Propulsion suggestions

[Mako2]

We have a 30’ x 12’ x 3.5’ steel barge all .25” plate which weighs approximately 17,000 lbs. It is used for dredging around our dock area; when working it has a 20,000 lb excavator on deck along with a 5 yard container for spoils. The total weight is approximately 45,000 lbs loaded. It is currently powered by a single 150 hp outboard engine which even at half throttle supplies plenty of power for our use. We would like to replace the engine with either hydraulic drives or submersible electric drives because the outboard cooling system has trouble operating in the silt filled shallow water.

Hydraulic Marine Systems, Inc., Harbormaster, and Thrustmaster all make really nice commercial systems but they are all out of my price range.

Our primary use would be for movement in and around the dock and boat house. Most travel would be limited to about two hundred feet from the shore and is on a lake so current is not a concern. This is all personal use and limited to about 80 hours a year.

We are exploring one of two systems:

1: Using twin electric submersible motors (similar to trolling motors but much larger) powered by battery packs.

2: Using single or twin electric motor(s) mounted inside the barge with a hydraulic pump mounted directly to it (them) which would drive the two hydraulic motors mounted in an outboard configuration. This would also be powered by battery packs.

The weight of the batteries is not a major concern; we would probably use AGM batteries because they would be below deck. The batteries would be kept on maintenance charge while not in use from shore power while tied to the dock. Considerable thought was given to using a small diesel to power the hydraulic pump but with the limited use we are leaning to battery power.

Obviously with a barge speed is not a concern even empty it would only travel about 5 MPH, we are only looking for pushing power. We think a pair of 18 to 20 inch diameter propellers with a shallow pitch; slow turning would give us the thrust required.

Considering we only use the current outboard at half throttle or less (it starts to cavitate above ½ throttle, most likely because of the small diameter high pitch prop) and still have more than enough performance; it would seem we could design the system for a total of around 30 to 40 HP and still have good results.

Thank you for reading, any thoughts or suggestions would be welcomed.

Mark

[Guest625101138]

...

Thank you for reading, any thoughts or suggestions would be welcomed.

Mark

Mark
The power and prop size you have in mind with the electrics seems ideal.

Getting into proven marine units will be expensive even for the smaller units you are thinking about.

There are some reasonably economic EV motors and controllers such as these:
http://www.thunderstruck-ev.com/AC_drive_performance.htm
It starts to get complicated when you think of the gearing required and the shaft sealing. One factor in your favour is the slow speed so the housing below water does not have to be tremendously streamline. I think some sort of pod on arms that allow them to be easily lifted out of the water would be worth some thought.

It depends on the engineering skills available and if you want to do a bit of design and development.

There are some decent size systems commercially available but you need to google around and be seated when you check the prices. There are certainly some referenced in threads on this forum.

Rick W

[gonzo]

You could replace the engine on the outboard with an electric motor. That can be a low voltage DC48V or an AC motor running off the generator

[Mako2]

Rick and Gonzo,

Thank you for your replies.

Do you have a recommended RPM at the propeller? If it helps I attached a few photos of the barge as it sits.

For planning purposes am I better to start at the prop and work back to the engine that would be able to supply the torque needed to power the prop or the other way around?

What were your thoughts about using hydraulics powered by an electric motor.

Rick,

Is there a reason you recommended an AC motor over a DC. I will be running directly from battery power.

Thank you again,
Mark

[Guest625101138]

Rick and Gonzo,

Thank you for your replies.

Do you have a recommended RPM at the propeller? If it helps I attached a few photos of the barge as it sits.

For planning purposes am I better to start at the prop and work back to the engine that would be able to supply the torque needed to power the prop or the other way around?

What were your thoughts about using hydraulics powered by an electric motor.

Rick,

Is there a reason you recommended an AC motor over a DC. I will be running directly from battery power.

Thank you again,
Mark

I do not like the brushes in DC motors. They are a source of maintenance that is avoided in AC. The electronics are so good these days that even the cheap stuff gives reliable efficient operation. No more complicated than a DC controller.

