Hi,
most 65151 engines like flipsky, maytech and others advertise with the ceramic mechanical seal - here are some pictures:
If I take a look at the technical data they are specified with 10m/s - see here for example.
If we have a 120kv motor with 12mm shaft, it has 38m/s with 12S in idle - way too much - what do you think?
Mike
How did you calculate? If we assume the max diameter of the gliding ring is 25mm and rpm is 5760 (12Sx4Vx120KV = 5760rpm) :
25/1000 * Pi *5000rpm/60 = 6.54m/s
if max diameter of the ceramic disc is 30mm, speed = 7.85m/s
Or am I wrong?
Hi Daniel,
you are right - the comma has slipped to the wrong place 
The max. diameter is 20mm and therefor it’s 5,23m/s @ 5000rpm.
So far everything is fine - which lubricant is the best for ceramics?
Mike
In my experience with transfer pumps that use these kinds of seals, they have only been rated for fresh water use.
It will be interesting to see how they hold up in the ocean. I also cant imagine these motors come with very high quality seals.
I’m happy to stick with the proven double lip seals. Not the ones they supply, but fresh nitrile lips seals from a reputable supplier.
I’ve seen mechanical seal used in salt water applications too. Good exemple here for a subsea motor with 8 year service intervals (at least that’s what they claim) :
This is a hell of a nice motor, but price is certainly also spicy haha
I was just speaking of the ones they appear to be using on the 65161 motors. Look like the cheapies to me.
Sure quality marine seals are available, but I dont think they have any major advantage over quality lipseals.
Also worth consideration is that an efoil is submerged in seawater and then let to dry repeatedly. I remember reading somewhere that salt crystal formation around these types of seals becomes abrasive, leading to premature failure of the seal. I would be super diligent flushing them!
I think the failures with lips seals and these motors comes down shit lip seals being installed at the factory.
I know the ones I pulled out of my 65161 were rubbish
I’ve seen these seals a lot on older marine pumps like black water and bilge pumps, they do the job, but needs replacing when they start to leak. The problem with the sealed motors is you won’t know when they start leaking. In my opinion, it’s a cheap repurposing for a temporary fix. I would rather put my money on a good double lip seal and keep it clean and lubricated, saltwater will destroy anything you use if you don’t rise properly.
All these points encourage me to replace the sliding seal with a lip seal.
At the moment I have two VR-sealing OBC here that should be better than the usual shaft seals because of less friction etc
In real the lips are much smaler
Well lipseals are not made for high pressure application while mechanical seals are. That’s the main difference here.
Even flite boards are using lipseals so yeah I don’t think we need mechanical seals to efoil.
Exactly - the lip seals can handle up to 10 bar and that should be enough 
Hi @SUP-MIKE: Which one you exactly choose? I want to replace my mechanical seal as well. In my first geared drive I have choosen two regular NBR WAS lipseals without any leakage. Even tough I used always unbalanced 3d printed props.
This is how my 65161 motor looks like after a halb a year of use -mostly in fresh water. I had like 10ml of water inside. I used CorrosionX HD from the very beginning. Now I would not recommend the HD version because its visocity is too high and it seems like that because of the heat it even raised the viscosity. The bronish looking surfaces is not rust. I can easily clean it by scraping with my fingers.
So I flushed the old CorrosionX HD out of the motor via a water jet and put the regular CorrosionX inside.
This is how it looks from the inside with water+old CorrosionX HD:
Magnets aren’t suppose to be aligned ?
That’s interesting! Never noticed that.
I also opened my 65161 today to check it. No water inside 
. Just clear greenish CorrosionX.
This one has a ceramic seal but only a few hours of fresh water use.
That’s a skewed rotor. This design helps for lowering the cogging torque of the motor and having a better sinusoïdal back EMF as well. However I don’t think there is a huge advantage here as this is mainly implemented in the automotive industry for high efficiency and regenerative (motor used as generator) purpose.
