Stabilizers: A Must for Passage-Making?

[mvweebles]

Maybe the idea just needs time to mature. Don't know, but I'm not writing it off.

I'll give it (ART) Last Rites for you. In the hierarchy of stabilization, ART is a distant last place behind roll chocks (which economically attenuate roll fairly well with zero unintended stabilitu consequences), and sail plans (which have benefits of get-somewhere propulsion). I'm sure there's some whacko somewhere that would give them a try, but no sane naval architect is likely to recommend one for a new build.

Ring-in the 23rd Psalm....

Peter

 

[Hippocampus]

I may have missed this in earlier posts, but the gyro stabilizers are an excellent option, e.g., Seakeeper.com

I’ve tried to expound on the pluses and minuses of gyros here and in other threads. For us the best solution for our coastal gunkholing and nearshore boat use program. We have been staying no farther out than 25 to 50nm offshore. OP was referring to blue water passages. In that setting think gyros still are in the running for large energy intensive vessels where a genset is running anyway 24/7 along with the air handlers, chillers and other accruements but think other devices maybe more suitable for small boats doing transoceanic voyaging.

 

[Marco Flamingo]

I'll give it (ART) Last Rites for you. In the hierarchy of stabilization, ART is a distant last place behind roll chocks (which economically attenuate roll fairly well with zero unintended stabilitu consequences), and sail plans (which have benefits of get-somewhere propulsion). I'm sure there's some whacko somewhere that would give them a try, but no sane naval architect is likely to recommend one for a new build.

Ring-in the 23rd Psalm....

Peter

Got it. Your citation to an ancient book of riddles explains it. One has to have faith that ARTs won't work because they are foreign and not traditional. Sort of like multihulls. Used by others, but not us. Can't work for power vessels despite the science. They turn turtle and everyone dies.
It is so written. No sane naval architect is likely to recommend a multihull for a new build.

Wait a minute, I think I've seen a multihull. They may be becoming more common. Maybe some naval architects understand them, have adopted the idea, and given them their blessing (after a few centuries). The multihull has risen. Maybe ARTs are next. Have faith.

 

[Hippocampus]

What killed multis in the US is Herreshoff designed several. They were so successful that they won every race in which they were entered. Response was to make them illegal in just about every available organized race. Even now there’s a separate Bermuda race for them and they can’t get rated for PHRF. Marinas back then had more sail then power. Given many sailors like to race on occasion they choose mono hulls. So marinas had slips designed to accommodate monos not multis. Even mooring fields are set up to better accommodate monos. Although few folks actually do passages many like to think their boat is capable of that activity. When totally dependent upon form stability you need to be above a given size to be safe in a seaway. Of course this doesn’t apply to small outboard powered center consoles and the like. But it does for a voyaging boat. It’s generally accepted for sail at least you talking over ~45’. That means boat bucks. Q.E.D.

 

[darkside]

Catamarans have been the go to design for ocean voyaging for the last 3000 years or so down our way. I agree with Hippos assessment that for sailcat voyaging 45ft plus is best. At that size the stability, living spaces, bridge deck clearance and most importantly load carrying all come together. Ours was 46ft.
In the 20 odd years since our voyage there are now far more cats in the Atlantic and Pacific crossing fleets.
For powercat voyaging perhaps it's bigger still like Domino. At that size they do get hard to find somewhere to park them.
For coastal we hope to get away with less.

 

[GoneDiving]

I agree that ARTs aren't common......

Maybe the idea just needs time to mature. Don't know, but I'm not writing it off.

I have no idea if ARTs work or not. However, this certainly wouldn't be the first time that engineers have abandoned a cheap and simple solution (essentially a bathtub of water) in preference for a costly, complex and maintenance intensive option (a 3 axis gyro c/w 24/7 genset, hull strengthening for mount points etc etc). ?

 

[ranger58sb]

When I first read Beebe, I began to think a combination of an anti-roll tank and bilge keels might be the bee's knees for semi-stabilization on a very reduced budget.

If I recall correctly, rolling chocks/bilge keels are counterproductive with flume tanks. @Marco may have more info on that from his readings.

Certainly could be the case.

OTOH, my first (uneducated) guess was that one might complement the other... in a purpose-built combination... so that tuning the bilge keels could mean a smaller anti-roll tank, or maybe tuning the anti-roll tank could mean smaller bilge keels.

