Pond Boss Forums GENERAL QUESTIONS Property Projects & Construction One gallon of air?

One gallon of Air trapped in a barrel will lift how many pounds of dock and people?

I am building my plan for a floating dock and have calculated the weight of all the material. Just have to add potential people and see how many barrels I would need. I can get a nice low 17" in diameter 30 gallon barrels.

Is there a general rule of thumb of how much one gallon of air trapped will lift afloat?

Cheers Don.

Each 30 gallon barrel will displace....30 gallons. If a gallon of water weighs 8.26 lbs, than a single barrel will float approx 248 lbs. The trick, is deciding on how far out of the water you want the dock to float.

To expound on what Sprkplug said, I figure that I'm ony using 15 gallons of flotation in a 30 gallon barrel because I don't want my barrel to be more than 50% submerged. If you want to get technical, then you also have to figure out what each barrel weighs and take that into consideration.

Note that when arranging the barrel if you will keep the barrel bung hole above the water level you are less likely to lose any bouyancy due to water intrusion.

Scott, if you want to get really really technical, you also would have to weight the air in the barrel and take that into account as the barrel is not holding a vacuum!!!

Sprkplug, esshup,
Are you saying you may want the dock closer to the water? I can imagine that makes a small dock less likely to tip. But what other reason do you have for wanting it lower to the water? Landing fish???

I think the desired distance from dock to water varies upon application. Like Scott, I don't want mine sitting low in the water....I remove it every fall, and the shallow draft makes that chore much easier. Also, we use it as a swim platform, and the kids desire as much "air time" as possible. If A 30 gallon drum will support approx. 250 lbs, then it will be doing so nearly completely submerged. If I remember correctly, when I designed my dock I also figured the flotation at 50%... instead of 250 lbs, I allowed 125.

(Although I used pontoons)

I used 55 gallon plastic drums with the small plastic threaded plug in the top. I floated my dock. When I got it where I wanted it I filled the barrels with water till it was stable and at the level I wanted.

Adding ballast is a good point!

Could the ballast freeze in the winter and damage the barrels?

That won't happen.

Even if it does there is plenty of room for the ice to expand.

I'm using 55 gal barrels and have them nested inside 2x12's on the outside of the pier. (it's not floating yet).

My barrels have 2 bungs, I placed them so both will be horizontal to the water. Either both will be underwater, both will be out, or both will be a little of both.

Wow guys great read and discussion. I really never thought about calculating off 50% of the displacement of the barrel. My dock weight is going to be about 4000#s with roof and Ipe decking.

This being a 16X16 how much people of live weight should I add? I was thinking 10 say 200# people max? 90% of the time there would be 5 people.

The plan is a 5 foot wide 10 foot long gangway to the 16X16 covered dock. Two 10X10 pine posts planted on the shore to hold the dock in place. Would 16~30 gallon barrels give me good floatation but good and stable? Would it be best half full with water for ballast? I figure that if I go half full of water I would need 30~30 gallon barrels. In that case I would see the dock would be 50% more stable. Am I correct in this assumption?

Any idea where I can get those nice galvanized hinges and corner brackets I see on some of these very nice floating docks?

Cheers Don.

Well, here's what I came up with:

A 30 gallon barrel's dimensions are 30" x 20", which means each barrel will occupy 600 sq. inches of dock space.

A 16' x 16' dock, converted to inches, has approx. 36,864" of surface area. Dividing 36,864 by 600 gives room for 61 barrels, in a perfect scenario anyway, which is not at all realistic... let's say you go with 54 barrels.

54 barrels utilized at one half flotation capability (125 lbs)gives us a capacity of 6750 lbs for your dock. If it weighs 4000 lbs empty, then you have room for 2750 lbs of guests.

At least, that's how it appears to me.

Yep! The math works!

Huuuwaaa? 54 barrels man maybe I should use 55 gallon pickle barrels. That is a pile of barrels. I guess I have till spring to start collecting.

I can get the 17inch in diameter 30 gallon barrel but 50 wow.

Thanks guys. I do love the math.

Cheers Don.

Just thinking more about the thought of placing 50% water in the barrels. In this case the barrel with out any weight on it will float half way out of the water right? When the weight is added it then would be totally submerged in the water.

I am thinking that it would be better to be half way into the water with these barrels so the bungs are at the water level. I can then figure the water level to my deck of the dock height to be say 6-8"s above 50% of the barrels if I use half as many.

Then planting an anchor with stainless cable and stainless pulley. Then one end would be hooked to the anchor the other a weighted ballast. Say two five gallon pails of cement for anchor and one as ballast. This should hold the dock in place and help stabilize it as well.

Thoughts?

Cheers Don.

Here's what you do.. Find the dimension of a dock you want.. Next figure out the most possible 55 gallon drums that will fit under it.. If you do that you won't have buoyancy problems that simple.. If you don't want the barrels as visible from the side you 2x12 for sides to hide more of it.. On your walkway to the dock try to make it atleast 1/3 the with of the side od the dock it's attached to and anchor it to the bank with no play very securely.. Don't over think it I coud have fit 6 more barrels under my dock and i throw big parties with 10+ kids on it at a time and I know I've been on it with atleast 8 adults and it's sturdy as can be although does sway a little from not using the 1/3 formula..

BGK, how many barrels did you use? Great looking dock!!

I don't even remember I think 18 and 2 where the pier meets the dock..

Here's where the hardware comes from. They have floats too. If you were going to go with composite decking, you'd have to use these floats because the joists would have to be on 16" centers.
http://www.dockbuilders.com/floating-dock-hardware.htm

They have a pier building program too. Just call them, tell them what size of a pier, and they can tell you what hardware and how many of what sized floats you will need.