Friday, December 29, 2017

N6837 Basics

Our Nordhavn 68 will be hull number 37, so in common shorthand, N6837.  Here are basic specs, and some of the things that we have done differently.  Later posts will dig into this in much more detail, but for now we can cover the basics.
  • First I should say that our prime objective was to optimize for how we use the boat 90% of the time.  That means the salon, galley, master stateroom, master head, pilot house, and engine room.  Other space matters, but not at the expense of the primary space.  We had to remind ourselves of this a couple times during the process, and will probably have to do so again before we are done.
  • We picked the wide-body, or asymmetric layout.  That means there is a walkway down the stbd side of the boat, but not the port side.  Instead, the salon extends the full width of the boat on the port side.  The alternative is a walk-around, or symmetric layout where there are walkways on both sides, and a correspondingly narrower salon.  The walk-around is convenient for boat handling on the port side, but we have an alternate solution to that challenge that you will hear about in a minute.  Recalling the prime objective, we felt that more space in the salon was more important, so wide body.
  • We are going with the aft pilot house configuration.  Almost all the 68s are aft pilot house, but there are a handful of forward pilot house variants.  Again, it's about optimizing for the primary space that we use day in and day out.
  • Once again we are going with a single main engine plus wing engine.  There are lots of good arguments in the twin vs single debate, and I don't think any right answer.  We have had both, and each has its benefits over the other.  For us, a little more space in the ER, plus a little better fuel economy leading to longer range were the deciding factors.
  • This time we are going with wet exhaust rather than dry.  Like with twins vs single, there are lots of good arguments in favor of both.  On the 68, we prefer to sacrifice ER and laz space for exhaust piping rather than interior space, so decided to go wet this time.
  • Like on the 60, we are adding the extended swim platform.  We use the 60 platform extensively for kayak launching and temporary storage, and want to do the same on the 68.
 We are also doing a few things that are deviations from the norm.  Some are just important to us personally in how we use the boat, and others I think represent trends in the boating industry that are destine to be the new norm in time.
  • We are building a large inverter system (13kw) that can carry large loads, and can do load assist and load leveling for a generator.  This allows for smaller generators than are normally used since the inverters can aid in powering short-term loads that otherwise exceed the generator capacity.  This allows the generators to be sized for sustained heavy loads rather than momentary peak loads.  It also allows for a wider range of appliance use while underway and at anchor when a generator is not running.
  • We will be using Lithium batteries for the house battery bank.  LiFePO4 batteries, to be specific, with the exact brand and capacity still to be determined.  But I am certain these are the future for house banks, so we are taking the plunge.
  • The 68 normally does not have any direct access from the cockpit up to the pilot house level deck.  To get up there, you either go through the interior and out a pilot house door, or you walk around the starboard side walkway up to the fore deck, then back through to the Portuguese bridge and around to the deck.  It's not really conducive to quickly walking the port side of the boat for various boat handling operations.  A narrow body boat with walkway solves the problem, but you don't have that on a wide body.  Our solution was to borrow from the 60, and add a staircase from the cockpit up to the pilot house deck.  With that, you can walk the whole length of the port side without having to stop and backtrack around the other side of the boat.  The staircase also creates a large storage locker which is very useful.
  • The fly bridge on the 68 is normally accessed from the interior of the pilot house up a flight of stairs.  Instead we wanted exterior access.  So we have another exterior stair case (open this time) from the PH deck up to the fly bridge.  This also opens up a bunch of space in the PH.
  • Initially we had a captain's cabin behind the PH, but we found ourselves struggling to make space for the cabin, and struggling to make space in the PH.  Then we remembered the prime object.  When underway, the pilot house is like the proverbial kitchen in a house - it's where everyone gathers.  What we really wanted was a spacious, comfortable pilot house with great visibility.  So we ditched the cabin and opened up the pilot house.  There is still a day head and a little jump bed for reading and napping, but that's all.  And we now have neatly 360 deg visibility which is a huge bonus for taking in the sights.
  • For the main engine, we are going with a Scania DI-13 instead of the more common John Deere.  More on this later, including the other alternatives considered.
I think those are the highlights.  More to come over time....

