An Alternate Way to Build a Nordhavn 68

This story is kind of cool. Nordhavn posted on their site an article about one of their salesman’s sons building his own Nordhavn 68, out of Legos!

And.. .on a different topic:

Yesterday afternoon, two of the other boats from our Siberian Sushi Run, Seabird and Grey Pearl, met with our “Siberian Connection”. We’re still working out the details of our arrival, touring and fueling, in Siberia. I’m in Cabo, so I had to miss the meeting. This morning, in my email, were
these photos showing the terminal in Kamchatka. Reading between the lines I’d guess that our guys had questions about the terminal we’ll be arriving at.

And, lastly…

My original plan for today’s blog had been to write about my hydraulic system. It’s the part of my boat I know the least about, and I figured that writing about it would give me the momentum to dig in and study. What follows will be dull to all but the most techie of you.. so, unless you have a high tolerance for pain, I’d suggest you stop reading here.


OK, still with me? Well, then let’s take a look at my hydraulic system, which controls a few things on my boat:

– Stabilizers
– Stern Thruster
– Bow Thruster
– Anchor Windlass
– Anchor Wash pump
– Hydraulic Bilge pump
– Hydraulic alternators

Under normal operation, while underway, there is only one item controlled by the hydraulic system: the stabilizers. The thrusters, and anchoring windlasses are only used when dropping anchor or entering a port.

There is, however, one other device, or pair of devices, that might be in use at all times: the Hydraulic Alternators. My boat has two hydraulically powered alternators which generate a combined 12kw of electricity. On my prior boat, an N62, I relied heavily on the hydraulic alternators while under way, and almost never ran my generator. On this boat, I did some early testing of the hydraulic alternators, and decided they consumed more fuel than just running the generator.

I’m now thinking I should take a new look at running the hydraulic alternators. It may be that even if the fuel burn is slightly more than the generator, that the alternators are still preferable. Here’s why: Generators need a lot of love and attention. Every 200 hours, you need to replace the oil. I tend to run a generator around the clock, which means I am changing the oil about every 7-8 days when cruising. This means LOTS of dirty oil to dispose of, and dirty filters, and lots of clean oil I have to keep around. And, of course generators also need new impellers from time to time, and new belts. The great thing about the hydraulic alternators is that you don’t need to maintain them. They just pump out electricity, as long as your main engines are running. Also, since I have two, I can decide if I want to run at full, or half capacity (run just one, or both alternators).

Nothing is free though. The hydraulic system is powered by a pump that sits on the back of my main engines, just behind the transmissions. This pump creates a drag on the engine, and it creates heat in the drive train. With a little creativity, I can compute the drag on the engine, caused by the hydraulic pump. There is a formula that converts kilowatts to horsepower. Each kilowatt is equivalent to about 1.34 horsepower. In other words, to generate 12kw puts about a 16 horsepower drag on my motor. Of course, that would be true if the alternators were 100% efficient. My guess is that their efficiency is closer to 80 to 90%, and gets less efficient at lower rpm. And, this is only the efficiency at the pump. There is also some inefficiency in moving the oil around the boat, and in converting that power to electricity within the hydraulic alternator. And, to really complete the story, the hydraulic alternators are 24v dc current. If I want 240v ac current, then the power needs converted by my inverters, which, you guessed it, adds another layer of inefficiency. My guess would be that to get anywhere near 12kw, I am actually creating a 20 or more horsepower drag on my main engine(s).

 

Where is the missing power you might ask? If I consume 20hp but only use 16hp of it for conversion to electricity, where did the rest go? The answer is: HEAT. Heat is an unfortunate side-product of all this converting, and is somewhat annoying. For instance, I monitor the temperatures on my transmission while underway. The transmission running the hydraulic pump tends to be at least 10-15 degrees warmer than the other transmission.

