VHF Power Supply - switchboard or independent?


Ah, you've got it I see! I initially missed the bit about the secondary isolator, that is EXACTLY the point I was making!

Yes, you'll find it's all there in my posts, including the one you picked up on. Earlier posts include this "spurred" supply option and one or two other variations on the general theme. It's easy to miss detail when skimming through the posts and, as if often the case even with elementary techy stuff, the devil's in the detail.

Battery > main Isolator live side > secondary isolator > secondary panel.
 
What evidence is there that all this faffing about solves a real problem? Is there an issue with distribution panels in yachts catching fire and, if so, how is it solved by adding another one? That's just twice as many to go up in flames and, frankly, I'd have thought that an electrical fire would be something to avoid even if the VHF still worked.

It all sounds like a rather complicated to a solution to a problem which if it ever existed has been long since displaced by the existence of satphones, EPIRBS and handheld VHFs.

For what it's worth, my VHF and GPS are wired, via a fuse, to the live side of the normal distribution panel, not because I am paranoid about fires or worry too much about the radio room regulations for ferries but simply so that in the event of an emergency my crew and I know that as long as the batteries are turned on, the radio has power.
 
Hardtack said:

Ah, you've got it I see! I initially missed the bit about the secondary isolator, that is EXACTLY the point I was making!

Yes, you'll find it's all there in my posts, including the one you picked up on. Earlier posts include this "spurred" supply option and one or two other variations on the general theme. It's easy to miss detail when skimming through the posts and, as if often the case even with elementary techy stuff, the devil's in the detail.

Battery > main Isolator live side > secondary isolator > secondary panel.
Click to expand...

Well, I could take issue with the claim it was there in all your posts but since we're actually saying the same thing it's silly to argue about it! :)

I'm still of the opinion that if it's considered worth going to all the bother of putting in an emergency supply for the VHF (and other vital equipment perhaps) you might as well go the whole hog and have a dedicated emergency battery as both you and I, and others, have suggested is best practice

Mind you, I'm somewhat of the opinion that for most cruising yachts the whole thing is a waste of time and the emergency VHF function is best served by having a decent hand held VHF anyway!
 

"Mind you, I'm somewhat of the opinion that for most cruising yachts the whole thing is a waste of time and the emergency VHF function is best served by having a decent hand held VHF anyway!"

A hand held is certainly better than nothing.

But if you're on a sailing boat with a VHF antenna at the masthead, the range of your handheld won't be anything like the range of your fixed VHF with its masthead antenna.

It's generally accepted that a VHF signal travels in a straight line, which means it's range is normally limited to the horizon defined by the antenna's height above sea level. In fact (and to be pedantic about it) this isn't quite so because atmospheric refraction allows the signal to travel a bit further. The point is though, under a given set of conditions, a masthead antenna will chuck the signal a lot further than a handheld.

So if you're reduced to using a hand held because the main set is off-line, it's not a bad idea to have an arrangement that allows you to interface the handheld's antenna connector with that of the masthead antenna. Of course, organising an interface lead and plugging it in may well be far too much of a rigmarole for some.

Different matter on many motor boats, where the main antenna will probably be no higher than you can reach (or scramble) with a hand held.
 
What evidence is there that all this faffing about solves a real problem?

It doesn't solve a problem. It might, however, enable one to avoid having to deal with a problem in the future.

"It all sounds like a rather complicated to a solution to a problem which if it ever existed has been long since displaced by the existence of satphones, EPIRBS and handheld VHFs"

But it's a very simple modification - inexpensive and easily implemented. And if we're not interested in making a vessel safer - and reliable communication is a safety issue - then why not expand that philosophy and not bother carrying lifejackets, liferafts, EPIRBS and so forth? You and your crew will hopefully never need those items - but they're there in case you do.

One more point - which might be regarded as trivial but it's relevant to quite a few people. Not everybody can afford a handheld, a satphone, an EPIRB and various other expensive, all-singing-all-dancing equipment. For those people, a reliable VHF set could be a life-saver, and for those people, the more bullet proof they can make the radio installation, the better.

Just my opinion...:)
 
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Bru said:
Well, I could take issue with the claim it was there in all your posts but since we're actually saying the same thing it's silly to argue about it! :)
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Yes, regarding the correct way to install such a circuit we're clearly in agreement and reading off the same hymn sheet.

On a point of detail, I didn't actually say the information was in all my posts. I said it was all there in my posts, which is quite different. Early in the thread we were discussing the concept in fairly broad, non-technical terms, and the more detailed information regarding circuit protection etc. started to appear later on.

I absolutely agree with the earlier comment that the isolator for a parallel back up supply should ideally be close to the battery, and I did in fact make that point in an earlier post. I additionally recommended that there should be circuit protection in the same location - thus protecting the entire back up supply cable downstream of the dedicated isolator.

