I'm planning on building a floating dock and am looking for advice on framing. More Specifically, i'm wondering if anyone knows what the maximum length I can span between two floats?
I inherited some pretty heavy duty floats (6ftx3ftx2.5ft plastic floats filled with styrofoam). From the research i've done, I think these should each have 1500+ lbs of buoyancy.
I was thinking about using two floats to build a 7' x 16' dock. The framing will protrude over the floats by 6" on each side (of the 6' float), and i planned on overhanging the framing by 1ft on each end. With that math, I will need to span ~8ft between the two floats (16ft – 2*1ft overhang – 2*3ft float). I don't want to add another float to the middle because the floats i'm using are already overkill from a buoyancy perspective. Here is a simple depiction of the framing. Realistically, I'll probably integrate the floats into the framing so it doesn't sit as high off the water.
I was planning on using 2×6 pressure treated spruce (between 12" and 16" o.c.), but wanted to know if this would be strong enough to span across the 8ft section?
I've checked a few deck joist sizing/spacing tables and it seems like with 2×6 @ 16"o.c. I should be able to span up at least 8'4"; however, I'm wondering if I can use this for a dock where it won't be in a static position and will experience some movement as it is floating on the water.
Any advice would be greatly appreciated!
Best Answer
Assuming just human loads on it then you can go by the information in the table as a guide. Consider that the pressure treating will affect things, reducing the strength by about 15%.
The two edge joists need to bear on the floats too, you show them not bearing on the floats, or they span the full distance between the end members.
I think that twisting will be more of a concern when the floats are in opposite directions as waves pass by them differently. At least add blocking between the joists in the middle of the floats or at the inside edge to add some rigidity. It might be fine without them. I've spent many summers around and on swimming floats (that's what this is, yes?) and they were built basically as you show it.