Efficiencies for Surface drives.

if you need to 2:1 just get a beckit block from a yacht of the correct load and shackle it to the bow eye

 

Thank you for the advise

 

Silly question, how well does reverse work? How is low speed handling?

 

Responsiveness is about 1/2 of what would be expected on the reversing drive. THe drive must be 100% down and to rotate the vessel about 1 second of forward requires 2 seconds of reverse on the opposing drive to prevent forward displacement. The "walking" is pronounces as well.

 

Yep, this what I thought. I have the same issues.

 

I wonder....if anyone has tried a single blade propeller for a smooth surface drive
It works for helicopter. https://www.youtube.com/watch?v=wxY9snBbAAw

 

I didn't try it, but admittedly I doubt this would be "smooth" at all. With a surface piercing propeller you have quite heavy load changes each time a propeller blade immerses or exits the water, so (in this respect at least) the more blades, the better.

Even on that helicopter operating in more or less homogenious air I'd expect some shaking with increased wear on the shaft bearings. The weight of the single blade is counterbalanced, but the centre of pressure/lift is not: It is circling around the main axis. You don't see this in the video, but I suspect it's due to the low load on such a lightweight model helicopter.

 

efficiencies for surface drive

https://www.youtube.com/watch?v=nk2lPg6cpkE

Hickman`s sea sledge had three blade twin, concentrating props which would have had a single blade on each prop in the water at one time and his heavy craft did better than 60 MPH.
Why are modern craft slow in comparison?

 

LOL... how simple. breaks a few rules... but if it works... well heck..

 

the hull bottom runs up to the aft, thats going to be slow, but his drive might make up for that
Outboard powered hydros have all the speed records

 

On another note, rudders and rotation on dual drive setups . I am still confused as to which direction props should turn. I see advantage and disadvantage to either. Rudders same thing, my guess is rudder should be inboard of props away from most of the wash if straight. So something like this O || O instead of | O O |
Running four rudders seems overkill | O | | O |
Is the curve area over the prop in the Levi needed if there is a big plate over that?

 

Any appendages other the necessary propeller and strut in the water creates unwanted drag defeating the reason to go S/P drive.
Rudders are not good at turning a boat and get less useful at speeds available with S/P drives. Twin shallow rudders behind the drive is OK going slow but not at speed and can be very good in reverse and even turn a slow moving boat in its own length making reverse not so necessary.
S/P drives must have a deep running rudder making them useless in shallows.
A quick turning surface drive is a must and most hydraulic steering can not make minor adjustments quick enough for a pleasant cruse like the "feel" with cable steering used in many fast craft. In my years of shallow water boating.

 

efficiencies

Where have you seen four rudders being used?
The only reason I can see to using multiple rudders would be to have less deep rudders but extra rudder to increase blade area.
Flat plate rudders do not "grip" the water and change the direction of a boat as smooth as a foil or wedge shape.
Flat plate rudders with big leading edge ahead of the shaft behind the propeller can change direction so quick you could be tossed out of the boat, but only give a small direction change before the rudder "stalls" and creates massive drag. In my experience.
Check Levi drive about their type of rudders, I have tried that design also but found the turning rudders interfere with the water flow to the prop if turned to far.

 

You can see why they invented sterndrives and why they are so popular.
Arnesons only really came into their own in boats with engines so large that sterndrives cant deal with them.
Now you have pod drives taking market away from shaft drives

 

If they made stern drives as efficient as surface drives for speed and made them jack able instead of their inherent awkward tilting and upsetting a good planing attitude with that weight on the transom they could possibly be more popular.
Like you say big HP and stern drives and all their complicated gearing and power loss don`t mix well.
I am sure shaft drive in all of it`s modes especially in long-tails would outnumber stern drives and be the most reliable and affordable boat propulsion.
You can do maths to show efficiencies about most things but maths still is a theory until proven by an observable experiment, and maths efficiencies do not take into account economic considerations.
Are pod drives versatile enough for all applications?