Hull Surface Treatment - HST - FAQ

Australia | South Pacific

Frequently Asked Questions

Is HST the same as hull scrubbing?

HST is a passive system that does not remove layers of antifoul paint. Scrubbing and underwater water-blasting is aggressive and removes layers of expensive antifoul paint reducing its effectiveness and life expectancy. Hull scrubbing is no longer allowed in Australian waters, as is now the case in many countries, in order to prevent the introduction of foreign marine pests into the local aquaculture and also to prevent toxic plumes from antifoul paints discharging into the water. HST is the only alternative to hull cleanliness other than dry-docking.

How does the system work?

HST uses hot seawater as its active ingredient to sterilize the hull. There are no additional chemicals used and the process does not disturb any of the anti foul paint so no toxins are released into the surrounding water. Although the growth is killed instantly it remains on the ships hull until the ship has sailed and is then polished off over the next two to three weeks using the accelerated hydraulic forces and wave action. No growth is disturbed so no foreign marine pests are introduced into the local environment. Consequently Hull Surface Treatment has been approved by the environmental authorities and can be applied safely in port and in many sheltered anchorages. Hull Surface Treatment is a very effective proven method of leaving ships hulls clean.

Does HST create harmful contaminants?

No, HST uses no chemicals but rather uses the local seawater. HST does not physically remove any growth. The treatment sterilizes the hull and kills the growth immediately. As the vessel sails over the ensuing two to three weeks the dead weed and algae is washed from the hull by accelerated hydraulic forces and wave action. No growth is disturbed so no foreign growth is introduced into the surrounding water. Consequently Hull Surface Treatment has been approved by environmental authorities and can be applied safely in port and in many sheltered anchorages.

How long does the treatment take?

The treatment to a Panamax sized vessel would normally take approximately two 8-10 hour days but can be completed in one day using two units simultaneously.

Will it damage the ship’s anti-foul coating?

HST is a passive treatment applied to the hull gently. No antifoul paint is disturbed or damaged. Unlike scrubbing, the paint becomes exposed after treatment over a period of 2 – 3 weeks and the paint is then able to continue its job of resisting fouling. Due to the sterilizing action the spores of the growth are also killed slowing down the regrowth.

Can HST be applied on the wharf side when the ship is docked?

HST is a diver-less system and can be applied to the ships hull on the dock-side whilst alongside in most cases.

Is HST environmentally friendly?

HST is a very environmentally friendly process. Not only does it not use chemicals or other contaminants it also reduces emissions. A clean hull means reduced CO2 emissions, big savings on fuel, decreased main engine wear and decreased dry-docking frequency.

Does the ship have to be out of the water for HST application?

The technology is specifically designed to operate whilst the vessel is in the water.

Does the application interrupt the operation of the ship ie loading and unloading of cargo?

HST can be applied whilst the ship is carrying out cargo operations.

Is there scientific proof that the technology works?

Yes. The Royal Australian Navy Science Organization has carried out extensive tests to the technology over a 10 month period and have scientifically proven that HST kills all the growth it treats and that growth is removed over the ensuing weeks.

Does the heated seawater present an environmental risk?

HST discharges approximately 10 gallons of seawater every minute. Less than most harbor work boats discharge out of their engine cooling system. This is such a low flow that within 3 to 4 feet of the applicator the seawater is at normal ambient temperature. Independent tests have been carried out by an environmental company to ensure this was the case.

Is HST just another coating applied over the existing coatings?

HST is not a coating, it is a treatment applied to existing coatings. HST is safe to use on any kind of underwater anti foul paint including the new generation fouling release silicon based coatings.

Can HST be applied to mature growth ie. barnacles and the like?

No, HST is designed to be a pre-emptive strike. The best way to prevent mature growth like barnacles is to stop them growing in the first place. HST is used in a maintenance program from dry-dock to dry-dock and keeps the hull clean. It can be applied to growth up to the level of immature tube worm. This also includes weed.

Can HST treat niche areas like sea chests and thruster tunnels etc?

HST is designed to treat niche areas for bio-security purposes and can be applied to seachests and thruster tunnels.

In what weather conditions and sea state is HST able to operate?

HST requires sheltered water to operate. A sea state of less than 0.5 of a metre is required.

How does fouling affect a ship?

Hull Fouling starts from the moment a ship is placed back into the water after dry dock and continues for the life of the ship. A coating of slime and algae can cause a ship to have an increased hull resistance of 12% with in increase in fuel consumption of 7-10%. If a ship has 10mm to 30mm weed covering its laminar flow areas the resistance can be as much as 30% with a corresponding increase in fuel consumption of 23-26%.

Is HST a proven technology and proven to demonstrate savings?

HST has been proven to keep a ships hull clean if applied in a maintenance program from dry-dock to dry-dock. If this approach is applied HST guarantees that a ship will save approximately 4% - 6% of the propulsive fuel costs over the dry docking period.

Does HST cost a lot of money like a lot of the latest environmental technologies?

HST is one of the few environmental technologies that saves considerably more money than it costs. Usually HST costs approximately 15% of the savings experienced with treatments.

How does HST help with dry-dockings?

HST can keep the hull of the ship clean for an extended period of time which has not been possible in the past. This is because HST is not abrasive and does not damage the coatings on the underwater section of the ship. Consequently it does not reduce the life expectancy of the paint. By passively keeping the hull clean on a regular basis it is possible to increase the time between dry-dockings.

Does HST damage or detrimentally affect anti foul paints or fouling release paints?

In all cases HST has not caused any damage to the underwater coatings of ships that have been treated by the technology. Anti foul paint companies have also suggested that the treatment may even help reactivate the paints.