Tasmania's largest shipping company says it expects its Devonport operations will be "substantially" impacted by a stop-gap measure to accommodate the new Spirit of Tasmania ferries and fears there is a "huge" risk of collision.

SeaRoad executive chair Chas Kelly told ABC Mornings that "when ships are getting very close together — everything's good, until it's not".

"That could, in our view, put us both out of business for a substantial amount of time," he said.

Port infrastructure at Devonport's berth 3 — set to be the permanent home of the new larger Spirit of Tasmania vessels — has been struck by delays.

When the first of the new ships arrive in the coming months, they will dock closer to the mouth of the Mersey River at berth 1, where the current spirits do.

However, that berth is smaller — impacting access to berth 2, where SeaRoad's two freight vessels operate.

"The current Spirits overlap the stern of our ships, and the longer ships [new ferries] will overlap them substantially more, which means that when we arrive we've got to go past them and then reverse back into our berth, which is a big risk," Mr Kelly said.

He said the Spirits should run a modified schedule given the situation was of ferry operator TT-Line's making.

SeaRoad operates an each-way, six-day-a-week service between Melbourne and Devonport with its two current vessels, the MV Liekut and the SeaRoad Mersey II.

It is also in the process of upgrading its fleet, with the new SeaRoad I arriving next year.

Harbour Master Captain Mick Wall said risk mitigation measures had been introduced and would be assessed going forward.

"Further simulations for SeaRoad have been scheduled by them for late September and this is part of the continuous risk management approach being undertaken," Mr Wall said.

TasPorts CEO Anthony Donald said both the Major Projects team and the Harbour Master would continue to engage with SeaRoad throughout the berth 1 project.

"We respect SeaRoad as a key customer and we are working with them on all opportunities to minimise disruption and optimise commercial shipping," he said.

The potential impact on SeaRoad's operations is the latest development to hit the troubled Spirit replacement project that has already cost former TT-Line chair Mike Grainger his job.

Delays to the port infrastructure were only revealed in recent months, with the government announcing plans to upgrade berth 1 as a temporary measure while berth 3 works were underway.

However, due to size constraints at berth 1, the new vessels will only be able to carry the same capacity as the older ferries.

State Opposition Leader Dean Winter said he was concerned about berth 1 being used to cover for the delays to port infrastructure, given the safety concerns raised.

A government spokesperson said TasPort was "continuing to work with TT-Line and SeaRoad on all opportunities to minimise disruption and optimise capacity in a way that supports all our port users".