Expanding on that point briefly, a lot of folks think a supply circuit's fuse / circuit breaker is there to protect the appliance from damage, which of course it ain't - and it often won't! Circuit protection in this context is intended to safeguard a power supply cable from overload. So I guess we'll be discussing cable types, cross-sectional areas, voltage drop and who knows what next. :ambivalence:
 
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Bru said:
If you insist, it's all in a days work for me! :D
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Hi again,

But not for me. Not for the next week or so anyway. Off to the east coast in the morning to do some sailing and a bit of work on the boat (new cockpit drains). I hope my on-board heating's on the button, otherwise I'll just have to warm my hands over all my fully operational, beautifully wired, and oh so reliable VHFs :D

I've enjoyed our brief dialogue because (along with a small handful of others here) it's refreshing to discuss ideas with somebody who knows exactly what they're talking about. With one or two others, trying to get an idea across and make the underlying philosophy understood is about as productive and enjoyable as standing on top of a cliff and pi**ing into an onshore gale.

Perhaps in my absence you'd be so kind - and so rash - as to field further posts that require accurate and reliable technical explanations!

And if you do - good luck with it!

Adios...
 
If by any chance you find your way to North Fambridge, look me up aboard Pagan (you can't miss us as you walk up the pontoon from the river!!
 
JumbleDuck said:
For what it's worth, my VHF and GPS are wired, via a fuse, to the live side of the normal distribution panel, not because I am paranoid about fires or worry too much about the radio room regulations for ferries but simply so that in the event of an emergency my crew and I know that as long as the batteries are turned on, the radio has power.
Click to expand...

+1
 
Hardtack said:
Different matter on many motor boats, where the main antenna will probably be no higher than you can reach (or scramble) with a hand held.
Click to expand...

Depends whether the boat has a roof or not. Smaller open boats have arches for mounting hardware. It also depends on the weather, no way I'm climbing on the roof with a handheld in rough conditions unless I'm sinking.
 
The height of antenna i probably less significant than the fact the fixed VHF is 25w and the handheld is only 5 or 6w.

My backup pushpit mounted antenna has a lot more range than the handheld.
 
Quick recap, my blackbox VHF is under a saloon sofa, with the batteries, supplied via the isolator > switch panel > fuse board in the battery compartment. The N2K network, which does depth and Gps (among other things) is well out of the way and wired the same. GPS antennas are also well away from most things. GPS receiver is above one of the aft cabin ceilings.

The switch panel is in the side of the companionway, which could mean an engine fire takes the lot out. But i could also suffer a simple switch/wiring/breaker failure.

Right next to the batteries is a fuse panel that has some fuses fired straight to the batteries, for the volt meters and solar charging etc. Some recent changes have left me with a spare fuse in this panel, wired directly to the engine battery. I'm also left with a double pole toggle switch and two carrier bags full of left over cable (don't ask).

So, a wire from this fuse to the toggle switch and then two wires to the GPS and N2K fuses on the other panel (equipment side of the fuses) would enable me to power the VHF and N2K network if i had to isolate the normal circuits for any reason, even taking the supply from a different battery. It's a no cost five minute job, so i'll be doing it at the weekend.

I do like some backup systems. so this has proved a useful thread :)
 
Stats007 said:
No, height is more important as VHF is pretty much LoS.
Click to expand...

No it isn't. LoS is no good if the transmitter won't reach the horizon.

I speak from experience. I have masthead and pushpit mounted antennas and a 6w handheld. There is no way the handheld has anything like the range of the 25w fixed set using the pushpit antenna.
 
JumbleDuck said:
.....
For what it's worth, my VHF and GPS are wired, via a fuse, to the live side of the normal distribution panel, not because I am paranoid about fires or worry too much about the radio room regulations for ferries but simply so that in the event of an emergency my crew and I know that as long as the batteries are turned on, the radio has power.
Click to expand...
Only if the main battery bank isn't flat!
 
PaulRainbow said:
No it isn't. LoS is no good if the transmitter won't reach the horizon.

I speak from experience. I have masthead and pushpit mounted antennas and a 6w handheld. There is no way the handheld has anything like the range of the 25w fixed set using the pushpit antenna.
Click to expand...

Sorry but you're wrong, it's basic mathematics that dictates transmission distance. A handheld is more than capable of transmitting beyond the horizon if at the right height.
 
Stats007 said:
Sorry but you're wrong, it's basic mathematics that dictates transmission distance. A handheld is more than capable of transmitting beyond the horizon if at the right height.
Click to expand...

No i'm not. I have the handheld, i have the different antennas, i can see what they are doing in the real World.

Besides, you don't seem able to work it out with your own methods. "A handheld is more than capable of transmitting beyond the horizon if at the right height". So if you have the handheld high enough to give it a 50 mile radio horizon you really think a 5/6w transmitter will broadcast that far ?
 
Sorry Paul but you are wrong - there is a crossover where height and power dictate transmission range. Maybe this will help you:

http://www.offshoreblue.com/communications/vhf-capabilities.php

In summary:

Antenna Height

When considering marine VHF radio communications, more important than all other factors is the height of your antenna. The higher you can place your VHF antenna the further you will be able to communicate.
 
DrSpock said:
Sorry Paul but you are wrong - there is a crossover where height and power dictate transmission range. Maybe this will help you:

http://www.offshoreblue.com/communications/vhf-capabilities.php

In summary:

Antenna Height

When considering marine VHF radio communications, more important than all other factors is the height of your antenna. The higher you can place your VHF antenna the further you will be able to communicate.
Click to expand...

Only to a point. Once you exceed the transmission range of the handset you can raise the antenna height as high as you like, it won't go any further.
 
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