He found Moore trapped and unable to talk.
Mr Clark alerted two other locals, Leonard Lumley and Dan Goldsberry, who rushed to the beach to try to free him.
By then the water had risen to just below the exhaust pipe of the column-shift van.
Two of the men tried to put the van into gear to drive up the ramp, but failing to do so decided to release the boat into the water.
Mr Clark held onto Moore to support him as the two other men lifted the trailer sideways to free him.
They desperately tried to resuscitate Moore, performing CPR for about 20 minutes, but neither they nor emergency workers could not revive him.
Coroner Shortland found Moore suffocated after he was trapped between the jack-knifed van and trailer.
In his findings, he said although launching and retrieving boats alone was appropriate sometimes, it was always safer for two people to do so.
"This unfortunate death serve to remind boat users of ensuring safe practices," he said.
Moore was the New Zealand Herald's travel editor for several years and went on to write a number of books.
He won a Qantas Media Award for his travel writing the month before his death.
Moore kept a bach at Taupo Bay which he described as a "slice of beachfront paradise" in a travel piece.
