The Re Power, Part 1

Yanmar 3JH5e

The re power process has been difficult for White Pepper. The first difficult decision was in February 2014 whether to re power the boat or not. The price to re power would be 25% of the retail price of the boat. This decision took about a half second of debate and discussion.  Someday Jan and I will not be able to continue the cruising lifestyle, but not this year.

The second decision was to continue with Yanmar. Yanmar did not cause the engine failure after 29 years.  I am still not clear what caused the failure although the transmission had a lot to do with it. If pressed I would say that an incorrect choice of transmission fluid was the proximate cause.

The next question was horsepower. White Pepper has always been under horsed. Indeed, these were the very first words from her original surveyor, Mr. Kershaw, in 1989. It has not been a problem until recently. The rule of thumb is that race boats should have 1 HP per thousand pounds of displacement.  This description fits White Pepper with the 3HM.  A cruising boat should have 2 HP per thousand pounds which works out to about 40 HP for the old girl.  The new C&C 41 by Alerion  will have a Yanmar 3JH as standard equipment.  The most capable cruisers will have 3 HP per thousand pounds which is way beyond what White Pepper can accommodate in her stern.  So the Yanmar 3JH5e, with 39 max. HP  was chosen.  The 3 stands for 3 cylinders.  The JH is the new line of high torque, low RPM, low exhaust engines from Yanmar. The 5 is for the fifth generation in the JH family. The "e" is for naturally aspirated, although some bloggers say it stands for export.

Choosing a mechanic was done on referral during the social hour at beach church at George Town, Bahamas. Cookie Monster recommended Al Blande of Al's Mobile Marine in Palm Coast, FL. Saber Tooth at St.Augustine seconded the recommendation.  Al was a great help over the phone at West Palm and in person at St. Augustine.  See earlier posts for details.

Matching the prop to the engine is extremely important.  This was subject to an earlier post which may need to be amended.  But for now an 18" x 15"  3 blade seems to fit.

Finally after months of waiting Al had assembled all of the necessary pieces and was ready to go in the last week of August, 2014.  Jan and I drove out from Texas to "help". The actual installation will be the subject of future posts.

The Story of Tabu

The following post is a mostly true story that happened several years ago.  Some of the names have been changed as I plan to return to George Town again next year.

John motored over in his fine dingy just as I was climbing into my C&C 41, White Pepper.  "Are you coming over to the benefit for Tabu on Sand Dollar Beach tonight?  Remember we discussed it earlier."  I did remember vaguely.  Jan was back in the USA, and I was at loose ends.  I made an extra strong rum drink and headed our trusty dink, Habenero, to the beach. The party was the usual pot luck beach rum bust that happens often in George Town, Exuma, Bahamas.  This one was different in that it had a guest of honor--Tabu.  John introduced me.  Tabu was a slight, gentle, pale, blue-eyed young man with a gentle French-Canadian lilt.  However, the body language and syntax instantly communicated "whoa, different planet here."

I knew who Tabu was.  His home was a derelict 26 foot yacht anchored 200 yards south of Volley Ball Beach, the epicenter of cruiser life in George Town.  I had passed it numerous times. At the sound of a motor a curly head would usually pop up, look around, wave, and then disappear.  He had occupied the same spot for two years.

Later my friend, John, filled me in on the details.  Tabu liver alone and supported himself by doing commissioned art.  Commissions being few, Tabu had become intensely interested in trash.  While he never actually begged hand outs were graciously accepted.  Rusty cans were welcome.  Left over lemons, limes, indeed any spices were actively solicited. Over dinner one night John showed me some of Tabu's art.  It was exquisite.  The small oils had a precision and vividness that were astonishing.  The colors were "too bright." Overall they reminded me of art created by autistic artists.  Later I saw some very abstract paintings that contradicted my initial impression. Regardless, with his overall appearance and his reduced circumstances there seemed to be something very chromosomal about Tabu.

To understand why 40 sailors were toasting Tabu that lovely March evening while hundreds watched in stony silence from their yachts, I have to describe George Town. The Bahamian George Town is a lovely settlement of 1700 gentle souls and is the regional capital of Exuma, a province of the Bahamas.  The George Town known to the boating community is an evanescent gathering of 300 to 400 yachts that arrive every winter season in the large roadstead called Elizabeth Harbor between Great Exuma Island and Stocking Island.  They start arriving every November to anchor and enjoy each other's company. We number 600 to 1000 sailors and become the second largest village in Exuma.  This community brings with it all of the strengths and foibles of small town America.  There is a mayor (by acclamation), a town council (volunteers), a town hall (the St Francis Hotel), a rec center (the volley ball courts on Volley Ball Beach), a bonding festival (the Cruiser's Regatta) and beach church.  I have come to thoroughly enjoy my visits to George Town.  There are also many explicit rules and implicit mores.  Tabu lived on the fringes of this community and had committed outrage.

