Notices
The Boating Forum

Fuel tank, usable volume?

Old 08-02-2020, 11:44 AM
  #1  
Member
Thread Starter
 
Join Date: Oct 2015
Location: far north
Posts: 80
Likes: 0
Received 0 Likes on 0 Posts
Default Fuel tank, usable volume?

I have 23ft boat with a 150hp outboard motor and a built in 200 liter / 53 US gallon plastic tank.
What is the usable volume of this tank before the motor will start sucking air?
Is there usually a trough in the bottom of the tank where the pick up tube is to corrall the final drops of liquid like many of the hand carried 4 gallon or so fuel containers?
The tank is about 1.2m or 4 ft wide. The pickup tube appears to be on one side of the tank, not in the middle.
If it does have just a flat bottom then I would guess the last 5 gallons or so could be unreliable unless the sea state is near flat.

What have other boaters experienced with similar tanks?
Old 08-02-2020, 12:18 PM
  #2  
Senior Member
 
Join Date: Dec 2014
Location: Land down under
Posts: 13,490
Received 2,784 Likes on 1,675 Posts
Default

Too many tank configurations to hazard a guess. Pick up tube lengths and locations.

With your boat low on gasoline, on the trailer, try and approximate the pitch angle of the boat in the water. Pump all of the gasoline from the tank. Top off the tank. The amount used to fill the tank will be about your useable quantity.
Likes:
Old 08-02-2020, 01:08 PM
  #3  
Senior Member
 
Join Date: May 2009
Location: St Petersburg, FL
Posts: 4,979
Likes: 0
Received 354 Likes on 199 Posts
Default

Really depends on how close to the bottom the fuel pick up goes.
Likes:
Old 08-02-2020, 02:01 PM
  #4  
Admirals Club Admiral's Club Member
 
Join Date: Apr 2005
Location: AL
Posts: 4,536
Received 770 Likes on 415 Posts
Default

The rule of thumb is 90% of the tank capacity is usable. That is a "safe" amount of fuel to use as your "empty" level. So in your case 47 gallons.

However, you never really know until you try it out. Put a 5 gallon tank in the motor well, run it until it quits then switch over and run it off the auxiliary tank, head back to the marina and fill it up. Ive got a 80 gallon tank in mine and it can use all 80 gallons + some it got from somewhere else. I ran mine down in the keys until it was flat empty and even after the gauge said I had used 80 (and I put 80 back in), it was still running.
Likes:
Old 08-02-2020, 02:11 PM
  #5  
Senior Member
 
Join Date: Aug 2006
Location: San Diego
Posts: 3,635
Received 452 Likes on 305 Posts
Default

An estimate is worthless. Either perform a real world test in the water (with a spare tank to switch to) or perform an Alloyboy approximation. I was comfortable with an answer after repeating the process numerous times on the water.

How you should go about it depends upon how critical the information will be for the manner in which push your fuel limit, and whether you carry an auxiliary fuel source.
Old 08-05-2020, 10:47 AM
  #6  
Member
Thread Starter
 
Join Date: Oct 2015
Location: far north
Posts: 80
Likes: 0
Received 0 Likes on 0 Posts
Default

thanks for the info. I have always kept they tank full, 200 liter, to avoid condensation, however the boat uses less fuel than i expected so I have never used more than 60 or so liters on a day trip. I have been transporting 200 lbs of excess fuel weight for nothing really. From now on I plan to keep the tank closer to half full during summers as the extra weight makes a difference getting on plane with passengers on board. Once I get down to a low fuel level I may take a couple of jerry cans with me as back up and do a real world test on the water.
Can there be problems restarting if I run it 'til it stops? what about debris in the fuel tank? I ran my car very low a while back and that didn't go well, it ran like the fuel injectiors were intermtantly blocked for 300 miles or so afterwards before it came right by itself. The boat however has a Suzuki combined water separator/ filter unit just downstream of the tank.
Old 08-05-2020, 11:16 AM
  #7  
Senior Member
 
Join Date: Oct 2005
Location: FL., GA, CO, Utah, WA, depends. In CA now.
Posts: 9,582
Received 324 Likes on 223 Posts
Default

Originally Posted by Jack Daniels View Post
I have 23ft boat with a 150hp outboard motor and a built in 200 liter / 53 US gallon plastic tank.
What is the usable volume of this tank before the motor will start sucking air?
Is there usually a trough in the bottom of the tank where the pick up tube is to corrall the final drops of liquid like many of the hand carried 4 gallon or so fuel containers?
The tank is about 1.2m or 4 ft wide. The pickup tube appears to be on one side of the tank, not in the middle.
If it does have just a flat bottom then I would guess the last 5 gallons or so could be unreliable unless the sea state is near flat.

What have other boaters experienced with similar tanks?
I've found that 10 to 15% of tank capacity is not accessible. That makes only 90 gallons or so your usable fuel.
Old 08-05-2020, 08:50 PM
  #8  
Senior Member
 
Join Date: Oct 2014
Location: N.E. CT
Posts: 3,633
Received 1,431 Likes on 734 Posts
Default

Running a tank down to empty (engine dies) may make it a bit tedious to get it going again. All the lines will be full of air and the fuel pump will have to pump all that air through the fuel system until it all gets filled with fuel and the engine starts running again.
Running the tank dry should not result in “crap getting sucked in”. The standpipe is always drawing from the bottom.


Oops,... yes you have an outboard (primer bulb), getting it started again should be no problem.
Old 08-06-2020, 02:35 AM
  #9  
Senior Member
 
Join Date: Aug 2012
Posts: 7,950
Received 1,021 Likes on 580 Posts
Default

Originally Posted by Jack Daniels View Post
thanks for the info. I have always kept they tank full, 200 liter, to avoid condensation, however the boat uses less fuel than i expected so I have never used more than 60 or so liters on a day trip. I have been transporting 200 lbs of excess fuel weight for nothing really.
I prefer to have plenty of fuel for peace of mind (as well as 10 gallons in portable tanks as a reserve or solution should something happen such as a pick up pipe drop off or a union break on the main tank) - yes you're carrying a bit of weight, but I've never worried about carrying an extra couple of guests, so I don't worry about carrying the extra fuel.

I've always gone by the manta: the only time you can have too much fuel on a boat is when it's on fire

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.