Building a Nordhavn 68

It's been really quiet here for the past 6 months, hasn't it.  Sorry about that, but between cruising and the title subject, I've been really busy and, frankly, distracted from the blog.  For well over a year, we have been casually interested in a Nordhavn 68.  It all started when I walked off our boat and onto our friend's 68, Kya.  I was just stunned by the difference in space.  You wouldn't think 7' more length would make such a difference.  Our 60 is 65' LOA, and a 68 with similar extended swim platform is 72' LOA.  But the difference is huge, all because of the increase in beam.  Then, a few months later at the Ft Lauderdale boat show, I ran into Dan Streech (PAE President) one evening, and over a few drinks we solved many of the world's problems.  As part of that discussion, we talked about our interest in a 68, and that resulted in a pile of drawings and spec sheets.  All this got us thinking, but it wasn't until this summer that we got serious.

We had been on the boat for 4 straight months, and with our guest bunk piled high with storage stuff, we were reminded that some more space would be nice.   Then we looked back over the 4 years we have had the 60 and realized that we are on board at least 6 months out of the year.  When spending half your life on board, it's nice to have it be like your home.

Meanwhile, all the counter thoughts were running through our heads.  It was a lot of work to build our 60, and a lot of work to get it dialed in and working well.  Did we really want to go do that all over again, especially now with the 60 working so well?  The past 2 years have been pretty much trouble-free.  And the 68 is a lot more expensive than a 60.  In fact, that's why we never took it seriously when we built last time.  But I also didn't appreciate how much more you get, not only in space, but in systems and features that are standard on the 68, and optional in the 60.  Finally, towards the end of our spring/summer cruise as we were departing Prince William Sound, we made the call.  "Dan, do you remember our solve-the-world's-problems discussion as FLIBS?   We want to move ahead with a 68 build."

Ever since it has been a whirl wind of activity.  We spent the next month cruising from Prince William Sounds down to San Diego in preparation for the fall CUBAR cruise to Mexico, made a trip to Dana Point for a few days discussions with PAE about boat details, back home to catch up on the rest of our lives, continually intermixed with boat drawings, specification, research, etc. as we developed the specs for 6837.  Then another month cruising from San Diego to La Paz Mexico.  Now back home with the holidays behind us, we just finalized the contract on 6837.

There is a healthy build backlog currently, and our boat won't go to mold until June 2018, with completion at the factory by the end of 2019.  And we should be commissioned and done sometime in the 1st quarter of 2020.  That's a long time, but it will afford us the time to pay proper attention to the build, and an opportunity to catch up on some land activities.

As for our 60, we plan to cruise Mexico until April or May, then sell her.  Actually, she is for sale now, though not formally listed, and we have a few people who seem pretty interested.  In a perfect world, where Tanglewood goes next after Mexico will be guided by her new owners.  It could be south, north, east, west, or stay right in Mexico.  The planet is the limit.

Tuesday, June 13, 2017

Blasting Through to Sitka


The next part of our trip was a mostly business transit through to Sitka.

First from Port McNeill around Cape Caution to Fury Cove. Fury Cove is a really pretty spot, so we stayed a second day and just hung out.

Next we did a somewhat marathon run past Bella Bella and Shearwater, all the way to Bottleneck Cove.

Then from Bottleneck into the Grenville Channel to Lowe Inlet and Verney Falls. Verney Falls was really running, and all you need to do is drop an anchor in front of it and the outflow current holds your boat facing the falls. Not a bad view for the evening.

Verney Falls, Lowe Inlet, BC

Then the next day we went straight to Cow Bay Marina in Prince Rupert. Prince Rupert tends to be windy and exposed, but the new marina really makes it a much more hospitable stop than it ever was before. And the food at the Cow Bay Café right by the Marina office is just outstanding.

Fog on the Grenville Channel

After two days in Prince Rupert, we crossed the Dixon Entrance to Ketchikan where we checked back into the US. We are members in the Small Vessel Reporting Service, or SVRS, and it is working much better now. The first time we used it three years ago, the local customs office wasn’t sure what to do with us. And to this day the special SVRS reporting phone number is a disconnected line. But this time the process went very smoothly, and as always the Customs officers in Ketchikan are courteous and helpful.

We left Ketchikan first thing the next morning and went straight to Exchange Cove on Baranof Island. Then from Exchange cove to Kell Bay which is a little ways up the Affleck Channel on Kuiu Island.

