Old 01-19-2021, 06:57 PM
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Join Date: Jan 2021
Location: South Ogden, UT
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Hi and thanks for the quick reply. For clarification, I'll be designing and building the hull because no kayak has the proper hull shape for the speeds I want. I looked at a Lifetime Hydros 85 and it was close, but still too much rocker and taper. Truthfully, what I have sketched up in Fusion360 shares more design language with a microskiff than a kayak but since my question revolved more around the power requirement for the prop in question, I didn't think I needed to extrapolate beyond it being a kayak. When I said 250- 275 pounds, I meant total weight including me, the hull, propulsion, battery, steering gear, fittings, ect. I'm about 180 on my own. To reference the Hydros again, that has a weight capacity of 225 lbs (on top of the 37 lb. kayak weight), is roughly the same beam and LOA, and due to the tunnel hull has quite a bit less volume than what I have drawn so far.

I meant twin straight shaft inboard drives. Again, my apologies for not being more clear on that point. As for the power, when I said 100V/95A, that's the upper limit of the 360KV 56104 motor I mentioned and I was really only using that as an example. However, I think I may have misstated my question. What I was asking was how much motor I need to spin these props up to 10K RPM in the water to even see if they'll stay together. I really have no concept of how much power a prop this small will absorb. 10K would give a theoretical speed through the water of 60 MPH with zero slip and 48 MPH with 20% slip, so I'm using that as my ultimate RPM limit. It may very well come to pass that I only have to ask for 5000-7000 RPM to get what I want. If the props can't stay together at 10K I'll go with jets, and I'd rather cross that bridge now before the hull is built. Oh yeah- I'll be running the props in pockets so converting from shaft to jet would be more than just cutting a few holes out. I love building, but I hate chasing ghosts.

To answer your curiosity about my experience, I've been around boats for almost 40 years, got home schooled on boat design by a retired naval architect and have designed and built four boats between eight and 14 feet, have extensive experience rigging all sorts of full scale propulsion systems, was an electrician on military aircraft in a previous life, and can turn a Detroit 12V71 inside out with my eyes closed. What I don't know is how much power this little prop will need to turn 10k and figured someone here with more experience with model boats would have a rough WAG ballpark idea of where to start.

Last edited by Snowdrift; 01-19-2021 at 07:06 PM.