lateral/longitudinal baffles

[TiredFeet]

Thinking of an UQ for a Bridge (any other?) and the choices available.

So far, we've thought that maybe longitudinal (end to end) baffles would accomplish some things better than lateral baffles:

1. sides - keep the sides better insulated by preventing the down from migrating under the hammock. Down migrating under the hammock would provide somewhat better insulation for the torso, but also tend to compress the down more.
2. manual bunching - the longitudinal baffles would allow for the down to be manually moved towards the torso if needed. This would tend to compress the down more, but if it got really cold, it may be necessary. It would leave the legs with less insulation, but the torso would be more important.?.?

So does anybody have any experience with longitudinal vs lateral baffles??

Any thoughts thoughts concerning one being better than the other??

Any thoughts concerning what any differences would be in use?

I see that the JRB Mt Washington has lateral baffles, while Younhgblood's Snugfit has longitudinal baffles.

Has anybody been able to do a side by side comparison taking note of the baffles?

Youngblood - why did you choose longitudinal baffles?

Pan - why did you choose lateral baffles?

[Schneiderlein]

I have very little experience with bridge hammocks, but from my first impression last night it seems that the bridge hammock is pretty much flat in the long axis and only curved side-to-side. I would probably go with longitudinal baffles, and make the outer shell larger to achieve a "differential cut", which prevents down compression when the quilt is pulled up against the hammock. Youngblood posted some nice pictures illustrating the effect a while back.

You mention insulation under your legs, so I assume you are thinking about a full-length quilt, so I thought I'd mention the following. When I made my first quilt, I initially had a lot of trouble controlling the stretch in the noseeum baffles when sewing them on. On my trial runs, I would sometimes get a huge discrepancy between the shell and liner, maybe over an inch on a 48" long baffle. If you know how to control the stretch, I would say go with the length-wise baffles even on a full-size quilt. On a short underquilt, definitely go with the lengthwise baffles and a larger shell than liner.

My recommendation, however, would be to join all the cool kids and make yourself a short underquilt. In a bridge, the sit pad under the legs works even better than in an end-gathered hammock, and I would go with a quilt about 54" insulated length (60" fabric width minus rolled hems).

[GrizzlyAdams]

This very day I finished an UQ for my bridge hammock. Differential in the shell sizes to eliminate compression. I chose longitudinal baffles, mostly because I knew I could cut straight baffles and have to worry only about the right widths for the inner and outer bodies in order to get the loft I want from the baffle height. People that have talked about differential quilts and gone the latitudinal route seem to have cut the baffles with a curve, to match the anticipated curve around the body. I'm not sure what curve to assume, and it seems to me that there is more tolerance for diffferent curves with the longitudinal approach.

Mine is 36" at the head, 30" at the foot, 60" long, and has 3.5" baffles.

Grizz

[Schneiderlein]

This very day I finished an UQ for my bridge hammock. Differential in the shell sizes to eliminate compression. I chose longitudinal baffles, mostly because I knew I could cut straight baffles and have to worry only about the right widths for the inner and outer bodies in order to get the loft I want from the baffle height. People that have talked about differential quilts and gone the latitudinal route seem to have cut the baffles with a curve, to match the anticipated curve around the body. I'm not sure what curve to assume, and it seems to me that there is more tolerance for diffferent curves with the longitudinal approach.

Mine is 36" at the head, 30" at the foot, 60" long, and has 3.5" baffles.

Grizz

I am looking forward to the equations describing how you computed the differential in shell and liner to achieve your desired down chamber volume. Oh, pictures would be nice, too!

[Youngblood]

Youngblood - why did you choose longitudinal baffles?

IMOH, a well fitting underquilt needs differential shaping along both the length and width as well as a good suspension system that will hold it where you need it to be. You can create the curves with both curved baffles and radially spaced baffles. You can orient the baffles length-wise or width-wise. I chose length wise because it gave me fewer baffles to fill.

For a 'flat style' top quilt you probably only need curvature along the width. For that case you could use curved width-wise baffles or radial spaced, straight length-wise baffles.

