Towing Warps - Actual Test Data?

[thinwater]

I can find data on anchors an d wind force and drogue resistance. However, I have not been able to find any actual test data on towing a warp, weighted or otherwise.

Any one ever seen any on the net? Not antidotal comments - actual forces at varying speeds, or something similar.

I did some tests on a Seabrake 24 and I would like to compare.

[tager]

I doubt that you are going to get any figures on this, and I wouldn't trust them if you did. Best to go out there with a strain gauge and a computer in varying conditions.

What are you gathering the data for?

[svHyLyte]

I suspect that most information on towing warps is anecdodtal. Coles' "Heavy Weather Sailing" discusses the matter at some length but the observations are largely based on reports from boats that used the method to more or less (usually less) advantage. It didn't work for the Smeeton's (twice); and Moitessier railed against the method after rounding the Horn using the techniques that Vito Dumas discovered during his own voyages. The closest you might come to "data" is the work that Jordan did in the development of his Series Drogue. Frankly, given the space that hundreds of fathoms of warp would take, compared to a Gale Rider or a Series Drogue, who would seriously consider that alternative today, eh?

FWIW...

[tager]

The thing is you may be carrying warps already if you have nylon rode.

[thinwater]

Originally Posted by svHyLyte

I suspect that most information on towing warps is anecdodtal. Coles' "Heavy Weather Sailing" discusses the matter at some length but the observations are largely based on reports from boats that used the method to more or less (usually less) advantage. It didn't work for the Smeeton's (twice); and Moitessier railed against the method after rounding the Horn using the techniques that Vito Dumas discovered during his own voyages. The closest you might come to "data" is the work that Jordan did in the development of his Series Drogue. Frankly, given the space that hundreds of fathoms of warp would take, compared to a Gale Rider or a Series Drogue, who would seriously consider that alternative today, eh?

FWIW...

But I am an engineer and like to see numbers, if only to see how they compare with more modern methods. As I said, I did some strain tests with a Seabrake 24 and a 5-foot parachute, and would like the info to build a table of sorts.

Yes, the JSD paper is very good.

[sneuman]

Originally Posted by svHyLyte

I suspect that most information on towing warps is anecdodtal. Coles' "Heavy Weather Sailing" discusses the matter at some length but the observations are largely based on reports from boats that used the method to more or less (usually less) advantage. It didn't work for the Smeeton's (twice); and Moitessier railed against the method after rounding the Horn using the techniques that Vito Dumas discovered during his own voyages. The closest you might come to "data" is the work that Jordan did in the development of his Series Drogue. Frankly, given the space that hundreds of fathoms of warp would take, compared to a Gale Rider or a Series Drogue, who would seriously consider that alternative today, eh?

FWIW...

I am not totally convinced by Moitessier. I think it may have had more to do with Joshua's design than anything else that "surfing" instead of slowing worked for him. I can't say, though, what exactly the difference was. It's just a gut feeling I had reading his explanation.

I have never tried warps, but on the one occasion when I used a drogue (28' modified full-keel mono, ala Alberg 30), I found that it was less about surfing than it was about directionality - the drogue definitely helped keep the ass end pointed toward the oncoming waves. That was before I read the Pardeys' book, however, and in any case, didn't have a sea anchor at the time. If I ever end up in a similar position, and I certainly hope I don't, I would seriously consider heaving to with a parachute anchor rather than running. The Pardeys are right about one thing - while running, eventually there will be one of them with your name on it.

[GordMay]

Methinks you’ll have to perform your own comparative tests, as only you would be able to duplicate the test conditions & procedures used on the Seabreak.

Of course, why you’d want to escapes me. A warp is merely an ineffective drogue.

Check out “Understanding Sea Anchors and Drogues” ~ by Earl R. Hinz, published by Cornell Maritime Press.

[imagine2frolic]

At the very least the warps help disassemble the oncoming waves. I would think that in itself would be a moral booster.........i2f

[svHyLyte]

One could actually calculate the drag load of a warp deployed from the stern of a yacht by treating the bight as a free body, and making some simplifing assumptions as to the speed of the yacht, the weight and size of a load--such as a pig of iron--at the head of the bight etc. The calc's would undoubtedly generate very precise numbers which would, of course, be pretty meaningless in "real life".

For the sake of the exercise, get yourself a fish scale and attach the top of that to a cleat on one side of your transome and the bottom to one end of the largest line you have aboard and the other end of the line to a cleat on the other side of your transom. Once you're underway, pitch the bight off your stern. Once the line is fully fed out, check your scale. You will find that the load ("drag") is next to nothing, Adding weights to the bight will increase the drag (don't use an anchor unless the depth of the water is greater than the lenght of the bight or your may find yourself with more "drag" than you're planning on!), but that will still be negligable in comparison with the loads on the yacht and have negligable effect in storm conditions.

