Engine size

[Stranded Mariner]

I am going to build a Dix 43, with steel hull and centre cockpit. I hope to start within the next 2 months, and am at present selecting systems and equipment.
An important one is of course the choice of propulsion engine. The standard design plans recommend a 54 hp Yanmar.
Now I am a marine engineer, and one of the problems of people in our profession is to want everything a bit bigger, stronger etc.

So I have been thinking about a 75 hp Yanmar or Volvo Penta instead of 54 hp. I was thinking it would be good to have a bigger engine in case I would have to tow somebody, or in heavy weather or current. On the other hand there is the extra weight of a bigger engine, gear and possibly extra fuel tanks.

A bit of dilemma. It's the first time that I have to deal with the details of a design. Any advice for me?

Thanks in advance,
Andreas

[cooper]

Hi Andreas
Im building a steel hull 38 foot Centre Cockpit. The original specs was for a 30 to 35 HP. I am putting in a 53 HP isuzu (keel cooled of course). The build weight is 10 000 KG half tanked......hope that helps. Do remember that diesel in the future is going to be vey expensive unless you live in Bahrain or similar..

[Boracay]

When choosing the engine gearbox for my steel Roberts 44 Offshore I initially considered the Yanmar but eventually went with the John Deere 4045D (75 hp continuous).

I was put off the Yanmar by the requirement that the engine be installed by one of the recognised installers and by concerns about the supply of spare parts. Parts were not generally available for the Ford 2042E/Kanzaki that I threw out.

I just could not find an installer who would commit to installing the Yanmar with the current shortage of skilled tradespersons in Australia.

My limited experience so far has been that John Deere takes their customer support very seriously. They have a world wide network of dealers.

I also went with a continuous rated gearbox (ZF63) to match the engine.

While I do not think that I will ever run my engine 24/7 the specs say that I could do it with full power if I ever wanted to.

The final bill for the 4045D withZF63 came to about $4k more than the Yanmar.

The Isoflex engine mounts arrived today, together with the rubber exhaust hose. Sea trials soon...

[donradcliffe]

Engine size depends on what you want to do with the boat. For long-distance cruising, you will spend most of your motoring time in calm water, and a smaller engine will be more economical and happier running at a higher percentage of its capacity. If you are a weekend sailor, you want the big motor to get you home on Sunday afternoon when its blowing 25 knots in your face.

[Stranded Mariner]

Well, thank you all for your input and advice.

@donradcliffe: That's interesting. I never thought about it that way.

@Boracay: I will have a closer look at John Deere. Never realized their engines make a good marine diesel. One question. You mentioned a ZF63 for a 75hp engine. That seems a bit oversized to me, or am I wrong? I built a FRP sloop with inboard diesel of about the same size, and it came standard with a ZF30.

[Boracay]

I probably overdid it a bit with the ZF63. The ZF45-1 probably would have done the trick, while the ZF25 looks a bit too small.

For some reason I got it into my head that the ZF45-1 did not suit.

The overdoing it bit did not come up when discussing the gearbox with both the John Deere and the ZF reps.

I have got the impression from this and the SSCA Forums that Cruisers tend to undersize their gearboxes.

Only a boat buck or so difference.

[Stranded Mariner]

Yeah, I think there's nothing wrong with being slightly oversized when it comes to couplings and gear. The ZF has a plate type clutch as opposed to the KM cone clutch, and from what I have seen, the plate type clutches are a bit more forgiving when it comes to overloading.