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Author Topic:   Anchor line length
JimU posted 06-06-2002 03:39 PM ET (US)   Profile for JimU   Send Email to JimU  
I know I've seen it some where but can't seem to find it. What is the appropriate ratio of anchor line length to water depth. I have a 17 foot whaler. thanks jhu
Bigshot posted 06-06-2002 03:45 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Triple. 20'= 60' of line. this is for ocean and rough water anchoring. If you are in a lake that is calm in 20', 30 should do you.
george nagy posted 06-06-2002 04:31 PM ET (US)     Profile for george nagy  Send Email to george nagy     
Don't forget the chain, very important!
LKS posted 06-06-2002 04:40 PM ET (US)     Profile for LKS  Send Email to LKS     
We follow the rule of 7' of line for every foot of water we're anchored in, unless it's quite rough, and then we up it to a scope of 10'. Of course, if it's calm and we're only doing a short anchorage, we'll cut it to 5'. Better to have too much line, than not enough. -- LKS
Duncan posted 06-06-2002 04:45 PM ET (US)     Profile for Duncan  Send Email to Duncan     
I've heard five times as much rope out as the water is deep but I would agree w/ Bigshot (3 times). If the wind and tide are pulling so hard that you need that much line...seek shelter!

I fish an area with a rough tide and rocky bottom and have lost several anchors. I'm now a big fan of cheap anchors sans chain. That way if you've got to cut away and leave your anchor you don't get those unbearable pains eminating from your wallet.

whalerron posted 06-06-2002 05:15 PM ET (US)     Profile for whalerron  Send Email to whalerron     
The USCG Auxillary Safe Boating Course as well as the BoatUS Safe Boating Course both recommend a 7:1 ratio for the anchor line.

If you find you are losing anchors due to a rocky bottom, rig the anchor with a tripline. Then, you should almost always be able to retrieve it.

Barry posted 06-06-2002 05:23 PM ET (US)     Profile for Barry  Send Email to Barry     
The amount of rode or scope recommended depends on many factors including the water depth, boat size, boat type, conditions, bottom type, anchor type, etc. Most of the recommendations that I've seen suggest 5:1 to 8:1.

Regarding anchor type the Digger anchor looks interesting. www.diggeranchor.com No chain and automatic release. However I think that they recommend at least a 7:1 or 8:1 scope.

I use a vinyl coated Minn Kota Crab Claw anchor on my Montauk with about 150' of line (no chain).

george nagy posted 06-06-2002 05:24 PM ET (US)     Profile for george nagy  Send Email to george nagy     
Duncan try a retreival bouy.
Taylor posted 06-06-2002 06:06 PM ET (US)     Profile for Taylor  Send Email to Taylor     
I've always seen the 7:1 recommendation in Chapman and wondered where in the world that really gets used and what kind of boat carries that much line. At 40', that's 280' of scope, which in a crowded harbor will have you swinging into a bunch of other boats. In the NorthWest we often have small harbours that end up being pretty deep, and seven to one will put you somewhere in the middle of the island!

Besides local practice, it also depends on what your anchor rode is made of. All chain allows you to shorten the scope since the sag in the chain yields a more horizontal pull on the anchor. That's one reason why the leader on an anchor rode is made of chain... for the weight, to make the pull more in line with the holding power of the anchor, rather than pull the anchor up and out.

So, it depends on the expected wind conditions, fetch, bottom type, boat type, draft, windage, anchor type, how long you plan on leaving the boat there, and a bunch of other factors.

I usually use 3:1 or 4:1 for a 30' sailboat and get up three times in the night to check position. I start with three to one, back down on the anchor hard to set it, pay then out a little more to get to 4:1. The key is backing down hard to set the anchor.

In the Northwest, most of our bottoms are hard mud or sand, so loosing the anchor in rock is not so much of a problem.

For the Whaler, I just run it right onto the beach :)

LKS posted 06-07-2002 08:55 AM ET (US)     Profile for LKS  Send Email to LKS     
We regularly use 7:1 scope when boating on the south end of Lake Michigan, even when anchoring in shallow water for swimming. We use this ratio for both the big boat (34' Sea Ray) and Whaler. If it's like glass with no boat action, we'll go 5:1. When there's any wave action on the lake, using anything less than 7:1, we've broken loose and drifted. Even though we primarily anchor close to shore, we carry a minimum of 200 ft. of anchor line with chain attached on the big boat, and 150' on the Whaler.

