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Author Topic:   Fuel Lines For Main and Auxiliary Engine
floater88 posted 03-14-2012 08:41 AM ET (US)   Profile for floater88   Send Email to floater88  
I'm upgrading the fuel lines on my Revenge 20 WT and I noticed that there are two brass connectors coming from the two tanks hoses and only one is going to my fuel filter as you can see in the linked image (below)

I just picked up a four stroke kicker that I'm going to plumb into that filter. Do I need to add that second inlet to the filter? Is there any benefit to having twice the fuel flowing to the filter? Thanks

newt posted 03-14-2012 10:15 AM ET (US)     Profile for newt  Send Email to newt     
Doubling the fuel capacity TO the filter cannot hurt, but in reality, your fuel flow would still be limited by the plumbing FROM the filter, which you would need to split in order to plumb the second motor.

Since you have a second pickup in the tank, why not add a second fuel filter for the kicker and provide yourself some redundancy? This way, if the filter for the main engine clogs up, you have the kicker with its own filter to bring the boat home.

floater88 posted 03-14-2012 01:19 PM ET (US)     Profile for floater88  Send Email to floater88     
Thanks newt. I was thinking the same thing. Since i'm replacing all the hoses anyways another filter wouldn't hurt. That second fitting coming out of that wood part looks like it will make it simple to do anyways. Thanks again
jimh posted 03-14-2012 08:56 PM ET (US)     Profile for jimh  Send Email to jimh     
Your URL points to a small image that shows an installation of the fuel system that was common on Boston Whaler boats c.1987. I had a very similar set-up on the fuel system of my 1987 Boston Whaler boat. Let me describe it:

From the factory, the fuel system was apparently rigged up to the point where the dual fuel lines were run from the fuel tank to the feed-through fittings on the wooden sump cover. The dealer or owner who would have installed the outboard engine probably rigged the rest of the fuel system from that point onward to the engine.

When I refurbished the fuel system on my c.1987 boat, I ran new fuel lines from the fuel tank pick up directly to the fuel-water separating filter, eliminating all of the brass feed-through fittings and the hose clamps connecting the fuel line to them. In this way, the fuel hose was a single run from the tank to the filter. This single line replaced two lines and the brass feed-through fittings. You might consider this method. It reduces the number of joints and connections in the fuel system.

jimh posted 03-14-2012 08:59 PM ET (US)     Profile for jimh  Send Email to jimh     
For rigging a fuel line to your auxiliary engine, you might consider running a new fuel line from the second tank pick-up, to a second filter, then on to a second primer bulb and thence to the auxiliary engine. You can rig to the brass fitting, or, as I suggested, perhaps you can rig directly to the fuel tank pick-up.

You do not want to run two engines off of a single fuel hose if you will be running one engine while the other is shut off. The running engine can suck fuel out of the non-running engine. Some installers use a shut-off valve in the feed to the auxiliary so the main engine cannot suck fuel from it.

L H G posted 03-14-2012 11:57 PM ET (US)     Profile for L H G    
On your installation, you only need one water separating filter, since these filters (at least the Mercury branded ones I am familiar with) will handle a fuel flow rate of 60 GPH. Of course you can use two filters, but for a main and kicker installation, it's a waste of time, space, clutter and money. For your kicker, all you need to do is activate the second withdrawl fitting from the filter. Because of the filter, neither engine will draw down the other's fuel line. All you need to do is carry a spare filter on board.

My twin engine 18 Outrage has been rigged this way since I bought it new in 1986, and never a fuel flow problem, even with twin Mercury 115 towers running wide open, both engines drawing off one filter. Nor do you need to rig two lines INTO the filter. That detail was furnished for twin installations where the engine manufacturer (usually OMC) specified a filter for each engine, as I don't think their filters could accomodate two input and two withdrawls. The Mercury filters have always had two in and two out.

jimh posted 03-15-2012 08:27 AM ET (US)     Profile for jimh  Send Email to jimh     
The fuel distribution manifold unto which a fuel filter element is installed does not provide any special means to prevent flow of fuel between its outlet ports. The two outlet ports of the fuel filter manifold are simply connected to each other and the output side of the filter.

If there is a fuel primer bulb connected on each outlet port, the one-way check valves in the fuel primer bulb act to prevent fuel flow toward the filter. In this way those check valves would tend to prevent an operating engine from pulling fuel from a non-operating engine. In some fuel installations the primer bulb is installed upstream of the fuel filter. When the primer bulb is upstream of the fuel filter it does not prevent backflow from one engine to another.

floater88 posted 03-15-2012 08:35 AM ET (US)     Profile for floater88  Send Email to floater88     
Thanks for the tips. Jimh you say when you redid yours you ran new feul lines from the tank pick up to the filter. Then you said you only had one line from the tank pick ups. I'm confused. Should I just plug one tank pick up and have only one line running right to the filter? Any idea what size those lines are that run from the tank to the fittings? Or can i plumb both lines right to the filter and then have two line running from the filter to both motors as LHG suggested? I'm also installing the Lowrance Fuel Flow meter and it calls for 3/8ths line. On my set up now the line looks like 1/4 so from the filter to the main motor I can make it a 3/8s with no issues? Thanks guys
floater88 posted 03-15-2012 08:55 AM ET (US)     Profile for floater88  Send Email to floater88     
Here is a pick of the two lines coming off of the tank

So I got two lines running from here to the two through wood fittings here

Looks like one brass fitting is plugged and one goes to the filter.

