The Offshore Voyaging Reference Site

An Efficient Foredeck Centreline Jackline


Last fall we wrote about our new centreline jacklines that enabled us to work our boat from cockpit to mast without resorting to clipping to sidedeck jacklines.

(If you doubt how dangerous using sidedeck jacklines is, please read, or reread, the last three chapters in this Online Book.)

Work Left To Do

But we were still left with installing a centreline jackline from mast to bow. A project with some problems to solve:

  • Because the cabin top extends forward of the mast, this jackline would be at ankle height on the foredeck, resulting in a nasty trip risk while coming alongside, anchoring, or wandering around the deck with a sundowner—this could be a bigger, or at least more frequent, risk than being dragged.
  • Interference with operation of the windlass.
  • Difficulty of stowing our dinghy in its inshore position on the foredeck.

Over the winter, encouraged by this comment from Dick Stevenson, we thought about the problem and came up with a centreline jackline from mast to bow.

The Details

The secret to making all of this work, and dealing with the above-listed issues, was to make the foredeck jackline easy to install and remove as well as tension.

It’s about the details…it’s always about the details. Let’s take a look:

Login to continue reading (scroll down)

Inline Feedbacks
View all comments
Dick Stevenson

Hi John,
Needless to say, I like the idea and its additional details.
I know we are talking jacklines here (so move this if necessary), but the goal is to keep people on board and, looking at your picture of the tether hanging over the toerail and under the lifelines with its person end hanging just above the water—empty– gives me a bit of the willies.
I wonder whether it is time to re-consider netting. I know racers have done so to keep sails from skidding overboard and I used netting to catch my children (never happened but did stop a few tools from going into the deep). I am thinking large square netting done with some strong small diameter (HM) line. Just enough that would ensure a person would get tangled up BEFORE they go overboard and while still on the deck side of the lifelines.
If the majority of POB go over the lifelines, then this idea makes less sense. I wonder whether there are stats on POB and how they get there: over, between top and middle, or deck to middle. I know my one real scare I was slipping out under the lines on the deck.
Other considerations: Put this netting on both levels of the lifelines or just the bottom– Just the foredeck or all the way back to the gate (front end of the dodger)—What boat operations get interfered with (both sailing and at anchor)?
Initial thoughts.
My best, Dick Stevenson, s/v Alchemy

Marc Dacey

You’ve already said what I was going to say, Dick! I think just the bottom (gunwales to mid-stanchion lifeline) would suffice, given enough height on the pulpit. Funny, I had foredeck netting when I got my first boat 17 years ago: I removed it when I decided I wasn’t going to race the boat, and now I’m rethinking that decision for ocean work on the new boat, which has pretty high and very sturdy piperails. Like you, I’ve never gone over them, but I did go under a lifeline in a sudden squall on the beam and was only saved from an almost certain death at night well offshore by a short tether. It does focus the mind.
John, your jackline tensioning blocks are great. Well done.


During my military training rappelling was one of the skills we had to master. After committing to stepping over the edge of a cliff tall enough to kill, It was fun, secure and safe provided one didn’t hot dog.

Then came sailing, and every time I looked at the fore deck in seas over three inches, I wondered why I couldn’t be tethered from above as well as from below.

Vertical tether (halyard) interference with the outer jib (and less so with the inner) were the main issue — one more detail to deal with in a potentially dangerous situation. However, once I worked out the geometry, I ended up with an approach that, absent halyard or mast failure would keep me out of the water at normal heel angles. I have considered adding blocks well down the mast to be rigged somewhat like running backstays as this would shorten the arc of swing should my grip otherwise fail.

It is imperfect, but it it is perfectible. It requires three tethers, but three is a very good number in structural engineering.

Drew Frye

I’d love to here a further explanation. I tried using a halyard at the suggestion of a cat sailor that feared (irrationally) tramp failure. There were several problems:
1. If there is slack it wraps around a spreader or something equivalent. I think most sailors hate the potential for tangles aloft.
2. If there is no slack you are prevented from getting low in a bump. In fact, it can lift you right off your feet as you move forward.
3. Problem 2 is worse if the cabin is raised.

In short, I found it to be a nightmare.

My jackline solution is different from John’s, but it is a catamaran solution, so I’ll leave it alone. What I am most struck by as I look at John’s solution and the foredeck that it is on, is how different the problems and solutions must be. It’s the principles that matter and the forethought a good system requires.


Hi John,

Yeh, its been a while. The sailing here approaches non-existent and health, family matters and bad weather-windows have kept us from the Abacos. (…and Florida is quite hostile toward people who have an anchor and prefer to use it.)

