Polyethylene or steel buoys — how to actually decide
The short answer: no material wins everywhere. Three things decide it — how tight your maintenance window is, how likely the hull is to be struck, and how many years you intend to manage this channel. Compare purchase price alone and you will almost certainly choose wrong.
1. Why unit price misleads
Steel hulls usually cost less to buy. That much is true. But a hull's cost is not a single payment — it includes every subsequent descaling, repaint, anode replacement, recovery, slipping and redeployment.
In salt spray, brackish transitions or water carrying industrial discharge, protective coatings reach end of life noticeably sooner than the design figure suggests. Once the coating is breached, corrosion spreads from the damage, and by the time anyone notices it is rarely a repaint job any more.
The decisive number is usually the cost of the trip. Fuel, crew and lifting for one maintenance sortie typically exceeds the price difference between hulls. Put differently: if a polyethylene hull saves one or two visits, the purchase premium is already recovered.
2. The maintenance window is often the real constraint
On many waterways the problem is not the maintenance budget — it is that there is no time to do the work. No operations during flood season, no extended closures on busy reaches, and offshore work limited by weather windows. A whole year may offer only a few workable weeks.
In that situation, choosing a material is really choosing how long an interval you can survive. A non-metallic hull needs no coating cycle, which reduces maintenance to checking the mooring, clearing fouling and swapping the lantern — most of which can be done afloat, without slipping the hull.
3. What happens after an impact is not the same
On a busy reach, contact with a hull is close to inevitable. What differs is the outcome:
- Steel hull. Light contact breaks the coating and starts a new corrosion site. A heavier strike can split the plate; the hull floods, loses buoyancy and either sinks or drifts, requiring recovery and redeployment.
- Polyethylene hull. UHMWPE typically deforms locally and partly recovers. The material does not corrode, and closed-cell foam fill retains buoyancy even with the shell damaged — so the aid is usually still on station and still working.
For the operator this is not only a repair bill. It is whether the mark is still there — and the navigational risk during the time a position is missing cannot be expressed as a maintenance cost.
4. When steel is still the right specification
To finish the argument honestly — steel or aluminium remains the better choice in these cases:
- Very large hulls. Beyond the economic range of rotational moulding, steel is stronger and cheaper for the size.
- Defined load-bearing requirements. Where large equipment is mounted on the hull, personnel board it, or additional structural loads apply, metal stiffness is easier to satisfy.
- Matching existing infrastructure. If the waterway already runs a large steel fleet, and crews, spares and tooling are all built around it, a partial material change can raise management cost rather than lower it.
- The tender specifies the material. No discussion — build to the document.
We supply metal AtoN for exactly these situations.
5. A workable decision order
- Start with the maintenance window: how many afloat operations and how many slippings can you schedule a year? The tighter it is, the more the answer leans non-metallic.
- Then impact probability: traffic density, floating debris, ice. Frequently struck positions favour polyethylene.
- Then hull size and loading: beyond the moulding range, or with structural loads, return to metal.
- Finally model whole-life cost, not unit price — including sortie cost, slipping cost and the risk of a missing position.
This order works for most inland and port projects. Open coastal water adds wave height and mooring loads to the picture and can change the conclusion — model those projects separately.