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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #81  
Old 10-03-2007
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Quote:
Originally Posted by SEMIJim View Post
Providing nobody comes up with any show-stopper comments regarding the latest (Harken) components we've selected, I'll order them this weekend and get 'em on their way.
I may be late to this party, but I thought that I should mention something that I didn't see spelled out above.

In the world of mechanical advantage (ropes and sheaves, levers, gears, etc.), you don't get anything for free. I saw it mentioned many times that your sheet loads are too high, and that it may be due to the 3/4 boom attachment, which is certainly possible. It was also mentioned that you didn't want too much line piled up in the cockpit when close-hauled. But remember that by going to more parts of line, the line-pull is lower while the amount of line needed is increased, but the change in distance between the blocks is reduced, so you can end up in the same place.

If the two blocks were in the same horizontal plane, then for a given sheet pull force at your hand (ignoring friction), and the same horizontal angular change in the boom, a 2-part system at the end of the boom is equivalent to a 4-part system at mid-boom. Same force at your hand, same amount of line used to bring in or let out the boom a certain angle. You'd be bringing in and letting out the same amount of line during a jibe.

So, assuming the original main sheet system was 4 parts at the end of the boom, and you now are connected at the 3/4-point, you would have 4/3 the force at the boom connection (for a given wind load and boom angle), resulting in a 33% increase in the force in your hand (not counting friction, which is substantial with low quality blocks). You would also only use 3/4 of the amount of line it took with the blocks at the end. You pull less line, but you pull harder.

To bring the single-part force and amount of line used back to where it was with the original configuration (assuming it was 4 parts at the end), you'd need 5.333 parts of line (4/3 x 4 parts). That leaves you with either 5 or 6 parts. 5 parts and you pull less line, but pull harder; 6 parts for a lighter hand, but a bit more line gets used.

If the boom attachment was at the 2/3 point, then a 6-part system would give you exactly the same force at the hand and amount of line used for a given angle change as the original 4-parts system at the end of the boom.

The whole problem gets more involved if the fixed block is now at a different elevation than it originally was, making the forces required when close-hauled higher if the block is now lower than it was originally, assuming you're trying to bring the boom to the same angle from centerline as before. If the fixed attachment is lower than original, then 6 parts is more likely to emulate the original configuration, though with a cost in amount of line used further off the wind.

Mind you, this is just a comparison of the original arrangement to the new arrangement - no commentary on whether what you think it originally had is right or even desireable. And, as mentioned before, the forces in the boom change as you move the block termination towards the mast, as well as the attachment forces going up. Even the reaction at the mast connection is different.

But I just thought that I should point out that if you match the number of parts to the relative boom location, you'll get the same force at your hand, and the same amount of line used for a given angle change, no matter where you attach it. Force times distance for a given boom angle change can be the same regardless of how many parts are used if you terminate them at the right spots and use low friction hardware.
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  #82  
Old 10-04-2007
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Let's compare my boat with his; just to give some perspective. If our main is full (300 ft^2) and we have 25 kts true wind; the sheet load will be 2000 lbs (harken calculator). My boat has appx 3/4 boom sheeting spread across 3 pulleys giving a 5:1 purchase. The approximate load on the sheet is 400 lbs. With a 2-speed winch on the doghouse at the cockpit the load gets reduced to 66 lbs at the 1'st gear (1:1 winch drum to handle; 6:1 leverage), and at 2'nd speed the force is 10lbs on the winch handle (40:1 leverage).

At 66 lbs of force on the handle it is a tough grind to sheet the main down to close-hauled from a close reach unless we luff and pull it in by hand. At 10 lbs force we can grind it down to proper trim but it does take some time and effort.

What I am trying to point out is that on Jim's boat with a 6:1 sheet he still will not have enough purchase to do much of anything with the mainsheet unless he luffs the sail. At a load of 1580 lbs on the blocks; the 6:1 setup will have a load of 265 lbs on the sheet. At that load you definitely would need to have a ratcheting cam to safely spill the sheet, and you won't be able to trim it in if you need to flatten the sail (without rounding up into the wind first). If Jim wants a "manageable" system I think a two speed sheet would be the needed (like a 6:1/24:1) setup.

