MainSheet Conversion

Moderator: GreenLake

Re: MainSheet Conversion

Postby Noley » Tue Aug 29, 2017 3:48 pm

Revising the mainsheet arrangement is another item on the punch list with my new-to-me 1979 Daysailer.

It presently has mid-boom sheeting with a 3X purchase run to the CB trunk. It works, but 3:1 is not the easiest to use in 12+ knots (especially for wife/daughter) and the puddle of line on the cockpit sole makes me crazy. Plus it tangles on the CB block and cam cleat. Am thinking an end-boom triangle led to a mid boom block with a cam cleat is the best approach. I used to sail Solings fairly extensively and most had mid-boom ratcheted blocks with cam cleats. Made it easy to control the main (rarely reefed) in 20+ knots.

I've sailed a lot, but am new to these boats and making my winter shopping list. ALL thoughts welcome!


TIA

Noley
1979 DS 2
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Re: MainSheet Conversion

Postby DigitalMechanic » Tue Aug 29, 2017 7:14 pm

I feel you, as I have mid boom sheeting as well (3:1 w/ ratchet). I have been considering converting the boat to use the split tail main system. Think it would perform better upwind in light conditions (allow the boom to come to center without too much leech tension). Plus it would potentially alleviate the need to have such a powerful purchase (which means extra sheet lying around to accommodate it). Definitely see the "sail control" advantage in light wind that the mid-boom sheeting does not offer.

Speaking of "sail control" Inhaulers are in the back of my head too... but one project at the time right? :wink:
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Re: MainSheet Conversion

Postby GreenLake » Wed Aug 30, 2017 5:50 am

The amount of main sheet in the middle of the boat is a constant / more or less.

Here's why: the work required (in the physics sense of that term of force * distance) to move the loaded boom in some fixed amount is the same, no matter the sheeting arrangement used to do it. So is the work required from the operator.

Only that the purchase will let him or trade distance for force.

Now, as long as the force felt by the operator is the same, the distance pulled must also be the same -- the only way you can save on the tangle of main sheet is by being stronger (pulling harder).

End boom triangles, split tails, or whatever, may require fewer blocks and sheaves, but unless you are willing to pull harder, they require the same amount of mainsheet pulled per degree of boom angle.

The end of the boom sweeps twice as far as the center. As the boom changes angle, the lines at the back of the boom get shortened about twice as fast as a line attached to the center of the boom. With some triangles, you have two lines going from the back of the boom, now you are shortening two lines twice as fast = four units. You also pull one unit because the remaining single block in the center of the boom comes closer as well, so now you have something that's equivalent to a 5:1 if it was center boom rigged.

You definitely pull that much line, but the whole thing uses somewhat fewer blocks, so your story gets better on friction; and it's a 5:1 not 3:1, so it's easier to pull (3/5 the force, 5/3 the amount of line).

I like my end boom setup and wouldn't change it (but also don't think I have too much mainsheet running around).
~ green ~ lake ~ ~
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Re: MainSheet Conversion

Postby DigitalMechanic » Wed Aug 30, 2017 9:58 am

Thanks Greenlake!

I see you added an extra full turn between the apex and the boom. Much shorter than from centerboard to boom. I think the defacto setup is to go through single block at CB trunk, then single block at mid-boom, and then single block at end of boom, then triangle. That is 3 half turns. 1.5:1 ?

If I read correctly your triangle is affixed separate, adjustable, and terminates at the apex with a block. Your sheet goes through blocks at CB, Mid-boom, end-boom, apex block, and back to end-boom becket. The turns are half, half, half, whole. What does that give you? 2.5:1 ?

Also, considering...
Only that the purchase will let him or trade distance for force.


I have a mid-boom 3:1 (well, it is whole, whole, half turn, so is it really 2.5:1?). Let's round length out here for simplicity. Lets say one full turn of my sheeting system presumably has roughly the same distance you have from CB to apex (which does not exactly, you will have a tad more sheet). Then let's say I have roughly twice the length of sheet on the second turn, compared to the turn you have between end-boom and apex block.

When sheeted in your setup seems like it would have near the same holding power. However, as soon as we start sheeting out, I presumably have to let twice the length of sheet out. The length between CB and end-boom is static for you. The turns between end-boom and apex are much shorter than the distance of my second turn. The length between all my turns is dynamic in length, in some exponential form increasing as the sheet is let out.

So, considering that the statements I have made are accurate (looking for a little reassurance here :wink: ), then I would presume 2 things...

1. The length of sheet that the 3:1 mid-boom setup requires is more? (Due to both turns being dynamic in length as the sheet is let out, and the second turn inherently starting at a lengthier position)
2. Based on trading "length for power", the 3:1 mid-boom purchase gets increasingly "stronger" the more it is sheeted out?

