Enough fuel?

Joined
Jan 19, 2015
Messages
67
Hello to all

My question is regarding fuel consumption for my 18' manta ray with a 99 mercruiser 3.0. I would like to take a little day cruise down the river and head back, the boat has a 30 gallon tank I my one way trip will run me about 40 miles down river. My question is do you think I would have enough fuel for a round trip with myself the wife and a cooler for drinks?

Thanks again
Chris
 

alldodge

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Staff member
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Mar 8, 2009
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40,581
My initial assumptions would be yes, using 4 to 5 GPH at about 25MPH. The 3.0 would burn around 10GPH at WOT. So 25MPH you would burn about 8 to 10 gallons. The down river part will be reduced by the current in the river (25MPH cruise, 3MPH current = 28MPH), and will also be increased by the up river trip. Maybe 15 gallons back up, so estimate 25 gallons on the high side.

Now you should know how much fuel you use every time the boat is out for the day. How much run time is there and how much fuel is used?
 

thumpar

Admiral
Joined
Jun 21, 2007
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6,138
I only had a 18 gallon tank on my old boat and would run 25 miles one way ,50 total, with no problems. There was even a little tubing/playing on the way. As long as you are cruising you won't eat up too much fuel.
 

Bt Doctur

Supreme Mariner
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Aug 29, 2004
Messages
19,092
you could get 2 outboard tanks and run 1 tank at a cruise setting and one at a slow cruise setting and see how far you go on each one.
then use that info for the built in tank
 

Silvertip

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Sep 22, 2003
Messages
28,758
Or install a fuel flow monitor and know at any point in time what fuel consumption is.
 

HT32BSX115

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Dec 8, 2005
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10,083
Or install a fuel flow monitor and know at any point in time what fuel consumption is.

I would agree. I installed a LOWRANCE LMF-200
http://www.lowrance.com/en-US/Products/Gauges/LMF200-en-us.aspx
LMF-200-main_lg.jpg


There's no better way to know FOR SURE if you have enough fuel at any time.
Otherwise, you need to have a spare tank you can switch to if you run out.
 

Silvertip

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Sep 22, 2003
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Even more important than MPG is GPH (gallons/hr). Why? If you pull away from the dock, get on plane, throttle back to cruise RPM and the GPH display shows something way different than normal you turn around and head back. This is an instantaneous reading. MPG is an "average" of fuel used distance/time. So you could be well into a trip before excess fuel consumption is noticed. MPG is also highly variable based on load, water conditions, wind, etc. Yes - GPH is affected as well but again, the reading is instantaneous so you can make minute by minute plans as to whether you need an alternate route/plan.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Even more important than MPG is GPH (gallons/hr). Why? If you pull away from the dock, get on plane, throttle back to cruise RPM and the GPH display shows something way different than normal you turn around and head back. This is an instantaneous reading. MPG is an "average" of fuel used distance/time. So you could be well into a trip before excess fuel consumption is noticed. MPG is also highly variable based on load, water conditions, wind, etc. Yes - GPH is affected as well but again, the reading is instantaneous so you can make minute by minute plans as to whether you need an alternate route/plan.

Absolutely. The above gage not only measures/displays GPH, but will also tell you how much fuel you have left by calculating total fuel used (or fuel remaining) regardless of how you operate the engine. If there's a GPS on the network as well, it also will give you MPG, and miles remaining etc.
 
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