Fuel supply problem with 473 in big seas.

[Tag team]

We have a problem with engine cut out when the fuel tank is under half full and beam seas are present due to the fuel surge in the tank causing the pick up to gulp air. The engine then begins to slow and enentually stop which is very dangerous when entering harbour in rough conditions.
The solution at the time is to bleed the line at the high pressure pump, not an activity one wants to get involved in during tight situations.
As a result I need to constantly top up the tank which can be inconvenient and time consuming.
Has anyone experienced this problem?
Ian.

 

[centerline]

this can be a problem in "modern" designed fuel systems where there is no return line to tank, but the return line loops back into the system in front of the filters (into the filter base)....and any air in the system is trapped and just builds up in volume until it either gets into the injector pump or until its bled off manually.

a system where the return goes all the way back to the tank, the air will get purged from the system before it gets into the injection pump.

the lift pump can supply a lot of fuel quickly, more than the injection pump needs, so even if it picks up a little air when the tank is shaken violently, as long as the fuel and air keeps looping back to the main tank in the return line, it will be able to keep the air tapped off before it gets to the injector pump....

 

[Tag team]

Thank you for your response. The suggestion you make about the return not diverting to the tank in this instance is not the case. The return feeds directly to the tank so that is not the cause. I think that the slow roll of the yacht causes the intake pipe to be out of the fuel for several seconds at a time which is causing the problem. The tank is quite wide and long and has a capacity of 250 litres so when half full I imagine there can be a significant surge. The pickup pipe sits aprox 10 mm off the bottom of the tank, so when rolling about in a sea with say a 60 degree roll from side to side it could be out of the fuel for some seconds.
I don't believe I will be the only Beneteau owner who has experienced this issue and would like to find an easy fix if possible before thinking about installing a gravity feed header tank or a fuel sump for the pickup.
Beneteau are not much help with this issue and deny there is a problem.
More suggestions please.
Ian.

 

[Ron20324]

Are you sure it is gulping air and not sediment?

 

[centerline]

Thank you for your response. The suggestion you make about the return not diverting to the tank in this instance is not the case. The return feeds directly to the tank so that is not the cause. I think that the slow roll of the yacht causes the intake pipe to be out of the fuel for several seconds at a time which is causing the problem. The tank is quite wide and long and has a capacity of 250 litres so when half full I imagine there can be a significant surge. The pickup pipe sits aprox 10 mm off the bottom of the tank, so when rolling about in a sea with say a 60 degree roll from side to side it could be out of the fuel for some seconds.
I don't believe I will be the only Beneteau owner who has experienced this issue and would like to find an easy fix if possible before thinking about installing a gravity feed header tank or a fuel sump for the pickup.
Beneteau are not much help with this issue and deny there is a problem.
More suggestions please.
Ian.

if the plumbing is correct in the return line, and the lift pump is pumping its full volume, and the filters are clean, there should be no problem with the air being able to tap off and return to tank before entering the injector pump.... it is one of its primary design functions.
if the lift pump is weak, it may not have enough flow/pressure left to push fuel/air back to the tank....
to check it, pull the return from the tank fitting and place it in a container.... if its all working fine, it should have strong flow and good volume like a miniature garden hose... if its kinda weak, something isnt working properly.... a bad lift pump or restricted line or filters.

but you are right, that if its gulping too much air for too long, then its just plain running out of fuel... and a pressure regulated header tank will be needed, short of redesigning the main fuel tank with a sump...

 

[RichH]

The most probable reason is that your tank has insufficient internal baffles. The constant 'through-sloshing' is probably mixing air with the fuel as the boat rolls, yaws and pitches.

