See full version: How to Choose the Best Size of Dock Lines, Type, Number, and more
Dock lines come in a variety of colors. While the color has no real practical use aside from aesthetics, keep in mind that darker lines will tend to fade quicker than lighter lines. Conversely, lighter lines shower dirt easier than darker lines.
For length, transient dock lines should be close to 2/3 of the boats length if being used on the stern or bow of the boat. For spring lines, they should be equal to your boats length. Ideally, you should have two stern lines, two bow lines, and two spring lines on board. At a minimum, you should have one bow line, one stern line, and two spring lines. As the diagram at the end of this article shows, you don't always need to use two bow/stern lines, but you should have them on board regardless, because there will likely be a time when you do need them. When you're expecting heavy/stormy conditions, consider doubling up your lines. more
Knowing how to tie a dock line is both one of the easiest and simplest techniques you can learn as a boater. The cleat hitch is the most popular way to secure your lines to a cleat and it is shown below. more
Your dock line must be nylon rope. Polypropylene degrades quickly in the sun, doesn't have the level of stretch needed, and has a low breaking strength so it is generally a bad choice. Dock lines most commonly come in three weave types: three-stand, braided and double braided. There's subtle differences between these three types of lines listed below, but ultimately, any of these types makes an adequate dock line.
Re: Anchor Rope Size Rules? here
I have a 15,000lb boat, and I have maybe a 5/8" line (maybe a little bigger, came with the boat and i've never put much thought into it) on what I'm guessing is a 16lb dansforth.
Like fireman said, 1/2" is plenty for your boat. Realistically, you could get away with 3/8" or even 1/4" ; 1200lbs is a light boat. My beast is 4800lbs dry and empty, and I use 1/2". You won't want to use the 3/8" though, it's tough on your hands. 1/2" is much easier to work with. here
Re: Anchor Rope Size Rules? here
The anchor, the reason you were dragging, is another story. Anchor style and size depends on what you're trying to grip into. Some anchors work better with some bottom materials, others better with other materials. You'll have to make the call on that yourself.
I like the dansforth, but it fouls easily on a weedy bottom, which usually isn't a problem for me, as Im usually anchored in 30-50ft of water, but occasionally, depending on where I am, it might take me a few tries to get it to grab.
When you buy, read the latest product information. Most boaters will use either one form or another of nylon and perhaps also polypropylene.
With today's new high-tech synthetic fibers and advanced rope construction, you can buy rope that's 10 times stronger than steel with extremely low stretch. Many racers and cruisers have switched from wire to all-rope halyards; others have also opted for high-strength, low-stretch, lightweight ropes for their running rigging. [links]
All-rope halyards have several advantages over wire. Wire is hard on your hands and gear. Rope is easier to splice, it won't scrape paint or anodizing from your mast, and you don't have to decide whether or not to rely on a worrisome rope-to-wire splice. The primary disadvantages are that rope is thicker, so it has more windage aloft (but around half the weight), and even the ultra-lowstretch fibers elongate more than wire. Quality rope costs more than wire but is easier to install, lasts longer, and can be recycled to a less demanding capacity.
I bought some rope from wal-mart. and on the back of the package, it says that 3/8 inch dock line is good for up to a 28 ft boat. I have a 26 ft sailboat, and I will not use anything less than 1/2 inch 3 strand twist.
The following is an approximate guide: [links]
Line Diameter Boat Length
3/8" up to 25'
1/2" up to 35'
5/8" up to 45'
3/4" up to 55'
7/8" up to 65'