Help designing a dock

[Stumble]

I am in the process of redsigning my dock to make it more user friendly and was hoping I could get someone to do some quick calculations so I know I won't wind up in the water as soon as I stand on it.

Right now the pilings are in place with 4X12's bolted perpendicular to the slip, then 2X12's set on top of the 4X12 running parallel to the dock. On top of the 2X12's are 2X6 deck boards (perpendicular to the slip). This is all pretty standard and I don't have any worries as is. The problem is I would like to widen the dock from its current 3'6" width to 5'. To do this instead of adding another 2X12 support I would like to just increase the length of the deck boards. If I increase the length as far as I would like this would give me about a 16" cantilever from the outside edge of the 2X12 to the end of the 2X6.

So the question is:

1) how long of a cantilever can I have using 2X6 boards assuming a working load of 400lbs?

2) would screwing an unsupported board to the bottom of the deck boards increase the load it could carry? The idea to make all of the ends flex as a single piece.

3) If what I am thinking won't work, does anyone have a suggestion about how to widen the deck without adding another 2X12 brace.

[mydauphin]

No, you can't cantilever so much on 2x6 .. may be 6 inch. POST picture , there might be other ways.
Adding unsupport beam just adds more weight.

[Luckless]

So you want to rip up the decking on the dock, and replace everything with longer boards that will overhang the side of your dock to make it wider? Are we talking about just on one side that won't have boats tied up to it?

I don't see how you could use a dock like that without destroying either the boat or the dock.

Is this fixed or floating?

Best answer is check with someone local that builds/designs docks. You might have to rebuild if you want it larger and stable. You could possibly look into going with more joist supports and a 1x4 or 1x6 decking if your current 2x6 decking isn't way over engineered. Doesn't sound like this is a work dock or anything, if it is, ignore the comment on the 2x6.

[mydauphin]

Yeah, Stumble post some pics and I am sure something can be done with it.

[Stumble]

I'll take same pics abd post them tomorrow.

[jtd]

I build houses for a living & if I understand your question correctly, maybe I can help.
simply put no you cant just over hang the deck boards, but you can sister joist's on to the existing ones witch I believe you said are 2x12. if you post a picture of what you have I would be more than happie to draw you a quick plan and fax it to you (free of corse) that would be easier than trying to explain it..
here's a pic of stairs I built last fall