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Dockline Thickness

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/09/2007 : 14:53:23

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 We get a huge storm surge when the wind is out of the North. I thought it was the equivalent of Seche (sp?) based on your prior posts but was corrected at a holiday party. It is surge, the old timers call it the bath tub effect...Water comes in pretty hard but cant get out causing it to surge back and forth. 3 to 5 foot shifts in less than a couple of minutes.<hr height="1" noshade id="quote"></blockquote id="quote">

I believe you just described a seiche...

[url="http://en.wikipedia.org/wiki/Seiche"]Seiche[/url]

Edited by - on

aeckhart
Master Marine Consultant

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USA
1709 Posts

Response Posted - 02/09/2007 : 17:36:53

To add fuel to the fire, it occurs to me that of the four lines used to safely dock a boat - bow and stern lines to keep the boat next to the dock, fore and aft spring lines to keep it in place forward and back, the spring lines would take far more strain and shock load in most situations than the dock lines. Would it then be prudent to use 3/8" line for dock lines and 1/2" for spring lines?

Just a thought.

Edited by - on

Steve Milby
Past Commodore

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USA
5895 Posts

Response Posted - 02/09/2007 : 18:22:37

I'd like to ask if anyone on this forum has ever parted a 3/8" dockline, in reasonably good condition, on a 25' Catalina? I used them for about 23 years and never parted one, and some of mine deteriorated quite a bit before I replaced them.

I remember that, many years ago, Jacques Cousteau anchored Calypso, a converted minesweeper, in mid ocean, in about 6 miles depth, on a 3/8" nylon line.

Edited by - on

Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 02/09/2007 : 20:18:55

Yeah, and now Cousteau is dead. I'm sticking with 5/8.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 02/10/2007 : 10:32:25

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 I'd like to ask if anyone on this forum has ever parted a 3/8" dockline, in reasonably good condition, on a 25' Catalina?<hr height="1" noshade id="quote"></blockquote id="quote">
3/8" double-braid is generally rated for between 4000 and 6000 lbs. load. Not likely our boats could put that much load on them due to wind or wave action--even hanging in the air on the lines (which would probably rip cleats out before breaking lines). On the other hand, the bigger line will go a little longer before it chafes through, but probably not much.

Edited by - on

Steve Milby
Past Commodore

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USA
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Response Posted - 02/10/2007 : 13:33:13

That's my thinking, too, Dave. Last summer I experienced my first near-hurricane. As I recall, it was about 63 kt. wind, on the Chesapeake.

My friend's boat is a 28' Pearson Triton. He had about 1/4" or perhaps 5/16" docklines on it, and none of them parted, although the boat was bucking and rolling violently in it's slip. In fact, one line was tied to a lifeline stanchion and it was serving as a spring line, and that line didn't part, but it ripped the stanchion completely out of the deck.

I put an extra dockline on each corner of my boat, and an extra spring line on it. I adjusted them so that one line on each cleat was slightly looser than the other. That way, one line took all the punishment. If it failed, the other one took up the load. My docklines on a 35' boat are 1/2".

Edited by - on

Brooke Willson
Admiral

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USA
983 Posts

Response Posted - 02/10/2007 : 15:38:48

Thank you, Steve and Dave. "Even Chance" has been docked in the Chesapeake for many years with 3/8" doublebraid. When a hurricane is coming, I double the lines. During Isabel, the 3/8" lines pulled a piling out of the bottom (the boat was fine).

In a big blow, HOW the lines are run is probably more important than the size of the line (given a reasonable diameter, of course): long lines crossed to allow lots of sea rise; bow pointed into the wind; sails removed to reduce windage. In our marina, the boats that were damaged were because of pilings, cleats, and docks that gave way, not line failure. Tidal surge was much more a culprit than wind, which is why the lines need to be plenty long. If the tide lifts a fixed dock and pilings, all our planning is irrelevant.