On a typical beach day, we'll drop the hook at 10-12 foot, back down to secure it, and play out 50-70 foot of line. By the time we've fallen back and swung nose to the wind, we're probably in about 6 foot of water.

We've found that part of the problem is not knowing exactly what we're anchoring in. We've anchored in areas where the bottom looks and feels like all sand and have pulled up chunks of clay attached to the anchor. The way I look at it, better safe than sorry -- it's not a good feeling to look out from the water at your boat to see it drifting away (or heading toward another anchored boat). And I'd rather spend a few extra dollars for overkill than lose my investment (and sanity).

Looks like we're finally going to have a great boating weekend. Happy Whalin' (and anchorin') everyone! -- lks

Bigshot posted 06-07-2002 10:34 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No offense to anyone here but.....

anyone that lets out 70-100' of line to anchor in 10' of water is either a complete idiot or loves a good workout. Once you get your line run over by everyone who comes by and loose a few anchors and get into a few fistfights because your anchor line took up the whole harbor, you'll change your ways.

again no offense, just my $.03

newboater posted 06-07-2002 11:13 AM ET (US)     Profile for newboater  Send Email to newboater     
All you have to do is say the word scope, and everybody's got an opinion.

If all you want to do is stop to fish, use whatever scope you need to keep the boat from moving, maybe 2 or 3 to one depending on how rough it is. A good "rule of thumb" around here is to have a boat length of chain tied to 200-300' if line. You should be able to anchor securely in 40-50 feet with this setup. A very small fraction of the boats going out on day trips carry this much crap with them though.

Chapman's recommended scope of 7:1 is really for larger boats on a nylon rode, under moderate/storm conditions, anchoring overnight. Boats carrying all chain rodes usually use a 3:1 to 5:1 scope.

I can't think of too many occasions you would want to anchor a Whaler with 7:1 scope, unless it was blowing snot and you had an undersized anchor, or you were going to leave the boat or spend the night.

In So Cal, alot of the anchorages are pretty tight and congested. Putting out 7 or 8 to one, is asking for a collision with boats near you that are anchored at 3:1 on an all chain rode.

When we're out in our sailboat, we're anchoring our home and it weighs more than a Winnebago. We carry 300' of 3/8" chain, 300' of 3/4" line, and a 45-pound anchor. In the Whaler we carry a small collapsing "grapnel" anchor with about 6' of chain and 50' of line. Both serve their purposes quite well.


Dave S.
San Diego

Bigshot posted 06-07-2002 11:30 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Well said Dave.
jimh posted 06-07-2002 02:15 PM ET (US)     Profile for jimh  Send Email to jimh     
I may have spent more overnights sleeping while riding at anchor than most: probably over 100 times.

We gently lower the anchor to the bottom, back off slowly while paying out the rode, and carefully set the anchor on a very long scope, typically 10:1. Using the boat's engine in reverse and
feeling the rode by hand, you can tell quite a bit.

Once the anchor has been set (usually takes but a single try, maybe a second attempt now and then), we reduce scope to more like 4:1 or so. If the water is not too deep (or cold) we usually swim down and take a look, too.

In all the nights we rode at anchor we never dragged. I did observe that the ferocity of the thunderstorms that passed were always in direct proportion to how much I had to drink the night before. Waking up at 3 a.m. in a downpour to check the anchor was my least favorite part of cruising.

More than once in a crowded anchorage we have hauled up and moved before retiring for the night to get ourselves away from the herd. It seems like people have a tendency to want to anchor too close; I guess they figure the good spot must be where everyone is already anchored.

Taylor posted 06-07-2002 02:41 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Here is one other 'local' criteria. If I backed down on seven to one and ended up in six feet of water (as LKS does in Lake Michican) and its the middle of the afternoon, by cocktail hour I might be sitting high and dry. Puget Sound has a fifteen foot tidal range on 'spring' tides. So when I figure scope in 20 feet of water I have to ask myself am I looking at 20-35 feet or 5-20 feet, or what. Out comes the tide chart, and I get to do some interpolation. That adds the vertical dimension to boating.

