I Energy requirements of a 4 wheel drive boat

[Colin Wilson]

TL;DR

Energy requirements of a 4 wheel drive boat

4 wheel drive amphibious boat (swamp buggy?)

My problem is trying to calculate the amount of energy, or a good estimate, that would be required to keep the boat levitated above the water at the approximate water line shown in the second drawing.

I don’t believe it will require as much energy as a helicopter as the blades are pushing against a semi-solid surface but I really don’t know?

A planing hull has a lift / drag ratio of about 5:1 with skin friction becoming increasingly more dominate and at an exponential rate as speed increases.

Lets say in a static test with the boat tethered to the shore it was found that at a blade speed of 20 mph the required lift was achieved would that not be a constant such that at a boat speed of say 60 mph the blade would have to spin at 80 mph? Making the boat increasingly more efficient than a planing hull as speed increases. Exponentially more efficient?

* ignoring air resistance which applies to both in any case.

 

[Baluncore]

I get the feeling that when travelling, your wheels as shown have top-spin, which will tend to pull the wheels downwards and stick to the water. You will need back-spin, like an undercut ball, or a bouncing bomb, if you are to get lift. https://en.wikipedia.org/wiki/Magnus_effect

Spinning a wheel will displace water from under the wheel, so the wheel will drop into that hole. To lift the wheels, you need to pump water under the wheel, while preventing that water from escaping sideways. Tractor tires have a tread that scrapes or pumps surface mud out sideways from under the tire, until the tire can grip on the more solid material below. You need a tread, that is a blade profile on your wheels, that is the opposite of a tractor tire.

If hull buoyancy initially supports the craft, then the wheels are paddle wheels, and the hull must plane at speed. If you want lift from the spinning wheels to raise the hull clear of the water, you will need a different approach. The same wheels cannot propel you over a solid and a liquid surface. I am sorry I sound so pessimistic.

 

[berkeman]

Why are the fin thingies facing backwards instead of forwards for the wheel rotation? That seems like the fins will just slip in the water instead of catching it and throwing it back to create thrust.

Edit/Add -- And do you understand the difference in efficiency of a propeller versus a paddlewheel for boat thrust?

 

[Baluncore]

Why are the fin thingies facing backwards instead of forwards for the wheel rotation?

Probably because they must plane on the surface, rather than dig in.
Traction is then from surface drag, with a drag coefficient proportional to the square of the wheel speed.

 

[256bits]

Spinning a wheel will displace water from under the wheel, so the wheel will drop into that hole. To lift the wheels, you need to pump water under the wheel

That would be definitely the situation when the boat is tethered to the dock. The paddles are pumping water away from a static location, and the only way to refill is with water flowing in from the surroundings. The refill rate will most likely not be adequate to refill the hole. The wheel spin rate at the dock should bear no linear relationship with spin rate necessary when under forward travel as the OP suggests.

There are competitions with skidoos skipping across water with the front skis providing planar lift from the forward motion and the rear track providing thrust and some planar lift being flat, bit still digging a hole as suggested.. The distance travelled across open water before dunking is mainly a function of initial forward travel speed, along with some machine features such as weight and under body design.
The same scenario is also seen for all terrain vehicles with spinning wheels providing lift and propulsion.
In essence, it is a contest to see who can hydroplane across the water the farthest.


For both contests, vehicle speed drops while travelling across the water. The propulsion from the track or wheels is not enough to overcome the drag. Final result is that few make it across the span of the water even when going full out.

If course these vehicles are not optimized for travel across water. The water builds up in front of the track and wheels more and more as the vehicle progresses forward, increasing drag, lowering speed, dropping the vehicle lower into the water, increasing buildup, and the cycle repeats.

If perchance a vehicle can be designed to skip across the water with a particular forward speed and wheel rotation so that each 'blade' hits new water, a lower speed I would think would end up with a dunk. Increasing the wheel rotational speed at the lower forward vehicle speed will mean each blade hits less of the water surface, digging the hole deeper and affecting propulsion.
I see it being very difficult to start the vehicle up from a dead start, depending upon initial sunken depth of the wheels and hull.

I am sorry I sound so pessimistic.

Justified I believe.
A light vehicle ultra buoyant might do the trick.
A heavy vehicle sunken into the water at stop not so much.
The OP needs to so some experimentation, buoyancy calculations, propulsion calculations.

 

[Colin Wilson]

Thanks for your input but I don't think the magnus effect applies. This is the interface between a gas and a liquid and the blades are simply push water in a downward and backward direction to create lift and forward propulsion.

 

[256bits]

Edit/Add -- And do you understand the difference in efficiency of a propeller versus a paddlewheel for boat thrust?

OP idea is two fold:
Utilize the paddles to provide:
- propulsion
- lift the hull out if the water to reduce drag.

 

[berkeman]

There are competitions with skidoos skipping across water with the front skis providing planar lift from the forward motion and the rear track providing thrust and some planar lift being flat, bit still digging a hole as suggested.. The distance travelled across open water before dunking is mainly a function of initial forward travel speed, along with some machine features such as weight and under body design.
The same scenario is also seen for all terrain vehicles with spinning wheels providing lift and propulsion.
In essence, it is a contest to see who can hydroplane across the water the farthest.

This is the interface between a gas and a liquid and the blades are simply push water in a downward and backward direction to create lift and forward propulsion.

Do you know what the tread pattern profile looks like on those vehicles mentioned that do this in competitions? Or do I need to find some images for you?

 

[Colin Wilson]

I did test a model years ago it did rise out of the water on a teather but then the motor died and that was that.

 

[berkeman]

Is your goal to maximize the rise vertically out of the water for a tethered vehicle, or to maximize the speed of a water vehicle?

 

[256bits]

Do you know what the tread pattern profile looks like on those vehicles mentioned that do this in competitions? Or do I need to find some images for you?

Here is a video.
The water might not be all that deep, but still.

 

[berkeman]

Yep, I was thinking paddle tires too. Although I would probably be too chicken to try it on my CRF450 with rear paddle tire from my Pismo Beach trips...

 

[256bits]

I did test a model years ago it did rise out of the water on a teather but then the motor died and that was that.

View attachment 367329

I imagine from the look that the hull was sunken at stop to axle depth, the vehicle being quite buoyant. Put some rocks in it to see its carrying capacity.

 

[Colin Wilson]

Well thanks for your replies but I was hoping somebody could provide some math as to the energy requirements?
I kept the wheels from the original model to use in an electric drive model but it would be nice to be able to refine the rquirements before hand.

 

[256bits]

Yep, I was thinking paddle tires too. Although I would probably be too chicken to try it on my CRF450 with rear paddle tire from my Pismo Beach trips...

View attachment 367331

https://www.frontaer.com/dirt-bikes-riding-on-water/
Not easy, Engrained video had a super song.

Easy across a lake.

Skis on front and rear

 

[berkeman]

Well thanks for your replies but I was hoping somebody could provide some math as to the energy requirements?

Energy requirements to do what?

Is your goal to maximize the rise vertically out of the water for a tethered vehicle, or to maximize the speed of a water vehicle?

Please define exactly and quantitatively what you want to do. Thanks.

 

[Baluncore]

Well thanks for your replies but I was hoping somebody could provide some math as to the energy requirements?

We are still trying to understand if it works, how it works, so we can use the right maths.

 

[Colin Wilson]

Perhaps it could be analyzed as each blade propels a mass of water at a certain velocity downwards and backwards at an average 45 deg. to the water surface?
I might ask how much more efficient would it be to a snowmobile run across the water?
Which does work sort of.