Where can I find more information about “pillow block bearings” that you mention in your book Offshore Cruising Encyclopedia under the section on Mega Alternators (page 870).
We have a Northern Lights 8kw genset aboard and I would like to mount a high output alternator on the unit. Presently we seldom place much of a AC load on the unit and by placing a big alternator on it we could “kill two birds with one stone”; charging our battery banks as well as providing AC needs and placing a reasonable load on the engine.
The folks at Northern Lights were not overly excited about this idea (side load on the front seal and bearings). Space constraints do not allow for an opposing “slave pulley” to offset the side load of the proposed alternator.
I noticed in your book a reference to a “pillow block bearing” which alleviates the side load problem. Any other ideas would be greatly appreciated. Fantastic reference book. Thank You, John and Deanna
Hi John and Deanna: Pillow block bearings are available from any industrial bearing supply house. The tricky part is how you support these.
In most cases the support picks up the front and rear mounts of the genset or engine, and projects forward. Sometimes there is enough of a bolt pattern to just put a set of mounts sandwiched between the forward mounts of the diesel–but usually it is best to pick up the forward and aft mounts.
What you do not want to do is to mount the bearing directly onto the boat as it will then not vibrate in sympathy with the engine–which will cause all sorts of problems.
The next step is a “stub shaft” which attaches to the front power take off on the crank shaft. This stub shaft includes the various drive pulleys, and a projection forward which is supported by the pillow block bearing.
The alignment must be engineered correctly–otherwise the front bearing and seal will give problems on the diesel.
There are two other approaches. One is to have dual, opposed alternators. Since you do not have space consider adding one or two really large AC battery chargers, rather than the alternators. It may end up that this is a simpler, less costly approach than trying to re-engineer the front end of the genset (although we use pillow block bearings on a common basis on our systems, we are working with ship engineers who are familiar with this approach, so it is cost effective). Good Luck–Steve Dashew
Posted by Steve Dashew (November 30, 1999)