So thanks for to Dave on the clarification of what Chapman was talking about, and thanks to Jim on the recomendation to set the anchor at greater than the final working scope. I'll give that a try.

I may not know much about outboards, but I certainly have opinions on anchoring :) My favorite trick - in a long narrow steep sided harbor (we get a lot of those, due to the geology) I like to run a stern line ashore. I was a pretty energetic anchorer in the past.

Bigshot posted 06-07-2002 02:56 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I think this thread should have been asked differently. It is too general. being it is a montauk, I answered accordingly to that. He/she will not be in 100' of water 40 miles offshore spending the night. If he was I reinstate the idiot remark:) But according to LKS'and some others ideals, I doubt they would have room for 1000 feet of line and 17' of chain, etc.

Now according to Chapman's and when you get your captain license, 7:1 is the rule of thumb but that is for "being on the hook" usually in a larger boat. It is the safe way to do it, but is it necessary in a montauk....I don't think so.

I asked my bud here in the office and he stated 7:1 but again that is up to 100ton boats, etc. we then discussed what we do and both agreed that we just let out line until it looks right or we stop dragging. Usually 3 or 4:1, sometimes less in shallow or crowded areas.

Taylor posted 06-07-2002 03:44 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Exactly. Its a Montauk. Just throw the old Mecury over the side and tie off with some 100# test superline :)
STEPHEN posted 06-07-2002 04:03 PM ET (US)     Profile for STEPHEN  Send Email to STEPHEN     
7 FT for every foot of boat, that is coast guard regulation
STEPHEN posted 06-07-2002 04:05 PM ET (US)     Profile for STEPHEN  Send Email to STEPHEN     
Excuse me, foot of water not boat
STEPHEN posted 06-07-2002 04:05 PM ET (US)     Profile for STEPHEN  Send Email to STEPHEN     
Excuse me, foot of water not boat
aubv posted 06-07-2002 06:22 PM ET (US)     Profile for aubv  Send Email to aubv     
Ultimately, don't you have to plan for 7:1 just in case? I.E. Breakdown in bad weather.

My main Anchor line is 300' and 12' of chain and I always carry extra coils of rope that range from 50-100' just in case I need to be towed/tow someone or have extra length for anchor. Modern soda crates work well for this, you can coil 100' of rope in the bottom of one and then stack another on top and so on. It turns out that the total height is no higher than the three empty crates stacked on top of one another.
Fwiw

Taylor posted 06-07-2002 06:52 PM ET (US)     Profile for Taylor  Send Email to Taylor     
THREE crates high!? aubv, where do you carry that in a Montauk?
aubv posted 06-07-2002 07:26 PM ET (US)     Profile for aubv  Send Email to aubv     
Taylor,

In the cc of my '96 17' OR. The total height of 3 crates stacked is less than 9" and the crates measure 12-1/2" x 19". A single soda crate can easy handle 200' of 3/8" rope neatly coiled if you don't want to stack one on top of the other.
Brian

Taylor posted 06-07-2002 08:01 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Oh.. I was thinking of milk crates. I'm not sure what a soda crate is. 9" I can handle.
triblet posted 06-07-2002 08:21 PM ET (US)     Profile for triblet  Send Email to triblet     
About 2:1 or 2.5:1. But then I'm going to
dive, and will see the anchor in person in
a few minutes. And maybe move it a bit to
a good secure place.

Chuck

LKS posted 06-09-2002 10:51 PM ET (US)     Profile for LKS  Send Email to LKS     
Beautiful weekend at the boat. Anchored out, was fairly calm at the time, sand, let out 5:1. By mid-afternoon, lots of wave action from larger boats passing; anchor did not hold once the waves kicked up. Next time, 7:1.
jimh posted 06-10-2002 12:22 AM ET (US)     Profile for jimh  Send Email to jimh     
Could someone cite the Coast Guard Regulation that specifies anchor rode length? I really don't think there is a regulation.

By the way, you must include the height of the boat in the calculation, so if your bow is 4 feet above water which is 11 feet deep, you base your ratio on 15-feet. At 7:1 that is 105-feet of rode.

triblet posted 06-10-2002 10:20 AM ET (US)     Profile for triblet  Send Email to triblet     
There's no regulation.

Chuck

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