Tuesday, June 10, 2014

Rethinking Water-maker raw water pre-heating

A while ago I posted about how I was going to try out re-plumbing the Kubota engine cooling system to pre-heat the sea-water in order to increase the output of our RO watermaker:

 Like all shade-tree ideas it is based on some sound reasoning:  RO membranes output is very temperature dependent.  And the warmer the input water, the more one can expect to get out of them.  So, last summer I re-routed things like this:

Good concept, bad idea.  Keep reading!

Note how the water flows through the Kubtoa engine 1st, THEN on to the watermaker!  Ha, Free Heat, Wow - really putting out the fresh water now..  This winter I am thinking about doing some more plumbing to the poor little Kubota, working to see if I can better manage its cooling and gets its operating temperate up (currently it runs around 160f or so, a bit too cool I think).  After thinking of several approaches the one I have settled on trying is a variable bypass of sea water around the heat exchanger.  Have located a sea-water safe 12v valve and will control it via the Arduino controller.

While I was at it I started wondering:  Just how much temp raise am I getting into the water maker using the above? Trying to measure it using an external IR thermometer did not give me too much of a raise.  And after all there are a few downsides to the engine-1st approach:
  • Increased hoses and complexity.  Starting to look like an early 80's GM car engine with all its hoses and such.
  • Health concern in case of faulre of engine heat exchanger, mixing coolant in with sea-water (I am not sure what the RO membranes would do and have been using low-tox antifreeze just in case)
  • Interjection of Zinc into stream of water passed on to the RO membranes, again not sure what all that does..
  • Lost fresh-water flush of engine when flushing out RO membranes after each run.

This last one kind of bummed me, as with the old plumbing every time I fresh-water flushed the RO system, the outflow would be passed down and fresh-water flush the engine as well.

So, Just for Fun I did some math this afternoon:
  • A BTU is defined as the amount of energy needed to raise 1lb of water 1f
  • A gallon of Diesel has 138,500 BTUs
  • The Kubota burns about .25 - .3 GPH of fuel
  • Seawater Pump pumps about 4GPM (per spec)
  • Rule of thumb says 25% of fuel burnt goes into the coolant (another 25% into work, and 50% out the exhaust).

So, lets do some math!
  138,500 BTU/Gal * .3 GPH  * .25(25% of heat into the coolant)  = 10,387 BTUs/hr of heat into the sea-water.
  10,387 BTU/hr = 10,387 Lbs*F/hr  (1 BTU warms 1lb of water 1f)

  4 GPM * 60 Min/Hr * 8.33 lb/gal   =   1999lbs/hr of sea water moved through the engine.
  (Sea water is actually heaver then this, but as this is the "back of the Blog" doodle, lets just use 8.33lbs/gal)

  Combine them:   10,387 Lbs*F/hr = 1999lbs/hr

  Solving for F we get:  F =  1999 / 10,387  = 0.19f temp raise.

Hum...  Less then 1 degree F raise.  Even if I captured ALL the waste heat out of the engine AND exhaust I would be looking at less then 1 degree F.

Bottom line:  It was a stupid idea and I will be taking it out next when I return to the boat this summer.

(And hey:  Math guys, dbl check I did this right.  I even worked to carry forward the Units;  my Physics teacher would be so proud!)

 4/8/2015:  Well, a Math Guy did dbl check my figures, and gave me an 'F'  (See comment below from Bruce).   Forest from Trees, did not do a simple 'sniff test' on that last formula - and the 'units' did not help me any as they were the same (and hence canceled).  So, Bruce, here we are - showing my work:

Combining them:  10,387 BTU/hr = 1,999lbs/hr  * Xf

or:  10,387 lb*f/hr  = 1,99lbs/hr * Xf

Solving for X -->    (10,387lb*f/hr) / (1,999lbs/hr) = Xf

the lb/hr cancel (See, units to the rescue!)  leaving us with:
  10,387f / 1,999 = Xf  

Xf = 5.19f     And even the units match!

