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Old 27-05-2006, 10:26   #1
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I "thrust" this question before you...

Okay, I'm seriously considering spending the stupid money for a bow thruster. She's such a cow in port, God love 'er, and soon her topsides will be perfectly pristine and it would be nice to keep them that way. I had financially triaged this "toy" way down into the "someday" pile, but Tom Neal's recent article in Soundings has renewed my Thrust Lust, and I'm at a juncture in Diva's refit where it makes some half-assed sense to do all the serious fiberglass surgery I intend to do now, before the final fairing and painting.

Intelligencia, help me out re spec'ing the proper thruster: I've heard that freeboard is more the issue than displacement. Given she's high and dry, and has been for years, and it's anybody's guess where her new waterline will be, I'm not sure how to figure her freeboard. But otherwise, here are her specs: 53 on deck, 59 overall, ketch rigged, full keel, 6 foot draft, 46,000 lbs. I'm no mathematical genius, so figuring the square footage of her area above water is going to be a bit of a challenge for me; but I am headed down to Trini in a week armed with 100' tape measure.

How bullet-proof are the working guts of a thruster? Should I be tempted by a used offering of undeterminable hours (there are three currently at Sailorman) or avoid it like the plague? And if you have one, what brand is it and how do you like it? Given I'd most likely be using it while the engine is running, is there any reasoning against a 12v model, as opposed to hydraulic?

Thankee,
Geoff
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Old 27-05-2006, 10:36   #2
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I know this will be only minimally useful, but... My neighbor has a 37' Spray with bow thrusters. He uses the extensively. He singlehands about 4 times a week, and I do not think he could dock without them as he is so used to having them. Our harbor is very dirty. We are fed from two seperate rivers, and the debris in this harbor has clogged many a raw water intake. He has experienced no problems with the thrusters over the past 3 years. They are 12volt. He has come in under sail once due to engine problems. The thrusters were invaluable getting him to the slip. It is not a luxury I would spend money on for my own boat, but it would be a desireable feature if I were purchasing a new boat.
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Old 27-05-2006, 12:00   #3
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The thruster’s size (lbs thrust and tunnel diameter required) is determined by the boat’s effective projected area (windage, or freeboard), the thruster’s fore and aft position in the hull, and the design wind speed. Manufacturers and installers will calculate your recommended thrust power.
Except for the smallest (and the very largest) thrusters, Hydraulic motors are generally preferred over electric. Thrusters generate around 25 pounds of force per horsepower. At 12 VDC, each H.P. requires over 60Amps.
Given a 50 something foot boat, and minimum performance requirements, you might want at least on the order of 200 to 300 Lbs of thrust, requiring 8 to 12 HP (>500A - 800A @ 12V, or > 250 - 400 A @ 24V). Higher performance would require significantly larger thrusters.
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Old 27-05-2006, 15:18   #4
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Gords spot on (as usual ) and the manufacturer will best spec what you need. You can then use that spec to determin if the secon hand units are a viable choice.
It should also be noted that electric units are rated for short term use.(short duty cycle) That is also determined by battery capacity as well. They suck up a lot of juice. Hydraulic is virtually 100% duty cycle. But you need an engine with enough spare Hp to drive the pump.
Electric units tend to be lighter in weight, and hyadraulic much heavier. The Electric "unit" tends to be cheaper, but can be expensive once you figure in batteries, charging, cable, splitters and all the other requirements. Hyadraulic "units" are much more expensive, but tend to come with all, bar the hosing. Hydraulic hosing and fittings are expensive and take room to layout. This stuff needs a good coduiting system run throught the boat for easy installation. It's not so easy to turn corners and pull through tight spaces as electrical cable is.
Hope this is helpful. any other questions?
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Old 27-05-2006, 16:18   #5
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Wheels, you'll be sorry you asked: This subject begets many more subjects. This sudden renewal of my interest in the subject is partly fueled by the used thrusters which have surfaced lately at Sailorman. Their prices are attractive compared to new (about half), but of course there's the spectre of unknown use and abuse lurking. The power aspect actually opens up a more global can of worms for Diva in general. She had a hydraulic system on her when I got her, which as far as I can tell was only there to run the windlass. It leaked, the main unit was fickle, and I ended up with my first taste of hydraulic anything being pretty unsavory. I was first counseled by my mechanic in Trini to eliminate the hydraulic and go dc electric for everything, including the windlass, creating (as Alan so well detailed) entire separate battery systems for high-load items like windlass, autopilot, etc. Just recently, he has recanted, and now advocates restoring an hydraulic system to make her steering hydraulic; evidently my current mechanical cable-driven rig has some fatal geometric flaws. So, domino effect prevailing, I'm wondering, if we put in a hydraulic system anyway, why not run pipes forward again and use it for windlass and thruster too? Given I've seen what can happen when hydraulics fail, I'm a little concerned to suddenly be considering making my whole damn boat practically 100% hydro. Plus, motor must be running to keep pressure up, right? Then, how do I steer while sailing without running the engine? Perhaps I've just psycho-analysed myself back to a more important question (hydraulics vs. electrics in general) that must be answered before I can consider the thruster thing. Thanks, Doctors. Is my time up? If not, feel free to weigh in further...
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Old 27-05-2006, 17:00   #6
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Geoff, hydraulics are rare on small craft mainly because of the added expense and space taken up by adding the pump unit. But, they control most commercial aircraft control surfaces (reliability being a Very Good Idea for that<G>) and all the earthmoving equipment. Not to mention shipboard uses in ships.

