Your inconsistency does make it a bit of a challenge to select an average weekly training volume. However the 8 month volume is decent considering the forced time off. I suspect that if you have the time to train consistently and spread the load out more evenly over the next 24 months you can handle more than a starting volume of 7 hours. If you are going to still be ship bound for 1/2 of the 24 weeks you might consider heavily loading the 4 weeks ashore with high aerobic volume and then switch to low volume with more strength and ME work while confined on the ship when time and space are limited. This is called block periodization and has been used effectively. If you are going to be ashore the whole 6 months then a more gradual progression in over all volume would work better. I think you could start with 8 hours/week from the sounds of what you’ve been doing.