Wing Mark
Well-known member
If one wants one's bacon saving in the event of a GPS failure, the cheap, low power option is probably a spare GPS?
Height of radar above waterline ?
- Thread starter sarabande
- Start date
sarabande
Well-known member
Unless, of course, as we have all experienced from time to time, that GPS is locally unavailable for military reasons. There is no cheap low-power option for broadcast GPS shutdown or blanking.
pandos
Well-known member
No matter how many GPS devices you have, if the system is not functional/ jammed or contradictory you need some other thing....
On that ocassion we had two different but credible positions from a fixed and a handheld gps...(never really resolved the cause)
I now have many separate gps position sources (Ais, Garmin plotter at nav station, android touch screen with Navionics, small plotter in cockpit, phone with Navionics, probably also a tablet with open cpn, )
jwfrary
Well-known member
I would tend to agree, 1/4 to 4 maybe 6 miles is about the realistic limit for most of the current yacht radars, even though they advertise capability at 48 miles or so, the pitures junk for anything but detecting cliffs.
A large ship will be detectable at 7-10 miles on most pole mounted sets, which is all you can really expect to be effective range wise.
Ps, merchant vessels more often than not have the radar set at 12 on the S band and 6 miles on the x band. So they wont see you much before they see you!
A large ship will be detectable at 7-10 miles on most pole mounted sets, which is all you can really expect to be effective range wise.
Ps, merchant vessels more often than not have the radar set at 12 on the S band and 6 miles on the x band. So they wont see you much before they see you!
Jamie Dundee
Well-known member
My radar is approx 10’ above sea level, picks up ships over 12 miles away.
Ian_Edwards
Well-known member
I've been messing with radars since the early 1970's, first on commercial vessels, and for the last 20 years or so, on my own boat.
There's a few things I've learned.
You can’t get way from the physics, the higher up the better.
Overlaying radar on the chart on an MFD really makes life much easier.
I’d go for a radar over an AIS any day, you can navigate in most places with just a radar. Unless you are surrounded by mud flats, you can see the coastline, big ships a long way off, small boats when you get closer. You can take a range and bearing off the radar and plot it on a chart. Modern radars have MARPA, which will track a target after it has been manually acquired and give you relative bearing and speed. However, an average yacht can only be seen at a range of between 1.5 and 1nm. If the closing speed is 12 knots that’s only 5mins.
Beware of trusting an AIS and any point where a collision is possible within the next few minutes. The AIS position is the last reported position, that position could be minutes old, because the AIS is a self-organising network, with different priorities for class A and B systems. If the network is busy, an AIS position displayed, may be well out of date. You can clearly see this when looking at a radar plot and AIS position of the same vessel on a MFD, especially for a fast-moving vessel. The AIS position will always lag behind the radar plot, and the AIS position will jump forward every minute or so.
If you use pole on the stern, make sure that the beam is high enough to go over the boom and any sail stacked on top of it. Motoring in thick fog, heading for Staff, using the radar, I was surprised and concerned to see a small motor cruiser appear on my port bow, having crossed ahead of me. It had been completely invisible on the radar on the starboard quarter. I realised that the radar was being blocked by the boom and a stack of wet sail. I fitted a longer pole.
If the radar is on the mast, beware of short tacking with a stay sail. An overlapping Genoa will slide over a radar dome, the leach of a stay sail may hit the radar dome. I completely demolished a radar dome, fitted to the forward side of the mast, short tacking down the sound of Mull in 20knots or so, with a stay sail.
There's a few things I've learned.
You can’t get way from the physics, the higher up the better.
Overlaying radar on the chart on an MFD really makes life much easier.
I’d go for a radar over an AIS any day, you can navigate in most places with just a radar. Unless you are surrounded by mud flats, you can see the coastline, big ships a long way off, small boats when you get closer. You can take a range and bearing off the radar and plot it on a chart. Modern radars have MARPA, which will track a target after it has been manually acquired and give you relative bearing and speed. However, an average yacht can only be seen at a range of between 1.5 and 1nm. If the closing speed is 12 knots that’s only 5mins.
Beware of trusting an AIS and any point where a collision is possible within the next few minutes. The AIS position is the last reported position, that position could be minutes old, because the AIS is a self-organising network, with different priorities for class A and B systems. If the network is busy, an AIS position displayed, may be well out of date. You can clearly see this when looking at a radar plot and AIS position of the same vessel on a MFD, especially for a fast-moving vessel. The AIS position will always lag behind the radar plot, and the AIS position will jump forward every minute or so.
If you use pole on the stern, make sure that the beam is high enough to go over the boom and any sail stacked on top of it. Motoring in thick fog, heading for Staff, using the radar, I was surprised and concerned to see a small motor cruiser appear on my port bow, having crossed ahead of me. It had been completely invisible on the radar on the starboard quarter. I realised that the radar was being blocked by the boom and a stack of wet sail. I fitted a longer pole.
If the radar is on the mast, beware of short tacking with a stay sail. An overlapping Genoa will slide over a radar dome, the leach of a stay sail may hit the radar dome. I completely demolished a radar dome, fitted to the forward side of the mast, short tacking down the sound of Mull in 20knots or so, with a stay sail.
