Acera vs Dyneema & Jordan Series Drogues

[UNCIVILIZED]

Originally Posted by NevisDog

Way off topic but very useful info nonetheless. I'm guessing this is some type of clever whipping of the rope end - do you have a quick reference so we can all check it out (I could do a search but this may be helpful to a few others too).

Originally Posted by NevisDog

Those reeving splices are neat, strong enough, and simple. Great - thanks for mentioning them.

So spank me, & then play nice eh...
Here's a link to reeving splices, & how to https://www.jamestowndistributors.co...t.do?docId=926

[james247]

Originally Posted by Lantau

This is probably getting to be too detailed, but I think it would also depend on the color of the cover. Darker covers will, I think, cut out more UV (at least it works that way with sail covers!).



But I doubt UV matters at all for a drogue. It'll be in a locker most of its life, and out for only a day or two at a time, very rarely.

Dacron is all you need most resistant to rot which is the greatest failing of drones.

[NevisDog]

Originally Posted by james247

Dacron is all you need most resistant to rot which is the greatest failing of drones.

Must have been the other drogue thread where Seaworthy Lass posted the weight of her Acera drogue rope - 7.5 kg I think she said, compared to my 35 kg (approx) for nylon (which weighs about the same as dacron). That's a massive difference, may even be the greatest failing of traditional series drogues.

[Seaworthy Lass]

Originally Posted by NevisDog

Must have been the other drogue thread where Seaworthy Lass posted the weight of her Acera drogue rope - 7.5 kg I think she said, compared to my 35 kg (approx) for nylon (which weighs about the same as dacron). That's a massive difference, may even be the greatest failing of traditional series drogues.

Yes it was in the long thread on series drogue. The difference in weight was even more dramatic: 7.5kg vs 47kg for length that I purchased. The Acera was actually higher in strength than the polyester, so the difference would be greater again if the same strength comparisons were made.

This was the post:

Originally Posted by Seaworthy Lass

As a matter of interest I looked up the weight of double braid polyester. These are the figures averaged from a couple of manufacturers:
½" (13 mm) 8.5 lbs/100ft = 0.126 kg/m
¾" (19 mm) 18 lbs/100ft = 0.268 kg/m
1" (25 mm) 35 lbs/100ft = 0.521 kg/m

So the weight of double braid polyester for our boat would be:
40m + 40m + 60m = 5 + 10.7 + 31.3 kg = 47 kg

The volume would also be substantially more, making both storage and handling more difficult.

Considering these drogues are deployed only in atrocious conditions, I think hauling an extra 40kg out of a locker and dragging it to the rear of the boat while trying to hang on becomes a safety issue.

SWL

[JPA Cate]

Huge weight savings, and also, space. Super.

Ann

[conachair]

Originally Posted by JPA Cate

Huge weight savings, and also, space. Super.

Ann

How slippy is it?
I've a (unused of course )JSD onboard and look at the weight of that first section of rope thinking wouldn't it be nice..., but then think of the stories of what a pain it can be to get back onboard and wonder if some slippy light rope at the front might just make that harder....


Edit - Ooops, asked the wrong person

[Seaworthy Lass]

Originally Posted by conachair

How slippy is it?
I've a (unused of course )JSD onboard and look at the weight of that first section of rope thinking wouldn't it be nice..., but then think of the stories of what a pain it can be to get back onboard and wonder if some slippy light rope at the front might just make that harder....

It is similar to dyneema (it just feels a bit stiffer), so it is slippery. Quoting Dashew though "the load is not that great when retrieving" (probably assuming conditions have calmed considerably by the time you are retrieving). From what I have read from those that have used dyneema, it winds easily around the winch as the cone attachment gives extra grip, but the line does need tailing.

SWL

[Seaworthy Lass]

I am super impressed by Acera. The bundles arrived last week (I ordered 8, 10 and 12 mm) and at first glance I thougt they must have supplied 4m of each, not 40m .

It was a surprisingly small package.

I have place an orange next to the Acera to give some indication of scale:

[Pauls]

The advantages of dyneema type rope for bulk and weight savings are significant. However, if you read Jordan's write up on the development and final design of his drogue, the primary target for the drogue is to prevent the boat being accelerated to a speed high enough to allow pitchpoling while keeping the stern to the waves. In other words it is designed for heavy wave impact. He used nylon rope for a reason which he describes clearly - to give enough spring to allow the boat to initially give to the wave impact before slowing its forward speed. This reduces the impact loads on the boat.

In his charts he includes one for additional rode strength required for less springy lines. If you choose to use a line as stiff as dyneema it would be a very good idea to apply that data. Under conditions of a heavy wave impact the loads on the rode will be significantly higher and the rode should be sized accordingly.

Also, and this is really important, the hull attachments will also need to be designed for these increased loads. Hull attachments built to Jordans original specs for nylon line will be understrength when using dyneema.

