Applying ablative is quite easy and economical. A 17ft. boat should only require 2 quart maximum of a good ablative like Micron-extra. Consider that the yard charges $70-90 / hour to apply this ... and then usually 'slops' it on with a coarse roller resulting in a rough surface that enhances 'slime growth' and retards the 'release' when the boat is 'moving'.
If you apply the ablative with care, using a short-knapped 1/4" foam roller and get the ablative as-smooth-as-you-can ... it will 'release' the growth easier and will last much much longer (due to the reduced total surface area of the smooth surface).
An alternative for the low salinity / brackish Bohemia would be to coat the bottom with a Copper/PTFE (such as VC-17) and then simply use a 'squeegee' on a long pole once every 2 weeks to 'knock off' the growth ... if the slime growth is constantly removed it will minimize barnacle attachment. VC17 will last for MANY seasons in fresh or slightly saline conditions. The only problem with VC17 or Baltoplate, etc. or any PTFE based bottom paint
is that it can not be applied over anyother bottom paint
... just over bare gelcoat, or barrier coat; plus you cant apply anyother paint
on top of it.
Especially if this boat has a trailer and you do get humongous growth, just 'short haul' with the trailer and then occasionally power wash or scrub the bottom - VC17 can safely be power-washed (at reduced power) as its considered a 'hard' bottom paint
If you select VC17, you may want to consider mixing a simple 'antibiotic' to the VC17 such as oxytetracycline (a veterinary anti-biotic) about 12-18 'pills' smashed and ground into a very very very fine powder and then mixed into the VC-17 before applying will take care of the slime for a long time; less slime = less barnacles.