While the Whanganui ferry link has been flagged before, he has taken a different approach.
"No one had gone to the marketplace - the transport industry especially - to assess their interest in a shipping service through Whanganui to the South Island," Mr Johnson said.
Using the Whanganui District Council-owned port at Castlecliff would not need any ratepayer contribution, he said. In broad terms his idea is to dredge seven metres depth in the port and through the harbour entrance.
The southern terminal would be through Motueka's waterfront, and the same issues would need to be overcome there - creating a serviceable depth in that port and reclaiming much needed land behind the wharf to handle the vehicles coming on and off the ferry.
"Whanganui's never had sufficient traffic to warrant continual dredging but without shipping and the berthage fees the dredging isn't going to happen or be funded.
"It has been dredged to seven metres before and it worked, but you can't dredge it once and leave it - it needs regular maintenance."
Mr Johnson said he had spoken to port operators including Gisborne which has a highly viable port. But again the key was constant dredging.
"They have large log boats going in there and now they're on the cruise boat schedule, so it can be done."
He said a Whanganui-Motueka ferry would work because it cuts hours of travel time for transport companies.
"We're looking at a ferry 135 metres and drawing about 5.5 metres. You'd get a maximum of 40 truck and trailer units on a vessel that big."
But it's not just trucks. Midwest Ferries would target campervans, cars and passenger fares.
"We reckon 28,000 crossings a year makes it viable. A crossing in this instance is one vehicle going one way."
Six years ago Mr Johnson canvassed the transport industry (he was secretary of the Road Transport Engineers Institute for some time) and said the response was overwhelming.
"On the basis of that work we had 42,000 indicative crossings from about 80 transport industry operators."
A Whanganui link cuts four hours off travel time for trucks going from Auckland to Christchurch, over Cook Strait through Wellington and Picton.
"The saving that brings for the industry is massive - and this is before we looking seriously at tourist buses, campervans and the like, attracting vehicles down State Highway 4 rather than State Highway 1."
If the service does eventuate, ferry would berth at the number 3 wharf at Castlecliff.
Mr Johnson has had several discussions with the Talleys about using Motueka.
"Just like our plans for Whanganui, we'll do the dredging and reclaim the land at no charge. Because we have to create our own facility to berth the ferry then the deal is we don't pay berthage."