Now let me try and prove myself wrong (or at least profess my insecurity based off the info I found... lol)

Based on D&R Marine's site:

The 3:1 mid-boom should have 25ft of sheet
The end-boom traveler setup should have 40ft

Reference:
http://www.drmarine.com/products.asp?cat=122

However... That 40 ft of sheet considered by D&R will continue to follow past the apex and continue to form (and be a part) of the triangle. You have made the triangle separate, so that length should be subtracted from presumed 40ft. At any rate, with the traditional traveler setup, (I think) the triangle length is still static, and should be subtracted if you are trying to compare how much sheet will be puddled in the boat. So for comparison's sake, if we wanted to find out which required less extra sheet puddled in the boat, mid-boom vs end-boom (either traveler or split-tail), I believe we need to know the length of sheet used up until the end-boom block on your boat?

So, in the least perverse way I can think of to ask this question... "How long is your sheet?" lol.
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Re: MainSheet Conversion

Postby jbrew » Wed Aug 30, 2017 6:16 pm

This is my first year of sailing a DaySailer and I am interested in alternatives for the mainsheet. I am tempted to try the split bridle arrangement Green Lake has described to replace the Crosby rig that came with my 1973 DSII. I also like K.C.'s idea of moving the boom sheeting point in from the end of the boom to avoid fouling the mainsheet on the transom, outboard, or other things near the back of the boat. I would be interested to know what other sailors have learned about the best spacing between the boom block and bridle block when sailing close hauled under various wind conditions and the merits of a movable bridle that permits the bridle block to shift its position from one tack to the other as opposed to being fixed close to the centerline. Thanks for any input.
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Re: MainSheet Conversion

Postby DigitalMechanic » Wed Aug 30, 2017 6:23 pm

Reading this back a second time, I think I am noticing some more points you make.

1. mid-boom is 3 lengths of rope between turns, but the distance when let out is less because the lines never lead aft.
2. The end-boom setups still have to give rope at mid boom to sheet out, but far less. However, they consume a lot more sheet at the end of the boom as the travel out runs on a path with much larger circumference.

My deduction is that you are saying all come out abut the same in length as to what is left over in the boat when sheeted all the way in :)

So, beyond technical preference, there is no obvious choice for extra tidiness.
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Re: MainSheet Conversion

Postby GreenLake » Thu Aug 31, 2017 2:49 am

Looks like you were following my conclusion.

The way I use to analyze a purchase is how much line gets pulled for each unit of movement of the load the purchase attaches to.

If you have a center boom sheeting where there are three parts between boom and swivel, then for each inch the boom moves, three inches of line need to be pulled. If you turn around the purchase so that you pull the free end away from the boom, then you get to add that inch for a combined four inches.

Traditionally, that's called rigging the purchase "to advantage" because with the same number of block you up the ratio by +1 (in this case from 3:1 to 4:1). I can't remember how to get to the correct ratio by counting the sheaves and taking into account which way something is rigged, so I always go back to the simple conservation of energy (work) which dictates that distance*force must the equal.

Anyway, we rarely are able to rig anything to advantage, and even if we could, we'd end up not pulling in a parallel direction.

Leaving the mainsheet. For vangs higher purchase ratios are needed. One way to do that is with a cascade. Using a 6:1 purchase "nested" in a 2:1 gives a ratio of 12:1. A cascade's main advantage is a reduction in the number of sheaves a line has to run over, which really helps with losses due to friction. It's main disadvantage is a reduction by 1/2 of the effective range of the purchase - for a vang that's more acceptable than for a mainsheet.

The actual items that determine preference might be friction - my setup has fewer blocks than a center boom purchase of same strength ratio. And, the configuration at the stern allows some slight adjustments in the angle of pull, which should affect the amount of leech tension for the same boom angle.
~ green ~ lake ~ ~
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Re: MainSheet Conversion

Postby GreenLake » Thu Aug 31, 2017 3:16 am

jbrew wrote:This is my first year of sailing a DaySailer and I am interested in alternatives for the mainsheet. I am tempted to try the split bridle arrangement Green Lake has described to replace the Crosby rig that came with my 1973 DSII. I also like K.C.'s idea of moving the boom sheeting point in from the end of the boom to avoid fouling the mainsheet on the transom, outboard, or other things near the back of the boat. I would be interested to know what other sailors have learned about the best spacing between the boom block and bridle block when sailing close hauled under various wind conditions and the merits of a movable bridle that permits the bridle block to shift its position from one tack to the other as opposed to being fixed close to the centerline. Thanks for any input.


I don't have another DaySailer to race against; that limits my ability to fine tune the rig for the best boat speed -- at the bleeding edge, the changes are so small that almost the only practical way to measure the effect is to compare otherwise identical boats. (Wind and waves make things too unsteady to use tools like GPS for more than very rough feedback).

