You are right.

"Gandola" is definitely "trailer" (sometimes glossed as such -- or as "mula" -- in internet sites).

"Batea" seems to refer to a certain kind of (low) trailer -- including in maritime contexts.

And "ballast trailer" is a term with a relatively high frequency of occurrence -- used even in German, and even toy ones are know as such. See, for example:-

VK_Schwerlast - ... Ballast-Trailer. Ballast-Trailer dienen dem Transport von Gegengewichten ("Ballast") großer Autokrane. Aber auch andere große und ...
http://www.vkmodelle.de/vkschwe.htm

Onnettomuustutkintakeskus - B 2/2000 R - ... B 2/2000 R. B 2/2000 R Passenger train and ballast trailer lorry colliding at Kuivaniemi, on 6 July, 2000. On Thursday 6 July 2000 ...
http://www.onnettomuustutkinta.fi/8251.htm

heavy haulage - ... Dutch heavy haulage and crane hire company Koekoek recently purchased this 600 hp MAN for towing this ballast trailer and other heavy haulage jobs. ...
http://www.mbmcargotech.nl/Introduction/heavy_haulage/heavy_...

... Transportation - EVC 1999 Events - ... runs out of fuel. Hill climb. How quickly the truck can pull a 7,000-lb ballast trailer up a constant 7% grade. Off-road event. How ...
http://www.transportation.anl.gov/ttrdc/competitions/ethanol...

Allsorts Die Cast Toys, Days Gone - ... DG106002... Sentinel Ballast Tractor - GR Tuby & Sons £4.99; DG110002... Scammell Ballast Trailer Jungle Ride £9.90; DG114001... AEC ...
http://www.reptileallsorts.com/die-casts/daysgone.html

Cats for Sale 123 - ... Antique & original brass hardware. 9 coats of Epiphanies on new cypress seats, oak rubrails and comings. 400 Lb. lead ballast, trailer. $11,800. ...
http://www.catboats.org/cats123.htm

The Triple Trailer ! (PDF) - ... The trailer is alternately used as a ballast trailer (50%) and as a heavy goods transport trailer (50%). This trailer is also very good. ...
http://www.broshuis.nl/pages/uk/pdf/okt2001_jrg2_nr2_UK.pdf

SCANIA TRACTOR 5AXLE LOW LOADER SCANIA SCANIA TRACTOR 144G/530 VD ... - SCANIA. ?? SCANIA TRACTOR 5AXLE LOW LOADER, SCANIA. SCANIA TRACTOR 144G/530 VD VLIST NOOTEBOOM BALLAST TRAILER, SCANIA. ??.
http://www4.ocn.ne.jp/~m-kenki/m-scan.htm

BVC-CHAT Saturday Ride - ... I'll be on tandem with child stoker and child ballast (trailer) most likely, so my average speed probably won't amount to much. ...
http://grimpeur.tamu.edu/pipermail/bvc-chat/2002-June/000513... Search within this site

Begleittieflader des LTM 1160 - ... einige Zentimeter gekürzt. und daraus einen Ballast-Trailer gemacht , wie er bei vielen Kranfirmen eingesetzt wird. Die Spanngurte ...
http://www.hansebube.de/extra/sb1162/sb1162.html

Melbourne's Classic Trams - The W Class Part 3 - ... The tram was converted to a sleeper carrier in 1964 for the Dandenong Rd reservation relay, where it was coupled to 4 - wheel ballast trailer 25. ...
http://www.geocities.com/z_class/wclass3.html

Modellbau - Demag AC 300 & AC 665. Ballast-Trailer. Liebherr LTM 1400 Thömen. New-Trailer-Pictures. Schwerlastspitze. LTM 1160.
http://www.kranwelt.de/Modellbau/body_modellbau.html Search within this site

Appendix B CLASS DESCRIPTIONS OF LEEWAY DRIFT OBJECTS (PDF) - ... Bottom One-design Sailboat B4.4 Sport Catamaran B4.5 Sport Trimaran B4.6 Full Keel Cruising Sailboat B4.7 Fin Keel Cruising Sailboat B4.8 Water Ballast Trailer ...
http://www.uscg.mil/hq/rtc/Ops/SAR/Leeway/Appendix B.pdf

Corgimodels - Models list - Page 8 - ... trailer, 36,81. 96871, Morris Minor Traveller black, 11,76, 16502, Scammel Highwayman Ballast trailer & caravan, 52,66. 97343, Morris Minor ...
http://www.corgimodels.de/Models/List/models8.htm