Expected speed and fuel consuption: Maiden Voyage

[pbrenton]

Hi Folks,

For my Maiden Voyage I need to take my new-to-me CP27/2 on a significant day trip.  I'm playing with Navionics and the trip at 5 knots is 11 hours, and at 6 knots its 9 hours.  I have to navigate the Cape Cod Canal and some harbor currents, just to name the most significant planning obstacles.  I want to make sure I have the requisite fuel on board with safety margin.

MY CP has the Westerbeke 18hp.  I'm not going to be afraid of motoring, although hopefully with the prevailing winds in this area we'll do some downwind sailing - or at least motor-sailing - to help push us along.  So here's the question;

Assuming no current, what's a reasonable cruising speed (i.e. Speed-Over-Ground) with the diesel running at cruise (about 2400rpm I believe)?  What's a good guess as to the fuel consumption at that speed?  I'm not looking for precision here, is it 1 GPH or 1/2 GPH or 2 GPH?  I'm new to this boat and my CP23 could cruise all day on a pint of gasoline.

I know there's a lot of other factors, but I feel real shaky about my baseline assumption of diesel consumption per hour.  I just need a reality check.  I can bring along jerry cans if needed so I can stick to the rule of 33% more fuel onboard than needed for the trip.  Also the basic assumption of the average speed we can make without considering other factors - I can do 5 knots in most conditions in the 23 without a problem, but have no experience in the 27.  I think it should be more (thanks to the hull length portion of the hull speed formula), but how much more adn at what (fuel) cost?

Thanks,  Pete CP27/2 "Nydra", CP 23/2 "Ella J".

[BobK]

You should use no more than 1 gallon of fuel for each 2 1/2 hours of running your engine.
BobK

[crazycarl]

No matter how efficient the engine, I would still bring a 5 gallon can of deisel if for only piece of mind.  You never know when fuel may become hard to find.  ie, last spring's pipeline shut down of gasoline.

[brackish]

Well Pete, I can't answer your question, my inboard days of a similar sized sailboat go back to the days of the Atomic Four.  But I do want to know what motor you have on your 23 that can run all day on a pint.

[Deadrise]

Hello Peter,

5.5 kts .65 gal/hr @2400rpm in reasonable conditions not accounting for current. Where are you departing from and what is your destination?

Congrats on the new boat,
John

[pbrenton]

Brackish; I may have exaggerated a little (!), but all the motoring in two months of summer in Casco Bay seemed to use less than 3 gallons on the 8hp Tohastu 4-stroke on that boat.  It never went all day really, but often had to bring us back upwind against the chop at the end of the afternoon.  I'll miss that boat!

Deadrise: She's at Falmouth Harbor in Mass, and I'm taking her to Chelsea Mass (in Boston Harbor) to get a minor DIY refit at Admirals Hill Marina in May.  By Memorial Day she will be back at my usual cruising grounds in Casco Bay, near Portland ME.  Hopefully by then the spaghetti wiring job will be straightened out, teak refinished and moderately shiny, and a number of other small odd jobs taken care of.  I also need to rip out a non-marine inverter someone though was a good idea to place right under the hatch, at the bottom of the companionway steps.  The surveyor looked at that and shook his head a lot.

Thanks to all for the great data.  I'll be packing a jerry can even with a full tank, but I'm sure I won't need it now.

[Deadrise]

Hello Peter,

I believe I looked at your boat back on Sept, she was being sold by a woman named Catherine and from what I remember the boat had an 11hp diesel not the 18hp. If that is the case you will most likely see less gal/hr than what I posted, but you might find her be a bit under powered motoring to windward.

Have a great season,
John

[moonlight]

It's a really old formula; but on my Islander 36 with a Yanmar 3HMF (30HP) about a quart of diesel an hour was average.

And while I've had CP 25's for 20+ years, both with Westerbeke 18HP; I never really developed a fuel curve for them.  One was traded off/sold a long time ago; the other absolutely must go this spring.  Anyone interested send me a message.  Fully loaded, lightly sailed, dry stored 2003-2008 (business needs first, then Katrina shook up Gulf Coast sailing needs); wet stored since 2008 but a recent (couple of years) full barrier coat and bottom job.  Just haven't gotten back into sailing with the combination of factors (lots of kids, lots of kids activities, and since I made boat work a profession instead of a hobby, my cup overflows; it's not the first thing I think to do on the weekends especially with all the amateurs that have taken to the water...)

Sorry for digressing and high-jacking the thread.

I think you're very safe presuming 5 gallons diesel for the whole trip (assuming a clean bottom).  More important will be spare filters, especially if the tank has been idle a long time.  Take her out and shake her up you could be changing filters at 30 or 60 minute intervals the first little while.  make sure to take a primer bulb along, and an ADDITIONAL way to blow back into the tank; I have had to dig sludge balls out of the pickup tubes that didn't even make it to the filter, but that effectively kill fuel flow.  Common at pickup tube if it's screened, also common at the 90-degree fitting coming out of the tank.