How to Cut the Bunker Bill

Ready or not, here it comes! No matter who you talk to, IMO 2020 promises to be a time of uncertain fuel prices. If fuel prices will go up, your fuel consumption needs to go down. Here are eight practical ways to reduce your fuel consumption.

Preparing for IMO 2020

1.0 Introduction

Ready or not, here it comes!  No matter who you talk to, IMO 2020 promises to be a time of uncertain fuel prices.  Starting January 2020, everyone will likely pay a higher price on their bunker bill, even if you have nothing to do with IMO rules.  Time to prepare.  If fuel prices will go up, your fuel consumption needs to go down.  Here are eight practical ways to reduce your fuel consumption.    (Some are even free!)

2.0 The Danger of IMO 2020

You can’t delay it or avoid it.  On January 1, 2020, the IMO severely reduces sulfur emissions for every single vessel in the world.  Sitting happy in 2019, the IMO allowed vessels to emit sulfur emissions (SOx) of up to 3.5% m/m (mass by mass), when operating outside emissions control areas.  That meant burning cheap, heavy fuel oil in most of the world’s oceans. 

Happy days are over.  Starting January 1, 2020, the new limit for SOx emissions dropped to just 0.50%.  Seven times lower than before!  Only two major ways to achieve that:  install an exhaust gas scrubber, or burn low sulfur fuel.  (Less common strategies include switching to LNG.)  We didn’t see a massive rush on exhaust gas scrubbers in the last few years, and if you didn’t install one before, it’s too late now.  They are not simply plug and play.  So for the roughly 50,000 commercial marine vessels in the world [1], most will need to start purchasing low sulfur fuel, starting January 1, 2020.

3.0 Rising Fuel Costs

But what if your ship doesn’t fall under the IMO rules; why should you care about this?  Supply and demand.  Starting 2020, every ship in the world will want massive quantities of low sulfur fuel.  Where do we get low sulfur fuel from?  Track the supply chain all the way back to the oil refinery and we discover that low sulfur fuel comes out of the distillation column at the same point as diesel fuel. (Figure 3‑1) 

In layman terms, low sulfur fuel is essentially diesel fuel, with an extra step to strip away the extra sulfur (catalytic hydrotreating).  Thankfully, we don’t expect the oil refineries to develop IMO low sulfur fuel as a new distillate.  Instead, they will likely blend ultra low sulfur diesel fuel with existing heavy fuel oil (HFO) stocks.  But even a blended fuel still means heavy demand on diesel supply. 

That could be a problem when most of those 50,000 ships suddenly want to buy low sulfur fuel instead of HFO.  Especially since most of those ships were the ocean freighters with the largest fuel consumption.  That delivers major competition for fuel, and when demand goes up, oil companies raise the price. 

No agrees on the exact in increase in price.  Some believe that oil companies have already prepared for the increased demand.  Others speculate about wild price increases.  Mansfield Energy estimated diesel prices to increase by 8-17% [2]  One thing everybody agrees on:  the following months promise turbulent times for diesel prices. 

4.0 Eight Ways to Cut Bunker Costs

What can you do about it?  Not pay for diesel?  Not likely.  In terms of real solutions, here are eight practical strategies to reduce your fuel consumption. 

4.1 Reduce Speed

We under-estimate just how quickly fuel consumption drops with speed.  Ignoring changes in engine and propeller efficiency, the fuel consumption drops off with the cube of ship speed.  (Figure 4‑1)  Two important takeaways from this graph.  First, even a small reduction in ship speed vastly reduces your fuel consumption.  Second, look closely at the slope of the curve.  Notice we have a steeper slope at the beginning.  The small initial reductions get more relative benefit than later speed reduction.  You don’t need to sacrifice a large speed for big savings.

Of course, it can’t be that simple.  Figure 4‑1 was just a generic graph and doesn’t consider the details of your engine or hull.  Consult with an engineer to decide how much a speed reduction can help you.  You may find that the potential improvement gets even better than Figure 4‑1.

