Scuba GPS

[MuddyFox]

I have searched these forums for a week now, gathering information. However I still am unsure about the unit for my specific need.

 

I am looking for a GPS unit with the highest accuracy (haha aren't we all) for wreck diving. I will not be under any tree cover, and have a view of the horizon in all directions. Some of the wrecks we dive are small fighters, one standing on its nose surounded by nothing but sand. So, the GPS has to be accurate for us to hit the wreck with the anchors.

 

Because of my location, Mircronesia, a map-based unit would be useless as I haven't seen any map softwares for this area.

 

As far as WAAS is concerned, I do believe the Pacific WAAS satelite covers this area, however I am over 5000 miles from the US meaning the closest WAAS ground station is extremely far. Am I correct in assuming that at this distance WAAS is virtually useless for me?

 

If so, then it seems the remaining variables are antenna choice and averaging.

 

I've been reading that the averaging features can be annoying, so is it safe to assume that I wouldn't want that feature for pinpointing a wreck? Keep in mind I will be on a boat, which will be difficult to keep still.

 

Finally the antenna. I know that quad helix antennas are favored for picking up signals under foliage, but are they more accurate than the patches under open sky conditions?

 

The electronic compass models... are they accurate? Do they point you in the direction of the target waypoint without being in motion or are the similar to other units where you have to be in motion?

 

Finally, what 3rd party softwares out there are able to upload and download waypoint to specific GPS units?

 

I'm pretty much down to the base ETrex model (patch antenna and CHEAP) or the GPS76. (WAAS, QUAD HELIX) Does the base ETrex remember waypoints that you mark? Someday when I get back to the States I'll buy a more serious unit for GeoCaching.

 

Sorry about the length, thanks for you help.

[Atilla the Pun]

... but have you looked at the Digital Navigation Assistant? Like the 76s it will have an external antenna connection. Also, you can add your own maps via SD card or just not bother with maps. The review that (I believe) markusby wrote spoke very highly of the unit.

 

AtP

[+Aussiegoldminer]

YOu are correct, where there is no basemap, getting a more expensive unit is a waste of money. This basic unit will do all you want, without the electronic compass. No, you don't have to be moving for it to work! It will remember waypoints. You can home in on co-ordinates without problem and it will get you to within 10m.

 

Download EasyGPS from this site for waypoint management.

[Kerry.]

Yes, WAAS totally useless.

 

Averaging certainly has problems and by the sound of it if you are on a boat then I definately can't see the point in averaging (but then I can't see all that much general application for averaging at the best of times )

 

Heaps of 3rd party software but for the best results can depend on the specific GPS unit.

 

If you're looking for position integrity (including accuracy) then there are augmentation systems available but they are subscription services (satellite based) and they do require specific hardware and they do cost. Just depends on how serious your accuracy and integrity concerns really are.

 

Also going up a level or two away from the simple recreational receivers will/can gain a "little" more integrity in most instances but of course the $$'s go up as well. Again it all depends on how serious the accuracy requirements are

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

Yes, WAAS totally useless.

 

Averaging certainly has problems and by the sound of it if you are on a boat then I definately can't see the point in averaging (but then I can't see all that much general application for averaging at the best of times )

 

Heaps of 3rd party software but for the best results can depend on the specific GPS unit.

 

If you're looking for position integrity (including accuracy) then there are augmentation systems available but they are subscription services (satellite based) and they do require specific hardware and they do cost. Just depends on how serious your accuracy and integrity concerns really are.

 

Also going up a level or two away from the simple recreational receivers will/can gain a "little" more integrity in most instances but of course the $$'s go up as well. Again it all depends on how serious the accuracy requirements are

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Alan2]

Any GPS will get you to within 20 feet without WASS since you're in the open. Also, remember, people hunting will be using the regular recreational GPS's they we use so you determining the coordinates with something more accurate with special antennas will have no real value.

 

Also, the water you dive has great visibility - certainly lots more than 20 feet.

 

Frankly your biggest problem will be luring divers with GPS's to hunt your cache. Of course I'm ready - if someone will pick up the air fare.

 

Alan

[+Alan2]

Any GPS will get you to within 20 feet without WASS since you're in the open. Also, remember, people hunting will be using the regular recreational GPS's they we use so you determining the coordinates with something more accurate with special antennas will have no real value.

 

Also, the water you dive has great visibility - certainly lots more than 20 feet.

 

Frankly your biggest problem will be luring divers with GPS's to hunt your cache. Of course I'm ready - if someone will pick up the air fare.

 

Alan

[Alphawolf]

Yes, stay simple and stay cheap. The basic Etrex will serve you fine on the ocean. Bear in mind, no consumer grade unit will put you on a wreck with enough accuracy that you can count on dropping the anchor onto the wreck. You will have to narrow it down with some other means, such as compass bearings to land objects or visual sightings of the wreck. But hey...in those waters, if you are within 30 ft., you can hardly miss it, right?

