using mixed rode in shallow water is cause of loss of over 6 boats in 3 years in an anchorage in west coast mx.I agree with Woods.
Having all chain for shallow water anchoring is abit extreme unless you have a motorized windlass. Other areas be it deep or hard rock bottom would require more chain. Not having a windlass, I can't see myself handling 100 ft. of more of wet/muddy/slippery chain.
I rarely anchor in 60+ feet so rope & chain for me works fine. You really don't want to go down in chain size from 5/16" to 1/4". You could be giving up 30% to 40% tensile breaking strength.
I use only stainless steel, as my old chain ate away at my fortress anchor in the locker. I was also unhappy with the fortress if it hit bottom on its side, it was a pain to set.
CR
Assume your 5/16 was NOT HT? If not then, moving to 1/4 HT is within the strength you need for your boat anyway. +1 on the size fitting the gypsy, though they can probably be swapped out for the correct size one.I am replacing old 5/16 60 ft anchor chain. I would like to go to 1/4 150ft. I'm thinking HT chain. ...