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PostPosted: Dec 7th, '17, 21:47 
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On the VHF proficiency course I just did an interesting side topic came up - how long will a VHF transceiver run due to the main batteries being submerged in salt water in a flooding situation.

I know I have the main battery on the floor (at least not below floor level like often in the case with a keeler) so would not be too long before the terminals are flooded and the main VHF goes off line. I do think that if that much water got in then the following is of no value as the boat is going down at this point . . . but . .

I am thinking of a small motorcycle sized battery (maybe even lithium for light weight) mounted up high with the VHF - charged from the main charging circuit but with a schottky barrier diode (low volt drop) in series with the charging circuit so that when the main battery is shorted by salt water, this will have no effect on the smaller "VHF battery".

I asked the question what about a VHF handheld ( mouth engaged before brain in gear) and that got a laugh from the instructor. I would want the full 25 watt from the main transceiver in a mayday situation - unless I could leap at least 2 meters out of the water and hold that height when using the VHF portable.

ps if you have not done this course - I recommend it. Good value.

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PostPosted: Dec 7th, '17, 22:03 
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Jim, INMA's VF fixed radio is backed up by the handheld VHF radio and the handheld radio has a separate battery pack that uses AA batteries. All the handheld radio bits are water resistant.

In an emergency the fixed radio's extra range due to the extra wattage of the fixed radio might be handy.

But if I disconnect the aerial from the fixed radio and connect it to the handheld it gives me a slightly more effective 5 watts.

I generally sail where the 5 watt handheld works well and I can't recall using the fixed radio with 25 watts.

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PostPosted: Dec 7th, '17, 22:31 
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Salt water isn't going to "short out" a lead acid battery very quickly. I would imagine you would have as much as an hour before salt water got in through the small holes in the cell caps and diminished the charge. With an AGM battery many hours.
That's just based on what I believe current flow would be under those conditions - I could be wrong. It's more a problem in a broach or capsize situation where the antenna is pretty useless.

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PostPosted: Dec 8th, '17, 00:30 
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I don’t know what the effect of salt water has on batteries but I do know what happens when your sailing back from Hobart, your three batteries go flat ,your engine cannot be cranked manually and it is 1980.
Your stuffed. Even with vhf as well as hf.
There is no emergency so you do not set off your epirb.
If it was a mayday or even pan pan I would activate the epirb.
In our case we sailed to the heads ppb . and hailed the first passing boat for assistance.
We had jumper leads.

When I got back into sailing recently albiet not more than 2 miles from shore the first equipment I bought was a hand held vhf , a dozen spare batteries.
and water proof bag for my cell phone.
Hooking up the hand held to an aerial sounds a good idea.
BTW seems we had a serious short that took out the two general batteries as well as the isolated by switch engine battery.


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PostPosted: Dec 8th, '17, 05:18 
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Lithium backup may have limitations, yes they are compact for a large capacity and I run one (20ah) on my kayak for the fishfinder but it will only deliver 2amps, you may get away with it for short bursts of transmit but a motorcycle type lead acid would deliver the goods for a consistent longer period unless you spend a lot on a high output battery (LiIon or LiPo).
A 25w transmitter draws more than 25w for it's rated output.

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PostPosted: Dec 8th, '17, 07:12 
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Modern 25w radios draw around 5 to 6 Amps. RF power modules are to blame.

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PostPosted: Dec 8th, '17, 08:04 
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Johny wrote:
Salt water isn't going to "short out" a lead acid battery very quickly. I would imagine you would have as much as an hour before salt water got in through the small holes in the cell caps and diminished the charge. With an AGM battery many hours.
That's just based on what I believe current flow would be under those conditions - I could be wrong. It's more a problem in a broach or capsize situation where the antenna is pretty useless.


Yes "short out" not correct expression - I think discharge quickly might be better. If all the connections to the battery were water tight and no other 12 volt wiring in the boat was submerged then I would expect an AGM to last quite some time. What the current flow from the battery through salt water would be would be the point. Some research required here . .

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PostPosted: Dec 8th, '17, 08:25 
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INMA wrote:
Jim, INMA's VF fixed radio is backed up by the handheld VHF radio and the handheld radio has a separate battery pack that uses AA batteries. All the handheld radio bits are water resistant.

In an emergency the fixed radio's extra range due to the extra wattage of the fixed radio might be handy.

But if I disconnect the aerial from the fixed radio and connect it to the handheld it gives me a slightly more effective 5 watts.

I generally sail where the 5 watt handheld works well and I can't recall using the fixed radio with 25 watts.


Greg, One point made on the course was that if it is complicated then forget it as an option in a MAYDAY situation. I would rate swapping antenna connections - although a dang good idea - as complicated, maybe not for you, but for others that might be with you. Dealing with such others and the situation - well - you will have other things to worry about I suspect.

re 5 watt - yes another valid point - to all readers - do not run your fixed VHF transceiver at 25watt (I am guilty as charged your honour) . . . please set to 5 watt. The lowest power required is all that should be used and as Greg pointed out - many of us sail where 5 watt is more than adequate.

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PostPosted: Dec 8th, '17, 08:37 
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Seems it is simpler to have AGM house battery full stop. It will run underwater fine. Simple . . .

