Anchor line length?

    My boat is an 18' rigid inflatable, which means it's a light boat. I have a 9lb standard fluke anchor with 6' of chain. I need to make loops in the anchor line at specific intervals so as to be able to clip the line to the boat depending on the depth we're diving. I've read that the anchor line should be 4-7 times the water depth, but I don't think we've ever used that kind of ratio. Anyways I only have 130' of line.


    So, how much line for 30' depth?


    60'?


    90'?


    Also I go out on nice days, no more than 4' waves. Thanks.

    I generally use about 4:1 when anchoring in sandy bottom with our plow anchor and with light winds. I think you need more chain, though. The chain doesn't just function as a chafe guard for the end of the rope. A substantial length of heavy chain keeps the anchor pulling horizontally on the bottom, even with a shorter anchor rope, and dampens the impact of waves. So if you step up to 15' of relatively heavy chain, you can get by with much less rope.


    I don't know your bottom conditions. But here, in soft sand, anything less than 3:1 is prone to drag.


    If you are going into water that is deeper than you can reliably anchor, then you might want to look into a small sea anchor in case of an emergency.

    With 15' of chain, in light conditions, I bet you can get by with 3:1. Bear in mind that I do most of my diving inside the Bay, where the consequence of a screw up is mostly just the aggravation of re-setting the anchor. If I'm offshore, or have to ride out a storm, I put out more rope.

    Dan, now that you have a boat that line is now the Rode and the ratio of line to depth will be the Scope.
    That anchor and it's rode is the thread that connects the lives of you and your mates to this world.
    I am a very experienced skipper with a life time of gale winds, big seas and heavy duty Zodiacs anchored in all
    types of bottoms and depth.


    At some point you want to consider shackling a small red poly ball to the end of your rode. If there is a emergency
    you can throw the ball and pick up a buddy ASP.


    I'm going to scan some Navy stuff this week end for you. Could you post some bow and stern images of your
    boat including the deck?


    Cheers, Don

    "Great mother ocean brought forth all life, it is my eternal home'' Don Berry from Blue Water Hunters.


    Spearfishing Store the freediving and spearfishing equipment specialists.

    Edited 6 times, last by Don Paul ().


    +1 on the quick release. I've always wanted to do one,never got around to it. Remember how small my anchor is? The 15ft of chain really helps it grab with ease. I don't think having sections in the anchor rope is a good idea. You'll be constantly having change out the length. Keep it simple. As far as amount of line, it really depends on conditions. That's why 3-1 or 4-1 is a general rule of thumb.

    Here the anchor usually catches on a rock. The more rope the better once you own a boat you'll see there a 100 different things going through your mind while you dive.


    One of them will be if that noise you hear is the anchor clanking against a rock or dragging on the bottom.


    When I dive a reef I do not set the anchor for the reef depth, I set it for the sand depth. So if it ever comes out of the reef it will drag or hopefully catch on the sand and not just float away. Usually I try to do a 2:1 ratio or in good conditions until the anchor holds hard in something plus about 20ft more.

    Davie Peguero

    Here's the bow eye.




    Bow and transom.




    I did a little reading in a RIB forum and some people rig the anchor exactly the way I said I was going to do it. Using a painter with a snap at the bow eye and making attachment points on the rode.

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