Tight lines or loose lines

Davy Jones said:

I would like to see some opinions on dock line tension.

I tend to snug all my lines up until my fenders are touching on both sides for times I am at the boat an back them off a touch when I leave just to save the gelcoat keeping the same amount of sag on all the lines. I cinch them down pretty tight on pending storms forecasting steady strong wind and double up on the bow and stern.

Just wondering what is the school of thought is from some of you old salts. Also what type rope do you perfer braid or strand.

Davy

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My boat is at a floating slip in an area with reversing tidal currents. You have to restrain it from moving back and forth. Spring line, stern line, etc.

I have my lines fairly snug, but loose enough that they can be removed from the boat without removing them from the dock cleats. The lines stay at the slip, I have others for travelling.

I use three strand nylon at my home slip and braided nylon when travelling.

psneeld said:

Yeah...maybe under constant strain or a shock load lasting long enough ....and doesn't it take max loading of say 15,000 lbs pull for 3/4 inch line to make it stretch that much???

Show me one video of a 3 foot piece of 3/4 inch nylon dockline stretching 5 inches when a boat moves from a passing boat wake and I'll believe you.

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I have a better idea. Why don't you show us one video or any data, that states nylon will not provide any dampening force whatsoever unless it is under maximum tension and we'll believe you.

CPseudonym said:

I have a better idea. Why don't you show us one video or any data, that states nylon will not provide any dampening force whatsoever unless it is under maximum tension and we'll believe you.

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Nice copycat...haven't heard that since grade school...

Think about it or go to any line stretch chart like I just did. The 15% is at max breaking strength. Sure there is some stretch but when you have short lines...if the stretch is even available that instantaneously, then it is used up (if a 3 foot line has 5-6 inches of stretch) pretty quickly when you are talking a 1-2 foot wake (if you guys are whining about 5 inch wakes...holy cow). And that only if each line is getting a 15,000 # jerk on it...imagine the tiny little stretch if only several thousand pounds per dock line....surely that gets all used up in even a gentle rocking on shorter floating dock lines. (again assuning a 3/4 inch dockline).

I've seen plenty of docks damaged from tight lines that were nylon...just not enough stretch that it mattered....but then again they were crappy docks....I've not seen a cleat pulled on a big fiberglass boat tied snugly to a floating dock even in hurricane conditions.

A lot of people use those rubber snubbers or rig things to dampen the shock loading on their nylon docklines because the "give" just isn't enough on anything but very long or thinner docklines. That is what I stated right from the very beginning. Use too thick a dockline to overcome the "chafe fear" and you lose the benifits of stretchy nylon.

psneeld said:

Yeah...maybe under constant strain or a shock load lasting long enough ....and doesn't it take max loading of say 15,000 lbs pull for 3/4 inch line to make it stretch that much???

No it doesn't and normal working loads for 3/4" nylon is ~1,500 lbs

"It has high elasticity and will
stretch 10-15% under normal working loads
and 40% as the load approaches breaking
strength. This elasticity makes it highly desirable
for use as anchor rode, for towing
and for dock lines, as the stretch absorbs​

shock.."


http://seagrant.uaf.edu/bookstore/boatkeeper/rope.pdf

New England Ropes says their 3/4" premium nylon will elongate just over 10% at 20% of the lines tensile strength and ~13% at 30% of the tensile strength.

http://www.neropes.com/Datasheets/MAR_3S_nylon.pdf

Show me one video of a 3 foot piece of 3/4 inch nylon dockline stretching 5 inches when a boat moves from a passing boat wake and I'll believe you.

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Sorry, they haven't made the movie yet.

psneeld,
I was very surprised at the degree of stretch in nylon several years ago. I was laying out a long spring line (about 30' and 1/2" dia) and pulling on it rather hard. It was like pulling on a big bungi. Made me wonder how much tension or stretch will nylon line take before it fails to return to it's original length. Perhaps it rarely does and if we could accurately measure it we'd find that even w a gentle pull nylon line elongates 1/2 a thousandths of an inch and if layed out in the shade for a day 99% of that would settle out and the line would once again be almost it's original length. Of course we'll never know but nylon IS very stretchy.

Just re-read your post and see your point ... at least what I think is your point. Yes in short lengths of mooring line the stretch is hardly worth talking about. But perhaps the very small amount of stretch in a short line absorbs shock in a very beneficial way.

Just re-read your OTHER post and see the bit about shock. Stretch 40%??? That's a lot of stretch.

So nylon does stretch and can provide some dampening.

Thank you for your reply.

psneeld said:

...Think about it or go to any line stretch chart like I just did. The 15% is at max breaking strength...

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I don't think you're reading the your stretch chart correctly or it's wrong.

Here's an other reference from the McGraw-Hill Boating Encyclopedia:

"Nylon is a synthetic plastic that was marketed after World War II. In fiber form, its stretchability makes it particularly suitable for anchor rodes, mooring lines, and dinghy painters. Under a 20 percent load, nylon has a working elasticity of about 22 percent, or more than a fifth of its length. This compares with a stretch of about 9 percent in Dacron, another synthetic plastic fiber. Nylon’s high stretch enables it to absorb the shocks a boat generates while at anchor— shocks that would otherwise part the line, unseat the anchor, or damage deck cleats or mooring bitts."

I'm not discussing that nylon isn't stretchy...it is...so much so that I am scared to use it when ungrounding boats at night because I have had them slingshot into me.