Kell Bay, Kuiu Island

Then from Kell Bay to Red Bluff, then Red Bluff to Appleton Cove in Peril Strait. The stop at Appleton Cove allowed us to align our timing with yet another narrows with fast current, this time Sergius Narrows. It runs between 5 and 7 kts and is not safe other than around slack water.

An early departure from Appleton placed us at Sergius at slack water, but with a 300’ Alaska State Ferry coming up from behind us with plans to pass through at about the same time. A quick discussion with them on the radio showed that we would make the narrows about 5 minutes ahead of them, so we agreed that I would speed up and they would slow down to give a little more separation. We both made it through as planned, and the ferry overtook us shortly after exiting the narrows. A few hours later, we arrived at Eliason Harbor in Sitka and got tied up for a few days while we re-provisioned and waited the arrival of some friends who would join us for a week of cruising.

While in Sitka, Ludvig’s Bistro was recommended by a number of people, so we checked it out. Wow, really excellent. I highly recommend it if you are ever in town.

Ludvig's Bistro in Sitka - great food.

Tuesday, June 6, 2017

Yaculta and Dent Rapids

4/17/2017 Yaculta and Dent Rapids

Our past trips north through southern BC have always been pretty direct runs north our south, and we have always gone via Seymour Narrows, Discovery Channel, and Johnstone Strait. This time we decided to take the more inland route and pass through Yaculta and Dent Rapids. These are some of the more treacherous rapids in the PWN with high currents, whirlpools, and other such things unsavory for boaters.

It’s essential that you transit within a narrow window around slack current. There is about a 30 minute transit time between the two rapids, so you need to decide whether to split the difference and hit one rapid 15 minutes early and the other 15 minutes late, or time one for slack and hit the other 30 minutes late or early. Since Dent is the more treacherous of the two, we opted to time Dent for slack current, and reach Yaculta 30 minutes early.

As is often the case, anticipation was the worst part of the trip. After lots of studying of current tables and charts, and consulting with friends who had been through before, we decided to anchor the night before our transit in Squirrel Cove on Cortes Island. An early departure the next morning would put us at Yaculta 30 minutes ahead of slack, and at Dent in time for the 9:00 or so slack current.

Planning the approach can be tricky too. Leading up to slack water there is of course current on the approach route – sometimes a lot of current. Our boat can only do about 9kts, so planning needs to account for any current against us. If we expect an average 2 kt current against us, then I need to plan the transit assuming 6-7 kts of actual headway. If there is less current it’s no problem – I can just slow down. But if there is more current than expected, there is nothing I can do about it, and the result might be a late arrival and inability to transit the rapids.  So you need to err on the side of assuming slower rather than faster progress.

If the current is with us, then I typically plan around 8-9 kts of total speed including the current. That way, if there is less current, I can still make 8-9 kts, and if there is more I can just slow down, or even circle back if required.

With all this in mind, we planned our departure and got underway. But not long into the trip, I started to worry that I had messed something up because instead of a favorable current sweeping us towards Yaculta, we had an opposing current and were not making the required speed to get there in time for slack. I had been warned that although the Canadian Hydro Service (CHS) chart tables were accurate, many other tide calculators were off by significant amounts – enough to miscalculate a safe transit. Another common mistake with tide tables is mixing up daylight and standard times. Some charts do the conversion for you, and others don’t. All these questions were running through my mind as we chugged along at flank speed trying to make progress against an opposing current when I was expecting a favorable current.  It was looking like our arrival time was going to be way off.

Fortunately, the problem wasn't as bad as I feared. The initial channel that we were in had current flowing against us, but as soon as we turned into the channel leading to Dent, the current shifted around as expected and we were back on track for a slack arrival.  Phew.  Dodged that one.

Passing through at slack water you might wonder what all the fuss is about. But just go look for Youtube videos of Dent Rapids and you’ll see that the fuss is well justified.

We passed through Yaculta with favorable but safe current, and 30 minutes later through Dent with nearly slack current.  From there, we had building current behind us pushing us along.  And it was early in the day (maybe 10:00) so we pushed on.

Next up were the Greene Point Rapids.  We hit them at near peak current, but it's a much larger area and safe to transit with higher current.  Once through Greene Point, we were in Chancellor Channel and would soon face a decision point.  We could remain out of Johnstone Strait and head for Wellbore Channel and stay the night somewhere in that area, or go into Johnstone Strait and head for Port McNeill.