If you operate a small vessel, running at faster speeds, you likely push your ship past hull speed.  Nothing wrong with moving faster than hull speed, but your fuel consumption does tend to climb drastically once beyond that limit.  (The one exception is planing vessels.)  Reducing speed to just below hull speed will do amazing things for your fuel consumption.  (See this other article for how to calculate hull speed.)

4.2 Trim the Vessel Forward

Starting today, you can potentially save 1-2% on fuel consumption, and it requires no vessel modifications.  This solution works especially well for ships with a long parallel midbody and a low deadrise.  If your ship has any aft trim, that parallel midbody deflects the water downwards, which creates additional resistance.  It barely changes the water pressure as it travels along your hull.  But your parallel midbody has a LOT of surface area.  ANY increase in water pressure still adds up to a significant addition in resistance. 

We do not want the parallel midbody adding to resistance.  We call it parallel because at worst, that section of the ship should be parallel to the waterline.  In fact, a slight forward trim of about 0.1 deg helps the ship.  Granted, you will need to convert 0.1 deg into a difference between draft mark readings for your specific vessel.  Your results may vary.  Test to see how much forward trim benefits your ship.  And if you want a more exact trim value, DMS recommends a trim optimization study.

4.3 Reduce Phantom Weight

We pay for every pound of weight that the ship drags through the water.  So minimize the weight.  Just like old houses, ships accumulate a LOT of miscellaneous stuff, and we fail to respect just how much weight that adds up to.  One vessel I inspected had these memorable items onboard:

1. FIVE spare pumps – enough to replace every major pump in their engine room
2. Raw materials for an entire machine shop
   1. Welding rods
   1. Steel plate
   1. Pipe
   1. Angle bar
   1. Etc.
3. Enough electrical parts to resupply an entire hardware store
4. TWO full sets of spare parts in screws, nuts, washers, etc. in literally every single size possible
5. TWO full sets of mechanics tools:  drill, ratchet, wrenches, grease gun, etc.
6. Spare fuel filters for engines (THREE engine models)
7. Spare air filters for engines (THREE engine models)
8. Spare propeller blades
9. THREE spare crane hooks
10. TEN sets of chain falls, various sizes

And those were just the more notable items, many of which were absolutely necessary.  Scattered across the ship, those little items may seem harmless, but they added up to over 10% of the light ship weight!  Literally dozens of tonnes that you pay in fuel to haul around.  So take a hard inventory of your ship.  Because it does cost money to store weight on your ship; it costs fuel.

4.4 Optimize Stability

The second part of reducing weight comes from stability.  Many older vessels are hampered with minimum weight requirements, due to stability reasons.  If your stability booklet mentions fixed ballast or requires minimum tank levels in ballast or fuel, this is you.  But the goal behind those restrictions is not really weight.  Ultimately, they want to keep down the center of gravity on your boat and maintain a minimum safe stability.

We have better ways to achieve this.  Instead of unnecessary weight, install a weighted skeg.  Think of the fin keels you see on sailboats (Figure 4‑2), but not nearly as deep and made of steel or aluminum (depending on your hull). 

The lower the skeg sits below your hull, the less weight required to achieve the same stability as before.  Less weight means better fuel consumption.  Even better, the skeg acts just like a fin keel on a sailboat, improving your vessel’s turning capabilities.  Skegs do require modification to the hull, with associated drydocking and renewal of stability documents.  DMS can walk you through the entire process, and deliver the following benefits:

• Improved fuel consumption
• Improved maneuvering
• New life for your vessel stability
  • Stop stability decay and regain lost capability. 
• Options for future adjustments

4.5 Optimize Total Transport Efficiency

Sometimes, heavy cargoes are not the best cargoes.  Granted, no one wants to see ships travel half empty, but we all know that ships burn less fuel when they travel with less cargo.  This is where we need to ask the smart question, which is more important?  Lots of cargo, or getting the best profit from the ship?  For some ships, those two may not be the same answer.  There may be an optimum point with slightly less cargo (less overall weight) that reduces the fuel consumption.  Reduced fuel consumption reduces operating costs for the ship and ultimately means more profit from that ship. 