Jim, it's possible that you could re-use your old schaefer blocks to get the 24:1 trim (until you decide you want a better pair of blocks for that part)!
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  #83  
Old 10-04-2007
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I have '78 P31 with mid-boom sheating in the same location as yours. It has basically the same setup that (6/1 Harken) you are considering and it works very well. The only difference is I use 1/2" line which is easier on the hands. In light airs I just convert it to 4/1 by taking one loop off of the blocks.

Overall it works well, feels comfortable, simple to use. My cam releases by pulling down, and I would not want it the other way. In a high stress situation the last thing you want to do is have to stand up to release it.

And by the way, my compliments on keeping you mind open with all the different opinions coming your way...
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  #84  
Old 10-04-2007
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Re: Unmanageable mainsheet

Your mainsheet has two problems. First, the blocks used do not have ball bearings. More than likely the PO took a much better system with him to his new boat. The older clamcleat with stainless jaws is a bear to operate. Second, the midboom sheeting leaves you with less leverage.

I suggest that you go to Layline's website and look at your options for various systems. You may want to go with fiddle blocks from Lewmar or Harken with a smaller cascade attached where the becket usually goes. This will give you a fine and gross adjustment system. The disadvantage is that you will have extra blocks moving across your cockpit. Try a new ball bearing fiddle block system first then add the cascade if needed.
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  #85  
Old 10-06-2007
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Jim,
Kudos to you. You've gotten and absorbed a veritable ton of advise, made decisions, and changed them. Throughout you've kept perspective and open mindedness on a fairly expensive topic. I am impressed more than a little.

I think it's also time that you and the Admiral sit down and try to reach a consensus of where the boat project is going, if you have not done so already. It's easier to spend money on the things you want than the things you need. And every time I spend money on something to get me by, I end up kicking myself later for not buying the product that will meet my long term needs now. Hey!, I got an excuse, I'm Dutch. That being said, your main sheet blocks will in all likely-hood be the last you ever buy, for this boat or any other and, as you realize, if you buy what you want to spend you may well end up buying again with remorse similar to mine. The meeting with the Admiral might be to no other purpose than you jointly assigning priorities to boat gear. There are people in similar straits to you who go light on the blocks and turn about spending $1000 on custom cushions. A joint resolution to make the boat an all-weather sailer first, a comfortable and beautiful boat second will go a long way to "uneventful" sailing.

I suspect that you know all of this, I just wanted to emphasize the need for a consensus on the battle order. A list with 3-5 levels of priority will aid in that. Many people end up having a boat for years and never do get down to those level 5 items-they're too busy sailing. It's also not a bad idea to have assigned an individual frivolous budget to each person annually. That is money that may be spent unilaterally by either party on something for the boat without permission from the other party. The item may not be frivolous, but it may not be a 1 or 2 priority to the other party. I believe that it was under this provision that CruisingDad acquired his third bbq grill! This makes it just a bit less contentious when either person just has to have something but does not have the logical argument for it's purchase ready to hand. Personally I do not favor a roll-over option on the frivolous purchase clause. That's how you end up with a really expensive oil lamp you'll never use, doesn't fit in the boat, and cost multiples of tuition payments at decent colleges. Annual amount, use it or lose it, or donate to the other party on the strict understanding, "you owe me".

By now you've probably opened a smaller than expected package, gazed upon the contents, and proclaimed, "that's all I get for all that money?" Every time I come home from WM and empty out my sack I have the same feeling-seems like it looked much more substantial when I was buying it at the store than sitting on the counter at home. And the receipt looks far more substantial than it did on the register, when laid alongside the purchase at home. You'll be comforted by the fact that your fellow marina members will be willing to give you about a dime on the dollar to take it off your hands if they're feeling particularly loose with their money that day!

Good luck with the rigging. Again, I am impressed with your level-headedness.
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  #86  
Old 10-06-2007
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Quote:
Originally Posted by sailaway21 View Post
Jim,
Kudos to you. You've gotten and absorbed a veritable ton of advise, made decisions, and changed them. Throughout you've kept perspective and open mindedness on a fairly expensive topic. I am impressed more than a little.
Thanks for the kind words

Quote:
Originally Posted by sailaway21 View Post
I think it's also time that you and the Admiral sit down and try to reach a consensus of where the boat project is going, if you have not done so already.
We've pretty much already done that. We work together well on this kind of thing, so, while there may be much discussion and gnashing of teeth, at times , we tend to come to mutually agreeable decisions.

