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Author Topic:   VHF Antenna for 170 Montauk
bigjohn1 posted 03-27-2004 10:13 AM ET (US)   Profile for bigjohn1   Send Email to bigjohn1  
Trying to decide on an antenna and a suitable mounting place for my new 170. I have searched around here and only see some older reference from last year made to the 4' antena mounted to the grab rail on the console. Has anyone mounted anything longer than 4'? Any other areas of the boat that would be suitable for an 8 footer?

To some old Whaler salts, this may beg the question,
"Why -- since a 4' antenna mounted on the console rail will be close to the same height as an 8' mounted to some lower point in the boat?" Given that VHF is line of sight and arguably limited to about 20 miles under optimum conditions, I just don't want to "short" myself if a longer antenna can be safely and securely mounted which might give me a few more miles of coverage.

Assuming clear conditions and no obstructions, could I get 20 miles from a quality 4' Shakespear mounted to that grab rail on the 170? On a really nice day, I WILL take this boat out to around 30 miles or so off-shore...and oh yeah, I'll make sure I have enough fuel:-)

Big John

jimh posted 03-27-2004 10:26 AM ET (US)     Profile for jimh  Send Email to jimh     
You will find a rather lively and fact-filled discussion of the range of VHF Marine radios in:

Range of VHF Radios
http://continuouswave.com/ubb/Forum4/HTML/000577.html

One ought to mount the antenna:

--where it is not likely to be used as a hand hold. The fiberglass marine antenna has a nasty habit of decaying and getting "frizzy" (a technical term). The little fiberglass particles really cause itching.

--where it is not likely to poke someone in the eye. This is especially important if you use a metal whip antenna.

--where the base of the antenna (from where most of the radiation emits) is high and in the clear. An antenna whose base is obscured will not transmit as effectively as a smaller antenna whose base is mounted in the clear. I would much rather have an 18-inch tall antenna mounted high and in the clear than an 8-foot antenna whose base is mounted low in the cockpit.

Consideration should also be given to lowering the antenna when it is not needed, as while fishing or hauling the boat on a trailer.

WT posted 03-27-2004 03:39 PM ET (US)     Profile for WT  Send Email to WT     
John:

I hope the pics help.

WT

bigjohn1 posted 03-28-2004 05:08 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
WT - what pics, am I mentally challenged or are they not there?

Jimh,
Thanks for leading me the great info previously discussed. I see where you are keen on a 4-5' antennas. I also see where the base of the antenna must be higher than any metal structure on the boat. I ordered my boat with the bimini top so presumably I need to mount the antenna with an extension which will move the base of the antenna above the bimini....I am onboard with this but can't get rid of the thought that the natural geometrical leverage of the antenna/extension would be too much for that rail. It would seem that the antenna naturally wanting bend back while the boat was under power would tend to place alot of strain on the grab rail. Am I all worried about nothing here? Is that console grab rail strong enough with all that leverage working against it?

As I stated, I will venture off-shore ocasionally out to about 30 miles in and around the islands of Guam, Saipan, and Rota out in the Pacific. There aren't many line-of-site obstructions between land and sea in this region but I want to make sure I do this right and choose the right stuff.....I'd rather spend more $$ now and know that I made the right choices.

Thanks again for the input,

John

Moe posted 03-28-2004 11:18 AM ET (US)     Profile for Moe  Send Email to Moe     
Let me strongly agree with Jim about getting the base of the antenna up above obstructing objects.

George Hefty uses an excellent Digital-brand 4' model 528, mounted as shown in his pictures below.

http://www.caico.com/170/

Digital brand antennas are here (I use the same antenna):

http://www.digitalantenna.com/vhf500.html

His antenna folds forward to allow the bimini to be collapsed fully forward, but appears to be just in front of it when the bimini is up on its struts. But yes, his antenna radiation pattern is compromised when the bimini is up. The solution for him, if critical long range communication is impaired by the bimini, is to fold the bimini down. This is probably as good as you're going to get, practically.

