I hope you are not finished and this is of some help...
I believe that once the vessel is on the blocks (in a traditional dry dock not a floating dock) it is no longer considered a ship and the law means that it has to be treated like a land based project. On large vessels, tankers, cruise ships and the likes, the yard take responsibility for the ship and apply their own safety regs, not the ships. This applies in the UK at present to my knowledge, for the rest of the world I haven't a clue! (Height Safety standards of the HSE (UK) -http://www.hse.gov.uk/falls/index.htm). Also, it depends on the size of your work force, HSE only applies to company employing over a certain number of employees, (I think it is about 4 or 5).
Scaffold or Cherry Pickers are now the norm. But again it depends on the size of our ship?
You may still use staging and Bosun’s chairs at sea. As mentioned previously I don't think for many more years as they are not the best bits of kit available.
Ultimately, you should make sure that the system you use is 'suitable and sufficient' especially if it is not you doing the work! Chose the safest option, not the quickest or cheapest.
Suitable and sufficient is repeated over and over for Risk Mitigation and Control. The only person who can tell you if you have done enough is a judge in a cort of law. So really think about it.