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Up Topic Welding Industry / General Welding Discussion / float tanks
- - By weaver (***) Date 08-11-2010 03:39
hey all, We have been asked to make some alunimum float tanks for some walk ways leading to docks. the walkway weighs around 800lbs. any ideas on formula's ?
Parent - - By DaveBoyer (*****) Date 08-11-2010 03:46 Edited 08-11-2010 03:52
Water weighs about 64#/CuFt [fresh water slightly less]. Don't forget to subtract the weight of the "tanks" from Your calks, and that You have to allow for people, dock boxes, golf carts or whatever will be on those docks.

As long as ther is more "tank" above the water, You still are safe, but once fully submerged, they will sink like a rock, so allow plenty of additional boyancy above expected loads.

I suggest You put "tanks" on each side with space between them for stability, and EACH side should be able to carry the total expected load, as everybody may be on one side of the dock.
Parent - - By 803056 (*****) Date 08-11-2010 04:10 Edited 08-11-2010 04:43
Building floats for docks can be tricky because you want them to support the anticipated loads times a safety factor, but you don't want them to overturn if everyone is standing to one side. That means they can not float too high out of the water thereby placing the center of gravity (think of the all the people standing up on top of the dock) too high above the water line. One way of providing stability is to make sure the dock is rather wide so that it doesn't overturn easily.

The volume of the floats has to equal the (weight of the floats plus the dock structure and the people times a reasonable safety factor / by the density of water) . The dock surface has to be high enough out of the water so that waves are not going to break over the dock or cause it to overturn. The shape of the floats can also influence stability. The floats could have a cross section that is triangular so that the heavier the load, the greater the volume of water displaced. The sketch is just a concept that might work. the actual dimensions, weight of the ballast, etc. would have to be calculated.

You have seen it mentioned here in the Forum a hundred times if you have read it once, a consultation with an engineer, in this case a Marine Engineer, is well worth the money spent.

Best regards - Al
Parent - - By Cactusthewelder (*****) Date 08-11-2010 10:17
AND, you MUST have a Floating Dock Stamp !!!!!!!!! or a Duck Stamp, I forgot which  one it is.
Parent - - By 803056 (*****) Date 08-11-2010 12:30
From what I've heard of late, the Ducks haven't fared well. One sank or malfunctioned in Boston and another one was recently steamrolled by a barge in Baltimore. So, I'm not sure about the "Duck Stamp."

Best regards - Al
Parent - - By weaver (***) Date 08-11-2010 13:36
the docks that are already there have floats made of plastic, the measurements are 24x48x72'', and the customers want to follow those measurements
Parent - By 803056 (*****) Date 08-11-2010 13:40
Make sure you select the right aluminum alloy and filler metal for the type of environment the floats will be in, i.e., salt water or fresh water. Some aluminum alloys (magnesium alloys) will exfoliate when sujected to a salt water environment.

Best regards - Al
Parent - - By DaveBoyer (*****) Date 08-12-2010 01:25
One just got hit in Philly, lost power in front of a barge & tug, if I remember right.
Parent - By 803056 (*****) Date 08-12-2010 03:53
I believe you are right. I had the wrong city.

Al
Parent - - By rcwelding (***) Date 08-11-2010 13:34 Edited 08-11-2010 15:57
LOL... Now that was funny..!!  Dock stamp..!!!!
Parent - - By 803056 (*****) Date 08-11-2010 13:43
The duck that was sunk by the barge in Baltimore resulted in two passengers drowning. An unfortunate accident. I haven't heard what the investigation turned up. I understand from the news reports that the tug captain didn't respond to the radio calls made by the duck just before the accident.

Best regards - Al
Parent - - By jwright650 (*****) Date 08-11-2010 15:27
Al,
From what I understood, the tug captain just thought it was some quack transmitting on the same frequency and didn't pay any attention.
Parent - - By 803056 (*****) Date 08-11-2010 15:52
Are you referring to the squawk box?

Al
Parent - - By jwright650 (*****) Date 08-11-2010 15:57
Yes, that fowl thing.
Parent - By rcwelding (***) Date 08-11-2010 16:02
I bet he flew off the handle after that..!!!!
Parent - - By warmka weld (*) Date 08-11-2010 23:19
As long as the floats are air tight they shouldnt sink even if they go below water level.  Try and sink a basketball. But extra float is always better.
Parent - By DaveBoyer (*****) Date 08-12-2010 01:28
If You put more weight on them than the water they displace, they sure as hell will sink, even if they are water tight. It isn't that hard to sink a basketball, just put more weight on it.
Parent - - By rcwelding (***) Date 08-11-2010 15:20
I was supposed to build a floating dock this month but when I looked up the cost of making the floats verses buying pre-made floats it wasn't worth it...  So the dock is on hold.. He still wants me to make the dock main frame but we are going to buy the floats...

