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Old 01-07-2013, 12:08   #1
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Capt. Allan

Can anyone tell me with a high degree of accuracy how much fuel I can expect to burn on a 45' Chris-Craft Commander gross tonage at 41000 Lbs and running at 1000 RPM with twin engins being Detroit 8V71N, Allison Transmissions M20 L/R. I am running 4 blade props in lieu or the standard 3 blade type, approx. 27"

I am trying to figure my fuel usage traveling the Intra-costal from Florida north. Leaving March early.

Any help will be valued.
Capt. Allan
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Old 01-07-2013, 12:15   #2
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Re: Capt. Allan

A lot!!!!!!!
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Old 01-07-2013, 12:27   #3
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Re: Capt. Allan

That my friend is without a doubt THE most accrurate answer, but It doesn't help except to more depress me. Thanks for it though.
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Old 01-07-2013, 12:34   #4
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Re: Capt. Allan

I have.a 40,000lb 44' chung wha with.twin 325hp cats. I burn 5-6 gph. At 1200rpm. Around 8-9 mph
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Old 01-07-2013, 12:38   #5
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I'll bet the average will be .67 nautical miles per gallon, unless you have stiff head winds. I know boat speak usually expresses it in gallons per hour, but to me that's not very useful.
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Old 01-07-2013, 13:29   #6
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Re: Capt. Allan

Interesting reply's. I was hoping for about 1 1/2 GPM and maybe even 3. Looks like I may be dreaming.

Anyone want to buy a boat or send me a young Irainian girl that owns a few oil wells. LOL
Or better even yet a nice American girl with lots of money that wants to share it with me. Yeah right. LOL
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Old 08-07-2013, 12:28   #7
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Re: Capt. Allan

I am intrigued by these answers. We have a 65,000lb 50 ft trawler with a single 280HP Cummins and large single 4-blade prop. We average 2.5gph at 1,650rpm and 7.5kt.
I know the CC is a twin engine and non-displacement hull, but at 1,000rpm it would still burn that much at low (trawler) speed??
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Old 08-07-2013, 18:27   #8
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Re: Capt. Allan

Quote:
Originally Posted by motion30 View Post
I have.a 40,000lb 44' chung wha with.twin 325hp cats. I burn 5-6 gph. At 1200rpm. Around 8-9 mph
Thank you for the info. This is more what I thought it should be but than just thinking it doesn't make it so. Your response just makes sense to be, thank you.
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Old 08-07-2013, 18:29   #9
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Re: Capt. Allan

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Originally Posted by chrisjs View Post
I am intrigued by these answers. We have a 65,000lb 50 ft trawler with a single 280HP Cummins and large single 4-blade prop. We average 2.5gph at 1,650rpm and 7.5kt.
I know the CC is a twin engine and non-displacement hull, but at 1,000rpm it would still burn that much at low (trawler) speed??
I wonder the same thing, thank you for the comment.
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Old 08-07-2013, 18:34   #10
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Re: Capt. Allan

Gross tonnage has little if anything to do with weight, which is displacement. I am surprised that nobody else chimed in on this. From Wikipedia:

Gross tonnage (often abbreviated as GT, G.T. or gt) is a unitless index related to a ship's overall internal volume. Gross tonnage is different from gross register tonnage.[1] Neither gross tonnage nor gross register tonnage is a measure of the ship's displacement (mass) and should not be confused with terms such as deadweight tonnage or displacement.
Gross tonnage, along with net tonnage, was defined by The International Convention on Tonnage Measurement of Ships, 1969, adopted by the International Maritime Organization in 1969, and came into force on July 18, 1982. These two measurements replaced gross register tonnage (GRT) and net register tonnage (NRT). Gross tonnage is calculated based on "the moulded volume of all enclosed spaces of the ship" and is used to determine things such as a ship's manning regulations, safety rules, registration fees, and port dues, whereas the older gross register tonnage is a measure of the volume of certain enclosed spaces."


