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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Tidal Surge vs Floating Docks

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Voyager
Master Marine Consultant

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USA
5376 Posts

Initially Posted - 08/26/2011 : 07:04:10

I'm on a floating dock that is a 22 foot x 3 foot deck, that's tied down to the riverbed using four helix anchors (they dig or screw into the bottom) on 1 inch thick stranded nylon rope.

The tidal range is approx 7.5 feet here in the harbor, but we expect a storm surge in excess of 12 feet on top of an 8 foot high tide. That will put us 20 feet higher than our normal high tide on Sunday at noon and at midnight.

I plan to double tie the boat snugly to the floating dock.

If the lines holding my dock in place in the harbor reach their max stretch limit at, say 14 feet, I would guess that the dock may get submerged. If the boat is tied snugly to the dock several things could happen:
1. The lines and cleats would hold and the boat will submerge also, and sink once the water level got up to the drain holes in the transom. Or waves come over the gunwales and flood the cockpit.
2. The lines chafe or the cleats fail and the boat floats off the dock and beaches in somebody's back yard.
3. The dock tears off the anchors and everything goes floating away.

If 1 happens, I'll have to somehow refloat the boat (air mattresses?)
If 2 happens, I can tie a few 10 foot long slack lines to the dock to keep the boat attached. Can tie to the mast, bow pulpit, stern, etc
If 3 happens, all bets are off.

Does anybody have any experience with floating docks, and whether the anchor lines would have enough range to deal with a tidal surge?

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - on

Davy J
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USA
1511 Posts

Response Posted - 08/26/2011 : 07:32:08

I cannot offer any advice on floating docks, however, during hurricanes Charley, Frances and Jeanne I used three extra anchors to keep the boat AWAY from my fixed dock. The boat rocked and bucked alot. This also allowed the dock lines to be longer to help with the surge. Fortunately, I have the room next to the boat to do this.

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redeye
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3476 Posts

Response Posted - 08/26/2011 : 07:55:45

<< Frances and Jeanne I used three extra anchors to keep the boat AWAY from my fixed dock. >>

I was just told similar advice from a coworker for a catalina 25 in Miami. He used 2 anchors away from the dock to assist with securing the boat somewhat away from the dock.

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redeye
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3476 Posts

Response Posted - 08/26/2011 : 08:28:28

Well.. I'll pray for less surge, you add more fenders... and take some pictures of your setup.

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redeye
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3476 Posts

Response Posted - 08/26/2011 : 08:47:50

I'm using 1/2in spring lines with snubbers, tying a bowline in the line to give a huge loop, almost the length of the available line after the snubber. This spring line runs the length of the boat and drops over the foward strbrd cleat. The large loops add additional line to help absorb shock loads.

The double bow lines are running under the pulpit and are small loops that drop over the cleat, just large enough to go over the cleat.

My aft cleats are similar. I added cleats midships to hold fenders.

The spring lines are looped similar on the dock cleats ( just a big loop around the whole cleat ), and the bow and aft lines (3/8) run through the middle hole in the cleat and after adjustment of length the are cleated to the cleat. The cleating holds the loops on.

The lines on the cleats are left uncleated until I push the boat around and get all the lines adjusted to an appropriate length, so that all lines hold the boat in a similar fashion. No one line gets too tight.

The spring lines are adjusted by changing the length ( location or pay out ) on the bowline knot.

In this manner I'm able to adjust how much payout, or extra line I want on all the docklines evenly. Keeps any one line from breaking.

Pretty easy to add extra fenders in various lengths also.

I hope this helps and this is my experience developed over time with trial and error. I've ridden out a coupla storms with this setup and only a few cleat bolts wallowed out.

Edited by - redeye on 08/26/2011 08:52:32

OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 08/26/2011 : 09:43:27

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by redeye
 << Frances and Jeanne I used three extra anchors to keep the boat AWAY from my fixed dock. >>

I was just told similar advice from a coworker for a catalina 25 in Miami. He used 2 anchors away from the dock to assist with securing the boat somewhat away from the dock.
<hr height="1" noshade id="quote"></blockquote id="quote">
I am missing something here!

How do you set anchors to keep your boat away from the dock if there's another boat right next to you? I must be picturing this wrong . . .

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Davy J
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1511 Posts

Response Posted - 08/26/2011 : 09:56:59

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I am missing something here! How do you set anchors to keep your boat away from the dock if there's another boat right next to you? I must be picturing this wrong . . .<hr height="1" noshade id="quote"></blockquote id="quote">
My boat is tied to the dock in my backyard, there are no other boats. So no, it would not work if you are in a regular marina.

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Voyager
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USA
5376 Posts

Response Posted - 08/27/2011 : 06:14:44

I have an opportunity now to move Passage to a fixed slip up river, around a bend, further from the mouth to LI Sound.
I can leave my neighbors on my floating dock and not have to worry that the dock, and others near it, will float away with the boat. The docks are a set of brand new transient slips where there will be no "neighboring" boats.
I think this is my best bet. I will double tie as Ray has suggested, and if possible, I will tie off to the opposite slip to keep Passage suspended between. Rain and wind are expected soon, so I'm outta here.

Edited by - Voyager on 08/27/2011 06:15:28

Voyager
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5376 Posts

Response Posted - 08/27/2011 : 16:33:54

Once I got in to the transient slip, I found I was able to tie up Passage suspending it off the dock with spring lines. I was able to use my 5/8" lines and my doubled-up 1/2" lines all around. I used a snubber to take the shock out of the stern and bow lines. Will post photos soon.

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Stinkpotter
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Djibouti
9080 Posts

Response Posted - 08/27/2011 : 18:46:43

Hope all of that works for my "old girl" Passage... But the net is, nobody knows. Floating docks are a big advantage up to a point--however you tie, that's how it'll be. But past that point....... (I hope I don't find Sarge and some of our floating docks in the mud across the river.)

We have a number of marinas with fixed docks here--particularly those that get some wave action. Big tides and storm surges can put them under water, and can pull boats under or leave them hanging on their dock-lines, which sometimes gets people hurt. The perfect solution would be floating docks on pilings that reach 20' above MHW. But in the real world, a hurricane is going to exceed some of our precautions--almost no matter what they are. Especially in this part of the coast, we just don't understand what they are capable of doing. That's partly why we buy insurance. A mere noreaster last year broke up a bunch of concrete floating dock sections in a Noank, CT marina--just one more learning experience.

Edited by - Stinkpotter on 08/27/2011 19:03:36

GaryB
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USA
4304 Posts

Response Posted - 08/28/2011 : 10:06:16

During Ike there was an entire floating marina that floated off the pilings at the upper end of Galveston Bay. The pilings were only about 10' above MHHW and the surge was 12' possibly higher in that part of the bay. Unfortunately there were probably 50 boats tossed up on shore still secured to the docks!

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