten and polish it all ?
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martno1fan

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Re: Jet sprints ...anyone built one of these
« Reply #21 on: February 16, 2011, 08:13:15 AM »

Id def stick with resin as gelcoat wont cure in the air unless you add additives to it.Yes you can add pigment to it wether you use poly or epoxy resin it doesnt really matter you can get both types of pigment.Epoxy would be stronger but more expensive but you could go thinner on the layup.Sometime later in the year ill be doing a writup on making a plug then a mould from it from scratch.
For your project i would use whatever colour you decide for the whole layup and maybe do one extra coat that can be sanded back to get the finish you want.
Mart
good source for materials+next day delivery if you want

http://www.ecfibreglasssupplies.co.uk/
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David Shaw

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Re: Jet sprints ...anyone built one of these
« Reply #22 on: February 16, 2011, 07:13:14 PM »

MHZ have just released a new jet drive called "Jet 4". It is made out of aluminium and rated for electric motor that delivers max continuos 5800 watts and max short peak power of 8100 watts. Also they are stating up to 23 cc petrol. Look on their web site www.mhz-powerboats.com ,which i think will be able to handle the power you want to run at.
Kehner's jet drives are good but I do not think they can handle the power you want to run. I also think that Graunpner's drive are rebranded ones from Kehner.
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