Sailing Uma have a pretty poor installation based on drop in lithium batteries and they can motor for 4-6 hours with their oceanvolt motor at a reasonable speed. If they chose to they could increase that range quite a bit by building a larger battery installation using prismatic cells to keep costs down. They don't seem to feel the need though despite clearly having the ability to get the kit in exchange for sponsorship
I wonder how these electric sail drives are for maintenance. Not being attached to a vibrating engine must be less damage to rubber seals and being small enough to unbolt and lift off it looks easy for DIY. The price difference between is 6000 euros more for the saildrive version than shaft drive SAILDRIVE 8 - Oceanvolt which seems a hell of a lot but at least if maintenance was some thousands of pounds less every few years that would be something to factor in its favour.
Don't think it has a flexible rudder seal from what I could sea. The mounting plate seemed to be glassed in solidly. The saildrive oil also circulates round the electric motor to cool it so there must be some sort of oil sealing between the two units. Damage to a traditional saildrive seal is almost non existent as anybody who has changed one will tell you. They seem more than capable of absorbing engine vibrations without degrading.
The statement that props are currently designed to accommodate the characteristics of a diesel engine is incorrect; you are looking at the horse from the wrong end. A regular, fixed pitch prop, no matter by what means it is turned, is only ever efficient in a relatively small range of RPM and power loading, i.e. blade area.
You don't need much power to motor at a 'reasonable speed' in flat water.
Well said. The key to making maximum use of electric as it is now is light weight if you want to achieve any sort of regeneration as you can only get this, even with appropriate props if you can achieve constant speeds under sail in the 6-8 knots range and to do this you need the longest WL and the largest SA/Disp ratios the hull design can cope with. one of the later Uma vids show this very well with their latest saildrive unit.. They get excited when they get 200w going in at 6knots which set against usage of 4kw under engine for 5.5 knots. Works for them (sort of) if they spend days under sail to in their words is enough to just about balance their domestic and navigational usage leaving capacity for 2-3 hours motoring when they arrive.
I do understand that you have strong opinions and I thank you for the little history lesson on powered craft. I also commend your faith in a linear development of technology that, apparently, has eluded all us lesser fools, even the pros.
But they are still fixed pitch - just capable of operating in a different direction when going forward so that they are able to generate instead of propel. The prop they are using seems to be much the same as a folding (not variable pitch) prop that can run in the reverse direction when going forward. Uma explains it in a later video. But again it is nothing to do with the torque characteristics of a diesel compared with an electric motor. He also shows, but does not explain why, the saildrive has a reduction ratio - this is to reduce the shaft RPM to allow it to swing what I guess was around 17 or 18" prop. A large diameter slow revving prop is generally more efficient - indeed the new saildrive was lengthened to increase tip clearance as the original was too close to the hull.
Peukert is zero with lithium.
<Cough> A horse is actually about 2/3 hp. James Watt established that the average horse could do 22,000 ft-lbs of work per minute, then set the horsepower at 33,000 ft-lbs per minute, probably so that a 4 hp Boulton & Watt engines would appear to the work much more easily than four horses.
But peak power about 15.
That's a lot of old pony....