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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 03-12-2005
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Falcon,
You seem to have your mind made up so I''m not going to argue with you. In fact, I don''t even know why you asked the question in the first place.
Get a Bruce, use it and you''ll see.
Respectfully,

Dennis
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  #12  
Old 03-12-2005
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Well, my mind isn''t made up. It''s my funds that are limited. I have been eyeballing several unused anchors on boats in the marina and have been trying to extricate a Bruce from a friend of mine who seldom anchors and on the rare occasion when he does, he uses his 45 CQR with 3/8 BBB. His Bruce 33 sits there untouched, and has for years.

Now, if I can get that from him, and hook it to my 1/4 BBB chain, I can give it a few tries and see what I think of the setup and the holding of the anchor.

Of course, I will still have to upgrade my chain and chain gypsy to 3/8, I will still have to trade off the 5/16 and 1/4 chain for a secondary 3/8, and I will still have to get a bigger second anchor, but by then I will have spent another $2000.

It goes without saying, now that it has been said repeatedly in this thread, that I have to upgrade. That''s why I asked. My mind isn''t made up, but I DO have personal preferences. I can''t allow them to mislead me, because after all, some people like multihulls and look where it brings them. Can''t have too many PDQ''s crisscrossing the bay.
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  #13  
Old 03-12-2005
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Falcon,
Good post.
While the CQR does have it''s down falls, holding power, in pounds, can be as high as 1600-1800lbs witch is far more than you will get with the Bruce but the CQR has a moving part witch is a future point of failure and is not always a bad thing as long as it does remain in the future. They are not good in grass. I''ve had my 35CQR drag effertlessly in the waters around Jamstown, R.I.and Newport But they have trouble setting somtimes and this is where the Bruce excells far beyond any other anchor. The Bruce''s holding power isn''t that great when compaired to most other anchors, but the reliability of the Bruce to set and reset after veering?...No anchor comes close.
So some people say that the Bruce 44 only has up to, say, 900lbs holding power(unless used in rock, then only limited to the breaking point of the anchor itself)but remember that on the average 32 foot sloop, it takes a gale to produce about 350-400lbs of pull on a road.
Although your boat is 32'', she still has a 22,000lb displacement and I would opt for the 44lb model that can be purchased for around $250.00.
The Bruce''s stats are based on winds of 35kts and not 20 or 25kts like all other anchor tests.
Regard''s

Dennis
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Old 03-13-2005
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Dennis erroneously claims that “... on the average 32 foot sloop, it takes a gale to produce about 350-400lbs of pull on a road ...”

The loads placed on anchor and rode are a function of current, waves, and wind, with the latter being the most significant in most situations. All these loads vary with the type and size of your boat. While calculating precise wind-pressure loadings generated by various boats is laborious, good estimates of drag due to wind have been calculated for various boat lengths.

ABYC H-40 Table I suggests much higher loadings (including wind, current, & wave action).
ie:
30'' Boat ~ Working Anchor (to 30 Kts) @ 700#, Storm Anchor (to 42 Kts) @ 1,400#
A GALE is defined as windspeeds of 34 - 40 knots (39-46mph), hence the anticipated loading is up to 1,400 Lbs, in this example ~ way more than the 300-400# cited.
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Old 03-13-2005
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Gord,
Thats right, I said wind. Just wind. Of coarse you''d have to figure seas, currant etc. Jeez, how ''bout a break.
I have never actually gone out there with a pull gauge and checked it myself, have you? I go by tables I''ve studied coupled with my experiance and what I''ve seen but you don''t beleive me because you read somewhere....
Keep on reading.
You jump on me because I didn''t specify added laods caused by currant, seas type of boat, etc. then you turn around and swallow thie ABYC table but they didn''t specify any other info but "30'' boat". For all you know thy might be using a 30'' heavy displacement gaff schooner for their test!
I can hold onto my mooring pennant in 20kts of wind and just barely be able to hold my boat from falling back but in a near gale I can''t. You could use a simple test like this to figure it out. And when the wind doubles, the force it creates is quadrupled.
I could copy out of a book also if I chose to.

