removing swirl marks and scratches from bare aluminum hull

[Mr Efficiency]

There is a lot of useful info given already. But, what you need to understand is the difference between standard aluminium fabrication results v end result expectations.

All aluminium fabrication, when done properly will have those score marks you show. Here is one example of a vessel post repair:

View attachment 154560

And another new build:

View attachment 154562

What you're asking is to just go to a "smooth" surface for aesthetics and presentation.
Which means you're left with 2 choices:-
i) An ever decreasing grinding disc roughness to make the surface smoother with each iteration
ii) leave it as it is.

It seems you're getting frustrated with the progress of i). Thus just leave it as it is. Bare aluminium oxides rapidly. Over a short period of time you will no longer notice those swirls and score marks (assuming them to be not deep and general fabrication ,as noted above). The only down side it will be a matt look, not a glossy look. If you want a glossy bare ally look, you'll need to do a bit of i) and then coat with a clear epoxy.

Leaving the hull bare unpainted is nothing new and is far more common than many posting on this thread would appear to suggest.
Technically, there is no reason to paint an aluminium hull, it is oddly, for aesthetics only. Aluminium's natural oxide layer protects the hull far better than any paint.

Yeah, well those zig-zags in the panel on the left of the second picture seem unrelated to any technical necessity.

 

[Ad Hoc]

Yeah, well those zig-zags in the panel on the left of the second picture seem unrelated to any technical necessity.

Buffing/cleaning/grinding, is not always related to a "technical" reason.
General tidiness and cleanliness post fabrication, in prep for other works is a sign of a quality yard.

 

[Mr Efficiency]

Buffing/cleaning/grinding, is not always related to a "technical" reason.
General tidiness and cleanliness post fabrication, in prep for other works is a sign of a quality yard.

Well "old mate" says he is not concerned with aesthetics, isn't painting, so why he is fussing over some grinding marks and wants rid of them, can only be because of some "technical necessity" he sees, supposedly. Either that or he doesn't know what he wants, or why ! The only concern I can surmise, is that he imagines it could be a corrosion issue, but I will defer to your opinion on that, the only time I have been aware of scratches in alloy being a problem is with painted surfaces and a concentrated focus for electrolysis where the metal is exposed.

 

[Pen Gwyn]

Ad Hoc, thank you for your very informative and ad hoc remark.
Very much appreciated.

 

[Pen Gwyn]

This forum is taking a turn I was not expecting.
I thank those who contributed constructively for their time and insights,
and will proceed from here with the information available.
Sincerely
Philippe

 

[Mr Efficiency]

This forum is taking a turn I was not expecting.
I thank those who contributed constructively for their time and insights,
and will proceed from here with the information available.
Sincerely
Philippe

You might want to explain why you want rid of "swirl" marks, but are not interested in the aesthetics of appearances. What's the problem, then ?

 

[fallguy]

Everyone questioned the yard using 40 grit.

I would not blame the forum members.

The hull looks very interesting. Best of luck.

 

[Mr Efficiency]

It might be too clever for me, this thread, but if you have something delivered to you by the builder that is not up to scratch (pun intended), then isn't it the job of the builder to rectify it ?