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mkrautha 06-05-2008 09:57 PM

Drop jib and come in under mainsail?
Today I was out sailing a 420 in a nice breeze. I was coming back into the dock and thought I would drop the mainsail and come in under jib alone which I have been able to do on a soling. On the 420 though this was pretty much impossible (we lost all our momentum and the boat wouldn't track all that well).
Later, one of the instructors told me that it was only really possible with a following wind. Another instructor sail that as far as dropping one sail goes, start with the jib because most of the power is derived from the mainsail.

I don't know though-- I guess I've read about people running under jib alone so the first instructor's comment makes sens.
The second instructor I wonder about thought because I've read that most power comes from the foresail (at least when its a genoa), so it seems to me that it really depends on the sails one is using.

The best I can figure is this-- we weren't flying a genoa and the jib is pretty small so maybe relative to the current we weren't getting much of a lift.

I wonder though is there some reason why sailing under mainsail alone makes sense in terms of center of effort?

Basically, what is a good general rule for flying only one or the other?


sailingfool 06-05-2008 10:05 PM

54 Attachment(s)
The jib on a 420 is so small it provides little drive by itself, on larger keel boats the reverse is often true - the jibs are larger than the main.

sailingdog 06-05-2008 10:15 PM

It really depends on the boat. Some fractionally rigged boats get most of their power from the mainsail. Masthead rigged boats often had much larger genoas and got more of their power from the headsail.

However, some boats can sail well with just a main, others with just a genny, and others require both sails. This is often determined by what boat your on, the sails it has up, and what point of sail you're trying to sail along. Sailing on the genny alone is often much simpler if you're sailing downwind.

IIRC, the Club 420 is about a 3/4 fractional rig or so, with a very small headsail area. The jib is about a third of the size of the mainsail from looking at this image.

The center of lateral resistance is determined by the underwater profile of the boat's keel and rudder. On centerboard boats, this can be shifted slightly, by raising the centerboard slightly, which tends to move the CLR aft. On keel boats, this is pretty much fixed.

The center of effort is determined by the sails that are in use. On most boats, using just a jib means that the COE is going to be forward of the CLR and that will tend to leave the boat with some serious lee helm, and it may have difficulty sailing to windward.

blt2ski 06-05-2008 10:42 PM

On that boat I would do a main only. There is one fellow with a San Juan 26, that regularly comes in to our marina under main alone right to his dock. Another fellow with an Etchels also comes in under main alone.

For me, I would do the main no matter what I was sailing, as I personally find that sail to be easier to finesse the boat if you will speed wise etc with the traveler/main sheet system vs the sheets etc on a jib. I used to dock a 12' boat I sailed that way to, under main, either dropping the jib, or letting it luff on the way in.


Coreyboy18 06-06-2008 02:06 AM

I find it much easier to drop the jib and come in on the main, especially since it is mostly me and my dog...and she doesn't contribute too much to the task. I'd rather not have a great deal of "horsepower" anyway. Actually, I have a pretty busy marina so most of the time I just motor in. Also worth mentioning, I am coming in on a much smaller boat, a Ranger 23.


merttan 06-06-2008 08:37 AM

On my boat, a 22ft light displacement, jib is fairly useful when approaching... However, as far as I was told, heavier boats do need mainsail to keep the manuevering speed...

chucklesR 06-06-2008 10:01 AM

The main is for power, the jib is for speed and pointing. Useful rule of thumb for all boats.

nolatom 06-08-2008 08:27 PM

If your medium and final approach to your mooring or dock is a beam reach or lower, you could make it on just jib alone.

Any higher than that, and assuming again you have to choose only one sail or the other (as with a 420 since no reefing), then choose the main.

DrB 06-09-2008 08:05 PM

Explain, please.

Originally Posted by chucklesR (Post 325518)
The main is for power, the jib is for speed and pointing. Useful rule of thumb for all boats.

What do you mean by power and speed? What is the difference? I have always equated Power to some extent with speed.

My boat is set up with mainsail and 135 genoa. When sailing at any points excpet a run/broad run, the jib will power the boat faster alone than the main alone. This is especailly true on a close reach or close hauled. In steady 15kt winds, I may be able to do 3.5 kts close hauled main alone and 7 genny and main. With genny alone I am in the 4.5 to 5 range, but the boat isn't as well balanced and I can't point as high. On a run or very broad run, the jib is essential useless as it is blanketed by the main when both are up. It's easoer to roll ing th genny, than it is to drop the main, so that is what I do. I may lose a little in speed, but since I am not in a race, I don't care..

I always thought (was taught) one can't point as high with a jib because the main has a third fixed point to the back of the boom (clew/outhaul) that a jib/genny does not. The fixed point means you can shape the sail closer to the wind and therefore point higher.


Plumper 06-09-2008 11:21 PM

When sailing to the dock in a large boat (tons) the sail you use is determined by the wind direction. If, once you are berthed alongside the wind will be from ahead then use the main, if the wind will be from astern then use the jib. That way, you can luff the sail to slow down as you approach. If you are using the main with the wind from astern then the only way to depower the main is by dropping it or sheeting it flat (if you are lucky). Using the jib when the wind is from ahead is challenging because most boats won't sail to weather under jib alone very well.

That is my approach. In dinghys it isn't as big a deal, just grab the dock and stop the boat.

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