Brooke

Edited by - Brooke Willson on 02/10/2007 15:53:12

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 02/10/2007 : 16:53:24

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by dlucier
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 We get a huge storm surge when the wind is out of the North. I thought it was the equivalent of Seche (sp?) based on your prior posts but was corrected at a holiday party. It is surge, the old timers call it the bath tub effect...Water comes in pretty hard but cant get out causing it to surge back and forth. 3 to 5 foot shifts in less than a couple of minutes.<hr height="1" noshade id="quote"></blockquote id="quote">

I believe you just described a seiche...

[url="http://en.wikipedia.org/wiki/Seiche"]Seiche[/url]

<hr height="1" noshade id="quote"></blockquote id="quote">

Maybe on a smaller scale - The lake itself might show zero signs of that phenomonon - but our basin will.

I did a full check of the docklines last evening. 2 bow at 3/4" 2 bow at 1/2. Four stern at 1/2 and a side line at 3/8.

We technically do not have a spring line, however with a 44 foot dock every line sans one is a spring line.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 02/12/2007 : 12:09:14

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by dlucier
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 We get a huge storm surge when the wind is out of the North. I thought it was the equivalent of Seche (sp?) based on your prior posts but was corrected at a holiday party. It is surge, the old timers call it the bath tub effect...Water comes in pretty hard but cant get out causing it to surge back and forth. 3 to 5 foot shifts in less than a couple of minutes.<hr height="1" noshade id="quote"></blockquote id="quote">
I believe you just described a seiche...
<hr height="1" noshade id="quote"></blockquote id="quote">Maybe on a smaller scale - The lake itself might show zero signs of that phenomonon - but our basin will.
<hr height="1" noshade id="quote"></blockquote id="quote">
I don't have a clear picture, but it sounds like the "bathtub effect" you have inside the basin might be caused by a seiche out in the on Erie stuffing a bunch of water into your basin. What makes me wonder is the numerous seiches I've seen on Lake Michigan are quite gradual--almost like a tide. But I also know about the bathtub effect--that's what makes the tide range so much higher on the west end of Long Island Sound (7.5-10') than on the east end (2.5-3.5'). The tide enters from the east, piles up at Hell's Gate at the west end in NYC (where some of it squirts through into the East River), and then most of it backs out to the east and around Long Island. It's a 100-mile-long bathtub with a wave period of 2 per day.

Edited by - on

Champipple
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USA
6855 Posts

Response Posted - 02/12/2007 : 15:11:05

Dave -

There are no major depth changes on the Lake, just in our basin. Most of the other clubs are inside the main breakwall so they do not get any effects either.

That is why I don't think its part of Seiche.

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/12/2007 : 15:33:04

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 There are no major depth changes on the Lake, just in our basin. Most of the other clubs are inside the main breakwall so they do not get any effects either.
<hr height="1" noshade id="quote"></blockquote id="quote">

So you get 3 to 5 foot depth changes in your marina, while the lake and other clubs remain unaffected?

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 02/12/2007 : 17:29:49

Duane: That's bazaar! Where is this basin? I've gotta look at a satellite photo to try to understand what's happening. Is it Edgewater? http://marinas.com/view/marina/605

Edited by - Dave Bristle on 02/12/2007 17:39:59

Champipple
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USA
6855 Posts

Response Posted - 02/12/2007 : 18:27:58

Yes, but that pic doesn't show the entrance. Look at the fifth one down.

There are plans to put in Keys at the end of the long docks to baffle the surge. It also only happens when the wind is out of the North West.

Edited by - Champipple on 02/12/2007 18:30:06

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/12/2007 : 18:52:02

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Duane Wolff
 ...It also only happens when the wind is out of the North West.
<hr height="1" noshade id="quote"></blockquote id="quote">

Duane,

If you keep describing characteristics of a seiche, then you are going to have to call it a seiche.

With the wind blowing out of the NW, water is going to build up along your shore while it goes down on the opposite shore. After the wind subsides, gravity does its thing and sloshes the water back to the other side of the lake until it reaches equillibrium.

From Wikipedia...

"Lake Erie is particularly prone to wind-caused seiches because of its shallowness and elongation. These can lead to extreme seiches of up to 5 m (16 feet) between the ends of the lake. The effect is similar to a storm surge like that caused by hurricanes along ocean coasts,..."

