Radar Reflector

[glythcott]

The race instructions require a non-octahedral reflector to have at least a 10 meters squared radar cross section. The 2" dia Mobri reflectors only have 2 meters squared cross section and the 4" dia ones a 4 meter squared cross section. How many of these things am I required to carry...2 of the 4"ers and one 2"er? It seem like a lot to have aloft. I hope I'm just not understanding.

George/TAZ!!

 

[AlanH]

The race instructions require a non-octahedral reflector to have at least a 10 meters squared radar cross section. The 2" dia Mobri reflectors only have 2 meters squared cross section and the 4" dia ones a 4 meter squared cross section. How many of these things am I required to carry...2 of the 4"ers and one 2"er? It seem like a lot to have aloft. I hope I'm just not understanding.

George/TAZ!!

While I had two Mobri knockoffs aloft in the 2008 TransPac, I only had them up there because I already owned them, and they didn't do me any good sitting in the berth. However, several independent tests basically tell us that the Mobri type reflectors are pretty awful. For one thing, their response drops off drastically when the things are at anything more than 5 degrees of heel?

You think you might be heeled more than 5 degrees, much of the time?

Just go by a big Davis Echomaster and string it up. It works. You can also buy a Luneberg reflector, but they cost a mint and weigth a ton. Go look at West Marine's prices on the Tri-lens..

Some radar reflector reports:

http://www.ybw.com/auto/newsdesk/20070409144703pbogeneral.html

This is old, now but well worth reading, especially as Stan Honey was pretty closely involved. The Mobri is in there.

http://www.ussailing.org/safety/Studies/radar_reflector_test.htm#INDEX

Here's the text of the rule from the LongPac Rules:

Radar reflector properly mounted at least 13 feet above the water. If a radar
reflector is octahedral it shall have a minimum diagonal measurement of 12 inches.
If the reflector is not octahedral it shall have a documented radar cross section
[RCS] of not less than 10 meter squared.

So you can have an octohedral radar reflector, as long as the diagonal measurement is 12 inches or greater.

http://www.davisnet.com/marine/products/mar_product_docs.asp?pnum=00153

Go to that URL, and grab the pdf for the instructional manual for the new Davis Echomaster. This is an octohedral radar reflector. It has 12.5 inch circular plates, and it satisfies the rules requirement for 50-something bucks

Here are West Marine's prices on the Tri-lens radar reflectors, which are not octohedral reflectors.

http://www.westmarine.com/webapp/wc...RL=true&storeNum=8&subdeptNum=52&classNum=275


Now look here for information on the Tri-Lens

http://www.tri-lens.com/trilensweb12002002.htm

There's a mini, a regular size and the large size. The only one of the three that has the equivalen tof 10 m squares area is the large size, and it costs $839 at West Marine and it weighs 12 pounds. Ouch.

The Echomax EM230+

http://www.landfallnavigation.com/sem230.html

and West Marine's prices...

http://www.westmarine.com/webapp/wc...RL=true&storeNum=8&subdeptNum=52&classNum=275

Actually has a greater-than 10meter squared profile, though hits 10m squared at 30 degrees of heel, but look at the price!

The answer to this is to just go buy a Davis Echomaster and get it up in the rigging 13 feet off the water for your inspection. Note that the reflector does not have to be PERMANENTLY mounted, just "properly" mounted. You can haul it up on a flag halyard, or a line slung off your backstay.

 

[AlanH]

Having said the above, if anybody wants to hang an echomax EM230+ 13 feet up their mast, I will certainly pass it. Ditto for the large size tri-lens.

 

[glythcott]

Thanks for the advice Alan.

I went with the Davis Echomaster. I've installed a pennant halyard and the reflector will be just below my lower spreader.

George

 

[Alchera]

Thanks for the advice Alan.

I went with the Davis Echomaster. I've installed a pennant halyard and the reflector will be just below my lower spreader.

George

If you want to keep it from flopping around, tie two short loops of cord one on each side. One loop goes around the nearest shroud, the other around the pennent halyard. When you raise it to the top it will be supported at four points.

