5/16" G70 chain

Morgan le Fay has an all chain rode composed of 275' of Acco hot dipped galvanized 5/16" G70 chain which runs quite well through a 3/8" BBB wildcat. How is this possible and why G70? Let's tackle (pun intended) the chain - wildcat issue first then go on to why use G70,

Originally Morgan came with 2 lengths of 5/16" HT chain. This chain just did not pass the windlass without problems. It was always binding links and skipping and otherwise causing problems to feed. That is really not surprising when you take into account that the windless is an Ideal Windless Company BHW fitted with a 3/8" BBB wildcat. It is common knowledge that the chain needs to match the wildcat to avoid feeding problems. I should add that the 5/16" G70 feeds flawlessly. So what gives? Why does 5/16" G70 work and 5/16" HT fail?

The answer lies in the dimensions of the chain. Specifically the inside length of each link. The wildcat has "teeth" which grasp the chain at every other link. Thus the pitch of the wildcat teeth is 2 times the inside length of the chain it is designed for. The wildcat engages every odd link 1,3,5 etc. The teeth of the wildcat form a pocket that the links settle into. This allows for some size mismatch. When the wildcat and chain pitches match life is good. But when they don't there are problems.

In the case where the chain pitch is greater than the wildcat pitch the first link engages the wildcat tooth and starts pulling the chain along (it is between the 1st and 3th chain link pulling on the 1st link). Remember that the wildcat teeth engage the back of every other chain link so as the chain link pitch increases the second tooth of the wildcat will attempt to engage the 3rd chain link (between the 3rd and 5th chain link) but because the chain pitch is longer than the wildcat is designed for the second wildcat tooth lands on the body of the 3rd chain link. This is an override and the full tension of the chain is in the 1st link only. The next tooth of the wildcat does the same, it tries to fit between the 5th and 7th links but strikes and overides the 5th link. Eventually the stripper attempts to pull the 1st link off the wildcat, if it is under heavy load it jams and will not strip. if it does strip there are no other links engaged with the wildcat so the chain runs. Hopefully to catch again and not take a finger with it.

In the case where the chain is too short the first link engages as above and pulls the rest of the chain onto the wildcat. The second tooth of the wildcat then fits between the 3rd and 5th links but does not engage the 3rd link. All the force is still on the 1st link. Depending on pitch mismatch each successive wildcat tooth may end up between odd numbered links and really not do anything in terms of sharing the load. With a lightly loaded chain the 1st link is stripped off the wildcat and the links settle back so that the next odd link takes the load. Each link in turn takes the load and then is stripped. With luck you do not have any feed issues. If the load is very strong the leading link will fail to strip and end up jamming the wildcat. Still not good. In cases where the pitch mismatch it too great there will be at least one wildcat "tooth" that ends up overriding one of the links. This often ends up with a jam as the override gets to the stripper and the chain jumps. Also not good.

So why does 5/16" G70 chain run in my 3/8 BBB wildcat without problems? The pitch of 3/8" BBB is 1.105" and the pitch of 5/16" G70 is 1.122. Thus the G70 is 1.5% longer than the BBB and appears to be "close enough". It may be that the 1st link takes the load and as the 3rd link comes into play it is close enough to draw the chain forward and engage the link thus releasing the tension on the first link and allows it to strip cleanly. And so on with each successive odd link.
In contrast:

5/16 HT has a pitch of 1.017" which is almost 8% shorter than the 3/8" BBB and just too short for my wildcat and thus jams frequently.

3/8" G30 is 9.8% too long
3/8" G43 is 11.3% too long
5/16" BBB is 10.5% too short
5/16" G43 is 6% too short.

I cannot say at what percentage mismatch problems start showing up. I suspect that the allowable mismatch are not the same too long vs too short. But it is clear that if the pitch is close it might be close enough.

Go to page 2 to see how much stronger 5/16" G70 is over 3/8" G30.