Also, where I race, the race course is littered with obstacles (drifting spectator boats, kayaks, swimmers and what not) and there's constant interference from other traffic (there are easily a hundred boats on the course at the same time, most of them bigger). Last race I was able to hold my own against a faster boat (not a DS) almost until the end solely because of better maneuvering at various congested points -- decent boat speed was still needed, but I had the slower boat anyway, so even had I dialed in the last few percent perfectly, it wouldn't have been enough on its own. We think this type of racing is great fun, even if the purists are mortified.

However, we hear via people who race against other DS's that while an adjustable traveler should give some advantage, it's apparently small, and the differences between various configurations potentially even smaller. A strong vang should be an advantage as it allows leech tension to be influenced directly, while the main sheet's function is to affect the boom angle. (This is the inverse of how a traveler and mainsheet work together: the traveler adjust the sheeting angle and the sheet controls the leech tension).

If you are sailing by yourself, the advantage that a strong vang promises is that it should keep the sail flat, so it doesn't power up as you play the mainsheet in a gust. That should make the upper end of the wind range more easily handled, which is something you'll enjoy even if not racing.

I wouldn't be surprised if you'd be unable to tell the difference between different sheet arrangements at the back of the boom (unless you race at a high level against other DS), so stick with something that works, or, if you don't have something there yet, some design variant you like. I moved from the triangle formed by the mainsheet itself to the traveler with mainsheet doubling back. The change wasn't night and day, but it works the way it is, so I'm leaving it alone.

Biggest effect of any change I saw was with adding a ratchet block for the mainsheet.

If you don't have a vang, you might look into that one as well. I'm not sure yet whether I can really tell a difference there, I suspect we don't often enough have the kind of stronger, gustier winds where that would seem likely to make the most difference. But I'm probably handicapped by doing all of these comparisons on a single-boat basis.
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Re: MainSheet Conversion

Postby DigitalMechanic » Thu Aug 31, 2017 7:10 am

+1 on the vang. The stock one (or I guess in many cases lack of) was pretty worthless. We added a 10:1 to my boat. So far the power it provides seems fine, but is easily upgraded to 20:1 via addition of a cascade if that proves different at some point in time. Currently I have it rigged to terminate on the cuddy top. That requires me to move about more than I like to adjust, or rely on the crew sitting forward to make adjustments (ussually less experienced and already happily pre-occupied with other jobs). Thus, ease, hike, trim is the usual routine, with less vang adjustments being made than probably should be.

Recently I was introduced to this little guy... http://www.racelitehardware.com/rl-860-swivel/

Which opens the door to bring the vang back to the skipper (on centerboard truck). I have the part in hand, and plan to install it, just need to rustle up some more cheek blocks to execute the master installation plan. It seems like this is a little less obtrusive on the DSI as it has an open cuddy. I think that to keep everything tidy on the DSII I will have to put a through fairlead in the cuddy wall near the floor to lead the vang aft without disturbing my jib sheeting setup. Anyway, I think it will go something like this... vang to through deck block, to cheek block on bottom of keelson, across floor through fairlead in cuddy wall, to cheek block on centerboard truck near floor (opposite side of centerboard up/down lines), up to and through magic swivel cleat job (in link above) placed near top of centerboard trunk.

This was obviously introduced to me by someone else (would have never find that part on my own). But if all goes well, it will offer up vang adjustments to both skipper and crew. Seeing how we are talking about vangs, I though I would share the idea that passed on to me (if you don't mind putting an extra hole or 2 in the boat).
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Re: MainSheet Conversion

Postby BananaCollision » Fri Sep 08, 2017 3:43 pm

GreenLake wrote:This picture shows the apex of the traveler when going upwind

1318



Hi GreenLake, thank you for this wonderful picture. I am trying to rig my DS I that came with no mainsheet. I have a rope traveller with block similar to yours, and I have the original end-boom block, attached the same as yours to a tang on the boom end, but my pulley does not have the becket where your mainsheet end is fixed. I'm not seeing anywhere to fix the mainsheet to the boom. How was your mainsheet fixed to the boom end before you installed this nice new block?
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Re: MainSheet Conversion

Postby GreenLake » Sun Sep 10, 2017 10:12 pm

Always had the block at the top of the picture - it may have been an upgrade by a previous owner. The bottom one I had to purchase. (I'm fortunate that I live near a well-stocked marine store with a great sailboat hardware section, so I can just browse their shelves. If you have something like that in the vicinity, I'd suggest you support it well :)).

My answer in your other thread applies to the case where the main sheet forms the triangle (and there's only one block on the boom, and not one in the middle like in my picture).
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