Why a single screw is unacceptable

Summary: A single-screw trawler is a bad idea. Itís a bad idea even with a ďget-home engineĒ because get-home engines donít work. Get-home engines exist because single-screw trawler manufacturers recognize that any engine can fail given the wrong circumstances. A single-screw boat always runs the risk of getting caught dead in remote waters or on a hard-chance lee shore. All Mirage trawlers come standard with twin diesels. Should one engine quit, the other will continue to propel the boat to safety at a respectable pace of more than 7 knots.

Why two props are better than one

Anyone who has cruised through the Bahamas and the Caribbean, or Baja California for that matter has observed that the American cruising fleet is overwhelmingly comprised of sailboats. This is in direct contrast to the protected waters of the United States, where the ratio of trawlers to sailboats is much higher. If trawlers and sailboats are designed to accomplish the same goal-and they are-why the discrepancy in numbers once we get just 100 miles from American shores?

We at Mirage Manufacturing think we know why. The vast majority of sailboats have two forms of propulsion-sails and an auxiliary diesel engine. The vast majority of trawler yachts, however, are single screw. Even though the types of folks cruising in sailboats and trawler yachts are very similar demographically, one group goes to the sea; the other hugs the shore within radio range of Sea-Tow. The trawler people arenít cowardly, just prudent. They donít buy claims that a well-maintained diesel never dies because they know that external factors such as plastic bags in the intake or lines around the prop can kill a well maintained engine as quickly as one that has been neglected.

If you happen to break down far from home in a single-screw trawler, what then? And what if the wind kicks up with a reef to leeward?

Yet some manufacturers continue to hype single-engine trawlers in the name of economy. This is a phony argument. These boats tend to have sailboat hulls (see Lesson Three), and lack the room for twin diesels without severe compromises. These heavy, ballasted hulls (see Lesson Four) require more horsepower to reach hull speed so there goes the ballyhooed savings in fuel.

They also say that twin engines would result in easily damaged props for want of a keel to protect them. The obvious answer is of course twin keels, and thatís how we do it at Mirage.

That doesnít mean single-screw trawler manufacturers donít recognize the downside of their product. They have to. They know the idea of a single-engine makes many would-be passagemakers uncomfortable, so they devised a half-measure, a placebo of sorts. Itís called a wing engine or, sometimes, a ďget-homeĒ engine. The latter is ironic because this little kicker is unlikely ever to bring anyone home unless the boat has stalled eight feet from the dock. Truth is: Get-home engines donít have the horses you need to claw your way off a lee shore. Youíd be lucky if you could use one to turn your bow into the wind. They just donít work. But they are helping some manufacturers make the sale.

An added advantage of this design is that the Great Harbours are easily careened. Careening is a method of below-the-water inspection, repair and maintenance that uses the tide instead of divers and travelifts. All you need is a minimum of 3 feet of tide. Just drive the boat onto a level, sandy spot and wait for low water. The boat stands up on the twin keels and its belly as if on a heavy-duty tripod. You can swap props or replace shafts, put in a new thru-hull or just clean bottom.

This is a great feature for cruising in remote areas where self-reliance is at a premium. And it can save you a buck or two back home as well.

The key to safe and self-reliant long-range cruising is a pair of economical diesels, with more than enough power to push a trawler at hull speed. Should one quit, the second engine will propel the boat at nearly the same speed. And it will get you home. Period.

Mirage President Ken Fickett first made these arguments in a letter to PassageMaker magazine in response to an article extolling the virtues of a single screw. To read the letter, click here.

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