Tool for cutting plywood neatly?

[LadyInBed]

I have a very high quality Makita professional jigsaw, the blade still wanders, not massively, but it does

It could be due to worn guide rollers on the saw.
A narrow blade will wander more than a wide blade see DEWALT DT2074 Flush Cutting Worktop Jigsaw Blade
that's why you can get a good straight cut from a semicircular multitool blade.

 

[Poignard]

Routabout. I've got one, it's superb. Only makes 250mm diameter round holes though. Choice of 18mm or 22mm depth; it's intended for making holes in chipboard flooring in houses for installing plumbing or whatever.

https://www.trend-uk.com/en/UK/trend/content/content_detail.php?record_type=Knowledge&id=15888

View attachment 100804

That's it.

 

[[163233]]

I’d like a front seat in the audience for when they try to get the laser cutting machine into his boat...
(I believe the seat plywood he needs to cut a hole in is fixed and part of his boat furniture. )

Ah my misunderstanding. There's always the screwdriver approach..

 

[ridgy]

I'm with the router group for perfect edges and round corners, though I would cut the hole out 2mm inside the line with a jigsaw and then use a router to tidy the edges with a template.
The router will spray sawdust everywhere if you use it for the full cut.

This is the only way for a perfect finish. A jigsaw will get you anything from pretty good to a complete mess and something on that scale might be acceptable to the OP.

In any case I would practice on some scrap first particularly if going the jigsaw way.

 

[tjbrace]

Beneteau have something that cuts the access hole to half the ply thickness then cuts a similar hole on the underside with smaller dimensions, then splits the laminates to produce the locker top with a hole and a lip and the hatch cover with the opposite lip. Both fit perfectly!

 

[Laminar Flow]

I have a very high quality Makita professional jigsaw, the blade still wanders, not massively, but it does. It is however 25 years old, so maybe its time for an upgrade.
I can get cuts which are extremely good (though not using a guide as you need to be able to compensate as the blade moves), but if I want a really perfectly straight cut, there is no substitute for a circular saw, I like the battery powered ones, home made straight cut guide & a plunge cut, quick easy and repeatable.

That said you're correct, the correct tool for the OP in this situation is a jigsaw. The cut won't be perfect, but its likely only the OP will notice.

I work professionally with wood, designing and building kitchens and furniture and doing fine home finishing. I have also designed and built several boats; I would suggest not to overthink this particular project too much.
If you accidentally butcher it, it is easy enough to put it back to rights by epoxying it back in, filling it and painting it over. Then, you can always take another run at it, when you feel ready.

 

[HappyAfloat]

If we are going down the router route my vote is for one of these

Shaper Origin: One Tool, Infinite Possibilities.

No templates or guides required, just guide it in the right direction.

 

[ridgy]

If we are going down the router route my vote is for one of these

Shaper Origin: One Tool, Infinite Possibilities.

No templates or guides required, just guide it in the right direction.

That is a fine looking tool but 3k euro to cut a hole in a locker might be considered extravagant.

 

[Rappey]

It can only be a jigsaw ? Makes the job easy, cut out, cut out becomes lid , a few straight bits of ply fitted on the underside of the opening to stop the lid falling through, finger hole or notch at an edge. Job done. It's not like he is cabinet making?
Cheap blades can bend over when cutting. Cheap jigsaws are terrible at cutting straight lines and square edges.
I have a makita 18v and a mains powered bosch professional.
The makita gives a better cut and never bends the blade to one side, I think it's superior .
I wouldn't rate a multitool as high as some. Getting a clean start into the wood without a little edge damage is not easy. The blade is also not as thick as a jigsaw blade so still need to plunge cut to get the jigsaw blade in the cut. With a good jigsaw and the correct blade a plunge cut can easily give a clean start in the surface of ply.
With such a great choice of power tools we all have our own favorite methods.
It's weighing up what "precision" is actually needed as to what we use.

 

[LadyInBed]

Beneteau have something that cuts the access hole to half the ply thickness then cuts a similar hole on the underside with smaller dimensions, then splits the laminates to produce the locker top with a hole and a lip and the hatch cover with the opposite lip. Both fit perfectly!

If you has one and can get to both sides, that would do a good job, but difficult on an already fitted surface with difficult access to the under side.