Best Equation to determine thruster force?
Best Equation to determine thruster force?
(OP)
Hello all,
What is the best equation to determine the reaction force for a tunnel thruster (bow or stern)?
I heard about involving windarea and even transverse current.
Please help me out!
Greetz,
Martin
What is the best equation to determine the reaction force for a tunnel thruster (bow or stern)?
I heard about involving windarea and even transverse current.
Please help me out!
Greetz,
Martin
Unigraphics NX4,NX3,NX2,R17
Inventor 2008,11,10,9,8,7
Solid Edge 20,10,9,8
Solid Works 2000,98
Mechanical Desktop 4,3
Autocad 2004DX,2000,R14, R12
Teamcenter Express 3, 9





RE: Best Equation to determine thruster force?
Tie your vessel to a dock wall and install a graduated gauge in your wire or rope spring. Ramp up the thruster and take your pull readings at various thruster speeds and angles.
Offshore Engineering&Design
RE: Best Equation to determine thruster force?
Unigraphics NX4,NX3,NX2,R17
Inventor 2009, 2008,11,10,9,8,7
Solid Edge 20,10,9,8
Solid Works 2000,98
Mechanical Desktop 4,3
Autocad 2004DX,2000,R14, R12
Teamcenter Express 3, 9
RE: Best Equation to determine thruster force?
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Best Equation to determine thruster force?
greetz
rob
www.technofysica.nl
RE: Best Equation to determine thruster force?
RE: Best Equation to determine thruster force?
Let me rephrase my question.
What are the inputs to determine a thruster in general?
The result is in kN. Thats a given. But what should I put in for the rest of the equation and what does the equation look like?
I have seen some calculations before, involving windarea and a pivot point.
Unigraphics NX4,NX3,NX2,R17
Inventor 2009, 2008,11,10,9,8,7
Solid Edge 20,10,9,8
Solid Works 2000,98
Mechanical Desktop 4,3
Autocad 2004DX,2000,R14, R12
Teamcenter Express 3, 9
RE: Best Equation to determine thruster force?
T = rho*pi*(D^2/4)*lambda*ve^2
where
rho = density of air
pi = 3.14159
D = diameter of propeller disk
lambda = ratio between velocity on propeller disk and exit velocity
ve = exit velocity
T=thrust
for a diverging duct lambda > 1
for a parallel duct lambda = 1
for a free propeller disk lambda = 0.5
the power absorbed is:
P = rho*pi*(D^2/4)*lambda*(ve^3/2)
so you can calculate the thrust by power (at fixed point):
T = (4*lamba*rho*(pi*D^2/4)*P^2)^(1/3)
this is tha maximum thrust because remebering that an equivalent form of thrust is
T = mp*(ve-v);
and at fixed point v = 0;
That assumes no friction and other losses, in practice you'll need anything up to twice that power to create the thrust.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Best Equation to determine thruster force?
1) given the dimensions of your vessel, what thrust do you need
2) given the thrust needed, what thruster power do you need to develop it
As to the former, it sepends on the size of vessel of course. But also on the preferences and policy of the owner and operator. If you look at ferries in Northern Europe, thirty years ago they might have had one bow thruster, then it became 2, and now it is three. The weather has not changed.
One way of asking the owner or operator to clarify their wishes is to specify the wind (or current) against which you would like the boat to move bodily sideways (or at least hold its position). Once that is defined it is easy to work out the thruster force required (it is the same as the applied wind and/or current force - equation given by Greg Locock - all you need are the drag coefficients).
When you have worked out the required force , a rough rule of thumb (for LARGE thrusters) is 100 hp per tonne of thrust. This does vary depending on size and type of thruster but should get you in the ball park.
Larger diamater and slower thrusters are more efficient and will give more thrust per square meter of blade area. But dont make the diamater too large or the thruster will ventilate.
Keep the thruster tunnel short (put it in a NARROW part of the boat).