Reply
 
Thread Tools Search this Thread
 
Old 30 November 2005, 17:58   #81
Member
 
Country: Other
Length: no boat
Join Date: Aug 2005
Posts: 623
Blimey.
__________________

__________________
hard1 is offline   Reply With Quote
Old 30 November 2005, 18:12   #82
Member
 
Hugh Jardon's Avatar
 
Country: UK - England
Town: Reading, Hants
Boat name: Juicy
Make: Sealine F43
Length: 10m +
Engine: 2 x 370hp
MMSI: TBC
Join Date: Sep 2005
Posts: 2,882
not sure my argos micrometer set will be up to that but could give it a go i guess
__________________

__________________
Hugh Jardon is offline   Reply With Quote
Old 30 November 2005, 18:20   #83
Member
 
Richard B's Avatar
 
Country: UK - England
Town: Devon
Boat name: White Ice
Make: Ranieri
Length: 5m +
Engine: Suzuki 115hp
Join Date: Jul 2002
Posts: 5,015
I expect you to use nothing inferior to a Mitutoyo!
Richard B is offline   Reply With Quote
Old 30 November 2005, 18:37   #84
DJL
Member
 
Country: UK - England
Make: Ribcraft 6.5
Length: 6m +
Engine: Suzuki DF175TG
Join Date: Apr 2002
Posts: 929
Quote:
Originally Posted by codprawn
Newtons 3rd law - for every action there is an equal and opposite reaction.

Way a rocket works in space - chucks mass out the back so it goes forward.
Thatís exactly it.

Youíre accelerating a mass, in this case water, out the back of the boat. To accelerate a mass you need force acting upon it. The engine/jet system is applying a force to the water to accelerate it out the back of the boat. Now according to Newtonís 3rd law there is reactive force acting upon the boat in the opposite direction, which moves it forward.

The reason itís more efficient to discharge the jet into air is that air applies a much smaller force onto the jet of water than water. Think about moving your hand through air and through water - its much harder to accelerate you hand in water than air. The same thing applies to the engine - it has to work harder to accelerate the water jet when discharging into water.
__________________
DJL is offline   Reply With Quote
Old 30 November 2005, 18:58   #85
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
Quote:
Originally Posted by codprawn
Stand on an ice rink and fire a gun - the bullet will go forwards - you will go backwards.

It is all down to the mass and the force it is propelled with. Fire a small calibre air rifle and you won't move much - fire an elephant gun and you will.....
That's not telling me how it works. That's telling me the result of it's action. Anyway, I understand that bit.

Draw a diagram to explain to me where in a waterjet the forces are being applied. Where is the force against which there is the reaction? Where is the propulsive reactive force applied, to the blades of the impeller and thence through a thrust bearing and on into the structure of the boat? To the inside of the casing?

I still don't understand it properly and I'm sure the notion of the fast stream of water squirting out the back somehow pushing the boat along is nonsense.

To Moll, you are being glib and flippant but you haven't taken the trouble to explain to us how the system works. If this thread is below you, I suggest you don't read it.

I'm Mr. Grumpy tonight.
__________________
JW.
jwalker is offline   Reply With Quote
Old 30 November 2005, 19:11   #86
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
DJL, thanks for that.
__________________
JW.
jwalker is offline   Reply With Quote
Old 30 November 2005, 20:05   #87
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
Quote:
Originally Posted by jwalker
.. I'm sure the notion of the fast stream of water squirting out the back somehow pushing the boat along is nonsense.
I take that back cos there's going to be a fair amount of kinetic energy stored in that water.
__________________
JW.
jwalker is offline   Reply With Quote
Old 01 December 2005, 03:22   #88
Member
 
Country: UK - England
Town: Brittany/Portsmouth
Boat name: Merlin
Make: Solent 6.5
Length: 6m +
Engine: 200
MMSI: soon !
Join Date: Jul 2003
Posts: 5,451
Quote:
Originally Posted by jwalker
Draw a diagram to explain to me where in a waterjet the forces are being applied.
Jeff, do you think the force being applied is the mechanical one of the impellor/stator? If that's what's accelerating the water (mass) out the back & through the smaller opening then that must be causing the initial action (like pulling the trigger or snapping an elastic band.) (Thus the action/reaction Newton bit).

DJL found your explanation about operation of the jet in air (as distinct from water) clear & helpful.


Quote:
Where is the force against which there is the reaction? Where is the propulsive reactive force applied, to the blades of the impeller and thence through a thrust bearing and on into the structure of the boat? To the inside of the casing?
Oh OK I think I get it. You want the exact mechanics of where the impellor acts and where the energy transfer actually happens ? Down to the nuts and bolts ?

This link posted by gArf is pretty helpful but I haven't checked it all to see whether it is demonstarting the specific mechanics of the thing.

Hamiltons here (again)http://www.hamjet.co.nz/index.cfm/Th...jet_Works.html

(Next build project? Pete 7 seems to be working on a Fareham version in the back garden so perhaps he will keep us posted )

BTW thanks again for all helpful contributions

missus
__________________
Happy New Resolutions!!! : RIBbing for the craic!!!
The Jackeens is offline   Reply With Quote
Old 01 December 2005, 03:54   #89
Member
 
Country: Belgium
Town: NIVELLES BELGIUM
Boat name: INDEPENDENT
Make: BWM RAPIER
Length: 9m +
Engine: Ob 2*250/2t yams hpd
MMSI: 235030702
Join Date: Aug 2004
Posts: 885
just come back . Wow ,what knowledge!!, what writing, what
prowess, Really been missing something!!!!!!!!!!!!.

jonathan
__________________
eupa is offline   Reply With Quote
Old 01 December 2005, 04:38   #90
Member
 
Country: UK - England
Town: Devon. uk
Boat name: bananashark
Make: me
Length: 7m +
Engine: opti 225
Join Date: Apr 2003
Posts: 323
Quote:
Originally Posted by jwalker
I take that back cos there's going to be a fair amount of kinetic energy stored in that water.
Now you are just laying traps for people. smack your wristies
__________________

__________________
But I may be talking Rubbish.
Expurt is a drip under pressure, and the difference between an Amateur and a proffesional is getting paid.
kitten is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 22:46.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.