hydraulic or electric?

Dixie Life · Apr 29, 2013

Ready to make the move on installing a bow thruster. But everyone gives different advice. So I'm turning to the pros. Here goes; A- how much speed will I lose do to extra drag (41', single, full displacement, 7.5kts @ 1800RPM) B- if I go hydraulic can I later use the system for my future plan to install a hydraulic steering system.

Phil Fill · Apr 29, 2013

If you installed a hydraulic pump with an electric clutch so it free wheel when not on, you will loosing hardly no thing. However, a hydraulic bow thrust is several time more expensive than electric. Unless you have some other hydraulic needs. The hydraulic pump/hose/tank required for a thruster is a huge over kill for a hydraulic helm. I would go with an electric bow thruster and separate hydraulic helm/steering.

The Eagle has a hydraulic pump with an electric clutch, powered by the gen set, that drives the hydraulic bow thruster but it also drive the hydraulic get home. The Eagle does have a hydraulic helm/steering but its not connected to the hydraulic pump.

Larry M · Apr 29, 2013

dhiggins said:
...how much speed will I lose do to extra drag (41', single, full displacement, 7.5kts @ 1800RPM)...

None that you will notice.

DavidM · Apr 29, 2013

Hey, we are all pros on this forum ;-). So here is my two cents:

At displacement speeds you probably cannot measure the difference with or without a bow thruster.

Hydraulic will be very expensive and not justified IMO for less than a 50' boat.

There is no hydraulically assisted steering needed on a 41' trawler. Hydraulic steering for this size boat is passive. Passive in the sense that the helm wheel is connected to a hydraulic pump that supplies hydraulic pressure that drives a ram to move the rudder back and forth. There is no external power normally. An autopilot does drive an electric hydraulic pump that is in parallel with the helm pump that drives the rudder. But this pump is very low power, maybe 200 watts and DC power works fine for this application.

I would only consider a central hydraulic system to run thrusters, windlasses and stabilizers on 50'+ boats.

David

Codger2 · Apr 29, 2013

djmarchand said:
At displacement speeds you probably cannot measure the difference with or without a bow thruster.

There is no hydraulically assisted steering needed on a 41' trawler. Hydraulic steering for this size boat is passive. Passive in the sense that the helm wheel is connected to a hydraulic pump that supplies hydraulic pressure that drives a ram to move the rudder back and forth.

I agree and think most others would also.

Dixie Life · Apr 29, 2013

Thanks guys. I guess electric is the way to go. My biggest concern was the hole in the bow slowing me down. I don't think I can take going slower than 7 kts.

healhustler · Apr 29, 2013

I agree with the above. When renting 43' diesel trawlers in Germany, I got a chance to experience their hydraulic bow thrusters, but the drive systems were also Nanni-Peachment hydraulic drives with stern mounted motors and props (17" shafts), so the pump was already there. It was a beautiful thing to be able to pull the throttle from full fwd to full reverse without even thinking about it, but it did loose a bit of efficiency over a standard type of inboard system. If you plan on making other systems like windlass, stern thruster, winches, etc. hydraulic in the future, maybe it would be worthwhile, but remember that running hydraulic lines takes a bit more space even if the devices themselves usually don't. Then there is the tank, the fluid, etc. etc., and if you haven't heard a hydraulic bow thruster going off in the morning anchorage, I can assure you that it will wake everyone in a 300 ft. radius.

Shoalwaters · Apr 29, 2013

When deciding on the power of your new electric bow-thruster, calculate according to mfg's chart then go at least one size larger. An underpowered bow-thruster is a real PITA. I would also suggest powering it from an engine-start battery, or its own dedicated battery. The sudden drop in voltage when you hit the little joystick can wreack havoc with your GPS equipment.

Boatgm · Apr 29, 2013

dhiggins said:
- how much speed will I lose do to extra drag (41', single, full displacement, 7.5kts @ 1800RPM)

Once I was working on a cruising sailboat. A lot of work was done on this drag question. As the boats speed increased the drag became noticeable but at lower speeds the effect was much less. there were two suggested fixes. An eye brow in front of the hole and a bar screen over the hole.

markpierce · Apr 30, 2013

Have no complaints with my electric bow thruster. But then it's 24-volt with an engine-powered, high-capacity alternator. No lack of power, no GPS or battery issues, whatever.

