Just one last drogue query!!

[peteandthira]

Apologies if it's bad form to start another thread here but I fear many will have stopped reading my old one.

I have just had loads of tips for drogues v paras and then, this afternoon, I came "into possession" of an ejector seat drogue. This device is the bit that pulls out the main parachute from the seat after an ejection from a jet aircraft. Its design includes the ability to support and stabilise both the seat and pilot if the ejection takes place too high to allow deployment of the main parachute to come out. It is quite robust.

It seems to be made of fairly heavy silk material, about 2m in diameter with a hole in the centre. There are 24 parachute cords attaching the chute to a substantial steel ring at the other end.

Does the learned panel think that this may be of any value as a drag device, or is it too big?

I assume it is too small to be a para anchor.

Further, assuming it is too small for the latter, would it not make sense to stream it over the bow anyway, rather than the stern, to at least bring the bow into the waves even if it allows downwind drift?

Again, apologies if I am beginning to bore the knowledgeable here but it is sitting high on my list of things to worry about!

Pops

 

[ChrisE]

Regarding the use of a para, I beleive that they are always deployed from the bow. Regarding sizes and more info on their use look at this web page.

 

[Aja]

Pops

I think you would have to satisfy that it is robust enough..
1 What mass does a man and seat fly out of cockpit at with this thing attached?
2 What mass is your boat when tied to it and taking a pounding?

If 1>2 you shoud be OK
If 1=2 nothing to lose
If 1<2 waste of effort

erm I think. was pretty crap at physics. Something to do with Van der Graffs vectors?

Donald

 

[Talbot]

Suspectthe material will be too light, A number of people have made use of surplus parachutes rather than buying the proper job, but the type that is used is a cargo paraachute of approximately the same diameter as that recommended for a normal para anchor. Even then, it is probably only good for one use, as the system is not made of materials suitable for immersion in salt water.

 

[peteandthira]

The boat would outweigh a bloke in an ejector seat by a massive margin, but I am not sure that the weight is the key issue. After all it is not supporting the weight of the boat, only the drag forces. I would imagine similar to an anchor chain and rode, except yer anchored to the sea. I am inclined to agree that the material would not neccessarily be as strong as a "proper job", but I don't suppose I have anything to lose by trying it out.

Am I right in thinking that if I stream it off the stern, and it tears itself to shreds, then I still have the benefit of a trailed warp anyway?

Keep 'em coming chaps, keep 'em coming!

 

[davidbains]

It does seem to be too small for a parachute and rather large for a drogue.
However baring in mind that you are unlikely to use it even once, and I
suspect it's as strong as a "yacht" drogue. Take it with you, if it destroys itself
you can fall back on tyres/anchors/sails or anything else to slow you down somewhat.

 

[boatmike]

Actually I would say try it and see is a good policy but don't wait until you need it.
Any safety equipment should be tried and tested so that it does not let you down when you need it and you have confidence in it when deployed. Personally I would be cynical and assume it didn't work until proven that it did. Dont forget that with this sort of thing you will need a tripline to recover it as well otherwise you will only deploy it once.......

 

[tcm]

Re: try it and see

i think this is excellent advice. Since they are only to be used in heavy weather, then some expertise in deployment is vital. I had a go with a para anchor in near flat conditions and a right pain it was, not least poncing about with zillion metres of octoplait. Makes the idea of just streaming a load of long warps out the stern and praps a single drogue thing very attractive. Also, things with multidunous strings need trying, pulling back up and trying again to see if the strings sort themselve out or not.

 

[bilbobaggins]

"......would it not make sense to stream it over the bow anyway, rather than the stern, to at least bring the bow into he waves even if it allows downwind drift....?"

It is clearly better - in most boats - to take seas bows on, as the front end of the boat is designed to take the loads better than the back end. There is plenty of evidence of companion hatches being stove in, helmsmen being swept and damaged, even engines destroyed due to water under considerable pressure being forced back up the exhaust outlet ( despite swan necks ).

A major problem with drifting sternwards is the destructive damage this does to rudders and steering gear, when picked up by a large sea and driven back hard. And there's more than one of 'em. The loads are immense.

So, if you intend lying bows-on to the large seas, you must keep driving forward - or lie stopped to a parachute sea anchor, when the elasticity in the rode pulls you through the top of the seas.

