Did a dream got shattered?

Hi Tugboat and Ron,
Thanks for the rule of thumb. the problem is, that the German manufacturers are making proper sized shafts and use quality material. Therefore for them you could use this rule of thumb. But those from Prince and also the ones Tugboat had listed in a previous thread, you have to do it by calculating it step by step. Both are using smaller sized shafts and therefore lower maximum torque quoted figures.

http://www.baumhydraulics.com/files/catalog/k23.pdf

The Prince one is only about +/- 4 Kg and that from Baum is +/- 40 Kg
Tugboat, you have to bite it through and work through the calculations to enable you calculate and to find the right sized motor. You can do it the CDK way, but he did not mention to divide the result by 75. Also he has kgf-m which is misleading.

You work first out the Revs per second..... example: 400 rpm = 6.66 revs/second
You take the maximum torque .....example 2405 inch-pounds (baum)
You take the conversion from inch-pounds to Kg-meter = 0.01143
This you multiply .... 6.66 x 0.01143 x 2405 = 183.07
The result you divide by 75 Kg/m/sec thus 183.07 / 75 = 2.44 HP

Tugboat, I don'ty feel so bad anymore. You should be able to find the right motor at a reasonable price for your boat.
Bert

 

wow--that throws a wrench in my gears CDK. What i dont understand is how Mako2 got to use his 22x22 props with(to the best iof my knowedge) almost virtually the same motors?...this is confusing for me...

so would 12 hp electric motors offer more torque??.i can gear them 10:1 if needed...or any gear ratio needed...one thing- when using the prop calculator or using Gerrs chart----does the same info work for electric engines as with diesel?..

 

You work first out the Revs per second..... example: 400 rpm = 6.66 revs/second
You take the maximum torque .....example 2405 inch-pounds (baum)
You take the conversion from inch-pounds to Kg-meter = 0.01143
This you multiply .... 6.66 x 0.01143 x 2405 = 183.07
The result you divide by 75 Kg/m/sec thus 183.07 / 75 = 2.44 HP

Tugboat, I don'ty feel so bad anymore. You should be able to find the right motor at a reasonable price for your boat.
Bert[/QUOTE]

Bert this is all much appreciated--I hope im not taking up your time for advise on your boat project--it wasnt my intention...but all the info I am learning a great deal...

2.44 hp--thats not a lot

 

http://www.boschrexroth.com/industr...Language=EN&VHist=g54569,g54574&PageID=p78408

what about this?--it gives KW's...rpms and flow rates...

 

You think you are learning a lot, so do I. Tugboat, I have a motor here which is rated 12,5 Kw for 10 minutes, with a shaft of 12 mm. Do you rally think the torque I need will last on a thin shaft? The moral of the story, look for what the motor manufacturer gives you as maximum torque ratings. The horsepower or KW does not mean that much. The answer is , YES a 12 HP EV motor will give more torque, if the motor is designed for it. But a 12 HP Hydraulic motor with an efficiency of 78% (i.e. also your oil input flow is not correct calculated) and a 30 mm shaft will give you less torque than a 12 HP EV motor with an efficiency of 91% and a shaft of 30mm . We have to compare apples with apples. Confused. Yes, until you stay focussed on what you want and need, then it is a piece of cake. The first thing you have to clear for yourself is : what do you need in making your tug doing what you like it to do. i.e. pulling, pushing, or both , sideways, backwards etc. May I see your list of what you like your tug to do?
i.e. I like to tow the queen Mary at a 0.5 knots or I like to tow sometimes a 10 ton displacement boat at 10 knots. Then we will help you to suggest a "powerplant".
Tugboat, dont worry, I am still busy doing my stability calculations. Now I can place my metal weight anywhere below the waterline, it makes my life easier. Sunday I am on the way to Cape Town again, thus only next week I will start claiming the thread again.
Bert
p.s. our time difference I believe is about 11 hours, is that correct? I can only roughly guess were you are living. Good night in that case, I had my breakfast just now.

 

Yes, the Germans have always been able to make solid mechanical constructions, they are masters in that field. Now we have to help you to use Newton-meter in your calculations. i.e. 1 inch-lb = 0.113 Newton-meter (Nm) or you probably like to work it in inches and pounds >>>> 8.8495 inch-lb = 1 Newton-Meter A Bosch unit of 8200 Nm = 72565 inch-pounds , You are able to pull the Queen Mary over land with your tugboat.
Bert

 

I can't make it better than it is tugboat.
Without any calculations, didn't it strike you as odd that an 11.6 lbs device would be able to spin a 22" prop and propel a boat? With an estimated efficiency of 65%, how is the 35% loss dissipated? I do not know who Mako2 is, so I cannot answer that.

With electric motors, the boundaries for torque and HP output are not sharply defined. If sufficient electricity is available, torque can rise much higher as long as the motor temperature stays out of the danger zone. But for prolonged operation, the motor must be able to reach the designated rpm, so you need a gearbox.

 

Hi Tugboat,

there is something not completely matching, like CDK said with that hydraulic thread from Mako2. My apology Mako2 , it is correct

They stating to use a 16 H.P. Briggs and Stratton, and they talk about a 6.2 cub inch motor and then they talk about 20 Gallon per minute (20 GPM)
and at 10GPM and 2000 psi they do 344 rpm.

