Next message: bob england: "T&T: Define trawler"
Hi John,
I gave you my very biased opinion on boat design a few weeks ago and now
will add more of my very biased opinion about cruising a turbo diesel boat at
less that 75% to 80% of wide open throttle. Keep in mind that this advice may
only be worth what you pay for it, so here goes.
I'll start with my own personal experience rather than a bunch of "here say"
or stories that I have heard on the docks or have read on T&T at some point
in time. Our 46 foot boat weighs in at between 35000 and 40000 pounds
depending on fuel and water loads and weather we are heading out fully provisioned
or coming home after a few months in the Bahamas. The boat is powered by a
pair of 3208 Turbo charged 375 hp Cats with over 3000 hours on them with most
of those hours having been run in the 1200 to 1400 rpm range which is just
below 50% of WOT. I do run the engines up and blow them out every week or so
when out cruising but never to WOT.
The boat is 20 years old and I know that 98% of the last 2500 hours have
been run at these lower cruising RPM's. The boat starts and performs just as
well today as it did when I only had 500 hours on the engines, and uses no
more oil or fuel than it did when we started cruising the boat back in 2000.
My normal cruising speed is slightly over 8 knots but we will average only
slightly more that 7 knots after slowing down for bridges, locks. no wake zones
and while meeting other boats in narrow channels or entering and leaving
marinas or harbor areas. I have kept running totals since 2001 and have
traveled approximately 20000 Statute miles in that time and these fuel burn numbers
include my 8 kw Onan generator which has over 2000 hours of run time since
the year 2000. My fuel burn is has been right at 4.25 GPH and we have
averaged just under 1.7 MPG, and remember that this includes the fuel for the 2000+
hours on the generator. I have heard all kinds of horror stories about
running larger turbo engines at slow speeds but can only report that my real life
experiences does not mirror all of those stories that I have heard over the
years.
And what would a post be here without some opinion thrown in, so here is
some of mine<VBG>.
Go on the web and check out the trawlers and cruisers for sale to see how
many Grand Banks, Flemmings , Defevers and various other similar cruising boats
are listed for sale with Cat 3208 turbos and then ask yourself how many
thousand have been sold with these engines over the last 20 or 25 years. It's
my opinion that most of these boats mentioned above are not cruising the
waterways with these engines running at approximately 2000 RPM (Or 75% to 80%of
WOT) as I have passed thousands of them over the years and I see very few
squatting down in the water moving fast and throwing a big wake, which is what
would happen to most of them if they were cruising at these higher engine
RPM'S. I'd be willing to bet that most of the hours logged with these boats is
more in the 40% to 60% of WOT range and I doubt that any of them have suffered
bad consequences from this kind of running if they have been maintained
properly.
While attending a Defever rendezvous few years ago I asked John Green, who
is director of training for Pan Tropic, the authorized Cat dealer with several
locations here in south Florida about running my Cat's at slower RPM's while
cruising. His comment was - "in 25 years of working around these engines I
have never seen an engine damaged by running it too slowly"!
I think I'll believe him!!!!!!--and that has also been my experience!!!!!
John and Karen Siscoe
CHATEAU/ Defever 46 Sport Cruiser
Karens Cell 813 765 6660 (Cingular)
Johns Cell 813 951 3610 (Verizon)
Currently
Remember that the best boating accessory is a good owner!
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