Yes, the flail of a halyard is certainly daunting. I’ve seen one bend a headfoil with one solid whack.

Your comment about tension tending sent me off on a tangent.

I wonder if we think of something small diameter with high tensile strength ala Spectra set up taught in an endless loop from mast base to an appropriate height. This line could be equipped with hard or soft loops for snapping into and a stopper for belay and position control. Its windage should be on the order of a flag halyard .



Yep, I may give it a shot. An osprey with a seven foot wingspan(!) decided our wind instruments were annoying, so she tore them off. So I have a masthead trip in the near future.

Jim Ferguson

Great comments everywhere. On Maggie we have been using that center backline technique as well and I will use John’s technique for snugging it up. Lanyards are attached and sit at the front of the mast I re-attach at the mast pulpit when I go forward. Between the cockpit and the mast on either side, I have been using my running backs which work very well using a very short lanyard. They attach just below the upper spreaders. I can work both sides of the mast for reefing. Since we’ve been in lower latitudes the last few years our we don’t set the staysail. It is a work in progress, but I’ve been pleased so far.

Jim Ferguson
S/V Maggie


How about stopping the jackline just aft of (or on) the windlass? It looks like your 5ft tether would be long enough to let you work on the bow and you reduce the risk of drag a bit.

Dick Stevenson

Hi Mathieu,
That is exactly what we do on Alchemy. We dead-end the jackline just aft of our staysail which, on our smaller 40 foot hull, allows me to reach out to the asym downhaul, as far forward as I am likely to need.
Dick Stevenson, s/v Alchemy

Raymond Smith

How, where is the jackline tethered and tensioned at the aft end?

Dick Stevenson

Hi Raymond,
John included a picture of his centreline jackline secured around his mast. My centreline jackline also goes to my mast base where it is secured to the mast collar.
Dick Stevenson, s/v Alchemy

Raymond Smith

Understood that, Dick. But the centreline jackline goes aft from the mast to somewhere, presumably so that you can move out of the cockpit already attached. I am not clear where and how it is attached at that aft end. I recognize that could vary depending on how the boat is laid out, but was looking for some thoughts.

chris f

Thanks for this series. You always give me plenty to think about as I refine my own techniques.

I have two questions. First as a former rock climber I’m always skeptical of complex mechanical devices in a self rescue setup. Why use blocks at the bow rather than stainless or aluminum rings? Rings would have the advantage that they are cheap and easy to inspect for fatigue. They can also give as much mechanical advantage as you want with additional wraps and might be a bit easier to tie off under tension. Blocks used in a static setting mean that all the load will be carried by only a small number of bearings in the raceway. That is probably not a huge issue but may not be the best use for a device designed for dynamic loads.

Second, A climber would hook his lanyard to a static climbing rope with a prusik knot or some other kind of locking attachment. The disadvantages are that it takes a second or two to hook in that way and you have to put a hand on the knot for it to slide. The main advantage is that if your hand is not on the knot it will lock in place. This would minimize the amount of travel before the lines stop you to the radius of the lanyard. When working at the bow you might leave the knot a few feet aft. Then the radius of travel could offer a few more opportunities for self rescue before washing overboard. Of course use of a locking device on the center line requires use of a round cross section rope.

Thanks again for sharing your experience. As always I look forward to your next installments.

Ed Finn

I suggested using a Halyard as a restraint device months ago. But your online response was so negative that it left me feeling publicly shamed and ridiculed.
And I did not elaborate on it any further.
Now, fortunately you seem to be entertaining the idea.
Did you recently come down with a case of ” open mindedness” ?
Well, Let’s hope it’s not chronic.

Richard Hudson

This looks like a really nice way of being usefully-tethered on the foredeck. I imagine that if you need to open the hatch, there is enough deflection in the jackline to allow it.

I especially like the bag mounted to the mast to store the jackline when not in use. It makes me think that a bag attached to the mast on my boat would be a neat way of keeping the tails of halyards (those that are too short to coil & finish off) off the deck.

Reuben Mezrich

I plan to switch to your center line Jacklines but am a bit uncertain about how much tension there needs to be on the jackline. you show a three block system to apply the tension….is that really necessary?

