On my recent trip to Ft. Pierce I learned a few things. When the wife and I were looking for our next boat, there were some items I was particular to. The main was a couple of small naturally aspirated diesels. I felt that 8-10 kts was sufficent cruise speed for the type of cruising I wanted to do. I also knew I would probably not be buying a full-displacement trawer but a semi-displacement. Well over a 460 mile round trip, here is what I found. When the scenery is nice 8-10 kts is very nice but when in more open water with a 20-30 kt headwind 10 kts sucks in a semi-displacement hull.
The Amar la Vida has twin 6-71Ti Detroit diesels. After working the numbers. At 1100rpms, depending on tide I run at 8.5-10kts. The best part of that is I am burning 7 gallons per hour total with a 20-25% load on a 15kw genny. Now at 1800rpms the engines are in a nice even stride, depending on tide she's running 14.5-16.0kts burning 18 gallons an hour with the same genny load. I do not think that is bad for a 50k pound aft cabin motoryacht. I am very happy with these numbers and I believe it gives me alot more flexibility in my cruise planning without breaking the bank.