Hi,
Apologies. I also missed a reply to your comment:
"The only measure to compare realistically and simply two different system is the pull ( in KG or pounds) from the same boat on a rope attached to a scale!!"
I'm afraid that isn't really true but I can see why you might say this. You are referring to a bollard pull test, which of course is static. What it will tell you for a given shaft rpm in a voltage controlled (rpm) system is how much torque (amps) you will pull at at that rpm for that boat and that particular prop. Where I think bollard pull is useful is to get an idea of the maximum current you may pull at top rpm. This is useful for choosing your prop and making sure the system is within thermal limits. You can design it so that it can pull a large load for a short duration or a long one. My goals were to have a short duration high load but optimise my system for weight, volume, power, number of batteries at a reasonable cruise speed and range (20 miles @ 4 knots) - all to keep costs down.
As regards Torqeeudo we were talking about their outboards which clearly come with a prop, hence for their inboards without props they spec input power and ICE equivalents rather than serial efficiencies.
Scott and I know each other over the net, for some years and we've followed each others projects. I haven't engaged much in conversations on here for some years, but I wanted to answer Scott because he said he was confused about Torqeedo's outboard ratings. To me they make perfect sense and are a great way to compare their ouboards to ICE ones.
Bottom line - when a company or someone says their outboard has a total serial efficiency of 56%, then that to me is a good figure which means they have the design right.
John R
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