Alternatively, run off downwind, and control your speed by means of a drag device - provided you have enough sea room. But you'll still have to steer - hour after hour after hour - until the wind and seas go down. Read Moitessier, Smeeton, Marin Marie and most of the other pioneering long-distance sailors. They graphically describe the problems and the solutions they tried.

What are you going to do when you get exhausted, and can no longer steer? That's what the para anchor was invented for. Stopping the boat - parked - in the best aspect to the oncoming seas, and going below for some needed rest......

If you're determined to avoid parachute sea anchors, then the Drag Device Database ( book! ) has plenty of examples of what has been used - successfully and otherwise. Your Martin-Baker seat drogue is likely to do the job, and the material is unlikely to dissolve in sea water. I think you will find that the special terylene fabric is far stronger than the PVC-coated awning material that the 'retail' sea anchors are made of. The loads on a drogue - and onto the rear deck fittings to which it gets attached - are huge and continuous. Chafe is a major problem, and once it starts, it develops swiftly, until you lose the lot - as many others have.

What then? /forums/images/graemlins/confused.gif

 

[peteandthira]

Thanks all once again for your time. All being considered.

Pops

 

[webcraft]

[ QUOTE ]
. . . control your speed by means of a drag device - provided you have enough sea room. But you'll still have to steer - hour after hour after hour . . .

[/ QUOTE ]
Some accounts suggest that with an efficient drogue streamed from the stern the rudder can be locked amidships and the boat will steer herself downwind quite happily under bare poles at a controlled speed while the crew rests. Of course you don't know it until you try it . . .

- N

 

[tcm]

hum, it sounds flaky tho, dunnit? Locking the rudder mite easily have not much effect with following sea, and constant battle to regain steerage as relative movment of rudder thru water is minimal and the boat rounds up across the wave train. Was it a nice fatso trudgeable long-keel MAB that can do this, i wonder?

Not sure he's gonna set off at this rate hehe...

 

[webcraft]

You are moving relatively (compared to a para anchor from the bows) rapidly downwind in this situation . . .

I think the way it works the water is moving faster than the boat and the drag from the drogue that holds the stern at right angles to the seas - not really any different in this respect from a para anchor from the bows, except that the boat is still running downwind and the strains are less.

Sometimes the windvane can still cope and all the drogue is doing is preventing dangerous surfing.

However, the US Coastguard report CG-D-20-87 sec 6-4 seems to indicate that just as with a para-anchor the boat can be left with a stern-deployed drogue in charge and the crew can retire down below . . . as Ann Davidson appeared to do several times during her Atlantic circuit in the Vega 'Rupert'. See the Coastguard quote below:

[ QUOTE ]
“With a series drogue deployed, a well-designed and properly constructed fibreglass boat should be capable of riding through a Fastnet type storm with no structural damage. Model tests indicate that the loads on the hull and rigging in a breaking wave strike should not be excessive.
Many sailors are reluctant to deploy a drogue from the stern because they fear that the boat may suffer structural damage if the breaking wave strikes the flat transom, the cockpit and the companionway doors. The model tests do not show this to be a serious problem. The boat is accelerated up to wave speed and the velocity of the breaking crest is not high relative to the boat. The stern is actually more buoyant than the bow, and will rise with the wave. However, the boat may be swept from the stern. The cockpit may fill and moving water may strike the companionway doors. The structural strength of the transom, the cockpit floor and seat, and the companionway doors should be checked at a loading corresponding to a water jet velocity of approximately 15 ft./sec.
When a boat is riding to a series drogue no action is required of the crew. The cockpit may not be habitable and the crew should remain in the cabin with the companionway closed. In a severe wave strike the linear and angular acceleration of the boat may be high. Safety straps designed for a load of at least 4g should be provided for crew restraint. All heavy objects in the cabin should be firmly secured for negative accelerations and drawers and lockers should be provided with latches or ties which will not open even with significant distortion of the hull structure”.


U.S. Coast Guard Report CG-D-20-87 sec 6-4

[/ QUOTE ]

I like the ease of deployment . . . as a last ditch measure it is far more appealing than struggling with sails or a para-anchor in surviuval conditions.

- Nick