6 x 6 Pressure Treated Posts

lakngulf · Dec 22, 2010

I have an idea on building a rope swing for my grandsons to swing into the lake. On each side of my five foot wide pier I have placed a 20 foot 6x6 pressure treated post. They extend above the pier about 9 feet. I plan to place another 6x6 on top of them with one end extending out across the water, with a rope swing attached to it. They will swing from the pier into the water.

So how in the world will the top 6x6 stay up there and support the swing?

I have two 12 foot 2x12's that will be bolted to the two vertical posts and to the one on top. Also, I plan to put in some angle support, either some 2x6's or a 4x6 cut to fit under the section of 6x6 that extends beyond vertical posts.

Something like this:
__________
| | b
| |
|_|
| |
| |

My first question is this: How far can I extend the top 6x6 over the water and it still maintain enough strength to hold the swinger (b) above? I am so sorry for the crude drawing.

Dutch445 · Dec 22, 2010

Can you use another 20' 6X6 and span both posts,
with the excess extending outward? You could half lap it
into the uprights, or just long carriage bolts, but
i would think some more support along the uprights
may be needed also, maybe a piece at a 45 coming
up from the deck.

rd_macgregor · Dec 22, 2010

I'm not sure I followed your drawing, but I set up what sounds like a similar swing in my backyard with a 6x6 on top of two vertical 6x6's. I had a regular two-chain swing in between the uprights and a bouy on a rope hanging from an outboard/overhang (of about 5'). I used PT plywood gussets to hold the horizontal piece securely on the two verticals. I suppose it could be keyed and pinned, but the gusset plates work just fine both to hold the horizontal piece down and to stiffen the two verticals so they don't go rhomboidal.
Over 15 years or so, the overhang/cantilever portion has sagged an inch or so, but is still plenty strong. An even stronger holddown method would be an inverted U-shaped steel strap over the top and bolted through the uprights...but plywood was an easier fabrication for me to do.

BOB

forgeblast · Dec 22, 2010

Thats what i was thinking, using two uprights and one to span them....like a goal post.

lakngulf · Dec 22, 2010

forgeblast said:
Thats what i was thinking, using two uprights and one to span them....like a goal post.

That's what I have, a 20ft post on each side of the pier. The pier is five feet across. On top of those will sit the third 6x6, and which will be sandwiched between 2 2x12's. I will bolt on the 2x12's to the two vertical and one horizontal 6x6.

SPIKER · Dec 22, 2010

what you might want to think about is using a pipe or board that can rotate around the end of the top 6x6 so that they can swing out & farther away from the end of the pier & also swing in closer to grab onto. not to mention if the pipe is bent up think hangs man type looking pipe that way the rope can be longer than just the 8 feet above the dock to help the swing out & away & then the pipe & rope can swing around pretty easy.

Mark

lakngulf · Dec 23, 2010

Here is an update with maybe a little better drawing:

I have on order a swivel attachment for the rope. SPIKER, this may get the effect you were mentioning. Also, a picture of the pier. The 20ft 6x6 posts are placed right at the end of the narrow part of the pier. Hopefully the word document gives a better rendition of what I am trying to accomplish.

dieselscout80 · Dec 23, 2010

lakngulf said:
Here is an update with maybe a little better drawing:

I have on order a swivel attachment for the rope. SPIKER, this may get the effect you were mentioning. Also, a picture of the pier. The 20ft 6x6 posts are placed right at the end of the narrow part of the pier. Hopefully the word document gives a better rendition of what I am trying to accomplish.

Where did you find that swivel?

Craig Clayton · Dec 23, 2010

On the issue of Pressure treated lumber the new movement is not to have it touching water ways. If you were redesign using cedar, doug fir , redwood it would be better for the future. I did not fully understand your design ,but I understand what you want for them.
Craig Clayton