Let me count the ways.  First of all Tabu was being expelled from the choir of beach church.  Tabu could not sing a lick.  None of the other choristers could either.  The only one who could sing at all was the choir leader who was also the mayor's wife.  She could sing like an angel but tolerated no nonsense.  Tabu had announced that he could not attend mandatory practice sessions because of the wind.  The winter had been especially breezy, and Tabu had to row everywhere. Tabu also had a sweet tooth.  After beach church he would eat ALL of the pastries offered during the social hour and, of course, never bring any of his own.  This gauche had earned a stinging rebuke from one of the ersatz vestry.  What had brought this simmering pot to a boil was that Tabu fished for sharks.  Without refrigeration he needed to catch a shark about every three days to supply his protein needs.  In order to catch sharks he would chum the water, presumably with the remains of his previous catch.

Now no one likes to have sharks about, especially 200 yards from where children are playing in the water.  An emergency meeting of the town council was called. A new rule was announced--no fishing in the harbor and especially no chumming allowed. Never mind that this new rule was contrary to current Bahamian law.  (In 2013 the Bahamian authorities did declare Elizabeth Harbor a no-take zone.)

Every community has a bully, and Wanderer was ours.  Wanderer was a loud and large man with bulky boat parked too close to the beach. He claimed to have two shot guns. Tabu and Wanderer had a confrontation on Volley Ball Beach.  Curses and shoves were exchanged. In this crises John and some friends (not me) went to speak to Wanderer.  He was unrepentant and aggressively asserted that he would indeed fire on Tabu if he continued to fish for sharks.  To be fair a few strong souls spoke up for Tabu at next Sunday's beach church and also at "open mike" on the 8:30 am cruiser's net on the VHF radio.  Later in the week John organized his "benefit" for Tabu on the beach.

Back at the party Tabu had brought for his contribution--a series of dips for the chips.  These were flavored with the rinds and left overs I mentioned previously.  He also used the rinds for pigments in his paints. I suspected that the chief use of these condiments was to mask the flavor of rotten shark. Naively and politely I sampled each one.  They were very tasty, but they were also unrefrigerated.  Later I paid for my indiscretion with two days of fever, vomiting  and copious diarrhea.  After a bit there were some heart felt speeches and the hat was passed around.  I threw in a twenty.  Tabu was sincerely touched  He announced that "you are my family, and I will live here forever."  Someone made a bonfire, someone else broke out a guitar, Tabu played the tambourine. We sang and drank the night away.

I wish this story had a happy ending.  I wish it had an ending at all.  You see, Tabu had aggravated the Bahamian authorities as much as the cruising community.  They refused to extend his visa.  He had to leave and soon.  One day Tabu came up on the net and plaintively asked if anyone had a courtesy flag for the Turks and Caicos that he could "borrow."  The next day he again came on the net to sincerely thank all of the friends he had met in George Town.  The next morning he was gone.

The weeks passed by.  After Easter the mayor departed with great fanfare on the VHF radio.  Later most of the town council left for Florida.  The anchorage thinned out.  The best Christian I have ever met, John, left for somewhere "south."  Net Control, the heart beat of the community, faltered and failed.  Beach church had one last service.  The community was dying to be reborn next November.  Finally on one brilliant morning in late April with a steady, fair wind from the south and with Jan back on board White Pepper headed out.  As we cleared the opening, Conch Cut, I looked out to the east.  It had seemed criminal to force Tabu out to sea in his  derelict junker of a sailboat.  However, the weather had been fair for weeks.  I hoped that he had made it to the Turks and Caicos.  He would not fit in there either.

Choosing a New Propeller

Part of the re powering project for  White Pepper involves choosing a new propeller to match the new engine.  Such a task is not easy.  A poor selection can lead to engine failure as well as poor performance.  Indeed I now suspect that some of  White Pepper's current problems stem from "under pitching" the prop when it was changed out in 2007.

