Asymmetric rig

Moderator: GreenLake

Asymmetric rig

Postby GreenLake » Mon Jun 14, 2010 4:32 pm

Just checked the position of my chainplates. The SB one is .75 to 1" further forward than the one on Port, depending on whether the mearsurements are taken from the stemhead fitting or to the transom.

The curious thing is that the chainplate is located at a spot where the deck has been reinforced by a bump that appears molded into the deck.

The stemhead is centered relative to the non-skip patters molded into the deck and the bow, and the meafurement to the transom I did by measuring to the crease in the deck, to have a consistent point of comparison (rather than the edge of the rubrail).

Did O'Day really manage to create a mold where crucial fittings are off by a whole inch. Yikes!

Is it just me, or are modern boats manufactured to tighter tolerances?
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Postby K.C. Walker » Mon Jun 14, 2010 8:10 pm

I suppose you could look at it as being reasonably close tolerance. Let's use the .75 inch measurement and assume that each chain plate is off by .325 inches, that's not too bad! :-)

KC
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Postby algonquin » Tue Jun 15, 2010 11:28 pm

K.C. Walker wrote:I suppose you could look at it as being reasonably close tolerance. Let's use the .75 inch measurement and assume that each chain plate is off by .325 inches, that's not too bad! :-)

KC


I agree with KC on this one. Really not to much of a variance considering the manufacturing process of the day. All things considered the mast my be off just enough that everything comes out equal. Of course with stacked tolerances that could easily go the other way. :? Brad.
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centerboard is off center

Postby Roger » Wed Jun 16, 2010 7:28 am

so I guess this is not the time to tell you that the centerboard trunk is not exactly on center either!

I can't remember which way it is off center but memory tells me it is off to port by about an inch.
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Re: centerboard is off center

Postby K.C. Walker » Wed Jun 16, 2010 8:01 am

[quote="Roger"]so I guess this is not the time to tell you that the centerboard trunk is not exactly on center either!

The funny thing about all this asymmetry is trying to figure out where to measure from to figure out what's off and where. When I was doing my "core project" on the bottom of my boat, Phill Root warned me to be careful not put additional asymmetries into it or a twist. That's when I noticed my centerboard was "out of plumb".

I think that the centerboard trunk exits the hull reasonably on center on my boat but it definitely leaned a half-inch to starboard. Sighting from the transom forward it was obviously not in line with the mast or the keelson. I did decide to straighten that out before making everything rigid again. I seriously doubt I would've been able to distinguish the difference in the sailing of the boat, though.

The DaySailer is not alone in this, for sure. The J-24 it is quite asymmetric. Rodney Johnstone built the 1st one in his garage. When they decided to go into production they just used his boat for the plug. I recall a comment of his that went something like, "if I'd known this boat was going to be so popular I would've been more careful about symmetry". Of course with one design you can't go back and fix things. :-)

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Postby GreenLake » Thu Jun 17, 2010 8:23 pm

From another thread about adding rowing seats to a DSII:
talbot wrote:My centerboard trunk is not in the center of my boat, the tanks are not parallel to the trunk, and the tanks do not even converge on the cuddy at the same angle.


Now are the DS optimized for racing around the buoys in a clockwise or anti-clockwise manner? :roll:
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Postby GreenLake » Sat Jul 10, 2010 10:59 am

I've checked some more and found that the fit of the mast partners around my mast is a bit loose, so the mast can turn a bit. Measured at the sail slot, it's nearly .5".

That would mean the mast can rotate 15-20°. I have no idea what that does to sailing, but it would mean that fixing a Windex to the mast, with the little tabs that demarcate the tacking angle is a hopeless thing - no matter how carefully you align them, they could rotate.

Don't know whether that much play in the mast partners is typical for other boats, but I was surprised at how large an angle the mast could rotate.
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Postby K.C. Walker » Sat Jul 10, 2010 12:23 pm

I would think that that amount of tolerance in the partner would be typical and you would need that much leeway to easily slip the mast through. I think the step would be what would keep the mast from rotating typically. I don't have a mast jack so my mast doesn't rotate even though I have room in the partner. You could always make some wedges for the partner if you wanted the mast to stay put.
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Postby GreenLake » Sat Jul 10, 2010 7:44 pm

You remembered - I do have a mast jack, so there's nothing that prevents rotation. The force needed to turn the mast when the stays are tight must be considerable, because I've never observed any play when raising sails, etc. However, wind at 10kt would probably load the gooseneck and sail-track with enough sideways force.

Aerodynamically, it might give a slight advantage (mast isn't the right shape, I think, to really profit from this), but it skews the Windex in perhaps not fully predicable ways. I tumbled to it when I tried to sail to the Windex as part of a test and another boat let me know my SB tacks were off 15° compared to my port tacks. First I thought I had my wires bent on the little tabs for the Windex, but then I found the real reason...
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