Something like that.

Part of the reason I was attracted to the idea of one or the other or both... is because there are no moving parts. (Aside from the sloshing.)

-Chris

 

[Hippocampus]

Curious about all this interest in ART for small boats. Think there’s a strong reason the complexity, expense and power draw of other techniques is justified if you endeavor to do passages. Once again it’s simple physics.
A key part in receiving a “A” rating is stability. Same applies to other rating systems such as Norske or Lloyds. Although comfort is dramatically improved by placing weight(and therefore inertia) above the meta center it has a detrimental effect on stability. Hence even with a light carbon fiber mast comfort is dramatically decreased if you lose the stick given all that weight is above the meta center and the effect increases as it goes up. Same with a ART. The higher up the weight is it both increases inertial effects independently of shifts in weight with resultant increasing dissynchrony to the vessels motion. However this is at the expense of AVS. So to get benefit from the ART you need to either increase its size or place it higher up. Both decrease stability. I wonder why in the world you would want to decrease the stability of a ocean going vessel. Particularly with a system you could not turn off with the flick of a switch. Draining a ART would take time. If the device was placed outside the accommodations it would involve risk to the operator.
Seems there’s a conflict between stability and some comfort measures. It’s unfortunate the term stabilization is used for these devices (fins, fish, Magnus gyros etc.). None improve stability. They only improve comfort.
Rolling chocks, bilge or full keels provide resistance to roll by increasing turbulence and/or drag with transverse motion. At optimal speeds if so configured may also provide some lift that resists roll as well. However, as history has shown there’s also an inherent risk in survival conditions whenever the ability to slide is decreased significantly. When a vessel is parallel to a wave face it needs to slide down that wave face laterally. If its immersed hull catches its at risk of rolling over. In multiple sailboat races full keeled boats where shown to be at more risk for this behavior than high aspect fin keels, multihulls with daggerboards up or centerboard monohulls with board up. These vessels has a greater ability to slide laterally so less risk of turning turtle. Rolling chocks/bilge keels present the same risk. Risk would increase with size of lateral plane projected. So if small minimal risk but minimal effect. There’s no such effect with gyros. Magnus or fins would have a modest effect with Magnus having nearly no effect if rotated in.
Again why would you install a device if it presented an additional risk in survival conditions.

Yes, if your AVS is extremely high these risks might be minimal. Similarly if you never see a storm, rogue or large wave these risks may not be encountered. But when thinking about modifying a vessel with intentions of blue water service unfortunately the expense and energy requirements of active “stabilization” systems would seem justified. We hear about boats lost in rallies or races. Occasionally hear about single recreational vessels lost at sea. Given the activity involves small numbers and even fewer end up in disaster few are reported. From word of mouth reports believe of this small number very few are reported to the public at large.
If you do passages in a small power vessel you are in a very select group. Would suggest you do not incur any risk (even if small) you need not incur. There’s enough stuff to worry about without adding to your list.

 

[DDW]

One factor that has been ignored (at least it was in the Quebec and Australian papers on the subject) is the stabilizing effect of the weight of the poles required for fish. This is alluded to in the Quebec paper, when they say at one point that simply deploying the poles had the same effect as putting the fish in the water. Also, though the boats were sister ships, one had poles and one did not. The effect on Gz and roll period was not assessed. While the weight of the poles improves dynamic stability, it reduces static stability.

In wave induced capsize, there isn't much sideways sliding effect as shown by tank testing. Generally the boat isn't moving sideways through the water much, but is picked up and thrown on its side by the breaking wave. A broaching rollover may be different.

 

[Hippocampus]

