I "thrust" this question before you...

[Alan Wheeler]

Hydraulics don't work by "pressure" as such. The first principle is that a fluid and in this case oil is being used, can not be compressed. So the first piece of equipment is a pump. The pump works by "pushing" the oil around the system. It is taking a mechanical motion and turning it into a fluid motion. At the other end is the machine that takes this oil flow and turs it back into a mechanical motion again. There is a resistance to motion. Firstly, there is effort required to pump the oil around the system. It has a lot of friction. The internals of the pump as small and oil which is a highly viscouse fluid, is forced through these small internals. The hoseing creates a lot of friction to the flow. Then the motor at the other end takes a lot of effort to make it turn. The load on that motor creates even more restriction to the flow. All this restriction to the flow has to be overcome to make the motor turn it's load and do the work. This is effort and the amount of effort is seen as pressure in the system. No effort, no pressure, lots of effort, lots of pressure. the turning motion comes from two things. Flow volume of oil and pressure of oil. The volume of oil determines how fast you can turn something. Volume takes power to make it flow. So a small electric driven pump can move small volumes of oil at great pressure, but you need a large engine driven pump to move a large flow of oil at the same pressure.
Because oil can not be compressed, you can not "store" pressure. It is produced solely by the work of the pump which is the work done by the motor. A hydraulic motor is called a Positive displacement pump. Each turn of the motor provides a set volume of oil. You can not alter that amount of oil per turn. As long as you have the hp behind it to turn it, it will continue to deliver the set amount of oil till something breaks.
With a winch, the amount of effort is large. It requires a large oil flow and working pressure to do the job. This will need to be done by an engine driven pump.

[GordMay]

A Thruster Article:
“Thrusters” ~ by Bruce McDugle
http://www.48north.com/aug2001/thrusters.htm

Some Additional Thruster Manufacturers & Vendors:

Hundested Propeller A/S:
http://www.hundestedpropeller.dk/default.php?id=4173

Skandvik (Max Power):
http://www.scandvik.com/index.cfm/me..._thrusters.htm

Western Marine Electronics (Wesmar):
http://www.wesmar.com/thruster.html

Side-Power Thruster Systems:
http://www.side-power.com/

QL Marine:
http://www.qlmarine.com/ql.asp

Yacht Controller:
http://www.yachtcontroller.com/

[Geoff S.]

As always, Gord, you're a veritable font of info. Mucho thanko. I will avail myself of those links, and when I come up with a new round of quasi-intelligent questions, I'll be back atcha. Thanks also to Wheels, Hello, Kirk and everybody who contributed to my education!

[Alan Wheeler]

No prob's. We'll send the bill.

[Geoff S.]

Hopefully I can pay my tuition in beer when I finally make it to Kiwiland! By the by, you don't know a delivery skipper named Mike Barker, do you? I think he's in Auckland. Good mate o' mine, currently recovering from a nasty motorbike accident a few months back.

[Alan Wheeler]

No sorry I don't. NZ has become a little more than the little backwater now. We are 4.5 million here now. Bit of a pain really. It means you sometimes have to share a beach with someone else. Only sometimes mind you

[skipperaris]

Bow thrusters can be impressive but learning the quirks of your boat and handling her without a bow thruster is more satisfying.

I have taught many sailors how to do this with their own yachts but of course we need to be on the same boat at the same time.

I wonder if I should not write about it...

[Geoff S.]

Please do write it up, Skip! And do it soon, in case you save me boocoo bucks on a needless thruster purchase and installation!

Greetings from Trini, all. It's farkin' hot here, but it's so good to be with the Old Girl...she's coming along very prettily.

[skipperaris]

OK Geoff, I'll get down to it real soon.

[skipperaris]

After two unsuccessful attempts to post it here I have finally written it in one of my sites. Go to http://www.skippered-sailing-yacht.com/advice.htm and on to the topic "Backing".

I suggest you take a printout of it with you on your boat.

Good luck

[Geoff S.]

Capt. Aris;

A most erudite dissertation, Professor. Good stuff, I will print and practice this as soon as she is floating free. Thanks for sharing the salt.