So, there is reaason to believe that hydraulics can and do work, robustly and reliably. Since you aren't trying to seal electric motors underwater, they don't suffer from all the potential problems of that. What you basically are looking at it plumbing, and if it is done well (proper hoses, proper connections, quality seals and time taken to install it all properly) the stuff is nearly bullet-proof. A "failure" is likely to mean a pinhole leak, which can be sealed, or a ruptured hose, which can be spliced, or a blown o-ring, which again can be replaced. And some more hydraulic fluid. If flex hoses are replaced on schedule (i.e. every 5 years) and you carry a selection of critical spares, you shouldn't have any surprises that are more than short delays. Plus, aviation and earthmoving repair shops are often more common and less expensive than marine sources. (Well, the earthmoving side at least!<G>)

If your mechanic hasn't had much experience with hydraulics, I'd be more concerned with how fast a learner he is, and whether you want him learning on your installation. I mean, it is just plumbing--but have you ever tried to find a good plumber?<G>
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Old 27-05-2006, 19:11   #7
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Hydraulics is a contentiouse issue. Ther are three main system types. Manual only, found mainly in steering systems and ram application on stay's etc. Electric drive of which there are two types. On demamd flow and and constant flow and then there is the engine driven constant flow system. Each respectively becomes more complex and thus more expensive and each respectively has advantages and disadvantages.
A large hydraulic system done correctly and well maintained can be very clean. Aircraft systems for example. You don't expect planes to drip oil for example. You certainly don't want oil dripping into your bilge. And you should expect that a well built system would not. However, eventually seals wear and something will drip, so it is a case of keeping a watch and carrying out maintanance when you see something.Hydraulics is one of those items that you maintain when you see a problem, not- '"oh I better get to that one day".
Hoses don't wear out. You only see hose failure on systems that are under hard abusive loading and shock. Such as an earth moving machine, where hosing flexes with extreme pressure pulses. If the hose has been spec'd for the load in the first place, well laid out and joints well protected, they should last forever. The big disadvantage and criticle aspect of large systems on boats, is that you require special machinery to crimp fittings. You can not do this yourself. A crimping machine is unbelievably expensive and very heavy.

OK, lets look at a system in respect to your boat.
Firstly, my opinion is keep stearing seperate to any other thing on the boat. You don't want a failure that makes you dead in the water. Second, you don't need a complex system for hydraulic steering. A steering system more than capable of handling a boat of your size is a simple helm pump at each wheel, low pressure (1000-2000PSI) plastic tubing, an electric hydraulic "on demand" pump for the auto pilot and a ram sutible for the rudder. The Ram and pumps are spec'd to suit the steering demad of the boat. All valving is usually fitted to each pump. I my opinion, I wouldn't have any other form of steering in any boat that is larger than tiller steered.

The next version if the system is for very large vessels that have generaters or some motor running for the hydraulic pump. These are large flow volume systems and have higher capacity and pressure hosing. The steering is done via valves being open and closed to control flow. Much like a power steering system on a car. On none sailing vessels, the pump is simply run off the engine.

Which brings me to the last point. Constant flow is what is rquired for the winches and bow thruster systems. Of course, you are always running your main engine when applying either of the other two. So hydraulic on these would be fine.
the one important point, as I said int he earlier post, is about available hp. Hydraulics are very inefficient. Most of the energy goes into trying to push a viscouse susbtance around through little galleries and hoses and connections. There is a lot of friction and it produces a lot of heat in the oil. All this robs the engine of hp to do a simple job. So if you have say a 10hp thruster, you need the main engine to produce 10hp PLUS the additional loss of running the system, which is very high, so you could need as much as 15 -20hp over top of what work your main engine is try to do to bring you in or out of the birth.
No I don't mind the questions. This is complex stuff, So keep firing away.
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Old 28-05-2006, 12:26   #8
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Geoff,

I'm certainly no expert, but...

I'd be more than a little suspicious of a boatyard mechanic who once convinced you to convert everything from hydraulic to electro / mechanical... and then advocates you change back to hydraulics.

It sounds to me as if he didn't do his homework the first time around and now he's trying to cover his tracks - at your (great) expense.