FF · Apr 30, 2013

I would chose hydraulic every time if you are going to cruise the boat.

A bow or stern thruster is nice , BUT a hyd windlass or Capstain (1st choice) is even better.

With Hyd an overload simply means the unit stops working , no white smoke or trips to the electric rebuild store.

The hyd can easily be used for a stern drum , or to lift a big dink.

Full time hyd steering has a huge advantage over the you power the rotary pump deal.

The auto pilot will not need to operate a DC 25-50A pump , off and on hours on end.

Instead tiny 1/2A solenoids will open and keep the boat on course , which is far easier than start stop 25+A for the AP.

IF you are really into desolate places Hyd can also start the main engine.

There is a big difference in cost , but then somebody said you only get what you pay for.

For utility Hyd wins hands down , IMO

sunchaser · Apr 30, 2013

FF said:
I would chose hydraulic every time if you are going to cruise the boat.

Not so Nordhavn. Up to 60', they favor electric bow and stern thrusters as well as an electric windlass, unless specified differently on a new build. Hydraulic pumps, hoses and fittings are not without their issues.

On larger vessels an electric driven hydraulic pump can be located very close to the driving propeller, crane or winch - rather than stringing hundreds or even thousands of feet of hydraulic hose to and from the main engine location.

IslandEagle · Apr 30, 2013

I will post a slightly contrarian response:

Why install a bow thruster at all?

It's complicated and expensive, it's another hole in the hull, it's another thing to maintain. And really, it's not needed.

A forty footer is not that hard to dock, a few days of practice will have you docking like a pro. Pay yourself $100 an hour for practicing, you'll still come out ahead

Scott Welch
Island Eagle (60 ft, single screw, no bow thruster)

GFC · Apr 30, 2013

I second the idea of going with a larger size thruster than what the manufacturers recommend for your boat. We were going to upsize one size for my boat but couldn't find one anywhere in the US. We ended up going up two sizes and now I'm glad we did. The boat yard did a very clean install.....

Peter B · May 1, 2013

IslandEagle said:
I will post a slightly contrarian response:

Why install a bow thruster at all?

It's complicated and expensive, it's another hole in the hull, it's another thing to maintain. And really, it's not needed.

A forty footer is not that hard to dock, a few days of practice will have you docking like a pro. Pay yourself $100 an hour for practicing, you'll still come out ahead

Scott Welch
Island Eagle (60 ft, single screw, no bow thruster)

Yes, I'm with you on that Scott. I can't remember the last time the thought entered my head that I need a bowthruster.

FF · May 1, 2013

"Not so Nordhavn. Up to 60', they favor electric bow and stern thrusters as well as an electric windlass, unless specified differently on a new build. Hydraulic pumps, hoses and fittings are not without their issues".

Nordhaven does not seem to consider an owner repaired vessel a possibility.

Electric can not be repaired by most owners underway.

Have you ever rewound a failed motor? Neither have !.

Replacing a hose or fitting is a snap, as is replacing a hyd motor or pump.

Rebuild kits are OTS for most and in most cases common tools and a clean work spot will do.

The modern aircraft setup of electric hyd provided on the spot is very expensive and not easy to repair.But light weight and great for fighters!

Remember most hyd stuff is built to common standards so a brand X hyd pump will fit where brand A unit was fitted when built.

Not so with electric motors , most are propritiary.

All choices are personal, when cruising I prefer to repair , rather than have repaired.

Guess that's why I don't have a Nordy, tho the Deerfoot 64 does look grand , but at $3.2 million a shot , a bit dear.

portager · May 1, 2013

In a hydraulic system, the majority of the run should be make with rigid line tubing and a short length of hose should be used at each end for shock and vibration isolation. These hoses have a finite calendar life and should be replaced on a regular basis (typically every 5 years). On an intelligently designed system all the hoses will be the same length so they are interchangeable, which reduces spares. Note: after 5 years on the shelf the spare hoses should be replaced and not placed into service.