Being a one-time radio-geek, I would probably mount a 4' extension on a ratchet mount on the windsheild railing, and come up with a block on the extension that rested on the front of the bimini, with bungi cords running under the bimini from that block to its frame on either side for lateral support, LOL!

Now all this being said, 30 miles from a receiving VHF station is what I would consider marginal on signal strength, and depends on a pretty tall receiving tower for line of sight. Here's a little LOS calculator. Use the height of the antenna midpoint for it.

http://www.vwlowen.demon.co.uk/java/horizon.htm

In waves, your radiation pattern, which is perpendicular to the antenna, is going to be shooting above that antenna, and diving into the sea well short of it as the boat rocks. The higher the gain of the antenna, the flatter the radiation pattern and the worse that is. It could result in your transmission being broken up.

The bottomline is that at this distance from a receiving tower, I personally would have a Emergency Position Indicating Radio Beacon (EPIRB) to send a distress signal to a satellite. But that's another discussion I won't get into unless you want to.

--
Moe

Divedog posted 03-28-2004 12:30 PM ET (US)     Profile for Divedog  Send Email to Divedog     
Great pictures on the caico site. What does George do when he puts the top up?
I'm curious if anyone has come up with a good compromise which would include mounting a 4' antenna as high as possibly while still being able to use a bimini top.
I ordered my boat w/o at top but it would be nice to install antennas in a location that would work if I ever added a top.
WT posted 03-28-2004 05:10 PM ET (US)     Profile for WT  Send Email to WT     
Big John:

I emailed pics to you. I have an 8 foot Shakepear antenna on my 170.

WT

Uncle Pug posted 03-29-2004 01:18 AM ET (US)     Profile for Uncle Pug    
I mounted an 8' antenna high on the grab rail using a ratching base that clamped directly to the rail. I drilled holes to run the antenna wire through the grab rail (using grommets at the holes to protect the wire.)

No Bimini to contend with.

Pictures here:
http://www.scubaboard.com/attachment.php?attachmentid=5987
and here:
http://www.scubaboard.com/showpost.php?p=545871&postcount=19

Moe posted 03-29-2004 09:02 AM ET (US)     Profile for Moe  Send Email to Moe     
For future reference, no one can view pictures posted to the scuba board unless they sign up and become a member.

Nice setup on the antenna, but have you swung the compass and checked the deviation since putting the radio speaker that close to it?

--
Moe

Knot at Work posted 03-29-2004 09:30 AM ET (US)     Profile for Knot at Work  Send Email to Knot at Work     
I have a 4ft Shakespeare Stainless love it no probs with Bimini up either
Uncle Pug posted 03-29-2004 10:57 AM ET (US)     Profile for Uncle Pug    
No I haven't swung the compass... but I do know that the GPS and depthsound affect it as well. With a working GPS the compass isn't an issue but if it goes down then I would switch off the electronics and us the compass... but I can't switch off the magnet in the VHF speaker so your point is well taken... I will need to swing the compass.

As for SB... I forgot about folks needing to sign on to view pictures... but at present that is the only site I have them posted at.

ghefty posted 03-29-2004 04:20 PM ET (US)     Profile for ghefty  Send Email to ghefty     
Divedog, the interference of the top with the antenna is a function of where I set the top. If the top is slid all the way back (covering the aft deck) the antenna can stand vertical without hitting the bimini. If the top is slid to the middle of the boat (best coverage for the console area) the antenna is leaning forward at a 45 degree angle, not good for vhf transmission, I haven't noticed a degradation of the reception in this position, but I have not attempted to test the reception with the tilted antenna.
If it were an emergency situation, I would stow the bimini in favor of the vhf. To be honest I mostly I do not use the bimini, I use sunscreen and a hat and leave the bimini stowed. It gets in the way when fishing. If I had to do it again, I would have saved the money I spent on the top, but I mostly fish and occasionally dive. Come to think of it, when I dive I want the sunshine during my surface intervals. So fat the top goes up only if it's raining.
Divedog posted 03-29-2004 04:39 PM ET (US)     Profile for Divedog  Send Email to Divedog     
ghefty-
Thanks for the feedback. I'm pretty much in line with your thinking. I'd rather not have the top on a sunny day and it would get in the way while fishing & diving. I probably shouldn't worry about it since I haven't even purchased a bimini. Although I may change my mind if I'm out fishing on a rainy Seattle weekend..........
divefan posted 03-29-2004 04:42 PM ET (US)     Profile for divefan  Send Email to divefan     
Uncle Pug:

Just installed the vhf. Checked for any movement on the compass as it was being installed. For what it's worth I did not notice any change on the compass heading whatsoever.