Reuben Mezrich

But in that post you indicate two desired attributes of a Jackline. One is low deflection (to keep the victim on the boat) and the other is high stretch (to lesson the shock loads). You achieve the first by using the blocks to keep the jacklines tight. But doesn’t that “preload” take some of the available stretch out of the Jackline?. I guess the answer is, as always, you have to compromise and in this case balance the deflection with the available stretch, but still, it would seem using 3 blocks might be a bit much

Neil Scott


a couple of questions:
– I am trying to understand the requirement for a snappy 3 block system for tensioning the forward-of-the-mast jackline, but with no such system for the cockpit-to-mast jacklines. How do you tension these?
– up till now, including on my trip from San Francisco to Cape Town where Galatea is currently berthed, I have used a “high” jackline solution (bow cleat, to shroud, to stern cleat). On reading your excellent material, I realize that I need to rethink things. I know it might seem ridiculous, given that safety concerns should be paramount , but one of my considerations behind taking the high jackline approach was that it would avoid the need for caribiners being dragged up and down the deck, cabin-roof etc, inevitably dinging up the gelcoat. What are your thoughts for substituting a sewn loop connection to the Jackline rather than a caribiner? I suppose this might result in more friction and chafe.


Hello John and fellow AAC followers,

On our HAllberg Rassy 46 we are thinking of replacing the upper lifelines that go from the stern pulpit to the side gates by stainless steel tubes a little like on the AMEL’s.

The main purpose is to have more space on the rails to fix MOB Ocean Safety DAN BUOYs on each side and of cours the rest of paraphenalia bbq slicing table fishing rod holders etc… Do you think guard rails are better than wire lifelines?

If someone has done this and would have suggestions? Just the upper lifelines or both the upper and lower ?



S/Y Hibernia II

Neil Scott

John, my understanding of a lashing is that it is used to tie two poles together, either in parallel or at 90 degrees. Could you please enlighten me as to how a lashing is made in the context of the two cockpit to mast jack lines.

Thinking through things overnight It seems to me that the positioning of cockpit to mast jacklines inboard the side decks will be difficult given the placement of running rigging lines, dorade vents and hatches on the cabin roof of my Island Packet 420. This is just another example of cruising fundamentals that have not been adequately catered to by Island Packet who held themselves out as being a top in class, blue water cruising boat manufacturer.


Hi John.

Thank you for this series; I have read it front to back twice. The principal of designing a jackline and tether system to ensure that you do not go overboard is well argued and I don’t disagree with you. The math you present that suggests we need stretch in the system so we don’t break our ribs, and significant pad-eyes for really big loads, also makes sense.

But have you considered the problem of small boats? There is literally no way for me to move around the deck and be safe. Consider the rule that all tethers should end 1’ from the edge of the deck. Makes sense until you consider my 8’-7” beam. There are literally only 2 places on the entire boat where I can place a padeye (not a jackline because there is literally only one spot) where this rule can be achieved and still attach a 3’-6” tether – the minimum I need to do a bit of work (base of the mast on coach top and the forward center of the cockpit). My boat is at the extreme end of the size range, but I’m sure there must be others out there with otherwise well founded boats that are scratching their heads as they try and apply the geometry.

I currently have jacklines that are as far inboard as they can be and for this season I have modified the jackline tethers to be 27” long. This requires me to crouch as I make my way forward, which is not uncomfortable as I’m basically as bent over as required to use the handrails, but I certainly can’t do any real work in this position. I’ve also moved the whisker pole to the face of the mast where it can (mostly) be set up and operated from my single safe position. I’m seriously considering moving the reefing to the cockpit….as others have noted above, there is no way easy way around the dodger. Also, without a safe spot on the foredeck there is also no way to make a headsail change, suggesting perhaps, that roller furling is a must on a small boat.

I’m looking forward to hearing more about using netting and how it might be able to keep a person on board at the end of their tether. Gaining an extra foot is very significant and would allow access to the foredeck and especially better tether lengths in the cockpit. In the meantime, we have decided that when someone has to go forward in anything beyond a moderate sea state, if at all possible, we will heave to. A stopped boat in it’s slick, is probably the best option given our parameters. This does set up some changes in how we sail – for example, we will leave the main up when running downwind. We also have color coded the tethers as to “safe” (a minimum of 10” to the edge of deck is achieved) and “not safe” (not achieved) so at least when clipped on we will know….

It seems to me that as we apply the “safety rules” to keep a person on board, to each individual boat, many other things (like furling headsails and whisker poles mounted on the mast), are no longer really choices but requirements.

Jim Ferguson

Well said and I agree with your concerns. We are 15m and I double my jack lines from the mast forward and have a separate tether attached there at all times. Leaving the the cockpit I have a trapeze line that snaps directly to my harness and it’s long enough to keep me above the lifelines either on the inside and hopefully not on the outside. It’s long enough even with the boom on a shroud. I can reef easily on starboard 1st & 3rd and 2nd on port. It’s still a work in progress and I did see this used in the Volvo race at times.

