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Sailing August · 07-02-2023, 07:59

I just sold my old Morgan Out Island 41.6 and purchased an Irwin 46 floating hotel. The reduced rig (48' ICW friendly) and shoal draft (4'8") is perfect for the East Coast of the USA and the Caribbean.
The Irwin will not be crossing any oceans bur it is perfect for our intentions.

She came with a Perkins 4-154 with about 2000 hrs.
- Good Compression
- New Starter
- New heat Exchanger
- New Water Pump
- New Alternator

Does anyone know what the expected hourly fuel consumption is on this engine?

SailingHarmonie · 07-02-2023, 08:26

Of course it depends a LOT on how hard you push the throttle, but a reasonable expectation at a modest cruising speed would about 0.8 to 1.0 gallons/hr.

Running flat out, full throttle, 3000 rpm assuming a properly pitched prop, will suck down almost 2.5 gal/hour

Fuel burn is going to be important to know on that boat

You can usually come pretty close on fuel burn rates by assuming 0.35 lb of diesel/HP/hr, and diesel weighs about 8 lb/gallon. A 4-154 is rated at 62HP at full rpm, and then power needed falls off with the CUBE of the boat speed below that (pretty close…).

So if full throttle 62HP plushies you at 7.5 knots, to go 5.5 knots only takes 24 HP, hence a huge drop in fuel needed.

Idaho · 07-02-2023, 08:50

Mine uses 0.667 g/h @ ~1800 rpm.

Morgan 41 Out Island.

Sailing August · 15-02-2023, 12:17

Thanks! Much appreciated

NSboatman · 15-02-2023, 18:26

I’m bang on 1 gal/hr @ 2200 rpm (6.75kt in typical conditions). 42000lb steel roberts cutter.

She’s a good engine. Oldie and oddball- parts can be a bugger to find - but it’s a very solid mill- like most old Perkins.

Watch for oil sludging. I had an issue; turns out the marks on the dipstick were wrong.

Lots of these were built for Mazda trucks and jcb skid steers- and they use a Japanese fuel pump (diesel Kiki) vs the more typical Lucas CAV. Some were used in container reefer units as well; and I’ve discovered recently that a good number of larger welders were fitted with them too. Obviously none of those had the marinizing.

My beef with the engine right now is a slightly unpredictable idle- I set it warm and then after a long hard run it goes down 350 rpm and nearly stalls. Probably wear related on the injector pump… we’ll see.

michaeld · 15-02-2023, 20:26

We have a Westerbeke 71C. As best as I can tell, it's a Mazda built 4.154. We burn about 1.5 gallons per hour at 6 kts. Maybe a bit more.

**Adelie** · 15-02-2023, 23:27

Quote:

Originally Posted by SailingHarmonie

...
You can usually come pretty close on fuel burn rates by assuming 0.35 lb of diesel/HP/hr, and diesel weighs about 8 lb/gallon. A 4-154 is rated at 62HP at full rpm, and then power needed falls off with the CUBE of the boat speed below that (pretty close…).

So if full throttle 62HP plushies you at 7.5 knots, to go 5.5 knots only takes 24 HP, hence a huge drop in fuel needed.

A. Diesel weighs 7lb/gal or perhaps slightly less depending on temp.
B. For engines following a propellor curve, fuel efficiency drops as RPM goes down. It doesn't go down as fast as the demand drops, so fuel economy will improve as you slow, but gal/hr will not follow the cube rule that power demand follows.
C. Currently the very best tractor motors get somewhere near 18hp-hr/gal or so, only one on the market has exceeded 20. These are diesel motors near 500hp. I cite tractor motors because there is very good data for these motors and it is available.
https://tractortestlab.unl.edu/test-page-nttl

At a max power of 62hp the engine should be using 3.4-3.7gal/hr (17-18hp-hr/gal)

At a power demand of 20hp, the motor should be producing about 12hp-hr/gal. so near 1.7gal/hr fuel usage.
At 10hp it'll be 9-10hp-hr/gal.
At 5-6hp efficiency will be near 7hp-hr/gal. For an Irwin 46 I would expect you to be using about 0.7-0.8gal/hr. That will be at a speed of about 5.5kt or so.