Sunday, 6 October 2013

Craftsman Marine Diesel Ordered

Hi everyone,
We've now selected a new engine for Zen Again.  We have ordered a Craftsman CM3.27 (3 cylinder, 27HP) and will keep the existing propellor.

Craftsman Marine is a quite new supplier of marine diesels.  They marinise Mitsubishi industrial engines in the Netherlands.  I've read plenty of positive comments about them and can only hope we'll be equally pleased.  Here's why we chose the Craftsman:

  • Fits in our engine compartment (and is smaller overall than existing engine)
  • Lighter (113kg compared to 123kg new Yanmar and 138kg existing engine)
  • 430mm mount spacing which matches our mounting beds.  It turns out our existing Yanmar has custom mounting brackets which extend their standard 370mm spacing.
  • Regular service items (dip-stick, filters, impeller etc) all on starboard and forward sides
  • Nice IP67-sealed instrument panel with hour, temperature, oil pressure, voltage and RPM gauges
  • Preheater (just in case we ever go anywhere cold!)
  • Nice looking engine with hoses NOT painted!

Craftsman Marine CM3.27
We expect to fit non-standard engine mounts since our engine beds are quite high.  We selected PolyFlex mounts which allow a minimum height of 65mm vice the standard mount minimum height of 85mm.

PolyFlex Engine Mount


We also plan to install a flexible coupling to provide a little "elastic" in the drive train.  We've chosen a PolyFlex...


PolyFlex Flexible Coupling

Our existing shaft half-coupling is rusty and its bolt hole pattern doesn't match modern gearbox couplings.  Again PolyFlex offers these, and drilling out to match your shaft diameter is included in the price.  So we'll get one of these...

PolyFlex Half-Coupling

We looked into the possibility of a smaller engine with a new propellor but that proved difficult due to issues matching available gearbox ratios to new propellors, and also a possible clearance problem between the P-bracket and an AutoProp propellor.

It will be interesting to see whether the new engine can drive our 16" Varifold propellor up to the engine's full rated RPM of 3600rpm.  The existing engine can only get to 2500rpm, but we suspect that's because it is producing less than its rated 27HP.

We used Nigel Calder's excellent book "Marine Diesel Engines - Maintenance, Troubleshooting and Repair" to calculate engine and propellor parameters for Zen Again.  Section 9 "Selection and Installation" provides all the necessary information.

For a yacht with the following characteristics:
  • 6,800kg (15,000lb) displacement;
  • 8.65m (28.4ft) waterline length;
  • 3600rpm maximum engine revolutions; and
  • 2.72 gearbox ratio
the calculations showed:
  • 15HP needed for a "racer", but 30HP recommended for a "cruiser"; 
  • Recommended propellor size of 16.5" (ours is 16"); and
  • Recommended propellor pitch of 14" (ours is 12").
So, if anything the boat should be slightly "under-propped" rather than "over-propped" with a new 27HP engine.  And so the new engine should work well.  Time will tell!

3 comments:

  1. Mike
    'that is a big task - but like you say you had to bite the bullet at some stage - pity - this effort in the marina where you did your major refit could have handled this quite easily -
    It will be interesting to see how this engines goes - power/vs fuel usage and general service ability.
    If I recall you did buy into a new folding prop also - again another plus and it will be nice to see how happy you are with the package - I can see you are not daunted by projects - the bigger the better obviously
    take good care - you will happy to get away from the dock and wander across the globe

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  2. Mike
    its been a while now - since I last wrote - but we do read your blog from time to time.
    We are looking at a re-engine of a yacht - and yes one of the considerations is the Craftsman - can you give me a heads up on how you have found this engine since installation -
    all is well this side of the planet I think - we just need a few grown ups in Govt - we were really close to buying this little yacht - http://www.apolloduck.co.uk/feature.phtml?id=484301 - regretably after significant expense and effort to organise things - the owner has turned out to be a bit duplicitous - and tried to hide issues that were found in the survey report. - a real pain - they are great little yachts.

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  3. hi...this is cemal from turkey...i just replaced the 47 hp bmc leyland with a craftsman 65 hp in my boat moody 40 cc (1979)..i kept on the 32mm shaft and the 17" prop and took to the sea for a trial and run-in of 50 hours...at full throttle of 3500 rpm, for a moment, i thought the boat was planing..:)..craftsman is good (mine is hyundai based), cheaper than volvo or yanmar with much cheaper spares...i was told craftsman was vetus's engine supplier but somehow they broke up the agreement and selling for themselves now..
    hope you enjoy your new engine just like me...

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