Tangled Lines
Get the right dock lines
for your boat -- or face
the consequences!


by Marlin Bree

Morning broke gray and chill, with the waters of the Bayfield (WI) city docks more than a little lumpy underfoot. Loris and I were aboard our 20-foot pocket cruiser, Persistence, and as usual we were beginning our day with a cup of latte. There was a bump, a bounce, and I grasped my cup. Something green caught my eye just above the centerboard trunk. The CB is open on top, and, what I was staring at for a moment was a surge of water that shot about a foot up the trunk and then slopped onto the varnished floorboards.
"What was that?" Loris asked.
"We took water inside," I said, surprised.
The night before, we had tied along the dock that forms an "L" shape, extending out into the West Channel. The big docks are massive protection from the seas that sometimes run in the beautiful Apostle Islands. It had been a serene, calm night, the kind that brings back fond memories of the beautiful Apostles.
But Lake Superior is ever changeable. The wind had come up, hard. And it had gone northly to builds waves in the North Channel. We were getting surge down the channel and into the docks.
I was not too concerned about our safety, for my Persistence is an ultra lightweight, centerboard flyer that sits lightly upon the surface. I had purchased two brand new 3/8ths inch fancy green-colored braided dock lines, the ones with the build-in eye splice. I figured they'd look good at the wooden boat show in which I was displaying Persistence.
As I stepped up to the dock I double-checked the line through my boat' s forward and aft cleats, which were secure enough, and checked the lashings I had around the huge dock cleats. We were walking down the docks toward the little coffee shop when someone shouted, "your boat's busted loose." I started running. One end of the new braided nylon dock line was in his hands, with boat attached, and he was holding tight. The other end hung limply in the water. It had broken.
The dock line was a name-brand dock line I had bought at a marine store. It had a braided cover over a white-colored core and had a breaking strength of about 3500 pounds -- more than twice the weight of my boat. But the sharp raps from the waves had snapped the dock line. I doubled up on some heavy nylon anchor rhodes and I began paying more attention to dock lines after that.
Season after season, I see other boaters in trouble, but they may not know it yet. Some use inexpensive-looking discount store nylon, some use worn out sheet lines that have a rough-looking knot in them. One boater even tied up his craft with clothesline. Some, like me, bought the colored dock lines. Now I know better. Here's a quick primer on dock lines:
Best types: The best dock line is three-strand, twist nylon line, which doesn't look fancy, but it is very strong. Unlike some braided, cored dock lines, the nylon line has elasticity to let it stretch to take up the surges and bounces of your boat as it works back and forth. A good nylon line will have about 10 percent stretch built into it. On my 20-foot boat, a good nylon line can stretch 2 feet, and, it can do that all day long without ruining itself because better nylon lines for boats are treated with a fiber lubricant. The strands don't wear themselves out rubbing back and forth.
Get the right diameter: It's important to size the line right, so you get some flex and the right strength. When cruising I use 3/8 inch three-strand twisted nylon for bow and stern lines.
Most manufacturers have general guidelines for size of boat (3/8-inch line for boats 20 and under, inch line for 20 to 30-foot boats, and 5/8ths for boats 40 and over. They also hasten to add that if a boat is heavier than average, or offers greater windage, you can easily go up one size. Another rule of thumb is 1/8 inch of line per 9 feet of boat. Frankly a slightly bigger size than recommended won't hurt, costs very little more, and even looks more shipshape. It's cheap insurance.

Marina vs. cruising needs: I need different dock lines while cruising, as opposed to just tying my boat up at a local marina. If you are at your own dock, you can get by with a line a little longer than what fits between your cleats and the dock's cleats, allowing some movement for your boat. When you go out for a short day trip, you just uncleat your lines.
In my marina, I have two bow lines, one stern line, and one spring line to keep the boat from surging forward and hitting the dock. Some boaters use two surge lines.
For cruising, a rule of thumb is to have dock lines two thirds to roughly the length of your boat, and, you will find this useful in the big docks, such as in the Bayfield city dock, Port Superior, Barker's Island, in Thunder Bay's marina, or even the tiny Rossport, Ontario, government dock. These are docks to accommodate big Lake Superior cruising boats and there's some distance between cleats, set high up on the docks. It's better to have too much line, and just coil it beside the dock cleat, than not have enough. Buy them all the same length and you can use them for bow, stern, or for spring lines.
The proper cleats: Naturally, you should have cleats that can handle the worst conditions, including those late-season storms. On Persistence, I have chrome-plated cast bronze cleats each with four bolts going through the deck on either side. There are two forward on the bow, and, two aft. These bolt through three-eights inch composite wood (a layer of teak, birch plywood, and a layer of Sitka spruce.) The cleats are backed with a quarter -inch of marine ply epoxy glued to the deck, and, the deck is set into a three-fourths inch thick Sitka Spruce deck shelf. The holes are drilled slightly undersized for the screws; screws are driven in, and then pulled out. The resulting holes with threads are epoxy swabbed, left to dry, and then the stainless steel bolts went back in, fastened with washers and stainless nuts. This is strong construction and it gives me peace of mind.
Docking: When I attach a dock line to the boat, I put the dock line eye through the eye of the mooring cleat and then back it around the horns. For the cleat at the dock, I use a cleat hitch, first inserting the line through the eye, then making a round turn, several loops, and, end it with a locking half hitch. If it's really rough, I toss in a few extra half hitches in the line itself. Call me Mr. Cautious, but I've never had a dock line come adrift.
On the bow, dock lines run from the two heavy cleats through two chromed bronze chocks. I have run my fingers inside the chocks so that I know there are no rough casting edges, as some chocks have to wear through the dock lines.
During a blow when cruising, I usually check dock lines for chafe. I' ve been lucky, because I haven't had any wear-through problems, even when the boat has been bouncing around. Once in a while, I let out the dock lines a little, just to get a different area of line exposed to the rubbing of the bow cleat.
Good three-strand dock lines are an inexpensive form of insurance for you and your boat. The right ones, correctly used, will take care of your boat and give you security of mind. They will also save you money.
I am reminded of one incident that happened in a local marina. I was down at my boat one day when a boating neighbor across the way called me over.
"Look at that," he said, pointing down. In his shiny hull I could see scratches and rub marks.
He pointed to the vessel in the nearby slip. "That got away from the dock."
It was the bane of all sail boaters - a pontoon craft, with those rough, welded aluminum spray rails.
I shook my head in sympathy. "What're you going to do?" I asked.
He told me that he had already talked to the marina office and had the satisfaction of listening to the manager's conversation, which was short and sweet. It went something like this to the pontoon owner:
"Your boat broke loose. It damaged a nearby boat. I'm going to fix it and you're going to pay for it."
End of conversation. It kind of sent chills up my spine. It also reminded me how inexpensive proper dock lines are.



Marlin Bree is the author of Wake of the Green Storm: A survivor's tale. His web site is www.marlinbree.com which has more pictures of his home-built boat, Persistence.