T&T: Running high horsepower engines at low speed.

[Bill Allen]

We have a 1973 43 hatt dc with 6-71's N. I ran her to Fl. from new jersey 
mostly at 7 kts. We got around 1.8 mpg at this speed. My detroits are non 
turbo and as long as they get to temp and run them up once a day they're 
fine. There has been extensive discussion of  this on the hatt web site. 
Turboed engines are a bit different and need a little different operation. 
You probally will not get a turboed engine to temp at hull speeds. At cruise 
I get .6 mpg at 13 knts so we don't do that often
----- Original Message ----- 
From: "Faure, Marin" <marin.faure at boeing.com>
To: <trawlers-and-trawlering at lists.samurai.com>
Sent: Wednesday, September 19, 2007 1:57 PM
Subject: T&T: Running high horsepower engines at low speed.


> >Can you buy an old Hat or Chris Craft, run it near hull speed (which
> generally uses about 1 gal/nm) and not damage the 8-71s, 6-92s, 3208s or
> whatever turbo'd engines that are in the boat?
>
>>From everything I've read and been told, if the engines are running
> within their proper operating temperature range, it doesn't really
> matter what the rpm is.  What I don't know is if this applies to turbo
> engines as well as non-turbo engines.  But I would think that if the
> cylinder temperatures are correct to ensure complete burning of the
> fuel-air mixture, then the turbo should be okay.  I wouldn't think it
> could be damaged by spinning slower but I suppose it could be damaged by
> having unburned fuel, soot, whatever, going through it.
>
> I don't know how you would determine in advance if the engines in an
> older Hatteras, Chris Craft, etc. would remain in the proper temperature
> range at lower rpms unless you took the boat out and tried it.  And at
> some point as you throttled back, the inefficiencies Capt. Maurice spoke
> of in his earlier posts are going to kick in, so that would have to be
> considered as well.
>
> There is one question that could be asked, and that is given the price
> difference between an older, "fuel guzzler" boat and a newer boat with a
> smaller, more efficient engine, how much fuel could you buy with the
> difference?   If you're going to be like most boaters, and use the boat
> a relatively low number of hours per year, it may be that the cost
> savings from going for the lower-priced, used "guzzler" will more than
> cover the cost of running it even at today's and tomorrow's fuel prices.
> Something to consider, anyway......
>
> ______________________________
> C. Marin Faure
> GB36-403 "La Perouse"
> Bellingham, Washington
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