I'd suggest that a rode with some length closest to the boat made of nylon - perhaps 1/4 of the length, and the balance made of dyneema might be an ideal design. Loads on the rode diminish further from the boat because there are less cones pulling. The springiness of the nylon therefore becomes less and less important towards the tail.

[conachair]

Originally Posted by Pauls

. He used nylon rope for a reason which he describes clearly - to give enough spring to allow the boat to initially give to the wave impact before slowing its forward speed. This reduces the impact loads on the boat.
.

Do you have a link to where he says that? Can't remember seeing that and can't find it on Google. Ta

Did come up with this though..

Note that non-stretchable floating Dyneema can also be used for the tow-line. It's main advantage is that the overall weight of the drogue becomes much lighter and so is much easier to man-handle on board.

http://dragdevicedb.com/drogues

[NevisDog]

Originally Posted by conachair

Do you have a link to where he says that? ...

Coastguard Final Report May 87, P52 para 2:"...model tests show that a highly elastic line is very undesirable because the boat may be capsized before the load builds up." Note those particular tests were done using a single drogue, so this concern is greatly lessened by using a series drogue.

P53 fig 24C, Effect of towline stiffness (i.e. lack of stretch) shows a 20% increase in load from a 200% increase in stiffness. Again these test results were from a single drogue, not series. I believe Thinwater has commented elsewhere on these threads that his tests show a far smaller increase in load with the series drogue, as we might expect.

Note also that nylon absorbs water; Dyneema does not, so zero increase in weight when it is recovered.

It seems the only downside of Dyneema/Acera is the slippery-ness makes retrieval more difficult.

[rgleason]

Originally Posted by UNCIVILIZED

So spank me, & then play nice eh...
Here's a link to reeving splices, & how to https://www.jamestowndistributors.co...t.do?docId=926

Is there a way to make something like a chinese finger which might do the same thing. -a bit off topic.

[Benz]

^^Electrical supply places sell various sizes of woven stainless wire baskets for pulling wires through conduit. They work really well. Dunno if there's any small enough for halyards, though.

[Seaworthy Lass]

Originally Posted by Pauls

The advantages of dyneema type rope for bulk and weight savings are significant. However, if you read Jordan's write up on the development and final design of his drogue, the primary target for the drogue is to prevent the boat being accelerated to a speed high enough to allow pitchpoling while keeping the stern to the waves. In other words it is designed for heavy wave impact. He used nylon rope for a reason which he describes clearly - to give enough spring to allow the boat to initially give to the wave impact before slowing its forward speed. This reduces the impact loads on the boat.

In his charts he includes one for additional rode strength required for less springy lines. If you choose to use a line as stiff as dyneema it would be a very good idea to apply that data. Under conditions of a heavy wave impact the loads on the rode will be significantly higher and the rode should be sized accordingly.

Also, and this is really important, the hull attachments will also need to be designed for these increased loads. Hull attachments built to Jordans original specs for nylon line will be understrength when using dyneema.

I'd suggest that a rode with some length closest to the boat made of nylon - perhaps 1/4 of the length, and the balance made of dyneema might be an ideal design. Loads on the rode diminish further from the boat because there are less cones pulling. The springiness of the nylon therefore becomes less and less important towards the tail.

I tried to do as much reading as I could before settling on UHMWPE rope.
Of particular interest is Jordan's detailed report in the joint paper with US Coast Guard that you mention:
http://www.jordanseriesdrogue.com/pd...uardreport.pdf

For me it is not clear how much (if any) stretch is optimal. Jordan used nylon double braid with significantly higher stretch than polyester. However, in several places in the report on several types of drogues (not specifically the series drogue) mention is made that stretch is undesirable. It will delay the time taken for the cones to act and allow the boat to accelerate down the face of a wave. The only issue seems to be the force on the boat's attachment points.

Both Ace Sailmakers in the US who sell Jordan Series drogues (they have patented the name) and Ocean Brake in the UK who sell a similar design of Series drogues currently offer unsheathed dyneema as an upgrade.

When I contacted Ace Sailmakers who now sell Jordan Series drogues, I was also offered double braid polyester. When I emailed and asked why this was used rather than nylon, I had no response. I think the issue of stretch is unclear even to the manufacturers.

UHMWPE rope is in use by other cruisers such as Dashew (reported the use of double braid Spectra) and Starzinger, which is good enough for me . I have selected line strengths greater than that recommended by Jordan and this should compensate for greater load on the line. The attachments on our boat are more than strong enough, eliminating any concerns in this regard.

For me, the ease of use is critical. Our drogue would weigh over 50 kg in nylon. In survival conditions, I think lugging this out of a locker and deploying would be plain dangerous for us two up. That would kind of defeat the purpose of using it at all.

SWL

[rgleason]

While thinking about chinese fingers, it occurred to me that 6-8" of the appropriate sized double braid cover might work by pulling out every third thread and heat sealing the ends, then just attach the light line to one end and use some whipping line to temporarily tie the chinese finger to the halyard. Perhaps someone has an improvement for winter/spring reeving of halyards.