We too replaced our Volvo 21B (rememvered on this boat as "that green piece of s@#t) with a Yanmar 4JH3. The Volvo drowned itself when the raw water pump seals failed - both of them - but we were happy to pitch it anyway, no support or parts from Volvo, and what was available was very expensive. We also replaced the prop and got estimates on diameter and pitch by e-mailing for prop analysis from various different prop shops. There are several different algorythms for "guessing" at size and pitch, but they all take into account the displacement of your boat, the horsepower at cruising RPMs of the engine, and the reduction of the transmission, and what type of prop (2 or 3 blade, rabbit ears or slim, etc.) so you get something that is specific to your situation. It is a bit of a guestimate because we got back four different size/pitch estimates and wound up taking the average on pitch and the largest diameter, which has worked for us. (We got a feathering prop which could be changed
in pitch anyway, but never had cause to change it once we installed it.) The Yanmars came with an attached transmission, so we had to shop for the "combination" and got an engine with an 8 degree inclined transmission with mirror thrust bearings, so it could work just as well turning clockwise or counterclockwise. (Kinda handy because if your transmission ever fails, it usually fails in forward gear. Then you change the "hand" of the prop, e.g. right hand to left hand, flip the lever on the tranny, and away you go in forward but with no reverse gear.) The inclination was nice because the engine sat almost horizontal, so the forward valve stems and springs got lubricated with oil too, just like the ones in the back. They last longer that way...
Good luck.
Michael & Elizabeth Kramer
S/V Cambria

N.B. We also did the change in the water. You can even change the prop shaft in the water. We just stuffed a short piece of 1.25" stock into the shaft log after pushing the old shaft out, tightened the short piece down, then pushed it back into the boat with the new shaft from outside (somebody in the water pushing) when the new shaft was ready fro0m the machine shop.




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Received on Thu Oct 27 17:08:25 2005