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PostPosted: Mon May 11, 2015 5:30 pm 
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And what the kayak sailors recommend is to glue the d-ring *inside* the hull with the ring sticking out through a small cut made through the skin of just sufficient size (which is of course then sealed by the patch inside the hull).
See here: https://kayaksailor.com/d-ring-patches/


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PostPosted: Mon May 11, 2015 10:38 pm 
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Ian I've seen that and have been thinking of applying some D rings to my T9 in this fashion... but it's a scary proposition... not sure I can do it. ha.

The series drone is something that I read about a long time ago and it really is a great idea. I did a little research and found this:

http://www.seriesdrogue.com/coastguardreport/droguereport.htm

The introduction is pretty interesting reading.

So having been reintroduced I'll say that your idea of using a series drogue for possible rough weather is definitely a solid one. Keep in mind that Taylor and Jordan are talking about real sailboats, the USCG refers to boats less than 45' getting into trouble with breaking waves... a 45' boat is a BIG boat. I'm not sure you need to bridle the drogue if you have it come of the center of the stern. Two thoughts: 1) The bridle could help bypass the rudder which would be good. 2) The bridle presents two opportunities for lines to get mixed up with the rudder...

The eye that the rudder lift line runs through could be the perfect guide for the drogue. Might be worth thinking about.

I still think the trolley system is a viable and durable way to make this work, and with a double ended boat such as ours, why not give yourself the option of deploying bow or stern. Also, the trolley can be very handy for anchoring and 'cruise' control for your rudder.

So how large are the cones you're having made? and how many do you think you'll use on how long a line? Did you find a formula or are you eyeballing it?

The strength factor is indeed a very complicated question... I'm glad you're on that one Greg.

Interesting thread with some numbers:

http://www.kayakfishingstuff.com/community/showthread.php?t=66878

d

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PostPosted: Tue May 12, 2015 12:30 am 
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mje wrote:
I would recommend glue-on D-rings secured to the hull, just below the deck. These will distribute the load far more evenly than will frame attachment.

http://search.nrs.com/search/?p=Q&w=d-ring


Than you for your suggestions, though I just don't see how two attachment points, affixed to the hull itself (even if glued on the inside with the rings passed through a slit in the hull) could possibly be as strong and distribute the force along the hull/boat with no stress (stretching) to the hull; rather than a strap which extends completely around the boat, affixed at the bow solely to ensure it remains balanced and doesn't slip/rotate around the bow, where there is no stress (stretching) risk to the hull itself and all force is taken longitudinally by the enclosed frame. I.e.:

Image

I would expect that the d-rings would pull off/out, and/or the hull would be stretched and hull/deck seam compromised, under the full force of the drogue in storm conditions.

The one concern that remains in my mind, and I'll need to eyeball things once I have the boat in hand, is the risk to the sponsons depending on how the strap runs along the length of the boat.


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PostPosted: Tue May 12, 2015 8:30 am 
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Hi Rhumby,

For the record, I think this D-ring stuff concentrates the forces too much. I think you were on exactly the right path in the first place: distributing the loads over as much of the structure as possible. With the provisos that I might glue instead of using hard fasteners and might build in the capability to stream from the bow as well as stream from the stern, I think you should stick with your earlier ideas. If someone with a mechanical or structural engineering degree has a contrary opinion, you could listen to that.

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Non-folding: '84 Hobie 16; early '90s Old Town Canoe.
Previously owned '04 Pakboat Puffin II and '05 Swift.


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PostPosted: Tue May 12, 2015 4:54 pm 
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No degree, but a few physics courses ;-) The D-rings that are affixed to patches and then glued to the hull distribute the load over a wider area than any frame attachment, which concentrates the stress in a few small areas. I don't know exactly which fabric Klepper and Long Haul use, but a similar one I found at a supplier's site has a tensile strength of around 800psi. These D-ring patches are what the river runners use on their rafts to secure gear; they're very strong.

Is a strap surrounding the boat stronger? Not necessarily. Keep in mind that the hull is in effect a very wide band surrounding the boat.

