I want to cantilever a dock out over my pond. Have tried to search the internet for the way I want to do it and found nothing. Basically I want to install a concrete base in the ground on the shore with 2 3/4" masonry threaded rods 4' apart sticking up about 6". Take 2 3" or 4" black iron pipe 20' long and drill a hole about a foot from the end of the pipe slip it over the rod and fasten with washer and nut. Put my deck on top. The pipe might end up being 15' out over the water.

You didn't state what size dock you have in mind, but even a small one might act like more of a diving board rather than a stable platform, given the construction details you've listed here. I'm thinking the supports for such a platform would need to be massive, if any hope of rigidity is to be realized.

Unless you're going to add posts or piers to support the free end?

Jaegles Cantilever Docks

Elite Cantilver Docks

It's going to be 5' wide by 15' long. The 4" black steel pipe is quite ridged and it would be 2 of them. How much flex is what I don't know. I'm not as worried about the concrete bolt anchoring system as I will make it beefy with re-bar and all that with a concrete tail in the footer. No posts. I have 4 28' steel light poles that go from 2.5"at the top to 6" at the base. One I used as a 25' commercial flag pole. Very ridged at that length. For this I was going to use 21' black steel pipe from the plumbing trades.

Beautiful! I'm drooling.

I wonder if a system of smaller dia. pipe, welded in a truss fashion, might be more rigid than a single, larger dia. pipe?

I noticed that one of the manufacturers Zep linked to uses a cable system to support the outboard end.

Yes the cable system would give the support needed with smaller lateral runs. I was looking for the simplest with minimal work. I got barrels for a floating dock that I was going to do at the beginning of the year, their still in my barn. I built a fish trap turned out beautiful and works, guys on the forums said they did it in a few hours after work, I took 2 days.

The cantilever docks that I've seen used I beams or a metal truss from an roof.

I would prefer I beams in a situation like this. Less overall hassle.

Metal truss is an interesting thought. Maybe get them from a junk yard.

I beams are so heavy but definitely strong. Cost is probably a lot.

Do the math on the lever arm forces that are exerted on the anchors. Threaded rod grade 2, 3/4" has a proof load of 18,400# and a tensile of 24,700#.

Live load is 30# per sq. ft.

How fast that will degrade when the threaded rod starts to rust is anybodys guess.

Wow equations! That's the only real way to know. Wish I was smart enough to figure it out. Do you think the weak link is the rod. That can be worked around. I can find out the thickness and grade of the pipe. The rod was going to be hot dipped made for exterior application.

I wouldn't use threaded rod for anchor bolts. At least make them out of 4140, and only thread the necessary part.

Yeah, there is a bit of math involved for cantilever designs. Really cool, but probably not the best option in a DIY situation if safety is a concern. You'll need a robust anchoring system, which will probably require a lot of concrete. You live in NY, so you have to consider heavy wet snow loads, so yeah, there is a bunch to deal with.

For reference, I just shot off an RFQ for (2) 12@31.8 x 40' American Standard I beams to one of our steel suppliers. This will be the highest priced supplier. I'll let you know what they say tomorrow.

Back in the 70's I had a lake friend that had a suspension dock that looked somewhat like 1/2 of the Golden Gate bridge that seemed to work well. The advantage of his dock not being in the water was that the winter spring ice would break up in large chunks and destroy docks that had been left in the water through the winter.

JCN
I don’t think 3" or 4" black iron pipe is going to cut it if your wanting a 15' cantilever. Even with 6" your still going to feel some spring, JMO.

Some of the long time PB members might remember this project I built 6 or 7 years ago. I had a vision of what I wanted and started with 2-80' long I beams and ran with it.

I guess my question is, why wouldn't you put a single steel post under the pier, and towards the end to add support?

Is the cantilever pier just a visual thing?

I was wonderin' when you were gonna jump in

Brettski, I figured those pics where long gone, thanks. JCN, I know my deck is not what your wanting to do , but it might give you some ideas.

