A Royal Navy sailor who sexually assaulted a colleague using a beer bottle in a drunken prank on board a warship while it was docked in Bournemouth has been found guilty by a court martial panel.

Logistician Andrew Donaldson, 34, was convicted of assault by penetration for using the bottle in the incident which happened aboard the Plymouth-based frigate HMS Northumberland as it was alongside the Bournemouth coast for the Air Festival in August 2013.

Leading Seaman Christopher Cook, 31, was also found guilty by the panel of senior officers of a charge of disgraceful conduct of an indecent kind.

A third defendant, Leading Logistician Roger Spratt, 28, had pleaded guilty at a previous hearing to the same offence of disgraceful conduct for filming the incident using Donaldson's mobile phone. He was sentenced to eight months' detention and was disrated to the rank of able seaman.

Donaldson, who will have to sign the sex offenders' register, and co-defendant Cook will be sentenced on a date to be set.

Nadim Bashir, prosecuting, told the trial at Portsmouth Naval Base's court martial centre that the victim had drunk six cans of Bulmers cider in an hour at an event at the petty officer's mess.

Having thrown up several times, the victim had fallen asleep on a seating area and someone had placed a duvet over him when the attack took place.

Mr Bashir said that a number of other members of the ship's company had also posed for photographs next to the victim's bare bottom either sticking their tongues out or with their thumbs up.

He continued: "To add to the humiliation of the complainant, the footage was emailed by Logistician Donaldson to himself to ensure a copy was kept on his computer for future use and he texted the footage, certainly to another member of the ship's company.

"He was showing the footage for his own amusement and to the amusement of others of what he had done. Word quickly spread about what had happened and resulted in the complainant being ridiculed."

In a statement read to the court, the victim said: "I was very drunk, for this to wake me up demonstrates the force used. At no time have I given anyone permission to touch me or carry out such an act."