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Old 02-03-2013, 23:32   #1
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Repower Engine Size and Type for 40 foot Yacht?

Hi, I am seeking advice on the best size of engine and a good brand to replace a very tired old Bukh 20dv (20 hp) for my 40 foot 8 tonne yacht.

The boat has great sailing performance, and I intend to use the engine mostly for calms and maneuvering. Where low fuel consumption is important. But of course occasionally the thing will have to be able to push her slowly into a decent lump of wind and sea if things go pear shaped.

I am currently looking at the Beta 35 and 38 hp engines. I would rather avoid yanmars and volvos with their expensive spares. The nanni's also look OK.

Also I have funds for a new engine... But occasionally much cheaper second hand equivalents come up. Worth the risk?

Cheers

Ben
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Old 02-03-2013, 23:44   #2
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Re: repower engine size and type for 40 foot yacht?

The 35 and 38 would be plenty of power. I have the Beta 38 in this 50 foot 10t yacht and she moves along just fine in a blow. In another boat, an 8t Cal 36 I have a little Beta 22. Definitely on the low side of acceptable power. However she does the infamous Baja Bash just fine. Can be slow with 35 knots and seas on the nose, but who cares?

I would not risk a second hand engine unless it comes with trustworthy records (rare).
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Old 03-03-2013, 00:10   #3
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Thanks daddle. Reasuring to get first hand info before handing over a significant wad of cash.

The agent gas suggested 30 hp Beta might do? Seems a touch small to me. And how do you like the Beta?
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Old 03-03-2013, 00:22   #4
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Re: repower engine size and type for 40 foot yacht?

Depends what you mean by "best size." For me, I like saving weight and money. If I want to go fast I use the sails. My boats are also easily driven because of design and complete lack of windage producing clutter. Others want to motor at high speed in adverse conditions with all the canvas, solar panels, kayaks, dinghies, BBQs and motorbikes on the deck...or are just motorheads...who's to say?

I would think 30hp would be fine. I, for myself, might go with even less. I like the Beta products. Well made, smooth running, inexpensive spares. I've never heard any complaints about them. The Nanni seems very similar.
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Old 03-03-2013, 00:23   #5
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Re: repower engine size and type for 40 foot yacht?

We installed the Beta 90 in our 48-foot, 20-ton ketch and have been delighted with it, however, it's nowhere near 90 horsepower. The Kubota service manual says that the engine will produce 73 horsepower intermittantly and 68 hp continuously. Be that as it may, the engine pushes our boat along at 6 knots running at 1,400 RPM and using 3 liters of diesel per hour in calm conditions. With over 1,500 hours on the engine, we don't use any oil in between the 500-hour oil change interval.

Good luck, fair winds and calm seas.
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Old 03-03-2013, 01:32   #6
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Re: repower engine size and type for 40 foot yacht?

Your desired power looks pretty close to the mark.

Do check that your propeller shaft can handle the extra power.

Have you considered another Bukh? Their DV 36 ME looks good and may not be too hard to fit in your existing space (do check!).



If you twist their arm about a trade in they may give you a nice deal.
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Old 03-03-2013, 04:48   #7
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Re: repower engine size and type for 40 foot yacht?

Thanks for all the feedback. So far I haven't heard anything bad about the beta's which is encouraging, and nobody has told me I need a 80hp turbo... I intend one day to head back to the higher latitudes, but hopefully the smaller engine will have enough grunt to deal with the odd occasion when I need to really wring it out! Seems to me the biggest factor is getting the reduction ratio and prop size just right rather than outright HP.

At this stage I am planning to use the old folding prop (23 inch, but might need re pitching), but I may go a feathering at some point.

The boat has a one inch shaft which is a touch on the marginal size I think, I could look into a duplex shaft. I still need to measure it all up, I might need a new shaft anyway.

Hopefully the engine beds will suit the smaller Beta.