We decided we would proceed based on the conditions in Johnstone.  If conditions were good, we would jump into Johnstone and make a run all the way to Port McNeill.  As we approached, I saw a boat maybe 10 miles ahead of us called Drumbeat, and they were now out in the part of Johnstone that is usually the worst, so I hailed them on the radio to see what conditions were like.  Where we were in Chancellor was dead calm.  Drumbeat confirmed that Johnstone was calm too, so we went for it.

The run down Johnstone was excellent, but as we started to reach the mouth and approach Alert Bay and Port McNeill beyond that, the wind started to kick up.  It's common for the winds to pick up in the afternoon, and this seems particularly acute around Port McNeill.  Once before we arrived in 20-30 kts winds and had a hard time getting docked.  This time was only slightly better.

The further in the docks you can get in Port McNeill, the better the protection there is.  At the outer most docks, it can be pretty exposed.  This time there were a couple of slips in pretty far that were available, and I thought the wind would be on our nose once I got turned into the slip.  But as we got in, the wind must have been channeling in some way because I found it holding us off the dock, and no matter how much I ran the thrusters I just couldn't get close enough to the dock to get a line one.  So we gave up on that and pulled around the other side of the docks to a side tie where there was a lot more room, and more importantly where we were not totally side to the wind.  This time, with a little effort and some help from the captain of Drumbeat, we were able to get tied up securely.

Monday, June 5, 2017

Underway for Summer Cruising

4/15/2017, Vancouver

Our summer boating got underway early this year. There is one, and only one thing on the agenda: Prince William Sound in Alaska.

We will visit lots of other places along the way, but the one imperative is PWS. Our hopes of getting there the past two summers didn’t work out for one reason or another, but we decided we didn’t want to leave the area without going, so it’s the priority this summer because…. We are finally heading south this fall.

When we first came to the Pacific Northwest, the plan was to stay for one year, then head south. Now, three years later, we are still here. It’s an amazing cruising ground, and one well suited to our tastes. Once our world cruising is done, we think this is where we will settle down with the boat.

Back in January we relocated the boat from Seattle to Vancouver. Washington State has a complex set of use tax exemption provisions for visiting boat, but the more time I spent with it, and the more I talked with different officials, the more it became evident that the rules were unclear, and different people interpreted them differently and were giving contradictory advice on how to comply and what constituted compliance.

With a nearly 10% tax at stake, it was a gamble we just aren’t willing to make, especially when the state holds all the cards, gets to make up the rules, and can’t tell you what the rules are. Our frustration, unfortunately, is very common among visitors, so everyone flees to Canada where the rules are much clearer. It’s a shame, and creates a situation where nobody winds except Canada. We don’t get to spend more time in Washington, which we would like to. Washington businesses lose the money we spend locally on the boat and other activities. Washington State loses the tax revenue on all that we would spend. And they don’t get the use tax on the boat either.

I don’t begrudge Washington their tax structure – every state has one of some sort or another. But until they can clearly articulate the rules, a lot of people, including us, won’t go back. Oh well, enough of that.

After a nice stay in Vancouver including visits with a number of friends, we pulled out April 15th heading north. The consensus is that June is the best month to be in PWS, so the plan was to spend 6 weeks working our way north, exploring some new places along the way, ending up in Sitka where some friends would join us for a week of cruising that area. Then on the PWS.

And so began our summer cruising….

Saturday, February 25, 2017

Electric Power Strategy

Since talking about the original design of our power system back when we were specifying the boat, I really haven't said much more about how it's working, what changes we are making, and why.
I've posted this article on our solar system, this article on reworking my main engine alternator system, and this article on the relative efficiency of generating power via the main engine vs a generator.  I have several more articles is process for other modifications, but realize I've never stepped back and provided an overview of what I'm doing, where it's heading, and why.  So here's the big picture.

Solar Panels

As you read through this, think in terms of cruising for extending periods of time, underway some days, but not all, and anchored at night or for several days.  Notably absent are marinas and shore power, so the boat needs to be completely self-sufficient from a power perspective.  Loads need to be powered, and batteries need to be recharged.

If you return to a dock each day and plug into shore power, this is a much easier problem to solve.  All you need is enough power to last until you return to the dock, and shore power can recharge everything.

Similarly, if you run a generator all the time, you will have plenty of power.  As boats get larger, this becomes the norm, and if you are in a climate where you want air conditioning all the time, a constantly running generator is the practical solution.

