Shipbuilding requires a lot of precision, including the timing of the launch to catch the right state of the tide.
So at 15.47 hours on Monday 11 October, very precisely, more than 6,000 tonnes of the good ship Duncan should be heading down the slipway at the Govan shipyard.
To catch the right state of the tide earlier this year, a patrol ship for the Trinidad and Tobago navy had to be launched in the middle of the night.
But what's the state of the tide for BAE Surface Ships' order book? Coming in or going out?
What it doesn't feature is much precision.
The history of the Type 45 Destroyer programme, of which Duncan (the seventh in a line of ships named after an 18th Century Royal Navy admiral) is the sixth and final ship, suggests plans change, and they change a lot.
Twenty years ago, when the Type 45s were first planned to replace Type 42, there were supposed to be 12 built, then eight, and for the past two years, only six.
But even with six, the programme is £1.5bn or 29% over budget, taking it to £6.5bn and it's two years behind schedule.
Last year, the Common's Public Accounts Committee was scathing in its assessment of what that says about Ministry of Defence procurement.
Part of the problem is that these ships are so complex.
Around 80% of the weapons and defence systems on it are new, and there wasn't an adequate assessment of the management risks associated with that, notably for the main missile defence system, designed to spot sea-skimming missiles.
The other problem with being so complex, and expensive, is that no-one else wants them.
Only the US does more complex ships, so this is not a design that can be sold for export.
That's what the Ministry of Defence and BAE Systems hopes to change with the Type 26 combat ship intended to replace the Royal Navy's current fleet of frigates.
With a standardised design, they hope they can sell it to other parts of the world.
A Memorandum of Understanding with Brazil was recently signed with the UK Government, which offers some hopes for naval exports.
India is building up its navy too.
Indeed, if you look at naval spending in Asia, it holds some of the best hopes for the Clyde.
The economic rise of China is associated with a fear about its military rise as Asia's superpower.
But with austerity across Europe, military spending is being squeezed tight, and nowhere tighter than in the UK.
That's brought into question the future of the two giant aircraft carriers being built in seven locations around Britain, the largest chunk of work on the Clyde, before floating to Rosyth in Fife for assembly.
What we now know is that the contracts were constructed as a sort of legacy to the shipyards from the outgoing Labour government.
Build two ships, and it costs £5.4 billion (it started at £4bn, and it's just crept up by £200m), but build only one and it costs £5.7bn.
The next bit of Labour's legacy was the Terms of Business Agreement signed last year with BAE Systems.
It promises a flow of shipyard work until 2025, mainly on those Type 26 ships, also known as Future Surface Combatants.
The idea is to build at a rate of one per year.
That agreement was followed with a £126m contract to start the design.
The deal required BAE Systems to slim down its capacity, but it's not clear how many of the 4000 current workers on the Clyde can expect to be shed.
Of Govan, Scotstoun and Portsmouth - BAE Systems' yards - it made clear there won't be enough work for all three. The only way to keep them all open is with export orders.
What's not clear from the high-level and very public lobbying over the carriers and the future of the MoD budget is whether this Type 26 programme is in play or whether it could be one of the victims of the capital budget squeeze in the second half of this austerity decade.
And of course, if both carriers don't go ahead, don't assume there will be the capacity, at least in terms of skills, still around for the time when Royal Navy orders get started again.
The threat, if a flow of work doesn't remain steady, is that the future Royal Navy will have to be built outside the UK. How much does that matter?
The uncertainties leave big concerns over the Scotstoun yard in particular.
It specialises in engineering work, outfitting and systems integration, with investment in docking facilities, but it's not where the investment has gone into building hulls.
One yard insider tells me that most of the staff are soon to shift across the river to Govan, more than halving the numbers in Scotstoun.
It's a flexible workforce across the two sites, so it's not a permanent departure for Govan or Rosyth, where 600 or so Clyde workers will work on the carriers as assembly works steps up.
But there are those at senior levels in the yards who are pessimistic about Scotstoun's long-term future.
It was once the case that a squeeze on military spending could let the Clyde focus more on commercial shipping, but other countries' shipbuilders now specialise in that.
The boom in offshore renewables could produce some fabrication opportunities. But even when Cal-Mac comes looking for new ferries, it's hard to see how Scottish yards can compete with the Baltic.
Then again, the European Commission has just begun a review of its unusually generous state aid rules on shipbuilding.
Could that help UK yards get back to a level playing field?
It looks a bit late for that.