Hull roughness cost cascade

Hull coatings are roughly 1% of the total fuel bill over a drydock cycle. The range is roughly 0.7% to 1.3% of the fuel bill. One thing to note is that the bigger the vessel, the stronger the asymmetry gets, because fuel spend scales faster than coating cost.

What’s for sure is that the wrong specification decision on that 1% can easily cost seven figures in excess fuel consumption alone (making the 1% lower, but you get my point) before you even factor in unscheduled drydocking, warranty disputes, cleaning or the operational headaches that come with a hull that is not performing. I don’t know how common unscheduled dockings are - I do know it’s a last resort for an owner, and because of that they will try to manage a bad situation, and with that comes a massive organizational cost of money and time.

This is the asymmetry that almost nobody in the maritime industry talks about honestly: coatings are a small part of total cost, but the impact is asymmetrically good or bad.

Take a mid-size bulk carrier vessel on a standard trade route:

• Fuel consumption: ~32 tonne/day at sea
• Operating days: ~250/year (68% for those whose arithmetic has left the building)
• VLSFO at $600/tonne (and right now, with Hormuz disruptions… higher)
• Annual fuel bill: roughly $4.8 million
• Over a 5-year drydock cycle: $24 million in fuel

Now look at the coating. A full hull recoat material only runs somewhere around $150K-$350K depending on the vessel and the system. Call it $300K.

That is 1.25% of your fuel spend over the interval between drydockings.

Here is where it gets expensive.

A coating system that is not optimized for your vessel’s actual operating profile - wrong technology choice, wrong surface prep standard, wrong recoat specification - does not announce itself. There is no alarm (unless, as you sail away, the paint stays in drydock).

What happens is a gradual increase in roughness that shows up as excess fuel consumption. If that roughness is from the application quality, surface prep or the coating’s flow/wetting characteristics, the efficiency is gone (unless you break out the 3,000 grit sandpaper). At least with fouling you can do something about it in service.

The famous study to quote is Schultz, stating light slime is around 10% drag (I think that one surprised a lot of people at the time). Side note: I remember scratching my head when I read the term “hydraulically smooth” for the first time.

At 5% drag/efficiency loss, excess on a $4.8M annual fuel bill, you are burning an extra $1.2 million over 5 years. See how it mounts up?

At today’s bunker prices closer to $1,000/tonne, those numbers roughly double.

And that is just the fuel penalty. To focus on fouling, the cost cascade looks like this:

• Accelerated fouling → more frequent in-water cleaning interventions (assuming your coating can tolerate cleaning)
• Shortened effective service life → drydock interval pulled forward, at $2-4M for an unscheduled drydocking, or in real life, just live with it
• Warranty disputes → manufacturer says application was off-spec, yard says they followed the TDS, owner is stuck in the middle
• Operational constraints → vessel cannot maintain charter speed without burning more fuel, or starts missing CII targets

So why does this keep happening?

Three reasons, and they all compound each other:

1. The people specifying the coating are often not coating specialists and don’t have time to be. Superintendent gets a recommendation from the manufacturer rep, the yard has a preferred product, and the spec decision gets made on relationships and convenience rather than a rigorous analysis of what the vessel actually needs.

2. Nobody is doing the total cost of ownership math. The decision is framed as “which coating costs less per liter” instead of “which system delivers the lowest cost per tonne-mile over 60 months.” These are completely different questions and they often produce completely different answers.

3. The performance data stays siloed. The coating manufacturer has their test data. The hull cleaning company has their roughness measurements. The vessel has its fuel consumption logs. Nobody is connecting the dots across the ecosystem to evaluate whether the spec is actually performing.

This problem is solvable. The data exists. The analytical frameworks exist. What has been missing is an independent party with no product to sell who can look at the full picture: your vessel, your routes, your operational profile, your actual in-service performance, and tell you whether your current spec is costing you money or saving it.

The coating is 1% of your cost. But getting that 1% right or wrong moves the needle on the other 99%.

That is the asymmetry. And most are on the wrong side of it without knowing.

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Independent. No manufacturer affiliation, no sponsorships.