That's a More Important Question Than 'Single Versus Twins'

Much of my time recently has been spent pouring over the google data about how many people are reading what on this website. One of the more popular older stories is headlined “Single or Twin Engines: Which Is Best?” and appears to conclude that one engine is better than two. As clickbait, this is a great story.

However, two things: 1. The author is actually asking the wrong question. The question should be: Do you have sufficient redundancy for the kind of boating you are doing? 2. One of the underlying premises for the author’s conclusion is just plain wrong.

I wrote about this myself for the pages of PassageMaker magazine a few years ago, and the builder of particular single-screw boat suggested I was criticizing his product, which I was not. I have thousands of sea miles in both single and twin-screw vessels, and I own a single-screw boat, albeit a sailboat.

I began my column with a true story about a single-screw vessel in distress, not in the middle some ocean but in the friendly Bahamas.

“Her oil cooler had ruptured, and she lost propulsion. Without a wing engine to get to port, or even to provide steerage, (the boat) lay beam to eight-foot seas adrift…Finally a Bahamian in an open boat came to the rescue and towed them to Nassau, losing one of his twin engines in the process and nearly running out of gas. The entire ordeal lasted 13 hours.”

For this poor family, redundancy in the form of a local fisherman was a matter of luck. Some Bahamian waters get pretty lonely. Sometimes no one is near enough to respond to a distress call over VHF.

Which begs the point about redundancy. If you are cruising U.S. coastal waters such as the Intracoastal Waterway, you are never too far from SeaTow or BoatUS towing franchises. Your VHF radio and SeaTow constitute legitimate redundancy, but if you would venture beyond towboat reach, your single-screw boat should have some variation of a wing-engine or sails to help deal with a loss of propulsion.

At this point someone might comment that single-screw vessels have crossed the Atlantic without any kind of back-up, and that person would be correct. I would parse that risk as having an 85 percent chance of success with a good boat and owner—odds that are not good enough for me, thank you.

The notion that bad fuel is responsible for killing most engines at sea is not supported by any hard data I have ever been able to find. This unsupported argument is the one that single-screw proponents use to explain that any fuel problem that kills the starboard engine is sure to kill the port motor as well. In all my miles in twin-screw vessels, including deliveries from Florida to San Francisco, I have had engines quit but never have both quit at once. In fact, with today’s excellent Racor filtering systems and a modicum of owner diligence, extreme fuel problems are rare compared to the olden days. That still leaves prop wraps, bad transmissions and myriad cooling system failures, such as the one described above.

The absolutely worst argument for venturing offshore with a single-screw vessel without redundant propulsion is to cite the example of the U.S. fishing fleet. To wit: single-screw fishing boats go offshore all the time, so it has to be a good idea. C’mon do you really want to use commercial fishing in a safety argument? As I wrote back then:

“Commercial fishermen are a lot tougher than most of the retired couples who forth in trawler yachts, and they tend to be much more clever as mechanics, too. (Read “Junk Under the Bunk.”) Tough and clever increases their chances of repairing and restarting a stopped engine even as their boat rolls through 60 degrees (like the one pictured below.)

Still they die in droves, nearly 500 of them in a recent three-year period. Interestingly more died on the U.S. East Coast than Alaska—165 versus 133. Overall the fishing industry fatality rate is 31 times higher than the national occupational average…Government studies attribute the majority of (fishing vessel) floodings to ‘hull and machinery failure,’ including engine failure.”

That being said, the Alaska fishing fleet is increasingly driven by twin-screws. A quick search on some of the big boys reveals that Ramblin Rose, Kiska Sea, Cornelia Marie, Alaska Leader all sport twins. Time Bandit and some of the other vessels featured on the popular television series “Deadliest Catch” also sport twins. The European fishing fleet likes twins and singles, but the single-screw boats often have one or more smaller engines as back-up. Redundancy.

This fishing boat, having lost power, has turned beam to the seas and subject to extreme rolling. 

This fishing boat, having lost power, has turned beam to the seas and subject to extreme rolling. 

I recently scrolled through the U.S. Coast Guard news archive using “fishing vessel adrift” and “fishing vessel distress” as search terms. There were many, many hits. From my column of yore: “The Coast Guard sends units to assist more than 3,000 fishing vessels a year, 60 percent of disable and adrift due to a stopped engine.”

So it would appear that the portion of the fishing fleet that lacks backup propulsion is using the Coast Guard for redundancy, judging from the number of Coast Guard pictures and videos of boats under tow (below). The problem with that is the distance that rescuers must travel to reach those in distress, often over 100 miles.

Toward the end of column, written in 2014 by the way, I introduce Lou Codega, a naval architect who has designed hulls for the Coast Guard, Navy and manufacturers of both trawler yachts and sportfishing boats.

“Codega says that when it comes to critical missions—and I’d like to think that when I’m far from land, my mission is critical—the Navy and Coast Guard are all about redundancy. ‘Boats in the 25- to 30-foot size range are often single engine; they are not expected to range too far from help. Combatant craft, even the small ones are twin engine,” he says. According to Codega, some of the exceptions are single-screw submarines, oilers, buoy tender and icebreaking tugs, but they incorporate myriad redundancies not possible in a yacht, making them nearly unbreakable.”

One of the hulls that Codega designed was a prior iteration of the U.S. Navy SEALs fast-attack boat. Codega likes to quote the SEAL philosophy on propulsion: “Two is one. One is none.” (Think: The Bahamian fisherman who rescued the trawler at the top of this story even though one of his engines had quit.)

Still, and let me stress this, the issue is not “twins versus singles.” The question is: Given your style of boating, do you have a Plan B to stay safe? Redundancy can include proximity to towing services, buddy boats, get-home engines, sails or, dare I say it, twin screws.