The police launch Lady Elizabeth IV was out on the Marlborough Sounds on Saturday, with the crew breathtesting boaties.
The breath screening tests were the first in the Marlborough Sounds and the boaties were not compelled to take the tests, Tasman police district prevention manager Inspector Brian McGurk said.
Ten tests were conducted and all were under the legal limit, he said.
"The majority of boaties spoken to agreed the same principles of testing on the road should be applied on the water," he said. Only one skipper refused to be tested.
The Wellington-based police maritime unit was called in to work with Marlborough police to help educate boaties about the risks of drinking while out on the water.
"Mistakes do happen and people can lose their lives," Mr McGurk said.
"We are trying to educate people that it's just not a good idea."
- The Marlborough Express