Center boom vs. End boom sheeting

Moderator: GreenLake

Center boom vs. End boom sheeting

Postby GreenLake » Sun Nov 08, 2020 2:21 pm

@Acornrunner asked in another thread:
I have seen some boats rigged with a traveler near the stern, with the main sheet rigged to it. My mainsheet simply hooks to the boom midway, and down to the centerboard trunk. Is there an advantage to rigging the traveler?


Well, the short answer is, that there are advantages to both and if it works for you. . .

Center boom sheeting puts more load on the boom. However, if your boom is beefy enough, and the DS booms I've seem all seem pretty sturdy, that's not an issue.

When the sheet only pulls at the center, it has 1/2 the lever arm compared to stern sheeting. Therefore, you tend to see 3:1 or better purchase rigged in the mainsheet.

I have the end boom traveler with a simple 2:1 at the end and no extra purchase at the center. However, that's equivalent to a 5:1 at the center. The 2:1 at the end has twice the lever arm, so it compares to a 4:1 at the center. And, the one part that goes up to the boom in the center gets added, to make a total of 5:1. The traveler setup therefore uses fewer sheaves for the same mechanical advantage.

The other difference is that the traveler redirects the pull. When you pull on the boom, you adjust two things simultaneously: the angle of the boom in the horizontal and the angle in the vertical plane. The former gives your "sheeting angle" which ultimately define the angle of attack of the leading edge (luff) of your sail to the wind. The latter affects the leech tension, which in turn defines how much twist you have in your sail. By changing the direction of the pull you can control the relative contribution. (See also the "Basic Concepts and Techniques" thread).

You can achieve a similar effect by rigging a strong vang (which primarily affects leech tension).

Unless the current setup really doesn't work for you (or you are sailing competitively), I'd tend to leave this as you have it.
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Re: Center boom vs. End boom sheeting

Postby Acornrunner » Mon Nov 09, 2020 3:03 pm

When the sheet only pulls at the center, it has 1/2 the lever arm compared to stern sheeting. Therefore, you tend to see 3:1 or better purchase rigged in the mainsheet.

I have the end boom traveler with a simple 2:1 at the end and no extra purchase at the center. However, that's equivalent to a 5:1 at the center. The 2:1 at the end has twice the lever arm, so it compares to a 4:1 at the center. And, the one part that goes up to the boom in the center gets added, to make a total of 5:1. The traveler setup therefore uses fewer sheaves for the same mechanical advantage.


Ok, so without a Geometry or Math major, you are saying it's easier to pull in the main sheet, right? My Force 5 has a traveler, and yes it does help point into the wind. On the Force 5 the traveler does not make the main sheet easier to pull in, no gain in mechanical advantage.

Is there a way I can easily gain some mechanical advantage, I do not have hardware installed to add a traveler on my DS2, what would I need, how and where would it be attached?

I'm thinking a few short years from now, my age will catch up to me, and I will be looking for help wherever I can find it.

Thanks. Ed.
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Re: Center boom vs. End boom sheeting

Postby GreenLake » Mon Nov 09, 2020 5:58 pm

The mechanical advantage in this case comes from the end-boom location of the DS traveler, not from the fact that there's a traveler. (If you had a center cockpit traveler on a track it would have the same lever arm as the main sheet - that is one half of the boom length).

If you don't have a vang on your boat, I would consider installing a high-powered vang. 12:1 or better (some people go to 20:1). We've discussed vangs here before, not that long ago, so you should be able to find relevant threads. A vang will help you control your boat (and with vang sheeting, you get some of the advantages of separating the control of sheeting angle and leech tension that you get from a traveler).

A center boom mainsheet is usually rigged with a purchase of somewhere between 3:1 to 5:1. Harken will have some diagrams on their website of possible setups (with handy part number in case you want to buy theirs). There are lots of variations out there, some using fiddle blocks, some using blocks with multiple parallel sheaves. As you figure out possible upgrades, I would try make sure you can fit a ratchet block in that setup. A ratchet block doesn't give you mechanical advantage, but it will help you hold the mainsheet w/o cleating it. That's a safety factor in gusty winds.

Finally, whenever you upgrade your sails next, make sure you have a reef point added, or two (and to install the reef hook and lines that go with it). Being able to reef means that you will be able to control the boat under a wider range of conditions. For example, by reefing early, you may not have to hike hard to keep your boat level, making the whole experience more relaxed.

As you get older, it also becomes more important to maintain your condition. Use it, or lose it.
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