View Single Post
Old 01-24-2015, 02:10 PM   #5
Art's Avatar
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 9,210
Originally Posted by djmarchand View Post
Controllable pitch props are expensive and are only available in bigger sizes than most 35-40' trawlers need. And "overpropping" with a controllable pitch prop isn't going to save much fuel, maybe 15-20%.

As Eric notes the better choice is to size your engine for the cruising speed that you need. But this is not always possible.

And finally running a big engine slow isn't going to use that much more fuel than one sized for trawler speed cruising. A modern 2 liter Yanmar common rail 80 hp engine uses about 2.3 gph of fuel at 50% load.

Most trawlers in the 35-40' size range will need about that 40 hp to cruise at 7 kts or so.

A much bigger 370 hp Yanmar uses about 20% more fuel at the same 40 hp power output or about 2.8 gph.

In a typical 200-300 hour per year useage, the cost difference is less than $500.

Thank you David. One of the best, clearest accounting yet as to why it is perfectly OK to have larger engines than required to move a boat at only very slow speeds. Hope Eric reads your post. Of course, full D hulls can not make use of the larger HP. But, SD and P hulls sure can!
Art is offline   Reply With Quote