This feed has helped me locate useful information. Thank you all.
I have finally found some youtube videos that answer most of my broader questions. Still to find a prop calculator that will give both trust and shaft torque for smaller props at 5 knots..
GRIN technologies have issued a range of videos over 6 years showing how a CAL 25 is using a hub drive bicycle motor.
Here is the first video I saw and it links to the series 1-6. https://www.youtube.com/watch?v=JuIG5Uqk4_c
Here are GRINs current website: https://ebikes.ca/product-info/grin-kits/marine-kit.html
Grin also gave a motor away to two fellows with a 31 Keel boat (I think episode 4 or 5?) and it worked well for them with being able to cruise at 5knots with 2kw power and 2 knots at 500w power. Now GRIN also found a way to couple multiple hub motors in series to produce more thrust. So with their system you could start off small and add as needed. BTW they found 72v motors most efficient so moving up from 48v should make better "steam". By using large diameter open windings I can see how air cooling could work here- three 5kw hub motors could provide enough cooling for 15kw and give good redundancy. . Just need to make sure there is goodish airflow into and out of motor compartment. Controllers are still an issue with heat. Heatsinks are not very big and not usually oriented to get enough airflow. BTY fans are notoriously unreliable systems. They always block up if you add filters and they gum up if you dont. Low speed high volume work better.
GRIN also provide data.
Here is a fellow that installed a Thunderstruck in a CAL31. He spends goodly amount of time on all the tech needed to achieve an good outcome and references GRIN.
Here is a graph showing hull drag. It has been referred to several times.
I estimated boat drag force using this. And I used the expanded green line in the upper left. Then used online calculator for props to get defined hull speeds and then guessed shaft torque. GRIN mentions some numbers and they were in the ball park of my guesses.
On 11 Jun 2025, at 8:29 pm, Larry Brown via groups.io <elcapitanbrown=gmail.com@groups.io> wrote:I wonder if there's a high temp solution for a clear cylinder with heat exchanging stainless components inside where the fresh water runs through the inner steel conduit and the saltwater runs around it but inside the clear sleeve. You could see the state of the exchanger like you can see the state of a raw water intake filter. Heat exchangers are normally all closed off and everyone avoids dismantling them for inspection. The other problem with water cooling is the intake aperture. Because it's as small as it is, with as much suction as it has, it's easy to suck plastic bags or floating grass into it to clog. I wonder if you had a plate made that was say 12" x 12" with a lot of smaller holes that would spread the suction out, it might not clog so easily. Another option might be to have an external hose above the water line connected to a stainless cylinder with holes around it like the strainer inside a raw water intake filter. This could be held at the back of the boat out of the water from a davit or similar with an arm that drops it down under the water's surface when you need the motor. It would be way easier to see if it has something fouling it. It would be super easy to clear, and it would not leave a permanent hole in the bottom of the boat. Downside would be that the hose would get eaten up by the sun if it was left out. Maybe it could be made with a regular garden hose and when not in use it could coil into a cockpit locker. IDK if that size hose would give sufficient flow etc but it would be fun to play with and see how well it works. It would require a self priming pump which will probably have a shorter life cycle.Having designed electronic equipment for half a century, I have some experience in reliability. Powers needed for effective propulsion need water cooling. Losses in copper and iron are significant and removing this heat out of the motor area is difficult but made considerably easier with liquid cooling. Also lower operating temperatures means performance does not to be derated for hot weather. The controller, even with the very latest design will be dissipating closer to 1kw - think of that nice electric heater keeping you warm. It glows red hot . Electronic systems are most reliable around 25c and above 50c things start to get difficult to design in reliability.Liquid cooling is a highly mature field of engineering. Salt water heat exchangers work exceptionally well if regularly maintained. However it might prove more reliable to run a heat exchanger like used on diesel engines with a radiator to transfer heat to air . Maybe both?Best regardsLee Eldridge0427874796On 11 Jun 2025, at 10:24, Matt Foley <matt@sunlightconversions.com> wrote: Air cooled is possible at 10-15kw as long as it's designed for it. Can even push it to 20kw with a lot of air exchange. Also keep in mind, I wouldn't do an air cooled 20kw, if you planned on actually using the full 20kw for hours on end.Matt FoleySunlight ConversionsPerpetual Energy, LLC201-914-0466ABYC Certified MarineElectrical TechnicianOn Tuesday, June 10, 2025, 8:30 PM, Lee Eldridge <lee@vombatus.com.au> wrote:
have a look at freerchobby.seems dodgy name but people I see on youtube are using their motors etc. outspinnermotors are highertorque lower speedBest regardsLee Eldridge0427874796On 11 Jun 2025, at 04:41, cammcnally10@outlook.com via groups.io <cammcnally10=outlook.com@groups.io> wrote:Thanks Peter,I would prefer an air-cooled system but did not see any engines listed on Thunderstruck that also met all my other requirements. I am still trying to figure out what specifications of an engine to value above others. I will definitely reach out to them as they have only received good reviews from this group.-CM--Larry BrownS/V FelicityPlacida, FL~~~~~~~~~~~~~~~~~_/)~~~~~~~~~ ~ ~~ ~~ ~~_/) ~ ~ ~ ~~ _/) ~
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