Mike Drummond

Is anyone aware of a roller device that can pass over attachment points of jacklines?

In the late 70s I remember an ad in Sail magazine for a roller that remained attached to the jackline wire running through stanchion bases. (Note, I’m not suggesting this is a better idea than webbing along centreline, I’m merely interested in such a device)

Also, has anyone tried inertial reel systems to reduce slack in the tether?
thanks for any help,

Tracy Tullier

Hi John,
Thanks so much for the work you have put into this book! I am working on refitting my boat (csy 44 cutter ketch) with Jacklines and tethers using the principles you have outlined here. Couple questions. Can you tell me what you considered minimum block and tackle arrangement at the bow for tensioning the centerline Jackline. Also others have discussed the cockpit to mast idea of wrapping jackline around the mast instead of lashing. How might you go about tensioning in this case. Third how did you attach your cockpit tethers? Jacklines just in the cockpit? If so where were they located?

Tracy Tullier


Lisa Rowell

I really like the basic design of your tethering system and am working them out for my boat.

One concern that I have is using the mast as an anchor for the jacklines running from the dodger to the mast. I have a production sailboat with a deck stepped mast and I’m concerned that in the case of a dismasting, the break point will be at the deck and I’ll lose my tether right when I need it the most (dealing with the mess). (Obviously don’t get dismasted is plan A).

I’ve thought about adding three large padeyes, two for going back and one for the bow jackline. This would reduce my dependence on the mast, but increase the system complexity and potentially just exchange one risk for another.

Do you have thoughts on this? One issue I see is that stretch of the jacklines between the dodger and the mast would be reduced compared to how you rig them, but that could be addressed with dynamic rope tethers on each side.

Lisa Rowell

Hi John,

Thanks for your thoughts on this. My boat is pretty non-ideal for blue water cruising with swept back spreaders and stays that have side by side chain plates. I’ve added a baby stay, but in general she’s a boat designed for a cocktail party being taken offshore because she’s the boat I have and the boat I know. I’m ultra careful with sail area, but I assume I have significantly higher risks of putting my mast in the water.

I think I’m going with the extra padeyes. I might a first pass at it with mast connection though since our cruising “plans” start with a long, slow traversal of the California Coast with lots of stops to work on things (and (learn to) relax).

For short jacklines, where you know the jackline won’t have the length to stretch out enough to give an angle to avoid the triangle of death problem, have you considered using low stretch rope, rigged with a slack that gives a desirable angle to reduce longitudinal force? My thought process being that if I have a short run of Dacron, it’s not going to stretch enough to reduce the force perpendicular to the body load. In order to get a safe angle I would need to make it slack, which would give me a loose piece of thick webbing on the deck that might bang around all night. I’m thinking a rope based solution might be quieter. Obviously, this absolutely requires the tethers on those jacklines to dynamic rope.

Another variation to your setup that I’m considering is to have a hard point connection (again with a dynamic rope tether) to get around the dodger. I just am not able to find tether lengths and jackline positions that work for my boat that don’t involve the positions where the tether can stretch to the rail edge. This will slow me down, but I think I’m ok with that.

Since my partner isn’t strong enough to pull me back on deck if I go over the edge (and visually impaired so very unlikely to be able to fetch me if I become detached from the boat), I’m extra careful to treat the rail as if it’s the edge of the Grand Canyon. To that end, I’m considering three options: 1) be even more conservative on the maximum tether lengths, 2) put in netting on the lifelines, or 3) wear a climber’s harness. 1 is difficult and I fear being constrained too much in movement with it. 2 is ugly, and more importantly, puts a lot of blind faith in the stanchions, parts that I haven’t rebuilt yet. I could rebuild the stanchions, but would prefer to do that later. 3 is kind of winning right now. It’s slower than my current Spinlock PDF/harness, but my bestie is a climber and assures me I’ll get quick at it. Thoughts?

If I go with 3, I’ll likely only add a PDF in rough weather and then go with a Type 1. I know that’s controversial. We haven’t thought through what my partner will do, probably stay with a Spinlock all the time. The balance is different for her since she’s small and I can easily lift her and I at least have a fighting chance of pulling of a POB retrieval.


Dan Sullivan

I know this is an older article but really appreciate the thorough analysis as well as the contributions from the commenters.
Have you considered elevating the attachment point at the mast end of the fore jackline? Attaching the aft end of the jackline at, say, 4′ above deck level seems like it would improve the geometry of the tether, and potentially shorten the required length. For those that have mentioned struggling to minimize tether length for smaller boats, might this be a good option? Assuming this could be done without interfering with the jib, I don’t see a downside.