Lets calculate. 6.2 cubic inch = 6.2 x 2.54 x 2.54 x 2.54 cm = 6.2 x 16.38 cubcm = 101,50 cubcm = 0.1 liter per second /per revolution .
For 344 revs/min = 5.7 revs per second i.e. they need 0.57 liter per second and is thus 34.2 liter per minute. The pump gives 10 GPM = 37 liter. Good enough

It is claimed at 10 GPM and 2000 psi they do 344 r.p.m. Tugboat this is correct.

1 Gallon = 3,78541178 liter i.e. 10 Gallon 37,85 liter and 20 GPM = 75 liter.

Tugboat, you need for yourself to understand every aspect and calculate, before you make any purchase.
Bert

 

Tugboat, could it be that because the motors are probably under water and as such the cooling is superb, but maybe it is exceeding the manufacturers specs. You have to find out to learn from.
Bert

 

Bert--CDK--thanks again...Cdk- yes that thought did occur to me--seemed counterintuitive that a small engine could make such power. My thinking was that since excavators use these--it should push a good sized prop--i wasnt so sure about continuous usage - so far what ive ;earned is this--the hydraulics although in thoery should be more practical- the system seems a bit expensive and the calcs seem to sketchy for getting the right motors--there seems to be a need for a lot of finite and precise measurments for the hydraulics to work...so the D.E. system seems to be for my purposes-more practical. at the moment--of course - and without any further investigation i wont rule out hydraulics.

also I can still go single screw for ease of usage-CDK endorses it so to me that works...i have come to see CDK having a elite set of knowedge over my abilities. as do you.
so i may stick to single screw or use twin 12 hp high torque Golf cart motors--geared 6:1 to use 24x25 inch props...or a single diesel- 80 hp cont- 94 rated(for 12 hours usage running from cold start) and 101 intemerittent for 1 hour.
I wish i could find two identical EV motrs for a reasonable price..in the 20 hp range...this will run a 36 x 34 inch prop..push the boat at 8 knots

also here is my list of "wishes" for the tug
1. maneuovrability
2. economy
3 power

wish to tow a maximum of nothing heavier or push anything heavier in displacement, than a 40 ft houseboat barge--however--if needed id like to have reserve power. In case i do get a job "off the log"-requiring more power...in this case the cat is the best ..but i wanted twins screw which would sacrifice power, add agility, and economy...its a conundrum...

 

Now that I have had time to think about it, you should give a skid loader package some serious consideration.

Used and in good shape, a machine in the power range you need, is a complete package, the boom and aux. hydraulics can be directed to other uses like winches or anything needing power. Used skid loaders in good shape can be found for under 10K US dollars.

Axel RPM might be low for your needs, but that can be adjusted with sprocket sizes.

Not knowing your design, I won't say anymore. Also all this should be in the other thread.

Good wishes on your project.

Ron

 

Lets start with economy.
1) A second hand engine will not have the latest technology and a new marine diesel one is very expensive. As an alternative a smallish Automotive diesel with the latest technology from the scrap yard. You need to convert this to marine environment. This will certainly mean economy and also power.
2) power. Your efficiency in converting diesel power to hydraulics is just over 50% and converting diesel power to electrics is about 75%. Thus in both cases you need to go for a bigger diesel engine to get the same sort of overall final result.
If you really one day have to do a for "extra pocket money job", you could hire or borrow an outboard engine and this together with your single prop, you have more power. No job, you run an efficient tugboat, extra work you have the extra power needed. All what you have to do is to prepare your tugboat for an extra engine.
3) Manoeuvrability. If you run a single screw, I would have a close look at the kitchen rudder. If you go for 2 EV motors, you will have better manoeuvrability, but your overall efficiency is lower. Hydraulics is still the easiest, but need more research by you and the efficiency is way out.
What I would do? I would go for single screw with an efficient converted automotive diesel. You are in soet water in anyway. Over and above I would have an small electric bow-thruster type of setup, controlled with remote control for comfort. Extra work? I would hire an outboard motor and put the cost on the invoice.

Tugboat, at the end of the day, it is you, who must make the selection, and where you feel happy with and comfortable with. Hope we have been able to help you. I am going to sleep now.
Bert

 

Thanks Cdk--thanks Bert and RonL and all the others---ill think about all that info--when i am ready ill get back to you and let you know-- Bert--your small electrics look great and I can tell you know what your doing and I am certain things will work out for you...
ill return this thread to its rightful owner--which i meant to do some time ago...
please keep me posted as to your stability calcs...

cheers!!

 

I am still battling with the stability calculations. I may have come up with the solution. I have received good advise in the past and love to know what your opinion is of liquid steel/lead ballast. i.e. steel or lead balls, like those ones in a ball bearing mixed with oil and poured into the keels. Then blown out with a small compressor or compressed air in a bottle. This is to reduce weight during towing the boat by motorcar from home to the slipway.
Problems foreseen:
a) heavier weight pulling out of harbour onto the launch path. I haven’t come up with a method to blow it out halfway out of the water. Pouring into the keel is not a problem, can be done at any time.
b) you need to find space at the yacht club to store the containers with this liquid ballast.

Advantages,
a) The inside of the keels are not filled with water but with oil, thus rust is not a problem
b) Weight below the towing capacity of trailer and no special license required.


Bert

 

Simple solutions:
For cavities with a regular shape, use iron blocks or bars (small ingots) with lifting eyes, approx. 25 kg a piece.
For irregular shape ones, sew bags from an old tarpaulin an fill them with balls.

I take it you won't consider mercury.