Geoff

[skipperaris]

Originally Posted by Geoff S.

Good stuff, I will print and practice this as soon as she is floating free.

Geoff

Good is as good does, Geoff but thanks for your kind words.
As I said in my first posting on this, we really need to be on the same boat at the same time for the 'lesson' to sink in. So I wrote as if I were talking to you which is the nearest I could think of to being there with you.

If you take your time with the exercises - repeat if necessary till you can really feel what the boat is doing - you will soon be an expert.

In fact I was thinking of you just a couple of days ago. The reason was a large yacht that was tied up alongside the pier and when he wanted to come away the wind was pushing him on to the pier. As the yacht had a bow thruster he felt very superior and instead of the obvious way he tried to come away with the bow thruster.

Just a little snag...
He did not understand how it worked.

Instead of thrusting to port he applied the thruster to starboard and ended up against another boat.

I was almost fast enough with the camera. I did not get the very beginning but there are some beautiful shots of him spewing out water on the wrong side and squeezing that other boat against the pier. Worth posting somewhere.

What he was doing was clear. What he thought he was doing was not.

[Rick]

Steering (and other hydraulic powered systems) may use mechanical drives or electrical drives to turn a hydraulic pump. The "static" type systems only have the pump turn when a force is required to turn the rudder by the hydraulic ram. Usually the direction is determined by the CW or CCW rotation of the drive mechanism to the pump.

At rest there is essentially zero hydraulic pressure in the system. One note is worthy here regarding the hydraulic fluid fill chamber in the pump. The steering helm pump and the autopilot electro-mechanical hydraulic pumpset (if you have one "teed" into your ram hydraulic lines with the autopilot as well as helm pumpsets having one-way check valves built in to prevent one pump from turning the other) have fluid reservoirs which sometimes are fed from a larger reservoir mounted at a location more convenient for filling and checking of the level. This auxilary reservoir can be mounted below the level of the other pumpsets if it is air pressurized to about 6-10 psi IF AND ONLY IF the shaft seals of the pumpsets are designed for that pressure.

Teleflex and Wagner (and I believe Hynautic) pumpsets are designed to handle that low "feed-line" pressure whereas the Kobelt (an excellent brand) pumpset is not. It is easier to fill and bleed a "static" hydraulic system with the pressurized reservoirs which may be pressurized to 20 or 30 psi only during the bleeding process which makes any air bubbles quite small to get them flowing out of the lines and back to the pumpset reservioirs.

The "static" hydraulic systems are very energy efficient becuase they only draw power by armstrong or only when a command is given to the pump to activate. Dynamic systems have a constantly running motor and pump with a spool valve which opens and directs the pressurized hydraulic output from the pump to the ram(s) (just like your car's power steering system) otherwise the hydraulic fluid merely circulates around a small closed system without going to a load cylinder. Yeah, I'm making this as simplified as possible and there are many different methods of controlling the pump fluid output. The main point is that if you have an engine running all of the time anyway it is easier to use a dynamic hydraulic pump system rather than deal with the problem of controlling the speed of the hydraulic pump shaft independent of the prime mover as does the static systems.

With energy conservative autopilot systems the electric motor speed, and therefore, the ram actuation speed, is usually controlled by a full-wave bridge pulse-width-modulated solid-state amplifier to give very good power and speed control without the use of a spool valve.

[Geoff S.]

Rick,

Thanks for a good overview, and for doing your best to bring it down to terminology accessible to us mere mortals. In terms of steering brands, you make special note of the Kobelt's quality, yet it is not included in the list of those able to handle the feed-line pressure...is this because it does not require it? Or is this one downside to an otherwise fine make? My mechanic has mentioned the names Hynautic and Teleflex so far as ones he likes.

Another related question that just occured to me; will it be necessary to do something to bypass the hydraulics, should we need to/want to use the emergency tiller (attached directly to the rudder post)?

I'm learning a great deal here, my friends. Continued thanks.

Geoff

[kimberlite]

My 10 horsepower thruster draws 325 amps at 24 volts- which would be 650 amps at 12 volts.
i wouldn't leave home without it.
fair winds,
eric