A good way to remove/prevent this air is to install an 'air removal knock-out pot' (just an inverted empty filter housing with a clear 'pig tail' with 2 cock valves on each end of the clear (tygon, etc) tube ... located somewhere on the pressure side of the lift/supply pump (on commercial vessels the entire fuel delivery system is pressurized and the knock out pot is usually located right after the pump at the tank.
The entrained air will become intrapped in the 'knock-out pot'; you can see when the oil is displaced by air; and simply vent the pressurized 'pot' occasionally when underway.
On large commercial vessels, the air purging is done automatically via solenoid valves and a photoelectric sensor on the 'clear' tubing. If you invert the air removal knock out pot, it becomes a water removal knock out pot. Most 'commercials' have 2, one for air, one for water.

 

[Tag team]

Are you sure it is gulping air and not sediment?

Yes, the fuel is clean and filters replaced even though they did not need to be. It is definitely air being sucked into the system. In flat seas there is no problem even with the tank almost empty.

 

[Tag team]

if the plumbing is correct in the return line, and the lift pump is pumping its full volume, and the filters are clean, there should be no problem with the air being able to tap off and return to tank before entering the injector pump.... it is one of its primary design functions.
if the lift pump is weak, it may not have enough flow/pressure left to push fuel/air back to the tank....
to check it, pull the return from the tank fitting and place it in a container.... if its all working fine, it should have strong flow and good volume like a miniature garden hose... if its kinda weak, something isnt working properly.... a bad lift pump or restricted line or filters.

but you are right, that if its gulping too much air for too long, then its just plain running out of fuel... and a pressure regulated header tank will be needed, short of redesigning the main fuel tank with a sump...

Thanks for your suggestions. I will check the fuel flow at return and the pump mechanism to ensure the flow rate is as specified for the pump. There must be a solution without having to change the system design or adding additional tanks be they header or sump.

 

[Tag team]

The most probable reason is that your tank has insufficient internal baffles. The constant 'through-sloshing' is probably mixing air with the fuel as the boat rolls, yaws and pitches.

A good way to remove/prevent this air is to install an 'air removal knock-out pot' (just an inverted empty filter housing with a clear 'pig tail' with 2 cock valves on each end of the clear (tygon, etc) tube ... located somewhere on the pressure side of the lift/supply pump (on commercial vessels the entire fuel delivery system is pressurized and the knock out pot is usually located right after the pump at the tank.
The entrained air will become intrapped in the 'knock-out pot'; you can see when the oil is displaced by air; and simply vent the pressurized 'pot' occasionally when underway.
On large commercial vessels, the air purging is done automatically via solenoid valves and a photoelectric sensor on the 'clear' tubing. If you invert the air removal knock out pot, it becomes a water removal knock out pot. Most 'commercials' have 2, one for air, one for water.

Thanks for the info re knock-out pots. I have never heard of them before and have just engaged Dr. Google in my quest for knowledge and understanding. I will check the flow rate of the pump and if that is up to spec I will look at your suggestion as a solution. It seems a simple change to make.

 

[Tag team]

Are you sure it is gulping air and not sediment?

Ron, it is definitely gulping air and I have since found out this is a common problem not only with sailing yachts but also with motor yachts.
I am investigating air traps for fuel lines as suggested by RichH another contributor to this post.
Ian.

 

[Tag team]

RichH, thanks for the info. I have Googled knock out pots and can't find anything which would suit my needs as far as size goes. Can you explain the clear hose with two cock valves set up ?
I understand the principle of inverting a fuel filter and I am thinking that a line from the filter base (now at the top) could be a return line to the tank with a very fine restriction so as not to interfere with fuel pressure to the injectors but let the air out of the trap.
I would love to hear your comments.

 

[down_shift]

Beneteau are not much help with this issue and deny there is a problem. More suggestions please. Ian.

Not being able to rely on the diesel during challenging conditions is unfortunate. If given the opportunity to reproduce a safe area, document the scenario with video. Thinking Beneteau would step up and take ownership with video proof. If pictures are worth a 1000 words, video is worth 1000^^n. Easy to post the video to youtube (private or public) and email them a link for review and consideration.
Good luck.