So what I want to know is when I replace the two thick red hoses that run from the tank what size they are or what size I can use to go directly to the filter? Can I run both hoses to the filter or will one do?

From the outlet side of the filter I will run two Merc 3/8 hoses and primer bulbs to both motors. Sorry for any confusion. THanks

andygere posted 03-15-2012 01:49 PM ET (US)     Profile for andygere  Send Email to andygere     
floater88, follow LHG's advice, it's spot on. I rigged the kicker and main outboard on my Outrage 22 the same way. If you are concerned about backflow of fuel or air from one motor to the other, you can easily install a small shutoff valve on the outlet of the filter housing for each motor's fuel line.

When I replaced the tank outlet hoses on my Outrage, I considered rigging it as Jimh suggests. In the end, I ran 2 new hoses from the tank to each of the brass fittings in the stern sump cover. One is plumbed with a fuel hose to my fuel filter, and the other is plugged. There are 2 reasons I rigged it this way. The first is that the above deck hoses are subject to UV degradation, and I expect they will need to be replaced more frequently than those below the deck. It was a lot of work pulling new hose under the deck and connecting it to the barb fittings on the tank. I want to delay doing that job again as long as possible. The second reason is that I like the redundancy that the second outlet provides. I can quickly rig a fuel line to the second tank outlet should I have any problems with the hoses or fuel filter, using nothing more than a barb fitting, and box end wrench and some thread sealant. I keep these items on the boat. If need be, the main or kicker outboards could be fed directly from the fuel tank, bypassing the filter and associated hoses and fittings. Both motors have an under cowl filter that would serve in an emergency. It's a little bit more work to rig it this way, but I had all the parts, and it provides one more way to bypass trouble should it arise.

L H G posted 03-15-2012 05:20 PM ET (US)     Profile for L H G    
Clarifying, you need only one 3/8" supply hose into the filter, and two engine lines, each with primer bulb, out of the filter. The fuel flow sensor should be in the 3/8" line before the filter. Since you are using a fuel flow meter, you only want one supply line into the filter.
jimh posted 03-15-2012 07:22 PM ET (US)     Profile for jimh  Send Email to jimh     
A narrative is a hard way to describe things like a fuel system, so perhaps my narrative was not clear. There were dual fuel feeds from the fuel tank to the fuel filter, as best as I recall, and duel fuel feeds from the fuel filter to the dual primer bulbs, then duel feeds to the engines, that is one line to each engine. The only element in the fuel system which was in common was the fuel filter itself, as I recall. I looked through my collection of photographs and did not find any that showed details of the fuel system.

The point I was making in regard to removal of those complicated brass feed through fittings with dual right-angle attachments was the complete elimination of all that brass--about four pieces in each fuel line--and all the hose clamps associated with the two hoses connected to each one. I don't see much value in that brass fitting and the right angle fittings. They just add complexity to the fuel system which can be replaced by just a few feet of fuel hose. I think the only reason Boston Whaler did that was to provide the dealer with a pre-rigged point to connect the outboard engine fuel primer bulbs and hoses.

floater88 posted 03-16-2012 03:17 PM ET (US)     Profile for floater88  Send Email to floater88     
Thanks for all the tips and info guys. I finished the job today and both motors fired right up. I Replaced both under floor lines with that USCG A1 fuel line and ran both to the filter eliminating the brass fittings. From the filter one line goes to the kicker with primer bulb. The other line I put the Fuel Flow Meter into pointing straing up and that one goes to the 200 Merc. It looks neater then it was and i've got piece of mind now as those hoses under the deck were in rough shape. Next project is to replace the fill and vent hoses as they look like they are 23 years old as well. Thanks guys.
floater88 posted 03-19-2012 08:41 AM ET (US)     Profile for floater88  Send Email to floater88     
I got out the REVENGE 20 W-T yesterday for a test run and the main Mercury 200-HP ran great. The fuel flow meter seemed to be doing its job. At 3,200-RPM at 23-MPH I was getting 16-litres/hours, and flat-out at 6,000-RPM I was getting 27-litres/hour--I guess I'll be doing a lot of cruising at lower speeds! I found out with this meter that I've been keeping the trim too low for optimum fuel mileage. Nice to see the $200 is gonna save me some gas. Thanks to all for tips and info.
jimh posted 03-19-2012 08:08 PM ET (US)     Profile for jimh  Send Email to jimh     
Something is way off with your data.

One gallon is 3.785 liters. A flow rate of 27-liters-per-hour is equivalent to only 7.1-gallons per hour. There is no possible way that a 200-HP outboard engine can only consume 7.1-gallons per hour. That would be a brake specific fuel consumption of about

7.1-gallons/1-hour x 6.25-lbs/gallon x 1-hour/200-HP = 0.22-lbs/HP-hour

There is no outboard on earth that is that fuel efficient. Your engine's BSFC is more like 0.55-lbs/HP-hour, and if it is making 200-HP, it should be consuming about

0.55-lbs/HP-hour x 200-HP x 1-gallon/6.25-lbs = 17.6-gallons/hour = 66.6-liters/hour

floater88 posted 03-20-2012 07:21 AM ET (US)     Profile for floater88  Send Email to floater88     
Ouch! This was the first run so I guess i'm still Calibrating the whole thing. After a few fill ups i'm hoping to get some better numbers. Thanks

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