For other boats, the power we consume comes from an alternator on our engine while underway, from a generator run periodically, or from power stored in a battery bank which of course needs to be recharged periodically.  Increasingly common are solar arrays that generate power as well.  Operating comfortably like this is our goal.   We ran for over a month last summer, never tying up to a dock, and never plugging into shore power.

All of these elements interact in infinite ways depending on how the boat is used, and how it is equipped.  It's important to understand that there is no right answer here, however I always find it interesting to see how other people have solved the problem, and hopefully our approach will prove equally useful to others.

The diagram below shows our power system.  We have ways to generate power; a generator, main engine alternator, and a solar array.   We have a way to store power in the batteries.  And we have things that consume power, some more than others.  It's worth spending a little time on the things that consume power, since they have a large influence on the over-all power system design.

Here's what we have discovered and done so far.

First, we have and continue to pay close attention to our electric loads, and select appliances that are as power efficient as possible without giving up the features we want.  I think we have been pretty successful so far, and have an at-anchor battery load that 1/2 to 1/3 what other boats of the same model report.

Relatively small loads can run off the batteries.  This includes things like lighting, entertainment systems, and various boat systems.  Heavier loads can also run off the batteries just fine as long as they are not prolonged loads.  Our house water pump, microwave, and coffee maker are good examples.  They draw a lot of power, but only for a limited time, so the total power consumption isn't huge.  The greater the cumulative load of everything, the larger batteries you will need and/or the more frequently they will need to be recharged.  Everyone needs to find their happy compromise between convenience of having gadgets, and the inconvenience of powering them.

For heavier, longer lasting loads, running off batteries usually doesn't make sense.  The batteries get drained quickly and need recharging, so it tends to make sense to just run the generator from the onset, powering the load directly, and taking the opportunity to charge the batteries at the same time.

This raises a couple of interesting questions for future articles.  For example, what is the dollar cost of generating power from a generator?  This article compares the fuel efficiency of generating power from a generator vs and engine alternator, but it is comparative only and doesn't quantify the costs in dollars.  And a related question is the cost to store and retrieve power from a battery.  It's not free.  But that can be the subject of another future article.

Batteries eventually need to recharged, and larger loads need to be powered.  We have a solar system, and it contributes nicely, but is limited by the space we have available for solar panels.  On a sunny day it more or less covers our standby loads while at anchor, but there is nothing left over to contribute towards recharging our batteries from the night before.  That still requires some other form of charging, even though the solar makes it less frequent.

That leaves us with two forms of power generation;  alternators on our main engine, and a generator.  Of the two, the generator is the more powerful with a 20kw output.  The main engine alternator is about 5kw.  If we are getting underway, we will typically just let the alternator recharge the batteries.  It can almost always do it before we reach our next destination.  But if we are staying at anchor for the day, we will run the generator and take advantage of the available power to do laundry, heat water, and of course charge the batteries.

But the decision becomes more complex when we are both underway, and when we want to do laundry or run some other larger load like our electric oven or air conditioning.  One option is to run off the alternator and inverters to power these devices.  The other option is to run the generator to power the loads, removing all loads from the alternator.

This brings us to the first enhancement we wanted to make, and the ensuing ripple effect of changes.

While underway, it is a great time to do laundry.  But it required running the generator, yet it's a very light load for the generator.  And our inverter system was 120V only, so we didn't have the option of running off the main engine alternator.  This spawned a project that I will write about in the future where we expanded our inverter system to run a few select 240V appliances - the washer, dryer, and oven to be specific.

Our inverters are capable of powering 7kw which will run two out of three appliances at the same time, and perhaps all three at once.  But our main alternator is only about 5kw, so we needed more alternator output or heavy loads will drain the bateries.  This triggered the first ripple effect and a project to increase our alternator output to about 7kw to match the power of the inverters.

Many people, including me, have increased their alternator and inverter capacity to operate some of these larger loads while underway.  Our initial focus was on being able to do laundry while underway without running the generator.  Laundry by itself isn't enough of a load to keep the generator busy, and not too large a load to power with our existing alternators, so it seemed like a good starting point.   The end result has been quite successful, I think.
One thing I have been wondering through the whole process is how far to take the alternator+inverter approach vs just running the generator.  The next questions I was facing was whether to allow for powering some or all of my air conditioning units via the alternator+inverter.  This question brought about a set of experiments that I ran last summer and reported in this article comparing the fuel efficiency of generating power via alternators vs a generator.  As a result of the experiments, it's unlikely that I will expand my alternator capacity since larger loads are more efficiently powered by the generator.