There are all different brands, lays , and makeup of nylon docklines...some have a LOT more stretch than others...but like I said...on a 3-5 foot dockline holding a boat tight to a floating dock...the elasticity is just not enough to matter that much....the bow and stern lines that are maybe 15-20 feet sure. And if you use long springs and don't use thos short lines...then yes...but that's NOT the way many boaters tie to a floater...they use short lines and at that point is where I said I doubt it really matters what you use (or go thinner diameter with good chafe guards).

If nylon was all that great because of stretch...why don't we use it instead of rubber bands???? Could it possibly be because of the different "stretchyness" characteristics????

Larry M said:

I don't think you're reading the your stretch chart correctly or it's wrong.

Here's an other reference from the McGraw-Hill Boating Encyclopedia:

"Nylon is a synthetic plastic that was marketed after World War II. In fiber form, its stretchability makes it particularly suitable for anchor rodes, mooring lines, and dinghy painters. Under a 20 percent load, nylon has a working elasticity of about 22 percent, or more than a fifth of its length. This compares with a stretch of about 9 percent in Dacron, another synthetic plastic fiber. Nylon’s high stretch enables it to absorb the shocks a boat generates while at anchor— shocks that would otherwise part the line, unseat the anchor, or damage deck cleats or mooring bitts."

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Again...based on my "salvage and towing" experience with nylon and other materials...it by far has the most stretchability. But outside the "testing lab" it just doesn't have this instantaneous, majic ability to absorb all that energy from rocking and rolling at a dock if the lines are short.

I've been looking to see the "rate" at wich it will stretch 10-20 percent, I see it in towlines all the time...yes I can visually see it with boats surging along...but it's far from the instantaneous tugs you get in a docking situation...so that would be some info that would interest me more than the absolute stretch numbers from a test lab.

And even if it does...my explanation that the full elongation of a short line probably isn't enough to take much of the load out of the size of waves/wakes that would severly rock boats like ours....only if the lines are much, much longer than the 3-5 foot short ones I am talking about.

Davy Jones - had a similar occurrence not long ago. I have a cast aluminum mooring bit with a "square" cross section, but with nicely rounded or beveled corners. I use a three strand nylon 1/2" keeper for the anchor with two spliced eyes. One eye over the bit, through the shackle on the anchor, and the other eye over the bit. No tension on it at all except, maybe, in rough water. Went to use it and discovered one eye had parted completely with what looked like, to my amateur eye, a chafing failure. The keeper was about a year old. I guess the lesson is that anytime you bend a line over metal, even if it looks rounded and not abrasive, there's the potential for damage/failure.

How about using snubbers?

Do any of you guys use snubbers to provide better shock protection?

I have a Shockles for an anchor snubber, but don't need to use mooring line snubbers in my shed.

I am considering changing out my twisted dental floss dock lines for a braided set.

Hey Fly,
looks like you could be using some chafe gear. That haws hole edge looks pretty sharp to me.

Braided cost more. You will wear out the outer cover in no time.

Sd

skipperdude said:

Hey Fly,
looks like you could be using some chafe gear. That haws hole edge looks pretty sharp to me.

Braided cost more. You will wear out the outer cover in no time.

Sd

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Those weren't pics from my boat, just examples from the 'net.

My dental floss mooring lines have drinking straws for chafe protection.

FlyWright said:

Those weren't pics from my boat, just examples from the 'net.

My dental floss mooring lines have drinking straws for chafe protection.

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Don't think dental floss is too small...I sure thought that way for the longest time till I got into commercial stuff.

depending on the line...it can be a whole different ballgame.

So if what you have is holding and not wearing too rapidly...you might have a good combination.

More chafe protection isn't usually bad...unless done completely wrong.

Like I said a long time ago...I got some cheap 1/2 inch for free so right after I bought the boat...I used it thinking I would replace it after the first season or sooner if wear developed. Neither has happened and I'm in an exposed marina with up to a 3 knot tidal current. Only during storms have I doubled up.

So dental floss may not be all that bad...as I've seen some lines that nearly chafed through in light conditions overnight (wow!) and other boats tied up with dental floss survive storm conditions.

Like most docking situations/requirements....each situation, combination and lines are adequate or not for THAT situation.

I wonder why a builder would put those what appear to be rollers mounter for and aft like that in a haws hole. When would such a set up be used.

Towing?

Mine are rounded off and polished by wear.

Looks like an expensive boat.

Sd

FlyWright said:

Those weren't pics from my boat, just examples from the 'net.

My dental floss mooring lines have drinking straws for chafe protection.

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I haven't tried the floss and straw method yet, but after reading this string, I'm just saying, maybe I should probably buy some stainless steal rope and tractor tires for keeping my baby safe in her slip!!

LB

Some people in our marina use the rubber shock absorbers that the mooring line spirals around, same as in FlyWright's second photo. I see them more on sailboats than powerboats but have no idea why. The only negative thing I've ever heard about them is that over time the rubber can break down somewhat in the UV and they become more susceptible to tearing apart if they are really strained. Don't know anyone that's actually happened to, however.

We don't use any sort of shock absorber on our mooring lines. The lines themselves provide sufficient shock absorbing. While there is current in the marina there is no surging.

We use breast lines at the bow and stern, long fore and aft spring lines off the center cleat, and an additional spring line running aft from the bow. The prevailing winds and storms come from behind us so the boat is usually being pushed forward in the slip, hence the additional aft-running spring line. We double the stern breast line for the same reason.

All our mooring lines are 5/8" braided with the loop ends fastened "permanently" to the boat's cleats.

Using chafe gear only on the forward dock lines as they cross over the gunwale through chocks. All other dock lines directly attach to cleats on the gunwale. No wear noted after 15 months. Shock absorbers not needed as the berth has no surge.