Quote:
Originally Posted by sailaway21 View Post
It's easier to spend money on the things you want than the things you need.
Ah, well, you see: That won't be a problem for the nonce. As the common wisdom, borne of experience, goes: This boat has already cost us far more than anticipated. So the well's pretty much run dry for now. IOW: Unless it's absolutely necessary, it ain't gettin' bought. Right now there are only two "must have" items remaining: An oil pump-out adaptor for the A4 from Moyer and an adequate pump, and a rebuild kit for the head. The only near-term "big ticket" item is we're considering having the aft 1/3 of the cockpit deck taken-up, re-cored and re-glassed by a pro, then paint the decks (ourselves). We realize the running rigging, while in serviceable condition, is showing its age--some of it. So we've got a plan to start replacing that incrementally. That one shroud with a couple broken strands will be replaced this fall, and the remainder of the standing rigging inspected when the mast comes down on haul-out.

The only "non-essentials" that are on the list are (possibly) a backup hand-held VHF radio and a backup hand-held GPS. (We have the latter, but it's an old GPS II and doesn't work all that well. It's slow, hard to read, tends not to acquire satellites well...)

Quote:
Originally Posted by sailaway21 View Post
And every time I spend money on something to get me by, I end up kicking myself later for not buying the product that will meet my long term needs now.
Well I know that effect. It's been one of the stories of my life.

Quote:
Originally Posted by sailaway21 View Post
Hey!, I got an excuse, I'm Dutch.
So's my wife. Right "off the boat." We were married in a suburb of Amsterdam .

Quote:
Originally Posted by sailaway21 View Post
A joint resolution to make the boat an all-weather sailer first, a comfortable and beautiful boat second will go a long way to "uneventful" sailing.
I think we both agree on that point.

Quote:
Originally Posted by sailaway21 View Post
It's also not a bad idea to have assigned an individual frivolous budget to each person annually. That is money that may be spent unilaterally by either party on something for the boat without permission from the other party.
We already do that. Have been doing it for about ever since we were married. We each get an "allowance" each pay day, to spend as we see fit. My Plastimo Iris 50 came out of my own, personal "piggy bank." One thing that prevents, other than arguments, is the "If you're getting this than I'm getting that" and then we end up broke from buying toys.

Quote:
Originally Posted by sailaway21 View Post
Good luck with the rigging. Again, I am impressed with your level-headedness.
Thanks!

Jim
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  #87  
Old 10-07-2007
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Jim,

I realize that I'm more than a few days late to this party, so I hope this hasn't already been covered.

A few pages back you had a question about "conflicting" advice about sail trim using the traveler. One guy says sheet the sail hard and use the traveler to trim. Another says to ease the sheet and trim with the traveler. Both are actually correct, dependant on wind conditions. Sheeting in hard and trimming with the traveler helps me point a little higher in light wind. Setting the traveler to windward and easing the mainsheet puts twist in the sail in stronger winds. A set of teltails on the leach of the main will tell you how much twist you need. The bottom ones are easy, getting the top one to fly takes a little work.

Good luck with your mainsheet.

John
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  #88  
Old 10-08-2007
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US27inKS,

I think somebody mentioned that in a mainsheet traveler question in the Learning To Sail" sub-forum. I'm not sure. But thanks for the info. I think I'll paste your comments into a "cheat sheet" file I have, that'll I'll occasionally re-print and keep on the boat.

Jim
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Old 10-08-2007
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Jim,

what's the deal? Which arrangment did you decide on? Have already tried it?
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Old 10-08-2007
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'When you moved the mainsheet forward you changed its leverage on the boom. Halfway up the boom would double the sheet tension, all else equal. A few options:

Get a mainsheet with 8 parts (yours is 4). Sheet tension would be back to normal. Maybe you could get away with 6.

Get a small vang and rig it between your becket and mainsheet. You use your old sheet for gross, low-tension adjustment, and the vang for fine, high-tension adjustment. I think Harken sells a complete system like this, but it must be very expensive. A 2-part vang would double the force on the boom, getting you back to your old sheet tension. A 4-part vang would quadruple the tension, so your sheet tension would be half of what it used to be when it was led to the end of the boom. These systems must be clumsy to use.
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