Seatrial

Yanmar requires an inspection of the engine installation by a qualified mechanic prior to activating their warranty. This inspection involves a physical examination of the engine installation as well as a set of measurements made underway. The inspection checks the integrity of the engine bed, air-flow, wiring, and similar measurements. The performance measurements check exhaust temperature, boost and back-pressure at various engine speeds. The inspection process takes about three hours, and is not included in the cost of the engine purchase. My inspection was done by a local Yanmar distributor, Winter Island Marine. The mechanic was very pleasant and seemed knowledgeable. I recommend their service. I had some difficulty scheduling an appointment with them because they were busy with already scheduled work during the spring. By the time I was able to get an appointment, I had about 70 hours on the engine. The regular maintenance schedule requires a valve adjustment at 50 hours. Had I thought ahead, I would have had the valves adjusted at the same time. Backpressure and exhaust temperature were measured by drilling small holes in the exhaust hose and inserting probes. The holes were later closed by inserting machine screws. The boat was taken out and run at specific engine speeds as shown by the stock tachometer. The actual engine speed was recorded by a separate instrument. Actual boat speed was measured using a GPS. Two runs were made, one out of the harbor and the other on the return. There was light wind at the time and the seas were flat. The boat bottom was clean. The refrigeration compressor was turned on and the batteries were partially depleted. The inspection went well. The only defect noted by the mechanic was the wire size I used for the starter battery. I used 4AWG battery cable for a run of about 6 feet. The mechanic recommended heavier wire. As noted on the Yanmar help pages, the engine tachometer read a little high at the top end. The tach showed about 4050 RPM at full throttle whereas the calibrated tach showed 3950 RPM. Test runs showed that 2500 RPM gave a good cruising speed of about 7 KTS. The boat would reach 7.4 KT hull speed at about 2800 RPM. More power could push the boat to 7.7 KTS. Most of this power went to creating a wake. Yanmar recommends that this engine cruise at between 2500 RPM and 3200 RPM, so the engine/propeller selection appears correct. I discussed engine choice with the mechanic. Specifically, I wanted to know if he thought the smaller 54 HP 4JH3 engine would have been sufficient for this installation. The mechanic indicated that since I have a large second alternator and refrigeration compressor, the larger engine is probably justified. In his opinion the smaller engine would probably work fine in similar installations that don't have these accessories. I don't think the accessories take much power. The compressor takes about ½ HP. The alternator will take about 5hp during the initial charge cycle, but will taper off to less than 2hp after the first 20 minutes or so. This means that the accessory load is typically less than 2.5 hp. In my opinion, the smaller engine would work fine, but you would probably need to run the engine hard to reach hull speed. With the larger engine, I can run the boat at hull speed while keeping the engine well within recommended cruising speed. As an example, I recently cruised from Provencetown on Cape Cod to my home port north of Boston. I hit some rough chop off Race Point, a streach of water off the tip of the cape known for rough seas. The seas and wind were right on the nose for about three hours. I had no trouble powering through them at close to hull speed, passing several other boats who having trouble pushing through the waves. There is a small but annoying vibration at about 2800 RPM. The boat runs smooth at speeds below 2600 RPM or above 2900 RPM. The mechanic indicated that this is not of concern. Many installations have similar behavior, typically caused by a natural resonance in the drive train. This can sometimes be improved by changing the geometry of the running gear such as moving the zinc. He suggested avoiding this speed if it bothers me. This is unfortunate, since this particular engine speed is where the boat reaches hull speed. If I am in a hurry, I'll have to run the engine at 3000 RPM, sacrificing some fuel efficiency. After discussing possible causes of this vibration, I suspect that it may be caused by a shaft that is too long. There is about 5 inches of shaft between the back of the cutless bearing and the propeller hub. The mechanic indicated that the maximum length here should be no more than 1.5 times the shaft diameter, or 2.25 inches. I'll re-machine the shaft this winter and see if the vibration improves.

After adding up estimated costs of the engine, fuel-tank, v-drive, and other items, I estimated that the repower would run me about $16000. I kept track of my expenses as the project progressed. I kept receipts for almost everything, including indirect charges for things like hauling and launching. Receipts added up to $21,175. I've attached a spreadsheet to this page so that others can fill in their own estimates to see what they should budget. My budget included some items could possibly be avoided such as a new propeller. I also tried to keep track of my labor. This is difficult to total because I would frequently spend just a few minutes on a task before getting distracted by other houshold chores. I also spent quite a lot of time scratching my head to figure out how things would fit. I estimate that I worked about 300 hours on the repower. An experienced mechanic could probably do this in less than half this time.