Aside from that, how can anybody tell you this with a "high degree of accuracy." I am not a physicist or mathematician or naval architect but I do not even know if there is a formula to predict this, but in terms of accuracy, that will also depend on your cruising habits, the condition of the bottom, the tankage, headwinds and currents etc etc. But the question I have for you, is why does it matter? You own the boat so it will burn what it will burn. Why not just go out and run the boat and you'll find out??? You could probably install a consumption meter in the fuel lines.
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Old 08-07-2013, 18:53   #11
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Re: Capt. Allan

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Originally Posted by Paul Annapolis View Post
Gross tonnage has little if anything to do with weight, which is displacement. I am surprised that nobody else chimed in on this. From Wikipedia:

Gross tonnage (often abbreviated as GT, G.T. or gt) is a unitless index related to a ship's overall internal volume. Gross tonnage is different from gross register tonnage.[1] Neither gross tonnage nor gross register tonnage is a measure of the ship's displacement (mass) and should not be confused with terms such as deadweight tonnage or displacement.
Gross tonnage, along with net tonnage, was defined by The International Convention on Tonnage Measurement of Ships, 1969, adopted by the International Maritime Organization in 1969, and came into force on July 18, 1982. These two measurements replaced gross register tonnage (GRT) and net register tonnage (NRT). Gross tonnage is calculated based on "the moulded volume of all enclosed spaces of the ship" and is used to determine things such as a ship's manning regulations, safety rules, registration fees, and port dues, whereas the older gross register tonnage is a measure of the volume of certain enclosed spaces."


Aside from that, how can anybody tell you this with a "high degree of accuracy." I am not a physicist or mathematician or naval architect but I do not even know if there is a formula to predict this, but in terms of accuracy, that will also depend on your cruising habits, the condition of the bottom, the tankage, headwinds and currents etc etc. But the question I have for you, is why does it matter? You own the boat so it will burn what it will burn. Why not just go out and run the boat and you'll find out??? You could probably install a consumption meter in the fuel lines.
Paul thank you for all that information about tonnage. The basis for my question was simple. I like to plan ahead as much as possible. Since I have not had the opportunity of running my boat any distance to measure consumption I was just asking for other experience. I have no intention of heading out anywhere without first having a fair idea of what my range will be. As far as just going out and "running" to find out; in my friends boat we have had to rescue several that were disable for doing exactly that and running out of fuel. I'm sorry but that didn't sound like sound seamenship to me, but I do appreciate your other information.
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Old 08-07-2013, 19:37   #12
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Re: Capt. Allan

I never mean to suggest you blindly go cruising and run out of fuel. You fill your tanks and you make sure your gauges work and you watch the gauges drop and drop and you measure and estimate accordingly. Or you put in a consumption meter as I suggested. If someone told you "20 per hour" and other one told you "50 per hour" you'd still have to do the same thing and plan accordingly and since this boat should have more than enough range to go from one fuel dock to another--REGARDLESS OF CONSUMPTION---just get out there and do it. You cannot trust any estimates we might provide you with anyhow. Whether your range is 500 miles or 1000 miles or 1500 miles, just plan accordingly and you'll know for certain after the first day! I'd say expect to burn between 20 and 50 gph. That's my very accurate estimate base doing serious mathematical formulas...or I just sort of pulled it from the sky, Who know? Only you will after one day. Have a good trip.
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Old 08-07-2013, 20:12   #13
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Re: Capt. Allan

IF and I repete, IF ya run on one engine at a time, and keep the rpm under 1800 (better 1100 to 1200) ya might get 1 NM per gal and maybe a bit more! But those 871s have really never been known as fuel savers!! and you will have to have CLEAN bottom to do that well !! Ive had a bunch of those motors in fishing boats over the years, and they are tough, but not the biggest fuel savers GM ever made!!
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Old 14-07-2013, 23:17   #14
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Re: Capt. Allan

If what I have read and understood V892TA will burn 1.37 gal per mile at 900rpm and it only gets worse from there! So I'm guessing 1.5gal per mile at 1000rpm's... That's in a 1983 Hatteras 50c. The tranny's will tell the story though, running only one engine will get you a burnt tranny on the stopped engine after a very short period of time if your running Paragon's transmissions. Don't run with only one engine without idling the other engine for transmission lubing.
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Old 14-07-2013, 23:21   #15
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Re: Capt. Allan

DD engines are not made to idle for long periods of time... it is better to run them above an idle for couple of hours and then run them at cruising speed for 20-30 minutes to burn them off and than return to idling them for couple hours, etc.
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