Cat Gensets

Don't be too hard on the guy who suggested doing a load survey then add 20 percent to size the generator. That is how generators are normally sized and it is the technique recommended by most genset builders. It allows for load growth.

Oddly enough, I have seen a lot of boats decreasing their loads by replacing older less efficient electrical equipment and lighting.

The upside is that a new genset will be perfectly capable of operating from about 25 percent load to 100 percent with occasional excursions to 110 percent. However, there may be manufacturer's load factor limitations that apply.

For example, if you get a genset with a JD prime mover rated for 60kW and your hotel load is a fairly constant 50kW, you will exceed JD's limit of 67 percent average power over 24 hours. It looks like you will need about 80kW and that is more than the 20 percent increase being sneered at isn't it?

Look at the generator ratings, many of them don't show the lower end but several do and they provide ratings down to around 25 percent. You can operate that low but there is little good reason to do so for continuous operation but it means you don't have to operate at 70 or 80 percent load all the time to obtain satisfactory performance and long life.

It also means you don't have to run two gensets because your loads routinely approach the top of the installed rating. That is just as foolish as grossly oversizing as it means you now have two generators operating at partial load just to stop the lights from flickering and next thing you know you are going to drop a $100K into a silly load bank.

Speaking of which, yes, the SeaClean system can function as a load bank, an exhaust cooled load bank that assists particulate filter regeneration. The only thing leaving the stack is a tropical breeze

Would you mind explaining what a load bank is?

That is what I was speaking to. Loads seem to be getting lighter with the advent of LED lights and more efficient electrical equipment.

But I see your point about lessening the need to run two gensets just to cover a slight over load condition.

Load bank - Wikipedia, the free encyclopedia

I have seen them for more. When you add in the installation of electrical supply cooling water plumbing, pumps and controls then buy fuel to heat the ocean or the chill water loop for a few months and maintain the thing you just blew $100K

There is more cost than just ordering the box of parts.

Thanks for the information.

Using your cost of USD $51000 to buy the box of parts and assuming annual use of the load bank is a conservative 50kW 12 hours each day for 6 months the first year with USD $4 per gallon diesel fuel, we are up to about USD $80K. If the boat is in Europe, add about a dollar to the fuel cost and raise the total to a bit more over USD$ 88K.

That is before shipping the box of parts, and installing the breakers on the SB, running wires, installing piping, strainers, valves, and painting it all.

Looks Like I might have been a bit too conservative.

I am opposed to all forms of artificially loading a generator for no purpose other than to increase the load. If the energy can be used to perform some useful work, then it may be worthwhile.

Heating the ocean is not doing useful work, especially when the cost of fuel to do so can exceed $200 per week.

Not to mention that the addition of heat to the ocean will increase the local evaporation rate and salinity!

Marine Generators

Some general comments:
1. The worst situation for marine gen sets its to NOT RUN.
2. The poorest situation other than #1 is to run occasionally at light load.
3. The best situation for marine gen sets is to ALWAYS RUN and maintain load 75-90%.

Its about that simple. All electrical equipment is rated on temperature rise as that directly relates to load. Now if the electrical equipment is not operated at proper temperature and load, just like diesel engines, it significantly shortens its life. Intermittent running is just as bad... use it or lose it. Windings develop micro cracks in the insulation but this does not effect operation except if the thing cools off and has condensation develop on the windings this wreaks havoc as it degrades the insulating varnish faster and opens the micro cracks. This must be monitored with insulation testing of the windings and other components in a marine situation routinely. This is done with a little test instrument that generates a high voltage and measures the charge leakage via a ohmmeter from the equipment being checked... a megger.

Megger Insulation Resistance Test | EEP

The various voltage control schemes (directly tied to generator design) used depend largely on the application size. Generally now-a-days they are solid state. Just like the varnish on winding solid state electronics do not like on and off cycles and prefer continuous operation. The reasons are actually quite similar.
Operate the equipment at a constant within spec. load condition (read temperature) and it lasts for a long time. Don't and it goes bad quickly particularly in marine environments.

Most any brand equipment if run continually will be better than the best brand run intermittently. That is the key... seem to say the same over and over because it is true.

Brand wise I have preference to CAT... but that is mainly loyalty to investment!
I actually consider your dealer service situation and you (if any) engineer taking care of the equipment more important than brand. Get good service guys and good maintenance and operational care you cannot really go to wrong. If you CAT mains and CAT generators and a good service situation and you spend the money needed to keep it up you are set. It's like fuel good fuel has few problems bad fuel no matter how cheap is more problem than its worth.

Now design wise... a very good experience marine servicing dealer can help but get professional experienced marine advice in the design selection phase... this is cheap in the long run. Classed boats have less margin for error and it is partly why you pay the Classification costs in the first place!

Testing Insulation Resistance

How to do insulation resistance testing is the same on motors, generators, transformers, switch gear etc.

How to measure insulation resistance of a motor | EEP

It may seem strange to many but all electrical components are basically the same. Contactors and Switches have coils operating them, motors have coils (even a squirrel cage rotor of an induction motor is a coil), transformers are nothing but coils of wire (but don't get the mechanical stresses of motors and generators... but do get the thermal and electrical stresses along with the environmental conditions), even simple wires are insulated.

On boats in the marine environment the biggest safety and operational failure issue on electrical and electronic equipment is insulation resistance failure. As the original article I posted previously states a motor or generator can be safe to touch but still experience failure due to stray currents from insulation failure.

Diesel engines have their own problems too... which I am sure many here can relate better than I.

The point is on generator sets and electrical equipment most of modern yacht operation and convince depend of proper operation of the electrical plant no matter how small or large the craft. If not properly designed, installed and maintained you can either develop electoral shock hazard safety issues or failure of the equipment. Unfortunately, failure of the equipment often results in a safety as sea issue. Even in the marina stray currents can cause bad things to happen... like galvanic corrosion that his extreme. Dock a a well regulated marina (like in Monaco) and you will find out you may be unwelcome guest if you don't have things well under control.

I often see many feel oh it is just a generator set... but lose it as sea and you will be crying a different story... and may experience a YF story of a burn to the waterline fire or sinking... we all wonder and speculate about... and maybe loss of life to go with the loss of the boat. It is a realm for professional advice, consultations, design, installation and maintenance not some mysterious thing that just runs below deck that is inconvenient when it does not work.

And I know of a set of C 18's used as Gennies that have gone over 20k hrs no major problems. Always run above 70%

Hi,

With a displacement hull you should try to get your engines rated to run at 80% MCR at cruise, you will have some left for your occasional top end runs and they will run happily for a longtime if the selection and maintenance are both well done.

Semi displacement are neither planing nor displacement so the usual rules have to be adjusted a bit.

Are you looking at SD for speed? By this I mean shortest time between points?