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Old 28-08-2021, 03:18   #1
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Drag Cost for Trailing a Line Astern

Interested in hearing some thoughts and opinions on the amount of drag induced by trailing a long line astern.



The discussion of trailing an "Overboard Line" is already in other threads.



I am looking for information on the amount of drag it would induce to a sailboat to drag 300' (92m) of polypropylene line astern.

The big question being, how much will it negatively effect sailing speeds?



This community is so full of smart people I am looking forward to some ideas on how to calculate the drag in pounds.



Part of my goal is to better understand what size line I might purchase for this purpose. Should it just be a spool attached to the arch of 5/8"- 16mm, with the multipurpose use of tying ashore, or should it be a light/thin line dedicated for the purpose say 5/16" or dare say 1/4".
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Old 28-08-2021, 03:34   #2
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Re: Drag Cost for Trailing a Line Astern

What is your reason for dragging a line astern? Under what conditions would you be doing it?


If it's to grab onto if you fall overboard, will it be knotted at intervals? What constructon? Will there be a big knot on the end? What's the minimum diameter you think you can hold onto when being dragged at several knots?
All of those will affect the drag.
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Old 28-08-2021, 05:18   #3
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Re: Drag Cost for Trailing a Line Astern

Can you really hold on to a line and drag yourself back aboard whilst traveling at approx 5 knots? Maybe the thought of the consequences would give you the extra boost in strength!
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Old 28-08-2021, 05:24   #4
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Re: Drag Cost for Trailing a Line Astern

If you’re looking for a warp to slow you down then thin polypropylene is probably not what you want.
The idea is to create drag so you want a line that is either rough by its nature or you need to create drag through knots or attaching both ends to form a loop that you then drag through the water.
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Old 28-08-2021, 05:33   #5
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Re: Drag Cost for Trailing a Line Astern

There are too many variables to actually calculate it. Diameter of line? Boat speed? surface roughness of the line being used?

And then once you have it "in pounds" what does that tell you?

Taking my engineer hat off, and just a touch of practical experience the amount of drag from a trolled line is: Trivial.

How do I know? Because I have pulled in lines that were dragging behind a boat, and you can easily hole them in one hand. Certainly the total pull is less than 10 pounds. I troll fishing lures than pull way harder than 100 feet of 1/2" line, and the drag on the fishing reel is set at 15 pounds. So there is an upper limit for you.

If you are asking because you want to climb back onboard after you have fallen off, just FORGET IT. You can not. You do not have the strength to pull yourself back to the boat if it is moving at anything more than a dead drift. Try it and see.
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Old 28-08-2021, 05:48   #6
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Re: Drag Cost for Trailing a Line Astern

I can't tell how much drag is incurred but I can say that once you reach hull, it doesn't matter anymore.
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Old 28-08-2021, 05:51   #7
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Re: Drag Cost for Trailing a Line Astern

Everyone,



Thank you for the great responses already. I guess I do need to explain my hair-brained plan.



We are planning a Pacific crossing for next spring and my partners biggest fear is coming on deck with someone missing. So we are exploring some ideas beyond the "harness at all times" thought process- which I find inhibitive. Obviously its a personal choice and harnesses have their place when the weather is ominous.



The intention of dragging 300' of polypropylene line behind the boat is for overboard retrieval, but perhaps not as you imagine because I agree with you, the drag induced by your body is significant and its unlikely you would be able to drag yourself up any appreciable distance- even under a high adrenaline circumstance as falling overboard.



I have for fun- under a planned circumstance- jumped from the spreaders, grabbed a trialing line dragged behind and climbed along the line back into the boat at 3 or 4 knots boat speed and its aided by, a swim suit, a head down swimming posture and keeping your arms and grip close into your body- like swimming. But this is impractical in any real world circumstance- especially if wearing clothes and a bunch of other reasons.



It does seem to me it should be possible to use a specifically weight rated fishing line as a gasket to the 300' of poly so when you get a "fish on" i.e. a fallen crew member grabs the trailing line and the fishing line breaks- this would then activate a bungee cord and disable the windvane, causing the boat to round up and hopefully alerting other crew, as well as allowing the fallen a chance to pull themselves closer.



Will this work? Is this silly?

Obviously it needs testing on the water. But I thought I would start by trying to find some number to work with from people smarter and more experienced than myself.
This is also why I was wondering the drag in pounds between 5/8 or 1/4".



The fishing reel comparison was a great point. Even a non-fisherman like me knows that 15lbs of drag holds back some big lures.


My thought was a foot size loop at the end of the line, no knots along it.
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Old 28-08-2021, 06:05   #8
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Re: Drag Cost for Trailing a Line Astern

Quote:
Originally Posted by BillKny View Post

If you are asking because you want to climb back onboard after you have fallen off, just FORGET IT. You can not. You do not have the strength to pull yourself back to the boat if it is moving at anything more than a dead drift. Try it and see.
That is not at all consistent with the french circus sailors I met who claimed to dive from boat to boat in open ocean and just grab the line behind. Also claimed at times everyone was in the water and no one onboard any boat because "a rope is for sure" actual quote from them.

I also used to swim without a rope alongside my boat when it traveled 2 knots or less in open ocean without too much worry, when it started to get difficult to keep up with I would climb back onboard.

Also met several single handers who like to troll with themselves among dolphins at 5 and 6 knots. It is for sure you can climb back on at these speeds just with a rope and no knots in it.


What if you fall overboard but miss the rope? You see it just in time, but then miss it, and that is it. Maybe without a rope you would be careful enough not to fall overboard.

As far as the safety rope is concerned it is normally connected to the tiller through a block and the tension held by a small fishing line that you can break from enough drag and then further tension causes the rudder hard over which usually causes the boat to stop anyway.
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Old 28-08-2021, 06:10   #9
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Re: Drag Cost for Trailing a Line Astern

Hmm, I've considered the same idea, but I sail single handed. In your case I would think some PLBs with MOB alarms would be far more convenient.
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Old 28-08-2021, 06:13   #10
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Re: Drag Cost for Trailing a Line Astern

I think it is an interesting idea, using that trailing line to trigger the boat into slowing.
The part I would worry about the most is that if I ended up in the water by accident, that could easily be accompanied by an injury or just plain shock and disbelief such that getting to that trailing line in time is questionable. As I do my contingency planning, I assume that if I end up in the water, I am unconscious.

I saw Christian Williams on his solo passages clip in whenever he exited his companionway, a requirement imposed by his wife. That strategy seems so much more effective that I would look for ways to maximize the comfort instead of finding ways to avoid using a harness.

In your Pacific crossing situation with others onboard, I would also be evaluating the personal EPIRB beacons as an option.
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Old 28-08-2021, 06:57   #11
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Re: Drag Cost for Trailing a Line Astern

Having the trailing line being a trip line that is rigged to cause the boat to head into the wind, as well as another line, that lets you drop the boarding ladder from the water are ideal for singlehanding. I dont recall where I saw it, but there was a guy who had his windvane set up that way and he wound up needing it during a crossing. I should note, swimming in a gill foul weather set gets awfully heavy very fast in you wind up swimming in it. Dual connection safety harnesses are much proffered over winding up in the water in the first place.
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Old 28-08-2021, 08:44   #12
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Re: Drag Cost for Trailing a Line Astern

Perhaps putting a measured length of line in the water and attaching the proximal end to something similar to a luggage or fish scale?


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Old 28-08-2021, 08:49   #13
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Re: Drag Cost for Trailing a Line Astern

Quote:
Originally Posted by BenBowSirocco View Post
It does seem to me it should be possible to use a specifically weight rated fishing line as a gasket to the 300' of poly so when you get a "fish on" i.e. a fallen crew member grabs the trailing line and the fishing line breaks- this would then activate a bungee cord and disable the windvane, causing the boat to round up and hopefully alerting other crew, as well as allowing the fallen a chance to pull themselves closer.
This has been invented already. By a guy named Rube Goldberg.
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Old 28-08-2021, 09:03   #14
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Re: Drag Cost for Trailing a Line Astern

Learning from someone else's mistakes:



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Old 28-08-2021, 09:15   #15
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Re: Drag Cost for Trailing a Line Astern

In theory it makes sense, but how practical is it after someone falls or is knocked into the water to orient themselves then find the line within 30 seconds, especially at night? (6 knots * 6067' per nautical mile means the boat moves 607' in a minute). They would still need a light or something with reflective tape to be seen.

Personally, I got used to staying tethered in at all times including a 48+ hour passage. Having enough attachment points really helps.

To answer your question about drag, I agree it's minimal (more impact in light wind).
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