Advice on guest list for a cruise wedding

Wait, are you saying you'll send out more than 50 no sailing invites, and once you reach 50 you tell them they can no longer come? You can't do that. That is extremely rude.

We considered doing this type of wedding and decided against it because of that limit and the time constraints they put on you that day.

There's really no way to assure you don't have more than 50 non-sailing guests other than to limit your guest count to 50. If you know before you send out your invitations that a certain number of people have booked than you can increase your guest count. Again, only if you know BEFORE invites are sent out, otherwise it's B-listing and very obvious, as the B-listers won't have time to book. This could be difficult in your situation because I'd assume you are going to send out your invites earlier than normal to allow people to book their vacations.

Are your guests local to the port? By local I mean 20-30 minutes max? If not I would consider changing to an actual venue. I know we were allowed for a 2 hour event when we were considering it, and that was just too short to have people drive all the way there, especially considering it would be a morning wedding. We compromised by having our wedding the night before so everyone we wanted could come, and invited all of our guests on a cruise with us the next day to Bermuda. Many could not sail with us, but by having the wedding the night before we were able to celebrate with everyone we wanted.

I agree with pp, you really shouldn't invite more people than can be there. Maybe try talking with people about it first and getting a number on who is sailing, then create an A list and B list of others you want to invite. The priority list should be no more than 50, then you could invite others if you have declines. This will be most beneficial for you, too, as you probably don't want to leave your guest list up to chance based on who RSVP's first.

I think you may have to cut down your wedfing list or find a new venue. Do your guest have to pay for a cabin and take time off to do the cruise?!

I would talk to important people(parents, siblings, grandparents) before booking anything or sending invites.
I would imagine that if people are having to travel for the wedding they’ll want to take the cruise.

I would just invite 50 guests. If you do so early and most of them ending up booking since many people book cruises way in advance, you can extend invites to the next "circle." But be very careful with this. It's technically B-listing which I'm not a fan of but I understand the limitations in your case. You could also talk to close friends and family members first to get an idea about whether they plan on cruising.