Hydraulic Motor In Water

Is that all the reservoir is for? Just to allow the hydraulic fluid to cool? I was thinking it was more like the accumulator in a refrigeration system - there to allow the fluid to settle down or something before coming back into the pump. Interesting.

Instead of 360lbs of oil (assuming 60 gallon reservoir), how about a heat exchanger running off seawater and whole lot less hydraulic fluid aboard? (Weight is a primary factor for my propulsion system)

My cat requires a pair of Yanmar 30HP engines, as designed. I think I'd have to go for the 30HP hydraulic motors as well, to make sure it'll move.

I saw you were using a 100HP engine to drive the pair of 30HP hydraulic motors. Is the efficiency that bad, or do you have a lot of spare horsepower for other loads?

 

what the reservior does is twofold- it allows hot oil to flow into colder oil -cooling it- and it gets strained so the oil remains pure through the system. as in a diesel -you want clean oil and cool oil through the engines-
the efficiency is around 90-92% but theres an alt to drive and for the larger 6.2 cu.in displ. it required about 65 hp to run two pumps- i investgated this further and decided i wanted to set mine up as seperate systems so one pump per motor eliminating a large expensive flow divider. (500.00) this way i just had two pumps one for each engine..to me it seemed logical but there are other ways to go about it...it will be around the same costs in the end...as far as the 100 hp- i probably could go with smaller but it is easier to find used larger engines than smaller ones that are good- or at least in my area- i,. i found an older 6v-53 running good for 750.00 but a 65 hp volvo was 3500.00 but i will likely go with less hp than the 100 hp--it was just a liberal hp guess- at the time, i was still talking to the guys at PAL hydraulics figuring this stuff out...two 27 hp yanmars would easily push your hull ...my tug 27 ft- for pleasure use- the designer suggests 1) 30 hp..and it will still tow another boat of the same size even with that...

 

do you have pics of your build? whats the stats on it? i.e. loa etc?

 

You need a reservoir, header tank to supply head pressure to the PTO. Oil is cooled with an oil cooler. Ive never seen the oil temp rises above engine room temp. High temps may be encountered with continous operation and need a larger oil cooler. I have a 100 liter volume header tank filled with 60 liters of Shell telus32 hyr oil feeding a 30kw PTO.

 

you may be right, but in the system i had set up- there was no head pressure created by the reservoir? the pressure is created entirely by pumps...for mysystem no oil cooler is needed...i looked into keel cooling- but it would be experimental..it should work in theory...i talked to them about oil coolers but my system doesn't warrant the extra expense...

i have the diagram for the system --it is engine to pump(gear or belt driven)
pump to spool valves- spools to motors(actually it might be the other way around spools after the motors) then from the spools to the reservoirs..and back to the pumps..there are two types of circuits too...but i dont remember them offhand -but think mine is a closed type.
ill go dig up the diagram...

 

The stats on the build are:

45' LWL (longer LOA)
25' Beam
18,000lbs (9 tons) loaded down like a dog to the waterline, which it will hopefully never see
It's a displacement hull - performance sailing catamaran
It's capable of exceeding 20 knots under sail, of course in very windy conditions.

The design calls for a pair of Yanmar 3ym30's. Yes, 27HP, not 30HP, you are correct there.

That system diagram would be a great thing. Obviously, I'm just barely learning the basics here about hydraulic systems to see if it might be a good alternative to gasoline/petrol on board. Outboards are really the only other way to get the props clear of the water when not in use, but I would much prefer not to have gasoline as my main fuel.

Design objectives for propulsion are:

1) Light weight system
2) Props clear of the water when sailing

 

I'm not an expert on Hydraulics, but I have experience of setting up an open circuit on my boat and a constant pressure system HPU at work.
I have never had any problems with heat build up in my boat although I only use it ocasionally with my thruster, if I leave the pump engaged, but idle, the fluid just runs back to my filter/tank.
The system at work has a variable displacement pump and there is a built in fan and radiator type of cooler and a 100 gal tank. It runs constantly at whatever pressure you set it to. We found that, with 70 gals in the tank, if it was left running idle the oil got really hot. The vendor (he's in the US and we're in Africa) said that I should be able to turn the pressure down to as low as 600psi when the unit was on standby, but for some reason we could not get it to go below 1200psi. It went up to the maximum 3000psi from there with no problem. I checked the regulating valve on one of my visits but there was nothing physically stopping it from turning down further, unless it was set wrong internally. When the pump dead heads like this there is only a small casing vent back to the tank. I worked out that we were squeezing and heating a full tank every hour through this vent. As it would cost a fortune to get an expert out we have put another 15 gallons in the tank and they switch the unit off if it is not to be re-used immediately. When it is pumping a huge chain tensioner cylinder or a 24 ton winch it does not seem to heat up, but we have to warn the operators about the problem.
I notice a lot of marine systems using constant pressure pumps but I have no knowledge of how well they work. My experience, rather limited as it is, suggests a simple open centre system is less trouble, especially if it is only expected to be doing one thing at a time.

 

Your boat sounds awesome...
hmmmm...we are a lot alike- i get really stubborn when i want something a certain way. ok i am assuming (correct me if i am wrong)..that the reason you want your props to clear when sailing is the drag from the props would hinder performance? this might be a difficult task... gas is more flammable than diesel. true-it has a higher flash point than diesel which is very stable...but i grew up on a huge lake with thousands of boats and i dont know of one incident when a boat blew up or caught fire-well maybe one caught fire - but diesel can too--just not as easily...

