Good morning Barry, welcome to the forum. The Ulises makes up into an attractive model, I hope you enjoy the build.
Medium size tugs like this need a motor that favours torque rather than revs, so it can swing a decent size propeller and if you are new to model boats, it's easy to get confused over the weird labeling on most of them. I could go on about various motors and how a 600 size motor includes some totally unsuitable racing types, but I won't. To make this easy, there are a few good motors, but I would use a Mabuchi 540 noise attenuated ( not any other type of 540 motor) suplied by a company called component shop, it costs about 9 pounds with mount. Mr google will take you to it. Similar motors are available from other places, but sometimes the specification will vary for a similar name, that's why I've specified the component shop one.
No doubt other people on here will have alternative ideas, so you should get some choice.
Good luck with the build, if you've any problems just ask on here.
Charles
Edited By Charles Oates on 01/04/2021 10:13:52