I would not fill with epoxy.. but rather epoxy seal a counter sunk Aluminium screw into the hole???
There is 'nead it' 'metal' epoxy filler product on the market.. other brands also... I think it is iron based, look around may find there is a similar Aluminium based one ????

It is an impressive product.. re built keyway slots on cranks, re tapped not heavy load threaded holes, even repaired the bale on a spinner reel where the body had broken around the wire.. not very good as a glue type application thu.

As above weld all.fillers do shrink bubble etc eventually.

Hi...

My trade is specialist welding.....Filling those screw holes is very easy using GTAW(Tig) welding as long as there is reasonable torch access. Remember "Tig" welding likes all surfaces very clean.
Any competent alloy shop should be able to do the job. If it was me I would insist it was done by the "Tig" process to ensure complete fusion/penetration of the parent metal. Some might want to use a "Mig" to do the job but for that very small weld area there is a high chance of weld faults because of the high deposition rate of the "Mig". This is compounded by the fact that a lot of the machines used for alloy "Mig" welding are not programmable to ensure a higher current ramp at the weld start to ensure fusion/penetration.
It is a very basic, simple job for a competent "Tig" welder. Pity you were not closer...I would have done it for a steak & kidney pie.

regards
Ross

hi....

Again...any competent welder will know the drill but to ensure a nice clean weld the oxidising layer around the screw holes will need to be removed as part of the weld prep. That can be done using a clean rotary tool(cutting tool not sacrificial abrasive). Depending on the hole location you want the prep to be done minimally on a area basis so the alloy is not "marked" unduly. I would prep the hole about 4-5mm back from the hole but plan on the weld fusing about 2mm + the hole diameter.
Again...depending on location I like to do both sides of the screw hole to "recover" the full parent metal thickness. It is easy to "just cover" the hole from one side but that is not really a satisfactory result.
This is a very easy job to do for a welder.
When you get the job done and inspect it there should be zero imperfections in the weld and it should just look like a slightly raised smooth dome where the screw hole was. Check that there is no visible line around the edge of the dome and no pitting or "black" coloured inclusions in the weld metal.

When you decide who is doing the repair....tell them what you want and what you expect to see as the finished result. I am sure you will have no issues.

regards
Ross

Ross, Can I sand back the finished weld to flat prior to painting? 

Not essential.  But it would be nice if I can do this on the outside.

Thanks Ross.  I'll be using a high build layer in the paint system so any imperfections in the alloy will be covered.  The transom fills I will just leave domed.  I'll be sure to ask around and find good a welder.

roscoes2 wrote: Pity you were not closer...I would have done it for a steak & kidney pie. regards Ross

I'm not a welder but I work with them. That's very good advice & I agree with Ross' suggestion you leave the weld slightly raised for the reason he has stated. I would cut & paste those replies and talk to your welder to see if he can meet those specs. If he can't then he's the wrong man for the job.

Listen to Rosco....
I have rebuilt old classic car steel similar he describes for the ally boat....except using brass dollys on the back... and when finished one cant see a repair on either side of the bare steel
To achieve this the welder HAS TO do the grinding off to make sure if any 'air pockets' are not underneath....then fill these as one would do skimming a patch with filler before the hi build goes over.
If one doesnt fill with steel/ ally hi build filler will show up after a season like whores draws  espec on a flat surface... espec so with ally.
You will also most properly find any reputable welder will insist that he finish the repairs... not because of cost.. but because he doesnt need the hassle of a job not up to his stds going out the door.. and a yr late someone ask u "who did the job..." going on his reputation.

So if u come across a guy who will let u finish....dont use him.

I have not painted Ally and not familiar with the paint systems for it.
But at the end of the day.. it what YOU notice that will realy P!%% u off every time u walk past the boat which will be in direct proportion to the effort u have put in.
If u are going high build and blocking back... After all the reason for high build is to take full advantage of the finish of modern paint systems...
I can see the reasoning to go the effort of hi build and not do the job properly..
All thats invovle in the little mounds is the welder hit them with a tiny grinder checks no air holes the weld is solid and then maybe a light sand.. couple minutes.. what is left the hi build will take care of nps
But leave a lump that may or may not have a air bubble or what ever just under the surface and paint over....just doesnt make sense to me.
May as well just screw and epoxy...

Sry...

Your painter will need to prepare the surfaces unless he can start within an hour or 2 of the welder finishing.

Because alloy starts oxidising as soon as it is exposed to air it needs to be primed within a few hours of being exposed so you painter will likely need to sand/grind back anyway.