Motorsailing in dead calm

[David van den Burgh]

Go sailing.

[bill2]

. . . author Annie Westlund writes:

"In flat conditions, keeping the mainsail up helps with economy by about 5 percent when motoring, according to Tom Cunliffe."

. . .

I maintain that if you are motoring in a dead calm at 5 knots, the apparent wind will be from dead ahead.

. . .

a JV brain teaser - what the heck - let's have a go with it . . .

My first thought is that I'm thinking flat conditions ( can you have flat conditions and swells ? - hmm - by flat I'm thinking level not rolling ) could still have a breeze - hmmm - so maybe by setting the mainsail and motoring I could save some rpm's by using the " lite breeze " - leastways up to hull speed at least IMHO - thereby saving a ( very ? ) little diesel fuel .

Now dead calm - I'd be thinking the other way. I agree that the more wind resistance you have the more you need engine rpm's to overcome the resistance. And I agree that the mainsail will generate wind resistance. But - ahhhh - what about crew/passenger comfort - well to reduce rolling by hoisting the mainsail might ultimately make even the capt happy.

of course I stand by my convictions till I change them

[marv brinn]

I think keeping the sail up increases your moment of inertia and moment of monkey grease ....which tranlates to who knows?
It is best to keep your motor running when the engine is on.....seriously can you just shut off the ignition switch on the yanmar ysm8 instead off pulling the shut off lever without harming the engine?

[Dean Abramson]

Marv,

DO NOT shut off your engine that way!!!

If you turn off the ignition, the engine, still running, will cause the alternator to send current which has no place to go.

This is not a truly scientific explanation, but it is sort of like putting way too much air in your tire. It can fry your electrical system.

DON'T DO IT! Pull the engine stop and after it is truly stopped, turn off the key.

Seriously,

Dean

[Warren Kaplan]

Is it possible to lock the prop while motoring and what effect would that have on boat speed?

Neil,

locking the prop while under power would increase boat speed quite a bit-- although the velocity would be centered around the axis of the propeller shaft and therefor angular and expressed in revolutions per minute. On a CD27, assuming a vertical distance of approximately forty feet from the prop shaft to the masthead, at 2,500 rpm and discounting the drag effect each time the mast and mainsail are dragged under water, that works out to approximately 1,136 miles per hour at the masthead, which of course would represent the distal extreme of the radius and therefor the point of maximum linear velocity.

Thank you for your attention,

Carter Brey
Sabre 28 MkII #532 "Delphine"
City Island, NY

Definitely need to have a harness and tether on if locking the prop while motoring.

[Andy Denmark]

Best explanation of this entire thread
________
Honda ST series specifications

[Al Levesque]

I have seen few really dead calm conditions without some sea motion. If there is sea motion I leave the mainsail up to minimize rolling. Since the mast is relatively rigid and the leech is not, I expect rolling provides the same forward force that dinghy sailors use when they run out of wind.

On the other subject of Yanmar running with the key turned off: I have had my key turned off accidently numerous times on our 3YM30 with no adverse effect except that the stop button and the tach don't work. I assume the engine designers took my carelessness into account. I don't know if they did the same on earlier engines. Turning the key wasn't something I would have tried on purpose.

[winthrop fisher]

Winthrop

[John Vigor]

Winthrop I am not a member of the CDSOA. I try not to irritate members by excessive posting on this site.

John V.

[Dean Abramson]

John, I am sure that you are not irritating anyone. Please post away!

Dean

[winthrop fisher]

John,
you have been coming this board for a long time,
thats does sound like you,
whats up.
winthrop

[Boyd]

Hi John:

First is he talking about speed increase or less fuel consumption?

How did he measure the difference? In a lab or open ocean.

I want to see the data. I think a 5% variance is well within the margin of error for measurements of this type. Measuring such a small increase or decrease under constantly changing conditions is pretty much impossible. After all you would have to compare condition one, no wind and no current, sail down, with condition two which is motoring under the same conditions with sail up. When have you ever seen conditions like that stay stable for a sufficient amount of time to get a solid fuel flow rate?

For instance if you ran 24 hours at .625 gpm sail down your fuel use is 15 gallons. The second run at 95% of .625gpm is a rate of .594 gpm using 14.25 gallons, for a difference of .75 gallons. When have you seen identical conditions exist for 48 hours. If you ran the test for 2 hours then the difference would be .031 gallons. Can you measure .031 gallons? Yes thats extreme but illustrates the point.

I spent 12 years trying to figure out my fuel consumption under all kinds of conditions. Despite meticulous records the fuel consumption varies way more than the alleged 5% this guy claims is possible.
I find my rates vary from .625 to .78 gpm under what appear to be similar conditions over long trips. A big part of the problem is accurately measuring the fuel in the tank, especially an odd shaped one. Getting an accurate reading from a fuel gauge is near impossible as the boat is in constant motion and the gauge bounces all over the place. Additionally its almost impossible to fill the tank to the same level each time. The question becomes "when is full full". I can get at least a quart in the fuel fill hose from the tank to the deck fill. My tank is advertised as 21 gallons but actually holds about 19.

Without a really expensive fuel flow meter I don't see how accuracy in this range is possible.

If he is talking about a speed increase then the measuring process gets even harder. Does the wind ever hold true zero long enough to get a fair comparison?

There seems to be a lot of bogus information bouncing around the sailing literature that has no solid basis.

I say go with whichever condition leads to the greatest crew comfort. A 5% increase in speed over 24 hours is only 6.6 km at 5.5 kt. It may change your arrival time by about an hour.

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

[Maine Sail]

We don't need to measure a 5% difference. We only need to find a flag that bends the flag pole INTO the wind to prove the theory..

Good luck with that..

As John's theory was posed it is; dead calm, no wind. Those are the rules, discussions of waves etc. are outside the proposed theory.

If those are the parameters there is no added efficiency, it is a net drag. Only when you create lift will you have added efficiency but dead into your own wind the sail is acting as a FLAG NOT a SAIL thus no added efficiency.

Raising my main sail directly into the wind, on the mooring, added 20-25 pounds of negative load to my mooring. No lift, no added efficiency. John V's theory is spot on as measured with a digital strain gauge.



When you guys find that flag pole that leans into the wind let me know I need to photograph it..

Why are these flags pulling away from the pole?

[river-rat]

Good discussion over almost nothing. I am in the school of about zero gain in economy.

Two experiences with centerboard boats without engines:

Sailing downstream on the Columbia River in zero wind relative to land I was able to sail faster than the current. I passed debris floating along side by a small but consistent amount. Current was about 2 knots.

Laser sailors frequently stand in front of the mast and flap their way home by rolling the boat from side to side when the wind quits. Think of it as continual roll tacking.

[Dean Abramson]

John V. gets us all bogged down in this discussion. He is out sailing while we are at our computers. The anchorages are less crowded for him this way.