Thoughtful post DDW. Still in every analysis of major events involving loss of vessels +/or life there was a direct and high correlation between immersed lateral plane and survival of the people and vessel. Doesn’t matter which race you look at. Risk would appear to be from highest to lowest.
Full keel mono hull
Fin mono hull
Dagger or center board mono with board(s) up
For multi hulls fixed keels of any sort did worst than those with daggerboards with them withdrawn.
That’s history not tank testing. Breaking waves look and act differently depending upon where you are in relation to the wave face. At the top the water may land right on top of you with you at risk of being overwhelmed and down flooded. Lower down you may be surfing if diagonal or perpendicular to the face. But parallel or near parallel in the mid portion or lower would think history would suggest merit to post #188.
Traditionally as suggested by Allard Cole and others technique is to climb the face on a slight diagonal. Go perpendicular at the crest. But resume a slight diagonal on descent to avoid pitch pole at the trough. Would suggest from experience with this technique avoidance of broach is key. It here that it is to your advantage if you can slide laterally a bit when you are to close to parallel from inattention or slow AP reaction. That allows you time to assume a more diagonal position. ( Personally prefer to hand steer and not depend upon a mechanical device). Dashew suggests (with great merit) to maintain speed above the train and assume a more perpendicular alignment. Risk of roll is decreased. This is great for higher speed long lean vessels but may not be practical for small FD hulls.
Yes most definitely just like the balance pole of tight rope walkers the poles (and associated guys) weight improves dynamic stability. But as you say at the expense of static. There’s another confounder. That’s when the end of the pole is immersed. Drag on the side suddenly increases which could effect your ability to avoid a broach.

 

[slowgoesit]

Folks, please the discussion about stabilizers. If you wish to debate the pro's and con's of mono-hull vs multi-hulls, please start a new thread.
TF Site Team

 

[Marco Flamingo]

So to get benefit from the ART you need to either increase its size or place it higher up. Both decrease stability.

If you want to maximize the effect from an ART you can increase its size or place higher up. To maximize benefit, larger and higher has its limitations and realize that one can't get gyro results from an ART. The only article I read where stability with an ART was a safety issue was a fishing boat where the crew had access to the fill on the tank. They increased the fill for increased comfort in relatively mild seas. It caused stability issues in heavy seas. Too much of a good thing. The captain drained the tank and supposedly didn't use it again. 20 lashes all round to the crew. Was the problem the viability of the ART or the ignorance of the crew?

I wonder why in the world you would want to decrease the stability of a ocean going vessel.

There are many traditional reasons. One is to have food, water, crew aboard.
Another is to have a raised bridge for better visibility. In the case of trawlers, a flying bridge from which to wave to the little people. Maybe that's not the reason, but I had difficulty finding a Taiwan trawler that didn't have an upper exposed helm. I would certainly exchange the dead weight aloft of an upper helm in favor of an ART.

Particularly with a system you could not turn off with the flick of a switch. Draining a ART would take time.

If one uses a garden hose. My experimental bladder has a 2.5 inch drain. That takes a few rolls to empty. If the ART was a tank with quick release ends, one roll period and the water is gone. But that may addresses a false concern. Not often, if ever, does one encounter an instantaneous dangerous sea condition. If such weather phenomena do occur, spinning up a gyro stabilization system would rate the worst system to address a magic wave. (For those who find irrational fears entertaining, I suggest the movie The Last Wave, 1977 directed by Peter Weir.)

If the device was placed outside the accommodations it would involve risk to the operator.

Not sure what this refers to, but I'm interesting and any risk to the operator.

Seems there’s a conflict between stability and some comfort measures. It’s unfortunate the term stabilization is used for these devices (fins, fish, Magnus gyros etc.). None improve stability. They only improve comfort.

And that is my only goal. I'm not looking to improve stability so that I can challenge the oceans of the world (which may be the OP's goal). I'm looking only at increasing comfort in my world (inside passages in the PNW). Increasing comfort, but not to the extent of compromising stability (i.e., safety).

Rolling chocks, bilge or full keels provide resistance to roll by increasing turbulence and/or drag with transverse motion. When a vessel is parallel to a wave face it needs to slide down that wave face laterally. If its immersed hull catches its at risk of rolling over.

And if equipped with paravanes, the vessel slides down the wave face, the vane pulls free from the surface of the following trough, flies through the air, hits the pilot house, killing the captain (that story is on the internet). It's always something. Everybody gets to make their own risk assessment, whether based on fact, or lore, or a combination.

1) if you never see a storm, rogue or large wave these risks may not be encountered. . . . 2) If you do passages in a small power vessel you are in a very select group. Would suggest you do not incur any risk (even if small) you need not incur. There’s enough stuff to worry about without adding to your list.

I plan on staying in group #1 given my cruising grounds. Everything above my CG (which, it turns out, is basically all "comfort" items) will be evaluated in terms of safety, with the understanding that there need be a risk/benefit analysis. Freezers, dinghys, electric davits on the flying bridge? Nope. An ART? That makes more sense.

