floating dock question

[Old Yeller Boater]

I'm building a floating dock for my lakefront lot. It is an 8x10 floater made of pressure treated wood. 2x10 sides and joists and 2x6 decking. I've calculated the weight of materials to be 1400 pounds (this is a conservative estimate, because weight is 1225 for the wood and other materials like bolts and brackets would add a bit more). Again on the conservative side, I've estimated the weight of 8 people on the floater each weighing 180 pounds. The two figures together is a total of 2880 pounds. (I'm rounding this up to 3200 for my calculations below to be conservative)

I've researched floats in a 24x48 size for weight capacity as follows:
12 inch tall - 450 pounds - quantity needed 8
16 inch tall - 600 pounds - quantity needed 6
20 inch tall - 750 pounds - quantity needed 5
24 inch tall - 850 pounds - quantity needed 4

I'm leaning toward getting 4 of the 24 inch floats and placing them on each corner. Does anyone have any experience/thoughts that I should configure it differently? As I'm not familiar with using floats and their capacity, I'm just guessing at what would be the right direction.

thanks!

 

[lakelover]

Re: floating dock question

This is interesting. Sorry I can't help you, but hope someone here can, I'm curious about the solution. How do you plan to take it in and out of the water? Or do you?

 

[joed]

Re: floating dock question

Have you considered how low they will sink into the water and how low/high that will make your dock depending on if the floats are up inside the dock framing or completely below the structure?

 

[Fishing Dude too]

Re: floating dock question

I have built a floating dock, I saw many built before I did mine. Some had end float way up, others had a yaw to them. Over the years mine has remained straight and level. No engeneer but did figure weight, then how to space floats. I would say go with 20 inch floats and 6 of them. The cost I had was delivery as came on a LTL truck thank god was a buisness address.

 

[Old Yeller Boater]

Re: floating dock question

Thanks for the replies guys. I may just ask a local dock builder since I'm really not clear on how to plan it. I have considered/thought about how low or high it might float in the water. That's one of the reasons I'm not sure what height floats to go with. I have a local company that has floats for fairly reasonable prices, so plan to get them locally and haul them to my lake lot. I've seen some basic plans online that call for 16 inch floats, but had a chance to get some used 24s, so that's what started me down the path of considering which would work best.

I am in the process of building the float on my lot at the lake and will get some buddies to help load it onto a trailer and will back it into the water at the ramp to launch it. Once in the water, it will never have to come out except for repairs.

 

[Old Yeller Boater]

Re: floating dock question

I've been doing some more researching and searching on the web. A good rule of thumb seems to be to multiple the square footage of the dock by 30 pounds to arrive at a total weight for floats to support. Generally, try to find an even number of floats that will cover that weight. For example, 8x10 equals 80 square feet. That calculates to 2400 pounds. If a float will handle 600 pounds, then you would need 4 of them. Some consideration should also be given to the depth of the floats too, as that will affect how much of the floater would be above the water. This is referred to as "freeboard". Based on some calculations I've done, I don't think that has a very large effect, at least not in my circumstance.

Here's some further examples of it using my 8x10 floater. These are based on some lumber weight calculations I found. My dock would actually weigh about 850 pounds.

using 6 24x48x16 floats, the float capacity would be 3600 pounds. that is 23.61% of the weight and calculates to 12.22 inches of the original 16 above water.

using 4 24x48x16 floats, the float capacity would be 2400 pounds. that is 35.42% of the weight and calculates to 10.33 inches of the original 16 above the water.

less than 2 inches difference without anyone standing on the float and just having the boat tied up to it.

The difference comes with how many people it would take for the floats to be submerged. using 4 floats would allow for roughly 1200 pounds of people. at 180 pounds each, that would be almost 7 people. if using 6 floats, that allows about 2700 pounds which would be 15 people standing on it.

Hopefully someone will find all this data useful.

 

[Bondo]

Re: floating dock question

Ayuh,... The I've built a few floaters,... I use 55gal. plastic drums,..

I find 'em for 'tween Free, 'n 10 bucks a piece... each floats 440 lbs..

All mine have floated,.. Nicely..

Lookin' back, from now on, I'll fill the available area with drums...

Even if ya don't need the flotation,...
Eventually, a drum will leak,..
bein' over drummed, it won't have to be pulled, 'n changed, for along time more...

My last is a steel I beam, 'n angle iron construction with 8 barrels,... shoulda put 8 more...
I launched it 4 winters ago, 'n it's Still floatin',... Nicely....
It floats as a dock all summer, 'n freezes into a slip over winter...

I've been changin' out a few rotten deck boards,...
The drums I've seen are still holdin' a full load of Air....