small horsepower hydraulic drive

[Paul No Boat]

I have been following along on many threads about hydraulic drives and it seems that heat is everyone's biggest concern. Is this only at very high horsepower and large loads? I am into riding scale model railroads where we run all day on 8-16 horsepower gas engines hydraulicly coupled to the drive axels and see no power loss from days start to finish and they run relatively quiet. I am planning to build a catboat in the 20 foot range and think hydraulic power from an 8 to 10 horse engine would be ideal. Any comments?

[CDK]

If the losses are say 10%, your 10 hp plant will generate 736 watts of heat in the pump, plumbing and hydro-motors and you won't notice it. If the quietness and easy of installation justify it, why not? You didn't choose the most efficient way to transport energy but that wasn't your goal.

With several 100's hp and the same relative losses the situation is quite different, especially if a lot of daily engine hours are involved..

[Paul No Boat]

What I like most about hydraulic transmission is the abiity to place the engine almost anywhere in the boat and not even necessarily inline. A 10% loss of power in a boat that is already overpowered to accomidate a generator or other systems would probably not even be noticable.

[gonzo]

It is a heavy inneficient drive. Losses of 25-30% are common. Hydraulic drives are good for winches and other uses where overload is a possiblity. The release valve prevents the system from damage. As a drive, unless you have a really unusual configuration it is not efficient.

[Willallison]

Vetus make a range of small hp hydraulic propulsion systems. www.vetus.com

[Paul No Boat]

I can see where hydraulic drives are inefficient in huge machinery including boats or in performance boats that are changing their inertia a lot but I don't understand the losses in a small boat such as a 20 ft catboat I am wanting to build. after all hydro drive is in our lives everyday in the form of an automatic transmission in our cars or power steering to garden tractors and nobody seems to give it much thought. I just like the idea that you can install the engine almost anywhere in any position and that if built using standard parts is easily maintained. and forward/reverse is nothing more than a simple valve. I love simplicity.

[marshmat]

Losses of 25-30% are common

Perhaps if the system is built from cheap gear pumps, gerotors and the like. But good quality, variable displacement piston pumps and motors are readily available with around 95% efficiency- for a pump, motor, and losses in the hoses, valves and cooler, total losses due to the hydraulics shouldn't be more than 15%.

Specify good components according to sound engineering principles, and it should work reliably for years. Specify cheap crap from the bargain bin (as is often done), and you'll be wondering why your pumps keep leaking and your fluid reservoir smells like burning.

Cooling won't be a show-stopper on a 10 hp, 2000-3000 psi system for a boat, certainly not when compared against a 500 hp, 6000 psi system for a concrete pump or excavator. The operating temperature, the oil's viscosity/temperature curve and the pump/motor's viscosity requirement all have to coincide- shouldn't be too hard to do with low loads and lots of water around.

The trickiest part, IMHO, would be if you want to automate things a bit, ie. a load sensing pump or auto-throttle on the engine, so that you wouldn't have to manually match the engine throttle and the pump displacement.

[Paul No Boat]

In the type of boat I am considering simplicity would be the order of the day. A boat typically powered by 5-8 horsepower. I would only be using a larger engine of 8-12 hp to power a generator and because the v-twins are so much quieter and smoother than singles. Not much more than a cub cadet garden tractor really.

[CDK]

When may we expect "Paul With Boat"?

In my humble opinion there is nothing to say against such arrangement (Matt and CDK pointed already out where some restrictions are)

BUT........installing the engine "where you want" is unfortunately not that easy.
Weight distribution in the boats ends, and the fact that IC engines do´nt like to be operated at heeling angles restricts the choices of installation, and commonly one ends up with a engine near the centre of movement again.

Yeah, and "Paul with boat" would be nice!

Regards
Richard

[Paul No Boat]

Ok guys, Got it. I should design some credibility into my name. I guess I could just as easily join a flying website and call myself "Paul No Learjet". lol

actually, I would be operating this boat on an 11000 acre lake in the midwest with light winds so it would be used more as a launch than a sailboat so heeling would not be as much of a consideration but I do see Apex's point that there might be other considerations than just engine placement or simplicity of transmission.

Location and heeling angle would be a consideration no matter what drive system is used. If the wind is strong enough to heel the boat why would I be using the engine anyway?

I am seeking a set of plans for John D. Little Catboat and posted but so far no replies. I know Mr. Little is deceased but his designs were sure beautiful and this is one of those common cases where a boat might be built but rarely sailed.

I joined a forum about it but there has been no posts in several years.
here is the boat I am seeking. http://www.sailblogs.com/member/flanderscat/

any help finding this plan or a very similar one would be appreciated.

Oh, ja, now I know which sort of boat we are talking. (did´nt even know what a cat boat is). I agree, that for such size of boat we are not talking about heel angles when underway, especially not on that lake. But bear in mind that you do´nt need much weight in the ends of the boat to keep her sailing performance!

Good luck!
Richard

[Paul No Boat]

Yeah the hydraulic system I would require would be not much more than that of a log splitter. We run them all day on park trains with no seeable losses or problems.

[marshmat]

Sounds workable to me.

Just don't try to put it together out of leftover bargain-bin parts. If you swipe a cheap gear pump off a logsplitter and couple it to whatever five-cc gerotor happens to be in the bargain bin this week, you'll probably be disappointed.

If you take the time to sort through the catalogues for a properly sized, variable displacement piston pump and a suitable motor (the ratio of pump to motor displacement giving your RPM reduction), and you actually sit down and do the pressure and flow calculations for the circuit, you should be able to make it work for your stated requirements. You might even find lawn tractor parts that are suitable, if you hunt around long enough and dig up actual specifications for them.

[Marine Nut]

I recently found this article as I was doing some research.. It may offer some insight to the "hydraulic question"

http://sbmar.com/main/articles/some_...ven_sailboats/

Cheers

Marine Nut