I had an interesting e-mail exchange with the designer of the EP Carry on the speed prediction. It turns out that there's a reason why the boat speed calculator they have on their site stops at 13'. This is because the formula they use for it becomes more sensitive to other parameters, such as beam, the longer and heavier the boat gets. The predicted speed for a boat as long as the DS is 4 knots, but the measured speeds are at least half a knot below that.
As I've been able to verify, the fore-aft balance matters a lot if you want to get the last bit of speed, and therefore distance: if you sit near the tiller, you lose up to another 1/2 knot, or .5 miles of range at full power. Now, the effect of beam a slow speeds is that it increases skin friction. When sailing in light winds, we know it pays to heel the boat so as to lift part of the hull out of the water, reducing the wetted surface. Sometime soon, I'll have to try that while motoring to see if it affects the top speed. It could be that at that speed range wave drag is strong enough to limit how much extra speed a small reduction in wetted area can generate. (At low speeds, at least, the effect is noticeable).
Now, all of this obsession about performance parameters is in good fun. 99% of the time I neither care about the speed or the range, because I'm looking at traversing a well-defined calm patch, or to get on and off the dock.
Speaking of parameters, the e-mail I mentioned lists the range of the battery as 70 minutes, instead of 60 (as I remembered, and may have written about). That I've been given to understand does represent an actual improvement in battery capacity, over the pre-pandemic model.
The same email, while clearly primarily intended as marketing material, has some nice background info, including several speed vs. electric power curves comparing the performance against a competing small electric outboard and a trolling motor. These curves show the steep rise in power required as you approach hull speed. One thing with the DS is that the EP Carry doesn't get us close to hull speed (5.4 knots).
I asked how I could link to the diagram, and have been given permission to post a
PDF of the mail here at the site and you'll find the diagram on p. 6.