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-   -   Why Am I Dragging ? (https://www.cruisersforum.com/forums/f118/why-am-i-dragging-49550.html)

lorenzo b 04-11-2010 16:07

Why Am I Dragging ?
 
For the second time in as many months i've found myself dragging, both times in 2 to 3 knt current and 15 knt wind pulling in the same direction.
I use a 350 pound Northill anchor with 1/2 inch chain anchored in 12 ft of water with 100 ft of rode. My boat does weigh 70 tons and shows a large profile to the wind.
I could either add 100 ft more of chain or 400 ft of 1 1/2 rope or both. What's going to work for me?
I use a barrel type winch that only holds 130 ft of 1/2 inch chain so adding to my rode is going to take some juggling, but I'm way too big to be banging into things.
What do I need to do here?

cfarrar 04-11-2010 16:18

What's the height from the waterline to your anchor roller / chalks, so we can understand the scope required?

lorenzo b 04-11-2010 16:58

about 6 ft
I also have a padeye welded to my front keel at the waterline that I sometimes tie a snubber line to so it's as low as I can get it and I don't have to worry about chaffing.

MarkJ 04-11-2010 17:06

You don't have enough chain out.
12 feet water plus 10 feet water to bow roller plus 8 feet tide = 30 feet

But I start with 60 feet of chain before I make the calculation!!!!!

You need 150 feet of chain in 15 knots without current.

Just today this guy behind me got caught up around a rock and I settled back on him at 4:1 in 15 knots. I had to pull in till I was at 3:1 and then the wind came up to 20 knots and I dragged. Had to do a lap and drop again infront of him at 4.5:1 and holding fine at 25 knots. So now I have 150 feet chain out on a 7.5 ton boat

3:1 will NOT hold a big boat like yours. I think you need 200 feet chain out in that current.


:)


Hope this 'elps! :)

capngeo 04-11-2010 17:09

What kind of bottom?

I'm not as big as you (story of my life, however I digress), but I carry 2 types of anchors; plow (CQR) and a Danforth (Fortress). BOTH are about 2x the size recommended for my boat. I use a nylon and chain rode, but only the last 15' is chain.

Can't say I never drag.... but it ain't often!

fishwife 04-11-2010 17:17

What sort of ground were you over when you dragged? The weight of your anchor should stop you dead on good holding over solid mud or packed sand I've never seen a Northill and had to Google it but I'd imagine it would penetrate fairly well. To increase your scope I'd consider steel cable with perhaps 30-40 foot of chain.

P.

atoll 04-11-2010 17:17

try setting the anchor in reverse,gently untill she bites then increase power till you feel the bow come down, ground tackle sounds more then adequet.

if you still drag under power the the problem lies either with the anchor or the bottom.
fake anchors or replicas can be un balanced and not bite,on a flat hardish bottom or roll over,
otherwise excessive weed or hard flat bottom,lime stone,broken coral can cause problems.
but number one rule is all ways set yr anchor,ideally with plenty of scope.

boatman61 04-11-2010 17:25

I work with the system I was taught in the Navy which is for normal conditions I drop 3 x length + drop... in your case 63 x 3 + 46 = 235ft.... if conditions go above comfort I'm prepared to lay more... :D

cfarrar 04-11-2010 18:07

12 ft depth + 6 ft to the roller = 18 ft
5:1 = 5x18 = 90 ft rode if you really have 12 ft of depth...

Add another 8 ft for tide = 26 feet
5:1 = 5x26 = 130 ft

If your anchor is dragging you might try a 7:1 ratio, especially with the windage and current. The rode lengths above would become 126 ft and 182 ft, respectfully. It sounds like you need a longer rode.

boatman61 04-11-2010 18:16

OPP's.... I read 12m instead of 12ft... its either to much wine or I need new glasses... Subtract 28ft.... sorry:whistling:

thinwater 04-11-2010 18:27

I had a Northill on my last boat and liked it fine. I'm sure someone will chime in for you to get a Rocna:D. 350 pound seems like enough (I had 10 pounds on a 2,000 pound boat and held in many storms), and the scope has been discussed.

  1. Is it a Northill or a Northill replica? If it is a replica, angles or balance could be wrong. Perhaps a local fisherman would have something you could compare it to.
  2. What is the bottom? They are not too good in thin silt; nothing is. In mud or sand they are very good.
  3. Does it come out after a tide shift? The Northill has a fluke exposed, and if the boat spins the chain can foul that fluke and pull the anchor out. That is a perpetual hazard; I generally only used this anchor in dual sets or when there would be no shift.

ActiveCaptain 04-11-2010 19:37

My bow is 10' off the water and I'm anchored in similar NC surroundings with a 35 ton boat (lighter than yours by 1/2). I started with 125' out and allowed it to slowly set over about 10 minutes. Then I let out another 25' and pulled back gently against it building up to 1,000 RPM's with both engines in reverse. In a tight anchorage, I'll often do that and then pull back in 25 - 50' unless there's high winds predicted. It's been 2 days now and we haven't moved an inch (testing a new anchor alarm too!).

If there's a storm coming, I like having 175 - 200' out in 10 feet of water.

It doesn't sound like you're letting out enough chain.

atoll 04-11-2010 19:41

thin water,you may have hit the nail on the head,was unaware the north hill had a fluke, this is probably whats happening fluke getting fowled on larger tides,hence only happening once a month when enough tidal stream to swing the vessel against pervailing wind or something similar,and unable to reset it self

MarkJ 05-11-2010 02:20

There is another way to test the pull of a 3 knot current on a 70 ton boat.

Test drive the boat in calm waters at 3 knots and check the RPMs.

Go to the dock and lash a line from the stern of the boat to the dock and then run the boat at those RPMs.

Test the amount of pull on the rope tied to the dock by
a) How far down river the dock is pulled
b) looping rope around leg of person on dock
c) tying rope to pretty girl's clothes

Repeat exercise with no current but 15 knot wind.

Add the force of tide to the force of wind and add extra for a gust.

I don't know nuffin about 70 ton boats but the reason why most of the big/huge/colossal/gigantic/gin palaces are parked out the back behind everyone else is cos they need a crap load a chain out :)

Remember: My boat WILL drag at 3:1

Boracay 05-11-2010 03:08

Mud, glorious mud...
 
Having looked up a Northill anchor it does look rather like an Admiralty with oversized flukes. Probably hold well around large rocks...

Most anchorages that claim to be good holding are mud: the nice solid sticky stuff that clings tenaciously to everything and needs a high pressure fire hose to get it off...

Now without wanting to get involved in another anchoring discussion I thought it was fairly well settled that an anchor needs a few things going for it. These might include a nice sharp point, a fair bit of weight and last, but not least, a substantial fluke area to stop the contraption from pulling through the mud.


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