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Swimdock

by Sep 15

Finished product first. 10' octagonal floating swim dock built between May and July, 2018.

My in-laws have a second home on forty acres about an hour from where I live. My wife grew up exploring the woods and swimming in the one-acre pond with her cousins. Now our kids do the same.

When my wife was a little girl there was an old floating dock but it finally rotted away. Then we got an inflatable "aquadeck" but the sun destroyed the PVC after about five years. This winter I decided to build a durable wood swim dock that could stay out year-round and last a long time.

I found this image online and thought "that would be perfect"

Then I found this image online and thought "I could build something like that out of wood"

So I started drawing. . .

. . .and came up with this framing scheme. From watching youtube videos I knew it would be hard to frame on the sloped shore of the pond so I wanted something I could build in sections and assemble at the pond. The framing plan is a 10'x4' main frame (running left-right in this picture) with a 2'x4' "sidecar" box on either side. At this point I wasn't too stressed about exact dimensions but just knew I wanted to start with 10' main rails. The yellow dots are places I thought I'd want some kind of gusset or bracket.

Math warning. Home Depot sells "Permafloat" dockfloats and the manufacturer has a chart showing how far each float sinks at certain loads. My structure and trex decking weight about 1,300 pounds total and I figured thirteen 160-pound people would swamp the new dock. That was fine with me. The kids loved to play king of the mountain on the old aquadeck and I knew they ever got 13 people up there they'd be thrilled if it sunk ankle-deep.

Challenge #1: You want a lot of flotation to hold the people who will be on it, but don't want the dock to ride too high when it's empty and look goofy. My original framing plan (bottom) would have been 25" tall (1" trex on top of 2x8s on top of 16" floats) so I came up with a way to nestle the floats between the 2x8s and save four inches of height (top).

The floats are 24" x 48" x 16" deep and I got them through Home Depot. They were delivered along with the framing lumber which was a big help because the house is 30 minutes from any town or store. I built the main frame and the sidecars upside-down on a nice flat deck which helped keep everything in plane and made it easy to install the 3" lag screws that connect each float to the 2x4s at its corners (red arrow).

Dog Tax. At this point the main frame and sidecars are still upside-down and just sitting next to each other unconnected. Note Simpson corner brackets at all inside corners (red arrow). I don't have pictures of carrying each section to the pond and bolting them together.

In this image, the main frame runs left-right and the sidecars are attached with construction adhesive and six lag bolts each (red arrow). It's a little hard to explain but the sidecars wanted to float higher than the main frame and I had to bolt it very tight to keep everything in plane. I'm concerned that over time these connections will loosen and will be tough to access and tighten.

Challenge #2: YouTube taught me it's tough to build a level dock on a sloped, grassy shoreline 100 yards from a power outlet and also taught me finished docks are too heavy to carry to the pond. I don't know the best solution but from this point on I pretty much did everything while the dock floated. That was stupid because I was often using power tools in and over water.

Secondary 2x4 farming in underway and diagonal rim joists are on. There's probably a better way to secure the diagonals but I used a 135-degree (gusset? stitchplate? I don't know the word) I found online.

Good view of the main frame, sidecars at left and right, and secondary framing. Some of the blocking is in but I really underestimated how much blocking my deck pattern would need.

Challenge #3: At this point the swim dock was tethered to a fixed dock at right and I was screwing in blocking while balancing on narrow joists on a tippy dock. Not an easy way to work

Potential deck patterns.

Added a fifth float in the middle, finished blocking and installed two main decking ribs. Decking is Trex Enhance Beach Dune. First group of diagonal deckboards are sitting loose as I figured out the gaps.

Starting to set decking. Boards are designed to be used with concealed fasteners but I was concerned that my framing and blocking were so uneven that the fasteners wouldn't work well. Drilled pilot holes and used 2 1/2" star head screws made for composite decking.

Eventually I drove a screw through the exact center of the dock and tied the screw to the shore on the left and to the fixed dock on the right, Then the whole dock could spin like a lazy susan while I sat on the shore and worked from there. I am most proud of this invention. Old drywall mud bucket filled with concrete will become part of the anchor.

Magical turntable screw in center. Deck boards running wild

ran out of deck boards, back to Home Depot.

almost done.

tails cut off. Did you know Trex sinks? I didn't.

A better carpenter would have made these gaps more consistent.

Matching trex 1x12 fascia was $90 for a 12' board. Needed four. Yikes.

a frog just jumped in the water.

Ladder lessons learned: The ladder is so close to the fascia there's not enough room for your foot when it's on the top step. Also should have notched the fascia so the ladder frame lays flush on the deck. On the plus side I'm really proud of this 135 degree fascia joint. The rest are pretty wonky.

Ladder attached through deck to blocking. Challenge #4: seven-step ladder is too long to be installed in shallow water where it would be easy to get underneath and attach nuts to 1/4" x 5" lag bolts. Solution: attach once the dock is anchored in deep water using an elaborate raft of pool noodles for stability while installing nuts.

Finished product (umbrella slips into 2" PVC sleeve attached to framing).

Hope you like it!

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