Monday, December 27, 2010

Perky's Redemption

If I wasn’t so damn happy about finally getting to the bottom of the problem with Perky, I might be slapping myself around for not listening to many of you who submitted comments suggesting that we consider the propeller as the source of the power loss.   But since experience is what you get when you don’t get what you want, we’re all now a bit more savy regarding diesel engine diagnosis and repair.  And what about poor Perky?  He’s probably suffered the most from this ordeal - having to deal with our repeated dockside testing, parts replacing, fluid changing, rewiring, dismantling, laboratory testing, forced introductions to probing “specialists” and our generally disparaging comments aimed pointedly at the heart of this little chugger.   He quietly took all the blows and unquestionably sprang to life every time we turned the key.  Perky is the real hero in this episode of Team Tiburon.

So why was I so adamant that it couldn’t be the prop?  Well, first I have to say that these MaxProps appear to be quite complicated at first introduction.  In a basic boat propulsion setup, the diesel engine has pistons which pump up and down like a road biker’s legs, turning a crankshaft in a circle. The turning crankshaft (with a transmission operating as a “middle man”) spins the propeller shaft which extends thru the back of the boat, thru the hull and into the water. The business end of that spinning steel shaft is the propeller.   As the propeller spins round and round, the individual blades function like a kayak or canoe paddle, biting into the water.  Feathering, or angling the paddle, allows for more or less bite depending on the level of effort you want to expend and the amount of propulsion you want.    If the blade angle is too sharp, too much bite ensues and the engine gets overloaded.  Too much feathering (too little angle) and the blade slices thru the water with little to no bite, allowing the shaft to spin easily at the expense of weak propulsion.   That’s why it’s so important to match the correct propeller blade angle (pitch) with the individual boat, engine and transmission. 

And when one reads the installation manual, it’s obvious that there are many gears and meshing teeth involved in setting the correct blade angle.   Furthermore, changing the blade angle requires a full dismantling of the propeller - which includes at least 10 heavy-duty components (see photo). 

When I called MaxProp in Lynnwood, Washington a few days ago and described our poor engine power, the representative assured me that it would be impossible to have the pitch angle on the blades spontaneously change without a catastrophic and obvious failure to the inner workings of the propeller.  And every time I went overboard with a dive mask to inspect the prop, all three blades smoothly feathered and were devoid of any obvious damage.

But after changing the fuel injection pump (an all-day affair) did nothing to improve the performance of Perky, we finally decided to spend the money and haul the boat just to prove, once and for all, that there’s nothing wrong with the Goddamn Prop!  The plan was to firmly establish that the prop blades were angled correctly for our boat (20 degrees) and that nothing was impeding the rotation of the prop shaft.  I was convinced it would be waste of time and money, but since Luke had continued to insist that the problem must be the prop, Andrew and I finally acquiesced, and agreed to haul her out.  With that, we drove the boat over to the boatyard in La Cruz. 
Hauling out in La Cruz

A few hours after hanging El Tiburon from the slings and dismantling the prop, it finally dawned on me that the manual we had on board, was NOT the correct manual for our prop.  The manual we had on board described an older style of prop, in which changing the pitch of the blades requires a full dismantling.  Our newer style prop has a nifty mechanism for quick pitch changes which according to the online manual (a very helpful document) can be “accomplished easily by a diver.”

The broken part

Once I had the correct manual for our prop, it quickly became apparent that the pitch changing device was not working correctly.  The hub shown above is supposed to have a mechanism which allows the correct blade angle to be dialed and then locked in place.  The inner teeth on the hub must have fatally sheared and therefore the blade angle was no longer locked, but rather opened to the fully pitched position in both forward and reverse.  Whereas we should have had 20 degrees blade angle, we actually were biting the water at 30 degrees, which was just too much load for Perky.   With hindsight in view, this explains many of the symptoms we were experiencing - such as mild over-heating, increased smoke at full throttle and 6 knots at just 1400 RPM.  It's as if you were forced to drive a manual transmission car in city traffic using only 3rd gear.  Very sluggish off the line, but once you hit cruising speed, it does just fine.

Having finally gotten to the root of the problem, we pulled the prop and packed it in a box for shipping back to MaxProp and installed a older prop we picked up from a fellow cruiser.  It's a 2-bladed folding prop at 19" diameter.  We cruised with it yesterday and Perkie had no troubles spinning this one at 2400 RPM.  This replacement has a wimpy pitch (we only do 5 knots at 2000 RPM) but at least it gives us safe maneuverability in the marinas - something we didn't have with the broken MaxProp.

Bottom line, it really pays to know your boat.  If I had known about the dial mechanism on the prop, I would have checked it much sooner.   Well, at least we know our prop now, and our engine, too!

Humbly submitted,


April channeling positive energy to our broken stereo.
Unfortunately, it didn't work.

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