One related side effect benefit of moving a few 240V appliances to our inverters is that we now have a way to run them while on 50hz shore power.  Our washer, dryer, and oven will only run on 60hz power, or at least that's what the manufacturer says.  I haven't tried it, so am going on what they say.  That created a problem when we get to locations with 50hz shore power.

Our 120V service is 100% serviced through inverters so that always runs at 60hz.  The 240V service, however, was direct connected to either the shore power or generator.  The generator is 60hz, so that would work fine, but not sure power.

By moving the laundry and over to our inverter service, it too now always run at 60hz, so it at least partially solves the 50hz problem.   However, on 50hz shore power our inverters never switch to charge mode and just keep inverting, drawing their power from the batteries.  So there is a need to keep the batteries charged and the inverters fed from shore power.

Back when we first designed our electrical system we considered this and added a universal shore charger.  It's a 100A charger that can run on either 50 or 60hz, and pretty much any input voltage that you throw at it.  So when on 50hz shore power, the charger provides DC that keeps the batteries charged and powers the inverter, and the inverter in turn powers the 120V loads and the 60hz sensitive 240V loads.  It works well, but with the increased inverter load from the laundry, there are times when the charger won't keep up.  So, in the same way we needed to increase alternator output to support the washer and dryer loads, a project for this year is to add a second charger to double its capacity and provide some redundancy when running on shore power.  That will happen sometime before we leave North America.

Hopefully this provides a little more context for some of my more recent projects, and a few articles that I have not yet written.

Sunday, February 12, 2017

Engine Alternator or Generator: Which is More Efficient?

This question keeps coming up, and is often debated at length.  Like most endless debates, they go on and on because nobody really knows the answer.  Here's an attempt at getting to a real answer, but I'll spoil it for you - the answer still isn't super clear.....

The question, in a nut shell, is which is more efficient, generating electricity with a big alternator on your main engine, or running a stand alone generator?

One of the first misconceptions is that power from your main engine alternator comes for free because the engine is already running.  Unfortunately that's not true.  Generating that power puts an increased load on the engine which in turn burns more fuel.  It's that old conservation of energy law in physics.  It just won't go away.

Once past that first realization, the debate quickly turns to other power losses, and which power generation source has more losses.  Here's a little score card tabulating the most obvious losses for each generation source.  Once again, there is no clear winner.

Drive losses
There is virtually no loss in the direct drive between the engine and alternator
Belt drives definitely have friction losses.  How much?  I really have no idea.
Initial form of electricity
AC.  Many people don't realize that your alternator actually generates 3-phase AC.  Inside the alternator it is rectified to DC, with associated losses
Engine efficiency
This will vary with the load.  At light loads, the efficiency is noteably lower
Your main engine will be propelling the boat, so likely operating in a favorable efficiency range.
Powering AC loads
The output is already AC, so no extra losses to power AC loads
The alternators DC output has to go through an Inverter to get AC at about 90% efficiency
Powering DC loads
The generator's AC output needs to go through a battery charger to get DC at about 85% efficiency
The output is already DC, no no extra losses to power DC loads

Of course we all know that running our generator burns fuel too, so the real question is which burns more, the increased load on the main engine, or the generator?  Sitting at the helm while cruising can sometime lead one's mind to wander, and mine always seems to wonder to technical things like this, so one day I decided to measure the fuel burn to generate power from my main engine alternator.  Generator manufacturers publish fuel burn rates, so that data is know.  With corresponding data for generating power from a main engine alternator, perhaps some light could be shed on the question.

To measure the fuel burn required to generate power, I logged my fuel burn for the first few hours after weighing anchor.  The whole time I ran the main engine at a constant setting, then logged the fuel burn as the alternator output went from full output initially, down to just maintaining the underway house loads.  Using the fuel burn rate and power load at the end of the experiment, I was able to tabulate the incremental fuel burn and corresponding power generation from each of the higher output stages.