Most of the electric motors used in radio control and EV these days are AC.

You would normally start with an estimated drag on the hull at the required speed. You could do a reasonable back calculation from your existing prop if you know the engine rpm and the gear ratio. So record the engine rpm at the desired barge speed. Get the prop details for pitch and diameter and the bottom gear ratio in the leg. These are usually in the outboard spec.

The design then goes into prop selection based on the required thrust at the target speed.

Rick

[gonzo]

Outboard engines run at high rpm which makes for a cheaper replacement. From your description, you need something like a 50HP motor. It should run at the same rpm as half throttle which is probably around 2800 or so.

[FAST FRED]

One big question would be endurance.

How many hours will this unit need to operate at one time.

Sounds like the power requirements are small and any 4 stroke outboard with a big prop would do fine.

Some mfg create geared OB models that swing big props , mostly for displacement sail boats, 1st choice.

FF

[Mako2]

Fred,

Thank you for the reply, as far as enduarance that should not be an issue. Almost all the time would be at or near the dock itself. Once a year I would take it to the marina to clean the bottom, about 4 miles (an hour run at the barge's break neck speed) we would have our regular boat incase there was an issue with the batteries going dead. The only problem I have had with the outboard was the cooling system, while digging there is so much silt disturbed that the system clogs.

Someone suggested converting the outboard to a remote water pickup. That is a possibility but I think we are still leaning towards the twin electric drives, most likely 48 volt motors with around a constant 12 to 15 HP each and peak in the mid 20's. With the correct reduction I should be able to swing 18" to 20" inch props. We are also still considering both direct electric and electric over hydraulic. Most of my current research has been in which motor to select. I'm sure I will have a few more questions as the choices get narrowed down.

Thanks again,
Mark

[apex1]

Cheap AC motors, cheap (Chinese) Diesel AC Genny (aircooled 1.200$) direct driven. et voila..............
These gennies live only for about 700 to 1000 hrs. But that maybe centuries in your application.

my 2c (€ Cent of course)
Richard

[mark775]

Rigs like what you have are commonly nudged around by a keel-cooled small boat. For as often as this thing moves, I wouldn't give it any repower but use the outboard when possible and get a push at other times. Maybe harbourmaster, http://www.harbormastermarine.com/ , makes a drive to suit your purpose...

[FAST FRED]

Since the power required will require a motor to operate anyway , the weight and expense of generators and pricy electric motors and dieing batteries is hardly needed.

I would use a hyd package , air cooled probably used , and cheap.

For a drive a hyd motor on whatever scrap big outboard , with blown motor you can find would do.

While hyd motors are waterproof , there really not built for sea water immersion,

An outboard leg IS.

Run it in the muck, all you fix is a prop, since efficiency is not a criteria lots of used spares can be changed out quickly.

FF

[blisspacket]

That Yamaha is probably a great engine, designed for your app with suitable torque and prop. Your local service man or a competent gadgeteer should be able to make a closed loop cooling system for it. Even a 55gal drum of fresh water and a separate electric circulating motor might work.

[kistinie]

Can you add a big fast oil connector to drive an hydraulic motor just like another hydraulic accessory you connect ?
Some Oyster boat are done this way with a vertical lifting
Can be made out of used part to be more affordable

[powerabout]

why not use an air cooled mud motor
http://www.mudbuddy.com/HyperSport.htm

[baeckmo]

Oops, never thougt I would be on the same train as Kistinie, guess the end is near.........but he's right: since you always have an excavator on board: They practically always have an oil power take off available. Use this, with quick connection fittings to hydraulichoses and a hydraulic motor at the bottom end of a vertical tube, or even mounted as a longtail engine.

Alternatively, mount a used Volvo or Merc I/O drive to the barge and connect your hydraulic motor to the inside shaft stub.

[kistinie]

Oops, never thougt I would be on the same train as Kistinie, guess the end is near.


