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  1. #1
    Lieutenant Commander bowman316's Avatar
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    Default What size rope to use for different boat sizes?

    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.

    It seems like these guidelines are not right. maybe a 28 ft sailboat will tug more on the dock than a 28 ft powerboat.

    I also use 1/2 inch anchor line.

    What rule of thumb do you use for rope size?
    I think 1/2 inch anchor line would hold up in a storm. 3/8 inch might break.
    16 ft runabout w/ 70 hp evinrude
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  2. #2
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    Default Re: What size rope to use for different boat sizes?

    somebody must have come up with a ratings system but the length of the boat has little to do with what you need; it's the force against the rope v. its strength. You aren't lifting it out of the water with it.

    I buy rope that is larger than needed according to the "ratings" b/c I want something comfortable on my hands when pulling on it. So for an achor line, or mooring lines where you will be pulling the boat against the wind, current, etc. go larger.

    I think it would be unusual for a line to just break; usually they get worn and weakened at a certain point.
    A man of constant boat tinkering.

  3. #3
    Master Chief Petty Officer
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    Default Re: What size rope to use for different boat sizes?

    First off, remember that it is only 'rope' onland. Once you put it on a boat it becomes 'LINE'.

    I've seen several places that post recommended sizes, for example:


    BOAT US

    http://www.boatus.com/boattech/dockline.htm

    <20 ft: 3/8" line
    20-30 ft: 1/2" line
    30-40 ft: 5/8" line
    >40 ft: 3/4" line

    According to Rope inc:

    http://www.ropeinc.com/choosingdockline.html

    Boats under 20 feet generally use 3/8" line:
    20 feet to 30 feet use 1/2" line
    30 feet to 40 feet use 5/8" line
    40 feet to 70 feet use 3/4" line

    http://powerboat.about.com/od/smallb...Boatline_7.htm

    The following is an approximate guide:

    Line Diameter

    Boats under 20 feet = 3/8"
    Boats 20 to 30 feet = 1/2"
    Boats 30 to 40 feet = 5/8"
    Boats 40 to 60 feet = 3/4"

    According to BoatUS:

    http://www.boatus.com/boattech/casey/21.htm

    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'



    I use 1/2 braideed dockline on my 28 ft boat (7,500lbs) and 5/8" braided for my bow anchor line. Keep in mind that 3 strand and braided will have differently breaking strengths for the same sized line. The write-ups in powerboat.about.com as well as BoatUS goes over details about different types of line and material as well.

    If you search on some combination of "Boat Line Size" or other such phrases you should find many resources that discuss this topic. In the case of variation in recommended sizes, just look at what the majority are recommending. If one says 3/8" line and five others say 1/2" line, then 1/2" line is probably the right answer. At the end of the day, nobody hurt their boat by placing line too large on it, PROVIDED that the line properly fits around the size of the cleats installed on the boat. Keep in mind there is such thing as line too large for the cleat.

    Yes Boat US has it posted with slightly different information in two different places, go figure.

    I hope this helps

  4. #4
    Lieutenant Commander 25thmustang's Avatar
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    Default Re: What size rope to use for different boat sizes?

    My boat is a 29'er according to the title. When I was standing at the counter buying Line I saw the numbers located above. 20'-30' and a 1/2" line was sufficient. I went with the 5/8". I'm sure the smaller line would have been fine, our marina rarely gets rocked by significant storms, but the piece of mind I had knowing the line was good for a much larger boat lets me rest easy.

    Personally, you having a 28'er I would say step the line up if you question it at all. Other than possibly be harder to handle, the larger line should really have no downside.
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  5. #5
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    Default Re: What size rope to use for different boat sizes?

    keep in mind the actual diameter of the rope isn't really that useful. a 1/4 inch spectra rope (line!) is stronger than your typical 5/8 poly line.

    both of which are overkill for an under 30' boat anyway, you will rip the cleats out by the time you get to 6000 pounds of force.

  6. #6
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    Default Re: What size rope to use for different boat sizes?

    Quote Originally Posted by smokingcrater View Post
    keep in mind the actual diameter of the rope isn't really that useful. a 1/4 inch spectra rope (line!) is stronger than your typical 5/8 poly line.

    both of which are overkill for an under 30' boat anyway, you will rip the cleats out by the time you get to 6000 pounds of force.

    I was under the impression that Spectra was static line. I could be wrong. Do they make this in a line that also stretch's? I've always been lead to believe that you don't want static line for docking or anchoring, but rather the stretch afforded in typical dock/anchor line is preferred. I was under the impression that static (non-stretch) line was more appropriate for rigging and towing. for towing a floating line is preferred, such as your typical ski rope.

  7. #7
    Admiral dingbat's Avatar
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    Default Re: What size rope to use for different boat sizes?

    I don't remember if I have 1/2" or 5/8" double braid nylon lines.

    Spectra is pretty useless stuff when it comes to applications where shock is an issue. We use #120 nylon monofilament on our planer boards. Some decided that #200 spectra would work better. No where close. The spectra snapped like twine. The Spectra doesn't stretch and can't take the intermittent shock like the mono can.

    Rarely is the line diameter about strength. Nine times out of ten, a line fails because of abrasion. A good multi-strand line will outlast a stronger line with fewer strands
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  8. #8
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    Default Re: What size rope to use for different boat sizes?

    spectra can be used if you have a rubber snubber somewhere in the system to absorb the shock.

    It isn't commonly used just because it is expensive, the 5/8 line of poly is far cheaper than a 1/4 spectra

  9. #9
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    Default Re: What size rope to use for different boat sizes?

    "Keep in mind there is such thing as line too large for the cleat."

    I would have to disagree; if the line is too thick, it won't fit as securely under the "arms" of the cleat and could come loose. But a line can't be too small for a cleat.
    A man of constant boat tinkering.

  10. #10
    Lieutenant Commander Beefer's Avatar
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    Default Re: What size rope to use for different boat sizes?

    ^^^ Pretty sure that's what he's saying.
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  11. #11

    Cool Re: What size rope to use for different boat sizes?

    This question frequently comes up with new boaters and those who really don't know. Keep in mind you want to use a nylon 3 strand twisted or braided rope (minimum). For every 8' of boat length you need 1/8" thickness of line (24' boat = 3/8", 32' boat = 1/2", etc). The next question frequently asked is how long do in need my anchor line? This is calculated by determining how deep the water is in which you will anchor. Multiplu that depth by 8 and you will have your length (20' of water = 160' line, 15' of water = 120' of line). I always round up to the next greater number on both ocassions. Good luck and have fun boating.

    Garza

  12. #12
    Supreme Mariner bruceb58's Avatar
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    Default Re: What size rope to use for different boat sizes?

    Don't post on old threads!
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  13. #13
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    Default Re: What size rope to use for different boat sizes?

    I've seen more cleats pulled out of docks and hulls than I've seen broken lines.

    Of course, I've seen more lines come loose than either of the above.

  14. #14
    Rear Admiral Fireman431's Avatar
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    Default Re: What size rope to use for different boat sizes?

    You can go smaller than normal with a dock line than you would with an anchor line. A dock line is never used solo as an anchor line is. Usually 2-4 dock lines are used to secure a vessel.

    And regarding what poster #3 said, a rope is a rope, even on a boat. It only becomes a line when it's attached to something.
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