Box barge hull shape - which is better?

[waikikin]

This seems to be a good discussion but unfortunately without some basic knowledge, the discussion becomes muddy with the OP not knowing to ask the right question.

It starts with a box design, plumb sides, plumb bow/stern. The block coefficient Cb or the fullness of the hull is 1.

When the front end is sloped, the Cb becomes less, the longitudinal center of buoyancy LCB shifts and further as the hull shape (ship types) transitions. It can shift forward or aft as the illustration shows.

As the ship types progresses from the slow barge to fast ships like containers and military type ships, there are other corresponding parameters that change or will work for the type of ship. This progression is best measured by the froude number or the taylors number, the ratio of speed to length. That is, a low froude number means a slow bulky ship, a high froude number a fast ship.

The first three images shows a box barge, a barge with slope front, a barge with sloped front and end. There is a corresponding Cb and LCB change.

These Cb corresponds to what is best in terms of speed to length ratio (froude number) in the 3rd illustration. Thus, very slow ship with plumb sides would not mind plowing thru the water. Sloping the bow would mean it will be better at battling the head water and thus have less resistance. Sloping the end would mean better flow of the water as it tries to converge back again and not be hampered by sudden transitions, causing residual resistance.

Rounding the bow like a spoon is an improvement and tapering the ends would mean lesser resistance. This is a "fish shape". As it goes faster, the ends are further refined and pointed and includes the width (beam) of ship. Note that even if you have a very fine ship, the resistance would almost be the same with the box barge if towed at a very slow speed, hence the froude number matters.

The attached sheet is based on the simplified assumptions written by various notable authors and establishments.

Great response RX,

Each I believe can be the best and worst given different conditions and loading, that Justa couldn't expand his proposed vessel to include dimension etc a shame... oh well..

Jeff

 

[ImaginaryNumber]

Dave Zieger is an interesting DIY sailor and boatbuilder of sailing barges. Perhaps you might find some of his ideas useful.

http://triloboats.blogspot.com

http://triloboats.blogspot.com/2015/03/roll-yer-own-roll-up-bows-for-boxy-boats.html

http://triloboats.blogspot.com/2012/01/where-ultra-shoal-square-boats-get.html

http://abargeinthemaking.blogspot.com

http://abargeinthemaking.blogspot.com/2013/11/want-need-can-manage-core-considerations.html

http://abargeinthemaking.blogspot.com/2013/11/considering-curvier-dogs.html

 

[Rastapop]

Wow, you guys really gave Justaguy a hard time in this thread. Unnecessarily, IMHO.

He gave enough of a target to point your answers at:

...
Optimized for what? Optimized overall in terms of performance (not ease of construction). If I had to describe the general scenario, I'd say, I'd like to identify that basic shape which would move most easily through the water, put up the least resistance, therefore reduce drag, therefore increase fuel efficiency, therefore optimize speed or at least ease of getting to its displacement hull speed. Assume it would be under its own power.
...

Generally speaking, making numerous assumptions, and guessing that I understand what you're asking (based on what you've written), the answer you're looking for is that #3 is the "best", Justguy. Even better might be a combination of #2 and #3 together, depending on the third dimension that we can't see.

Unfortunately it's not uncommon for some of the more knowledgeable people here to refuse to make a leap to an assumption asked by someone with less knowledge, and instead try to force them to ask the question they want to hear.
I suspect in some cases this is deliberate, and in some cases it's unthinking and automatic, especially in the cases of engineers who spend their careers making sure the answer they give is definitely the correct one, and not a guess.

In this case all you were asking for was a very rough and broad generalisation based purely on the information you'd offered, and not on anything you hadn't.

 

[waikikin]

Wow, you guys really gave Justaguy a hard time in this thread. Unnecessarily, IMHO.

He gave enough of a target to point your answers at:



Generally speaking, making numerous assumptions, and guessing that I understand what you're asking (based on what you've written), the answer you're looking for is that #3 is the "best", Justguy. Even better might be a combination of #2 and #3 together, depending on the third dimension that we can't see.

Unfortunately it's not uncommon for some of the more knowledgeable people here to refuse to make a leap to an assumption asked by someone with less knowledge, and instead try to force them to ask the question they want to hear.
I suspect in some cases this is deliberate, and in some cases it's unthinking and automatic, especially in the cases of engineers who spend their careers making sure the answer they give is definitely the correct one, and not a guess.

In this case all you were asking for was a very rough and broad generalisation based purely on the information you'd offered, and not on anything you hadn't.

A combination of a vertical headlog to deck edge, an angled(30 better than 45) swim end and a radius transition/tangent to bottom panel could be closest to ideal..... all this knowledge supplied- so a OP can know a combination is the best.... therefore all are best, and where not used are worst
Seemed that the OP wanted to confirm a preconceived conclusion when all as drawn were poor choices, all you really need to do is go look at some self powered barges, the operators and designers are not inept.
Jeff.

 

[Mr Efficiency]

I'd go with the design of the Royal Barge. Good enough for Her Majesty, QE II, good enough for a bloke who calls himself "Justaguy" !

 

[Mr. Diy]

Wrong foot

NavalSArtichoke,

Somehow, we've gotten off on the wrong foot. It happens. For my part, I'll back up and assume that you generally want to help. Intended or otherwise, your tone distracted me. You certainly did provide some useful information in your first reply. I failed to acknowledge that. That was my mistake.

I do know mostly what I want to do with this barge. For example, I mentioned that it would be self-powered. While that is only one piece of information, again, that is purposeful.

What I don't want to do, in the beginning, is approach this like a NASA engineer. That is not due to a prejudice or lack of ability on my part. There is a very specific educational reason for that.

Simply put -- if you're going to teach someone something, you have to meet them where they're at, not where you're at. Additionally, people new to a subject learn in a sequence, beginning with generalities, and moving to details. Why? Details tend to be rejected as irrelevant or incomprehensible until there is a relevant and comprehensible generality to hang them on.

So, Take 2?

The problem that you haven't faced is that your barge is a PROJECT - the project includes exactly what you want to do with it....its main purpose or function in your future life where the project includes owning a barge. The two great disasters we face with PROJECTS is firstly lack of holistic clarity.... daydreams intrude about what we 'might' do with project entities and this can lead to OVER-REACH and lack of clarity...not coming down to earth to focus on the essential function...what we must do to complete the project. The other disaster is obsession with small details, looking for a silver bullet fix in order to economize and save money perhaps can lead one to not see the forest for the trees. This obsession leads one into more dry gullies than Burke and Wills ...wasting time on dead-ends. I'm sure I've wasted about two months myself with disasters on both fronts. Perhaps Zabana rum ($2) rather than my old favorite Myers($38) didn't help! NavalSArtichoke is trying to save you from the mistakes I made.