Your are always welcome ;-)

Glad you like the idea, and i find your D.I.Y solution, excellent.
An end, is always the beginning of something else ;-)

[Mako2]

Thank you for all your replies. I did pick up schedule 80 pipe, 3 inch for the down shaft and 5 inch for the lower unit. I was going to put the hydraulic motor in the lower unit and attach the prop directly to it. Someone mentioned that with that set up there might be damage to the motor from the forward and reverse thrust with out an additional thrust bearing installed.

In the past day I have come across a pair of twin 50 hp out boards, one with a blown power head. I have an appointment to look at them tomorrow. If they are any thing like the photo I will pick them up and remove the power heads and install the hydraulic motors in their place. With this set up I will not have to be concerned about the water pick up and cooling.

As far as the motor to power the pump it will either be two 18 hp Briggs & Stratton power packs, or twin 18 hp continuous EV motors with about 42 HP peak. Either of those would be mounted below deck.

Thanks again,
Mark

[M-Sasha]

Your are always welcome ;-)

Glad you like the idea, and i find your D.I.Y solution, excellent.
An end, is always the beginning of something else ;-)

Irony is not within your very limited part of knowledge and understanding?:P

To use the new SI unit: ---80 dK---- for this one.

Sasha

[kistinie]

Irony is not within your very limited part of knowledge and understanding?:P
Sasha

Sasha, Mako2 needed help.
Sasha : your name means : Defender or Helper of mankind (http://en.wikipedia.org/wiki/Sasha_%28name%29)

I much prefer the second option as it seems you are often misunderstanding, doing the first.
I guess Mako 2. :-)


To use the new SI unit: ---80 dK---- for this one.
Sasha

80 ! Thanks, Be my guest.
But do not forget to recall all the story.

http://www.boatdesign.net/forums/hybrid/iso-normalised-electric-generator-create-jobs-31205.html#post338887

Thanks again for your help about this, my friend.


Mako2, happy to know you are on the way for a solution. Good luck !

[Mako2]

Thank you, will keep the post upto date as progress is made

[powerabout]

I like the hydraulic unit on the excavator bit, good idea.
You could even mount it on the boom so the crane will lower the prop into the water and also steer it.

Just depends on installing and removing the motor with prop on the end of the boom every time you move becomes a problem to not.

Plus's
no fouling as out of the water when not used.
easy maintainence
easy to mod
can use all around the barge so get thruster like operation

We had a similar project in the marina where I used to work and we went with the walking spud system as you needed the spuds to hold yourself still while operating so mod them to tilt. Ok if you need to move a long way, tow it?

[Mako2]

An update on our progress:

We picked up a pair of hydraulic power packs each is a 16HP Briggs & Stratton vtwin attached directly to a 10 GPM, 2000 PSI pump. We also have a pair of 22" 4 blade propellers.

We are looking at purchasing a pair of hydraulic motors to be mounted in the outboard pods. The motor we are looking at are Charlyn 2000 series because of the axial load. These are low speed high torque motors, The 8ci motor is rated at approximately 500 RPM at 20 gpm, at the 10 gpm the rpm will be approximately 350. We would be direct coupling the propeller to the motor so the prop RPM will be the same.

The 350 prop RPM should be about the same as an engine idling at 700 RPM with a 2 to 1 gear.

I would be interested in any thoughts on the combination of the motor with the parts we already have.

Thanks,
Mark

[Guest625101138]

You will be able to swing a big prop at that rpm that will give impressive bollard pull compared with what you have now.

At this stage to do any reasonable design you need an estimate of the boat drag at the target speed.

The most reliable way to get an indication on the barge drag is to tow it with another boat at the speed you would like to achieve. Need some sort of force measurement. If you are handy with hydrauliocs you can make a load cell with a hydraulic cyclinder and pressure guage.

I expect you will use a directional valve to get forward and reverse on each drive. I also expect you will also need pressure relief for the reversal and the event you drive the prop into something.

Rick W