Very Light Weight Battery.

[noelex 77]

The first thing I would do is to change to LED navigation lights. With incandescent you are going to need a much larger battery size.

For internal lights I would just use headtorches. KISS.

Led navigation lights can easy be powered by a small sealed lead acid battery. The size will depend on the number of hours you need to run the light, but something around 5-10AHrs will probably be ideal.

You will get much greater weight savings going for lithium instead of lead acid, but the expense is greater and you do need to to put in fair bit of effort to learn a bit about the correct charging profile etc.

[mcarling]

Get a lithium motorcycle battery. Seems like 5-10 AH should be enough capacity. This one, for example, weighs less than one pound:
LFX07L2-BS12 - Shorai Lithium Batteries

[cptmclark]

Are there LED lights that fit the fixtures that the incandescents came out of? That would be too easy I suppose. Would I need to replace the entire fixtures?

[Adelie]

Originally Posted by cptmclark

Are there LED lights that fit the fixtures that the incandescents came out of? That would be too easy I suppose. Would I need to replace the entire fixtures?

Yes. Exact prices would depend on the original bulb size, the LED manufacturer, the color and the amount of light desired. Figure about $10-20 per bulb. Not cheap on a per bulb basis, but cheap in terms of what it lets you do with the rest of the system.

Fuses are the for protection of the the wiring, don't want to have a short and start a fire. If the circuit has a 3amp fuse that means the normal load on that circuit is less than that.

[Zil]

Ther are many venders, here is but one; https://www.superbrightleds.com/cat/...acement-bulbs/

[GILow]

I would not use the fuse rating to estimate the power draw from the lights. Fuses might have been replaced with something way oversized (or undersized) or might simply have been oversized to begin with.

Most conventional interior light globes would be around 12 watts or so, hence 1 amp each. I did find a couple of 5 watt globes in an old light fitting recently but that was for the red night vision mode.

Most of the navigation lights I have seen had either 12 or 18 watt globes. The only deck light I have had direct experience of was a 50 watt halogen, so I don't know if that was normal.

I am yet to find a conventional 12 volt incandescant globe that cannot be replaced with an easily purchased LED equivalent, though often the price of the replacement LED globe is more than the cost of replacing the entire light fitting. I have, despite this, kept a couple of light fittings and swapped them to LED because it is hard to find a nice looking LED light fitting (in my budget range) that suits an older boat like ours.

Anyway, in the OP's situation, I would start by making a count of all the globes I needed to replace if I were to swap everything to LED. Then if the price was in budget I would go that path and then purchase either a small Sealed Lead Acid battery (10 - 15AH should be adequate for evening races if all lights are LED) and then it would be small enough to bring home with me to charge on the shed bench during the week (assuming a weekend racer here). The advantage of this option being that no rewiring should be required and all the switches remain where they are currently (and no running round the boat at dusk turning on small battery operated stand alone lights. I've done this, and I found it tricky, though that was on a 20 footer). That being said, those battery operated LED nav lights lasted for years and were still using the original batteries when I sold the boat.

Lithium would be even lighter than the SLA battery, and if cost was not an issue, then it too could be brought home to charge at the end of the day.

That's my suggestion.

Matt