Dennis
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Old 03-17-2005
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Do some math. (flatplate pressures)

34.7 knts wind = 5.9 lbs/sq ft pressure
48.1 = 11.5
65.1 = 20.0
78.1 = 29.6

A typical 32'' heavy displacement sailboat may have around 50-75 sq ft of wind resisting area?

That''s 1480 - 2220 pounds of wind pressure on the anchor line at 78.1 kts...not including wave action and surges on the line. The pressures get insane at 120+ kts.

Figure when you''re cruising in the tropics to get t''storms that gust 30-40kts easy. I wouldn''t gear up for cruising for under 110+ kts. The questions is...How much can your cleats hold?

In the practical world I''ve found anchor mfg holding specs to be VERY conservative.
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  #17  
Old 03-19-2005
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Billpjr:
Thanks for providing a simple formula for determining wind load.
The loads you calculate, for a 32'' boat, are much smaller than I would (by a factor of at least 2).

Doing the math’ for a 34.7 knot wind:
34.7 x 34.7 x 0.00256 = 3.08247
5.9 / 3.08 = 1.9
Hence Billpjr has used a combined “constant factor” of about 1.9.

How was this derived?

Billpjr also assumes an equivalent flat plate area (EPA) of between 50 to 75 square feet (for our 32'' example).

How was this derived?

A common engineering calculation for determining wind pressure on structures:

Wind Pressure in Pounds = 0.00256 x (V x V) x Kz x GRF x Cd x EPA

Where:

0.00256 = the mass density of air at 0̊C and normal air pressure.

V = the three-second-gust wind speed (velocity) at a height of 33 Feet.

Kz = the Velocity Pressure Exposure Coefficient. For structures, Kz varies from 0.92 to 1.40 depending upon structure overall height. For wire, Kz varies from 1.0 to 1.50 depending upon the height of the wire above ground.

GRF = the Gust Response Factor. For structures, GRF varies from 1.02 to 0.83 depending upon overall structure height. For wire, GRF varies from 0.63 to 0.93 depending upon span length and wire height above ground.

Cd = the Shape Factor, generally 1.0 for cylindrical elements like wire and round utility poles, or 1.7 for flat surfaces. Most standing structures including cars have a Cd of 2.0.
See: Shape Effects on Drag http://www.grc.nasa.gov/WWW/K-12/airplane/shaped.html

EPA = the Effective Projected Area (cross-sectional area) of the structure being evaluated.

Not considered above is the Material Surface Resistance Factor.

The ABYC standards are undoubtably very conservative, but given the difficulties in determining accurate loading data, and the importance of providing sufficient capabilities - I’m willing to accept the figures as the best available, until a better method is revealed.

How much can your cleats hold?
The ABYC tables are actually designed to designate the loading characteristics of deck hardware. So if built to ABYC standards, your cleats should hold:
30'' SailBoat @ 9'' beam at least 2100#
35'' SailBoat @ 10'' Beam at least2700#.

FWIW,
Gord
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  #18  
Old 03-19-2005
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Gord,
My objective was to show windspeed pressures and stimulate folks to do their own homework for pull force. It''s been a long time (maybe 25 yrs) since I pulled my engineering handbook out and crunched all the variables for accuracy. I didn''t use the "book" on my WS example but it highlighted how the WP cubes. In the real world the boat hunts at anchor and/or the wind shifts quickly which blows the "frontal" formulas to pieces...and then wave action is added. Anyway, to the best of memory my 42''x30''DWLx 12''x5''x24k lb cutter calculated at approx 11,000 lbs (not 1100) pull on the anchor line at 120+. Hard numbers done by the book but I don''t remember the actual frontal area. Being that I live and cruise in the south and likely gear up for higher winds than the AYBC probably specs.

Since we are getting technical...Gale conditions may need some clarification as defined in earlier postings.

Beaufort Scale...
#6 = Fresh Breeze = 29.5 kts
#7 = Very Fresh Breeze = 34.7
#8 = Moderate Gale = 41.6
#9 = Strong Gale = 48.1
#10 = Very Strong Gale = 56.4
#11 = Violent Gale = 65.1
#12 = Hurricane/Typhoon = 78.1
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Old 03-19-2005
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bad on me, double click
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