As far as down shifting, for the SnugFit I used a proprietary calculation that I derived to minimize down shifting, or migration. What it amounts to is a precise calculation that fills the chambers regardless of their shape when the quilt isn't stretched out. The calculation takes in to account both baffle spacing and baffle height. Smaller baffle spacing with more baffles requires less overall down and yields a more consistent quilt. If you don't do that the down can shift at times. It is basically a calculated overfill. It adds warmth and more consistency in how the down is distributed (less issues with cold spots).

[GrizzlyAdams]

..
As far as down shifting, for the SnugFit I used a proprietary calculation that I derived to minimize down shifting, or migration. What it amounts to is a precise calculation that fills the chambers regardless of their shape when the quilt isn't stretched out. The calculation takes in to account both baffle spacing and baffle height.

Cool. Not to try and figure out your calculation, but I am interested in what physical principles they rest on when figuring out what down does inside a chamber. What kind of literature ought the interested reader be looking into?

thanks.

[Youngblood]

Cool. Not to try and figure out your calculation, but I am interested in what physical principles they rest on when figuring out what down does inside a chamber. What kind of literature ought the interested reader be looking into?

thanks.

Grizz,

I couldn't find much when I looked around on that or differential baffles. Certainly they are not new issues or subjects but I couldn't find much info on the Internet and had to figure much of it out for myself. I gave some clues on various threads to generate interest in my designs but it seems the primary beneficiaries on my theory on differential baffles have been my competitors as they have likely used it to help re-design their products, who folks seem to have more interest in. I would feel better about all this if I actually got most of the benefits from my work.

You can find some info on down fill versus baffle width/baffle height on the Internet. What I found on Stephenson's site was inconsistent with my own analysis and in this matter I have more trust in my own analysis as it is actually pretty straight forward (aren't a lot of solutions like that, if you know the answer there isn't much to it ).

Grizz, I will give you this clue. Think about the cross sectional shape (and then area) of a single baffle and then a series of side by side baffles. The limp cloth that makes up the chambers aren't smart fabric, they don't know what they are suppose to do and what shape to be and when to be that shape. They are like "Whatever man, I don't care, I'll be whatever you want me to be!" If the down in the baffled chamber doesn't fill up one of the many shapes the fabric makes, then gravity can determine where the down ends up.

[GrizzlyAdams]

Grizz,

I couldn't find much when I looked around on that or differential baffles. Certainly they are not new issues or subjects but I couldn't find much info on the Internet and had to figure much of it out for myself. I gave some clues on various threads to generate interest in my designs but it seems the primary beneficiaries on my theory on differential baffles have been my competitors as they have likely used it to help re-design their products, who folks seem to have more interest in. I would feel better about all this if I actually got most of the benefits from my work.

You can find some info on down fill versus baffle width/baffle height on the Internet. What I found on Stephenson's site was inconsistent with my own analysis and in this matter I have more trust in my own analysis as it is actually pretty straight forward (aren't a lot of solutions like that, if you know the answer there isn't much to it ).

Grizz, I will give you this clue. Think about the cross sectional shape (and then area) of a single baffle and then a series of side by side baffles. The limp cloth that makes up the chambers aren't smart fabric, they don't know what they are suppose to do and what shape to be and when to be that shape. They are like "Whatever man, I don't care, I'll be whatever you want me to be!" If the down in the baffled chamber doesn't fill up one of the many shapes the fabric makes, then gravity can determine where the down ends up.

Fair enough. Your competitors must be pretty smart---I've read and re-read those hints, and without figures, in my reading, they leave themselves open to different interpretations. This is a pretty common phenomena with me though (to see potential alternate meanings in what to someone else may be straightforward).

