Using the mast jack

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Using the mast jack

Postby dsheer » Fri Mar 24, 2006 11:23 am

My DS1 has a cuddy stepped mast and a mast jack. I freed the plate on the jack, and now it turns easily. I've never had a mast jack before. Seems like a nice, easy way to adjust the shroud tension for the wind, especially if the jib halyard is providing tension on the forestay line. I notice that some posts seem to imply this is illegal for racing, however.

I assume that when the shrouds are at sailing tension, the jack set just high enough so that when lowered to the bottom it unloads the forestay and makes it easier to detach and then re-attach the stay when stepping the mast. Or, does the jack tend to slip when underway and does everyone just leave the plate at the bottom and do all tensioning with the turnbuckles? Or, is there some mystical incantation that must be used in determining a proper setting. Should I ask Hermione or Harry (Potter that is)?

Dan
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I think you are mis-understanding the purpose of the jack.

Postby captainseasick » Fri Mar 24, 2006 2:12 pm

The mast jack is not designed to control shroud tensions. That is done with the turnbuckles once mast jack is set. The fact that the tension changes as you adjust the jack is incidental.
moving the mast butt back, adds more bend into the lower 1/3 of the mast. As it goes forward , less bend in this portion of the mast is induced. Mast bend is designed to match the luff curve of your mainsail, and will make the draft (belly) of the sail fuller (with less bend) or flatter (with more bend) a fuller sail gives more power in light air, but as wind increases, a flatter sail causes less healing and gives more forward drive. The fore stay tension controls the upper section of the mast's curve. The top third of the sail's curve is not adjustable, and depends on the stiffness or taper of the spar above the hounds. Racing rules merely state that you must set the jack before a race, but adjusting during competition (to respond to wind strength changes) is not allowed, nor is it practical, as as you noticed, your tensions will also change and would need readjusting.
I hope this helps you
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Postby dsheer » Fri Mar 24, 2006 2:59 pm

Thanks for the reply, and sure 'nuf, if the mast jack is to move the mast butt fore and aft, I don't understand. Certainly that's not how it's set up on my boat. I Just bout the boat and haven't sailed it yet, so sorry to sound so dumb. Smart enough to ask, though.

My mast has a hole in the bottom plate that fits very nicely over the screw on the mast jack - about a 3/4 inch hole. The boat came with the mast jack screw in the hole, with the mast resting on the adjustable round collar. Adjusting the collar moved the mast up and down, not fore and aft.

Please tell me how things are supposed to fit together or if there is a picture somewhere I can look at. I'm guessing I'm missing a part or parts.

Dan
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Postby dsheer » Fri Mar 24, 2006 4:36 pm

I just looked up the mast jack function in the DS1 manual (duh). The purpose described is as I originally thought - to "take the slack" out of the standing rigging. The manual describes the installation I found on my boat. So, back to the original question, rephrased - Does anyone use the mast jack this way, or do most people set it at the bottom and do everyting with the turnbuckles? How do you set the tension on the stays to take advantage of the jack? I understand that you are not allowed to mess with the jack during a race, but would you do it if you could?

Also, how do you move the base of the mast for and aft as you described? There is a slot in the keel on my boat that would allow such movement, but no adjustment absent drilling a new hole for the single bolt that positions the mast jack. Is there a device that can be put in the slot to adjust the fore and aft position of the mast?

The hole for thet bolt that holds my mast jack (and there is only one hole on my boat) is a little worn. Does it take much stress? Should I reinforce it? How? Glue a stainless steel strap on both sides of the keel?


Thanks for taking the time to inform a novice DS1 sailor.

Dan
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Using the mast jack

Postby DS 129 » Fri Mar 24, 2006 4:49 pm

I have an early DS 1, I was surprised to find that the originally designed shrouds had no turnbuckles. What you do is get the mast upstraight, with the heel of the mast in place on top of the jack mechanism, with the "hand wheel" lowered. Connect the shrouds at the "chainplates", pull the top of the mast forward with the fore stay, connect the fore stay at the stemhead, go under and screw up the "handwheel" to get tension in the rig. (you may need a wide mouth pliers, a spanner wrench, or such). That's it, it only goes up or down not back and forth or sideways Now, as far as mast bending philosophy is concerned, thats all poppycop on a DS 1. Mast bending probably wasn't even invented when the DS was introduced almost 50 yrs ago, its only a "day sailer". Enjoy
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It's "only a Daysailer"