Sandy
Well-known member
I find AIS very 'laggy', meaning it is way behind what I see with the eye. Having just looked up the transmission rates for Class A, between 2 and 10 seconds, and Class B, between 3 minutes and 30 seconds, I now know why.
boomerangben
Well-known member
I don’t have radar nor a boat that would take one, but I’m always nervous of a low slung radar. I’m sure the dosage of radiation is small but quite frankly I’d rather it be 20’ up the mast than 4’ above my head. The radar I use every day (aircraft) has a minimum safe distance of 100’, (it’s only got a 120deg arc so it’s safe to sit 4’ behind it!)I know boat radars are less powerful but even so…….but is there a minimum safe distance in the small print of your radar instruction manual?
Black Sheep
Well-known member
Sticking to the question (I know...) rather than joining the debate about radar/ais/gps/eyeball that I'm sure the OP has considered...
When I had radar, it was on a stick at the back. Range was plenty - it's not just to your horizon, but add the horizon distance of the ship's superstructure.
As mentioned above, I believe sea clutter is reduced for a lower height. This might be important for close targets in particular (pot markers etc).
Do the calcs for EMF exposure; it will depend on height of radome, and distance to your watchkeeping position; remember to factor in the duty cycle - ie how much of the time it's blasting in any one direction.
Mast shadow? I never noticed that, maybe because there's enough yawing of my vessel that targets will appear anyway. But you might get a mast reflection, eg you're passing land a mile to your stbd, but you see a small target a mile off your port bow; that's the land reflected off your mast.
On a stick suited me. Putting the dome halfway up the mast seems like a lot of weight aloft (but your judgement will vary - less critical with a larger boat), plus the complications of another cable to deal with when dropping the mast.
In my view, for my sailing, there's no compelling reason to put it up the mast.
When I had radar, it was on a stick at the back. Range was plenty - it's not just to your horizon, but add the horizon distance of the ship's superstructure.
As mentioned above, I believe sea clutter is reduced for a lower height. This might be important for close targets in particular (pot markers etc).
Do the calcs for EMF exposure; it will depend on height of radome, and distance to your watchkeeping position; remember to factor in the duty cycle - ie how much of the time it's blasting in any one direction.
Mast shadow? I never noticed that, maybe because there's enough yawing of my vessel that targets will appear anyway. But you might get a mast reflection, eg you're passing land a mile to your stbd, but you see a small target a mile off your port bow; that's the land reflected off your mast.
On a stick suited me. Putting the dome halfway up the mast seems like a lot of weight aloft (but your judgement will vary - less critical with a larger boat), plus the complications of another cable to deal with when dropping the mast.
In my view, for my sailing, there's no compelling reason to put it up the mast.
blush2
Active member
On Blush it's on a pole at the stern, I guess about 15ft up. Seems to work pretty well for us. (In fact it is on the boom off himself's first boat S'Agapo - RobbieW is familiar with this boom.)
Using radar with AIS gives an idea of ship size without having to interrogate the AIS data in the first instance.
johnalison
Well-known member
I would want my money back if I could only detect ships at six miles, or even 7-10 max. I normally use mine in open water at the 6 mile range (with AIS covering the distant range). I would rather the set had larger range scales than too little. Longer ranges are occasionally useful for things such as rain.
prv
Well-known member
There will be - but modern solid-state transmitters emit so little power that it’s no longer relevant. I believe my Raymarine Quantum says the safe distance is “within the radome”. At work (where we also encounter some bigger stuff) people sometimes call these modern small leisure sets “huggable radars”.
Pete
doug748
Well-known member
If I had to tackle the job I would fit one of these:
LMB-F1 Forward leaning Backstay Leveller self levelling Radar Mount for Sail Boat
£1000 but very elegant. Are they worth it, anyone got one?
.
LMB-F1 Forward leaning Backstay Leveller self levelling Radar Mount for Sail Boat
£1000 but very elegant. Are they worth it, anyone got one?
.
Sandy
Well-known member
That is a lot of beer tokens for some bits of pipe and a swivel.
Daverw
Well-known member
Ours on top of arch , about 3.5m above WL, range over 15miles easily, only 165mw so no issue with emf
LadyInBed
Well-known member
I put mine half way up my mizzen. If I were doing it again, I would mount it lower.
Daydream believer
Well-known member
When sailing single handed I have enough to do & look at. Operating the AIS is awkward enough on a rolling boat, fingering the chart plotter, whilst trying to helm, or watching where one is going . The extra hassle of radar would be system overload for me. The only time I would apreciate it would be in fog. Then I would possibly too busy helming & gazing into the abiss to operate it, even though it is supposed to do the staring for me. I just could not sail/motor along without physically looking, rather than staring at a screen 6ft away from the helm- or worse still down below.
Skylark
Well-known member
Given that the OP is asking questions regarding installation, I imagine that he has already decided to install radar after evaluating its versatility, hence value to have on board a small boat.
johnalison
Well-known member
I don’t single-hand but if I were out in fog I would certainly want radar. I have a tiller and the screen is below at the chart table. It might be easier if i had the screen at a binnacle with a wheel but I could easily manage by having it on view on my iPad in the cockpit. Having the confidence that there is nothing large ahead of you is an irreplaceable benefit and has saved my bacon and possibly my marriage more than once.
Csfisher
Member
I'd be surprised if any radars for a leisure boat are that hazardous. The commercial radar for all the large ships I've worked on (ships around 150 meters) have never had hazard distances of more than about 0.5m and that's for radar as old as 70's technology. The newer radars have been even safer, to the point where in theory I could sit on the antenna as it's radiating.