Ford Lehman 80hp fuel consumption at 1000rpm

Hello. My friend has a 45 foot ketch with a Ford Lehman 80hp. He replaced it with a stationary engine version as it was blown. The injection pump has weights to suit the stationary engine use and it will only rev to approx 1000rpm when used as propulsion in his yacht. We can almost get 5K out of it which is good enough for now.

We plan to move the boat, but we need to know approximate fuel consumption. How much fuel would you expect the Lehman 80 to use at 1000rpm, obviously the prop will not be absorbing much power at this RPM either.

I was guessing about 3L/h?

Anyone got any ideas?

 

The rule of thumb is one gallon per 20 hp

So an engine producing 80 hp is 4 x 1 gallon

You will need to guess how many hp at your choosen cruise speed

If you google you may find a rpm, power output , fuel burn graph for your engine.

 

The rule of thumb is one gallon per 20 hp

This is for a fairly modern engine that is well loaded (so efficient) .

Easier to plan on 15 hp per gallon and be pleasantly surprised

 

Dennis
With a diesel you set the RPM with the 'throttle' and the fuel pump delivers the amount of fuel required to maintain that RPM up to the max power available.

Looking up the data on the 2712E Lehman 80HP engine it's max power available is around 30 HP at 1000 rpm and depending on the prop diameter and pitch it will use up to 0.35 lb/HP/hr ( pounds weight of fuel per HP per hour)

30X.35= 10.5lb/hr and at approx 1.9 lb/L makes 5 1/2 Liters/hr max to produce 30 HP.

You'll probably only use that into a head sea and wind.

[edit added] And both MichaelP and FFred have it about right too from their rules of thumb.

 

Thanks guys.

So 5.5L/h when producing the max power possible of 30hp.

Now in reality, the old engine uses to rev far higher than 1000rpm so obviously the prop would be sized to suit. IE at 1000rpm the prop would be unable to absorb anywhere near 30hp, so in reality fuel consumption will be a fair bit under 5.5l/h right?

We will work off 5.5l/h for safely margin.

Also we have the old corroded injection pump. How would be go about changing the "weights" from the old pump to the new stationary engine pump so we can get our RPM back?

 

In Smooth water, that is correct. In a head sea you will load the prop enough to absorb the full power.

And no unfortunately you can't just change the Gov weights, the shot volume/ramp height also differs. Prob best to get an exchange injector pump or one off a takeout engine heading for recycling. They are a common engine presuming it's the 2712E.

 

Thanks Mike.

We plan to sail from Yamba to Scarborough this Friday. There is a southerly buster coming, so we hope to not use the engine. But we still need some fuel just in case. This will be the first time we sail the boat after a long period of refitting. The major thing being replacing the original Lehman with a Lehman sourced from a trawler which was powering the generator.

I am not sure on the model number, but I think thats right. I will keep a lookout for a new injection pump. If anyone knows of one for cheap please let me know.

Cheers.

 

Also Mike, you said you looked up the data. Can you please provide a link to this data if possible? I could not find much info on the net.

 

From that old fashioned ink on paper sitting on a shelf in my office !

What are you after specifically ?

 

hehe. What is the max RPM and at what RPM does it produce max power and torque?

 

Here's a scan of the pertinent page.

 

Very good! Thanks Mike

 

You are very welcome, good luck with the trip.

I have various manuals, and I emailed a contact who has a full service-rebuild manual on PDF that I could get him to send if you need it just PM me or email.

 

Great. PM sent