Postby captainseasick » Sat Mar 25, 2006 9:45 am

Spoken in all probability from someone in the back of the fleet! mast bending not invented 50 years ago? Tell that to George O'Day and Uffa Fox. I have not seen a boat with no tension devices for shrouds, or a jack that doesn't go fore and aft, I can learn something new. I think Daysailers are a very elegant design, way ahead of its time. These boats are responsive to tuning.
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I just discovered

Postby captainseasick » Sat Mar 25, 2006 2:15 pm

I don;t know JACK
Michael D. Schreibman
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Postby dsheer » Sat Mar 25, 2006 9:34 pm

Mike,

My boat clearly does not have a jack that moves the mast fore and aft, it only moves up and down. What do fore and aft jacks look like and where can I get one if I want one.

Thanks

Dan (maybe soon to be back of the fleet).
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Mast ram

Postby captainseasick » Sun Mar 26, 2006 8:34 am

Harken has a page that shows you how to construct one
I actually didn't understand that the mast jack described was not a mast ram. It didn't dawn on me that the system they used was not designed to back and forth, where some benefit could be gained , instead of a tightening device.
You can see a mast ram at:
www.apsltd.com/Tree/d3000/e743a
I apparently confused a mast jack, with a mast ram.
Mike
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oops, I tried my own link and it didn't work

Postby captainseasick » Sun Mar 26, 2006 8:48 am

Try googleing APS mast ram
Also several suppliers for the 505 one design describe how to construct a mast ram. As long as they are not adjusted during a race they are class legal
Mike
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using the mast jack

Postby DS 129 » Sun Mar 26, 2006 1:40 pm

Didn't really want to get anybody, as they say, "all bent out of shape", but for historical reasons just wanted to point out that the DS129 (1959 genre) currently still has original rigging as configured by the factory at that time. As I say, no turnbuckles, the only "tuning device" is the unusual mast jack mechanism. Now this leads me to believe that this was put out as an entry level sailing platform. Even so, people will be inclined to race anything, some will enjoy racing in bathtubs, paddeling away. I would suggest that if you are going to do "one design" in the DS's, it would best be done without didling with the rig, so that novices learn to sail and maybe a little about racing rules, before they try any serious racing, then move up to high tech if so fascinated. "Keep it simple".

Now if you really wanted to try mast bending, the DS fractional rig is ideal. What you do is use an "adjustable backstay" from the top of the mast down to the stern, and tighten to get the desired bend. But not practical with the low aspect main, so you need an old method used such as a pair of "running backstays", one to each side, but then you would need an extra crew to handle these.

Once upon a long time ago, did crew on a 17' "Thistle", a moulded plywood hull, I believe designed by Uffa Fox and I believe the first mass produced sailboat able to get up to plane.
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Postby dsheer » Sun Mar 26, 2006 9:50 pm

Never knew I would start such a discussion. But thanks to you both, I've got a course of action. I got some guidance on shroud tension from other posts. I think it's probably a good idea to use the mast jack to de-tension the entire rig for stepping, so I'll raise the mast, mark the jack so I know where I had it, and set the tensions, and lower the mast for stepping.

I certainly need to get familiar with the boat before I plunk down $200+ for a mast ram. Since I can't adjust it underway while racing anyway, I'm thinking that a line of strap reinforced holes for the bolt that secures the mast jack to the keel could easily serve as a poor man's mast ram. Since I can use the mast jack to unload the rig, I might even be able to change the setting while luffing the sails in order to experiment.

That's my story and I'm stickin' to it. Thanks to all for the info. And a wonderful forum it is, too.

Dan
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Postby Phill » Wed Mar 29, 2006 9:48 pm

The mast jack has great value for adjusting the rig tension as mentioned above. One very successful current racer still uses it for fine tuning to the conditions before each race. (as mentioned NOT legal to adjust durning a race) Once the forstay, shrouds and mast butt location are tuned for the boat, I have not changed them for a few years. Only rig tension is adjusted with the mast jack.

JMHO phill 8)
G.S. Lollipop
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ram - jack

Postby crawford » Tue Apr 04, 2006 5:24 pm

Thank you all for your intensity. My 1960 DS1 has no adjusters on shrouds but am buying one for the fore stay, soon to arrive from Duckworks) Then I hope I can put a little bend in the stick by raising, tightening, the mast jack.
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