Following cuts to the service, responsibility for the west of Scotland lies with Belfast, in Northern Ireland.
The SNP said figures it has seen show Belfast has the biggest understaffing problem in the UK.
Previously concerns were raised about levels of staffing in Aberdeen.
The figures, obtained by campaigners against coastguard cuts under freedom of information laws, showed Belfast with a high number of shifts when staffing was "below safe risk' levels.
It ranged from 8% in October to 85% of shifts in June when levels were not considered safe.
In Aberdeen, the levels were from 11% in October to a high of 53% in December.
Over the year, Belfast had the highest average of unsafe staffed shifts at 56.9%. Aberdeen was 39.9%, compared to the lowest, Milford Haven at 3.8% and Brixam at 4.1%
Stuart McMillan SNP MSP for the West of Scotland said it was proof the decision to cut the Clyde Coastguard Station at Greenock in December 2012 was wrong.
He said: "These latest figures make worrying reading, and demonstrate the utter folly of Westminster's decision to axe the Coastguard centre on the Clyde.
"Closing the vital centre on the Clyde and losing valuable local knowledge was bad enough, but for the replacement service in Belfast to be dangerously understaffed is completely unacceptable and puts lives at risk.
"Scotland's Coastguard services are poorly served by Westminster, and it is no wonder that experts are calling for responsibility in this area to be held by the Scottish Government."