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PostPosted: Tue May 12, 2015 9:15 pm 
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Why don't you write to Mark at Long Haul Folding Kayaks and ask him. He builds boats for the US Navy Seals and has had his boats dropped from helicopters and subjected to all sorts of abuse... then he goes and repairs them. If anyone can give you an informed suggestion, it's him.

A very simple description, perhaps including that diagram above, and the fact that you intend to use a series drogue, possibly exerting stress equal to the weight of a loaded boat; should be all he needs to give you his opinion on best bang for the buck here.

That is absolutely what I would do... and if I talk to him in the near future I will ask him about this.

I was just thinking about Michael's point about the rubber mounted D rings... If the bond is really that strong... how could you have a stronger connection to the drogue than the entire rubber hull itself. That's a pretty impressive strap in it's own right.

d

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PostPosted: Wed May 13, 2015 12:43 am 
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All very good points about the d-rings. I'll ping Mark at Longhaul and see if I can get his expert input.


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PostPosted: Wed May 13, 2015 2:55 pm 
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Interesting discussion!
A few of the top of my head points:
A drogue or sea anchor sounds like an excellent idea. Feathercraft actually makes a nice sea anchor.
Both drogues and sea anchors are dynamic brakes, they need to move through the water to generate resistance. From USGS testing on series drogues, I would expect around 4-5 lb of resistance per cone.
So, it is not as though your kayak will be suspended from a stationary attachment point while loaded to capacity. Realistically, I would expect much less than a 900 lb max. load.
I would be hesitant to make permanent modifications to a brand new kayak skin. I would want to try things out first just tied to the kayak. Maybe start out with a line draped over the coaming peak and secured there, then running back towards the gunwales at the end of the cockpit. Also a transverse tie at that point. Think of a bridle on a horse. Test it out in "conditions", then make adjustments etc. And please, have a quick release and a line cutting rescue knife on you.
Additionally, if you go out in conditions warranting a drogue: I would invest in, and test!, an implosion "proof" neoprene spray cover, all normal personal sea kayaking gear and dress for immersion etc. Kayaks with large open cockpits don't do too well in dumping waves.
Interestingly, I normally go out with a tow belt and paddle float: Have to try the float clipped to the tow line as a drogue next time I am in following waves!

Chris O.

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PostPosted: Thu May 14, 2015 4:26 am 
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ChrisO wrote:
Both drogues and sea anchors are dynamic brakes, they need to move through the water to generate resistance. From USGS testing on series drogues, I would expect around 4-5 lb of resistance per cone.
So, it is not as though your kayak will be suspended from a stationary attachment point while loaded to capacity. Realistically, I would expect much less than a 900 lb max. load.


While in most conditions, yes, the load will be much less than the full weight of the loaded kayak, but one designs a drogue for the worst case scenario.

I'm not sure where you're getting the 4-5 lb per cone resistance. A 100 cone drogue is rated at a max load of 7500 lbs, which would be the maximum load (drag) imposed by the drogue under the worst case scenario. A resistance of 5 lbs per cone, assuming that is the maximum drag at highest velocity, would only provide 500 lbs drag, which does not seem to match the design data in the USCG report.

I've studied the USCG 1987 report several times over the years (and I've done a bit of solo open ocean sailing in larger boats) and my understanding is that the drogue load increases proportionate to the velocity and that the maximum load at maximum worst case velocity is calculated to be roughly equal to the displacement of the boat, until you start getting to very large boats (tens of thousands of pounds displacement) where the maximum load decreases to less than displacement of the boat.

From the USCG report:

Quote:
The design load is the maximum load that will be imposed on the drogue, towline and attachments in the event of a very severe breaking wave strike. A load of this magnitude would be encountered rarely if at all, possibly once or twice in the lifetime of the equipment. ... It will be noted that at a displacement of 7500 lbs. the design load is equal to the displacement and at a displacement of 60,000 lbs. the design load is 60% of the displacement.


