Quick Answer
For surface preparation directly before painting, HP fresh water blasting above 750 bar is the minimum required to produce an acceptable surface quality. Below this pressure, mechanical preparation (abrasive discs or sandblasting) is still needed after blasting. One person with an HP blaster can prepare the same area as 4–6 people using power tools — and to a higher standard.
Why HP Blasting Is the Most Efficient Method
HP fresh water blasting is the most effective method for corrosion maintenance on ships in operation. In a single pass, it removes loose paint, corrosion, and salt contamination while roughening the surface for painting.
The efficiency ratio is significant: one trained operator with an HP blaster achieves the same output as 4–6 workers using conventional power tools — and with better surface preparation quality.
This makes the higher initial investment considerably more affordable than it appears when comparing purchase price alone.
Pressure and What It Means in Practice
Pressure determines what the blaster can do — and what it cannot:
Pressure range — What it achieves
Below 350 bar — Salt removal only. Mechanical preparation still required.
350–750 bar — Removes loose paint and light corrosion. Preparation still needed before painting.
Above 750 bar — Acceptable surface preparation for direct painting.
Above 1,000 bar — Full surface preparation. Removes all but the best-adhering original coating.
A general guide: if the pressure cannot remove it, it was probably better than what will go on next.
Types of Nozzles
Straight jet (0°): Concentrated, high-impact jet. Good for removing heavy corrosion and well-adhering old paint. The nozzle type responsible for most HP blasting accidents when used incorrectly.
Rotating nozzle: Takes the straight jet and spins it. Increases surface area without reducing pressure. Most cost-effective way to increase output.
Fan jet (10–60°): Wide coverage. Good for cleaning. Less effective for surface preparation.
The Most Common Reasons HP Blasters Stop Working
Investing in an HP blaster only pays off when it runs when needed. The most common maintenance failures seen onboard:
- No stock of consumable spare parts (nozzles, seals, hoses)
- Hoses worn from vibration and sun exposure — causing pressure loss
- Oil level and filter condition not monitored — causing breakdowns
- Worn nozzles not replaced — lowering output pressure
- Safety boots used for other tasks and unavailable when needed
A recommended spare parts kit for each vessel should reflect job scope and trading pattern. BSO Svendborg can assist with specifying this.
Water Consumption
Water consumption is a real operational consideration.
Estimate: approximately 6–8 metric tons of fresh water per effective working day. Never use sea water — salt will corrode internal components and contaminate the prepared surface.
Ensure the vessel’s fresh water generator capacity covers maintenance operations alongside domestic, machinery, and cargo hold consumption requirements before planning an HP blasting project.
Frequently Asked Questions
What pressure is needed for HP water blasting before painting on a ship?
A minimum of 750 bar is required to prepare a surface directly for painting. Below this pressure, additional mechanical preparation (abrasive discs or sandblasting) is still needed after blasting.
Is HP blasting better than grinding for ship surface preparation?
Yes, in most cases. HP blasting removes salt contamination as well as loose paint and corrosion in a single operation — something grinding cannot do. One HP blaster operator can prepare as much area as 4–6 grinder operators.
Can you use sea water in an HP blaster on a ship?
No. Sea water will corrode internal components and leave salt contamination on the prepared surface. Only fresh water should be used.
What is flash rust after HP blasting?
Flash rust is light surface oxidation that appears when fresh, clean steel is exposed to moisture after HP blasting. Light flash rust (lighter than the colour of a carrot) can be painted over. Heavy flash rust requires re-preparation.
How much water does HP blasting use on a ship?
Approximately 6–8 metric tons of fresh water per effective working day.