Just like a car, if you keep your records and receipts your warranty stays intact. Boat and car dealerships thrive on that fear. 100 hour service for my 205V was 400 at the dealer, about 100 in parts at the stores. Nice to save 300 bucks (aka 3 tanks of gas) by doing it myself.
from yahoo answers.
Can I do my own service and keep my warranty? i.e. 20,000 mile service (should be the same for a boat)
you can do most any normal maintenance on the car w/o voiding the warranty. by LAW the dealer cannot 'force' you to go to their shop to have work done. (and voiding the warranty counts as forcing).
now, as to whether you should or not, depends. what all is included in the 20k service? is it just fluid changes? %90 of fluid changes can be done by the home mechanic, cheaper and faster than a dealer can. just make sure to keep receipts, mark the mileage down etc.
later on, if there is an issue, the onus is upon the dealer to PROVE that something you did destroyed the vehicle. so keep you receipts saying "purchased 6 qts oil on 3/22/06" whatever. shoot, you have to keep the receipts of the work done at the dealership also, since they don't keep track of everything.
now. if you replace the spark plugs, and the engine blows, and it turns out you put the wrong kind in...well, then you are screwed.
so make sure you are putting the write fluids/pieces in(should be in the service manual) and keep track of everything.