Underwater light positioning

Nigelpickin

Nigelpickin

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www.cornishcottageholidays.co.uk
The boat is going into service next week so we are getting three lights fitted to the stern. Nothing to give JFM a fun for his money :) but hopefully will create a glow for evenings on the swim deck, late night coffee and fish watching.

So how far below the waterline should they be placed and if the answer is more than 10 inches, is it ok to place them underneath the trim tabs.

Many thanks in advance.
 
It's not as critical as some people say, so don't over worry it. In the range 150mm - 400mm below the w/line is perfectly fine, and is where I would aim for, but you will often be constrained by the access to and kit in the aft part of the boat and will have to do the best you can in the circs.

If you get them close to the w/line so that they lift above the w/line in an anchorage with small waves, they will annoy your neighbours (if they're as bright as Lumishores) so try to avoid that if you can, ie 200mm is better than 150mm below w/line

Try to avoid creating shadows from underwater hardware, and try to get them all the same height. I don't understand your comment "underneath the trim tabs" - how is that possible if the tabs are right down on the transom-hull bottom corner/chine?

That new MBY video went on about poor performance because the lights were too low below the waterline - that comment was cra@p in the context of the boat in the picture, imho. The poor performance was because the builder had bought the very base level Lumishores (less than I have on my tender) and put them on a 60 foot boat, probably due to cost cutting

FWIW here are pics of mine showing the light position and the effect...

9841E3E8-B07F-4C45-AE02-FF1773A268E5.jpg

70EEE788-032B-496F-AC3F-C94D10833B89.jpg

2A6893D2-2F86-4ED1-842A-0C30A4553CD2.jpg
 
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Nigelpickin said:
So how far below the waterline should they be placed and if the answer is more than 10 inches, is it ok to place them underneath the trim tabs.
Click to expand...
In principle, the lower the better. But how can you have any room left on the transom under the trim tabs?!?
 
John you are going to put google out of business. Many thanks.

I haven't crawled in for a look, it just appeared that there was a bit of space 'neath the tabs. But there's just a few mm...
(Thee lights are bar not round).

Thanks agin
 
Agreed, the lower the better, due to the issue jfm mentions of the lights lifting above the waterline at anchor in a swell. These are incredibly bright lights, so it's a bit anti-social to dazzle your neighbours whilst they're relaxing in the evening.
 
Nigelpickin said:
they're alibaba specials
Click to expand...
Errata corrige:
Do NOT put them as low as possible - above the w/l might actually be wiser.
When they will fall apart, you don't want to have several high pressure water ingress...
...bye now, looking for my coat! :D
 
At last, an underwater lighting thread I can reply to. Although everyone has already given the right answer i.e. as deep as necessary to avoid the lights breaking through the water surface when gently rolling at anchor. Lights breaking the surface understandably irritates those looking directly at you. So not too 'shallow' .
 
A stupid question then (mine are approx 15cm below w/l btw)

How is it possible to annoy someone in an anchorage? all boats will be more or less "looking" the same direction and most boats have ppl sitting on the aft (or central say) section.
so unless it's 45C and you want to cool on the bow sundeck or you have a portugese bridge, I fail to see how aft to aft one can annoy the other! OK, side placed lights like M2 are an exception.

I can also confirm that teens really love them and go diving, climbing up, off to the paserele, diving again at infinitum until they collapse out of exhaustion. A go pro also helps as well... Definitely a good buy, as they then leave the "elderly" to relax on the aft deck with their drink...

cheers

V.
 
vas said:
A question then (mine are approx 15cm below w/l btw)

How is it possible to annoy someone in an anchorage? all boats will be more or less "looking" the same direction and most boats have ppl sitting on the aft (or central say) section.
so unless it's 45C and you want to cool on the bow sundeck or you have a portugese bridge, I fail to see how aft to aft one can annoy the other! OK, side placed lights like M2 are an exception.

V.
Click to expand...

I have to answer that with another ' Im stupid but it must be simple ' observation ! I've never understood why boats do NOT all face the same direction in an anchorage -- in some places ( Villefranche comes to mind) it doesn't seem to matter what the sea state or swell is but boats seem to face different directions. I've always put it down to depth , underwater currents . hull shapes and anchor chain length but I can see the weakness in some of the physics there. At 100 degrees beams can be very wide as well so you only have to a few degrees off 'alignment' to cause offence.
 
vas said:
A stupid question then (mine are approx 15cm below w/l btw)

How is it possible to annoy someone in an anchorage? all boats will be more or less "looking" the same direction and most boats have ppl sitting on the aft (or central say) section.
so unless it's 45C and you want to cool on the bow sundeck or you have a portugese bridge, I fail to see how aft to aft one can annoy the other! OK, side placed lights like M2 are an exception..
Click to expand...

Anchorages, by their nature, tend to have land on 2 or 3 sides of them, so there's potential for winds or currents to swirl around them, and of course boats will all yaw at anchor in wind anyway. Boats in becalmed anchorages with no tide can end up facing any direction (often the case in Villefranche), and swell can still come though from passing boats or distant storms, and when there is wind and tide yachts will, relatively speaking, sit more to the tide and mobos more to the wind.
 
Thanks for all the advice. Light positions have now been agreed 200mm below waterline. Just a basic set of 3
blue-white-blue

Will post a picture in a couple of weeks, not sure how excited to be as the lights are only about £330 quid a piece...
 
Here is a pic of mine. As you can see they are about 18 inches below the waterline. I only have 3 poverty spec Lumishores across a beamy boat but they still give plenty of light for late night dips and attracting fish. The centre one failed earlier this season but even 2 functioning lights were pretty bright

WP-20150319-15-37-23-Pro.jpg


I would be wary of placing them too near the waterline. I had some OEM u/w lights on my previous boat and those used to fail regularly because they were too near the waterline and got overheated if they were clear of the water. Not sure whether the Lumishores would suffer in the same way
 
Deleted User said:
Here is a pic of mine. As you can see they are about 18 inches below the waterline. I only have 3 poverty spec Lumishores across a beamy boat but they still give plenty of light for late night dips and attracting fish. The centre one failed earlier this season but even 2 functioning lights were pretty bright

WP-20150319-15-37-23-Pro.jpg


I would be wary of placing them too near the waterline. I had some OEM u/w lights on my previous boat and those used to fail regularly because they were too near the waterline and got overheated if they were clear of the water. Not sure whether the Lumishores would suffer in the same way
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Brilliant thanks, I have sent the new instructions to the yard.
 
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