Dumb barge design

[Vinassman]

Dear all,

I know my question will not raise innovative comments regarding new technologies but I have it in my mind and I would like to settle this.

Everybody knows the dumb barge you can see especially close to the river where the larger vessel cannot go? If you see them being towed, they never reach higher speed than 3-4 knots. With a length of let's say 100 m, we have a froude number around 0.03... Which is ridiculously small isn't it? So, knowing that at this kind of froude number, the wave resistance is nearly inexistent, why did the designers make such a "good work" on the bow shape? It would have been me, knowing there is no propeller, I would simply make a box (and a real box, square everywhere)...

What do you think? Am I missing something? And I guess this is more or less the same thing for Self-propelled barge, unless they have a higher value of froude number (around 0.15) and propeller so designers have to work the stern shape. But still I cannot see any reason not to have a box-bow-shape...

Thanks for the attention,

VM

P.S: by the way, is there any work/documentation/publication/literature/material on barge and self-propelled barge? Cause I guess all the usual factor such as to estimate the weight or the usual ratio length/beam are quite different. Might be interesting to get some materials on that.

 

[JRD]

well there is the small matter of form drag.....

 

[Perm Stress]

box , even at 3-4 knots of speed WILL create waves in the water

 

[Vinassman]

Yeah for sure a box or anything will create waves at 3-4 knots, very true . My point is more to say that at this kind of very low froude number, the shape has nearly no influence on the resistance since, comparing two shapes, one like a box and the actual shape of the dumb barge:

- frictious resistance: wetted resistance will be slightly higher so we might expect a few percent of increase
- residual resistance: there will be an higher increase on this resistance.

However, at froude 0.03, the total resistance is maybe 95% frictious and 5% residuals, so the total increase will be mainly due to the increase of wetted surface.

So, since speed is usually not a critical point for these barges but their deadweight yes, then I would suggest to go extreme and to make nearly a box which will increase the resistance by 5% so will decrease the speed by 0.1 knots but which will allow to load 100 MT/voyage (estimated figure but it's just to illustrate)

I hope it's more clear . Thanks for the replies though

VM

 

[Perm Stress]

I can assure you, box generated waves will make more than a few % of difference.
5% or so , as you mention is true for reasonable decent designs only.

 

[Vinassman]

Alright Perm Stress, I understand. Do you have some recommended literatures for this matter (influence of shape, especially with high Cb on the resistance) so I can go further?

Thanks again.

 

[yipster]

You can have resistance calculated with for example delft / freeship

 

[pistnbroke]

get it up on the plane no problem with drag /waves etc

 

[Perm Stress]

Alright Perm Stress, I understand. Do you have some recommended literatures for this matter (influence of shape, especially with high Cb on the resistance) so I can go further?

Thanks again.

As I did found out in last few years of work in design office, barge hullshape design was stagnant for nearly 30 years (in Europe).
In general, design of hulls for ships with block coefficient ~0.9 and above, as well as ship hydrodynamics in shallow water is developing intensively just now, so good place to start would be towing tank facilities websites.

 

[tspeer]

well there is the small matter of form drag.....

Exactly. Even if there were no wave drag, there would be large separation bubbles at the bow corners of the box. These would cause lots of drag. There would also be drag due to the base area of the box at the stern.

At low speed, the water surface can be approximated as a solid boundary, allowing the flow to be approximated by a reflection plane model. Hoerner shows that for a rectangular cylinder, the drag can be cut by 80% by rounding the corners with a radius of 20% of the height of the cylinder. This still leaves 60% of the face as a flat surface. So even in the absence of wave drag, some shaping instead of a pure box can significantly reduce the drag.

 

[Vinassman]

@Perm Stress:

Thanks for the update, I appreciate. However, what do you mean by "towing tank facilities websites"?

 

[Perm Stress]

@Perm Stress:

Thanks for the update, I appreciate. However, what do you mean by "towing tank facilities websites"?

first that came to mind (my former company partner's office was close to them) is Hamburg Ship Model Basin at "www.hsva.de"; however, barges and extremely thin water ships are not their main concern.
Try to google "ship model basin" and select basins specializing at barges -just before the crisis there was a large boom in barge building/commissioning in Western Europe, feeding the scientific investigations along the way.

 

[Vinassman]

@tspeer:

Are you refering to Hoerner's fluid dynamic drag?

 

[tspeer]

@tspeer:

Are you refering to Hoerner's fluid dynamic drag?

Yes, that's the one.