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Old 16-06-2009, 03:31   #1
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Motors for 40' Cruising Cat

I am busy with the specs for a 40ft cruising catamaran that I am buying. The standard motor is a Yanmar or Volvo 29hp. I have checked and to upgrade to a Volvo 40 is not too much money and only 31kg extra weight for each motor. Where I will be keeping the boat for the first few years normally has about 20 to 35 kts wind in the evening when it is time to head back to the harbour. (Murphy's law upwind!) The Volvo is also a four cylinder which I am sure will be smoother. I have looked in the engine section and seen the pro's and cons of Yanmar vs Volvo, length of time between saildrive boot changes etc. Any views and opinions from sailors with similar size cats and motors?
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Old 16-06-2009, 05:05   #2
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In those circumstances and with a 40ft cat, I would also be considering an upgrade of 35 to 40hp. But not Volvo! My preferece is for something like a Beta engine which is a marinised Kubota engine. Much cheaper for spares.

Dont forget that with the bigger engine, you will also need larger fuel tanks, and will also have to re-think weight distribution.
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Old 16-06-2009, 05:32   #3
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Quote:
Originally Posted by paulrack View Post
I am busy with the specs for a 40ft cruising catamaran that I am buying. The standard motor is a Yanmar or Volvo 29hp. I have checked and to upgrade to a Volvo 40 is not too much money and only 31kg extra weight for each motor. Where I will be keeping the boat for the first few years normally has about 20 to 35 kts wind in the evening when it is time to head back to the harbour. (Murphy's law upwind!) The Volvo is also a four cylinder which I am sure will be smoother. I have looked in the engine section and seen the pro's and cons of Yanmar vs Volvo, length of time between saildrive boot changes etc. Any views and opinions from sailors with similar size cats and motors?
We have 29hp Volvos in our 37' cat and the power feels about right. Friends have 15hp motors and they are definitely underpowered and have limited single engine capability. If we have no headwind, we can power on one engine at 5.5kts and with some help from the sails we can increase speeds to 7+ knots.

If you go for the bigger engines, make sure you have enough bouyancy aft to handle the extra weight of engines and fuel. Check with the manufacturer for their recommendation also. If you put too much weight at "the ends" of a cat, you can develop a "hobby-horse" motion when punching though seas.

Since you will be powering into strong head winds/seas, recommend a 3 bladed prop to increase your thrust. Folding or feathering props will also make a big difference in your speed while sailing.

Enjoy your new boat.
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Old 16-06-2009, 05:33   #4
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Go ELECTRIC!!!!

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Old 16-06-2009, 05:58   #5
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The Volvo is also a four cylinder which I am sure will be smoother.
3 cylinders are inherently smoother than 4 unless the 4 is a 'flat' 4 like a Subaru or old air cooled VW. I'll let the engineers here tell you why because it is beyond me.
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Old 16-06-2009, 07:28   #6
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a 'flat' 4 like a Subaru or old air cooled VW.
That'd be a boxer engine, the water cooled VW are boxers as well. An inline 4 can be quite smooth, it really depends on the manufacturer. Most of the modern direct injected diesel engines are inline 4 bangers (1.9l TDI). The super high mileage diesels of Europe are 3 cylinder (Polo etc).

If that is a concern you can remove the rotating mass and have it balanced, it is not that expensive if you do the labor yourself and it can make a huge difference.

We are going to do your upgrade when our MD 2030s kick the bucket, the extra 62kg is not a significant increase in weight, I wouldn't worry about it. There may be other concersn though, I would talk to the manufacturer about it.

Parts for the Volvos are expensive and hard to find but ours have been reliable. The boots on our boat are 12 years old and still intact, YMMV, with 120s saildrives.

PS; thanks for the hatch!
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Old 16-06-2009, 08:16   #7
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We've buddy-boated on and off with a Lagoon 410 with 40hp Yanmars versus our St. Francis with Yanmar 27's. The Lagoon has 3-blade feathering props, our St. F has 2-blade folding.

We pretty consistently found that the St. F was more efficient -- we often motored on 1 engine and maintained consistent speed with them when they were using 2. When we were using both engines, we would slowly pull away from them, although we were both motoring at the engines' respective "happy points" (which was at about 2700 rpm for the 27's and 2500 rpm for the 40's). We had slightly (but I'd say insignificantly) lower fuel consumption. We were probably about .5 kt faster on both engines.

