A couple of years ago we replaced our old Babbitt stern bearing with a new high-tech plastic. Last week we discovered when we removed the propeller that the new bearing had shifted and was somewhat chewed up inside the housing. This was one of those projects we had not planned on doing since we were under the impression that it was good-to-go forever. The question that Jeffrey has been pondering for the last week has been whether to try another new plastic bearing or to go back to the original technology of 1929 with a poured Babbitt bearing.
We decided to go with the Babbitt option since the bearing that we replaced had lasted for more than 75 years and the new one had lasted for just two.
In case you are wondering what Babbitt is, it is a soft-metal concocted by Issac Babbitt in 1839. It’s properties were developed specifically for engines as a way to decrease the amount of expensive oils being used to cool brass bearings.
In 1848 Babbitt applied for a patent and submitted numerous letters and references concerning bearings that were being tested with his soft-metal. The letter below is from the Secretary of the Navy and describes the benefits of using the new metal for bearings.
Washington, April 15, 1842.
Sir : Referring to a conversation with you this morning upon the merits of Babbitt’s anti-attrition metal, I beg leave to submit, that Mr. Babbitt’s invention consists of substituting a soft unctuous metal, for the hard brass or composition heretofore used to sustain the journals and other moving parts of machinery; which soft metal is enclosed in ribs or ledges of harder metal, to prevent its being spread by the weight of the shafting or pressure.
This metal has been long enough in use fully to test its merits, and I have no hesitation in saying, that it is one of the most valuable improvements, in the construction of moving machinery, that has come to my notice.
The effects produced are,
1st A great diminution of friction.
2d. A saving of oil to the extent of one half or more.
3d. An economy in the original construction, as the brasses which receive the journals may be made much lighter when lined, than when they come in direct contact with the hard metal.
4th. A saving in repairs, as the soft metal will wear longer than the hard, and they may be relined at small cost.
5th. A saving of fuel consequent upon a reduction of friction.
My opinion is, that the introduction of this metal into the government steamers will be of essential service.
I herewith transmit a copy of a letter from Capt. J. Erricsson,>the engineer employed by Captain Stockton to superintend the machinery of the ” Princeton,” United States warsteamer, which gives his view of the subject. Long experience in the use and construction of machinery, entitles his opinion to great weight.
I am, with much respect,
(signed) S. V. MERRICK.
Hon. Abel P. Upshdr,
Secretary of the Navy.
So now that we’ve decided that we are going back to a Babbitt bearing Jeffrey’s dream of playing with hot molten metal is going to be coming true this weekend or early next week. We have 20 pounds of Babbitt on the way and it’s a special lead-free mixture of 88% tin, 7% antimony and 3% copper. We will be melting down and pouring between a mandrill and the housing. Once it’s cool we’ll be able to break it free and send it to a machinist who will be boring out and in a couple of weeks we should have a shiny new stern bearing.
I’ll be posting pictures of the pour when it happens so standby…
Here’s a link to the Patent Report published in 1848.