Machinery and hydraulics is about how you move, control and steer the boat. Of course this includes the engine which generally moves you backwards and forwards, with the help of a propeller. But there are also several other bits of equipment to help you with that! Bow and stern thrusters are for sideways movement at the front and back of the boat. They help to turn the boat quickly or move in a sideways direction. The rudder is what steers the boat through the water.

Hydraulic systems use pressurised fluid – hydraulic oil – to drive motors instead of electricity. As a result, there is a network of hydraulic hoses throughout the boat and a 30 litre fluid reservoir at the heart of the system.

Main Engine

Destiny runs on a single John Deere 6090SFM85 marine diesel engine. It has been downrated to M1 rating of 325HP @ 2100 RPM. The engine is a 6 cylinder, 9 litre engine. The tier 3 classification means that it has very low emissions. The engine is carefully balanced with the prop with the objective of producing the most fuel efficient cruising. The calculation of the prop size and pitch, to best work with the engine, was made by the prop manufacturers in Taiwan. During sea trial, we were not 100% convinced that it is correct – so we will continue to monitor closely ourselves in a true cruising environment. Potentially, we may need to make some changes.

Sea trials for Selene can only be done in the area of the local river delta. Due to regulations in China about private yachting, the yard captain is only allowed within a very limited area. As a result, the boat never really gets a proper sea trial before delivery. It’s only possible for a few hours on the water, upstream and downstream, to measure speeds and RPM. Of course , this is enough to make sure things are working – but not enough to properly tweak the configuration. Our shakedown cruises will be a lot of monitoring of systems and performance.

The engine is controlled by a ZF control module at the pilot house helm and on the flybridge, so the boat can be equally driven from either location. The engine is also linked to the Dockmate remote docking module, although driving by remote control is only in tick-over for safety reasons. The performance of the engine is monitored continually by the Maretron ships monitoring system which accurately measures the fuel consumption, distance/range among other things.


We’ll talk more about the electrical generation side of the generators when we cover the electrical systems. In this article, it is relevant to talk about them as engines and sources of hydraulic power.

We have two generators – both of them Northern Lights. The larger one is 26kw (50Hz/220V) and is used as our emergency get home system – with a PTO (power take off) which drives the main shaft. The 2nd generator is a 10kw (50Hz/220V) which is intended to be the day-to-day house generator – although we also have high power inverters, so the situation is a little complicated.

The large generator is required for hydraulic power. It is the secondary “get-home” power source in case of engine failure. In addition, the bow and stern thrusters, as well as the windlass and other equipment are powered from the large generator. The configuration of the electrical system is such that we can run the 26kw only for the purpose of hydraulic power/get home and run the 10kw generator at the same time, diverting all power from that into the house AC system.


When underway – and also when laying at anchor in a bouncy sea – hydraulic stablisation helps to STOP you moving! At least, it stops you moving in the wrong direction and rolling around. The design of a trawler means it does have a tendency to roll from side to side in the waves. When waves come from directly in front or behind, it also pitches (tips from front to back).

Stabilisation works with fins on each side of the boat – “active fins” – which continuously move to keep the boat flat at all times. They have sensors which monitor the movement of the sea and send smooth counter acting energy pulses to flatten the wave impact. We have chosen the StAR system from ABT-Trac – which offers a fully integrated hydraulics package.

Get-Home Emergency System

And what do you do when the engine breaks down and stops running?

With a single engine boat, you need an alternative power source which can provide propulsion to get you back to the nearest port. There are several different options for this and each one has its pros and cons. We have tried to put together the combination of machinery which works best for us. None of the solutions is a perfect choice. They each have their pros and cons and the choice will be a trade-off, depending on your cruising needs.

In making this decision, you need to consider :

  • Cost – both original purchase and ongoing running costs
  • Availability of space in the engine room and how important it is for you to have ease of access to equipment
  • The range you need – if you are cruising coastal where fuel is available, then range may not be the top priority. But for a boat intending to cross oceans, this is a critical factor.
  • Efficiency of operation in get-home mode. How far would you potentially have to drive the boat in get-home mode, and what sea conditions might it need to handle?
  • Importance of redundancy of other propulsion components – such as rudder, shafts and prop
  • Electrical and hydraulic power needs for other systems – do you need a big generator anyway to supply power needs?

Twin Engines

The first, and most obvious, option is to opt for a twin engine boat. If one engine fails, you always have the other one, right? It isn’t often quite as simple as that (we experienced this problem once in a fast sports cruiser we owned!). Twin engines have twin props – which means each one is off centre from the boat. Running on just one of them means propulsion is not central and will be difficult to counteract with steering. The engine is one of the highest cost pieces of machinery onboard – so clearly if you have twin engines, the cost will be much higher.

Twin engines also means double the maintenance costs for oil and parts – but NOT double the fuel costs. Two engines running together would normally be smaller engines than the one single, and although fuel costs are more, they are not double. In an engine room of limited size, twin engines obviously take up double the space – compromises will have to be made and this is often a compromise on the size of fuel tanks. Reducing fuel tank size has a double impact on range – you need more fuel for the same distance as you have twin engines, but you have less fuel available because of tank space constraints – so range is disproportionately affected.

On the plus side, twin engines are easier to manoevre so you may find there is no need for stern thrusters – a potential financial saving but not enough to cover the cost of the 2nd engine. With twin engines you also have full redundancy for all components of the steering system since you have dual rudders, shafts, props and engines.

Wing Engine

The second option is to use a wing engine (a very small secondary engine with it’s own separate prop and shaft). This option does save some space, as it is smaller than a secondary twin engine. However, since the engine serves no other purpose that getting home in an emergency, there is a danger it will never be used and may not work effectively when you need it. Although you do have a separate shaft and prop, this again is offset from the centre line for les efficiency. And, this time, the engine power is much less, making propulsion difficult in a headway/current. Maintenance costs are increased as the engine needs to be maintained even if not used. In this case there is no benefit of savings on other equipment as this engine serves no other purpose. Space wise, you may also find yourself constrained, with no room for other equipment but it is less space than a 2nd main engine of course.

PTO Get-Home

The third option is what is called a PTO pump, which is a hydraulic pump attached to a large generator which drives the main prop shaft and propeller albeit it with less power than your main engine. To generate enough power to drive the boat, the generator has to be very big. For our boat, we needed to have a 26kw (50Hz – 220V) – if you are in the USA (or some other countries), this would be bigger in kW as you are operating at 60Hz and 110V. The generator producing 60Hz would run at 1800rpm instead of 1500rpm, so will consume more fuel – because it is obviously running 20% faster. The results of PTO propulsion are still not ideal.

A generator of this size can have a cost similar to a 2nd main engine – but the upside is that of course the generator is serving many other purposes.

Deck Equipment

As our main systems are hydraulic, we have also taken the hydraulic route for other equipment on-board. This includes the anchor winch (windlass) and crane for the dinghy. All this equipment can also work on straightforward electrical power. However, hydraulic power is more reliable and powerful, with no risk of batteries running flat.

Fuel and Oil Management Systems

Diesel fuel must also be carried in large quantities to run the main engine and the generators. Our tanks have a total of 2200USG (about 8250 litres) – although you can’t access the last bit in the bottom of each tank. It’s very important that fuel is good quality to avoid clogging up the systems – so we have a “fuel polishing system” which treats all the fuel coming into the boat to ensure it will not cause any damage. There’s also a cross-pipe between the two fuel tanks to allow you to keep the tanks in balance, and a network of fuel filters.