NAME THAT BOAT: ROUND 2
In “Letters to the Editor” in our April issue, we asked for help identifying a good-looking steel trawler that a reader spotted while cruising in Poulsbo, Washington. Several readers responded, saying they thought the “mystery boat” was the 55 Cape Horn pictured on the cover of our Winter 1999 issue.
At first glance, this appears to be true—the boats have similar lines and the same paint job. However, upon closer inspection, there are differences that make it clear the mystery boat is not a Cape Horn. We contacted Graham Oakley, who oversaw construction of Cape Horns for A.F. Theriault & Son, and he confirmed this, saying: “While the mystery vessel has a hull paint scheme similar to the second 55 Cape Horn trawler, M/V EOS, the wheelhouse shape and the windows are quite different. Also, the Cape Horns didn’t have as many portlights in the hull.”
And so the mystery continues. Feel free to write to us at firstname.lastname@example.org with your theories.—John Wooldridge
THE GREAT VOLTAGE DEBATE
When I read in John Wooldridge’s March “Waterlines” column that there was a new edition of Chapman Piloting & Seamanship, I searched our trusty library and checked out a copy. Being an electrical nut, I turned to Chapter 19, where on page 657 it says that a 12-volt deep-cycle battery is considered fully charged when its no-load voltage is 12.6 volts or higher, and fully discharged at 11.8 volts. It goes on to say that a battery is considered 75 percent charged at 12.4 volts, 50 percent charged at 12.2 volts (the voltage at which it is desirable to switch to another battery or begin charging), 25 percent charged at 12.0 volts, and 0 percent charged at 11.8 volts.
This goes against what I believe I learned from PMM articles years ago. I thought a 12-volt battery was fully charged at 12.6 volts, 50 percent charged at 12.4 volts, and 0 percent charged at 12.2 volts. Which is correct?
Sechelt, British Columbia
Battery voltage figures are a bit of a moving target. They differ from type to type (flooded, AGM, or gel) and even from manufacturer to manufacturer, in some cases. Generally speaking, a flooded lead-acid battery that has rested for six to eight hours (24 hours is better), with no loads and no charge sources, will measure 12.6–12.8 volts if it’s 100 percent charged. At 50 percent charge, it will measure 12.3–12.4 volts. For the purposes of battery longevity, a battery is considered dead at 12.0 volts, while most electronics and marine electrical equipment manufacturers consider 11.8 the voltage at which gear will no longer operate. If you want to derive the greatest number of amp hours from a battery over its life span, you should avoid discharging it beyond the 50 percent mark.
Having said all this, resting battery voltage measurements are of little use because it’s impractical to take these measurements while the boat is in use. If you want to monitor the condition or state of charge of your battery bank, you should rely on a high-quality amp-hour meter. This tool is like a gas gauge for your battery bank, providing you with a clear picture of how many amp hours you’ve used and how many remain.—Steve D’Antonio
GAS VS. DIESEL
I think I have a pretty good understanding of diesel engine life, but I know nothing about gas engines. For example, what would you estimate the engine life to be, in terms of engine hours, for a well-maintained Crusader 350-cubic-inch twin-engine installation in a 31- to 36-foot planing-hull cruiser?
Chester Springs, Pennsylvania
This is an interesting question and not an uncommon one. Rather than point out that gasoline engines don’t last as long as diesel engines, it’s probably more appropriate to emphasize that the longevity of diesel engines is nothing short of legendary. The lubricity of diesel fuel is significantly greater than that of gasoline; all of the engine parts exposed to diesel fuel—pistons, rings, cylinder liners, and the fuel injection system itself—are continuously bathed in this ultra-slippery medium. As a result, these parts tend to last a very long time. Additionally, because of diesel fuel’s very low vapor pressure (0.022psi, versus 7–9psi for gasoline), it does not evaporate at normal atmospheric pressure and typical temperatures. Thus, all of the aforementioned parts also are coated in a natural corrosion inhibitor.
Gasoline shares none of these attributes, which makes life for a gasoline engine somewhat more difficult. What’s more, because the pressure developed inside a diesel engine’s cylinders is much greater than that inside a gasoline engine’s cylinders, diesel engines need to be much more heavily built, and heavier, “stronger” engines tend to last longer. For the most part, diesel engines turn much more slowly—albeit with greater torque production—than their gasoline brethren. Slower turning invariably produces less wear.
Estimating engine life is a tricky business, and the variables are nearly endless. While diesel engines are more economical to operate, more reliable, inherently safer, and simpler (well, they used to be), in my experience most recreational marine engines—both gas and diesel—die of “accessory failure” rather than a failure of their internal parts. The bolt-on stuff, such as exhaust manifolds, circulator pumps, fuel injection systems, starters, and alternators, tends to fail before the engine itself gives up or wears out.
The best way to stay on top of the health of any engine, whether gas or diesel, is to carry out regular fluid analysis. Your engine’s transmission fluid, crankcase oil, coolant, and other fluids provide a window to what’s happening in the places you can’t see.—Steve D’Antonio