CD 28 main sheet traveller suggestions

[J&P]

We recently bought a CD 28 and are looking to update the original main sheet system. I have seen the earlier postings from several years ago...but was curious to see if there has been any recent updates. We are debating whether to keep it aft and fixing it or moving it to the cabin top. What are your thoughts?

We live in MA and would love to look any any CD 28 main traveller systems. Please let me know if that is possible.

Thanks,
Jodie

[John Ring]

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Phil, Jody,

Early CD28 had a mainsheet system that runs in a triangle, between blocks mounted outboard aft of the cockpit. That's how my boat was set up. Later versions had the mainsheet on a traveler running on a track in the same area, freeing up some space.

It's a lot of work, but you can move it to the cabin top, as I did. It will free up lots of space in the cockpit, and make the boat more livable for cruising. It will allow a longer bimini if you'd like. The aft mainsheet is fine for a tiller boat, but completely in the way if you have a wheel, as my CD28 has.

As my CD28 has wheel steering, and a bimini (on hot days), I really like my cabin top mid-boom mainsheet system. Note the the addition of a third block system on the boom in the upper photo. The two block system in the lower photo didn't provide enough mechanical advantage to move the boom in a breeze. With the mainsheet attached half way down the boom, the loads will be twice as large as they were off the end of the boom (less lever).

Best,
John Ring
CD28 Tantalus

[Ldybg]

I replaced the original traveller with one from Garhauer.

Mine originally was not the triangle John mentions but a Schaefer track & car w/ pin stops. The stops were a pain to adjust, the Garhauer is line controlled.

I can get pix if you wish to see.

Dennis

[Angela and Tom]

I replaced the original traveller with one from Garhauer.

Mine originally was not the triangle John mentions but a Schaefer track & car w/ pin stops. The stops were a pain to adjust, the Garhauer is line controlled.

I can get pix if you wish to see.

Dennis

Would very much appreciate it if you post pics--especially if you've kept it in its original placement.

[The Patriot]

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... Note the the addition of a third block system on the boom ... The two block system [alone] ... didn't provide enough mechanical advantage to move the boom in a breeze ...

I may be way off on this, but I don't actually think the last block on the boom that directs the sheet forward adds an element of mechanical advantage to this setup. If the sheet, after running through this block, returned to the block on the traveler, then I believe it would add mechanical advantage. In the present setup I believe it merely re-directs the line forward without affecting the MA. Note that I am assuming that the setup without the additional block also ended the mainsheet on the block where it's presently located.

I am quite ready to hang my head in shame if I am wrong, but I am also prepared to blame all my erroneous ideas on a faulty academic memory. I would very much like to hear from a mechanical engineer (or even any freshman physics student with a good memory) on this (smileys omitted for sanity).

[Neil Gordon]

I may be way off on this, but I don't actually think the last block on the boom that directs the sheet forward adds an element of mechanical advantage to this setup.

That block is there in both the before and after photos. The third block was added between the two, as is shown in John's upper (after) pic. I haven't counted the blocks or done the math, but the added block is not just a turning block... the line that runs through it goes to the cabin top and back to the boom.

[barfwinkle]

I am inclined to agree with kerrydeare.

I was under the impression that in order to gain mechanical advantage the line had to "return to whatever it was moving". I installed a new traveler on a previous boat and it could be a 2:1, a 3:1 or a 4:1 and this was determined by the number of times the line went to the traveler car.

In this case (the pics above) the line goes through two more blocks, each providing a fairly significant degree of re-direction and I would think adding more resistance not less.

But then I am certainly not an engineer.

JMTCW.

Fair Winds

[Neil Gordon]

In this case (the pics above) the line goes through two more blocks, each providing a fairly significant degree of re-direction and I would think adding more resistance not less.

The blocks at the mast and on the cabin top are turning blocks and add no mechanical advantage. Not so for the rest of the system.

Also, I know it's early in the morning, but count the boom bails in photo #1 vs. photo #2.

[John Ring]

I believe Neil, Kerrydeare and Barfwinkle are all correct.

The forward block is present in both pictures, and adds no mechanical advantage, as it doesn't return the sheet to the traveler car blocks. It just redirects the mainsheet to run forward under the boom. I believe it's effectively a 3:1 system, same as what used to run off the end of the boom, and not enough for a mid boom arrangement. Taking the load from half way up the boom (lever) the loads will be twice as great, and call for twice the mechanical advantage to create an equal pull force on the sheet.

I added a bail between the two, and I moved the 3 line block to the middle, and put a 2 line block in the aftmost position. This new plan adds the needed mechanical advantage to work the mid boom system properly. In the current arrangement (upper photo) the aftmost block goes up and down twice, adding 2:1 advantage, and the middle block with its 3 runs, 3:1. All together I think I've got 5:1 now. None of this considers leverage of the boom.

The current set up is fine, however I do see one potential improvement. I may swap positions of the 2 line and the 3 line block (yeah, putting the 3 line block back aft again) as I believe it would improve advantage by moving the 3 block line further aft on the boom, thereby gaining more mechanical advantage through greater leverage. I believe it would then be 5:1 with a bit more leverage.

EDIT: Here's a question. Granted the fwd bail isn't doing much, but is it really doing nothing? What if it were moved all the way fwd to the gooseneck? What if it were moved back near the aft bail?

One more block and a bit more leverage, and I could haul this fish aboard! Ahrrggg!

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Cheers,
John Ring
(heading for the Boston Harbor Islands Regatta)

[Al Levesque]

A quick way to judge the mechanical advantage is to count the number of lines between the boom and the car on the traveller. In the final analysis the position of the bails on the boom also affects the advantage because of the leverage effect mentioned above. Since the tail leads off parallel to the boom it does not contribute.

[Neil Gordon]

Taking the load from half way up the boom (lever) the loads will be twice as great, and call for twice the mechanical advantage to create an equal pull force on the sheet.

Right. So in order to move the boom, you haul in the same amount of main sheet no matter where the attachment point?

[SeaBelle]

John,

Your physics is correct but your biology is not; that's no fish, it's a mammal very remotely like us.