The arrest of two panamax bulkers in the US has lifted the lid on arms smuggling allegations against Greek shipowner Dileton Maritime, over a tanker that has been held for more than a year.

Lawyers for trader Swaidan Trading claim it is set to lose up to $33m over its charter of the 47,600-dwt MR2 product tanker Androussa (built 1995). The ship loaded a Swaidan cargo at Djibouti immediately before it was stopped off Yemen by Saudi-led naval blockade forces in early April 2017.

Vessel tracking services show the tanker has remained in Saudi waters since its detention.

The Androussa's last voyage was an expensive one for both sides.

Lawyers for Swaidan said their client bought 309,000 barrels of gas oil from Litasco Middle East for about $20m. The Androussa’s cargo was loaded in Djibouti on 1 April 2017 for discharge at Ras Isa Port in Yemen in a voyage brokered by Ifchor Tankers Genoa.

The ship was stopped the next day and the cargo was confiscated, and Swaidan has racked up more than $8m in finance costs since then for the undelivered gas oil.

The Androussa's detention was reported last year but the reason remained a mystery. Now Swaidan's filings in two US court cases show that a Saudi tribunal determined the ship had smuggled explosives in a ballast tank as well as carrying what the Saudi investigators said were weapons' components, and falsifying its logs.

Emails found on the master's computer indicated that plans had been made to offload a ballast tank cargo onto trucks at the quayside, and investigators said they found traces of RDX and PETN weapons-grade explosives in a ballast tank.

The Saudi tribunal also believed that "large quantities of steel pipes in engine room" were actually weapons material.

"The pipes are suspicious because some of them look like projectiles and other pipes look like gun barrels," wrote tribunal members in a report accepted by Saudi customs official Abdul Rahman Bin Dhawi Al Mohana.

"Inside them, there are objects [that] look like plugs and furrows contained in the gun barrels. In fact, such pipes are used in military purposes."

The tribunal also determined that the Androussa spent parts of November and December 2016 with automatic identification system devices switched off. And it found that someone had tampered with maps and navigational devices on the bridge to show the ship had been at Khasab, Oman, and not Bandar Abbas and Lavan Island in Iran.

When contacted, Dileton chartering director Sotiris Papantonopoulos referred questions on the case and its commercial effects to another company official, who had not responded before TradeWinds went to press.

Meanwhile in the US, Swaidan's arrests of two Dileton bulkers were meant to secure a total claim in an ongoing London arbitration of nearly $33m on the voyage, including legal costs and future interest.

Dileton is fighting the arrest of the 76,400-dwt Donousa (built 2004) in Oregon. The 75,700-dwt Erikoussa (built 2005) was arrested and released in Louisiana last month after posting security of $12m, a sum limited by the value of the vessel itself.

The Donousa lingered off the US Pacific coast facing arrest for nearly two weeks before it entered US territorial waters last week in Oregon.

Dileton's lawyers are still contesting the seizure of the Donousa and accusing Swaidan of wrongful arrest in the Erikoussa case.

But in the US arrest cases, the owner's side has insisted that all the ships in question are owned by companies legally distinct from Dileton, which acts as a third-party manager.

Meanwhile, Swaidan's lawyers have asked the District of Oregon and Eastern District of Louisiana federal courts to pierce the corporate veil on the grounds that Dileton and its registered owning companies are operated as a shipowning group controlled by founder Dimitrios Papantonopoulos.

Besides the Androussa, Donousa and Erikoussa, Dileton's fleet includes the 44,500-dwt product tanker Hydroussa (built 1996).