Here's what the data looks like:

Main Eng burn (gph)
Alt output (A)
Power (KW)
Inc Power (KW)
Inc fuel (gph)

So if you consider the last line as the baseline, each line above it represents some incremental amount of power generated (Inc Power column), and corresponding incremental fuel burn (Inc fuel column).  The fuel efficiency to generate that incremental power can then be calculated as show in the last column.  The resulting numbers jump around a bit, I think because the precision of my fuel burn numbers are limited, but they are clustered together enough to be generally believable, even if not exact.

With this data in hand, it can now be compared to the fuel efficiency of a generator.  My generator is a 20KW Northern lights, and unfortunately they only publish 2 fuel burn data points at 50% and 100% load.  I wanted more than that, so picked the published data from an Onan 21KW unit.

Power (KW)
Fuel Burn (gph)

At higher power levels, you can see that the generator is more efficient than the alternator, but it's not a huge difference.  And very noteworthy is the significant drop in efficiency at lower power levels where the diesel engine is less efficient.

Plotting all this on a chart helps put it all in perspective.  This chart shows the fuel efficiency of generating power in each device's native form; AC for the generator, and DC for the alternator.

From this you might conclude that for any loads greater than around 35% of the generator's capacity, the generator is the more efficient way to generate power.  That's probably not a bad rule of thumb, but there is still a bit more to the story.

Depending on your generation source, and the type of load you want to power, there might still be another conversion step involved with associated losses.  Let's look at two cases to illustrate this.

First we can look at powering DC loads, including getting your batteries charged up after a night on the hook.  In this case, the power coming out of the alternator requires no further conversion to charge your batteries.  But to charge the batteries from the generator, you need to run the generator's AC power through a battery charger, and they are typically around 85% efficient.  This favors the alternator and handicaps the generator.  The graph below shows the adjusted fuel efficiency of charging batteries from each power source.

You can see that the generator needs to be loaded to around 50% (10KW in this example) of it's rated power to match the efficiency of the main engine alternator when powering DC loads.

The second example is looking at powering AC loads like air conditioning.  In this case, the generator's output is ready to use with no further conversion, but the alternator's power output needs to be run through an inverter at about 90% efficiency.  This favors the generator and handicaps the alternator.  The graph below shows the adjusted fuel efficiencies of powering AC loads.

Now you can see that the generator load only needs to be a bit above 25% to match the alternator efficiency, and quickly becomes a good bit more efficient.

So what's the take-away from all this?  I think two rules of thumb:

1) When powering DC loads, it only makes sense to do so from your generator if you can keep the total generator load up over about 35-40%.  Note that this is the total load on the generator, not just the DC loads.  So if you have your generator on to make water or run your air conditioning and you load is up over 35-40%, then by all means use it for your DC loads as well.   But if you are just plodding along with loads less the 35%, let your alternator do the work.

2) When powering AC loads, the generator pretty quickly becomes the preferred power source, starting at around 25% load, and quickly becoming far more efficient.  For those thinking that giant alternators and inverters might be a good idea to run air conditioning on your boat, think again.  That generator is most likely the more fuel efficient way to power it.  Only modest loads make sense to power from your alternator.

Caveat emptor:

This is just an analysis of one boat and one generator, and not even my own generator.  So please just take this as what it is; just one example and not an exhaustive study.  Maybe I picked a particularly efficient generator, or maybe it's particularly inefficient.  I think it's a representative example, but honestly don't know.  And I have no idea how the efficiency of power generation from my main engine alternators compares to other, but I again expect it's a good representative example.

Monday, January 30, 2017

Propane tank level gauge

One problem I expect other cruisers encounter is knowing when your propane tank is getting low.  It's much harder than you might imagine.  Liquid Propane, or LP gas, is stored in a liquid form in your tank.  If you lift the tank and shake it, you can feel the liquid slosh it around.  The gas that is drawn out to fuel your stove or grill is the vapor that accumulates above the liquid fuel.  As vapor is drawn out, more boils out from the surface of the liquid to replace it.  As it boils out from its liquid form into vapor, the liquid level drops until there is none left, and which point your grill unexpectedly shuts down.

Because most tanks are aluminum or steel, you can't see the liquid level, so you can't visually assess how full the tank is.  There are a few companies that make fiberglass tanks where you can see the level, but they have been problematic with a number of recalls, and some refill stations won't fill them at all.  I've also heard that some countries won't allow them to be filled.

A pressure gauge doesn't help assess how full the tank is either.  Because of the whole vaporization process in the tank, the pressure remains pretty much constant right up until the tank is empty.  So a pressure drop is kind of a sudden-death indication that the tank is empty, just like seeing your grill flame go out.

