Local knowledge of busy shipping areas will be lost when coastguard stations in Wales close, it has been claimed.
A plan to close stations in Holyhead and Milford Haven and to downgrade the base in Swansea "doesn't make sense" to one yacht club commodore.
The proposals will leave Wales with just one station - Mumbles, Swansea - and lead to job losses.
A spokesman for the RNLI said he believes there services will not be reduced.
A 14-week consultation has been launched ahead of the Milford Haven station closing in 2012/13 and Holyhead a year later, with their function transferring to new Maritime Operations Centres across the UK.
Under the plans Mumbles, which covers much of the Bristol Channel, will, in 2013/14, become a sub-station open only during the daytime.
Swansea Yacht and Sub-Aqua Club commodore Wayne Morgan said: "I just think they haven't thought it out properly.
"The closure of Swansea during the night is ill-thought out because a lot of incidents happen during the evening period, especially in the summer as a lot of our yachtsmen and fishermen go on extended cruises to the Scilly Isles and all parts of the Bristol Channel.
"Local knowledge will be lost. It's the same with Milford Haven. It's a busy shipping area; we have seen that with incidents that have happened there in the past, tragic incidents.
"The point about Swansea is that if it's good enough to close it at night, why keep it open in the day if they can do without it?
"It just doesn't make sense at all."
Colin Williams, the RNLI's divisional inspector for Wales, said he was "confident" services would not be reduced.
"I think we need to understand this is something that has been discussed for quite some time," he said.
"We have to accept some tough decisions have to be made and, coupled with that, there have been great improvements in technology.
"I personally feel confident that this will be done in a phased way and we won't see a reduction in service."
Preseli Pembrokeshire MP Stephen Crabb is due to meet constituents to talk about concerns.
"I think the policy is essentially sound... I am concerned about the jobs that will go," he said.
"The discussions I was having in London yesterday reassured me on some points but I am meeting with the harbour master at Milford Haven and local people today and will be taking these concerns back to London."
Under the proposals, the number of stations in the UK will be reduced from 18 to eight. Only three - in Aberdeen, Southampton/Portsmouth and Dover - will be open 24 hours a day.
Five sub-centres, including Mumbles, will be open during daylight hours.
There are currently 23 posts at Milford Haven, 28 posts at Swansea and 23 posts at Holyhead.