Accurate fuel consumption Perkins 4.236

[mvweebles]

My Willard 36 trawler is powered by a Perkins 4.236 75hp diesel. I have a fairly good idea of consumption but wondering if someone might have a more accurate measurement.

Anyone with an accurate fuel consumption curve for their Perkins 4.236? Ideally at 1600 RPM? Is 1.0 GPH as good an assumption as possible?

We're southbound along the Pacific side of Mexico running 1600 RPMs (between 6 and 6-1/4 kts). Pretty sure I'm burning right at 1.0 gph. Tough to tell with relatively large 450g fuel tanks that are not well calibrated. Fuel is getting a bit more scarce south of Acapulco and some of the places charge markup at the fuel dock so trying to plan.

Thanks in advance.

[rslifkin]

At 6 kts on your boat I certainly wouldn't expect less than 1 gal/hr. Probably not much more either, so your estimate is likely close for fairly calm seas. The only curve I can find for a Perkins 4.236 is for one rated 84 hp at 2800 RPM. Assuming it's propped to reach 2800 at WOT, the included prop load curve estimates an output of about 17 hp at 1600 RPM, so just over 1 gal/hr is likely reasonable.

Based on the planning info you have, what's the longest hop you need or want to make between fuel stops?

I'd probably plan based on 5 nm/gal in fairly calm weather (which would give some margin for error in your estimates, as that would assume 1.2 gal/hr to do 6 kts). Assuming you plan on a 100 gallon reserve (so plan to use 350 gallons) that gives you a usable range of 1750 nautical miles.

[martinwinter]

Originally Posted by mvweebles

My Willard 36 trawler is powered by a Perkins 4.236 75hp diesel. I have a fairly good idea of consumption but wondering if someone might have a more accurate measurement.

Anyone with an accurate fuel consumption curve for their Perkins 4.236? Ideally at 1600 RPM? Is 1.0 GPH as good an assumption as possible?

We're southbound along the Pacific side of Mexico running 1600 RPMs (between 6 and 6-1/4 kts). Pretty sure I'm burning right at 1.0 gph. Tough to tell with relatively large 450g fuel tanks that are not well calibrated. Fuel is getting a bit more scarce south of Acapulco and some of the places charge markup at the fuel dock so trying to plan.

Thanks in advance.

I have a 4.236 with very low hours and would agree at 1800 rpm i burn about one gallon per hour USG Typically only see about ten percent deviation on that number depending on conditions.

[mvweebles]

Thanks. Mostly trying to plan. At fuel docks along this stretch of Mexico (PV south) that charge a markup, effective cost is $6.50/gal. Putting on even 300 gals which will take us from Acapulco to Panama Canal is a couple grand. I know, small potatoes in the big scheme of things, and Weebles is about as efficient as a 36 foot boat can be, but still.....$2000 fuel bill is a bit startling.

In 1987, a sister ship went from Long Beach to Hawaii and burned 335 gals of diesel. From the owners documents, best I can figure is he burned around 0.9 gph and averages right at 9 kts. His boat - a pilothouse version - carried a modest sailplan so it's possible he got some lift from that too.

I was hoping that since the 4.236 Perkins was so common in 42-55 foot sailboats back in the 70s and 80s that someone may have better consumption data than I have.

[rslifkin]

Is there anywhere along the way you might be able to arrange truck delivery to fill the tanks and give yourself a significant distance without needing fuel?

[MicHughV]

A quick rule of thumb is to anticipate 1 gal/hr for every 20 hp....so 17 hp at 1,600 rpm is right in the money..

[donradcliffe]

If it took your sistership 18 days to go from California to Hawaii, that's about 122 miles per day or a bit over 5 knots. I agree that 5 mpg at 6k would be a good planning number, but you should include some for the genset. At 5 mpg, you should burn 280 gallons from Acapulco to the Canal, where fuel should be about $4/gallon.

For a more accurate number, the burn rate is dependent on rpm and transmission ratio. What is the fully loaded weight of the boat?

[Kettlewell]

Our Finnsailer 38 has a Perkins 4.236 and I always assume 1 gal. per hour at 6 knots, but can throttle back to 1500 and burn less than 1 gal per hour making over 5 knots. I'm surprised diesel is that expensive over there!

[HankOnthewater]

Fuel consumption depends on the boat you have as well, but more about the throttle position (RPM) and sea state.
I have that engine. I had the boat for 8 years, and consumption is at best 4.35 liters per hour, at 1500 RPM, when seas are calm. Hehehe, if there was wind, I would be sailing. I motor at these revs 5.5 to 6 knots. For planning purposes I 'use' 5.5 litres per hour at 5.5 knots (I litre per NM). The actual figure is nearly always less.
My boat's displacement is approx. 22 tons, loaded up.

[mvweebles]

Originally Posted by donradcliffe

If it took your sistership 18 days to go from California to Hawaii, that's about 122 miles per day or a bit over 5 knots. I agree that 5 mpg at 6k would be a good planning number, but you should include some for the genset. At 5 mpg, you should burn 280 gallons from Acapulco to the Canal, where fuel should be about $4/gallon.

For a more accurate number, the burn rate is dependent on rpm and transmission ratio. What is the fully loaded weight of the boat?

Boat sits at 33,000 lbs id reckon. 33 LWL so running 1.1 SL. I forget the reduction on the Borg Warner - 2.61:1 but I could be wrong. 22x20 4-blade prop.

I would think the speed would vary by sea state, but gal/he would not.

Diesel on the street is running 25-pesos per liter. Exchange rate is around 17MXN to 1USD so pretty close to $5.50/gal. Many fuel docks are associated with a resort and tack on 15% - 20%. Oddly, the bigger your boat the higher the percentage which seems counterintuitive. Their house. Their rules.

This guy passed me an hour ago on approach to Acapulco. I'd guess he's doing 22-24 kts and burning 60 gph. 20x worse fuel economy than I'm doing to do 4x the speed.

[rslifkin]

Originally Posted by mvweebles

Boat sits at 33,000 lbs id reckon. 33 LWL so running 1.1 SL. I forget the reduction on the Borg Warner - 2.61:1 but I could be wrong. 22x20 4-blade prop.

I would think the speed would vary by sea state, but gal/he would not.

Diesel on the street is running 25-pesos per liter. Exchange rate is around 17MXN to 1USD so pretty close to $5.50/gal. Many fuel docks are associated with a resort and tack on 15% - 20%. Oddly, the bigger your boat the higher the percentage which seems counterintuitive. Their house. Their rules.

This guy passed me an hour ago on approach to Acapulco. I'd guess he's doing 22-24 kts and burning 60 gph. 20x worse fuel economy than I'm doing to do 4x the speed.

If the trans is a Velvet Drive 71C or 72C, reduction is probably 2.57:1. The reduction options were 1.52:1, 1.88:1, 1.91:1, 2.1:1, 2.57:1, and 2.91:1.

Sea state will definitely affect speed. It can also increase GPH a little at a given RPM. Diesels are governed, so if you're running at 1600 RPM and partial load, an increase in load from a wave slowing the boat will cause the engine to throttle up the injection pump a little to maintain 1600 RPM (instead of allowing RPM to drop).

[MicHughV]

have that engine. I had the boat for 8 years, and consumption is at best 4.35 liters per hour, at 1500 RPM, when seas are calm.

4.35 litres is right there at 1 gal/hr. using a British gal ( 4.5 l/gal), slightly more using a US gal (about 3.8l/gal) , split the difference and you get 4.2 l/gal.

It would seem that using 1 gal/hr is a reasonable estimate for the rpm stated, given that the engine is producing around 20 hp at that rpm....