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-   -   Pratical depth limits when setting anchor (http://www.sailnet.com/forums/seamanship-navigation/61074-pratical-depth-limits-when-setting-anchor.html)

MazeRat7 01-05-2010 07:01 PM

Pratical depth limits when setting anchor
 
So for my boat with what is currently on board (1 Bruce, 2 Danforths, and about 150' of rode), to hit the suggested scope of 7:1, I need 100' for every 10' of bottom depth.

This is in a lake and the Admiral loves to fish for Catfish that run deep. Typically she likes to fish in 30-40' of water. Considering I don't have a windlass is it practical to think I'm going to retrieve a 20kg anchor at the end of 300' of rode by brute strength ?

The bottoms here are mostly a mix of silt, rock, & tree stumps. Any suggestions or experience in anchoring deep would be appreciated because we all know that if the Admiral isn't happy..... :D

Peace,
Maze

Tempest 01-05-2010 08:17 PM

7 to 1 scope is a general rule of thumb for an overnight anchorage.
That scope could be increased if conditions warranted.

If you're just fishing, having lunch, not leaving the boat and in calm condtions you just need enough rode to hold you in place...3-1 to 5-1 would probably suffice in good holding ground...

so at 3-1...at 35 feet...add 4 feet for freeboard = 39 ft. ..round it to 40...

40 x 3 = 120' sound better ? ..

As far as pulling up a lot of anchor rode, you use you engine to assist you make way in the direction of the anchor and stop once directly over....then you're really just using muscle to pull the last 40 ft.

...trees stumps always make me nervous..

bacampbe 01-05-2010 08:28 PM

How do you figure 100 ft for every 10 ft of depth? At 7:1, it should be 70 ft for every 10 ft of depth (measured to your anchor roller or chock). So if your depth is 30 ft, and your anchor chock is maybe 5 ft above the waterline, you're talking about 7 * 35 = 245 ft of rode. (No tides to worry about on the lake, and I assume you don't plan to stay anchored long enough to worry about seasonal depth variations).

Also, keep in mind that the 7:1 rule assumes you plan to spend a while at anchor--like overnight, when you really don't want to drag. If you're actively fishing, then you're probably also keeping a close anchor watch, and you're probably not that close to other boats or shallows. If a storm comes, you'll probably weigh anchor and head home. You're in a position where dragging would be an inconvenience, rather than a catastrophe. You could probably get by with well less than 7:1.

I've done lunch with as little as 3:1 in my Bene 31 on Lake Lewisville (with a fortress anchor on a muddy bottom). I was nervous about it, but it held. And even if it dragged, it would have been no big deal to start the engine and reset it.

bacampbe 01-05-2010 08:29 PM

Oops, Tempest types faster than I do :-)

T34C 01-05-2010 08:29 PM

Rope or chain?

dillybar 01-05-2010 08:34 PM

C'mon it's only the last 40' that's hard!
While fishing for halibut in Hains AK. the charter captain had us anchored in deep water.
When it was time to leave he attached a large round fender to the anchor line with a block, threw it in the water and gave it full throttle. The anchor was up next to the fender in about 10 seconds, we circled around gathering up the line and presto.
His system relied on the large fender offering up lots of lateral resistance in the water so the line would pull more or less straight up instead of straightening out. And realize this was a high HP fish machine.
For a sailboat you would probably have to attach a small para anchor to the float or... get the Admiral to put down her rod and help.

klem 01-05-2010 09:16 PM

There are 2 separate issues here, scope and hauling up the anchor the last 40' or so of anchor rode.

Regarding scope, 7:1 is really excessive if you are just going to fish. Chances are that if you are in 40' of water, you could drag quite a ways before it became an issue and since you are fishing, you will notice it. The more scope that you get, the less added benefit there is. Most anchors take something like 3:1 to set with any holding power and then have diminishing gains with scope. For example, with a completely straight rode, the difference in pulling angle on the anchor between 5:1 and 7:1 is 11 degrees and 8 degrees from horizontal. You should have more than enough rode to anchor there for a few hours of fishing.

The other issue is anchor retrieval. If you use an all rope rode, you will just have to retrieve the water weight of your anchor which is around 40lbs. However, if you have a lot of chain, the weight will become much greater. The advantage to shallow water and chain is that you never have to pick it all up at once. Depending on how your boat is laid out, you may well be able to use one of the halyard winches on the mast to haul up the anchor although this can be difficult if you are using chain. With a little bit of work on the helmsman's part, you shouldn't have to do anything until the anchor is broken out.

As long as you are reasonably fit, this is completely doable.

tager 01-05-2010 10:16 PM

I am pretty sure you could get away with a ten pound hook and nylon line if you are just fishing for catfish. Use good judgment.

MazeRat7 01-05-2010 10:21 PM

Great input but there are a couple of points I need to clarify. First, yes I'm talking about overnighting since the best fishing is pre and post dawn (according to her). ;) Hence I'm going to be in one spot for a while. Second, I've got a little over 4+' of freeboard so a 10' water depth + 4.5' freeboard = 14.5 * 7 = 101.5 for the 7:1 Third, I've got about 10' of chain on 150' of rope.

That being said, I like where Tempest is heading with all this. I don't think I would overnight with 3:1, but 5:1 maybe if I knew those crazy Texas winds were going to be somewhat calm while out. Dragging can be an issue since my lake is basically a river channel or canyon. Long, but not very wide. If I break loose in the night, I'll be aground rather swiftly. The tree stumps are a pain. I had to have a diver friend retrieve the danforth from my C22 after it became entangled. That was only a #8.
Sounds like the best I can hope for with the equipment on board is about 20' water depth using something around 5:1. I'm pretty sure I can heave it to deck once free and hence why I will try motoring up to it prior to hoisting.

Also, dillybar may be onto something. I've not considered how to apply mechanical advantage via fenders, blocks, or existing winches. Hummm. I'll need to "study" on that.

Thanks again folks. I'll be giving it all a try this weekend. Who know what the outcome will be.

Peace,
Maze

RainDog 01-05-2010 11:42 PM

A few thoughts:

1) If you are in most of the central Texas lakes, if you anchor drags, you will move into shallower water and soon be at 7:1, so as long as your anchor resets, no problem.
2) If you add another 100' of rope to your rode, I do not think it would be any harder to raise your anchor than it currently is. This should get you to 5:1 in all the good fishing water.
3) If you are catfish fishing, Texas tradition demands you stay awake all night drinking Lone Star, so you will be awake even if your anchor drags.


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