- Mark

 

[BobJ]

If you want to keep it from flopping around, tie two short loops of cord one on each side. One loop goes around the nearest shroud, the other around the pennent halyard. When you raise it to the top it will be supported at four points.- Mark

I mount mine a little loose so the main won't grind on it as much (when running). Also, those stamped-out edges are sharp - sand around all the edges and apply a couple layers of rigging tape to them (white electrical tape works best). Beats slicing up your main.

 

[blighbaum]

Last year before the SHTP, I e-mailed the Davis company and asked whether putting electrical tape around the edges of the echomaster would impair its effectiveness; they replied that it would! Based on that, I sanded down the sharp edges and left off the electrical tape. Some ships said they could see me on radar, and I still have my mainsail, so I guess that worked. - Tom Kirschbaum, Feral

 

[Alchera]

Last year before the SHTP, I e-mailed the Davis company and asked whether putting electrical tape around the edges of the echomaster would impair its effectiveness; they replied that it would!

I find that very hard to believe. Sounds like you may have gotten a response from the company lawyer rather than a techie. From what I understand, plastic is pretty invisible to the radar spectrum, that's why it's ok to mount radar units behind plastic. Anyway, I've had plastic tape on my Davis edges for years and ships have seen me just fine.

- Mark

 

[blighbaum]

Well, that's what they told me. Maybe they realized that I am a lawyer, and, as you suggest, gave me the legal department. But would one lawyer give another lawyer bad information? Is there no honor among thieves? Perhaps my e-mail to them asked specifically about duct tape, if that would make any difference. Maybe the reason my echomaster worked better on the SHTP than on the Longpac is that I had it tied laterally with a loop to the shroud on the SHTP but not on the Longpac.

Anyway, have a great Fourth!

- Tom Kirschbaum, Feral

 

[Alchera]

Perhaps my e-mail to them asked specifically about duct tape, if that would make any difference.

I don't know about duct tape, I think the standard brand duct tape made from vinyl and fabric would be perfectly OK. But the metal foil tape which is actually used for sealing heating ducts would not be good, since that would affect the radar signal. Maybe that's what they thought you were referring to, which might explain their response.

- Mark

 

[BobJ]

Keeping the Davis reflector in hanging basket ("catch rain") orientation is the most important factor. A bit of slack in its halyard should help as the boat heels. Davis also recommends it be 10" below the spreader, with a loose loop around the shrouds to keep it from spinning. Our rules require it be 13' above the water - this might be close on smaller boats with upper and lower spreaders.

As to the tape, I use plastic electrical tape. I think it's thin enough around the edge for the taped-up reflector to still be in compliance with the diameter requirements (per Alan's post above). Besides, given the choice of a possibly weaker signal or damage to my primary means of propulsion (my main), I'll accept the weaker signal.

 

[Thom]

Again...OLD technology

Sure you can stick some clunky mainsail cutting octagon device up your mast...but you can also just put up what is essentially a whip antennae (another one) which is a radar target enhancer. It retransmits the radar sweep it receives at a cost of 350 mA. Only works in X band and some ships still have radar in S band...but still, you will get seen better by most. Sea-Me?

http://www.theradarreflectorsite.org/

 

[BobJ]

Ruh, roh . . . can a Mini discussion be far behind?

The Sea-Me has been floated out here before. It's less than a pound (plus mast-length power cable) but is supposed to be at the masthead. One of the math gurus (like Thom!) can tell us how that compares with the Davis Echomaster at the lower spreader.

But the main thing is the Sea-Me's $750 cost (at today's exchange rate). I paid $35 for my Echomaster and have had it eight years.

 

[haulback]

Another place to mount radar reflector is to permanently lash it on to the backstay.

I put mine there and it looks to be sitting on a more-or-less 'catch rain' position, beats the regulation 13 feet above LWL and far out of the way of having any chafe issues with the main.

Jim/Haulback

 

[tiger beetle]

Ruh, roh . . . can a Mini discussion be far behind?

The Sea-Me has been floated out here before. It's less than a pound (plus mast-length power cable) but is supposed to be at the masthead. One of the math gurus (like Thom!) can tell us how that compares with the Davis Echomaster at the lower spreader.

