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. With advances in metallurgy though, BBB became a relic of the past as stronger and lighter heat treated chains came to the market.
HT is commonly used to denote this class of chain, but there is some discussion as to what the "HT" actually stands for. HT chain is made out of high tensile strength links which are also heat treated. Lastly, the chain tests higher than BBB, leading to people also referring to it as high test chain. Luckily, all of these terms start with H and T, but sadly, it leads to people referring to the same thing under many names: High Test, High Tensile, Heat Treated.
The chain is further classified by the manufacturers into various groups that also all mean the same thing. The manufacturers refer to this chain as Grade 4, Grade 40, and Grade 43. The important thing to look for on the chain is a 4 stamped onto the link. BBB chain links will have BBB or 3B or G3 or G30 on it, while HT chain will have G4 or G40 or G43 stamped onto the side of the link. Basically, if you see a 3, you have regular chain, if you see a 4, you have HT chain (43 is just there to confuse you, but it has a 4 so it is HT).
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 HT was formed from a 5/16" wire, while 1/2 HT was formed from a 1/2" wire.
Common dimensions for HT 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 G4 has a working strength of 3,900 pounds; and a breaking strength of 11,700 pounds.
3/8 G4 has a working strength of 5,400 pounds; and a breaking strength of 16,200 pounds.
1/2 G4 has a working strength of 9,200 pounds; and a breaking strength of 27,600 pounds.
The interesting thing to note is that the breaking strength is 3x grater than the working load, giving this type of chain a significant safety margin, but still a smaller margin of safety when compared to BBB. 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 gives you the confidence that your chain will hold up well when you depend on it the most!
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 G4 weighs 1.1 pounds per foot.
3/8 G4 weighs 1.5 pounds per foot.
1/2 G4 weighs 2.5 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 G4 would weigh 330 pounds.
3/8 G4 would weigh 450 pounds.
1/2 G4 would weigh 750 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.
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. This is what made HT chain virtually replace BBB chain, the same strength could be had in a much lighter link which saves on the weight of the entire ground tackle. This weight savings could add up to hundreds of pounds located at the tip of the bow on larger cruising yachts.
When looking at G4 chain, an important feature to evaluate is Strength to Weight Ratio.
5/16 G4 is 3,900:1.1 = 3,545:1 working load, and 10,636:1 breaking load.
3/8 G4 is 3,600:1 working load, and 10,800:1 breaking load.
1/2 G4 is 3,680:1 working load, and 11,040:1 breaking load.
Lastly, you need to evaluate strength to cost ratio, as this will directly affect your wallet;
5/16 G4 costs $5.59 per foot
3/8 G4 costs $6.39 per foot
1/2 G4 costs $10.99 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 G4 697.7 pounds per dollar
3/8 G4 845 pounds per dollar
1/2 G4 837.1 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 G4
Weight: 330 pounds
Working Load: 3,900 pounds
Breaking Load: 11,600 pounds
Safety Margin: 3x
Bulk Discount Cost*: $1,146
300 feet of 3/8 G4
Weight: 450 pounds
Working Load: 5,400 pounds
Breaking Load: 16,200 pounds
Safety Margin: 3x
Bulk Discount Cost*: $1,536
300 feet of 1/2 G4
Weight: 750 pounds
Working Load: 9,200 pounds
Breaking Load: 27,600 pounds
Safety Margin: 3x
Bulk Discount Cost*: $2,010
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.