I don't think the chanty genre —pre-folklorization — was particularly gendered as male.

Chanty can be recognized as a genre that spanned spaces, contexts, and applications. Only one of those spaces was the deck of the sailing ship. Only one of those applications was shipboard work. That particular context was dominated by male participants.

Women participated in singing chanties in other contexts. These included work applications, where the work was on land.

if you're limiting your view of chanties to at-sea labor, then I suggest that is influencing your perception of chanty singing being gendered as male. However, I think it's illogical to apply rules to a genre based on one narrow context of performance.

You'd be better off saying that songs sung in exclusively male spaces are gendered as male— which could also be questioned, but would make more sense than to let "chanties" stand as equivalent to "songs sung in exclusively male spaces."

For these reasons, I think many of the remarks in this thread have it backwards. They present the past/original as male-exclusive and then seek (or not) to rationalize how present can part from that. In reality, the past/original was not male-exclusive; it's later folkloric performers that project an idea of male-ness onto the genre.

I guess it stands to reason that if folkloric performers project male-ness onto genre, i.e. as one of its meaningful traits, then performance by women will disrupt that meaning. Some will respond, "Fine, let the meaning be disrupted," caring more for maintaining their gender-blindness. Some others will say, "Okay... let it be disrupted... but as long as you understand that you have changed the very thing. It's something else you're doing than what the thing really is."

It's up to the individual whether they deem male-ness as one of the meaningful traits that define chanty singing. What I am asserting is that during the pre-folklorized time, chanty-singing does not appear to have been gendered male in particular. Up to you whether you want to go on your personal perception (i.e. "I've always thought about it as X, due to Y...") or consider, more objectively, the meaningful traits of the genre among historical practitioners.

A far more pressing/relevant question for me would be: Should chanties be sung according to a fixed text?

However, I'd be curious to know whether and to what extent current performers might view their masculinity as something significantly meaningful to their engagement of the genre. Are you showing others your maleness when you perform? Are you getting in touch with your male identity? Are you building a male social space? etc. If it's just that you're male and your voice generally has a different timbre as a female's, then I don't think that makes the issue a gender one.