The main advantage of a hydraulic thruster relative to electric is the duty cycle. Most electric thruster motors have a limited duty cycle before they overheat and the thermal protection shuts them down. In a hydraulic thruster the hydraulic fluid provides cooling to the motor so you can run them continuously without overheating (provided the pump is properly sized and the system has a heat exchanger).

Hydraulic thrusters can be made to be as quiet as electric, but they are commonly designed to reduce cost instead.

Electric thruster installations commonly use a battery near the thruster to avoid running heavy gauge wires from the battery bank to the bow and back. Make sure you consider the total weight increase in the bow. Many boats are carrying heavier anchors and more chain than the designer intended, so they are already running bow down, which can impact performance. You may need to move some weight aft (the mass time the distance to the CG should be the same) to compensate for the increased moment and restore the trim angle.

Regarding the drag of the tunnel, at 7.5 knots the drag should be minimal if it is installed properly.

sunchaser · May 1, 2013

FF said:
Nordhaven does not seem to consider an owner repaired vessel a possibility. All choices are personal, when cruising I prefer to repair , rather than have repaired.

I'm not saying what is good or bad, I'm telling you what builders are doing in regards to thruster and windlass design. The owner has a choice, hydraulic or electric with electric preferred. Weight of batteries is hardly an issue when 1000s of lbs. of ballast are utilized in the designs of Nordhavn and KK for that matter.

Maybe take up your arguments with the builders to dissuade them from building what the new build savvy group of Nordhavn or KK trawler owners desire.

portager · May 1, 2013

sunchaser said:
... Weight of batteries is hardly an issue when 1000s of lbs. of ballast are utilized in the designs of Nordhavn and KK for that matter.

Nordhavn and KK are not the subject of this thread. They are only a digression in this thread. This thread is about adding a bow thruster to the original posters Litton 41'. I could be wrong, but I don't think the Litton 41' has 1000s of lbs. of ballast. Last time I checked the Litton 41' had a displacement of 29,000 lbs.

sunchaser · May 1, 2013

portager said:
Nordhavn and KK are not the subject of this thread. .

What a dull forum this would be if we stuck to the OP's comments or questions. But that said, here goes - "Don't install a hydraulic thruster on a 40' trawler that does not have a 15 HP or so Vickers or similar brand hydraulic pump already in place on your engine. Go electric as most if not all of us do."

So would anyone care to raise the ante and comment on your after market installed hydraulic thruster system?

GFC · May 1, 2013

This thread seemed to have taken a couple of twists and turns, one of which was to question the OP's desire to have a thruster.

Shouldn't that be his decision? When someone asks for help with a problem, why do people on here continually inject their desires into the OP's world? Why not simply answer his questions as best you can and leave your opinions about what he needs to yourself?

portager · May 2, 2013

sunchaser said:
So would anyone care to raise the ante and comment on your after market installed hydraulic thruster system?

I think this might be a mute point since the OP already decided to go electric, but I would only retrofit hydraulics onto a 41' boat if I planned multiple hydraulic devices. If you intend to add active stabilizers then hydraulics are mandatory. Once you opt for hydraulics then a hydraulic windlass and/or hydraulic winches make sense. One of my pet projects has been to drive a high output alternator with a hydraulic motor because the hydraulic motor can operate at a constant speed over a wide range of engine speeds and higher speed improves cooling and efficiency.

Hydraulic systems can get quite complex, so unless you are a mechanical engineer, you may need some help engineering the system. The power source could also be problematic. Some main engines and/or generators can drive a power take-off which can be used to drive a hydraulic pump. The best pumps are variable displacement pumps, so you can vary the hydraulic power output to meet demand over the engines operating speed range. However, variable displacement pumps are very expensive. Some systems use a constant displacement pump with an electric clutch. This is OK for infrequent use devices such as a bow thruster, winch and windlass, but the on/off operation isn't good on a continual basis like for stabilizers. The most common power source is an electric motor driving the hydraulic pump. In the high power range, AC motors are cheaper than large DC motors, but if you go AC you have to run the generator to have hydraulics.

sunchaser · May 2, 2013

portager said:
Once you opt for hydraulics then a hydraulic windlass and/or hydraulic winches make sense.
QUOTE]

On my vessel I have hydraulic stabilizers, electric thruster and electric windlass. This is a very common arrangement.

hydraulic or electric?

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