Use of drogue/parachute anchor on Catamaran

[mikereed100]

Originally Posted by kmacdonald

A computer study shows that two seconds after wave strike, the series drogue will develop 40% more load than an equivalent cone or chute. Similarly, if the breaking wave strikes at an angle to the towline rather than directly astern, the series drogue will build up load much faster than the conventional types.

I have read several accounts of boats lying to a parachute anchor off the bow that were struck by waves traveling at an angle to the dominant wave train. So-called rogue waves seem to be notorious for this. The concern is that it takes a few moments for the slack to be taken up by the parachute, allowing the boat to be pushed sideways to the wave. I have long wondered if using a series drogue as the parachute anchor rode might not provide immediate resistance in these situations, allowing the boat to come bow-to the wave until the slack is taken up by the parachute.

[thinwater]

Originally Posted by mikereed100

I have read several accounts of boats lying to a parachute anchor off the bow that were struck by waves traveling at an angle to the dominant wave train. So-called rogue waves seem to be notorious for this. The concern is that it takes a few moments for the slack to be taken up by the parachute, allowing the boat to be pushed sideways to the wave. I have long wondered if using a series drogue as the parachute anchor rode might not provide immediate resistance in these situations, allowing the boat to come bow-to the wave until the slack is taken up by the parachute.

Interesting. Even in my limited testing, yawing cause by waves from 2 angles was a persistent characteristic. In fact, if there is only one direction and period, waves are seldom dangerous. It's the confusion that makes them crazy.

One thing to consider is that NO DROGUE has any real effect within 100-150 feet of the boat. This includes JSD. The reason is that the elements in this range are nearly always pulling out of the water due to rode tension. Then, in the case of the JSD, there are not too many cones in the next 100 feet. The point is that the real drag force will always be coming from at least 200-250' from the boat and any drag devise will take some time to rotate, even JSD. I saw this time and again in testing.

Something that I believe deserves more investigation is deploying drogues in tandem, the first 200-300' back, and the second 100-200 feet beyond that (they need to be pretty far apart to be in different wave sections--50 feet was often not enough in testing). One advantage is improved resistance to yawing from angled strikes (the force starts closer). The other is that both will not be pulled from the same wave face. 200-300 feet is really too close for a single drogue (it will get pulled out), but it works if there is another farther back to pull it back and in to the wave (it cannot be thrown forward). It has the recovery and storage simplicity of a conventional drogue, but with much of the robustness of a JSD.

No, I do not have an answer, just an observation. A breaking wave from a severe angle can easily do mischief before any devise can add breaking force. The question is "how great an angle is probable?" In most cases, off axis waves are only about 30 degrees to the side. If they are big and breaking from 90 degrees... I think you're cooked.

[pir8ped]

The drogue I've used in rough weather was the same as JohnT used. I had a Galerider on board, and a JSD. However, the wind was blowing me right to my destination, so I didn't want to stop, and I wondered how the boat would cope if stopped by a JSD and the waves slammed the stern. So I used warp and chain, lead from the plates I'd installed for the JSD and to a sheet winch on the coach roof. This made the system adjustable which I found extremely useful as when the wind began to die, the waves were still big enough to make the boat surf to stupid speeds. Having a short length of rope and chain out in those conditions just took off the top speed of the surfing, and allowed for fast and safe sailing.

Photos of the setup and a video of it in action here.

I still haven't used the JSD, but it stays on board in case there isn't the searoom for dragging simple ropes and chains.

[thinwater]

Originally Posted by pir8ped

The drogue I've used in rough weather was the same as JohnT used. I had a Galerider on board, and a JSD. However, the wind was blowing me right to my destination, so I didn't want to stop, and I wondered how the boat would cope if stopped by a JSD and the waves slammed the stern. So I used warp and chain, lead from the plates I'd installed for the JSD and to a sheet winch on the coach roof. This made the system adjustable which I found extremely useful as when the wind began to die, the waves were still big enough to make the boat surf to stupid speeds. Having a short length of rope and chain out in those conditions just took off the top speed of the surfing, and allowed for fast and safe sailing.

Photos of the setup and a video of it in action here.

I still haven't used the JSD, but it stays on board in case there isn't the searoom for dragging simple ropes and chains.

I notice that the warp was pulling out of waves faces, drag going to nearly zero, about every 10-15 seconds. This is symptomatic of drogues on too short a line, since every time a wave approaches it is like being on very short scope. You really needed more weight and a lot more length. I imagine it helped just a little, but I doubt the drag was over 100 pounds total. I bet you could have held it in your hands.

A speed limiting drogue will generally slow you to about 4-6 knots, and a JSD to 2-4 knots. Just depends what you want or need. But remember that undersized speed limiting drogues and warps become unstable over about 6 knots, which is part of what you saw, becoming rather useless just when you need them. To be safe, they need to be able to slow you to about 4-5 knots. They are simply undependable over that speed, and this has been the root cause, I believe, in many reported failures; too small, too much speed.

[pir8ped]

Thinwater,

You are right, the chain did pop out at times in the roughest weather. I think I had 100 metres of rope on a loop, and I had 10 metres of chain.

I could have added another anchor line, but it wouldn't have run through the block, so it would have taken a little setting up. I was on the verge of adding another length of chain. The chain was attached to a bit of water pipe that slid down the rope, so adding another 10 metres of chain would have been pretty easy.

I felt the pull - and you're right, I could - just - hold the pull in my hands. But that was just one side of the loop.