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/14/2007 : 12:38:04

This realtime [url="http://www.glerl.noaa.gov/res/glcfs/glcfs.php?lake=e&ext=wl1d&type=F&hr=00"]Lake Erie Water Level Displacement[/url] graph illustrates the bath tub effect.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 02/14/2007 : 12:50:37

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by dlucier
 This realtime [url="http://www.glerl.noaa.gov/res/glcfs/glcfs.php?lake=e&ext=wl1d&type=F&hr=00"]Lake Erie Water Level Displacement[/url] graph illustrates the bath tub effect.
<hr height="1" noshade id="quote"></blockquote id="quote">
Not what Duane described locally in his basin. That's the whole lake--precisely the seiche effect.

Edited by - Dave Bristle on 02/14/2007 12:51:58

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 02/14/2007 : 12:58:56

What Duane described defies the laws of physics,...but then again, it is Cleveland!

Edited by - dlucier on 02/14/2007 13:02:44

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 02/14/2007 : 13:41:12

Sounds like hydraulics to me.

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 02/14/2007 : 15:54:41

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by dlucier
 ...but then again, it is Cleveland!

<hr height="1" noshade id="quote"></blockquote id="quote">
Oh, that's right... the place where the water burns.

Edited by - on

cat1951
Admiral

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USA
636 Posts

Response Posted - 02/14/2007 : 15:55:02

It's all of the water whooshing out of the Cuyahoga river. ;-)

Edited by - on

Champipple
Master Marine Consultant

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USA
6855 Posts

Response Posted - 02/14/2007 : 21:07:06

<hr height="1" noshade id="quote"></blockquote id="quote">

Not really - water gets in but can't get out quickly so it smashes against the bulkhead and then smashes against the other bulkhead and etc...it drains much slower than it filled up; meanwhile the lake does not change depths as drastically. But I'm sick of arguing with you. You can call it what you will and I'll call it by the generally accepted local term. Your word sounds French and I'm still bitter about them planting trees on the side of the road back in 42 and 43.

The commonly accepted term here is Storm Surge - so I'm sticking with that. If I ever come over on your side of the lake I'll consider swapping out the contents of my lexicon.

Edited by - Champipple on 02/14/2007 21:08:16

Stu Jackson C34
Admiral

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844 Posts

Response Posted - 02/15/2007 : 11:57:20

Regardless of the size of line you choose, looping the dock lines through the boat cleats is not a good idea, as mentioned earlier, because they are a PITA to get off, and it takes more time. Simpler is better.

However, many people are rightfully concerned about a dock line simply placed over a cleat on the boat coming loose.

One of our members came up with this (see second photo down): http://www.c34.org/projects/projects-ron-hill.html

Edited by - on

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 02/15/2007 : 12:30:06

Ya know, if you think about Lake Erie as this big body of water (with current albeit negligible) and the EYC as a small lake off that body of water, it really does make sense that this Seiche, bathtub, storm surge thing occurs in this isolated body of water and when the rest of the lake nor other marinas are unaffected. This is particularly true if you realize that the only inlet and outlet for water is on the windward side of the "lake". Take a look at the photo again and, if ya didn't know the scale, the layout of the marina could be called a small lake in some parts of the world. Indeed, I've seen smaller ponds in some parts of Texas that were called "lakes" by locals.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 02/15/2007 : 21:45:09

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Stu Jackson C34
 One of our members came up with this (see second photo down): http://www.c34.org/projects/projects-ron-hill.html
<hr height="1" noshade id="quote"></blockquote id="quote">
That's not bad--for the little "security lines", you can use my "all-purpose quick-release sailor's knot"... One half-hitch, then fold one tail over and wrap the other around... oh you know--you learned it back when you learned how to tie your shoes.

I prefer to drop the loop over the cleat, and then cross the sides of the loop back over the cleat and around the opposite horns. Easy to put on and remove but can't fall off.

Edited by - Dave Bristle on 02/15/2007 21:46:12

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