August 8, 2010

Ignore the experts

(Every Monday, Wednesday, Friday. How many times do I have to tell you?)

NOW AND THEN a sentence in a boating magazine grabs my attention. This one was in an article by Annie Westlund, in the latest issue of Small Craft Advisor. It said: “In flat conditions, keeping the mainsail up helps with economy by about 5 percent when motoring, according to Tom Cunliff.”

Well, my brain cells sat up straight and started paying attention when I read that. I don’t know how much Annie Westlund knows about Tom Cunliffe, apart from the fact that she can’t spell his name, and I don’t know how much Tom Cunliffe knows about the law of conservation of energy, but I have to wonder if he’s ever heard of it.

Cunliffe, in case you’re wondering, is a British sailor and writer who operates from a cottage in the New Forest. Westlund operates from a 17-foot Slipper sailboat in Lake Huron in Ontario. Between the two of them, they have some explaining to do.

Lots of sailboats around here go from island to island under power in summer, when the winds are light or non-existent, and many of them raise the mainsail while they motor. I have done it myself countless times.

But I’ve never kidded myself that it was helping the boat move forward in any way. Let’s face facts: if you motor at 5 knots in a calm, the apparent wind will be from dead ahead at 5 knots. The mainsail will lie back along the centerline and flap uselessly.

You can sheet it in as tight as you like, but it will still billow and empty without providing any forward drive. To keep the mainsail quiet, many of us will move the mainsheet track over to one side or the other, and pin the main down there. In this position it is filled on one side and lies quietly, but anyone with the sense of a fried oyster will know that a parallelogram of forces shows that the force it is creating is directed aft and to the side. There is no forward component at all. In other words, it is making the work of the engine harder, not easier, as the Westlund/Cunliffe combination claims.

What this proves, I have to tell you, is that you can’t believe any darned thing the experts tell you. I’m sorry that this is not good news, but it’s the only subject I could think to write about on a Sunday evening and as soon as I finish this I can go and have another beer. So you’ll have to be brave and figure things out for yourself, as I do, and ignore the experts. Sadly, it’s the only way. Cheers for now.

Today’s Thought
Science is wonderfully equipped to answer the question “How?” but it gets terribly confused when you ask the question “Why?”
— Erwin Chargaff, Professor of Biological Chemistry, Columbia U

Boaters’ Rules of Thumb #80
Floating junk. The rule is that flotsam is what remains floating after a vessel has accidentally sunk. Jetsam is cargo or gear deliberately thrown overboard to help save a stranded vessel or one in heavy seas. There is no linguistic requirement that jetsam should float. Furthermore, if you attach a buoy to your sunken jetsam it might better be described as lagan. Yes, lagan. It’s in the dictionary, honest.

“I notice that Bert’s business seems to be perking up.”
“Yeah, he started taking the pins out of the map and sticking them in the salesmen instead.”


Aaron Headly said...

I can't see any fuel efficiencies either, but I know that leaving the main up saves 100% of my energy that would have gone into re-hoisting it when the wind picks up.

On a winch-less gaffer, that can be a pretty big consideration.


Tim Flanagan said...

I'm not about to CLAIM TO KNOW the answer either way, but I can come up with a semi-plausible explanation for any fuel savings, if such can be demonstrated empirically.

Here's my guess: To the extent you can prevent a boat from rolling, you keep it slipping forward more efficiently.

To take it to an extreme, it seems intuitively obvious that a boat that is rolling side to side is probably moving slower than one that is not rolling at all, assuming the same sea-state for both.

So I would suggest that it is at least POSSIBLE that hoisting the main and sheeting it amidships could reduce roll and increase fuel efficiency. Assuming the added drag didn't eat up all the savings.

I'd need to see some rigorous experimental test results to be convinced, though.

Timmynocky said...

I suspect that Ms Westlund has misinterpreted whatever it was that Tom Cunliffe supposedly said.

I have a great deal of respect for Tom, he has been sailing for too many years to make such an unqualified statement.

In a completely flat calm there is only one point for having the main up and that’s so it is ready just in case a breeze does pick up and that bloody engine can be turned off.

paul miller said...

If your boat can sail to weather, then there MUST be a forward force vector due to the passage of air over the sail. Motoring in a dead calm, the air motion over the sail is entirely due to the motor, but, none-the-less, produces a forward force vector that aids progress and reduces fuel consumption.

John Vigor said...

No it doesn't Paul. There is no forward force vector if the wind is coming from dead ahead.

John V.

paul miller said...

Dead ahead? Of course not. But the iron wind creates an apparent wind to the sail, allowing you to sail at some angle off the wind "to weather" which aids the motor. Whether the increased efficiency (over water) compensates for the additional distance traveled is beyond the scope of the argument.

Tacking is required to maintain a compass course.

John Vigor said...

Paul, if you're motoring in a calm the wind only comes from dead ahead.

John V.

John Vigor said...

This thread continues on the Cape Dory bulletin board:

John V.