I received several off list comments since I suggested the outboard
powered trawler. I confess that I didn't really think the problem
through. But here are some back of the envelope calculations showing
that not only is it possible but that it would require only a few
modifications of a conventional outboard.
Assume a displacement hulled trawler 40' LOA with a 38' waterline
length. I estimated a displacement of 30,000 lb. Most 40' trawlers
weigh a bit more but they are burdened with heavy inboards. It would
take about 43 hp at the prop to move this hypothetical trawler at it's
hull speed of 8.26 kt.
Now about the power plant. If we use a 50 hp 4 stroke outboard running
at 5000 rpm with a 3:1 reduction gear to swing the required 15.9" x
10.3" prop it would push the boat to its hull speed. According to a
good propeller calculation program, this would be a relatively
efficient prop. With two outboards, you could probably get by with 12"
props. 12" x 10" props are a standard item for 40 to 50 hp outboards It
would take some reengineering of the lower end to to mount a 15" or 16"
prop but I'm sure it could be done. If the motor could be turned the
way it is on most smaller boats, docking would be much easier. Of
course the outboard motor(s) would have to be fitted with a remote
control and steering.
I know that heavy barges and mooring tenders can be moved slowly around
harbor areas with ordinary outboards. It is a common shipyard practice
in the New York area. But they hardly reach hull speed. And, of course
the Murray and Tregurtha Harbormaster engines are still used for
pushing big barges. But these are far bigger than what I had in mind.
Several people suggested suitable trawlers that could be outboard
powered. One suggsted the Nimble Nomad. This is a very nice boat for a
cruising couple. In fact we almost bought one a while back. But at 24'
it was a bit too small for me, my wife and two teen aged children.
Others mentioned the possibility of fitting outboard mounts on a flat
transomed trawler. This would be a good idea for someone who already
has such a boat with a blown engine.
As for me, now that my kids are grown and have children of their own, I
might reconsider the Nomad or something of its ilk.
Larry Z