All systems go!
For many engineers, this is where the “real” hours are put in, especially on a Kraken. We have to dedicate a lot of time to ensure everything is sized and installed properly. The walk in engine rooms are a testament of that. Before you lay all of the valves nicely on a wall, you must first design the system. This is what we are going to focus on in this article.
Referring to the design spiral, we are coming off the general arrangement and onto the systems. The main systems, such as drive system, i.e. prop shaft, propeller, engine and gearbox and the steering system will generally remain constant, but other systems may vary according to the options the owner has chosen.
When starting systems design, especially during the first trip round the design spiral, I like to establish the defining points on a few key systems:
Propulsion & Stern Drive
I would look at the resistance figures of the hull, desirable cruising speed and top speed to size an appropriate engine. On the Kraken range, we work with Yanmar common rail engines with very good results. On the Kraken 58 the hull speed is 9.6 knots and there is no point to try and achieve more under engine alone as resistance peaks and therefore fuel consumption increases significantly for very little increase in speed. The general cruising speed will be around 7-7.5 knots.
With this in mind the correct engine size is the 4LV150. With 110kW peak power it will push the boat at around 9.5 knots max speed and with peak torque at 1700rpm. Its cruising speed of 7.5 knots is also very suitable and at 1700rpm it achieves a cruising speed of 7.5 knots. At this speed the cruising range is maximised due to fuel consumption of only 5 lts per hour.
To achieve the best performance from the engine and gearbox we calculate we need a four blade 22’ Bruntons Varifiold propellor. This excellent prop, which is fitted as standard on the Kraken 58, is chosen because it provides excellent forward propulsion whilst also giving good reverse gear performance and is fully auto folding when under sail.
Here we want to follow the very robust rod steering system we used on the Kraken 50, but up spec’d to deal with the heavier loads produced by the larger Kraken 58 rudder. We work with Jefa Steering for our steering and autopilot systems, which allows us to install the autopilot in the cleaner, dryer and more accessible engine room, rather than the aft lazarette.
This design is based on torque tubes and bevel boxes. We like it because it is all but maintenance free, whilst having almost no play and good autopilot integration. Because the design office is familiar with this system it is relatively straightforward to prepare for it. At the early stage of design, we have to ensure that there are no surprises, like component load limitations or production discontinuity.
Overall this is the biggest single system onboard, especially if digital switching is involved. In the initial design stages we consider the following:
- The basic consumer list. All major consumers need to be identified, how much power can be pulled at once, how much of that in AC and how much of that in DC. How much in a standard 24H period.
- With power scenarios established we can focus on how to power it, what generator and how big. Onan is our go-to supplier but we are looking at alternatives based on recent developments in the field. Especially if hybrid propulsion is on the cards.
- The generator provides AC and the house battery bank provides DC. A way to convert from one to the other is via an inverter charger, in our case this is a Victron Quattro. Sizes vary depending on the consumer list but a 6.4kW unit can happily supply the needs of the basic spec boat.
- Battery bank capacity is sized up next. All our boats are 24VDC and the house bank follows suit. If we use AGM cells then we run the batteries in a series of 2 to step up the voltage from 12V to 24V. With lithium cells, we fit 24V batteries from the get-go. Here we have to work with the client as to what they want to achieve. We arrived at the standard capacity of 960Ah as a very comprehensive package that should see most owners satisfied, but if the brief from the client is to achieve silent running of the aircon overnight, then the battery bank must be sized up.
- This owner has chosen a modular EmpirBus digital switching system combined with MG systems Lithium Batteries, so the electrical systems will be up to the minute state of the art.
- With the basics covered, the system can be understood and space for it is allocated on the boat. This is enough for the initial design. This also allows for an electrical subcontractor to start work on cable lists, detailed wiring diagrams and BOMs (bill of materials) which can all be integrated into the design. If digital switching is selected, this is when it gets integrated into the system.
What’s outlined above is of course not the whole boat, items like windlasses, bow thrusters, watermakers, air conditioning etc all have to be designed in and with full access allowed for maintenance, servicing and repair or replacement, should the need arise in the years ahead. We follow pretty much the same process in all Krakens; outline the system requirements, size up appropriately, make sure it fits and integrates with the rest of the boat. The “does it fit” part is especially interesting. One of the first things an engineer would do is draw up a simple box of the outside dimensions of whatever it is they are working on to check if there is enough space for it in the boat. At the early stage of design, when all systems are being hashed out, the inside of the boat looks like a messy garage with random shaped boxes all over the place. We use full 3D modelling for the interior and exterior layouts, which gives the design team maximum flexibility should the owners specification change as the project progresses.
The biggest challenge is the full integration of all elements of the various systems into the finite space we must work within. As an example, consider the air conditioning system, which may be technically described as ‘stand alone’. They are however, far from being able to be installed independently of all the other considerations we have in every area, they and require:
- Raw water system for cooling water
- Grey water for the condensate
- 230VAC electrics for the handlers and main chiller unit
- 24VDC for water pumps
- Its own 24VDC circuit with integration to Victron/Empirbus
On top of that, there are all the interior considerations in terms of vent location and sizes which play an important role in the interior layout and styling. This is also a good example of why there are numerous passes around the design spiral, with so many interlinked systems you can never account for every variable from the start, corrections and updates must be made as the design progresses.
What comes next?
In the next instalment, we will focus on the structures of the craft. Yet another interesting topic, specifically given our unique design approach to keels, skegs and more.