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Archive for October 2nd, 2008

You may have followed the post about the demise of our dinghy’s outboard motor. I’ve decided that we’ll buy a new one in the spring but it was a disappointment to lose this essential piece of cruising equipment.

Now it looks like our sailboat’s main auxiliary power plant has gone to diesel heaven. &%$#@%!!!

We’ve been having trouble with it since the spring. Problems first showed up on the yacht club’s opening day. The engine began stalling when it was in gear and at idle. This makes slow speed maneuvering and docking perilous because as soon as you drop the RPMs to idle the engine would stall. I had our mechanic take a look at it and he determined that there was resistance in the transmission. After they changed the gear lubricant it seemed to improve a little. The lubricant was in terrible condition. There were lots of clutch pieces in it and it had a burnt odor.

The next issue that they called out was that the propeller was over pitched. A boat’s engine has three critical factors that have to be balanced: the engine’s optimal cruising rpm, the boat’s hull speed and the configuration of the propeller.

  • A diesel engine has an optimal power band. It should do most of it’s running in this band or it will tend to become caked with carbon inside. Our old Universal M4-30 has it’s band from 2900 rpm to 3500 rpm.
  • A boat’s hull speed is the maximum speed that a boat of a given waterline length can achieve without planing. Darwin’s Folly has a deep displacement hull and is incapable of planing under engine power so the hull speed is a physical barrier. This barrier is governed by the properties of water and the boat’s waterline length. The formula for hull speed in knots is 1.34 * square root of the waterline length. Darwin’s Folly’s waterline length is 29.666 feet making its hull speed 7.3 knots. No matter how much power is applied the boat will not go faster than 7.3 knots.
  • We have a folding propeller made by MaxProp and the pitch can be altered by a mechanic when the prop is off the shaft. The operating characteristic of a boat or aircraft propeller is described by the value of its inches of pitch. The inches of pitch are how many inches the propeller would travel in one revolution if there is no slippage or turbulence. Our 16″ prop was installed by the previous owner and the blades were set at 18 degree which equates to 9.8 inches of pitch.

The situation we experienced was that with our engine, our boat, and a prop with 9.8 inches of pitch, we would achieve hull speed at about 2200 rpm, well below optimal. If you increased the engine power it would labour, make black smoke and suck the transom down. We finally bit the bullet this spring and had the boat hauled and repitched the prop to 6.4 inches of pitch. Now the boat would cruise at 3200 rpm and not reach hull speed until 3600 rpm which was much better. However, the stalling still occurred.

This past week we had some further service done. We had the gear oil changed again and the injectors rebuilt. The mechanics had a terrible time getting the engine started after this. They decided to check the compression and the valve clearances. The compression checks are all over the place. One cylinder was at only about 25% of proper compression and another was at about 50%. The valve clearances were very high which suggests that the valves and the valve seats are coked up. The mystery of the stalling engine has been solved. The poor old thing is very sick. It’s time for a new engine.

We could have the old engine hauled out of the boat and rebuilt. It would probably cost somewhat less than a new engine but we would still be left with a 20 year old engine. If we go for a new engine we will have a modern power plant with reduced emissions, better fuel efficiency, a 5 year warranty with all new components. It will be expensive but it will be worth it. I am now waiting for the estimate and then we will go forward delving deep into our line of credit. But that’s what a line of credit is for, after all.

“When you’re a little guy operating out of a garage, you have to pay all your own bills.  But when you get more successful, you get a line of credit, and the bank starts paying your bills.  Then you get a little more successful, and the bank won’t pay anymore, so you pay your bills slowly–30, 60, 120 days late–and now your vendors are paying your bills.  Now you’re even more successful, you get venture capitalists, and they’re paying your bills.  And it used to be when you reached the highest level of success, you could go public and have the public paying your bills.  But nowadays, when you finally reach the pinnacle of financial success–like Chrysler–you’re so successful you can’t be allowed to fail, and the government starts paying your bills.” George Morrow

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