- nevertheless- if you take pre-cautions and use blowers etc -its pretty safe.. i have an internet freind that built a beachable tug/dory. he had to go with an outboard. same reasons...

there are a lot of great people on here that know more than i do - but i can say that your options are limited...have you thought of an I/O unit for both sides? yes expensive...but hydraulics raise and lower the props- they use uncomplicated hydraulics that run off 12 volt systems and are reliable ..
feathering props?...have you considered electrics? they can be golf cart engines and run off an alternator from one main engine too??..still it gets complicated. hydraulic drive wont get your props out of the water when sailing--they would be fixed...as would your yanmars.
there is an old system called DP or disappearing propeller drive that was used on smaller boats. it had a joint in the prop shaft and was hauled into the boat to beach or go to shallow waters...
this seems overcomplicated to me...
to me the easiest cheapest and most practical solution would be either diesel or gas outboards or simple feathering props.. ..two small outboard engines would push your boat to hull speed im quite sure...
there is also hydraulic drive in the form of an outboard style..http://www.youtube.com/watch?v=ta5EjYYN3bk

you can of course go quite small-mount the motors -epoxy them as you said- mount under the water on long hinged steel tubes. just stop and haul them up when unreefed. they look ugly though. but work...look at the above vids for reference to outboard hydraulic motors...

gas isnt as bad as you might think --but i never discourage anyone from trying out other ideas...also look at feathering props--that should help and its easy to install and maybe the easiest way to stop drag...and you can use inboard yanmars...
i will do my best to get you that diagram..its probably buried in my tons of other boat plans- papers-designs etc... i am learning too-- so dont worry..
what i have found is that if you keep an open mind solutions have a way of finding YOU...id love to see some pics of yoiur build--bet your using lots of epoxy?? dom you find the hull to be strong? i am a steel guy but- wondered what others say about wood or fiberglass as a rigid material...?

 

one other thing i thought of--
http://www.youtube.com/watch?v=WHaTIHpuIZY&feature=related

 

Thanks for that post, Tugboat. To the annoyance of all the other members here, I have been through every possible propulsion system known to man, except hydraulic and nuclear.

The only ones that fit my criteria are outboards with a gasoline powered generator (that's why I don't want gasoline) and possible this hydraulic system.

Also, diesel engines, in my experience just run - all the time - every gasoline engine with a carb I've owned has stopped running at some point.

I do want a fully clean bottom with no "junk" below. Also, cost is a bit of a factor (as my wife reminds me).

We also need massive power generation ability to run 3-4 tons of air conditioning and heating in the boat, or hydraulic HVAC, which I just saw existed today. We do charters.

So... it may still be outboards, but those are more than 200lbs each in the size I need. They actually don't come in 30HP, nor is there a diesel outboard that is right either. The only outboards for displacement hulls are the smaller 25HP and the larger 50-60HP. They don't make a 30.

I didn't want to drift the thread too much. Everything I'm saying has been gone over a lot on this board already.

I was thinking the hydraulic system might make sense...

Re: the hull strength, there are a couple things going on. First, you have to feel a piece of core cell properly glassed to understand just how strong and light it is. Steel is very strong and ideal in impact and it deflects a little. Core cell and glass is just a rock, but it weighs like a piece of wood. I'm happy with it. The other thing going on is that the boat is engineered to be light weight, which reduces the stresses on the structural members, which in turn lowers the required weight of the member, which in turn reduced the weight of the boat, etc...

Anyway, I have several pictures of the build on this forum. I would have to find them all. We are infusing all the big parts.

 

Wolfhart, I looked at you website and have a question. There appears to be sliding motion in the alignment mechanism between the "fingers" and the somewhat spherical pieces mounted on shafts with springs behind them. Are there any concerns about wear of the sliding surfaces? Does that part run dry or is it lubricated?

 

catbuilder- (laugh)- your not an annoyance to me at all...i love talking about this stuff...i always learn in good discussions..

.I did up some 1/4" panels of core cell once--i fell in love with it--but then fell in love with nida core--if you could build a tug out of it--i'd have done it!!but then the thickness must be increased and the glassing--then steel becomes more attractive at the lower price...hmmm though maybe..what if!?...(thinking of a nice core cell tug)
I did try to find your pics but had trouble --it wasnt in your gallery--
also if your chartering--go with the diesel...at least thats what i would do--they are more reliable in mho. Hydrauics i also think would be good-- then a single engine to run twins....i think if your using enough oil and small engines you'd not need a oil cooler but check into it...they will be lighter...
if you ahve to though go with outboards..remember(and i have to remind my self of this too) boats are all about compromise..i have learned this the hard way...

im sorry to the original poster,i dont even know what this thread is about an d have to go check now to see who started it......hopefully its about hydraulics...

Catbuilder--did you use all epoxy?! if so wow!...

 

Yes, 100% epoxy, but I'm not done. I'm about 1/2 to 2/3 of the way done the surface area, but the next bit is easier... all flat panels. Hulls are done.

I welcome your enthusiasm about the build, but I'm curious... why so impressed about the quantity of epoxy? It wasn't anywhere near as expensive as Corecell.

I dug up this picture of the first hull being infused. You can see a little dry patch at the top (by the stern which is closest to the camera). That is because this picture is taken mid infusion.



I'll keep the thread drift down now... sorry, OP.

 

sorry also OP-

Catbuilder- uuuuhhhggg - got "drool" all over the comp!!



i figured epoxy would be more costly than poly- but yea the corecell--thats gotta hurt!!...wow again!..very nice..ill reference you if i ever build in this ...thanks!
yea going with hydraulics in each hull seems -at least to me--not such a bad idea--

 

to build a boat--im learning requires real patience??!!!