This feeds into the idea of a ship transport factor.  We examine the utilization of a ship on a specific route to determine the net benefit compared to cost.  Higher transport factor makes for a better utilized ship.  Easy to describe, harder to implement.  Everything hinges on the details, specific to each ship and route.  Take an example of a ship working a regular route, transporting containers for a fixed price per tonne.  Factors to consider would include:

1. Fixed costs
   1. Crew
   1. Maintenance
   1. Victuals
2. Fuel consumption variation with draft
3. Fuel consumption variation with seastate
4. Revenue from cargo
5. A host of other minor factors

Thankfully, these optimization efforts involve very little risk and minimal cost. They just involve paper exercises.  No actual modifications to the vessel.  Companies naturally try to optimize ships and minimize operating costs.  The ship transport factor just extends that concept to include the physics of the vessel load.

4.6 Optimize the Propeller

Rather than getting a stock propeller, you can always order one that gets customized to your exact vessel.  This involves CFD and possibly towing tank testing to understand the local flow conditions around the propeller.  The propeller designer then tweaks the blade design to specifically match the flow patterns on your ship (wake adapted propeller).  Of course, this means buying a whole new propeller.  No small expense.  This option does not pay off unless you definitely know that your current propeller suffers from extreme inefficiency or operates outside of its original design condition.

4.7 Add a Thrust Augmentation Device

Even the best propellers cap out near 65 – 72% efficiency, but why stop there?  Add thrust augmentation to boost another few percent.  The market offers a host of devices to boost your propeller efficiency. (Figure 4‑4)   And most of these devices can be added as a retrofit.

Looking at the figure, you notice that everything claims improvements in the range of 2-5%, which definitely helps your fuel budget.  But the real magic happens if you combine multiple devices together.  The cumulative effects cut your fuel budget by 6 – 14%, stacking up to huge fuel savings.  This comes with a note of caution, because combinations of propeller devices don’t automatically mean equivalent fuel savings.  It depends on principles behind each device and how they interact.  DMS definitely recommends CFD modeling to confirm fuel savings before investing in any modifications.

4.8 Barges:  Swap Out for High Lift Skegs

Last but not least, a special tip to everyone working with barges:  ditch those chunky skegs!  Conventional barge skegs account for 20 – 30% of the total barge resistance.  This is completely ridiculous for an appendage whose only job is to help the barge tow in a straight line.  In any conventional ship, appendages only add 5 – 10% to the total resistance.  Conventional skegs on a barge suffer from bad design, plain and simple.

The better alternative is high lift skegs.  One example would be the brand name Hydralift by Nautican. (Figure 4‑5)  These high lift skegs use thin lifting foils to give you the same directional stability, but with much less resistance.  Nautican claims 35 – 50% reduction in resistance.  Many modern barges install them from day one.  Definitely worth investigating.

There are only two exceptions to the high lift skegs.  You want to keep the existing skegs if they are watertight and provide buoyancy, or if they function as part of an ATB ladder system.  In that case, the more important feature for those skegs is their structural connection, rather than their directional stability.

5.0 Conclusion

Several of the fuel saving tips in this article cost you nothing but a little time.  Or invest in the more advanced options for a larger payoff.  In either case, IMO 2020 demands action.  The biggest danger of IMO 2020 lies in just ignoring it.  Regulations push us forward, requiring change.  We can’t stop it, but we do control the mechanism of that change.  We can decide that 2020 will involve more than reacting to uncertain bunker prices.  Time to decide on a lower fuel bill.

6.0 References