The world of speculation is great fun isn't it
Thanks to Steven for publishing the fuel consumption figures for the various High Speed Ferries. I had them before but had lost them. Apparently the throttle-back of the HSS 1500 saves about 30-35% in consumption so lets say that Explorer now runs at about 350t/24h. Still a lot obviously but a noticeable difference and running with a decent load makes her a slightly better financial proposition!
The sum I'm trying to do though is to find the point where it would make sense to replace Explorer with Carisma (as has been considered before). Just in the land of speculation of course for this one. Carisma is more expensive to run than Swift for instance (Swift runs at about 180t/24h apparently) but obviously Swift is a bit smaller (about 15% less capacity) and is not so good in terms of trips missed which has to be factored in too! So Carisma would be about 25% less expensive to run than Explorer (a bit more if she was throttled back to 32knots) but obviously provides less capacity at peak times.
Realistically, what I'm trying to explore is the possibility of whether Carisma could double trip in the high season when she would traditionally be very busy (so lets say running at 75% loading per sailing as Explorer does at her busy times) and then being cheap enough to single trip off season when she could fill the gap in the day between conventional sailings and take the dozen or so trucks that need a particular timeslot along with the tourist/leisure trippers.
I think Giftgrub mentioned converting Explorer to LNG before which of course would solve all the problems at a stroke but I just wanted to tease out another option!