I have been reading Dashew's Storm Tactics book and a letter from Don
Jordan the developer of the Series Drogue.
The Dashew book has the relevant material scattered around the book in
several places and it is hard to get ones arms around the subject of Series
Drogues. But I conclude that a Parachute Anchor is a good choice for
moderate to severe but not survival storms. That the Series Drogue is the
weapon of choice in the Ultimate Survival Situation.

It helps to think of all this as a rubber band. If you have trouble with
this then imagine this as bungee cord jumping off of bridges, where you
bring your boat with you. It should be obvious that if you don't use the
right bungee cord engineered just right, you and the boat will end up at
the bottom of the river instead of bouncing back just before eternity
overcomes your hold on life. I hope this use of words is sufficient to
carry across the dramatic flavor of this kind of activity.

So, now the task is to engineer the bungee cord. First we know that a nylon
rope will stretch around 40% before it will break. Our bungee cord must at
a minimum be strong enough to not break, but not so stretchy that we and
our boat will hit bottom, although even a few inches of space will do, if
necessary. Since we can't be sure of exactly how far the cord will stretch
even in repetition, it is necessary to have some safety margin. Unless you
like being squashed like a bug between your boat and the river below the
bridge. Of course all this about bridges and bungee jumping is only
remotely related to drogues and boats, but the image is useful in order to
come to an understanding of the issues involved.

Nylon rope increases in strength as the diameter goes up and at the same
time the amount of strain that it takes to stretch the rope goes up,
although not in lock step. In other words, the smaller rope stretches
easier and has a lower breaking limit  than a larger rope. On the other
hand if the rope is large enough, it will not stretch enough to be of any
use as a rubber band and it's strength will be so high that it could if
large enough tear the boat apart, or tear the attachments out of the boat.
Don Jordan points out that in the Loss of the Winston Churchill the load on
a parachute anchor rode would have been over 700,000 lbs. that's right, 7
hundred thousand pounds. Think about the amount of stretch versus breaking
strength that would be needed to unload(stretch) that without breaking the
rode or it's attachment points.

This is very hard to explain all the subtle details, but I hope this
clarifies one, of the issues.

Mike

Capt. Mike Maurice
Tualatin(Portland), Oregon

I think this will reinforce your opinion that a bunch of little
parachutes is better than on large one.

http://www.sailrite.com/droguereport.htm

If you're handy, you can buy a kit and make the system your self.

http://tinyurl.com/4l99z

tom

The Leonards
M/V Sea Breeze
Myrtle Beach
MTOA #2743

-----Original Message-----
From: passagemaking-under-power-bounces@lists.samurai.com
[mailto:passagemaking-under-power-bounces@lists.samurai.com] On Behalf
Of Mike Maurice
Sent: Tuesday, February 15, 2005 11:00 PM
To: Passagemaking Under Power List
Subject: [PUP] Bungee Cord Jumping with your Boat

I have been reading Dashew's Storm Tactics book and a letter from Don
Jordan the developer of the Series Drogue.
The Dashew book has the relevant material scattered around the book in
several places and it is hard to get ones arms around the subject of
Series
Drogues. But I conclude that a Parachute Anchor is a good choice for
moderate to severe but not survival storms. That the Series Drogue is
the
weapon of choice in the Ultimate Survival Situation.

It helps to think of all this as a rubber band. If you have trouble with

this then imagine this as bungee cord jumping off of bridges, where you
bring your boat with you. It should be obvious that if you don't use the

right bungee cord engineered just right, you and the boat will end up at

the bottom of the river instead of bouncing back just before eternity
overcomes your hold on life. I hope this use of words is sufficient to
carry across the dramatic flavor of this kind of activity.

So, now the task is to engineer the bungee cord. First we know that a
nylon
rope will stretch around 40% before it will break. Our bungee cord must
at
a minimum be strong enough to not break, but not so stretchy that we and

our boat will hit bottom, although even a few inches of space will do,
if
necessary. Since we can't be sure of exactly how far the cord will
stretch
even in repetition, it is necessary to have some safety margin. Unless
you
like being squashed like a bug between your boat and the river below the

bridge. Of course all this about bridges and bungee jumping is only
remotely related to drogues and boats, but the image is useful in order
to
come to an understanding of the issues involved.

Nylon rope increases in strength as the diameter goes up and at the same

time the amount of strain that it takes to stretch the rope goes up,
although not in lock step. In other words, the smaller rope stretches
easier and has a lower breaking limit  than a larger rope. On the other
hand if the rope is large enough, it will not stretch enough to be of
any
use as a rubber band and it's strength will be so high that it could if
large enough tear the boat apart, or tear the attachments out of the
boat.
Don Jordan points out that in the Loss of the Winston Churchill the load
on
a parachute anchor rode would have been over 700,000 lbs. that's right,
7
hundred thousand pounds. Think about the amount of stretch versus
breaking
strength that would be needed to unload(stretch) that without breaking
the
rode or it's attachment points.

This is very hard to explain all the subtle details, but I hope this
clarifies one, of the issues.

Mike

Capt. Mike Maurice
Tualatin(Portland), Oregon

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