For a very long time, BBB was considered to be the epitome of perfection when it came to anchor rode. BBB is very strong, galvanized to protect against corrosion, and produced in a calibrated method that allowed it to run smoothly through a windlass.
The biggest advantage that BBB chain has, which also led to its eventual decline in modern day usage, is its weight. BBB is considered to be the heaviest chain available for a given strength. The links of the chain are formed from low carbon steel wire, and the size of the link is actually referring to the size of the wire that was used. For example, 5/16 BBB was formed from a 5/16" wire, while 1/2 BBB was formed from a 1/2" wire.
Common dimensions for BBB chain are 5/16", 3/8", and 1/2". Larger and smaller links are available, but these are the three sizes that you will encounter in most marine chandlery stores.
5/16 BBB has a working strength of 1,900 pounds; and a breaking strength of 7,600 pounds.
3/8 BBB has a working strength of 2,750 pounds; and a breaking strength of 11,000 pounds.
1/2 BBB has a working strength of 4,500 pounds; and a breaking strength of 18,000 pounds.
The interesting thing to note is that the breaking strength is 4x grater than the working load, giving this type of chain a significant safety margin. When the chain is manufactured, it is then subjected to a rigorous test of strength, followed by a close inspection of each individual link. This strict quality control set BBB chain apart from other link forms that were in production at the time.
Aside from strength, the next important factor to consider is the weight of the chain, as this directly affects the holding power of your anchor that is desperately trying to hold onto the bottom!
5/16 BBB weighs 1.1 pounds per foot.
3/8 BBB weighs 1.6 pounds per foot.
1/2 BBB weighs 2.8 pounds per foot.
A standard recommended length for an all chain rode on a cruising yacht is 300 feet. This will give you the ability to anchor in 25 feet of water with a 5 foot freeboard and still maintain 10:1 scope for storm condition anchoring. The weight at these particular sizes are as follows:
5/16 BBB would weigh 330 pounds.
3/8 BBB would weigh 480 pounds.
1/2 BBB would weigh 840 pounds.
This weight will help cause the chain to sag and pull towards the bottom, creating a catenary curve. The curve will make the chain fall vertically from the bow, but curve away from the boat as it runs. The chain will lay on the sea floor because of its weight and cause the load on the anchor to be parallel to the sea floor. This will help the anchor set, and hold, as all the load will be sideways and not upwards.
In the years when BBB was introduced, crusing boats were all heavy displacement, full keel boats. This made them much less sensitive to how weight was loaded and how much weight was added to them. 480 pounds of chain with a 65 pound anchor meant that the ground tackle would weigh 545 pounds, all located at the tip of the bow.
If you tried to do this same setup on a modern ultra light displacement boat, you would sink the bow into the water so much that the rudders would start to come out of the water! Modern light displacement boats are very sensitive to how much weight is added and extremely sensitive to where the weight is added, as it will drastically affect the trim and handeling of the yacht.
When looking at BBB chain, an important feature to evaluate is Strength to Weight Ratio.
5/16 BBB is 1,900:1.1 = 1,727:1 working load, and 6,909:1 breaking load.
3/8 BBB is 1,719:1 working load, and 6,875:1 breaking load.
1/2 BBB is 1,607:1 working load, and 6,429:1 breaking load.
Lastly, you need to evaluate strength to cost ratio, as this will directly affect your wallet;
5/16 BBB costs $6.19 per foot
3/8 BBB costs $6.79 per foot
1/2 BBB costs $8.20 per foot
If you look at the pounds that can be held (of working load) per dollar, it starts to look like this:
5/16 BBB 306.9 pounds per dollar
3/8 BBB 405 pounds per dollar
1/2 BBB 548.8 pounds per dollar
As you can see, the weight, cost, and strength of the chain all increase with size, but your money goes farther at holding your yacht as the size of the link increases. These numbers are all well and good, but how do they relate to your actual setup? Lets look at what the actual values would be of actual 300 foot rodes.
300 feet of 5/16 BBB
Weight: 330 pounds
Working Load: 1,900 pounds
Breaking Load: 7,600 pounds
Safety Margin: 4x
Bulk Discount Cost*: $1,182
300 feet of 3/8 BBB
Weight: 480 pounds
Working Load: 2,750 pounds
Breaking Load: 11,000 pounds
Safety Margin: 4x
Bulk Discount Cost*: $1,422
300 feet of 1/2 BBB
Weight: 840 pounds
Working Load: 4,500 pounds
Breaking Load: 18,000 pounds
Safety Margin: 4x
Bulk Discount Cost*: $1,731
When you buy large quantities of an item, most chandlery stores will give you a discount. Being how you are not buying 300 individual feet of chain, but instead a 300 foot length, this is a rough estimate of how much you should expect to pay if you can negotiate the price down, and thus the amount of money that you would save by negotiating.