Detroit Diesel questions

[maj75]

Thinking about a larger (60-70) Hatteras. Something that we can cruise to Bahamas or up and down the East Coast without
needing our own oil tanker to follow us. Could be SF or MY. Function as floating hotel at destination so a tender is a requirement.
We don't fish but do dive. Most larger Hatteras I've seen seem to have DD.

My question is that most of these are said to run 15-22 knots (or faster for SF). (I'm not interested in the
Long Range Cruiser Hatteras otherwise, sailboat) I imagine the fuel burn at these speeds is pretty high.

I understand that the DD are supposed to be run at the designed cruising speed. My question is can they be run
at idle or just above for extended periods and what kind of fuel burn rates would be expected at slow speed.
I hope to be able to run slow and fuel efficient for the long distance but still have the ability to go faster when
required by weather or tide of timetable.

I realize this is a broad question, but I'm trying to see if I could live with a DD boat or must look for that Unicorn,
a Hatteras that's been repowered with fuel efficient diesels, without screwing up seakeeping.

[capttonyf]

You didn't mention age or budget, but 60 to 70ft and DD Powered I'm assuming your looking at boats in the 1980's to late 1990's in the $200 to $500K Range? A CPMY, say a 67 Hatteras will be a Mid to high teens cruise, say 16 to 20 Knots, and a 65 Convertible would be Mid 25 +/- Knot cruise. Either would be good for your intended use. Depends on which way your leaning. Using those two boats as an example. The 67 CPMY has a smaller cockpit, with walkaround decks, and the tender would be mounted Way up High on the Rear end of the Bridge, with 3 Staterooms and be more rolly polly at displacement speeds. The 65 Convertible will have a bigger< lower to the water cockpit, possibly Larger Dinghy on the bow, 3, possibly 4 staterooms. and the ability to get up and move out regardless of sea conditions when you want to. It's really a matter of preference. I'd lean toward the 4 stateroom 65 Conv myself. Bets of both worlds, motoryacht accommodations and speed and sea keeping abilities of a high performance boat.

As far as being able to run the engines at low RPM to conserve fuel that's fine. Fish boat put 1000's of hours on at idle without any ill effects. It's not a bad idea, weather permitting if you've been chugging all night to bring it up on plane for 10 to 15 minutes and let it blow itself out and come up to full temperature but it's not necessary to do every time. For my Convertibles have always been the best way to go because they are the most rounded, best all around boats out there in my opinion. You can use it like trawler, you can go at high speeds, you can use it like a Motoryacht and you can dive, swim, and fish off it. No other boat out there can do everything like a convertible, it's a jack of all trades type boat. Not as efficient as a trawler, not as roomy as a MY, but can do both, and it can also out run a storm in bad weather. The 65C can run 20 to 25 knots in some really nasty weather and not miss a beat.

If you can get a little more specific in your wants, needs, intentions, and budget there are more then a few qualified people on here that can make some suggestions to help lead you do a good decision.

Tony

[maj75]

You've hit it exactly. I love the looks of the Conv, but they usually have much higher rated engines than the MY. I
was concerned about the fuel use of these bigger engines even a slower speed. I've seen the bitter theoretical discussion on this forum about running DDs "too slow."

What's the gpm of a 65 Conv running 1100-1200 rpm with 12v92s?

[northshoreone]

18 to 20 GPH total at 1,100 rpms
83 GPH at a cruise speed of 1,850 rpms

[maj75]

I want big tanks for extended cruising. I wouldn't mind faster cruising speed and top speed but not at the expense of terrible Gpm at slower speed. The Conv works better as a dive boat than most of the MY out there.

I'm thinking that by now, none of these older Hatteras are operating within their design parameters what with all the added luxury items, dingy davits, granite counter tops and vanities...

[maj75]

18 to 20 GPH total at 1,100 rpms
83 GPH at a cruise speed of 1,850 rpms

What's that in gpm? That's my measure of whether there is a significant trade off between speed and fuel consumption. My Intrepid gets around 1.5 gpm from 25 knots to 45 knots. Comfort dictates the speed😉

[northshoreone]

2.8 gpm at cruise +/-

[northshoreone]

Keeping in mind your not pushing a 10k lb Intrepid but a 100k lb Hatteras

[jrbrein]

Just divide the GPH by 60 to get GPM (gallons per minute).

So...

60 gallons/hour X 1 hour/60 minutes = 1 GPM


Jonathan Brein

[maj75]

I'm talking about gal/mile, not gal/per minute...