Tied Up in Knots, Part 1
Somewhere around February, 2004, after 10 months of mounting frustration, we sent a three-page engineering report to Carver documenting our trials (as in "sea" trials) and tribulations in attempting to get this yacht to go as fast as advertised. Now, before you choke yourself with laughter at my seeming naïveté, I need to tell you that when the boat was turned over to us by the dealer, after 3 months and 88 at-sea hours of shakedown, it did go as fast as advertised. And I have the 38 Excel spread sheets to prove it.
On our first shakedown cruise – four days in placid fjords and sounds of British Columbia, equipped with instrumentation that was only slightly less geeky than the crew – we logged every 50 RPM from idle to wide open throttle (WOT) several times over several days, until we knew exactly how the yacht performed under what conditions and loading, and exactly how much fuel we used at each setting (which would be important for the long ferry trip from Vancouver to Los Angeles at some future date). We even derived a mathematical equation that exactly fit the curve. That how geeky we were (are).
What we discovered was that at wide open throttle, the 506 turned in about 23.5 knots – approximately the figure in the enthusiastic sales brochure. At WOT less 200 RPM – Volvo's recommended cruise operating point – we were getting a blazing 20.8 knots. Fuel consumption, at every speed setting on plane, from 13 knots to 23.5 knots, was a constant 0.47 miles per gallon (2.2 gallons per mile). (In displacement or "trawler" mode, by contrast, the fuel economy increased dramatically to 1.3 mpg at 8 knots, and 5.6 mpg at 6 knots. But I digress...) Since it cost the same point-to-point to go 20 knots as 13, we happily operated the yacht at 20. Even on the ferry trip, where we had a 2,100 lbs of diesel fuel in a bladder tank on the sun deck, we were able to maintain 19 knots in cruise. At such speeds, you have great flexibility in itineraries.
Then, suddenly, it all went away. On a milk run to clear the pipes one day in April, 2003, just about one year after we did the speed trials above, we turned in a shockingly low 15.8 knots at wide open throttle! We'd lost almost 8 knots – nearly 32% – right off the top. Suddenly, destinations in Southern California that were an easy day trip became overnighters. But that was just the effect. To a geek, it's all about the cause. Where did the speed go?
The next 10 months, before I gave up and wrote Carver, were an Odyssey of suppositions, modifications, tweaks, and trials, involving a constant stream of mechanics and money. Everyone had an opinion.
Some of the things we explored were:
This was sort of the state of the union when I finally wrote a long letter to Carver, including a blow-by-blow engineering report on the performance history and parameters – complete with color-coded graphs. I felt like Arlo Guthrie.
Carver convinced their Southern California dealer to get involved, and so for short, several-week period, we actually interacted – the dealer and I, including a speed trial with their head of maintenance onboard. We were additionally accompanied by the dealer's preferred outside Volvo mechanic, Clark Hurley. When the dealer lost interest in the problem, I inherited Clark. His story, and what we learned, is in Part 2.
On our first shakedown cruise – four days in placid fjords and sounds of British Columbia, equipped with instrumentation that was only slightly less geeky than the crew – we logged every 50 RPM from idle to wide open throttle (WOT) several times over several days, until we knew exactly how the yacht performed under what conditions and loading, and exactly how much fuel we used at each setting (which would be important for the long ferry trip from Vancouver to Los Angeles at some future date). We even derived a mathematical equation that exactly fit the curve. That how geeky we were (are).
What we discovered was that at wide open throttle, the 506 turned in about 23.5 knots – approximately the figure in the enthusiastic sales brochure. At WOT less 200 RPM – Volvo's recommended cruise operating point – we were getting a blazing 20.8 knots. Fuel consumption, at every speed setting on plane, from 13 knots to 23.5 knots, was a constant 0.47 miles per gallon (2.2 gallons per mile). (In displacement or "trawler" mode, by contrast, the fuel economy increased dramatically to 1.3 mpg at 8 knots, and 5.6 mpg at 6 knots. But I digress...) Since it cost the same point-to-point to go 20 knots as 13, we happily operated the yacht at 20. Even on the ferry trip, where we had a 2,100 lbs of diesel fuel in a bladder tank on the sun deck, we were able to maintain 19 knots in cruise. At such speeds, you have great flexibility in itineraries.