Adding 20hp in drag to one of my main engines is fairly material. My normal cruise speed is around 9 knots, at 1,350 rpm. At this speed each of my engines is putting out around 125hp, and burning around 7 gallons per hour. I have the option of running either or both hydraulic pumps, and have always run a single pump. In other words, one of my engines is putting out 125hp, to run the boat, plus some additional horsepower, to run the hydraulic pump. Assuming the hydraulic alternator were the only incremental drag, then I would be adding 20 horsepower. However, we’re forgetting the stabilizers. The stabilizers require some amount of horsepower, and I have no idea what that is. I scanned through all the literature for my stabilizers and wasn’t able to find it. Nor do I know if it is a constant drag on the engine, or if the drag goes up as the stabilizers get more active.

 

One would think that moving those giant fins through the water would take a fair amount of energy, but how much? I did a bit of detective work, and by looking at my records on fuel consumption, I can see that the engine running the hydraulic pumps tends to use about three quarters of a gallon more in fuel than the engine that isn’t running the pump. Interesting. Were I just a bit smarter, I bet I could back into how many horsepower the stabilizers are costing me. I do have a little data, so I can ballpark it. I know that my 16kw generator eats around 1.25 gallons per hour, and I’ve seen that my 12kw of hydraulic alternator uses approximately the same ( which is what convinced me that my 16kw generator was more efficient). So … my math is not accurate, but it feels like the stabilizers eat roughly the same fuel a 8kw generator might .. or, around 12 horsepower. In other words, my ballpark guesstimate, is that if I am running with both the hydraulic alternators, AND the stabilizers, I am consuming somewhere around an incremental 32 horsepower, which translates to somewhere around an additional 2 gallons per hour.

 

Why does this matter? Well, it may not, or it may. I don’t know. I’m still trying to puzzle these things out. I remember that when I took delivery of the boat, I was told to run both hydraulic pumps if I am running both hydraulic alternators. It seems to me that I’d rather have the load balanced between the two engines. Historically, I haven’t been running the hydraulic alternators. I never run both pumps, except when running the thrusters. Perhaps I should run both pumps all of the time? I won’t bore you with the details, but I researched the spec sheet for my hydraulic pump and computed the maximum horsepower output. By my math, the hydraulic pump is capable of putting out as much as 117 horsepower, at 1,800 rpm. At the lower rpms I run, the pump maxes out much lower; probably around 80 horsepower. If I only need 32 horsepower, then I shouldn’t need both pumps. So, why Nordhavn’s recommendation?

 

Here’s my theory: Perhaps it is because of the impact the hydraulic pump might be having on my main engines. Let’s say that I’m cruising at 1,350rpm, and running a hydraulic pump only on my port engine. I would be asking my starboard engine for 125hp, and my port engine for 157hp (125, plus the 32 for the stabilizers and hydraulic alternators). According to the charts, my port engine SHOULD be running at 1,500 rpm if I want that much horsepower out of it, but obviously it can’t. The two engines need to be in sync at 1,350 rpm. So, how does it work? What happens when two engines try to run at the same rpm, but with dramatically dissimilar loads? Hmmm… My guess is that this is acceptable within a few percent, but that if you have materially different loads, you overload one of the engines, which I assume has negative consequences somewhere along the line.

 

Remember I said that hydraulic pumps are less efficient at lower rpms? My guess is that with just the stabilizers the difference in horsepower requirement on the two engines is immaterial, and I am better with one pump running inefficiently, than I would be with two. When the extra drag of the hydraulic alternators occurs, I must run both pumps, or I’ll ultimately have engine problems. That’s my thinking anyhow.

 

That’s it for today. My brain is hurting thinking about all of this, but I do think I am learning a bit with all this research! This feels like a worthy line of enquiry….

 

-Ken W

 

9 Responses

  1. Patrick: Thanks for a great post. I looked at the links you sent, and had heard about the Mustang Ocean Commander. I want to know that everyone on my boat, including myself, have the best survival suit possible. I’m not planning on swimming, but if I do, I’d like my odds to be as high as possible.

