Large discrepancy in anchor sizing

Mako, You can get over 14,000 pounds (about 1/2 the mean breaking load) of pull from 400' of 1/2" chain in 12' of water. As I've said before its the chain that anchors the boat and the anchor that anchors one end of the chain. In 410' of water the chain weighs around 877 pounds, but it's the leverage of that weight multiplied by the scope ratio that does the magic. One of the cool things about an all chain rode is that you can use the catenary to pull the boat forward to retrieve the anchor without an engine (no you are not using the windlass to pull the boat forward if you just lift the weight of the chain off the seabed). I did this regularly on a 40 ton sailboat with 1/2" chain and a hundred pound cqr I think it was. Anchored five days in Madeira in 50 plus kts for 2 of them waiting for the winds to shift.


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What type of bottom/s will all this be taking place over?

So the knowns are force 11 and boat size. The unknown are duration, bottom and fetch.


Force 11 yields 37' to 52' waves on open conditions. In shallow or near shore those waves will be breaking.
I don't know how you can plan for that.

bayview said:

So the knowns are force 11 and boat size. The unknown are duration, bottom and fetch.


Force 11 yields 37' to 52' waves on open conditions. In shallow or near shore those waves will be breaking.
I don't know how you can plan for that.

Click to expand...

You plan on running the engine(s), and prayer.

I appreciate all the feedback so far. To answer the above questions:

* Bottom conditions will of course be varied, so I'm trying to size anchors based on somewhere in-between the holding loads reported from hard sand to soft mud. Just an average, trying to be conservative. For the first few years she will be based out of the west coast of Malaysia where previously we had encountered either sand or sand/clay.
* Sizing for force 11 winds to calculate aerodynamic drag. I can't recall the last time someone tried to anchor in 30 to 50 foot seas

Design and calculations are always based on assumptions, ideal conditions, etc., but in the end selecting anchors is based on experience, gut feeling, etc. My previous boats all came with anchors and the only new one that I built (small fisherman) was easy to decide on ground tackle because it was a day boat anyway.

Desiging and building a new boat is exciting and fun and very frustrating all at the same time.

"Force 11 yields 37' to 52' waves on open conditions. In shallow or near shore those waves will be breaking.
I don't know how you can plan for that."

Running up a river would be my solution .

Depending on the bottom contour anchoring in 400+ ft of water might keep one out of the steep breaking water.

IMHO - Although the Beaufort Scale is good rule of thumb... conditions mentioned at wind speeds are broad outline.


http://www.spc.noaa.gov/faq/tornado/beaufort.html






Less than 1
Calm
Sea surface smooth and mirror-like
Calm, smoke rises vertically


1-3
Light Air
Scaly ripples, no foam crests
Smoke drift indicates wind direction, still wind vanes


4-6
Light Breeze
Small wavelets, crests glassy, no breaking
Wind felt on face, leaves rustle, vanes begin to move


7-10
Gentle Breeze
Large wavelets, crests begin to break, scattered whitecaps
Leaves and small twigs constantly moving, light flags extended


11-16
Moderate Breeze
Small waves 1-4 ft. becoming longer, numerous whitecaps
Dust, leaves, and loose paper lifted, small tree branches move


17-21
Fresh Breeze
Moderate waves 4-8 ft taking longer form, many whitecaps, some spray
Small trees in leaf begin to sway


22-27
Strong Breeze
Larger waves 8-13 ft, whitecaps common, more spray
Larger tree branches moving, whistling in wires


28-33
Near Gale
Sea heaps up, waves 13-19 ft, white foam streaks off breakers
Whole trees moving, resistance felt walking against wind


34-40
Gale
Moderately high (18-25 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks
Twigs breaking off trees, generally impedes progress


41-47
Strong Gale
High waves (23-32 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility
Slight structural damage occurs, slate blows off roofs


48-55
Storm
Very high waves (29-41 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility
Seldom experienced on land, trees broken or uprooted, "considerable structural damage"


56-63
Violent Storm
Exceptionally high (37-52 ft) waves, foam patches cover sea, visibility more reduced



64+
Hurricane
Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced