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Old 28-08-2021, 17:55   #31
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Re: Drag Cost for Trailing a Line Astern

I know for a fact anything over 2 knots , and I can’t hold on , never mind hauling myself along the line. If you have heavy weather gear or boots , there’s zero hope, zero. Above 2 knots you get dragged under anyway and you can’t clear your airways

When I brief my crew , I say “ heres my mob routine “ , I turn and wave bye bye to the stern . Do everything in your power not to fall off the boat , causes the chances of surviving are slim

As for drag , can’t say , but we streamed 300 feet of warp in a U behind the boat in a big storm , it was bar tight in the water and needed a winch to retrieve it.
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Old 28-08-2021, 18:07   #32
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Re: Drag Cost for Trailing a Line Astern

Like most people, I’d recommend PFDs and harnesses tethered on after dark.
They’re really not that bad once you get used to them.
AIS MOBs are also good and will set off the alarm on your VHF to wake up the crew.

Other options (that I don’t recommend):
Harness only (no PFD) and tethers. Attach the AIS MOB to the harness.
Put the AIS MOB in a “bum bag” (I think they’re called fanny packs in the US) and just wear that. You can then hand the bum bag over to the oncoming crew member when you change over. Won’t stop you falling overboard but will let the crew know that you’ve gone.
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Old 28-08-2021, 19:20   #33
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Re: Drag Cost for Trailing a Line Astern

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Originally Posted by BenBowSirocco View Post
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.
Yes, it is a personal choice for you and your partner. If safety for two people (the second of whom probably couldn't single hand the boat on a remote passage) is the important consideration, then you need to get beyond this harnesses are inhibiting point of view. A harness with PFD is how you do this. You aren't going to grab a line as it streams by you and pull yourself back to the boat in the event of an MOB. And if you just want to tell your partner that is the plan so you won't have to hear about this anymore - shame on you.
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Old 28-08-2021, 19:52   #34
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Re: Drag Cost for Trailing a Line Astern

Just for fun, I decide to test the theory that a floating line could trip a sea anchor stopping the boat. Bottom line?


  • It worked on my 2000-pound boat at speeds up to 12 knots and could be easily engineered to boats up to ~ 20,000 pounds at 7-8 knots using different materials. Heavier than that is quite possible but I did not investigate it.
  • That line streams by faster than you think. You will notice I'm about 140' behind the boat (about 6 knots in the video--some tests were twice this speed) by the time I get to the line. Yes, I jump off an outrigger and I don't really rush, but likewise, it is planned and daylight. You should allow 250 feet of line.
  • Even with the boat slowed to 2 knots, it's a bit of work to hand-over-hand that distance. And I go rock climbing every week. Not terribly hard, but allowing for weather and heavier clothes, hard enough.


As I said, this was just a fun summer experiment that has possibilities if someone wanted to take it on. The line is very low drag (few pounds) because it has no knots and only a small float (you really do want a float, for visibility and grasp) and loop at the end.


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Old 28-08-2021, 21:20   #35
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Re: Drag Cost for Trailing a Line Astern

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Originally Posted by rickpyne View Post
If you want to know how much drag is caused by a trailing line, while dragging line attach boat end of line to a set of fish scales and get the reading in pounds or kilograms. 300ft might need a big set of scales...

That sounds familiar.
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Old 29-08-2021, 09:43   #36
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Re: Drag Cost for Trailing a Line Astern

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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.
Well said. Certainly 300 feet of 'overboard line' is ridiculous. 30' would be a tough climb...unless you're a gymnast.
We dragged 100' of 3/8" floating line that was supposed to disconnect the wind vane. Even for that purpose it's slippery, and you'd better have some knots in it. Towing warps are something else entirely of course.
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Old 29-08-2021, 10:12   #37
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Re: Drag Cost for Trailing a Line Astern

Length is more than some of you think.
  • Boat will be going 7-8 knots if it windy enough to fall off.. At least, we should assume so. 13.5 ft/s at 8 knots.
  • The fall will be a surprise and will most likely be from the extreme beam. figure 3-4 seconds to orient yourself, 3 seconds to swim to the line, and 2 seconds to grasp and get a good grip. That's nearly 10 seconds, or 140 feet, assuming no disorientation or injury, and that it is daylight.
It took me 8 seconds in my video, and it was daylight and I dove in. The boat was pretty far away. I had 150 feet of line out and barely got to it.

Really, 200 feet is the bare minimum. 300 feet is sensible. That's only 20 seconds to surface, get your wits about you and find the line (not obvious in the dark). 30 feet is stupid short--you won't even have surfaced yet.


Streaming a warp in a U is compeletly different and the drag is far, far higher. But easy to recover once you release one end, which is an advantage. BTW, trailing a warp only works if you weight the center with chain to get it to sink.


That's just the math.
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Old 30-08-2021, 10:38   #38
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Re: Drag Cost for Trailing a Line Astern

Have not read all the other responses so this could be redundant.



I bought a personal AIS MOB device. If anyone goes over when on watch alone (and has it on them) the unit will activate the AIS alarm on the VHF radio. It is loud enough to wake anyone down below sleeping.



I like this over the personal PLB since rescue by a nearby boat is much quicker, and surer, than waiting for the EPIRB responders to find you.



I've dragged behind a boat while underway and, from my experience holding on for an extended period at anything over 2-3 knots is probably not going to happen.
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Old 01-09-2021, 21:13   #39
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Re: Drag Cost for Trailing a Line Astern

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Originally Posted by BenBowSirocco View Post
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".
If you're only dragging this in heavy weather, your boat has plenty of wind power.
If you drag this most of the time, it might slow you by half a knot or less in light winds. If this gives you peace of mind, it is well-worth the reduction in speed.
Kon Tiki (raft that crossed the Pacific) dragged its inflatable dingy on their longest line during heavy weather. They knew that no one could swim and catch up with the raft. A sailboat is much faster. Poly line is a good choice. A small fender and a loop at the bitter end might be a good idea.
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Old 01-09-2021, 21:58   #40
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Re: Drag Cost for Trailing a Line Astern

There is a blue poly line that is partially UV resistant fibers. I use it for dingy painters and can trust it for 2 years in tropical sun. Since poly does not splice fair, I use zinc-plated "rope clamps". They are metal pounded together with a hammer and they last 2 years without failing. I put a small net buoy near the end of the painter so the metal rope clamps will not sink.
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Old 01-09-2021, 22:34   #41
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Re: Drag Cost for Trailing a Line Astern

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Originally Posted by Seman View Post
When I was single handing I dragged a floating sky rope behind the boat with a large coke bottle attached to the end. The + autopilot wire I cut and re-connected with a spade connector. This connector was tied to the floating line with a small diameter rope. Any pull on the sky rope would disconnect the auto pilot and the boat would stall. Another small rope connected to the throttle/gear would stop the boat when motoring.
Something like that is the only way I'd consider this idea. (And I wouldn't consider it. It's a false sense of security.) It would have to also kill the engine completely and pop the clutches to douse the sails too. A boat that rounds up and heaves-to is often still sailing... on the other tack, albeit slowly. Or depending on what sails are up, it may just come around and gybe.
And the whole thing would have to be fool proof to be of value.
Things like this help to drive home how valuable a good harness is.
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Old 03-09-2021, 07:42   #42
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Re: Drag Cost for Trailing a Line Astern

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Originally Posted by landsend View Post
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!
I know we have done this on night watches when there was 2 of us onboard on passages
more of a security blanket but certainly not easy to pull yourself anywhere at 5kts or even slower speeds
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Old 03-09-2021, 08:10   #43
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Re: Drag Cost for Trailing a Line Astern

There are several personal alarms available should you become separated by more than a few feet. I have an AIS personal alarm which shows position relative to the boat.

My thoughts of a drag line is that it could be rigged to trip the autopilot so could be quite light.

Our rule aboard is lone on deck clipped on. And at night, in the rough and in fog too.
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Old 03-09-2021, 08:35   #44
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Re: Drag Cost for Trailing a Line Astern

A towed generator cost us about a quarter knot. Much more drag than 300m of line.
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Old 03-09-2021, 08:48   #45
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Re: Drag Cost for Trailing a Line Astern

Quote:
Originally Posted by BenBowSirocco View Post
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.
This doesn't sound like a bad plan as it would give the MOB a way to stay with the boat. Climbing back on would be difficult if the boat didn't round up due to being on auto pilot or windvane. You might do it on a catamaran but probably not a monohull. The rest of the crew could get you back on board (assuming you had crew). If soloing, you'd need a way to release the swim ladder from the water. I'm guessing that the real question here is how much negative effect a drag line would have on boat speed - something I'd be interested to know. If it didn't result in too much negative drag, it would be well worth doing.
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