    A friend asked yesterday if we’d try to do some sort of survival suit for Shelby, our dog. The sad but true answer is: no. If the boat goes down, Shelby will be going with it. I’d like to think we could save her, and if it is possible, we’ll certainly try, but I suspect that if the boat is sinking, I’ll have bigger problems, and plenty of humans to focus on.

    As to diving: I’m strictly a warm water diver, and our plan is to take a fully equipped cold-water diver on the trip across the Aleutians. I change my mind daily on whether or not to buy a dry suit. If I meet my goal of never being in sub-70 degree water again, after this next trip, it might never be used (which would be just fine with me).

    -Ken W

  2. I guess I should clarify about the dry suits. I meant dry suit as apposed to a wet suit which most people would have on a boat for fun. There are a wide range of “dry suits” from surface level dry suits for workers on boats and even surfers, to surface level immersion suits for boat workers, floods, etc, and then there are total immersion work suits and deep sea dive suits, and finally surface level survival suits, some with floatation devices built in.

    It really runs the gamut but something like this would be good for your emergency suit:
    http://www.mustangsurvival…. (http://www.mustangsurvival.com/products/product.php?id=420)
    Or maybe even this if you are going do far north or south runs:
    http://www.mustangsurvival…. (http://www.mustangsurvival.com/products/product.php?id=599&mc=48)

    For your underwater work, assuming you don’t already have a cold water dive suit you may want to look at something like this (again if you are up north or south a lot this might not be warm enough):
    http://www.scuba.com/scuba- (http://www.scuba.com/scuba-gear-19/066871/Bare.-D6-Pro-Drysuit.html)

    One note is I read they recently changed standards and so there may be wait time to get your suit since I believe they are usually custom orders, so you might want to look into it pretty soon to find out the lead time required.

    Have you ever had to dive for repairs on your boat while at sea?

  3. Sam M: The survival suits, and the dry suits serve different purposes.

    I’m not an expert on either, so I don’t know the pros and cons .. but, my understanding is that the dry suit is for cold water diving, which I hope I won’t have to do, although I want to have the equipment on board. The survival suit is for use in an emergency situation, when abandoning ship.

    Between now and May, I hope to become intimately acquainted with both these suits. I want to do at least a couple of dive classes, and also do some abandon ship drills where we actually put on our survival suits and dive in. I’d also like to deploy a life raft….

    -Ken W

  4. KF: That’s not a dumb question. I know, because I’m not smart enough to answer it!

    I’ll venture a guess. Perhaps the horsepower required to spin the big alternators is probably more than a belt could handle? My guess is that running them via the hydraulics is more reliable than a belt-driven solution might be.

    -Ken W

  5. I’d stick to survival suits. Dry suits make great body bags; they’d also be harder and more time consuming to put on. Usually, when you need either, you won’t have time to fiddle around. But, it might be nice to have around if you have to dive under the boat

  6. Wow! Kamchatka looks like its THE tourist spot to be! I’ll bet you just CAN’T wait to get there! 🙂

    Looking forward to reading of the trip though….

  7. Patrick: A long list of questions! … following is your posting, with my responses preceded by ***

    -Ken W

    “…Here are some of my thoughts while reading, but first two questions. I went searching for the answer to the first question and came across a post about rouge waves and I was wondering if you have dry suits, especially considering your Siberian trip?

    *** We have survival suits. I will probably also buy a dry suit. As of now, I’ve never worn either, but need to practice with both before our trip begins.

    Now the question I went searching for. Do you run the ship at night and is that done via auto pilot, and what is your electricity usage at night?

    *** There is virtually no night in the Bering Sea! That far north it will be daylight almost all the time, and night won’t be very dark. We do typically run around the clock when on the move. My boat is a bad one to ask about electricity. I have lots of electronic gadgetry and probably run 10-15 amps (at 240v) at all times, plus air conditioning. As air conditioning won’t be a factor on this trip, that’s probably my total electrical consumption, 24 hours a day.

    Maybe you could run a hybrid approach and run the generator at night, or depending on if you’re at anchor or put in at night you could run the generator during the day to take the load off the engines.