Btw, I like your vhf antenna install very much. Very cool work.

ghefty:

Thanks for confirming my choice of NOT getting a bimini. For full time diving I thought it would just be more trouble than it's worth.

Divedog posted 03-29-2004 04:55 PM ET (US)     Profile for Divedog  Send Email to Divedog     
Knot-
From your pictures it looks like your antenna is mounted just above the profile change in the console. This is where I was planning on installing my antennas. So, with the location you used, will the top clear the antenna?
Knot at Work posted 03-29-2004 07:01 PM ET (US)     Profile for Knot at Work  Send Email to Knot at Work     
Dive Dog,

Yessir with about three inches to Spare. It also folds down really easy from that location so I dont stress and clamps or co-axials.

bigjohn1 posted 03-30-2004 06:12 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
WT: Thank you for the pics...the installation looks very clean and I also love the general layout of your boat overall.

MOE: Your point on EPIRB is well taken. Being in this part of the world with lots of water and only small islands, I had already planned on that being the VERY FIRST item I buy for the boat. All the other electronics will be "second fiddle" to the EPIRB. I am also of the opinion that one must be competent in compass navigation prior to relying on a GPS. Still, the GPS will come.

I am going to ask the Coast Guard Station Marianas in Guam how high their tower is. It must be fairly high as guys with quality radios and properly selected and installed antennas are getting back to shore from 30 miles (+/-) with no problems. This is about as far off as I'll take her.

I opted for the bimini top due to the wife and kids. If it were up to me, I'd shelf the idea but at only 13 degrees latitude, the sun rays in this part of the world will roast you in short order - much worse than Florida or even Hawaii.
My previous boats were all open-deck RIBS without tops and it just got old hearing all their complaints. For me, I'm happy with a good hat and sunscreen:-)

Based on all the feedback, it looks like I should go with a 4 footer mounted to the console rail BUT it will need to be on an extension that will place its base above the bimini. Heck, if I were 30 miles off shore in need of the Coast Guard, I'd also stow the top down just to make sure it didn't interfere.

John

Rich M posted 03-30-2004 12:57 PM ET (US)     Profile for Rich M  Send Email to Rich M     
John,

I have a 4' base loaded Shakespear mounted with a ratchet base near the top of the starboard side of the console on my 170. I keep the boat in a covered lift so I needed to be able to lower the antenna. Even at this slightly lower location (than a grab rail mount) RX/TX is excellent. Depending on conditions 20 miles is easily done on a regular basis.

Rich M
03M170

Chuck Tribolet posted 03-30-2004 08:51 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Bigjohn: check this out this ghart of Guam USCG VHF coverage: http://www.navcen.uscg.gov/marcomms/cgcomms/charts/14guam.jpg

Note that coverage to the east and southeast sucks. There's
probably a mountain in the way.


Chuck

bigjohn1 posted 03-31-2004 04:35 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Chuck,

Thanks a million.....this is great info and a little reassurance that you are well-covered there at sea. I guess that's why people are getting back to shore no problem from 30 miles. Yes, Mount Lam-Lam (about 4,000ft I think) just about splits the island in half and is a big block. Not to worry though as all the good off-shore spots are to the East/Southeast of the island. Due to the predominant, Northeast trades 9 months out of the year, the eastern portion is not too safe to navigate in a 170 except June-August when the winds shift out of the West. Thanks again!
John

jimh posted 03-31-2004 05:51 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is the index page to more of those coverage charts:

VHF Distress Coverage Charts
http://www.navcen.uscg.gov/marcomms/cgcomms/nds.htm

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