Thus, my understanding of the report is that for the expedition kayak in question, the drogue and all attachment hardware should be able to withstand a load of 450kg, even if such a load would very rarely be encountered, if ever.


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PostPosted: Thu May 14, 2015 1:59 pm 
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Oh, that number is from figure 6. Perhaps more interesting is figure 19, a speed versus resistance graph of 90 cones with 5" diameter. I don't think you will be going much over 8ft/sec ( =5.56 mph) in a loaded Wayland double.
Don't get me wrong, I am not questioning your desire for a solid attachment of the series drogue. In addition I think that a drogue is an excellent idea! I would just start with a bridle made from line (rope to land lubbers) or webbing temporarily attached to either bow or coaming peak. Permanent set-up would follow from feedback from testing in some conditions.

Chris O.

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PostPosted: Thu May 14, 2015 2:03 pm 
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ChrisO wrote:
Oh, that number is from figure 6. Perhaps more interesting is figure 19, a speed versus resistance graph of 90 cones with 5" diameter. I don't think you will be going much over 8ft/sec ( =5.56 mph) in a loaded Wayland double.
Don't get me wrong, I am not questioning your desire for a solid attachment of the series drogue. In addition I think that a drogue is an excellent idea! I would just start with a bridle made from line (rope to land lubbers) or webbing temporarily attached to either bow or coaming peak. Permanent set-up would follow from feedback from testing in some conditions.

Chris O.


I expect that is what I will do. Wrap the strap around the bow, secured in some non-permanent manner, and over the top and along the deck, secured in some manner to the deck line d-rings. When I'm happy with the arrangement, I'll consider more permanent attachment options.


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PostPosted: Fri May 15, 2015 10:43 pm 
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Using the D rings holding the safety line would essentially do that wrap around, you could attach the two bridle ends of the drogue at the cockpit. The drogue bridle could ride up through the stern D rings. If you connect the forward wrap and bridle ends with bowlines on each side you can easily untie the two drogue ends and let them slide out of the D rings for release - a float could be positioned behind the rudder where the bridles come together. Bowlines are the strongest, easiest and quickest to tie and release in my experience... and keep that knife on your vest just in case.

I like the testing idea before making permanent changes, especially on a nice new boat. Pretty exciting...

d

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PostPosted: Sun May 17, 2015 10:55 pm 
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Not recommending the procedure, but I attached a large drogue to the quick release line of my rescue PFD. My body transferred the pull to the kayak body via the seat cushion, no narrow stress point on any sewn D-ring. Easy to detach too if unwanted complications develop... :)

Once again, not recommending it, but it works for me.

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PostPosted: Mon May 18, 2015 12:52 pm 
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Wow, can't believe I forgot about this. Mark over at Long Haul put together a sea anchor system with a pouch holding the anchor for deployment along the side of the cockpit and a very nice and strong looking anchoring system attached to the back of the cockpit going out over the rudder. The system has a quick release in case the anchor snags on anything - with a float pulling out to contain the end of the line if the emergency release is used. Looks like a pretty good system for beach landings or rough weather. No reason a series drogue couldn't be used with this system.

https://www.youtube.com/watch?v=qSU9a4h2eiw

d

PS - DoiN. - Hate to see you leave your first mate alone in the boat while you're out body surfing... not sure I'd continue that practice... .02¢ :shock: :P

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PostPosted: Mon May 18, 2015 1:31 pm 
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Funny. Just got a reply from Mark and came to post it, and the same link to the video.

Quote:
Greetings Patrick,

We have a short video on a rear deployable sea anchor for surf landings check it out on our YouTube channel.

Our deck anchor point is at the rear of the cockpit (sewn) also hooks to the frame.
The information that we have is the sea anchor line needs to be 10X the length of your boat.
That's why I came up with the spool system. The line should pass thru a stern loop at the very end of the kayak.
Hope this answers your question. You can also call me at the number below.
Thanks, Mark

Mark Eckhart, Owner
Long Haul Folding Kayaks


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