But the main thing is the Sea-Me's $750 cost (at today's exchange rate). I paid $35 for my Echomaster and have had it eight years.

The key feature disqualifying the Sea-Me from the LongPac RRC is that Sea-Me is a powered unit, and of zero value if the boat has no electrics. While it appears to be a good unit on X-band, the RRC requires the yacht have a passive radar reflector.

- rob

 

[jfoster]

The key feature disqualifying the Sea-Me from the LongPac RRC is that Sea-Me is a powered unit, and of zero value if the boat has no electrics. While it appears to be a good unit on X-band, the RRC requires the yacht have a passive radar reflector.

- rob

If you are looking for an active radar reflector, anyway, ( you could have both types on board) the state of the art seems to be the Echomax Active X Band from dealers all over the world.

John Foster
Blueberry, Nonsuch 22 Sail #48

 

[Thom]

You make my point for me

The key feature disqualifying the Sea-Me from the LongPac RRC is that Sea-Me is a powered unit, and of zero value if the boat has no electrics. While it appears to be a good unit on X-band, the RRC requires the yacht have a passive radar reflector.

- rob

The RRC (again) is behind the times. You can't have it both ways, in my opinion. Either the insistence on 85 amphour batteries and associated masthead power users is outdated OR the insistence on passive radar reflectors is outdated.

Is the goal to make rules because you like making rules or is the goal to keep people safe? Is there thought about what is to be accomplished or is there just "rote acceptance" of tradition or someone else' rules? Based on what I've seen, it's the latter--but then I'm a multihull guy and you all know how untraditional we are.

 

[BobJ]

The most frequent problems skippers have had offshore are with electrical systems, therefore it makes sense that key safety items not be reliant on them. The second GPS is another example - it must not be dependent on the electrical system. Ditto the primary bilge pump.

I also know first-hand that rewriting the RR&C's is a time-consuming task and at times involves wearing a target on your chest.

It's not an "us vs. them" thing.

 

[tiger beetle]

The RRC (again) is behind the times. You can't have it both ways, in my opinion. Either the insistence on 85 amphour batteries and associated masthead power users is outdated OR the insistence on passive radar reflectors is outdated.

Hi Thom -

I'm confused by your post; are you perhaps dismissing reliability in pursuit of improved performance?

To make the point: the purpose of the batteries is to power navigation lights. The purpose of a radar reflector is to be seen.

If you want to increase failure points in radar reflectors then you can go with a powered radar transponder and introduce power requirements, cabling, electrical connections, printed circuit boards, and an amplifier. These elements, combined, are more useful for being detected by someone else's radar than a passive radar reflector - at the cost of complexity and increased points of failure. If any element in the chain fails then you become invisible. The statement within the rules, to date, has been that the benefit of improved radar detection does not outweigh the complexity of the system, at a minimum.

On batteries - an 85 AH battery provides a useful 30% capacity of power, or 25AH. Three navigation lights operating at deck level of 12 watts each will consume the 25AH in 8 hours; an 85AH battery is about the mininum one would want on a boat such that the navigation lights could be used at night.

An alternative to battery-powered lights are kerosene lanterns (as a kid my job was to fill and light the kerosene nav lights on my parent's sailboat - I am quite familiar with them). In contrast to the radar reflector, the rules have accepted that the benefit of electrically operated navigation lights outweighs the complexity of electrical lights - therefore electric lights are allowed and we require the minimum battery to support them.

It would be helpful to me if you would amplify what is meant by 'associated masthead power users'. What is an associated masthead power users? That has me stumped.

- rob

 

[Thom]

geez, do you read what you write?

Re: nav lights...again, LED lights use SO MUCH LESS POWER than incandescent that the 85 amphr stuff is OUTDATED.

Re: other masthead power users...VHF radio antenae, SSB radio Antenae, Stobe light (for gossake)...

When you write about kerosene running lights...honestly...are you trying for the title of "ancient mariner"?

Yeah, you have a target on your back every time you "impose" your rules on someone...I appreciate that. BUT, realize that you have accepted the mantle of "Knowing best" in the face of others' experiences and it would be "nice" to hear of an occasional acknowledgment that maybe you don't know it all (after all, I'm the only one who does )