Loving this thread (with apologies to the OP). As to my experimental bladder ART, I filled it up quite a bit more yesterday. The result was that the "tank" was slightly more sausage shaped. This "tighter" bladder inhibited the wave form, thus more water did not produce more weight transfer, i.e., more stability (comfort).

 

[Hippocampus]

We’ve discussed this in terms of survival conditions but would suggest it’s also a concern in more mundane circumstances such as crossing a bar, passing through standing waves, wind against wave. Even coastal boats may experience such conditions.
Swells are big circles but with breaking waves the breaking portion has left the circle with just gravity as the predominant force. But also the circle is moving forward as it’s formed from energy from the wind. So as a boat floating in it depending upon where you are in relationship to the wave you may experience more or less lateral and vertical vectors. And the vectors reverse direction as they past under you or you pass through the wave. To whatever extent you are moving with rather than against those vectors you will be perturbed to a lesser degree. If you are moving at the same speed as the water you have no steerage. Hence, less force against your boat with a JSD than a sea anchor. But you need movement pass your rudder to steer with any active technique in a seaway. Same thinking in above posts.

 

[Hippocampus]

MF I was addressing the OP. Read it again. Still think he’s thinking about blue water. I currently own a SD hull with a SeaKeeper. There’s no way I would cross oceans with this vessel. It’s not suited for that activity. Similarly your situation makes the risks he maybe subject to irrelevant. Different boats for different folks. Been speaking to the OP’s concerns nothing else. Truly appreciated DDW’s post. Particularly liked his use of dynamic v static stability. Avoids confusion. Think for YOUR use of YOUR boat the concerns expressed aren’t applicable. That’s great!!! But don’t think that’s applicable to the OP.

 

[DDW]

Discussion of tripping on lateral plane is not off topic. Individual experiences are just that, and trying to relate them together to tell a story can be misleading. Tank testing, while not "real", is at least controlled. Very few people still believe that a long shallow keel is more seaworthy overall than a fin. On powerboats with rolling chocks (at least mine) the keel, being much deeper than the chocks, overwhelms the effect of the chocks.

Batwings might be large enough and with enough leverage to have an effect in a sideways slide or broach, but of course they can be retracted. Fish poles cannot be jettisoned when the conditions get sporty if it was decided to be an advantage. Every once in a while I contemplate a custom trawler, with a deep daggerboard or centerboard for roll control.

 

[Simi 60]

One factor that has been ignored (at least it was in the Quebec and Australian papers on the subject) is the stabilizing effect of the weight of the poles required for fish. This is alluded to in the Quebec paper, when they say at one point that simply deploying the poles had the same effect as putting the fish in the water. Also, though the boats were sister ships, one had poles and one did not. The effect on Gz and roll period was not assessed. While the weight of the poles improves dynamic stability, it reduces static stability.

Depends what they are made from

Steel is heavy
Aluminium is not.
Using the h frame flopper stopper arms we installed as an example, it can be raised and lowered with one hand, very light.
The stainless steel variant of same others have need a 4:1 pulley

The arms they are talking of in that paper are the massive steel arm and supporting structure that commercial fishing vessels have requiring winches to deploy.

Ours in her original format

Most recreational vessels won't have anything like that weight aloft or extended if lowered.

 

[DDW]

Steel is heavy. Aluminum is less heavy. Carbon fiber lighter still. But ALL of these, that far from the CG, affect dynamic roll stability. Most poles used for fish are much longer, and have to be stronger than those used only for flopper stoppers. Anything you put on a boat above the waterline increases its roll (and pitch) inertia. This is why racing sailors are willing to pay $100 per GRAM to eliminate weight at the masthead.

 

[Simi 60]

Steel is heavy. Aluminum is less heavy. Carbon fiber lighter still. But ALL of these, that far from the CG, affect dynamic roll stability. Most poles used for fish are much longer, and have to be stronger than those used only for flopper stoppers. Anything you put on a boat above the waterline increases its roll (and pitch) inertia. This is why racing sailors are willing to pay $100 per GRAM to eliminate weight at the masthead.

80mm X 6mm X 6metre aluminium tube which is a full length and what we'd use for a stabiliser arm weighs 22kg and would have no affect on a 65tonne boat.

The solar panels we have on the roof weigh more.

