I couln’t help looking at the battery life aspects. Lift have probably chosen Lithium-ion (Li-ion) cells because they have a better energy capacity, are cheaper and safer (explosion risk) than Li-Pos. However, both have a Recharge Life of 300 – 400 cycles, say 350. This means the battery pack should be renewed every 3 months in a school or rental place if recharged 4 times a day ! That’s a serious operational cost to take into account in a feasibility study ! From 8 or 9 am to 6 or 7 pm, only 8 persons riding 30 minutes each can use the board every day. That’s not many to make profits.
The idea I had in mind when creating the thread … a place where users could post their retro engineering info even if I am aware that users who can spend 12.000 USD in such an equipment are not legion on this forum … Hopefully, as soon as the Lift eFoil appears in various places across the globe, comments and picts with valuable info for home builders should pop up …ESC, motor, cooling, remote control, …
Edited, they are folding and not retractable propellers.
When the engine is switched on, folding blades are spun outwards by centrifugal force.
When the engine is cut off, the pressure of waterflow forces the blades back in place streamline. Since the roots of the blades are linked with geared teeth, they open and close together with the same angle.
I’m not sure about that. Lift are so comfortably ahead of the competition that they can take time to test this kind of fancy prop not so difficult to 3D print or mill by the way.
They have probably been inspired by tests like this one from 2009:
On boats, folding props have proven their efficiency. Prop open, you can get better forward speed and pull compared to a fixed-blade one. Then, when folded, the drag is so marginal that it is difficult to measure. This feature seems to be praised by Lift when going down waves.
Unlike our eFoils with fixed blade props and nozzle. When the motor is cut-off the drag is present and can be measured by a luggage scale towed by a boat.
In addition to what @Clarin has written in the previous post, I’ve noticed they have different names: Boat cam latch, Boat deck latch, Boat Latch, Hatch latch, Hatch Lock, compression latch. Sometimes, they are sold much cheaper without cam.
Although similar, they must not be confused with the pull (caravan) latches which don’t have cam (no compression needed) - 5 to 10 USD.
You can find the stainless steel models (SS316 only) on amazon, ebay, aliexpress - 12 to 30USD per piece:
According to LIFT, in the ocean swell, a switched-off motor = a folded propeller = more battery life
A few remarks though. So far I was thinking that propeller blades :
1- needed to be three and not two for max efficiency (as Flying Rodeo is doing)
2- needed to be twisted in order to cut through water and not push water (Straight blades = swirl so perfect for food mixers / Twisted blades = efficient thrust for propeller blades)
Food for thoughts:
Here, the Lift team seem to favour the two-bladed and hardly twisted propellers as in the 2009 Yachtingmonthly.com propeller test above:
Maximum speed p94: untwisted two-bladed folding Flexofoil prop faster than
twisted three-bladed fixed version
"(...) Interestingly, some of the best performers were two-bladed props,
which are widely assumed to perform worse than three-blade versions."
Forward Bollard pull p95:
" the three-bladed folding Flexofold – generated a greater bollard pull than the
standard fixed prop" (with twisted blades)
the two-bladed folding Flexofold – generated equivalent bollard pull as the
standard three-bladed fixed prop with twisted blades.
It would be interesting to know the bollard pull of the LIFT folding prop versus the standard fixed and twisted three-bladed props delivered with the LIFT E1 and LIFT E1 Sport efoils.
While three bladed propellers are more common than two bladed, they are in general not superior. On the contrary: propeller theory says clearly that efficiency decreases with the number of blades. The main reason for five or seven bladed propellers on large ships is to dampen oscillations (= noise prevention).
Propeller design is a trade-off, to improve a certain aspect means a decline in one or more other aspects. So you have to decide which goal is the most important, depending on the special application of the propeller.
Yes its proven the fewer the blades the more efficient a propeller is but there are trades offs.
The open propeller to me is really dangerious. Infact any propeller-driven surfboard is ban in Canada by transport Canada becuse they are so dangerious and easy for a mistake/accident to happen. Its only a matter of time before some with an open prop gets really badly injured.
What about the ducted props ? Is the Canadian market also closed to models offering a ducted solution (LIFT, Fliteboard, …) so only allowed to waterjets (VeConcept) ?
Regarding the possible prop ban, among the existing solutions:
1- There is a patented “safety propeller”: Colin Chamberlain from Australia has added a thickened leading edge to existing metal propellers with low impact on performance.
First licensee, Turning Point Propellers of Jacksonville Florida https://turningpointpropellers.com/ has produced a whole range of the “Safer” propeller under their brand name, “Aegis.”
It would be interesting if sbdy with sound CNC skills (David @Flying_Rodeo ?) could make a prototype of a propeller with thick leading edges (Inventor trail) or thick blades (first licencee trail) to demonstrate the inventor claim stating very low impact on speed.
2- the LIFT folding prop has already rounded blades which could be thickened and, better still, fold when hitting a hard stuff (arm, finger, knee…).
3- ring propellers offer a solution (seems that there is an efficiency issue due to rotating quard increasing the wet surface)
In my limited experience I have never fallen on the prop. I have fallen on the mast, the board and the wing but never on the prop! I have smashed my head, broken a rib and cut my arm. The sport has its inherent risks as all sports do, let common sense prevail. This is the reason I wear a helmet and impact vest.
I did talk with Transport Canada and they were very clear that ANY PROPELLER DRIVEN SURFBOARD with our without duct is ban in Canada is what I was told plus a $350 fine if caught using one. Jet driven surfboards are allowed.
Those rubber props I saw on this forum last year, they really are great for a family boat that does lots of towing…