It made a big difference to the performance. Without the drogue I'd been occasionally hitting 20 knots, which is a terrible speed for a single-hander mid-Atlantic on a 30' cat. I was definitely in danger of pitch-poling. With the rope and chain out, it didn't go above 12-14 knots, which the Autohelm handled fine. And it didn't go less than 5 knots of so in the troughs, which suited me fine.

[Bulawayo]

We have used our JSD and perhaps experienced some different results. We also have chain and a small anchor on the end of our JSD and have experienced a fully functioning device - with real world testing. It did not pull out. What is being talked about are lengths of rope with chain weights , a quite different beast.

Originally Posted by pir8ped

Thinwater,

You are right, the chain did pop out at times in the roughest weather. I think I had 100 metres of rope on a loop, and I had 10 metres of chain.

I could have added another anchor line, but it wouldn't have run through the block, so it would have taken a little setting up. I was on the verge of adding another length of chain. The chain was attached to a bit of water pipe that slid down the rope, so adding another 10 metres of chain would have been pretty easy.

I felt the pull - and you're right, I could - just - hold the pull in my hands. But that was just one side of the loop.

It made a big difference to the performance. Without the drogue I'd been occasionally hitting 20 knots, which is a terrible speed for a single-hander mid-Atlantic on a 30' cat. I was definitely in danger of pitch-poling. With the rope and chain out, it didn't go above 12-14 knots, which the Autohelm handled fine. And it didn't go less than 5 knots of so in the troughs, which suited me fine.

[thinwater]

Originally Posted by Bulawayo

We have used our JSD and perhaps experienced some different results. We also have chain and a small anchor on the end of our JSD and have experienced a fully functioning device - with real world testing. It did not pull out. What is being talked about are lengths of rope with chain weights , a quite different beast.

"It did not pull out." That is exactly the strength of the JSD. Because the pull is distributed over a long length, even though some cones will be exposed from time to time on a steep face, the effect is minimal and averaged out. The down sides have been beaten to death and are just part of the compromise.

This is why I have suggested well-spaced tandem drogues as an interesting middle ground. A single drogue can be used on short rode for moderately bad conditions (the short rode allows adjustment of drag) and for emergency steering (failed steering is a leading cause of rescue). As things get worse it can be eased back for more grip. When they get worse, a second drogue goes in and the combination resembles the JSD in robustness. I'd love to read of more real-world experiences.

[Bulawayo]

Thinwater,
I'ld be happy to share our experiences - we have not used our JSD massively but it has seen significant event use. We updated to a brand new JSD a couple of years ago, the previous one we had being second hand. We also had a Fiorentino para-anchor previous to that.

Originally Posted by thinwater

"It did not pull out." That is exactly the strength of the JSD. Because the pull is distributed over a long length, even though some cones will be exposed from time to time on a steep face, the effect is minimal and averaged out. The down sides have been beaten to death and are just part of the compromise.

This is why I have suggested well-spaced tandem drogues as an interesting middle ground. A single drogue can be used on short rode for moderately bad conditions (the short rode allows adjustment of drag) and for emergency steering (failed steering is a leading cause of rescue). As things get worse it can be eased back for more grip. When they get worse, a second drogue goes in and the combination resembles the JSD in robustness. I'd love to read of more real-world experiences.

[mikereed100]

Originally Posted by thinwater

One thing to consider is that NO DROGUE has any real effect within 100-150 feet of the boat. This includes JSD. The reason is that the elements in this range are nearly always pulling out of the water due to rode tension. Then, in the case of the JSD, there are not too many cones in the next 100 feet. The point is that the real drag force will always be coming from at least 200-250' from the boat and any drag devise will take some time to rotate, even JSD. I saw this time and again in testing.

I see your point. I suppose it could be argued that having the drag force begin 200-250' form the boat is better than 400-600', as would be the case with a parachute alone, but then I wonder if 200-250' is too far to make a difference. I hope I never get a chance to test it.

[thinwater]

Originally Posted by mikereed100

I see your point. I suppose it could be argued that having the drag force begin 200-250' form the boat is better than 400-600', as would be the case with a parachute alone, but then I wonder if 200-250' is too far to make a difference. I hope I never get a chance to test it.

There will be some force downwards and back on the windward bridle leg. It also takes some force and energy to pull the rode sideways through the water.

[thinwater]

Originally Posted by mikereed100

I see your point. I suppose it could be argued that having the drag force begin 200-250' form the boat is better than 400-600', as would be the case with a parachute alone, but then I wonder if 200-250' is too far to make a difference. I hope I never get a chance to test it.

There will be some force downwards and back on the windward bridle leg. It also takes some force and energy to pull the rode sideways through the water. I've always felt this is a good argument for having a long bridle made from heavy line; when a wave is catching you from an angle, it will be in the water. It is also a case for keeping the attachment point low. In some of my testing I played with anchoring the bridle low and there was some benefit.

[mikereed100]

Thinking a little more about using a JSD as rode for a parachute anchor, it occurs to me that the rode of a parachute anchor will behave differently from the rode of a drogue. While there is constant tension on a drogue, I believe the tension is more cyclical on a parachute anchor. I have never used a parachute anchor, so maybe those who have can help me out here, but I seem to recall accounts in the DDDB in which yawing was a problem due to slack in the rode as waves passed and the rode stretched and contracted. I believe Fiorentino sizes their parachutes a bit smaller than most other manufacturers in with the thought that this, in conjunction with a riding sail, will allow tension to be maintained in the rode. Maybe Zack can set me straight if I'm making this up. In any case, it may be that the JSD could help to dampen the cyclical load on a chute, helping to prevent slack in the rode as well as providing some resistance to side strikes from waves.