PS Advisor April 15, 2001 Issue

PS Advisor 04/15/01

Single or Double Lifelines?
Does PS feel strongly about whether you need single or double life lines?

-Al Lorman
Via e-mail

Double lifelines are certainly preferable. The Offshore Racing Council (ORC) regulations require double lifelines. A crew falling across the deck has a better chance of being stopped by the lower lifeline in a double set. Of course, crew should be wearing safety harnesses with tethers clipped to jacklines (never the lifelines) anyway.

Aside from safety, an added benefit of double lifelines is helping keep sails from blowing over the sides.

Deck Choices
What are the advantages and disadvantages of wood covered decks over fiberglass textured non-skid decks?

How do you maintain wood decks? What problems can occur with wood decks? What should one look for when considering a sailboat having wood decks? How are wood decks made and what type of wood is used?

-Rick Dall
Via e-mail

Wood decks on sailboats are universally teak, the most rot-resistant wood available. And it provides good traction for shoes and bare feet. Teak decks were very popular for many years, owing to their good looks…and despite the fact it’s hard to keep them looking fresh (a lot of oiling and sanding).

In recent years, they have fallen from favor for several reasons. They are heavy (and make the boat top heavy). Upkeep can be considerable, unless you just let them turn silver (the best idea…just wash with detergent so as not to scrub out the soft wood from the grain). And the screws that hold each board to the fiberglass underneath inevitably allow water to enter the deck core, which may lead to delamination of the underlying deck. Cost to repair such a boat is very high—maybe $25,000 for a 45-50-foot boat.

Radar Current Draw
In reference to your Radar Current Draw response to Willy Albanes (January 1, 2001), how can you say that a radar unit that transmits 2 kW only uses 2 to 4 amps? If the transmitter output is 2,000 watts at 12 volts, that equates to a current draw of 166.67 amps. How did you arrive at your answer? My answer assumes a 100% efficiency in the radar as well (hardly the case in real life). Some of the energy will be lost to heat and transmission losses in the RF line. Maybe I’m missing something, but to get 2,000 watts out, you need 2,000 watts in.

-Jake Brodersen
Via e-mail

The radar transmitter does not operate continuously. It sends out very short pulses. These are approximately 1 microsecond long and are transmitted about 1,000 times per second. This translates into a duty cycle of about .1% (We haven’t done the actual math lately, so feel free to check our numbers). Therefore: 2000 watts x .001= 2 watts of input power needed on a continuous basis given a 25% efficiency factor (just a guess) the result is a current draw of about .67 amps. The display, especially a CRT, will use considerably more than this. The figures we quoted previously were manufacturers’ specs.

Also, there are no transmission line losses with radar. The transmitter and receiver are located directly below the antenna and the signals conveyed by a very short piece of waveguide.

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