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Wotname 03-09-2008 08:31

Para-Anchor Fabric Question
 
OK this question is open to all - meaning those who have some experience and also those who only have an opinion :).

What is the most suitable fabric for a para-anchor?

I am thinking of making a 10 ft diameter para-anchor and can't decide what fabric to use. So far I am considering the following:

1. 8 oz nylon similar to what is often used for sail bags. Should be strong enough (I think) and has some stretch (which is good). Not sure if it will be too heavy or not.

2. 1.5 oz ripstop nylon similar to what is often used for spinakers. Probably not strong enough.

3. Dacron - too stiff and not enough stretch ???

4. Shade cloth. A knitted HDPE fabric. Initially thought this would not be strong enough but perhaps it is. Most shade sails seem pretty robust. I don't think the porosity of this fabric is an issue but it still doesn't seem quite right.

Any suggestions are welcome.

For those who are interested in detail, I am designing the para-anchor to be an semi ellipsoid with a y to x ratio of .707, 10 ft diameter and 8 gore panels. 16 shrouds about 25 ft. Circumference and gore seams reinforced with 2 inch webbing with 1 inch webbing reinforcing down the centre of each gore panel.

Talbot 03-09-2008 09:56

I question your decision to trust your life to a last ditch safety system, that is not only an unknown design, but also unknown material. IMHO not a good place to be looking for savings - next you will be making your own liferaft

Ancora Latina 03-09-2008 19:21

Quote:

Originally Posted by Wotname (Post 201322)
OK this question is open to..... those who only have an opinion :).
I am thinking of making a 10 ft diameter para-anchor

What about a Jordan Series Drogue?

Jordan Series Drogue

Evan 03-09-2008 21:00

Paratech uses a 4oz woven nylon

Whimsical 04-09-2008 01:50

Quote:

Originally Posted by Talbot (Post 201366)
I question your decision to trust your life to a last ditch safety system, that is not only an unknown design, but also unknown material. IMHO not a good place to be looking for savings - next you will be making your own liferaft

Given a little research into construction materials and method I think it is a quite reasonable undertaking especially as the originals are only the same material using the same low tech construction - sewing.
A life raft on the other hand has specialised methods that can't be readily reproduced at home.
And beside Wotname is an Aussie and we have an inbuilt gene that tends to compell us to make something :D

Evan
Is the 4oz across all sizes or does it get heavier as they get bigger.


Mike

Wotname 04-09-2008 02:22

Quote:

Originally Posted by Evan (Post 201663)
Paratech uses a 4oz woven nylon

Quote:

Originally Posted by Whimsical (Post 201728)
.......Evan
Is the 4oz across all sizes or does it get heavier as they get bigger.
Mike

Thanks Evan, Mike has asked the same question that is on my lips :).

I have found an 8 oz ripstop nylon today and it seems pretty good and quite flexible. Unless I get better info, it looks like this will be my choice.

Wotname 04-09-2008 02:27

Quote:

Originally Posted by Ancora Latina (Post 201646)
What about a Jordan Series Drogue?

Jordan Series Drogue

I have nothing against a Jordan Series Drogue however I am wanting a para-anchor. IMHO, they do different jobs and are not necessarily interchangeable.

Wotname 04-09-2008 03:37

Thread Drift Alert
 
Quote:

Originally Posted by Talbot (Post 201366)
I question your decision to trust your life to a last ditch safety system, that is not only an unknown design, but also unknown material. IMHO not a good place to be looking for savings - next you will be making your own liferaft

Quote:

Originally Posted by Whimsical (Post 201728)
Given a little research into construction materials and method I think it is a quite reasonable undertaking especially as the originals are only the same material using the same low tech construction - sewing.
A life raft on the other hand has specialised methods that can't be readily reproduced at home.
And beside Wotname is an Aussie and we have an inbuilt gene that tends to compell us to make something :D

......Mike

Hmm... didn't take too long for some thread drift :D.

Interesting comment Mr Talbot and while Mike has answered it succinctly, I wish to expand on his answer (as is my want :devil:).

1. Look at this the other way, why trust your life on something that others have made, especially an item that is not built to an "approved standard".

I am not saying that some else's item is bad, but if it is not built to a standard, then one still has to assess it's design and "build quality" to see if it appropriate to put your life on. If it is built to an "approved standard" then a reading of that standard should still be undertaken.

2. There is an assumption that DIY is for savings rather than say knowing the quality of the final product or for reasons alluded to by Mike (above). And yes, savings do come into the picture but only after the other aspects are addressed.

3. Unknow design !!!. The commerical para-anchors are hardly high tech items. Basic parachute design was pretty well perfected in the 1940's during WW2 and built on in the 1950's in rocket developement.

Again as Mike states, sewing is not a complex concept. I work with people who are approved seat belt and cargo netting suppliers. While they know their trade, they don't need PHD's in applied physics. Get the basic information on thread selection, needle size, stitch style, length and tension and that is pretty much it.

4. Unknow material. Well maybe, but already 99% of available fabrics have been ruled out and even this thread is part of refinning the selection. If I believe I can't confirm the final choice of fabric as being suitable, then the project is dead in the water.

5. Last ditch safety system. Not really, IMHO, the para-anchor on my vessel is part of a complete system enabling the vessel to heave to under expected sailing conditions and will be trialled, tested and used as such. Such use will enable it's suitability to be determined (or extrapolated) for more severe conditions.

6. My (almost) last ditch safety system is the integrity of the hull, deck and cabin. I am trusting my life to this system every time I cut a piece of wood, mix epoxy, fit a through hull, add a bulkhead, replace a chainplate, make a replacement cabin window or whatever. It is not a long leap to trusting one's ability to research and construct a para-anchor.

7. The true last ditch safety is stepping up into the liferaft and I am not filled with confidence what is available on that score but as Mike state's, these are items that don't lend themselves to DIY.

Morgan Paul 04-09-2008 05:47

Florentino uses 8 oz. nylon.
Quote:

Fiorentino uses similar construction techniques on both its 9-foot sea anchors. The offshore-designated FPA-9 and the lighter-duty Coast-9 use a multi-section canopy fashioned from 8 oz. nylon, with 2" nylon webbing sewn onto the skirt and 1" nylon webbing on the vent hole opening. Shroud lines are multi-braid nylon line rated at 2,500 lbs. breaking strength. To make a solid connection to the canopy, each shroud line is sewn directly to the canopy over a total length of 14".
http://www.sea-anchors.com/prac.sailor.htm

Wotname 04-09-2008 06:08

Thanks Morgan Paul, this exactly the type of information I am looking for :)

dcstrng 04-09-2008 06:56

Quote:

Originally Posted by Whimsical (Post 201728)
we have an inbuilt gene that tends to compell us to make something :D


We used to have that gene in NA too, but it was bred out of us… now only authentic shrink-wrapped (and OSHA, AARP or Good Housekeeping, approved…) products are authorized… ;)

Wotname 04-09-2008 07:47

Don't worry Larry, it is slowly happening downunder as well but there are still a few of us doing our best to keep that gene alive. :)


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