Paddle wheel torque calculations 1

[tritoon]

I'm designing a paddle wheel drive house boat and need to do some calculations to see if the parts I have on hand can do the job.

Paddle wheels will be 6' dia. with 8 paddles by 3' long . Paddles will be 3' long by 10" and will have the tops of the paddles submerged by 2" to 3" when the paddle is vertical.

I want the mid to high end RPM to be about 56 Rpm. I figure this will give me about 10 Mph with 20% loss from the hull and paddle efficiency loses. Hull is 3 - 25' aluminum pontoons no more than 50% submerged.

I'll be driving the paddle wheels with 2 Hydraulic motors that will Rpm at 556 with 458 lb-in torque. Probably chain drive reduced 10 to 1. Flow and pressure are not an issue to produce, but I'm wondering if the motors will be up to the task.

Any help or direction to resources would be appreciated.

Regards
Bert

 

[Jackofalltrades2]

Bert,

The last paddlewheels I built were 100ft long and weighed about 50,000lbs, for shallow river operations.

Here is what I learned.

The paddles were about 90% efficient. The rotational speed of the paddles only slipped about 10%. But ours were 80% of the width of the boat.

Your motors will only generate 4 HP each. That is a total of 8 HP. Ask yourself, would a 8 HP outboard push your boat at 10 MPH. Probably not! My experiance says it takes 6 HP to push an empty 17 ft canoe at 10 MPH with two people.
The paddles may be slightly more efficient than a screw, but you will have have the same hull HP. What ever outbord power it takes to push your boat to 10 MPH, is the approximate HP it will take hydraulically. You can do the math from there.

Good Luck!

Tom Nelson
Application Engineer (CFPS)
CATCO Parts and Service
St Paul,MN

 

[tritoon]

Thanks Tom. I guess my next step is to calculate the force needed to push a 3' X 10" board through the water at a known velocity. I can work backward from there to come up with appropriate hydraulic motors. My pump driving motor will be a 3 cylinder diesel with about 22HP.

Thanks for the help.

Regards
Bert

 

[tritoon]

Tom:
It just occurred to me that I will be reducing the motors out put by around 10 to 1. Wouldn't this net 40 hp per motor?

Also there will be two 3' wide paddlewheels with separate motors for better steering control.

Regards
Bert

 

[Jackofalltrades2]

Bert,

Think about your last statement!

You need to know how much HP it will take to drive the pontoons at 10 MPH, not the boards.

Adding a gear reduction increases the torque output and reduces the speed output.

The net HP remains the same. If you start with a motor with the ability to generate 4 HP of power, that is all the power you can pull from that motor. HP is a calculation of torque and speed.

If you already have the engine, work backwords from the engine. with a 22 HP engine, you will only get about 16.5 HP maximum to the paddles (about 75%) and that is if you use piston equipment. Gear pumps and orbit motors drop that to 60-65% of input HP.

So, a motor capable of generating
8 HP at 560 RPM = 75ft/lbs, 900 inlbs Chain reduction 10:1
CharLynn 2000 series, 6.2 in/rev, 1100 PSI 16 GPM each motor.
8 HP at 280 RPM = 150ft/lbs, 1800 inlbs Chain reduction 5:1
CharLynn 2000 series, 6.2 in/rev, 2200 PSI 8 GPM each motor.
16 GPM at 2150 PSI = about 23 HP input

8 HP at 56 RPM = 750ft/lbs, 9000 in/lbs Direct drive
Big stuff $$$$

Twin padlles are nice you can spin it around and it works great for docking, but you will need a rudder to steer.
And remember the rudder sees reverse forces when backing up!
Be carefull about oil leaks, The Coast Gaurd gets real excited when they see oil leaks in the water!!!!

TN

Tom Nelson
Application Engineer (CFPS)
CATCO Parts and Service
St Paul,MN

 

[tritoon]

Good Lord........I feel like an idiot. I put those emoticons in after my 40 HP sentence but they didn't show in my reply. I know you can't create HP by gearing down. Just trying to be funny. Since your last e-mail I have been looking at other motors and they aren't cheap. I buy a lot of lost freight and returns. So I have a 28 GPM/3000 PSI pump. double float valves and the motors. I initially thought the motors might be too small to marginal so your insight and information has really helped me accurately gauge what I need for a drive system. I really don't want to go bigger than a 3 cylinder diesel, I'll go for more HP. My other plan was to buy an inboard/outboard donor boat and put the unit in an aluminum box at the rear of the tri-toon. But the thought of shallow draft still interests me. I don't plan on launching for another two years so I'll see what presents itself.
So are those CAT skid steers way better than Bobcat brand? I'm looking at a used one with 500 hours.
Regards
Bert

 

[Jackofalltrades2]

No experiance with either

Tom Nelson
Application Engineer (CFPS)
CATCO Parts and Service
St Paul,MN