The cash shortfall must be bridged to pay for the 1947-built vessel’s winter maintenance in dry dock so she can sail again next summer.
An appeal was launched in September after the ship lost almost all her income this year by only being able to operate for two weeks because of the Covid pandemic and a collision with Brodick pier in Arran.
Paul Semple, general manger of operator Waverley Excursions, said £130,000 of the £500,000 needed by April had been raised so far.
He said: “As we stand at the moment, we don’t have the funds to complete the refit.
"The single biggest expense within the refit is the annual dry docking.
"If we don’t secure sufficient funds, then Waverley can’t move to dry dock on time, which then risks the 2021 season.
"We must be confident of meeting the full cost of dry dock before she goes in.
"If she isn’t dry docked, she will not be able to enter service.
"Next year will be the 75th anniversary of her launch.
"When the ship did sail this year, passenger numbers were limited to under 30 per cent capacity, resulting in a dramatic reduction in income.”
“Waverley normally carries over 100,000 passengers annually, but this season we saw fewer than 6,000 aboard.
"The ship needs to operate a full summer season to earn sufficient funds and cover costs.
The work in dry dock will include replacing the bow which was damaged in the collision, although the cost of that will be paid by insurance.
Waverley’s current plight comes after she missed last year’s season – only the second in her history – while undergoing a £2.3 million boiler replacement.
A total of 24 people were injured in the Brodick collision in September which happened as she was about to berth at the Arran port.
A law firm this month launched a damages claim on behalf of two passengers which it said had suffered unspecified “terrible injuries” in the incident.