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PostPosted: Dec 8th, '17, 09:15 
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err! the trick of course is to not get yourself into that sinking feeling. Forever optimistic that I will not do that.

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PostPosted: Dec 8th, '17, 09:24 
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On submerging some sealed batteries some time ago, the issue wasn't the batteries, but that electrolysis destroyed the small cable connections to the batteries... only discovered when everything was dried out and accessible and being restored. the batteries lasted for some years after that event.
:-(

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PostPosted: Dec 8th, '17, 12:21 
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bachus wrote:
re 5 watt - yes another valid point - to all readers - do not run your fixed VHF transceiver at 25watt (I am guilty as charged your honour) . . . please set to 5 watt. The lowest power required is all that should be used and as Greg pointed out - many of us sail where 5 watt is more than adequate.


Yes the radio instructors are hot on this one, I think by letter of the law it may even be illegal to run on High power if it isnt required, paraphrasing the wording is "Transmit on the minimum power setting in order to relay your message clearly".

It was very annoying to keep hearing Safety Beach Yacht Club contact with their race control boat from the middle of Westernport, when we are doing race control for Hastings.

We are in the group of fixed radio in the cabin with batteries in the bilge (so we could maybe take 18 inches of water before losing battery power), but have a hand held right next to the cabin entrance, by line of sight reckoning we could maybe get 5Nm of range with the hand held while standing on the cabin roof

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PostPosted: Dec 8th, '17, 13:48 
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Jim, INMA has flotation built in that would mean she will swamp and float reasonably level. She would need to be broken into bits to sink. Even broken the bits would probably float.

The house radio is high and the AGM battery would probably still work. I would have time to change the aerial.

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PostPosted: Dec 8th, '17, 13:54 
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Mike most fixed on land stations have the aerials up masts.

This means a 5 W transmitter on the water will do a lot better than 5 miles in most protected waters. In the Whitsundays where the repeaters are on prominent points giving a range of 20 miles for most radios.

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PostPosted: Dec 8th, '17, 19:55 
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INMA wrote:
Mike most fixed on land stations have the aerials up masts.

This means a 5 W transmitter on the water will do a lot better than 5 miles in most protected waters. In the Whitsundays where the repeaters are on prominent points giving a range of 20 miles for most radios.


I try and work on the worst case scenario, I know I can get 5Nm on my hand held any more is a bonus

On my fixed unit on the hard at hastings I couldnt get the Arthurs Seat repeater, but from the middle of Westernport I can get the repeater on my hand held (I have spoken to Melbourne Radio on it) , I guess all the clutter gets in the way on the hard

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PostPosted: Dec 8th, '17, 21:58 
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Hastings to Arthurs seat would not have line of sight so communication would not work, no surprises there but Hastings to Westernport would be pretty reliable.

In an emergency, transmitting to any reliable receiver is all you need.

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PostPosted: Dec 9th, '17, 08:17 
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Added as a curiosity, I was hearing voices in my driveway every so often but there would be no none there when I looked. Eventually I found that the VHF was still turned on and I was recieving the weather reports from Coast Radio Melbourne with no antenna attached. I'm in Mckinnon and not particularly close to the water, but where's the line of sight.


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PostPosted: Dec 9th, '17, 08:30 
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MOB, you might be receiving from a repeater station somewhere.

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PostPosted: Dec 9th, '17, 17:21 
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The person running the VHF operator course I attended is involved with the Hasting yacht club, he says there is a "VHF funnel" from Brighton across the peninsula to Hastings and that the Brighton yacht squadron (keelers) inane jabber can be clearly heard in Hastings and is apparently very very annoying and especially to him the bad radio procedures in play.

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PostPosted: Dec 9th, '17, 18:59 
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bachus wrote:
The person running the VHF operator course I attended is involved with the Hasting yacht club, he says there is a "VHF funnel" from Brighton across the peninsula to Hastings and that the Brighton yacht squadron (keelers) inane jabber can be clearly heard in Hastings and is apparently very very annoying and especially to him the bad radio procedures in play.


So you met Dono (Peter Donaldson), he is a top bloke, very knowledgeable and really funny

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PostPosted: Dec 9th, '17, 19:11 
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Yup, yes to listen to him the course is worth it alone.

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PostPosted: Dec 12th, '17, 11:46 
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bachus wrote:
Johny wrote:
Salt water isn't going to "short out" a lead acid battery very quickly....

Yes "short out" not correct expression - I think discharge quickly might be better. ....

Point taken Jim. I was trying to keep the concept simple. I agree with later posters that other devices connected to the DC system and electrolysis will probably be the bigger issue.

John

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PostPosted: Dec 12th, '17, 12:25 
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I just realised, the VHF will cease as the aerial goes under.

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PostPosted: Dec 12th, '17, 12:32 
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:lol:

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PostPosted: Dec 12th, '17, 17:46 
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INMA wrote:
I just realised, the VHF will cease as the aerial goes under.


Given how much of both Port Phillip and the Gippsland lakes seems to be 6m deep, and that Jim's mast is 8.6m long, this may not be a problem.

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