Thanks

Impressive

If I remember the next time I'm at the lake house I'll take some measurements for ya. We cantilevered I-beams out of the house for a porch and ended up putting in support columns because of the deflection.

Yea I think it's a cool look plus I thought it would be less work.

Nice. I personally have always liked working with steel over wood.

My dock It is made of 8" light I-Beam (don't remember the proper term for it, but it is lighter than standard I-beam). It has 4' of cantilever off the end with an 8'hinged connection to a 12x16 floating dock.

Here for any cantilever you need to be 4-1 for every 1 foot of cantilever the engineers want four feet back anchored.

Cheers Don.

Everytime I think of a cantilever design I see Wile E. Coyote nailing those unsupported wooden planks together, trying to make a bridge over to the other side of the canyon. As I recall it usually ended in freefall.


Snrub I hear you on metal over wood..... I much prefer the welder over the nail gun.

Engineers always ask for 4-1 on cantilevers but 3-1 is usually the most economical when calculating out structural sizes. Less than 3-1 just increased the footings, anchors and beam sizes which increase cost. I would not go less than 3-1 without an engineer doing calcs. and detailing the connections. The dock at Jim’s place uses 80’ beams for a 20’ cantilever.

I would also suggest using square tubes and not pipes, lot more strength for the cost. I also think they look nicer than I-Beams.

Jim do you have any photos of the finished dock?

Those are 2 good reasons for sure.

Here is the thread - with pics

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=87582&page=1

This pic is back when the pond was at full pool. My female friends say the little bit of spring at the end of the deck made them nervous...added a few more braces and all is well. Just a little FYI had 11 adults out on the end at one time and only 9 walked back….you can guess what the other did.

Yikes!

Don't beat me up to bad guys but what if i stick with my 4" pipe and weld angle iron across the two ends and then from the center of the angle one support in the pond. There goes my cantilever.

JCN, nobody here will beat you up whatever you decide. Go with whatever works best for you. Most of us do something out of the norm all the time, and some great stuff is learned by all because of it.

If you want a cantilever go for it. You could always add a brace after it's done if you need or want to.

I would also consider adding "Y" braces.... from the outside edges of the pond/pier down to the center support. Without them, I think it would still move around anywhere except right over the support.

JCN, like FireIsHot said "If, you want a cantilever go for it" Hell, if it wasn’t for people trying new things we would still be living in caves.

JCN,

Beams came in at $1,310.00 each (those were the 40')

It depends on the end fixity of the beam in a solid setting, and how solid that foundation is.

If you used I beams, I think you could bore in and pour 4 concrete piers, use 24' beams, with 9' anchored on the piers and 15' hanging over the water.

I think that would be reasonable, but there is a lot of number crunching involved.

I really like the idea, but like I said, It's probably not the best candidate project on a DIY level, if you are not familiar with the engineering involved and want to make it safe for everyone you love.

Actually Jim, there are a lot of people dead because someone was trying new things that they didn't know what the hell they were doing. Worst thing is, they killed someone they loved from their ignorance.

You know!! A number of years back I was in Circuit City trying to learn about HD tvs, always been an audio video guy. Back in the day all you had was the sales man for any tech information. Some had great knowledge, most not. I was shooting the bull with another customer and said just check it out on the AVS forum. Well the knowledge I gained from that forum was amazing. First HD TV was a 50" 720p Panasonic plasma for 3400.00 dollars ordered from the internet. Who ordered a TV from the internet for 3400 bucks? A lot of people but certainly not the majority. I've been lurking on this site for a while. Could not find enough specific information on the web. So I threw my question out. The knowledge to gain From The Pond Boss forum is really amazing along with many forums. Just thought I'd throw this little story out there and appreciate the conversation.

Thank you very much for the info, gives me an incite to that approach.

Way cool Jim!