Tune with alternator running or not (boat related)

[Nitrousbird]

I have a Polk D4000.4 in my wake boat that was running 4 Exile Audio SXT65 tower speakers for the last 8 years.  Amp is rated for 125x4 RMS, which is how I was running it, which was the rating of the speakers.  I had it tuned to the bleeding edge previously (using my SMD-DD1, also have a CC1 for the crossover).  

 

I upgraded head units this year, tested for distortion (0), tuned it with the boat off, no H/U distortion - batteries always fully charged as I have an onboard 20amp dual bank charger.  Our last outing I was wakesurfing, had it cranked and all of a sudden my tweeters distorted like mad.  Wife driving and it happened for a bit before turning the volume down.  Resulted in 3 blown tweeters along with one blown woofer.  I am guessing I clipped hard.

 

So now I am going from those 4 tower speakers to two much larger Wet Sounds REV 10's:

https://www.wetsounds.com/product/REV-10-B-FC-SS-V2

 

For the remainder of the season, I plan on just running this amp bridged @ 4ohm, which is a claimed 400x2 RMS.  These speakers are rated for 300RMS but it is well known they can take up to 500.  I also don't believe this amp puts out 400x2 bridged, even though Pasmag years ago rated it at 140x4 at 14.4V (they never tested it bridged).  

 

My question:
- Should I tune it with the motor running or when the boat is off?  I have always done off previously.  I don't have any alternator whine or other noise in the system running or off; I wired everything from scratch when I put my original setup together.  I will cove crank it when off and crank it when surfing, so it will see max use case for both scenarios, so I want to tune for the situation that is most likely to have distortion.

- I tried tuning it tonight (my speakers aren't here yet) on the bridged terminals and could not get any distortion on track 4, 1kHz @ -5db.  I could measure distortion, that went away turning the gain down, at 0dB.   I find that odd that this amp has no distortion bridged at -5dB but does un-bridged.  Yes, crossover was set to full, loudness off, EQ flat, H/U @ 100%, etc.

 

 

[1point21gigawatts]

It doesn’t matter. Same thing. The rca signal would have the same voltage either way. That’s what the gain has to match. And the crossovers just need to sense a frequency. So it doesn’t matter if the alternator is on or not.

[BassMunky]

Wouldn't it be louder?

[CstrokerV]

I do mine  whichever The car happens to be at the time lol