 

[The Shadows Know]

quote:

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Finally the antenna. I know that quad helix antennas are favored for picking up signals under foliage, but are they more accurate than the patches under open sky conditions?

---

 

I believe the quad helix antennas are more accurate in all conditions, however make sure any quad helix unit you look for has the capability to shut down the WAAS feature. "All Magellans we have reviewed can receive corrections from the AOR-East geosynchronous European EGNOS satellite. The units are permanently in the WAAS mode which can't (easily) be switched off. This will be a problem for users far outside the WAAS and EGNOS correction areas. For example, users in Australia have reported significant position errors introduced by receiving the POR satellite's WAAS corrections." from http://www.gpsinformation.net/mgoldreview/sportrak-pro-rev.html

 

Good luck in finding the right GPS

[MuddyFox]

Does anyone know if the Garmin GPS76 has the option to turn WAAS off?

[+Mopar]

quote:

---

Originally posted by MuddyFox:

Does anyone know if the Garmin GPS76 has the option to turn WAAS off?

---

 

Yes, its easily turned off.

Another plus of the 76 for boating/scuba is its watertight and floats. Yes, I know the Meridians have the same IPX (water resistance) rating, but they just dont seem to seal as well. I really have to wonder if the Meridian's rating includes the battery/SD card compartment. It doesnt seem to be watertight on the units I've seen, and I haven't been able to convince the owners to test it, lol. Plus the 76 has lots of boating related features that are nice out on the water, but useless for geocaching.

 

Illegitimus non carborundum!

[jbwcpa]

I would buy the 76. If you could install a Blue Chart, you would have one heck of a GPSR. Only problem is, I don't think they make a Blue Chart that includes the Marshalls. I know they have one for New Guinea and most of Indonesia. I think they also cover the Solomons.

 

And do turn off the WAAS. Since there are only two WAAS stations in operation and both in North America, WAAS is going to be worse than useless in the Pacific. It also uses a lot more energy.

[jbwcpa]

I would buy the 76. If you could install a Blue Chart, you would have one heck of a GPSR. Only problem is, I don't think they make a Blue Chart that includes the Marshalls. I know they have one for New Guinea and most of Indonesia. I think they also cover the Solomons.

 

And do turn off the WAAS. Since there are only two WAAS stations in operation and both in North America, WAAS is going to be worse than useless in the Pacific. It also uses a lot more energy.

[peter]

Another plus for the 76 (or Map76) is that it accepts an external antenna. This would be nice if you want to get fancy and use the GPS unit while scuba diving. You could tow an external antenna unit that floats up on the surface and has a cable leading down to a waterproof enclosure for the GPS. I'd think this would be useful for underwater searches by letting you see relative positions of yourself, your waypoints, and your tracklog - for example if you wanted to search by spiraling outward from a marked waypoint.

[MuddyFox]

I heard over dinner that the "Oceania" software had the Marshall Islands on it, although I don't remember reading about it. Oceania is a Garmin product, correct?

 

Where's the best place to buy my 76?

[MuddyFox]

I heard over dinner that the "Oceania" software had the Marshall Islands on it, although I don't remember reading about it. Oceania is a Garmin product, correct?

 

Where's the best place to buy my 76?

[CountryLover]

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You could tow an external antenna unit that floats up on the surface and has a cable leading down to a waterproof enclosure for the GPS ...........

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A thought just occurred . .

 

Would the position that is reported by the GPS the actual position of the GPS or the position of the external antenna ?

 

Anyone knows the answer ? I seem to think whenever you use an external antenna, its the position of the antenna that is reported . . . is this correct ?

[Kerry.]

WIthout any type of offsetting system the position is always technically the L1 (electrical) centre of the actual antenna.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

WIthout any type of offsetting system the position is always technically the L1 (electrical) centre of the actual antenna.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+GeoManhattan]

Since you're on the ocean you shouldn't have any issues with getting solid readings.

 

I'm also a diver and have used a GPS to find wrecks at 90ft in lakes with 10-15 foot vis. Any modern GPS will easily get you within 50 ft of the wreck.

 

There isn't much benefit to the electronic compasses. I trust my wrist mounted dive compass instead. Plus I can dive with it and no batteries required.

 

GeoManhattan.com

[captnace]

Go with the cheapest one ! With virtual horizon to Horizon open expanse you will not have a problem getting within a few (~3 or 4) Meters from your mark every time. Yes turn off Waas. The antenna is the determining factor to your position, so if you are underwater trailling an antenna on the surface, the antennas location is what your unit will display, so take in to account the fact that you are not directly under it. The only options for getting increased accuracy is to buy an expensive surveying system, or by getting a unit that uses both the US and Russian GPS systems, but for what you need, any good GPS Receiver will serve you well on the open seas, as well as on land. I have been using a GPS for Diving, and Search and RescueFor a few years now, and the only problems i have encountered are dense foliage fades, or Mountain Valley fades.

Captnace