 

[Hippocampus]

Would suggest 65 tonne may not be the appropriate variable to focus on Simi. Nor the 22kg. Needs further calculations. I don’t know architecture or stability calculus for your boat. Much like a hand clap bringing down untold tons of snow in an avalanche small changes can have big effects. DDW is right to point out the vector is weight times distance. From the small picture of your boat you would appear to have a relatively small weight as tophamper and a stable boat. Seems unlikely to be a issue. But have no opinion as to impact of the poles and associated rigging on your boat. Don’t know enough about it. Still going back to the OP question and subsequent posts by others I would involve a N.A. before adding anything such as birds/fish, rolling tanks or other on a boat which will see open water service. Recall the classic video of a 100+ foot yacht turning turtle upon her maiden launch. They obviously missed a detail.

 

[Circumnavigator]

Like everything else in boating, it depends. If your passage making will always be short enough and with enough time that you can pick your weather and avoid beam seas, then stabilization may not be necessary. If you go places that take a week or two to get to, then yes.


Three choices:
Paravanes require strong rigging and can be dangerous to handle. Not useful in any kind of constricted waters. Can be very effective and certainly safe enough if you deploy and retrieve them in calm to moderate conditions. The $5K number seems low to me, as even manual winches for handling them will cost more than that unless you really scrimp on quality.


Fins are the traditional yacht stabilizers. Their drag will take something off speed, and in areas where there are lobster or crab traps whey will be a real nuisance. Fairly complex mechanically with maintenance.


Gyros have been around for 100 years (Atlantic Liners) but are more recent additions to the possibilities in yachts. We installed one from Quick in Fintry (79', 150 tons displacement, gyro weighs 3,000 pounds, takes 7kW @ 240VAC, cost $135K installed) and more recently in Morning Light (42', 40,000 pounds displacement, gyro weighs 1,060 pounds, takes 2.7kW @120VAC, cost $35,000 installed). Night and day. Crossed very comfortably in Fintry from Cape Sable to Boston in 35 knot wind 10 degrees abaft the beam, ten foot seas. Essentially no roll at all.


Note that fins require space inside in specific places, while a gyro can be installed anywhere that you can attach it to the hull very securely. It does not have to be on center. The gyro maintenance cycle is 2,000 hours. See https://www.quickitaly.com/en/products/anti-roll-gyro-stabilizers/mc2-xseries-ac-en/


Jim

 

[Muirgen Afloat]

Three choices:
Paravanes require strong rigging and can be dangerous to handle. Not useful in any kind of constricted waters. Can be very effective and certainly safe enough if you deploy and retrieve them in calm to moderate conditions. The $5K number seems low to me, as even manual winches for handling them will cost more than that unless you really scrimp on quality.


Jim

We've only had out boat a year and half and have used the paravanes many times. I am wondering what I'm missing if I need to have more caution in using them. What danger is there? So far it's like a 5-10 minute deployment or retrieval.. am I missing something? They have worked great underway and as flopper stoppers. Want to be prepared instead of surprised. Thanks, Laura

 

[Circumnavigator]

A paravane is a heavy weight swinging on the end of a line or chain. Under difficult conditions one could put holes in you or the boat or knock you overboard. If you handle them carefully, they should be OK, but "should" is always a difficult word in boating. If any part of the rig fails, you could have a serious problem.


Jim

 

[Mac2]

Recall the classic video of a 100+ foot yacht turning turtle upon her maiden launch. They obviously missed a detail.[/QUOTE]

To be fair, the vessel in question, was launched without ballast (fuel, water, etc) and one of the launching mechanisms’ tires flattened, initiating the capsize during launch-if it’s the same incident in Anacortes Wa.
I mention this because no one has talked about adding ballast to counteract added weight up high to make stability equal to original stability. Is this a thing? I know sailboats take this into account with their mast and ballasted keels, so why not a trawler adding paravanes?

 

[mvweebles]

A paravane is a heavy weight swinging on the end of a line or chain. Under difficult conditions one could put holes in you or the boat or knock you overboard..... If any part of the rig fails, you could have a serious problem.

More dangerous than 2000 lbs of dead weight spinning at 10,000 rpms powered by a generator? What could possibly go wrong? (Tongue-in-cheek)

Paravanes are, by far, the most common form of stabilization on the planet. They are not perfect, but they work very well and have many benefits: simplicity, durability, reliability, and affordability being high on the list. The Canadian fisheries watchdog pops up with a white paper and suddenly paravanes are a ticking time bomb even though no one on this forum uses their boat in a manner even remotely similar to the subject vessels (few have ever even used paravanes).

