While I understand replacing bulbs with LED in high use areas, like salon, anchor light, the steaming light is mainly used while motoring at night, so the alternator would easily replace any battery amps used for the streaming light. Just puzzled why you feel the need for that change.
I am pretty sure I replaced the steaming light with a festoon LED lamp. The replacement was not a coast guard certified (or whatever that would be) lamp, but has worked just fine and bright for a few years with lots of night use. Let me do some research in the morning to see what I did.
All those little loads add up!
Chris is right - electric drive so no alternator. Additionally I want to replace the anchor light. The current bulb for the anchor light is 10 watts @12 volts festoon (with indentations on the ends) 1 3/4" long.
Assuming you have the ML-2, Defender sells the Forespar LED replacement for the steaming part of the fixture. It is pricey. I can't find my original order, but I think I spent some time researching this and purchased an identically spec'd "off brand" festoon LED lamp for just a few bucks.
Forespar PN 132325
For the anchor light I got one with a photocell that turns it off automatically. I am certain this has saved me countless hours of sailing around with my anchor light on.
Have you tried Marinebeam. They have a chart where you can pretty much match your bulb to pictures on the chart.
Then call them to confirm. They have always been very helpful and I have been happy with their lights. I have replaced all
of the bulbs and/or fixtures on our current E32-3 as well as our former boat, an E27, which also was electric powered BTW.
Another vote for Marinebeam. Well made and reasonably priced, at least compared to other brand names. I replaced all lights, internal and external with their units.
Another thing to consider is a retrofit LED bulb vs. a new sealed LED unit. Retrofit will be significantly less expensive, less work and may or may not satisfy USCG regulations. Sealed unit costs more but prevents bulb/receptacle corrosion and is USCG certified. Just look inside any old navigation light. I am really surprised they work at all.