I don't entirely disagree yet would like to point out a few ideas. With the increase in marine traffic it is neither safe nor prudent to go cruising without a diesel
engine. As such that engine MUST be always kept in reliable running condtion. PV and wind
generators, therefore, must take secondary priorities...they just are not safety
The center of the "bell-shaped curve" of cruising sailboats describes a 40 HP diesel and around 400 Amp-hour battery bank size which supports a less than 50% depth-of-discharge daily cyclical use of energy with ease. The daily energy consumption
is around 150 Amp-hours (again I am describing the general overwhelming numbers of users, not the extreme ends). With a properly set up adjustable s-step alternantor regulator and a 165A hot rated (you can get close to 200A cold) alternator you have a large frame unit (that means 1 inch larger in diameter to the usual 105A small frame units) you can recharge in about 1 hour a day of engine run time if you have no additional sources of power like PV or wind
. The cruising design must not be dependend upon wind or sun to be reliable.
What really makes this work reliably is a properly designed pulley ratio and often a custom alternator mount with dual 1/2 inch belts. The alternator bearings are huge compared to the small frame ones and will last a very long time. So will the belts. What you might not realize is that with the proper pulley ratio you can pick a "nice" fast engine idle speed which does not cause undue noise
or vibration, such as 1300 rpm
. With the correct pulley ratio you can properly load even a 50 HP diesel at that rpm
using just the alternator and not have problems attendant with unloaded diesel operation...look at your HP/touque/fuel consumption
curves versus engine rpm and THAT is the answer. You DON'T GET 50 HP from a 50HP diesel at 1300 rpm.
As the rpm drops the alternator output current
versus spindle speed curve drops thereby automatically unloading the engine. Obviously one must check the curves to verifty that at max engine rpm that the max rated spindle speed of the alternator is not exceeded.
I've done this with several engines and the first one that I did in 1980 is still working well with the same alternator. The original Hitachi alternator is also still there running only the engine electrics and, therefore, lightly loaded saving its own belt for longevity.
There are several problems with those small single-cylinder diesel/alternator combos. They are very noisy, they vibrate like hell, the mounts, mufler and everything attached just want to shake off and fatique the attachment brackets, etc. and the overall installation
takes WAY more space than a properly installed large frame alternator on the main engine. Fine for a backup yet the customers with which I am famaliar never have as reliable of an operation than their main engine gives them.