  Here is one site I found and there are many more out there..

  http://www.dockaccents.com/floating_docks.htm#Float

  RC
Parent - - By jwright650 (*****) Date 08-11-2010 15:24
RC,
Wow, I can't see anyone trying to build thier own, when those are that cheap.
Parent - By 803056 (*****) Date 08-11-2010 15:40 Edited 08-11-2010 20:02
That's true with most things, if someone is already manufacturing something, it is almost always cheaper to buy it than to build it yourself.

However, there is something to be said about the satisfaction and frustration of trying to build it yourself. It is  hard to imagine going through life without a  few, "I told you you would get hurt if you tried to build it." or "Who's going to replace the wall you had to knock down to get it out of the livingroom?" or "Now that you're done, how are you going to get it out of the basement?" or "You want me to hold it while you do what?"

"Aren't the floats supposed to be under the dock?"

I suppose I really do have to get back to the Level III examinations I'm supposed to be writing. Writing examinations is like having your teeth drilled.

Best regards -Al
Parent - - By rcwelding (***) Date 08-11-2010 15:49 Edited 08-11-2010 15:51
That's what I ran into... This customer has been great to me for the last 8yrs so when I found this site I told him my bid was way out of sight and we could do it much cheaper...  I lost some money on it but it makes him happy and trust me more, so I will make it up on another project for him down the road...

    RC
Parent - - By 803056 (*****) Date 08-11-2010 15:53
Best policy in the long run.

Al
Parent - - By Tommyjoking (****) Date 08-11-2010 19:45
Just as an aside.....nobody here ever mentioned filling the floats with a styrofoam.   That should always be done as a safety backup.   For water displacement, load calculations etc.  Really good information, formulas/regulations, can be obtained from the US Coast Guard.
Parent - By 803056 (*****) Date 08-11-2010 20:00
Good idea.

Al
Parent - - By rcwelding (***) Date 08-11-2010 20:44
Those pre-made floats come with it already in them...
Parent - - By weaver (***) Date 08-11-2010 23:34
we looked at the pre made one today, talked to the customer, (government job). And they want custom tanks. so it should take me about 5hrs to tig up about 100 linear ft of weld, tig tig tig ... I love to tig weld
Parent - - By rcwelding (***) Date 08-12-2010 01:48
They have a two part flotation foam that you can put into the tank for a safety factor.. Weld up your tank... Drill a hole in the top and put the foam in... It acts like expansion foam and will swell...When it runs out the hole you are good... A friend of mine builds bay boats and he puts it in special chambers for a safety factor...  It is a special foam I don't remember the name of it...

   I trust your welds but if a boat hits it or some idiot shoots it...  Down goes your dock... Just a thought

    RC
Parent - By Bob Garner (***) Date 08-16-2010 18:49
The secret to a float that is stable and not "tippy" is to make sure the center of gravity of the float is below the center of buoyancy, the farther the better (known as the metacentric distance).  The center of buoyancy is the at the center of gravity of the displaced water.  As an engineer, I usually "run the numbers" to make sure my design is stable.  But one way to accomplish this without the math, is to make the float deeper than you think you want and pour gravel or similar into the tank.  That lowers your float's center of gravity and enhances tipping stability.  And you can pour in just enough gravel to get the freeboard you want.  Too much and you can remove some.

Bob
Parent - - By Tommyjoking (****) Date 08-16-2010 19:27
The two part foam comes in tanks...getting even small tanks of the stuff is pricey...It works great tho.    I do not know if you can find someone who will rent the tanks and mixing gun, weigh it then weigh it when you bring it back and charge by the pound.    When I was building boats we used an appropriate density styrofoam block.  It is cheap and just about any boat manufacturer can get you some sticks of it.  We would cut it with a hot wire and use it inside bench seats and such.  Even when doing floors or decks, scrap foam was put in before we used the spray stuff because of cost.     If you are making say a square box....put the foam in with 45 degree angles cut where your weld seams will be,  have it about 3 inches away from each weld seam and you can weld it up without a fire easy.

Don't forget to thread you some aluminum plugs to put a sealing/drain bolt in.....awful hard to seal that last inch of weld.
Parent - - By JLWelding (***) Date 08-16-2010 22:08
Where do I get a Duck stamp?
Parent - By DaveBoyer (*****) Date 08-17-2010 02:08
Closest thing I know of is a "Migratory Bird Stamp" for Your hunting liscence. Check with the game commission...
Up Topic Welding Industry / General Welding Discussion / float tanks

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