I got a question earlier this year that essentially asked: I can’t quite reach full rated RPM under load but I’m only 50 to 100 RPM low in my Bayliner 4788. I’m considering playing it safe and repitching my props but my dealer recommends that I not bother until next season.  Is it OK to wait until next year since I’m close to correct and don’t run the boat hard for long periods of time?

My response:

When giving other people advice, I'm conservative.  Having spent 6 or 7 years servicing cars professionally, I know just how upset a customer can get when you say "it'll be OK” and it ends up not being.  The safe answer is to remove 1" of pitch.

However, you aren't nearly in as bad shape as many 4788s.  Since you clearly care and have a good strong set of engines to start with, invest up front in great instrumentation.  Buy boost gauges, pyrometers, and digital tachs.  Boost gauges and pyrometers provide valuable engine load information to help avoid overload (http://www.mvdirona.com/TechnicalArticles/DieselEngineOverload/Default.htm). The standard Faria tachs tell you when the engines are running but not much more—get good digital tachometers (http://www.mvdirona.com/TechnicalArticles/DigitalTachometer.htm).  Also get the fuel curves for your engine from the local distributor or the Cummins marine support team (wave.master@cummins.com).  From the fuel curves sheet you'll see exhaust gas temp at full rated RPM.  It'll be around 850F.  My general rule is to not cross that line although many argue this is unnecessarily conservative.  Some engines have acceptable load levels that produce exhaust temperatures above those at rated RPM. I chose to avoid this condition entirely.

The right answer is to do both: 1) get the instruments I recommend above and 2) re-pitch right away.  However, if you are careful, don't run hard, and watch the instruments, you'll probably be fine running with the current pitch.  The pyro's will tell you for sure. 

I needed to take out a second inch of pitch in mine, but since I'm both careful and cheap, I didn't want to re-pitch the second time right away. Instead I did three things: 1) ran light at lower RPM, 2) watched the pyros and didn’t ever go over the max rated temp (I prefer it 50F under), and 3) read the fuel burn.  From fuel burn you'll know the HP you’re consuming at cruise.  With your engines, multiply gallons/hour/engine * 19 and you'll find how much HP you’re asking for at cruise.  The constant 19 is the horsepower produced per gallon per hour and it’s very constant across all high speed diesels.  Newer common rail engines are closer to 20 HP/gal/hour but these numbers are remarkably stable across all manufacturers.  I was introduced to this approach by Tony Athens (http://www.sbmar.com/Articles.cfm).  Ensuring the HP you are using is always less than the manufacturer performance curves at that RPM will ensure that you are not overloaded.

In your case, I lean slightly towards re-pitch now. That way you can get to know the boat with everything running correctly.

James Hamilton

jrh@mvdirona.com

http://www.mvdirona.com/

I get the odd query, and this one is perhaps of broader interest.

Gerald Albertson wrote:

Hi James and Jennifer,

I absolutely love your pics, especially Desolation Sound at Christmastime.

It is a fine goal that I obtain the proper skills and confidence to do an Around-Vancouver Island adventure one day.

One of the next additions that I plan on making is the digital tachs that you describe.

My 34 Tollycraft has 210 hp 5.9 Cummins diesels of late 1988 manufacture….turbocharged but not aftercooled.

My neighbor has a 37 Nordic Tug that has a Cummins diesel (approx 350 hp) and it came with a block heater.  I think his is a simple headbolt heater as opposed to a tank heater, but I’m not sure about that. 

Anyway, I thought the block heaters might be a nice addition to my boat.  What do you think?

James’ response:

We don't chose to use block heaters on Dirona but they are a good option to increase engine longevity (cold start with cold oil is hard on them) and to warm the engines and engine rooms (decreases condensation and reduces rust).  Mechanically injected engines such as ours tend to smoke a bit when cold, and a block heater can reduce cold start smoke markedly.

Cummins sells core plug block heaters.  These are installed by removing an engine block core plug and inserting a block heater to take its place. They heat the coolant and it circulates by convection.

Another solution I've seen  is a pump and heater in the coolant.  A variant of that used in over-the-road applications uses a diesel furnace to heat coolant (and heat the cab) when the engine isn't running.  This allows the cab heater to function when the engine isn't running, and warms the engines.

A common installation I've heard used successfully in Cummins marine applications is Wolverine oil pan heaters: http://www.wolverineheater.com/.  They are used by Seaboard Marine extensively on Cummins with good success: http://www.sbmar.com/. They sell at reasonable prices and can offer wattage advice for your conditions.

            -jrh

James Hamilton

jrh@mvdirona.com

http://mvdirona.com

The Seattle Boat Show seminar schedule has just been posted. We’ll be presenting on the red stage at 4:15 on Saturday February 2^nd. Our presentation will include highlights from our upcoming Waggoner sister publication Cruising the Secret Coast: Unexplored Anchorages on British Columbia’s Inside Passage.

While docked in La Conner recently, we were fortunate to walk past the Pacific Mariner plant at just the right time. They were wheeling a huge, empty hull, likely of a Pacific Mariner 85, around the building. It appears that they mold the hulls on one side of their property, then transport them to the other side for completion. Another large boat looking near completion was next to the slot where this one was destined.

The tractor operator did an amazing job—the clearance at many points was barely inches.

On a recent trip from Elliott Bay to Mats Mats Bay, we passed the Washington State fast ferry Snohomish running south. The last we’d heard, the ferry was still mothballed in Eagle Harbor. A successful lawsuit by Rich Passage residents had taken the passenger-only Snohomish and its sister ship, the Chinook, out of service to prevent further erosion caused by their wakes. Both are to be sold.

When we saw the Snohomish that day, it was in temporary service between Port Townsend and Seattle. The two 80-year-old ferries on the run between Port Townsend and Keystone recently had been condemned, and no other car ferries in the fleet had a shallow enough draft to negotiate the approach to Keystone.