Home grills often indicate the tank level by means of a weight scale.  The tank is held by a sprung mechanism with a pointer indicating the tank level as its weight changes.  But on a boat, the tank is secured in one way or another, so a scale won't work.  And for the same reason you can't easily pick them up to feel how heavy they are.

But recently, a few companies have started selling tanks with an actual float gauge built into the tank valve.  U-Haul carries them, and I tracked one down at the local U-Haul in Seattle and decided to give one a try.  It was a standard gas grill size tank, and I watched the gauge go from empty to full as the attendant filled it up.  I'd say the gauge was not exactly a proportional representation of how full the tank was, but it was a whole lot better than sudden-death.

I figured I had this problem solved - at least until I got back to the boat.  It turns out my tanks on the boat are a different shape than the standard grill tanks, standing a little taller and little narrower.   I couldn't fit two of the new tanks in my propane locker, and they wouldn't work with the lock-down brackets in the boat.  And so began my unexpected education in propane tank valves, valve manufacturers, dip tubes, and dip tube lengths.

What made the most sense was to replace the tank valves on my tanks with valves that included the float gauge.

For obvious reasons, tanks and valves are highly regulated with requirements to meet a variety of standards, be stamped with the approval numbers, inspection dates, etc.  Valves are all equipped with a dip tube that is used to prevent over filling.  There is a little bleeder screw on the side of the valve that opens the dip tube to the atmosphere.  This is opened while the tank is being filled, and vapor will come out of the bleeder while the tank is being filled.  But as soon as the liquid level reaches the bottom of the dip tube, liquid will start spitting out, and you know the tank is full.  Tanks are all stamped with the required dip tube length.  For example, a 4" dip tube will start to spit when the liquid is 4" below the valve neck.

To retrofit my tanks, I needed to find the gauge valve vendor, confirm I could get them with the correct dip tube length, then get a certified propane shop to order the valves, swap them onto my tanks, and re-certify the tanks.  I had been working with Sure Marine in Seattle on some other projects, and asked them if they could do the work if I could find the valve.  They said sure (no pun intended).

Rochester Gauges in Texas makes the tank valves with float gauges.  But the more common gas grill tanks use 4.0" dip tubes, where my tanks require 4.6" dip tubes.  That posed a complication.  Rochester did indeed offer a 4.0" valve with gauge, but the only other one was 4.7" designed for a 30lb tank (mine are 20lb).  A quick check with the folks at Sure Marine confirmed that using a LONGER dip tube is ok, but not a smaller one.  With a longer tube, the tank will just read full a little bit sooner, so you lose a bit of capacity.  But it's perfectly safe.  If you used a shorter tube you would be over filling the tank, and that's not good.

So I decided to proceed with the 4.7" dip tube valve, and had Sure Marine order two for me.  When they came in, I dropped my tanks off and they swapped the valves and re-certified and filled my tanks.  And now, finally, I have gauges on my propane tanks that at least give an idea when they are starting to get low.  I don't remember the exact cost, but I think it was about $50 per tank, much less than replacing the nice aluminum tanks that I had.

Float gauge indicating actual (approximate) fuel level

One interesting thing is that there is no mechanical coupling between the float mechanism in the tank, and the gauge on the outside.  This makes sense from a fuel/leak containment perspective.  The gauge just clips onto the valve body, and I expect uses some sort of magnetic coupling between the indicator needle and the float.

Gauge just snaps onto valve body, presumably with magnetic coupling to float

Wednesday, January 11, 2017

Some Winter Cruising in the Pacific Northwest

We are out for a little winter cruising.  We went from Seattle to Port Townsend yesterday.  20-30kt winds on the nose most of the way, but sea state was fine.  I was a little worried about getting into Pt Townsend in the wind, but it was fine.  It's a very tight dog leg entrance, then immediate 90 deg turn into the slip.  With strong cross wind, it can be interesting.  Last time we came in here was one of our first trips in the boat and the thrusters started working intermittently as we were making our entrance in a very strong wind.  I had pretty well resigned myself to hitting the breakwater, docks, or some other boat, but we managed to get in without unauthorized contact.  This time was much better.

We plan to spend the next week or two poking around the San Juans and Gulf Islands, ending up in Vancouver where we will keep the boat for a while.