I might be totally wrong in the below description, then enlighten me about charging, but both Swi-Tec and Watt & Sea, are programmed to charge batteries and not to feed the boats consumption, which has the strange consequence, that even when you consume a lot of power during sailing the hydro-generator only produce so much current as the batteries would take even if you where not consuming any energy. Don't ask me how it works but I talked with an owner of a Watt &Sea and he explained the issue for me but I can't repet the info, He was in contact with Watt & Sea who confirmed, they gave him info so he could reprogram his regulator, (out of my competence).
Both his experience and mine is they do not give as much as expected, when looking at the amp meter the current varies a lot jumping often between 5-8 Amps at speed around 6-7 knots but seldom above 10 amps even at speed exceeding 8 kn.
Speed reductions is negligible.
but not the issue of cleaning the propeller from sea weed
Mounting; as I have a stern platform it was rather straight forward but do not see that it should be more difficult without the platform, I attache a few photos om my installation.
If someone is interested I would consider selling our Swi-Tec hydro-generator,, used less than 14 days