Are you trying to book the direct train to Sicily (which goes aboard the ship) or take separate train to Vila San Giovanni then walk onto the ship?

If you take the direct train, you just reserve to Palermo. If you want to take the ship separately, you can just buy a ticket at the dock.

No; I’am just using a regional train from Tropea to Villa san Giovanni. And when I’am on the other side of the Messina Street, I would take a few hours to visit the cathedral before continuing with an other regional train to Palermo. So may I expect capacity problems at the ferry in San Giovanni if I have not bought  a ticket in advance?

I don’t think you’ll have a problem. They go every hour and you can’t reserve in advance for the fast passenger ferry.

Worst that happens is they say come back in an hour.

Fine to hear; thx for your explanations. 

I’am back from my Italian trip (Incl Sicilia) and here is my feedback on crossing the Messina street during LOW season (2nd half of Nov 23).

1. Crossing was cheap  : only 2,5 Eur ONE WAY for passengers without car, scooter, bike..  The crossing took 20 Min + another 15 Min to get OFF board. From the train station you walk to the ferry ticket selling offices and vice versa.  Buying a ticket costed me one or 2 Min as there was no queue at the desk. Even in Nov, ferry capacity was for 80% used. So even in Nov, it does not seems unpossible that you have to wait for a later ferry.  
2. During this low season, there was no continuous traffic : For example on Nov 30; I arrived in Messina by train around 0950 hr  and I had to wait until 1150 hr for a first ferry to cross for Villa San Giovanni. And at the other side I had to wait another 2 hours for an IC-train to Rome. So I lost a lot of time at the Messina crossing (from 0950 till 1400 hrs). And if you travel by IC-train, be sure to have a seat reservation because 90% of the time the Italian train personnel is asking for your train reservation above your Interrail pass. Not only in Messina but in the whole of Italy. It’s worth mentioning that the interrail website has a nice very helpful tool for making these seat reservations. No need to stand in long queues in train stations. 
3. Train Station Messina Marrittime was not served by trains. So  an extra walk to Messina Centrale (500 Mr along the rails) was needed. A detail if you’re loosing hours as I did for my return trip to the mainland, but in case the shedules for ferry and train are really close, it could be very disappointing to miss train/ferry due to this unforeseen walk.   

1. If you don't want to loose time, then always check timetables. The ferry timetables are on trenitalia.com and of course on the ferry website.
2. Reservations are mandatory in Trenitalia IC trains. Reservations are best done on tickets.oebb.at or in Italy at a ticket office (but that can indeed be busy at the big stations), since Interrail charge an extra booking fee.
3. Only the trains that go onto the ferry serve Messina Marittima.

Hoi Railmaster;

 I know OBB site and I use it occasionally for bookings on ICE trains in Germany. Last few weeks, I tried more than once OBB-app to make reservations for Italian trains but I got always a reject as “no tickets available”. Bizar because for the same train, the interrail app had tickets available. So I took the 2 times 2 Eur extra interrail cost as an acceptable inconvenience.  Positive for the Interrail app is that you can filter for trains were you do not need a reservation and all trains (with or without reservations). 

30 Nov/1 Dec were lately announced strike days in Italy. That day I had 2 reservations made on the interrail app : one for a daytrain from Villa S Giovanni to Roma and another for the night train from Roma to Milan Centrale.  Unfortunately both trains were cancelled due to strike. Do you have experience with rebooking seats in such chaotic situations?

At the end I was happy that the Trenitalia personnel behind the desk at Villa SG did it for me. It took them (specialists I think) 20 Min to arrange a seat on the next day on a direct Frecciarossa connection between Villa SG and Milan. ….  And it costed me nothing more than lots of patience in al long queue of people with comparable problems. Great service in a difficult situation! Apps are fantastic tools for specialists but occasional users ( like me ) are no specialists. Therefore happy that desks still exist in train stations. 

It's a bit tricky to use ÖBB for Italy but you need to add Interrail/Eurail as a discount and then select one-way tickets (not reservations only).

Trenitalia has a fixed timetable for strike dates so that's good in my opinion. Obviously the trains running will sell out quickly. Rebooking isn't easy (you can always contact customer support) so I would buy a second reservation for 3-13€ and then get it refunded.

Apps are supposed to help the common travellers but I agree that they can be confusing, incomplete, unreliable. I like SBB and DB Navigator app but at short-notice (especially in other countries) don't expect them to work perfectly.

OK and thanks very much for explaining “special” procedure in OBB-app for Italy. I appreciate that much more experienced users in this community  share their knowledge with the less experienced people like me.