This is not to say that the 27's are "better", but that there are many variables involved that probably have as much, if not more, to do with hull shape, weight and load distribution than all-out hp. The St. F, though 3 ft longer, is a lighter boat than the 410. The engines are mid-ship on the St. F vs under the aft bunks on the 410. The St. F hulls are narrower, but this then limits load carrying some (although you wouldn't know it by all the stuff!).

In terms of motoring into the wind/chop, we saw conditions similar to what you describe a fair number of times and never had any problem maintaining a decent speed into it.

If I were you, I'd consult the designer and see what they say. You might be surprised at the answer.

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Old 16-06-2009, 09:12   #8
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I have 2 Yanmar 3GM30's and find that they are both smooth and quiet. They are also provide more than adequate power, although I must say that if you are consistently expecting head winds in that range the upgrade makes good sense.

As to the inherent balance for an engine, as I recall the formula is:

360 degrees
(number of cylinders )
2

Sorry, my keyboard does not work for mathematical formulas, but in essence it is 360 degrees divided by the half of the number of cylinders. Hence:
8 cylinder engine, 90 degrees (360 divided by 4, or 1/2 of 8);
4 cylinder engine, 180 degrees(360 divided by 2, or 1/2 of 4);
6 cylinder engine, 120 (or 60) degrees;
3 cylinder engine, 240 degrees.

So your typical inline 3 or 4 cylinder engine is not inherently balanced. It really only poses a problem with larger displacements and at higher RPM's (which is where various auto maunufacturers went to balance shafts etc. to counteract the problem in 4 cylinder engines). On a diesel in the range that you are looking at, although neither is inherently balanced, more cylinders typically makes for a smoother engine than less.

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Old 16-06-2009, 09:31   #9
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I vote for the 30hp. 62kg is a significant amount of weight to add to the stern of a 40' cat. When you speak of returning home against 20-35 knots I wonder just how fast you would want to be traveling into the waves? You will have to use both 30hp instead of one against that kind of wind but they should push you as fast as you would want to go. When I owned a 42' cat the Volvo 30hp were perfect with only occasional use of both motors simultaneously. I wont get into the Volvo vs Yanmar thing because I have owned both and both are fine products.
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Old 16-06-2009, 10:41   #10
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Not sure about the Volvos, but I would go with the Yanmar 35HP over the 3GM30. It's reportedly a more robust engine all around. I had two 3GM30's in my 42 cat and it was a little underpowered at times, and both engines didnt last long either....
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Old 16-06-2009, 11:00   #11
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Had good experiences with both the yanmars listed above in hire fleets. They are inherently a light engine compared to old style engines but are remarkably robust. Treat them well and they will return the favor. Spares are readily available too which is a big plus and there are mechanics all over the world who know their way around them. There may be better options out there, but for ease of installation, reliability and maintenance they are pretty hard to beat. My only comment is that they seem to very temperamental about oil quality.Not sure why but they seem to really dislike oil that is getting to its sell by date. But that is easily overcome by scheduled maintenance.

But the volvos as commented on are also fine motors. In my experience spares are available but not as widespread as yanmar in some parts of the world. But maybe that is just me.

Power-wise, well the choice is yours up to a point. Never felt underpowered in a cat of that kind of length with two 3GM30s. And the decision is so much based on the kind of sailing/motoring you foresee doing.

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Old 16-06-2009, 11:07   #12
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A couple of times trying to maneuver in a crowded anchorage with the wind gusting hard, my 42 would not turn. I had 3GM30's and Max Props. Without much way on, a cat relies on the lee engine to turn. Caterpillering is an option... if you can allow the boat to be blown downwind while you are doing it. When I had the engine rebuilt (less than 2500 hours) I researched options, if I remember right the 35 HP was a heavier engine and not much more money. Take a peek at the HP curves for the two engines and you can probably sort it out...
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Old 16-06-2009, 12:02   #13
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Hi paulrack,

Have you checked out the Lombardini diesel engines? I believe they are the lightest of their class, possibly offsetting any extra weight due to your required power increase.

Are you planning to fit folding / feathering props? If so, the May 09 issue of "Yachting Monthly" has just done a big test on these props with some interesting results.

Where are you planning to keep her intially?
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Old 16-06-2009, 12:26   #14
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I agree wtih Niccol's observation about part availability favouring Yanmar over Volvo, at least in North America and the Caribbean. I should also point out that the current model for the Yanmar is no longer the 3GM30, but I believe the 3YM30 (or some such designation). I have no direct experience with them, but believe that they were not a radical change from the earlier model and hence suspect that the comments would still be of general application.

Brad
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Old 16-06-2009, 12:57   #15
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Brad,

You are correct. It is now the 3YM30.
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