Replacing an engine: your thoughts on what unit to choose?

[Tranona]

I don't agree about diesel electric not being viable below 45' in monohulls.

If we started again - with diesel electric as opposed to all battery in mind - then on the Sadler 29 we could fit a 4kW DC diesel-powered generator and at least one 9kWh battery where the Bukh diesel engine used to be. We could fit a smaller diesel tank to reflect the greater efficiency of the whole system, and then another 9kWh battery in the space saved there. Weight-wise that would be about neutral, and that's before we decide to bin the 2x12V domestic batteries (say 50kg) and run that load off a DC to DC converter. We might have got rid of two gas bottles too, if going for an electric galley.

There is at least one Cornish Crabber Pilot Cutter 30 with a diesel-battery-electric pod drive installation. It was at Southampton boat show and not built on spec, ie belongs to an actual customer.

It is definitely possible, just depends if you want it and can afford it. It won't make financial sense on an elderly boat, but often a new diesel engine doesn't either.

A diesel electric system would actually have more range per litre too... if you keep the same size diesel tank it's a way to get more range than a straightforward replacement diesel. And most of the time you'll be motoring around in silent, vibration and fume-free bliss. Even when the generator is running it's likely to be quieter than a diesel propulsion system, and not mechanically connected to drivetrain (soundproof box, soft mounts).

Electric motors are not the problem, they already exist in suitable sizes for powering yachts. Batteries are getting better but still nowhere near the energy density of fossil fuels, particularly if you want LifePo4 (which is the safest chemistry). The energy density issue is not quite as dire as it first seems, because electric motors convert electricity into propulsion much more efficiently than small diesel engines do (heat, noise etc are all waste products but nonetheless represent energy consumed). But still you get a lot more miles from a kilo of diesel than a kilo of battery.

I remain in agreement that it wouldn't suit everybody but price apart either "all-battery" or "diesel-large battery-electric drive" can be made to work in most scenarios.

The pollution point. Yes you could argue that chucking out carbon monoxide, nitrogen oxide and particulates (soot) from a not very efficient (by modern automotive standards) diesel engine doesn't really matter at sea, especially in the context of oil tankers and container ships. But it's still harmful to the marine environment, and also those on board if you're motoring downwind. And we are non-essential leisure users... sooner or later there will be tighter legislation, for new boats at least.

Ian, Nestaway Boats

It can be done physically - and has been more than once. However that does not mean it is viable in terms of getting the best out of the propulsion and generation system. By that I mean when you get to that size boat the space and complication drawbacks become less of a problem and perhaps more importantly the electricity requirements for other than propulsion potentially become greater - electric cooking, air conditioning etc. It does not become more economical in terms of propulsion because of the losses converting diesel into electricity then into propulsion rather than direct from diesel to propulsion. it only starts to make sense when the majority of power requirement is for non propulsion, hence its almost universal use on cruise ships - but not on cargo ships.

Despite both hybrid and diesel electric systems being on the market in one form or another for over 15 years the take up has been minimal. Sure, there are boat like the Crabber or the various Spirits but these are one off indulgences that simply don't stack up in the mainstream market. sure pods, regeneration, better batteries and control systems start to sove some of the problems, but there will never be the volume to justify the research and mass production to make them viable alternatives to cheap industrial diesels.

Really no different to cars. Premium small volume (relatively) cars are price competitive with IC in total usage (initial cost and lifetime running) but only because of the huge subsidy on fuels and the lower proportion of the initial cost being for the propulsion. 40-50% premium in initial cost for small cars and a substantial reduction in usability because of the limited range.

 

[penfold]

Yes but if is not actually green, which batteries are not - and there is no great need to restrict local pollution, which is a non issue for sea going small liesure boats - and electric generation is heavily dependant on fossil fuels, which it will be until new nuclear comes on after the normal 25years -then the only motive to change to battery electric seems to be a quieter drive train

Added to that electric is essentially more vulnerable to sea atmosphere damage than the humble diesel and seems to cost twice as much for less capability

Striving for less bangs for your buck??

"These new-fangled internal combustion engines are much more vulnerable to sea air than the humble steam engine."

The cost per kWh of batteries falls annually. Electric drives allow better packaging and weight distribution, no need for an exhaust, one less seacock, no fuel tank, no soundproofing.

 

[jdc]

One kWhr from a diesel engine makes about 767g of CO₂. The UK's latest figures for the grid produces 193g per kwhr.

It's therefore simply not true to say that electricity generation is so dependant on fossil fuels that electric propulsion's saving on CO₂ is not worth it - electric propulsion is better by a factor off 4, and it's getting better year on year, provided you charge from the grid not from a diesel generator.