New 55 Hatteras SF, 1271TI's

We too were full time liveaboards. As expected the Hatts are heavier boats, my 56MY being 74,000 "dry". (18'2" wide as well).

You can use 15w-40 in Detroit Diesel 2 strokes if it's CF-2 rated, D.D. sells 15w-40 that's cf2 rated. That's what D.D. recommends for colder climates, if I remember correctly. Some dealers use it here on DDEC motors from what I've seen as well. I prefer straight 40w in the D.D. 2 strokes.

3. For continuous high temperature operation (over 200 F or 94 C coolant out), the use
of an SAE grade 50 lubricant in DDC two-stroke cycle Series 53, 71 and 92 engines is
required. SAE grade 50 lubricants are also required for all Series 149 engines where
ambient temperatures are above 95 F (35 C).
4. At ambient temperatures below freezing (32 F or 0 C), sufficient starter cranking speed
may not be achieved to start the engine with SAE 40 grade oils. Where starting aids are
not available or at very cold temperatures (0 F to -25 F or -18 C to -32 C) even if
starting aids are available, the use of multigrade SAE 15W-40 or monograde lubricant
SAE 30 will improve startability. These lubricants must possess a High Temperature
– High Shear Rate Viscosity (measured by ASTM D 4741 or equivalent) of 3.70 cP
minimum. These oils must be replaced with monograde SAE 40 lubricants as soon as
ambient conditions permit. Do not use multigrade or SAE 30 grade lubricants in
two-stroke cycle marine engines or Series 149 under any circumstances.
5. At lower ambient temperatures where sufficient starter cranking speed may not be
achieved to start the engine with SAE 50 grade oils, SAE grade 40 oils may be used. SAE
50 grade oils are not recommended below 45 F (7 C) ambient.

https://www.demanddetroit.com/public/technicianguides/technav.asp/

See #4. It is recommended you run straight 40 weight in a 2 stroke almost always, unless in weather that gets below 32F (without starting aids: block heater etc.) . But, Detroit Diesel does sell a CF2 rated 15w-40, I forgot the part number for it and it's murder to try to find the part number online. But for cold weather, they do allow use of a 15w-40.

Rcrapps- you beat me to it, but on your chart for marine, under secondary oil #4 is listed, but see figure 2-2 and number 4.

No and No, but it can get down to below 32F in Panama City. I'd talk to the local dealer as I've seen them recommend it in winter regions where ambient temp is regularly below 60F and the motors didn't have block heaters. Personally I'd use 40W, but don't necessarily feel that 15w-40 is the end of the world to use in a 2 stroke in Panama City in the winter, if it's rated properly. I can tell you that trying to get a 12v71 to light off with 40W oil when it's 50F is a real mother. If the motors don't have block heaters, I'd be inclined to wait until March to change it to 40W.

Considering the lowest water temperature in PC is around 60*F in the dead of winter it is unlikely that the engine or engineroom temperature will be in the 30's.

DD has its reasons to make the use of multi-grade lube an exception, not the rule. The propulsion world is full of short term special condition exceptions to manufacturer's recommended fuels, lubes, and operating conditions. You can pour cod liver oil or baby oil in the engine and run it for a while, any oil will work for a short period but that doesn't mean it's a good practice.

Thanks to rcrapps for the below chart..
Not wanting to take away from the topic too far but does anyone have something similar to the below for an Ocean Alexander 440 CPMY? Dry, it should be about 27,000 lbs and has a 300 Gallon fuel tank running twin Cat 3208's.
I'm new to this boat and gathering info so any help is greatly appreciated.

Most of the 12v71 TI's I've run, will have an idle oil pressure of less than 12 lbs, one would be around 4-5 lbs at idle with hot oil. 1900 rpms would generally net somewhere around 35-50 psi depending on how worn they were.

Make one yourself. Get a propellor curve chart from CAT for your HP, and read the fuel numbers at a given RPM off the propellor curve chart (provided your RPMs reach WOT), you're fuel burn will be within less than 5% of whatever the chart reads, record your speed at each given RPM. Wait about 2 minutes after bringing it up to each RPM point for speed to settle out.

Quite the encouraging comment; frankly I post in hopes that others will feel this way and I read so that I might learn something new. Cheers.