SailNet Community

SailNet Community (
-   General Discussion (sailing related) (
-   -   Hypothetical Radar (

Jammer Six 10-21-2018 10:33 PM

Hypothetical Radar
Time to play hypothetical questions.

Let's say I have a boat. What boat isn't important. Let's say it has radar. Let's say there's a race called, say, Swiftsure. Let's say this race usually lasts a long day and two nights. Let's say it can go longer.

Now let's say I want to run radar for the entire race. The reasons I want to do so are my own, and aren't the question here.

First, is that doable? If it is, what will it take? Radar is an enormous drain on batteries, I'm aware of this. So okay, we shut off the reefer, we don't use hair dryers during Swiftsure and we observe some semblance of battery discipline during the race.

So begin. Is there a radar small enough, a battery large enough or a charging system capable of keeping up with a radar running all night?

capta 10-21-2018 11:00 PM

Re: Hypothetical Radar
A radar uses very little juice on 'standby'. Once it is powered up and adjusted to the range you want, you can just put it on standby and power it up when you need/want it. This can be on a schedule where if the screen was clear, another vessel or danger could be 1, 5, 15 or 20 miles away, or every so many minutes, or any variation thereof.
Most radars take less than a minute to go from standby to full operation, as there is no warm-up time necessary. You could actually have your cold beer and your radar, too!
That's how we run ours unless we are using it for real-time navigation. It is just too distracting to have running all the time. We prefer the chartplotter page full time.

Barquito 10-21-2018 11:58 PM

Re: Hypothetical Radar
Presumably you could put in as many batteries and solar panels on board as you need to keep the radar running non-stop... and run the vacuum cleaner while your margarita mixes in the blender.

Minnewaska 10-22-2018 08:37 AM

Re: Hypothetical Radar
Does this race not permit you to run your engine in neutral to charge batteries. While you can't charge well at idle, even at ~1500 rpm, it's pretty fuel efficient and the alternator would probably keep up with everything aboard and then some.

At night, I like to run the radar overlay on the chartplotter chart screen. Especially, when viz is down. I've crossed the Gulf of Maine when I could see nav lights departing Europe. This past summer, we had vessels cross within a mile that we never saw. When on the Maine coast, we had one at 1/10th mile that we could hear, like we were standing aboard, and never saw it. Had to be a lobster boat doing 15 kts, we were under sail. We tried to avoid, but it kept turning randomly. Our best best was to standon and hope they saw us too. I'm sure they did. When we got close, their course changed to pass port to port. But close...... my wife and I were both on watch and at the ready.

SeaStar58 10-22-2018 09:08 AM

Re: Hypothetical Radar
If its a race then the weight of the extra batteries could become an issue so I would be inclined to go with a larger alternator on the inboard if possible with more frequent runs for charging or a light weight Inverter Generator along with Solar Panels to keep up with the load on the existing batteries.

colemj 10-22-2018 09:37 AM

Re: Hypothetical Radar
Not enough information on battery capacity or charging ability.

Radar and its display uses 2-3A in full operating mode. Let's say 3A. This will use 72Ah/day, 108Ah for the 36hrs you note, or 216Ah over 3 days assumed maximum time. Pretty moderate power consumption, actually.

This is running full-time, which doesn't seem necessary, but you asked for that. It is also at full-rated spec, which I find conservative - actual use is generally less.

So with modest battery capacity or recharging ability, it is easily done.


knuterikt 10-22-2018 09:42 AM

Re: Hypothetical Radar
Measure your power consumption with all electronics active. Do the maths ?A*h=Ah.

You can increase battery capacity by replacing your lead batteries with LiFePo4 batteries, more usable capacity and less weight.
AGM 1.5 Ah/kg
LiFePo4 7 Ah/kg

outbound 10-22-2018 11:34 AM

Re: Hypothetical Radar
The Li thing has been beaten into the ground. Noteworthy is many if not most cruisers have not converted to Li. You may want to look at morgancloud for a discussion.
Currently have lifeline agms. 1025 ah. When they go will replace with firefly. Have several of my friends who have done so with good results and much less expense. No need to rework and buy new devices for my electrical system. No fear of over charging and fire or explosion. More than adequate weight to usable ah ratio.
At present on passage turn the radar off and on. Not to standby. Do sweeps every two to four hours depending on situation. If in shipping lane leave on standby but watch AIS and sweep if anything on AIS or every hour. If in fishing grounds (e.g. off PR) will leave on at night or low visibility.
Radar use depends on commonsense. If there’s risk of collision turn it on. If not then not.
Remain surprised how often you see something well before it shows up as a target (if at all) particularly at night.

colemj 10-22-2018 12:27 PM

Re: Hypothetical Radar
Since the OP was specifically asking about a race, I assume the radar would be used full-time for tactical reasons. Weight would also be an issue, but it wouldn't make sense to spend on LFP batteries for a single race. Otherwise, installing LFP batteries is probably the best decision we have made, and best piece of gear added, to our cruising boat and lifestyle. Simply a game-changer on so many levels. Lots of bad information and practices out there, and fire/explosion myth is at the top. Overcharging them will likely ruin them, as it will gel and agm lead batteries, but easily avoided with normal charging practices like used with gel and agm. However, undercharging them is of no consequence at all, while it will quickly make slag out of gel, agm, and flooded lead batteries. Undercharging is probably happening on 80% of all boats equipped with lead out there, while overcharging is so rare as to make news when it does happen.

Morganscloud should not be used as a definitive source of information for anything. So much of that is uninformed, misinformed, or outdated opinion. Much is good too, but one should definitely exercise caution and seek corroboration of their opinions. As for choices most cruising boats are making wrt batteries, there is unfortunately a wave of conversion to LFP going on right now. To the extent that there are long wait times for supply. I say unfortunately because there is a lot of fly-by-night and snake oil sales popping up now, and many consumers refuse to educate themselves. Frankly, I'd be happy if everyone else stuck with lead.


Minnewaska 10-22-2018 02:01 PM

Re: Hypothetical Radar
My next house battery upgrade will be LiFePO. This newer technology does not explode, like older Lio batts could. The newer technology is not affected by water, like original Lithium batts. In fact, you can explode any lead acid battery, via rare overcharge or short faults, so I don't see this as a difference.

LiFePO are lighter, contain more Ahr capacity (per equiv size lead acid) and you can run them down to 20% of capacity, as opposed to the 50% floor on lead acid.

They also charge in a fraction of the time, significantly reducing generator time. They are also much less effected by partial charging.

Effectively, you get 2 times the useful capacity in the same footprint. The only downside I see is that they currently cost 3 times as much to buy. I expect that will compress. Of course, you'll need charging sources that have settings for this battery type. Mine does.

All times are GMT -4. The time now is 08:42 PM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
(c) LLC 2000-2012

For the best viewing experience please update your browser to Google Chrome