Something smells fishy down in Trinidad.

Consider having an accredited marine surveyor look into this before you proceed.

And I'd be looking for another mechanic, too. It sounds like this guy is taking you for a ride.

Kirk
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Old 29-05-2006, 08:55   #9
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I appreciate your concerns, Kirk, thanks. It's really not the mechanic's fault; I have been sending some seriously mixed signals about what I want and when I want it. To be honest, I do not reside anywhere near the proper tax bracket to be rehabbing a 50-something-foot boat. I vacillate between Poorhouse Panic and Optimistic Gold-plater on a weekly basis. Plus, Diva is a very odd boat. There might be few other examples of the Cuttyhunk mold out there (and I've been searching for them; let me know if you ever hear of another one), but except for the hull, she's a one-off. And her original mechanicals appear to have been an afterthought. No, I think I'm a fair judge of people, and have learned the hard way not to suffer fools for long; and mechanic Morton is one of those crusty old German ex-pats who tell it like it is. He's probably said bad words in Deutche connected with my name more than once.

We've only recently dealt head-on with the bad steering geometry (which I knew was there; on our near-death delivery trip the gear kept walking down the shaft and the binnacle chain would rub against some hex bolts in the bulkhead...chain broke at least six times, usually at the worst possible time). It doesn't surprise me much that he's not sure there's proper swinging room in there for a proper rig, and it's definitely a royal PITA to work on. It will be only tighter in there when we mount the generator above the engine, another project we're just getting to now.

What I need to do is commit to, and plan for, her major high-load systems. Of course, I want it all: windlass, thruster, autopilot. My opinion of hydraulics were skewed by a bad first experience with an ancient and poorly-maintained system...comments above (thanks, gentlemen) have largely straightened me out on that topic, and it's sounding like hydraulics indeed may be the simplest and most rugged approach.

So, Wheels, back to Hydraulics For Idiots...I'll practically always have the engine running when I'm using either thruster or windlass; do I need to have something running to keep the pressure up for just steering? And what about an hydraulic auto-pilot? Lotsa beef there, I've got to think it needs energy needs to be continuously fed into the system...
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Old 29-05-2006, 13:18   #10
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I suggest you keep the stearing seperate to the rest of the system. You need steering to be as bullet proof as possible. Plus a steering system can be designed to be totaly none reliant on external power, all except the autopilot pump, which is "on Demand" only. So in otherwords, it only runs when the pilot says I want to turn slightly to correct course, then the pump shuts off.
The system needs to be correctly designed for you. the design should be free and then you can get an idea of price from that and see if you are in the ballpark. Then installation is easy, with the main engineering part being the fitting the ram to the rudder.
I suggest you contact marine steering companies that have Hydraulic steering. Seastar and Hydrive come to mind, but if Gord is reading here, then Gord, maybe you could come up with a list of companies Geoff can contact. I have to get to work right now Geoff, but if gord hasn't seen this, I promise to do some research tonight on who you could contact.
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Old 29-05-2006, 13:48   #11
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Basic (manual) Hydraulic Steering Systems are powered by the Helm Pump (wheel), and do not require an external source of power. External power is only required with Autopilot steering systems.

Hydraulic Steering Systems are offered by Teleflex, Hynautic, Vetus and others.
For lots of good information, goto Teleflex and select: Hydraulic Steering (seastarsteering)
http://www.seastarsteering.com/
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Old 29-05-2006, 13:54   #12
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In Other Words…

In a hydraulic steering system, the helmsman is the pump.
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Old 29-05-2006, 22:22   #13
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Well, actually to be picky. No, the pump is on the back of the helm. The motor is the helmsman. (its called an armstrong model;-)
Reminds me of a story when I was a Kid of about 8. My Dad went to borrow a concrete mixer. He rung a friend of his and the friend said yep I got one. It's an armstrong concrete mixer. We went around with car and trailer to pick it up. But Dad stopped short and said, but it's missing the motor. The guy replied, yeah, it's an armstrong model. Huh!?!?, You know, Armstrong, you need a strong arm and you turn it with the handle on the front of the mixer.
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Old 29-05-2006, 22:55   #14
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Any old trucker here in the states can tell you about armstrong power steering
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Old 30-05-2006, 11:58   #15
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Thanks, Gord for the Teleflex link; I've downloaded their custom quote page and I'll fill it out and see what they say.

Okay, so I'd want two completely separate hydraulic systems, then? One (non-powered? Is that a fair way to describe it?) for the steering, and another for all the other stuff? Is there anything that maintains the pressure in the steering system, or is simply pre-pressurized and left that way? And then, in the case of the autopilot, how is the on-demand pressure applied? Electrically? If so, hopefully the amp draw to keep hydraulics up is a lot less than an actual dcv autopilot would need.

I appreciate your collective patience with this remedial student.
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