So, bottom line:  I should expect a 5 degree F raise in the feed-water temperature into the RO membranes.. Using this table from Dow:

Temperature vs Rated Fresh Water Production

Degs F
Degs C
% of Rated Production









and starting with 50f water (perhaps a little warm here in the PNW), that 5 degree rise might get me an extra 7% output.   Perhaps worth it.   As of 2015 I had replumbed to remove this pre-heating.  I think I will take some actrual inlet / outlet measurments from the engine heat exchanger and see how those compair to the calculations - then deside what to do...

Thanks again Bruce, and like your You-tube clip of your rig: 


Saturday, June 7, 2014

Plans vs Intentions...

noun \ˈplan\
: a set of actions that have been thought of as a way to do or achieve something
: something that a person intends to do
: a detailed agreement for telephone service, medical care, insurance, etc.

verb \in-ˈtend\
: to want to do (something) : to have (something) in your mind as a purpose or goal
: to want (someone or something) to do or be something
: to want (something that you control, provide, or have made) to be used for a particular purpose or by a particular person

For some time folks might have noticed I have a thing against the 'P' word.  When full time cruising, Planning just does not make sense.  Planning to be somewhere at a specific time can be dangerous (weather), and it also gets one into a mindset not appropriate for the Relaxed Lifestyle.  When full time Cruising, Kristi and I found making Plans was just silly.  Things happened, weather happened, boat happened, family happened.  Plans were for the dreamers;  Ever hear the joke how to make God laugh?  Tell him your Plans.

Instead we said we had intentions.  We 'intend' to head towards Pirates Bay next week.  We 'intend' to cruise to the Gulf Islands this Spring, heck, even up to last Fall we were starting to say we 'intend' to look into Desolation Sound the summer of 2014.  (Even using the 'I' word we were careful not to look too far out, a month at a time or perhaps less, seemed about right).

But now that Kristi and I are Dirt Folks for the year I am finding the 'P' word coming into use more and more.  I 'Plan' on flying back to Viking Star August 20th, we are 'Planning' on a Dr. Visit on the 16th.  What are our 'Plans' for this weekend??? Perhaps it is a result of being in a fixed position most all the time, of having roots - roots one can make 'Plans' around.   I know, being a bit silly, but at the same time there is a different energy around the P word vs. the I word.

I like the 'I' word better...

And with all of this we have a new Plan.  Kristi and I are Planning on extending our stay in Minnesota until the 1st week of April 2015.  We will then fly to BVI to join friends on a week-long Big-Cat charter in the Caribbean (hey, not a bad way to get back on the water!).  Then it is back to Friday Harbor, retrieve Viking Star and get her ready for getting back into Intentions...

Sunday, June 1, 2014

Cost to not cruise - May 2014

For May we had a few extra costs in Travel, I purchased my tickets to fly back to Viking Star and see how she is doing.  I also have planned a few tasks:
  • Finish re-installing the Kubota DC Generator
  • Repair two rot-spots I found, and look for others.
  • Apply a coat of Cetol to the bright work
  • Re-pickle the water-maker
  • Re-prepare the boat for another winter alone :-(
  • Anything else I find.
Will be back there in August for a bit over a week.  Might get some other visiting in, but not likely.

Miscellaneous is a bit higher this month, as this is where we are putting stuff into that is more 'household' vs. 'boathold'.   OK, about it for this month.  After we get a few more months under way will be interesting to look at Land vs. Sea averages, but I think we need a few more dirt-months before we can do that.


And now here is the standard explanation: If this is your 1st time looking at costs, and want some more background on why we are reporting what it costs to not-cruise on a cruising blog - well, we are taking a break by moving back to Minnesota to help out Kristi's folks.  And we thought it would be interesting to be able to compare our costs on Land vs. on Sea., see more here:   mvVikingStar.blogspot.com/.../cost-to-not-cruise-january

For reference here is a summary of what it did cost us to cruise last year:

For Reference, Costs for Cruising in 2013
Again, following the link above will give you access to more details, or you can click on the Costs label to the right.