Being a nerdy engineer, when the Captain announced we were skipping Puerto Plata at 9am on Feb 18th and sailing straight on to Miami, I wanted to consider this interesting implication I will discuss here and that is how much less fuel Riviera will burn in the journey home.
The instant the announcement was made, I checked the Navigation Display. It said there were 701 nautical miles to Miami. By foregoing stopping at Puerto Plata, we immediately gain 8 hours to cover the remaining distance. Thus, we can travel at a slower speed, and thereby do so using less fuel.
At 9am Atlantic time on 18-Feb, there are 46 hours before our arrival in Miami at 6am Eastern time and thus our average cruising speed would be about 15.2 Knots (nautical miles per hour). If we had left Puerto Plata at the originally scheduled time of 5pm, there would be 38 hours before our Miami arrival and we would have to average 18.4 Knots to make our 6am docking.
This translates into fuel burned. A ship obeys a cube law relationship of horsepower versus speed – halve the maximum speed and the horsepower is cut to 1/8th of the maximum speed horsepower. Assuming Riviera uses 100% horsepower at 20 Knots (the maximum speed I have seen on this cruise), then we can fill out the table below:
Speed
% Full Horsepower
Hours Sailing to Miami
Full HP Hours
15.2 kts
44.2%
46
20.3 Full HP-hours
18.4 kts
77.9%
38
29.6 Full HP-hours
So, by skipping Puerto Plata, Riviera will use about 2/3rds the horsepower-hours had we stopped and thus burned about 1/3rd less fuel. I am not saying that is why Oceania bypassed Puerto Plata, DR today – I do not doubt the difficulties in maneuvering a 15-deck high ship in a narrow channel with a bad crosswind – I am just saying that doing so gave the company a bonus in the economic bottom line. Just an interesting observation.