The universally acknowledged expert in selecting a prop is David Gerr and his book, "Propeller Handbook."I ordered one from Amazon and set to work.  I must say that I have never spent better money on a nautical book. I wish I had learned this stuff years ago.

Mr. Gerr's book is for those who want to know why and not just the answer.  The book is well written but dense.  I had to read some sections several times.  The math is about the level of a good Algebra II class in high school.  I used the scientific calculator on my smart phone.  My chief complaint about the book is the poor reproductions of the  graphs.  I really had to squint at times. There are propeller calculators on the internet. Indeed I used one from Max  Prop and got the same answer, but I felt more comfortable having worked it out myself.

The process starts with consulting the power curve of your engine.

Power Curve for Yanmar 3JH Series

Where the two lines meet is the only spot where the propeller is optimum, that is at 3000 RPM and 38 mhp. MPH is metric horsepower which is almost identical to an English horsepower.  Then chose a reduction gear.  Yanmar has two--2.4 and 2.6.  The 2.6 gear will turn the prop at 1150 RPM.  This slower speed allows for a larger blade and less chance of cavitation. Torque is slightly higher for lower RPMs since torque is power divided by RPM. Variable pitch propellers are available which will allow the two curves to match up.  These are so expensive they are only for tug boats and mega yachts.

The "Propeller Handbook" provides two methods of estimating propeller diameter and pitch from horsepower, shaft RPM and boat dimensions.  There is the old traditional slip method of Crouch and a newer, more numerical, but not necessarily more accurate method called Bp-delta. For those who do not know, the pitch of the propeller is how many inches it would advance in one revolution if it did not slip.  A typical sailboat slips about 45%, so a boat with a propeller pitched at 13 inches would advance about 7 inches each revolution.  That works out to 9,250 inches per minute (at 1250 RPM)  or about 7 nautical miles per hour.

The slip method yielded a suggested propeller dimension of 18" in diameter by 14" of pitch for the 2.6 gear.  This was close to the propeller suggested by the Max Prop calculator on the internet.  Max prop suggested 18x13. 

The Bp-delta method gave 20 inches for the optimum diameter.  I thought that this was too large for the aperture.  Choosing an 18" blade,  gave a pitch of 15"  and an efficiency of 46% (55% is the best you can do.) This choice was confirmed by a call to Michigan Wheel, the premier manufacturers of bronze propellers.

Bp-delta diagram for a 4 blade prop

By comparison the current prop is 18" x 10".  The Yanmar 3HM was rated at 3600 RPM and 27 horses max.  The last time the old girl saw 3600 RPM was the day she raced for a bridge opening in 2009.  The transmission failed the next day.  Based on calculations of diesel consumption, I estimate that the power output was down to about 8 HP by 2013.

The Bp-delta method also allow you to calculate expected speed, 7 knots, and thrust, 880 pounds.  I was surprised at how low the trust was.  A full press of sail will generate thousands of pounds of force on the rig and anchor loads in a brisk wind are in the thousands of pounds.

David Gerr speaks glowingly of the advantages of a feathering prop and calls it ideal for the long distance cruiser who need to sail and power.  He reports that the drag of a fixed three blade prop is equal to the drag of the entire under body of a well designed yacht.  Compare that to the drag profile presented by a fully feathered propeller.

3 Bladed Max Prop looking forward when fully feathered.

I exchanged e-mails with Max Prop.  The price of the 3 blade classic is "only" $3300.  which is a bargain compared to the price I paid for my old two bladed prop 15 years ago.  I lost that one to electrolysis, but nowadays the Max Props are fitted with a large zinc bolted directly on to the hub.  That is what you are looking at above.  I asked about the new heavily promoted 4 bladed Eccowind Max Prop that has a spring which automatically adjusts the pitch to the load.  Unfortunately it will not work at the RPMs generated by the Yanmars.

The blades are obviously flat and efficiency suffers without the familiar twist we all see in traditional propellers.  However, the degradation is only 5%.  Furthermore, according to Dave Gerr  the efficiency enters the velocity and thrust calculations as the cube root, i.e. 2%.  So the expected speed for the re powered  White Pepper will still be 6.8 knots and thrust 836 pounds.  I can live with that if she will sail at 7.4 knots.

On the other hand a fixed 3 blade prop from Michigan Wheel Co would cost about $600.  The yacht would likely motor at 7.4 and sail at 6.8.  The fixed prop would likely be slightly more powerful facing a headwind and chop.  Choices!