So I've made all of two down quilts in my whole life. The spacing between baffles on the first one 6 inches, because I'd planned to put measured volumes of down in baggies, stick my hand in there and open it up. Which is what I did. And didn't want to do that again

The one I just did I was also spaced at 6" on the inner body, but I learned the trick (I think mikeinfhaz described it) of using a vacuum cleaner to transfer down. I could easily had baffles separated by 2.5", just what is needed to get the vacuum cleaner hose in the chamber. Which I wish I'd done. Because, as you just pointed out, if the down isn't shaped by the chamber then gravity will cause it to settle. I didn't figure gravity in my calculations.

This whole differential quilt thing is a whole lot simpler for a bridge hammock, because the body lays in a straight line. At least when one's body is laying in a straight line....remains to see what happens when I curl up a little.

But I'll also say that the idea of a differential cut quilt would not have occurred to me were it not for the snug fit, and there's no way I would have thought to try and make one myself had it not been for others on HF that did. By all accounts the snugfit is a brilliant piece of engineering. And remember, imitation is the sincerest form of flattery.

BTW, if you're reading this mikeinfhaz, thanks for the vacuum cleaner tip! While I could only move about 2g of down at a time, it was sooo much cleaner and straightforward than what I'd done before...

Grizz

[TiredFeet]

We're strongly leaning to longitudinal baffles for several reasons:

1. fewer baffles - we want a full length UQ. After reading BB58 review of the Mt Washington, a full length is just so much easier to use. Also, if a pad is needed for the legs, a means is needed to suspend the pad, either a pad pocket or something suspended from the hammock. Since we don't anticipate ever using a pad pocket and since TeeDee and I both have learned from experience that a pad in the hammock is just not a viable solution for eiher of us or anybody that we know, we would have to suspend something. That just then really complicates things - easier to just suspend the UQ and forget the pad unless needed to give the UQ a boost. And like Youngblood pointed out, the fewer the baffles the easier it is to make.
2. easier to fit to Bridge Hammock - lateral baffles would require just too much experimentation to get the inner and outer radius's of the baffles right. With longitudinal baffles, the baffles can be a constant width since we don't anticipate needing to have a curve on the length of the Bridge Hammock. The Bridge simplifies things considerably in that respect.

We will use parabolas to compute the differential shells. Can use the same program TeeDee has for the end panels, just increase the depth of the parabolas by the anticipated loft desired. The parabolas used for the end panels fits the curve of the Bridge exceedingly well and so we anticipate that they would fit the full length of the hammock.

[GrizzlyAdams]

We're strongly leaning to longitudinal baffles for several reasons:

1. fewer baffles - we want a full length UQ. After reading BB58 review of the Mt Washington, a full length is just so much easier to use. Also, if a pad is needed for the legs, a means is needed to suspend the pad, either a pad pocket or something suspended from the hammock. Since we don't anticipate ever using a pad pocket and since TeeDee and I both have learned from experience that a pad in the hammock is just not a viable solution for eiher of us or anybody that we know, we would have to suspend something. That just then really complicates things - easier to just suspend the UQ and forget the pad unless needed to give the UQ a boost. And like Youngblood pointed out, the fewer the baffles the easier it is to make.
2. easier to fit to Bridge Hammock - lateral baffles would require just too much experimentation to get the inner and outer radius's of the baffles right. With longitudinal baffles, the baffles can be a constant width since we don't anticipate needing to have a curve on the length of the Bridge Hammock. The Bridge simplifies things considerably in that respect.

We will use parabolas to compute the differential shells. Can use the same program TeeDee has for the end panels, just increase the depth of the parabolas by the anticipated loft desired. The parabolas used for the end panels fits the curve of the Bridge exceedingly well and so we anticipate that they would fit the full length of the hammock.

The one I just did used circles to compute the differential shells.

Does it matter? Maybe not. It's easier. You don't need to write a program to do the math, just need to remember the formulae for circumference and area that Sister Mary Augustine tried to teach in 9th grade math. I thought about using a parabola, but while my head is pointy mostly my butt and shoulders aren't, so I thought a less articulated shape at the bottom made sense.

In my experience over these last months using a partial length UQ, I've found that a small pad inside the hammock to put my feet on isn't a problem. Stays put. That's me though.

Grizz