(Of course the same does not hold true to catching a fish trap on your rudder in a race, after which you spedd will be reduced to nothing, eh?)

FWIW...

[barnakiel]

Chuck yours overboard, tie to a scale and you have your test ready (ah, yes - get the boat moving ;-).

Surprisingly, I found the streamed 300' to create more drag then when looped.

b.

[thinwater]

... extrapolated and correlated and came up with some results that were at least of use to me. No, I didn't go out in storms, but I think I developed some real-world flat water drag numbers that can be compared on a level basis. I have warps, a Seabrake, and a chute, so I tested those. For others I collected published data and scaled it as needed. The opinions and conclusions are, of course, nothing more than opinions, and I was only really interested in my boat and my style of sailing.

Still, I thought this was worth sharing. If you have data you think is worth adding, please let me know.

Sail Delmarva: Drogue and Parachute Sea Anchor Testing: A Summary for Small to Medium Cruising Catamarans

[Albro359]

thinwater

I looked at your blog , tried to leave a comment but couldn't

theres a question on there about the right line to use to tow a seabreak

I've been down this road. The info on their website is contradictory.

I contacted Seabreak to ask them and their advice is :

Use BRAIDED polyetser (like sheet line ) to tow it NOT nylon. The line should NOT stretch much

countrintuitive ? maybe but thats their advice

[thinwater]

Originally Posted by Albro359

thinwater

I looked at your blog , tried to leave a comment but couldn't

theres a question on there about the right line to use to tow a seabreak

I've been down this road. The info on their website is contradictory.

I contacted Seabreak to ask them and their advice is :

Use BRAIDED polyetser (like sheet line ) to tow it NOT nylon. The line should NOT stretch much

countrintuitive ? maybe but thats their advice

... a less stretchy line will transfer the load to the drogue more quickly and prevent surfing from statring. Remember, we are not talking about steel cable (there is some stretch) and we are not talking about a sea anchor of ground anchor (the drogue will accelerate through the water). There is going to be shock absorption. When I dumped the Seabrake over the rail at 7.2 knots it took about 4 seconds for the boat to slow to 4 knots. We barely felt it. Yes. I was using nylon (so that I could spread the load over time) but I still think the logic is sound, for this application and for other drogues. The JSD allows for both nylon and low-stretch ropes, because it makes less difference with that design; the shock absorption and quick load acceptance features are not closely related to the rope characterisics. I would have a very differnt opinion regarding a parachute, where a very long (300 feet +) stretchy line is needed to keep some load on the chute between crests, to prevent colapse/fill cycles.

Also, if the wave is coming from an angle, the sooner the load transfers, the better. This is an advantage of the JSD.

I think there is an optimum amount of stretch beyond which the bungee effect and it's hazards out weight the impact attenuation advantage. This applies to both drogues and ground anchors.

[erasmos]

Greatly fond of this subject and highly appreciative of you mates interest into it.

I never deployed a parachute in rougue seas. Something has been puzzling me reading about seaanchors and drones, so Im after your opinion. Please forgive the following miscrafted piece of illustration.



It seems that a lot of people who are using parachutes or sea brakes just deploy one if heaving to in really scary rogue swell and un-sailable conditions. The broad sided tactic when deploying parachutes seem intuitively wrong (for some reason) and if theres something I learned over the years it is not always to accept the 'norm' when the gut stirs.

Im no ocean veteran but reading about the few reports that are on the matter, about pitchpoling and how capsizing accidents really happen my common sense (and sparse but efficient experience from surfing and dodging waves) supports that the problem is to not get caught and swept away by the tremendous force of a 20knt moving white water (crashing the boat into the trough). Not surprisingly.

YouTube - Rogue Wave Full Version XVID

The best way one initially supposes is like a surfer to adopt the submerged missile position head to the wave direction (if there is one), but the problem then of course is the lack of drift with the wave motion and the subsequent drift to leeward in between the waves (when the line to the longer sea-anchor slackens).

Does anybody use the above setup?

Parachute
the standard parachute positioned at the suitable waveheight lenght, not 1 wavelenght (which will incur massive slack due the height difference of the trough and top) but half so one is always in exact opposite fase with moving water. the trick would be to get this EXACTLY right. If just 20% off there would be massive drift and slacking (the dangerous element is the snapping due to shock loads)



Seabrake no1
A short heavy duty 20-50ft sea-brake to prevent the bow drifting off from the wind

Sea brake 2
A lighter brake with only 20 ft line to stop the boat from getting too much speed down the face of the wave head to wind.

The suggested setup here should additionally include a release line for the chute edgers for easy retrieval at will.

What do you see as the issues associated with the above suggestions?

[erasmos]

the wind comes from the left.. west of course.. Im from the North atlantic..