    *** I have 14kw of inverter capacity, so I can easily run the boat off the inverters, and the batteries have several different ways to be charged.

    1) The main engine alternators
    2) The hydraulic alternators
    3) The generators
    4) Shorepower

    If I’m not running air conditioning, I can usually run the boat at anchor on three to four hours a day of running the generator. That said, I haven’t had the boat long enough to really say. I’ve been in warm weather climates and running the generator non-stop, because of the air conditioning.

    Also, have you looked at harnessing the extra heat via a heat pipe and create energy from it, or at the very least exhaust it?

    *** No … The second Nordhavn does have an interface to capture the heat from the generator, for hot water heating. I already had plenty of complexity on my boat, so I passed on doing this.

    What would the repair cost be for replacing a pump that died? Am I correct in deriving that it would require the engine to be out of commission, but the engine wouldn’t need anything as drastic as being pulled from the ship to be repaired?

    *** There are a great many pumps on my boat – but, I’m assuming you’re talking about a hydraulic pump, since that was the subject of today’s blog. If I had to replace a pump, I’m fairly certain I’d have to do a haul-out, and pull a prop-shaft. It would not be fun. My hope would be to run without it until I could haul the boat out. I looked up the average lifespan of a hydraulic pump, and found one estimate at 60,000 hours. That’s a LOT more hours than I’ll ever be putting on the boat, so I don’t think it will be an issue.

    Also, what are the possible side effects of one engine suddenly losing 20 HP, or your hydraulic system losing pressure? I’m assuming that if you were running both pumps and one didn’t provide the proper output in pressure that the other would compensate for any vital systems?

    *** I did have this occur last summer. I was backing the boat into the slip when all hydraulics failed. Suddenly, I had no thrusters. Luckily there wasn’t much wind, and I got into the slip without incident. A pressure gauge had failed dumping all the hydraulic fluid into the bilge. It was a total mess, but there was no damage beyond being a nightmare to clean up.

    Maybe the logic behind running the pumps on both engines is to lessen the likelihood of failure and to prevent lurching in the event the pump shut off and came back on? The engines look pretty close together and the mass of the vessel makes it unlikely but perhaps the lost of the extra HP could be enough to make someone fall or add undue structural stress? Anyhow just some thoughts while reading….”

    *** My guess is that some sort of fluid loss (a leak in a hydraulic line) is infinitely more likely to occur than a pump failure. If the hydraulic line fails, the whole system is dead. Having two pumps going won’t provide any extra security.

  8. Wow, thanks for the lesson. I’m learning a lot. Now if you can write a blog about how to make enough money to buy one of these boats I would be set! Unless you need a cook for you boat? ?

    Here are some of my thoughts while reading, but first two questions. I went searching for the answer to the first question and came across a post about rouge waves and I was wondering if you have dry suits, especially considering your Siberian trip? Now the question I went searching for. Do you run the ship at night and is that done via auto pilot, and what is your electricity usage at night?

    Maybe you could run a hybrid approach and run the generator at night, or depending on if you’re at anchor or put in at night you could run the generator during the day to take the load off the engines. Also, have you looked at harnessing the extra heat via a heat pipe and create energy from it, or at the very least exhaust it?

    What would the repair cost be for replacing a pump that died? Am I correct in deriving that it would require the engine to be out of commission, but the engine wouldn’t need anything as drastic as being pulled from the ship to be repaired?

    Also, what are the possible side effects of one engine suddenly losing 20 HP, or your hydraulic system losing pressure? I’m assuming that if you were running both pumps and one didn’t provide the proper output in pressure that the other would compensate for any vital systems? Maybe the logic behind running the pumps on both engines is to lessen the likelihood of failure and to prevent lurching in the event the pump shut off and came back on? The engines look pretty close together and the mass of the vessel makes it unlikely but perhaps the lost of the extra HP could be enough to make someone fall or add undue structural stress?

    Anyhow just some thoughts while reading.

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