I've created a chart for
TI motor suitability within varying weather conditions. The Torqeedo 403 vs gas outboard motor section is based upon my experience with both motor types mounted on a TI. For the trolling motor, it's based upon my past experience with such motors on boats other than the TI and projected for use with the TI. This reflects my opinion only but I believe it to be quite accurate. Others may have different opinions.
The difference between the two Torqeedo ratings is that the 403/403A models use a 320 Wh battery and the 403C/403AC use a 915 Wh battery. The larger battery allows you to run the motor faster and longer for a considerably greater safety margin in bad weather. The Trolling motor battery is assumed to be a typical 12V lead/acid heavy-duty marine battery. All batteries are assumed to be near a full charge.
The gasoline engine ratings assume a nearly full tank of gas (1 liter) which typically gives an hour's worth of run time. Of course, more gasoline can be carried, but I can tell you from experience that it's difficult to refill the tank in very bad weather conditions.
The ratings are not only based upon available torque, but also the motor's ability to maintain adequate torque over the time and conditions it must typically operate, especially in potentially dangerous weather.
The ratings assume you are running without the sail. Running with the sail would improve the ratings in good weather conditions, and possibly in bad weather conditions provided you know how to sail properly in bad weather. If not, running with the sail in bad conditions could possibly make things worse.
The bad weather scenarios assume you are making a run to shore with no sail within an hour's worth of running time. If you're using the TI in areas where dangerous weather conditions can suddenly occur and you are over an hour's distance from the nearest shore, then I would consider that to be beyond the reasonable safety range of this particular boat even with a motor (although I admit to doing this myself).
The ratings are as follows:
E: Excellent, the motor will perform without problems.
G: Good, the motor will be adequate if not ideal in these conditions.
F: Fair, the motor will be performing adequately but is near or at its limits.
P: Poor, the motor may still help but it is beyond its limits and may not be able to overcome the current conditions.