Without being able to pay or contribute anything toward the expense of the trip I think you might be expecting a bit much dear young people.
Boat owners usually want people who know what they are doing , and can be of practical help with proven experience and
references or they need people to share costs with or without experience . It can be a bit tricky because if a
boat owner engages a couple for a length of time and the couple is not competent to the level required of them then the boat owner will himself be out of pocket and inconvenienced if they jump ship.
As a couple also , often one partner is of higher competence of the other so sometimes that can create friction. If a couple would be "surplus " as in they are not needed to assist , then why would anyone take them on if they cannot contribute to the cost of the trip.
It costs a lot to sail a boat , inexperienced crew can stuff up easily ,can be a
danger to have on board etc etc, so the risk to boat owners is quite high , thats why its not easy for you to get a ride . Also if you were on land you would have to pay for your
food , so why not be willing to share costs for that on board?
Marinas cost
money ,
water and electricity cost
money as does gas to cook with and
fuel for the
engine, just the time the
skipper needs to register you in new
ports takes time and effort on your behalf.
If one wants good experience , its like taking a lesson , so I think its reasonable to expect to contribute towards gaining that experience.
Personally i would rather pay double to be with good crew and on a good boat than be with someone for free on a dodgy boat .