Then, suddenly, it all went away. On a milk run to clear the pipes one day in April, 2003, just about one year after we did the speed trials above, we turned in a shockingly low 15.8 knots at wide open throttle! We'd lost almost 8 knots – nearly 32% – right off the top. Suddenly, destinations in Southern California that were an easy day trip became overnighters. But that was just the effect. To a geek, it's all about the cause. Where did the speed go?
The next 10 months, before I gave up and wrote Carver, were an Odyssey of suppositions, modifications, tweaks, and trials, involving a constant stream of mechanics and money. Everyone had an opinion.
Some of the things we explored were:
- Pitch of the props. Where formerly we could crank out 2650 RPM at wide open throttle, we were only getting about 2300 RPM. Now, that might not seem like much to the layman, but when this boat is on plane, every 50 RPM is worth 1 knot. Our Volvo mechanic told us to flatten the pitch of the props. So a diver removed them, and we sent them in to be hammered into the new profile (either that, or $10,000 for a new pair). The rule of thumb is 50 RPM per inch of pitch change, and that's what we got – 50 RPM. And a big bill from Wilmington Propeller. But no change in speed.
- Ballast. Although we were dragging 2,100 lbs of extra diesel fuel on the aft-most deck of the Vancouver-San Francisco ferry leg, and only lost 1.8 knots in speed, we convinced ourselves that the 450 pound dinghy, motor, and davit system on the aft edge of the swim platform was causing the yacht to "drag her tail", necessitating excessive trim – and hence drag. So we added 750 lbs of lead forward of the longitudinal center of buoyancy (see "Un-making a List", November 1, 2002). No improvement. But the master bath tub now drained...
- De-calcify heat exchangers. This one came from a Volvo expert in the Turks and Caicos Islands, by way of a friend and crew member. There are three heat exchangers on the Volvo TAMD74P-A diesels, including the critical fresh water/seawater heat exchanger. According to the theory, the capillary tubes in these heat exchangers get increasing build-ups of scale on the insides, narrowing their diameter, and restricting water flow. This in turn causes the engine to run hotter, which decreases the power output. Our Volvo-certified mechanic said that in some cases, you have to ream out these tubes every few years, and that ours definitely were severely restricted, after only 280 hours on the engines. (Apparently, if you run these diesels hard, and then shut them off abruptly, without allowing them to run until they are quite cool, the water boils inside the heat exchanger, accelerating the scale build-up). So he took both engines apart, and reamed away for several weeks. I won't tell you what that cost. No improvement..
- Flooded swim platform. The Carver dealer in Newport Beach reported having seen a similar speed problem, and said that it was caused by a "flooded swim platform", caused by some sort of leak. Normally, most of this 40 cubic foot structure rides just above the water, so if flooded, the thinking went, there would be another 2,400 pounds of deadweight all the way aft. This theory, which necessitated either a haulout or drilling some sort of inspection port in the platform upper surface, was what finally drove me to Carver. I needed engineering drawings to find where I should install a small deck plate to be able to "sound the well" as it were. Although I did chase this one down, eventually, I'll leave it to a future post to tell you what a wild-goose chase that was.
This was sort of the state of the union when I finally wrote a long letter to Carver, including a blow-by-blow engineering report on the performance history and parameters – complete with color-coded graphs. I felt like Arlo Guthrie.Carver convinced their Southern California dealer to get involved, and so for short, several-week period, we actually interacted – the dealer and I, including a speed trial with their head of maintenance onboard. We were additionally accompanied by the dealer's preferred outside Volvo mechanic, Clark Hurley. When the dealer lost interest in the problem, I inherited Clark. His story, and what we learned, is in Part 2.
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