 

[Tag team]

Not being able to rely on the diesel during challenging conditions is unfortunate. If given the opportunity to reproduce a safe area, document the scenario with video. Thinking Beneteau would step up and take ownership with video proof. If pictures are worth a 1000 words, video is worth 1000^^n. Easy to post the video to youtube (private or public) and email them a link for review and consideration.
Good luck.

Thanks for the thought although nothing to video.
Could only show tacho at zero and me bleeding the injector pump.

 

[down_shift]

A GoPro on a short handheld grip (with lanyard of course). Film a short documentary while narrating the events to the camera. Film the rolling seas and stable diesel at a fixed RPM and throttle setting, the turn the helm so the waves introduce that 30 degree side-to-side roll of the hull. Then check back to the dropping RPMs and constant throttle setting a few times and continue narrating what is occurring. Then make another recording of the same sequence with someone down below filming the diesel and controls/linkages that verify the throttle settings remain constant while it starts stifling out. Film the bleeding process if you happen to take it that far, etc. Not sure how to confirm the fuel level of the tank other than filming the gauge and pump after filling her back up. Just a thought. I'll even loan you my gear and do the video editing for you. PM me off line if interested.

 

[RichH]

RichH, thanks for the info. I have Googled knock out pots and can't find anything which would suit my needs as far as size goes. Can you explain the clear hose with two cock valves set up ?
I understand the principle of inverting a fuel filter and I am thinking that a line from the filter base (now at the top) could be a return line to the tank with a very fine restriction so as not to interfere with fuel pressure to the injectors but let the air out of the trap.
I would love to hear your comments.

Here's the process.

Basic Physics Concept - If the oil is slowed sufficiently in velocity, any entrained air will have dwell time to separate and rise to the top of the mixture. The knock out pot provided the time for the phase separation of oil versus air:
A bowl side up / head side down carbon steel filter housing and NO filter is installed in a pressurized section of the fuel line.
With both inlet and outlet on the bottom, any air entrained oil slows down due to the expanded volume of the filter housing and allows the air to rise to the top of the assembly (the bowl portion).
To the normal drain port of the bowl a cock valve (A) is applied and further connected to a translucent tube (Tygon etc.) connected to a second (and higher in altitude) cock valve (B).
In air knock-out operation, valve A is left open, valve B is closed.
When air accumulates in the (inverted) bowl it will displace the oil in the tube and you will see the color change difference between oil and air.
When color change occurs denoting air is present, open valve B, let the pressurized oil rise to displace the air in the bowl ... until oil almost completely fills the tube, then close valve B.
Valve A is a safety valve and is normally closed during 'normal' conditions.

Disadvantage in a typical vacuum motive boat fuel system .... the knock out pot is downstream of the lift pump. The lift pump will occasionally be pumping air, air/oil mixture, and oil ... the action of the internal action of the lift pump diaphragm will tend to 'chop up' large slugs of air and create small slugs/bubbles of 'foamed oil' ... the smaller the air bubbles, the longer it takes to 'rise' in a knockout pot.

For Water removal, the above knock out pot is inverted: ie. 'bowl down'.



Lastly, If this is a 'serious' boat intended for long distance passage making or long distance coastal cruising, Id recommend that the tank be altered with a better internal baffle arrangement ... OR consider to replace the present tank with one that has sufficient and 'effective' internal baffles ... to mitigate the 'sloshing' and oil impact with the tank walls, etc. that is causing the air/oil mixing/foaming.
From your description given, there is an exponentially high probability that your tank clearly has insufficient or ineffective internal baffles. The knock out pot system fixes the symptoms, not the problem ... which most probably and based on you description/symptoms is poor tank internal design.
If this is a recent 'new' boat, such correction should be covered under warranty by Bene.; if not, Id still contact Beneteau as they may have a 'workaround' ... such as baffle 'inserts', etc. available, etc.