Every use case is a bit different. For me, gyros are my last choice - a distant third behind fins and paravanes. Nothing wrong with gyros, just don't fit with how I want to use a boat. But I have extensive experience with fins and paravanes, mostly as a delivery skipper where weather boundaries are often pushed a bit. Both work well. Neither felt dangerous. I don't know where the fear of paravanes comes from, but does not align with my experience. Not even close.

Oh.....while not Maine, the pacific coast has its share of crab traps. I have caught kelp once with fins (mine, before i installed deflectors).

Peter

 

[Mako]

To be fair, the vessel in question, was launched without ballast (fuel, water, etc) and one of the launching mechanisms’ tires flattened, initiating the capsize during launch-if it’s the same incident in Anacortes Wa.

Understand your point, but to clarify, fuel water stores anchor etc. are load, but not ballast. If that boat capsized because it had none of its designed ballast installed (lead, concrete, etc.) then that would be a logical explanation. But otherwise, the boat was launched lightship and it should not have capsized. Of course anyone interested could probably Google the actual reason that the NA's developed to divert attention from their <possible> ineptitude.

 

[Mako]

@mvweebles, sounds like it would be interesting if you started two polls of what order of interest for various roll attenuators for: (1) coastal cruising; (2) bluewater remote cruising.

Suggestion: paravanes, rolling chocks, flume tanks, fins, gyros, etc.

 

[Simi 60]

A paravane is a heavy weight swinging on the end of a line or chain. Under difficult conditions one could put holes in you or the boat or knock you overboard. If you handle them carefully, they should be OK, but "should" is always a difficult word in boating. If any part of the rig fails, you could have a serious problem.


Jim

Although there are some apparently using ply blades so I imagine, less weight and less damage.


Here
https://www.trawlerforum.com/forums/s3/learning-how-fly-fish-paravanes-64293.html

Here
https://www.trawlerforum.com/forums/s31/building-your-own-paravane-system-6339.html

 

[mvweebles]

@mvweebles, sounds like it would be interesting if you started two polls of what order of interest for various roll attenuators for: (1) coastal cruising; (2) bluewater remote cruising.

Suggestion: paravanes, rolling chocks, flume tanks, fins, gyros, etc.

This thread has a lot of confirmation bias - justifying what people already have. Understandable. What I'd find interesting are people who are on a second build with a clean sheet of paper and what choice they made and why. I forget what Ken Williams went with on his GB60, but he's built a bunch of boats. On this forum, a contributor has cycled through 3 nordhavns and a helmsman. What did he chose and why? TwistedTree would be another interesting data point. The folks on Sea Venture considered a SeaKeeper but went with paravanes due to cost as I recall, but I'd be interested in their feedback on the sky-is-falling claims about how dangerous paravanes are. Personally, I just installed new fins but if I were to do it again, I would more closely consider paravanes (air draft would likely rule out for me).

These would all be interesting perspectives from experienced power cruisers with skin in the game who wrote a check based on a decision (vs buying a used boat that happened to come with a type of stabilization, my first time around)

Peter

 

[rslifkin]

Personally, I just installed new fins but if I were to do it again, I would more closely consider paravanes (air draft would likely rule out for me).

I've always wondered if paravanes could either be done with more manageable length poles, or ones that fold along the hull sides instead of straight up.

 

[Marco Flamingo]

These would all be interesting perspectives from experienced power cruisers with skin in the game who wrote a check based on a decision

That's the kind of perspective I tend to discount. A Cadillac SUV has to be best because 1) it is a Cadillac, 2) it is expensive and 3) they have good TV commercials. Same with Louis Viutton luggage. Has to be the best. But are these purchased because of skin in the game or clueless with a fat wallet?

I can see that it is very difficult to numerically quantify roll attenuation, and even more so to quantify comfort and ease of operation. Still, it is the professional studies with head to head comparisons between one technology and another that interest me. Sure, paravanes have that "commercial fisherman" look to them that appeals to some (write the check). Sure, others have covered moorage that makes paravanes unappealing (don't write the check). But spending or not spending based on either consideration doesn't address the actual effectiveness of the system.

We are free to spend our money as we please, with the exception of contract killings (darn it), heroin, etc., but that doesn't really establish the merits of a product. So, no easy answer.