I dont know if the drives on our tandem are tight or loose but they seem to operate just fine. I did realize, after our first few weeks of use, that fine and coarse grains of rock, sand,shells and mud would seem to get stuffed into the chains and fin guard housings, while folded up against the hull during beachings. When returning to the water and trying to pedal out, sometimes the pedal mechanism would stick and or there would be frequent crunching or grinding noises. Since this discovery, we have tried not to drag the thing up on the beaches and instead have been lifting it up and setting it down on the beach whenever possible so as not to pack bigger wads of dirt deeper into the drive units. When we get back I have been hosing , cleaning and relubricating both drives after each use. While hosing the drives I also articulate and inspect both units for awhile to further loosen and remove any of the stubborn pieces of rock grit and sand that always seem to get lodged deep into the works. After all the cleaning is done I lube all chains and any pivoting and moving surfaces with Aervove #937 Tef-Lube spray with PTFE (teflon?) The drives feel silky smooth after that process and then I wipe up any excess drips and runs. Finally I finish it all up by spraying those same areas moderately with Aervoe #933 food grade lube grease spray to seal it all in. Its a non-melting waterproof grease with PTFE thats designed to seal out water and resist chemical attack under extreme pressures and forms a tough durable film of lubrication that prevents metal to metal contact. Its used in food processing plant equipment on slides, guides, and chains etc to keep things running smoothly. I wont spray it on my breakfast toast in the morning but I think its a fairly "Green" lubricating product that wont foul up the water as much as automotive grease might. So far that has been my method of keeping things going and I think It has worked pretty well up to this point.
Have fun out there..