Fuel System Design

[pmagowan]

The other thread on inspection/cleaning hatches got me thinking. For a 40 odd foot sailing boat what things would you think go to make the best fuel system?

Some thoughts;
1) Placement- should the tank/s be low and central for stability or should they be at the 'chine' on either side to reduce roll? Is it better that they gravity feed or is a lift pump there for lifting?

2) Number: how many tanks and how to connect them. Completely seperate or connected so that they are used equally or a combination like 2 connected and one reserve?

3)Integral or removable- glass fibre tanks can make good use of available space and turn the hull into a double skin to improve strength and prevent risk of sinking from being holed.

4) Monitoring- what is the best way to do this?

5)Construction- baffles, sumps, drains, inspection hatches, what would you want?

6)Everything else I haven't thought about.

 

[sarabande]

built in fuel polishing and really good filtration, with easily operated changeover valves.

Also, vent p ipe(s) led to somewhere safe (and accessible, to remove spiders every three years)


I think that jfm designed his so that he could transfer fuel from one side of the boat to the other to enable compensatory ballasting.


Filler points either under cover, or raised above the deck, so that rain and dust cannot get into the tanks if the cap O ring ever deteriorates.

I'd make the tanks removable so that they can be taken out and properly cleaned if necessary, say after heavy contamination.


Inspection hatches at least 20cm dia to allow arm access to elbow.


Sequential filtration; coarse sedimentary/water filter -> 30 micron - 10 micron -> pre- pump filter.

 

[Tranona]

Have a look on the Tek Tanks website for their guidance on tank design. Will answer most of you questions about design of the tank itself. As to placement, number of tanks and interlinking etc that depends on how you are going to use the boat and of course the space you have available. No hard and fast rule and you need to work through what is sensible for you.

 

[lw395]

A lot depends on the boat and how you are going to use it.
If you are going to motor a ketch upwind a lot, you might want a different system to someone who just wants back-up and a manoeuvring aid on a boat that is sailed everywhere.
Self defeating to have twin 200 litre tanks if you're only using 50 litres a season.
But if you want long range and high reliability, perhaps twin tanks, a small 'day' tank and a reserve can of clean stuff?

 

[William_H]

An ideal tank (and I think one is enough) is tall with a vee or cone shaped bottom. In the bottom should be a valve to permit draining of water and sediment on a regular basis.
Fuel pick up for the engine should go from a point slightly higher. ie a capacity of .5% which is water trap and not accessible to the engine. It should also have an inspection port.
A sight guage or dip stick should be adequate and accurate.
I don't know if mounted low for stability matters much in a heavy boat. For a high capaity tank it would matter but in many ways the smaller the tank the better in terms of fuel turn over (new added) but of course you don't want to run out or have to carry extra fuel. Again much dpends on fuel capcity you want but there is much to be said for removable tanks even like an outboard fuel tank but if you do that you would need to remove and clean it out often. good luck olewill

 

[fisherman]

Ideal for me if starting from scratch would be large tank(s) low down with a day tank above the engine. The fuel can be filtered as it is delivered up to the day tank for constant polishing. Either have a pump system constantly topping up the day tank, which has a bigger overflow back to the main, or have manually or automatically switched and/or hand pumped top up. The day tank should have a filler so it can be topped up from cans and used independently in emergency. The day tank should be tall and thin for good settling of crudinesses, or have a good sump, outlet feed to the engine well above crud drain. Seemples!

In re air vents, ideally these should be from the extreme P&S sides and crossed over before going up above deck, so no chance of fuel exiting when listed or rolling.

 

[Caer Urfa]

The other thread on inspection/cleaning hatches got me thinking. For a 40 odd foot sailing boat what things would you think go to make the best fuel system?

As already said depends how much and where you use the engine,I sail more than motor but I want the engine as reliable as possible and fuel problems is the usual number one so on advice from an engineer with the RNLI I designed my own system as I do not agree one tank is best, any fuel supply problems then you are dead in the water.

I only have a small 27.5 hp engine so I started from scratch and installed twin tanks, EACH one runs separate from the other.

Each tank has it's own shut/off valve, then to primary filter, then to change over valve.

At sea I can run off 'either or both tanks', any problems I can just shut the one tank fuel supply down and run off the other tank.

Also on the 'fuel return' I can again send the return fuel into either tank.

Both plastic tanks are from Tec Tanks with inspection lids and fuel level monitor senders, as said you can get different sizes

Mike

View attachment 43921

 

[Stemar]

My ideal system would have a main tank or tanks, depending on usage and desired range, as low as possible in the boat with an electric pump through filters (a pair in parallel, with taps to switch between them) to a day tank. Fisherman's big overflow back sounds like a good idea. I'd have a gauge - electric or sight tube) for the main tank and a low fuel alarm at a couple of hours' supply in the day tank.

All tanks would have hatches to allow cleaning & William H's shape, valve & pickup position.

 

[Slowtack]

The normal prefilter and final filter arrangement is polishing the fuel continuously.
However here is a purpose builty system: http://www.eddievan.com/isabelle/fuelsystem.htm

 

[prv]

How complex do you want to go? I'd say the minimum is to have the primary filter in a changeover arrangement with a "hot standby", with some kind of pump (squeeze bulb is fine) just after the tank to make bleeding fast and easy. I've installed this on both the boats we've owned. On Ariam I've also added a suction gauge between the lift pump and the primary filter - this shows how hard the lift pump is having to suck to pull fuel through the filter, and thus how blocked it's getting. The gauge is next to the companionway steps, and when we're motoring I glance at it each time I go in or out. I would definitely fit such a gauge on any future boat. I think this system is appropriate for a coastal cruiser.

People building blue-water voyagers tend to get more sophisticated. Here's a typical example: http://www.odysseyyachts.com/Odyssey_Yachts/BUILDING_BLOG/Entries/2013/8/5_Fuel_System.html . I'd say the defining feature of these fuel systems is the ability to shuttle fuel around independently of the engine - especially through a polishing filter, often very large and separate from the route to the engine. I've also seen one where the pump could be connected to a wandering suction/discharge hose, for taking on fuel in places where it comes out in 200-litre drums in small boats - just lower the hose over the side and suck it up. Or pump out fuel from your own bunkers to give or sell to someone in need. Really, you could go on adding complexity forever...

Pete

 

[fisherman]

I have done about 24000 hours with this boat. My tank is 1000 litres, it looks like a skip, transverse, three baffles, two hatches, has a sump under the central baffle, but never get any muck from it, the muck I have is always in suspension. The fuel is drawn from 50mm off the bottom of the tank. The original rig was a syphon, but someone altered it, as I did with my previous boat. It goes to the primary sedimenter, a simple transparent cone with a drain off, drain every 40-ish hours. Change the engine filters every 400-ish hours. The only problems I've had were a delivery of part water from the Falmouth barge, and a scar on the seat under the final filter bleed screw which took years to find, when the filter was part blocked the revs would drop, had to throttle back to match the available supply. This is a simple system that has worked well, but I would still like what I propose above.