Horsepower requirement of the tugboat towing the pipeline

Hello everyone,
Is there any rules to calculate the hp of a tug boat required for the pipeline installation for a desalination plant project ?
If there is no rules .. how can we determine the tug's power according to the pipeline specification ?
Thanks in advance

 

You need to calculate all the forces acting on the tug and sum them. There will be friction from several sources and wave making resistance. What are the specifications?

 

I totally agree. The thing is that simple: all the forces are calculated, one by one and without forgetting any, and added together. Beware, you have to add them, not subtract neither multiply. What forces are and how are they calculated? : we'll leave that for someone who knows something about the subject.

 

Despite the previous silly answer, I tried to find out what you need and I can not find out.
Would it be possible to have some complementary explanation? Do you want to calculate the power needed to tow the pipes?

 

Yes, this is what I need.

 

I suppose you could assimilate the pipes to a ship and apply any of the traditional methods for estimating the towing power. The most common, and very reliable, is that of Holtrop-Mennen.
It should also be assumed that the pipes are floating, not submerged .Is that correct?

 

Hi and thanks for your answer.
Some of the specifications are:
SM/1515,
Internal Diameter: 2.5m,
External Diameter: 2.752m,
Thickness: 126mm,
Maximum water depth:20m,
Wave height: 0.5m,
HDPE pipe unit weight: 1350 kg/m,
Pipe length: 144m

 

Thank you, yes they are floating.

 

We have calculated the forces. They are about 10 ton. Wave height is 1.5 m, current is 1 m/s and the pipes will be moved about 2 km.
How can we calculate the tug boat horse power then?
Thanks.

 

What I have calculated with Hullspeed, for a set of 5 joined tubes, is what is shown in the attached file. That is the power that a self-propelled ship, of those shapes and dimensions, would need to move at each speed. I do not know if this is what you are looking for or if that can help you in something.

 

There is no way the pipe resistance could amount to 10 ton, ie 10e4 N!

Use the total surface of the pipe, decide on required towing speed, add current and calculate Reynolds number, based on total speed, outer diameter and actual water viscosity. Then use conventional lambda/Re diagram with actual surface roughness to get lambda value. Finally, calculate friction force using lambda-pipe surface-dynamic pressure. For a Square pipe end, add a dynamic drag from the pipe section area x dynamic pressure x loss factor (roughly ~1). With the waterline length of 144 m, you can neglect wave making resistance.

Propeller efficiency at towing speeds is normally low, say 40 %, so towing power is total resistance x speed/efficiency. This is the towing power, add the power to propel the tug itself at the required towing speed, and you are done.

Edit:
OOps TANSL, your post landed while I was writing. Not clear if your Hp-figures are shaft Hp or net. Suppose they are net, then the diagram shows 1000 hp @ 6 knot for bundles of five. That's roughly 49 kN/pipe, which sounds fairly reasonable.

 

Thanks for kind reply. The pipe is floated therefore only a small portion of it is in touch with water. Do you have any example of your calculation? Cheers.

 

An efficiency of 65% has been estimated.
This method is appropriate for trawler or tug type vessels.

 

Probably the maximum amount of reaction force will be generated by friction at the guide piles. You can make a rough estimate by using friction of wet steel on steel. However, remember that before moving you will use a coefficient of static friction that is much higher than dynamic friction.

 

Have you considered a barge with a winch?
Poida