In 1806 the Naval Chronicle described Nelson’s coffin being lowered into the crypt ‘by balance-weight’:
Quote:
Precisely at thirty-three minutes and a half past five o'clock, the Coffin was lowered into the grave, by balance weight, secret machinery having been constructed expressly for the purpose.
The Monthly Mirror also said ‘it solemnly descended by balance weight’.
This suggests a system of pulleys to me. It was only the coffin that was lowered, not the sarcophagus, so I wouldn't have thought the weight was a problem. Although his body was actually contained in three coffins, which would indeed have been heavy, it had been carried onto the platform during the service.
According to the Literary Gazette, ‘the machine for interring Lord Nelson’ was invented by Mr Wyatt, and the same machine was used in 1827 at St George’s Chapel at Windsor for the funeral of the Duke of York. James Wyatt was the surveyor-general of the Board of Works, responsible for Nelson's funeral, and the carpentry contract was awarded to his brother Samuel Wyatt. Both were architects responsible for many public and private works. The same machinery was also used at St George's Chapel for other royal funerals, including the king’s, during the ten or twenty years prior to 1827. Royal funerals at St George’s Chapel have continued to use machinery for lowering the coffin into the vault, including George VI’s funeral, and it would be interesting to know what machinery is currently installed!
At St Paul’s in 1852, Wellington’s coffin was lowered by chains and pulleys:
Quote:
We have previously described the last scene of lowering the coffin into the crypt, which was so highly commended by all who witnessed the solemn ceremony. The apparatus employed was of the simplest, yet most effective kind, under the direction of Mr. Nicholson, chief engineer to Messrs. Cubitt and Co., who had the sole management of all the machinery employed on the occasion. It consisted only of two “crabs” [capstans] connected together, so that they acted simultaneously; and four chains, one to each corner of the platform, on which the bier was placed, which received the coffin from the funeral car. As the men worked the “crabs,” the chains gradually lowered, and the coffin descended beneath the pavement of the cathedral. A strong framing of timber was raised in the crypt, to carry the platform on which rested the bier, and all the chains and pulleys used in lowering the platform, so that there was no strain on the vaulted groining of the crypt.
Source: E. M. Cummings - The companion to St. Paul's cathedral