What is 'trimming'?

[rockhopper037]

When you guys talk about trimming a sub, what do you mean exactlly, and why is it important to do it?

Thanks

[tsenecal]

simplistically speaking, "trimming" is adding

simplistically speaking, "trimming" is adding flotation (usually foam) and ballast (usually lead) to the model until it floats at its proper trim both surfaced and submerged.

[raalst]

the sub tends to "float"

the sub tends to "float" differently underwater as opposed to above water.
when it goes under it often dives nose first or stern first.
when combined with forward motion this means the sub goes under faster or not at all because it basically goes where it's nose points to. Planes
can only correct so much..

Trimming is the art to have it go down evenly or in the orientation you want. Then there is the challange to combine that with a natural looking
stance when surfaced.

Indeed, a lot of adding, substracting and moving foam and ballast.

[rockhopper037]

OK, to add weight i

OK, to add weight i can use lead solder, but what sort of foam should i use to help the sub float?
Also how should a sub dive?
Should it go straight down, or should the bow go first?

[raalst]

diving : a matter of

diving : a matter of taste.
research vessels go down as level as possible. warships dive with speed and nose first.

personally I feel all boats should "sink" level when they have no forward speed.
then the "nose first" approach can be commanded by using the dive planes and forward speed.

if you trim the boat nose-first when it is completely submerged, it will tend to go deeper
at any time you do not compensate with the dive planes

So, a nose-up stance when fully submerged might be considered a precaution as it will surface by default.

on foam : some people use a blue or pink insulation foam but I have never encountered it locally.
I used some yellow foam used in car chassis building, which I coated with epoxy glue. for my small Kilo that is enough.

When you dive deep, you have to make sure the foam is not compressed.

basically, whatever floats & is not compressed easily will fit the bill. being able to easily shape the stuff to follow the hull is another important quality.
beware some foams act like sponge, that sort should generally be avoided.