Stupid diesel question

[John F.]

We’re halfway through putting our two kids through college, and I’d really like to get another boat. This time, the boat will be used for fishing (Bay and Sound type fishing—not offshore), cruising, and maybe even as a weekend condo. So, as much as I loved by B31, we may go a little bigger—maybe a B35 (or a downeast), but not a trawler. I still have this thing for older SFs.

Can a diesel boat, like a B35 with 3208s, be cruised at displacement speeds for extended periods of time, with the idea of saving some fuel, without hurting the motors/turbos/whatever? I’ve been told you can’t run diesels like that because they won’t get to full operating temp., and will dirty up the turbos, which is bad for the motors. On the other side, when we fished, we’d run for a few hours to wherever, troll at displacement speeds for 7 hours or so, and then run home---pretty much what everybody else does. That 7 hours never seemed to hurt anything—was it the run home that blew things out? Can you just cruise for a few hours and now and then run her up to accomplish the same thing? Does it make a difference if the diesel has turbos? For example, could you run a B31 with 210 6bts at displacement speeds without hurting anything, but not a B31 with 315 6btas?

Sorry for what may be a stupid question, but I’ve asked the boat show repower booth guys and have gotten different answers a few times.

[Bruce]

John,
If your not black smoking a diesel, you can run it all day at 200 below max down to idle.

[John F.]

Thanks Bruce. Is black smoking from overpropping?

[Bruce]

Over propping, over loading, air restrictions especially below deck installs.

Ever see below salon floor engine installs that have the floor carpeted and theres a nice outline of the below carpet hatches?

Half the sportfish boats I worked on had that issue.

[John F.]

Thanks.

[JohnD]

John,

What you describe is how I use my B35 for the past 3 years. Most trips are idle speed + for 1-2hrs, quoting Uncle Vic "Howdy Boating", no black smoke. The recommendation, from my mechanic when I had the checked out was to spin them up to 2300 or so for a couple of minutes at the end of the day just to clear things out.

A diesel B35-38 wouldn't burn much more fuel than your gas B31 use to, with the added comfort of a "Living Room".

br,
JohnD

[John F.]

All those ponies and you're idling around....

[JohnD]

Yup, better to have it and not need it than need it and not have it;