6 x 6 Pressure Treated Posts

[lakngulf]

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]

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]

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]

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

 

[lakngulf]

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]

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]

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]

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]

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

 

[lakngulf]

Where did you find that swivel?

https://www.swingsetaccessories.com/shopping/pgm-more_information.php?id=44&=SID

 

[Johnbro]

I wouldn't use a 6x6PT across the top as your top beam. First of all, you don't need PT unless you have ground contact or the wood is constantly wet, which you won't since it's up in the air. Second, a 6x6 will be very heavy, difficult to get up there, and won't offer as much strength as a built-up beam will.

If it was me, I'd just sister the two 2x12s (hem-fir) with some blocking in between and call it good.

as to the question of how long the cantilever can be, two 2x12s on edge would make a strong beam--if it's not quite strong enough for the load it will flex a bit (just like a tree limb sticking out over a river that some kids have used as a rope swing). I'd use some Simpson strong tie metal to anchor it to the two posts as further insurance.

 

[Dutch445]

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.

Congrats on your waterfront , it's beautiful!!! It makes me jealous as I used to own a piece myself till I lost it in a divorce, I doubt I'll ever be able to make it happen again. Enjoy it!
(sounds like you do!)

 

[lakngulf]

Second, a 6x6 will be very heavy, difficult to get up there, and won't offer as much strength as a built-up beam will.

If it was me, I'd just sister the two 2x12s (hem-fir) with some blocking in between and call it good.

Please expound on this. Sorta have an idea but could use more details. Distance of the post from outside to outside is 7 feet. I want the extension over the water to be seven feet from post if possible. Can I do this with the beam approach?

 

[lakngulf]

Well I forged ahead with most of my original plan. It may not be all that pretty but I think it will be enjoyed by grandsons (6,3,2,4 months). Poppa will have to give it a try also.

Of course, the water has to come back up before any swinging. Each year our lake is drawn down 10 feet.

I tested the rope and there is almost no give when all my weight is on the rope. There is some give when simulating the type of swinging that will be done from the pier. The "swing around" does cause some rocking of the posts

 

[EddieWalker]

I've been confused on what you were trying to do, so didn't say anything. Seeing the picture makes it all clear to me. Must have been the bald in me!!! LOL

That sure does look like a lot of fun!!!!!!

Eddie

 

[weldingisfun]

Hey Eddie, that was a good one. Instead of having a BLONDE moment, you had a BALD moment.:laughing:
Now wait a minute, what is my excuse going to be, I'm neither blonde nor bald?