Mainsail block on deck?

[barry208]

I am just getting my SJ21 ready and I see many boats have a block from the deck to the boom just aft of the mast. How important is is that for cruising and easy sailing?

[Ben G]

Are you speaking of a boom vang?

[San Juan Sailboats]

There are many different main sheet systems. The one you may be talking about is the Head Knocker.
This is a block and cleat attached to the boom somewhere aft of the companion way hatch.
In section 3.4, Paragraph 9 of the Class Handbook; Mainsheet: All parts of the mainsheet shall lead between the boat and a block or blocks on the boom any distance up to and including 36" in front of the black band. A "head knocker" is permitted. A traveler is permitted, but it must be located no further forward than the same 36" in front of the black band.

The black band is located than 8 feet 9 inches from the aft edge of the mast.

Our booms can break if you have the mainsheet/Traveler system on top of the cabin like some boats.

Most of the mainsheet systems you see today are the aft Rope Traveler, the mid cockpit traveler, or the head knocker. We have an article on travelers at our website, http://www.sj21fleet1.org/tips-and-tricks/travelers

[bluepearl]

I think you may be referring to a boom vang which should go from the the base of the mast and connects to the boom. So do you 'need' a boom vang? Probably not, but I sure wouldn't leave home without it, especially in a blow. The boom vang helps pull down on the leach and reduces twist, which is quite helpful when the wind is up. A lot of people will say this is wrong and what you want to do is open the leach in a blow and let the air spill off of the sail. While this is somewhat true, in my experience not using enough vang in a blow turns the main into a twisted and uncontrollable POS. Its hard to get too much vang in a blow and really easy to have not enough. The problem with not using the vang in a blow is that you will tend to pull the main in to the point where it isn't flogging, especially on a reach. But without the vang on hard the foot of main will be in much farther than the head to prevent flogging and this will overpower the boat. I have my vang controls lead back to the cockpit and I adjust it often, even when 'cruising.'

[San Juan Sailboats]

A vang is used primarily when you are on a reach.
With the stock main sheet system, as soon as you let out the sheet, the boom will rise up as well as move out. With the vang, you can control the amount of rise.
If you have a traveler, you can move the boom in and out without the boom rising until you run out of room on the traveler.

[barry208]

I found out what I was referring to is called a "Cunningham" and it is for adjusting the shape of the mainsail. According to my new rigger, they are nice but not important for cruisers and primarily "fair weather" sailors. Thoughts?

[bluepearl]

A cunningham can be a nice thing to have, but isn't really necessary for cruising. A cunningham can quickly flatten your main, but so can tightening your halyard. The only time a cunningham is really convenient is when you need to reef your main and you can use it to pull down on the reefing point.

[San Juan Sailboats]

The primary use of the Cunningham is to move the draft point of the mainsail.
When the wind picks up, the draft point moves aft. The pulling the Cunningham adjusts the draft back forward. It is the same as putting tension the halyard, but our sails are cut to span the entire length of the 23' of allowable space, so the Cunningham does the luff tension.
I agree that it isn't a necessary item if you don't want to trim your sails to the enth degree.

[barry208]

Thank you all!