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Old 03-03-2013, 06:13   #8
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Re: repower engine size and type for 40 foot yacht?

I dont really like the idea of running a bigger diesel at lower power. Normal usage ought to have it running at 70 or 80% power. I think the beta 35 will do just fine, maybe you ciuld even go a bit smaller. Anyway the Beta will be a practical and cost effective NEW engine installation.

I dont see anything wrong with a good used engine in a well used boat. For instance I would seriously consider a freshwater cooled $1000 used Universal to replace the original A4 in my $2000 boat but I would hesitate to put a new engine in her that costs 4 times what I paid for the boat. OTOH a nice boat costing more than a small house deserves a new engine and it would be penny wise and pound foolish to go used unless the engine had a reliable record and low hours.

Would you say that the 20hp Bukh, when running good, would be a LITTLE too small, or a LOT too small? I am seeing a trend toward overpowering sailboats these days. Vendors are certainly not doing much to discourage this LOL! So consider your realistic needs and think carefully before installing an engune that will mostly be idling.
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Old 03-03-2013, 06:30   #9
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Re: repower engine size and type for 40 foot yacht?

my 35 ericson has a 20 hp yannie and runs well...my 41 formosa has a 4-108 perkins and i LOVE it....
good luck. dont forget the stringers and placement for engine--and re alignment and such other lil things to do when repowering...
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Old 04-03-2013, 00:31   #10
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Re: repower engine size and type for 40 foot yacht?

Ben, it might be helpful to know a bit more about the yacht... things that affect how easily driven it might be. Big differences between 40 foot boats in that respect, ya know!

And FWIW, Insatiable II, 46 ft LOA, 44 ft LWL, light ship 9.5 tonnes, estimated cruising weight around 12 tonnes with full tanks, easily driven hull shape, low wetted area. Engine is a Nanni 43 which is based on a 2 litre Kubota tractor engine. Quite adequate power through a Flex-O-Fold three blade and 2:1 reduction. We run it at about 2000 rpm for cruise, which gives about 6.5 knots in calm conditions and clean bottom, burns 2.5 L/hr doing that. Pushes into head winds adequately, but that's hard to accurately quantify. Have pushed into 40 kts apparent at around 5 knots and 2400 rpm. Around 4K hours on it, no issues beyond the usual belts, filters and hoses plus one lift pump, sourced from the tractor store!. Very happy with the engine, and imagine that the Beta conversions are just as good.

Good luck with the repower!

Cheers,

Jim

PS Will be in Kettering starting tuesday AM, sail delivery Weds morning on the wall at the marina.
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Old 04-03-2013, 01:16   #11
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Re: repower engine size and type for 40 foot yacht?

You might want to include WM Diesel in your research Witchards Marine - inboard diesel engine manufacturers for yacht or motor boat - WM Diesel. Their base engines are Kubota, same as Beta and Nanni. I repowered with WM Diesel a few years ago, very pleased wth the service and the result. At the time, WM were way cheaper than Beta or Nanni.

Modern engines such as Kubota are generally smaller and lighter than older diesels. Means you can increase engine size without incurring weight penalty.

The horsepower ratings put out by Beta are inflated, I think they always refer to the intermittent rating. If you get the engine model, you can go to the Kubota site to get all the specifications.

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Old 04-03-2013, 03:13   #12
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Re: repower engine size and type for 40 foot yacht?

I also support your Beta direction, particularly if your engine bay is orientated to the front as most are. Aside from being decent, tirquey diesels with cheaper-than-most spares, this is a particular strength of theirs in their smaller ranges.

A one-inch shaft turning a 23 inch wheel? That seems quite large to me. You will want to do the math on pitching the prop in order to avoid both lugging or not being able to wring out every rev. It sounds as if you want torque power as opposed to speed while motoring in the flat stuff. Prop pitch will therefore play a role for you.
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Old 04-03-2013, 04:16   #13
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Re: repower engine size and type for 40 foot yacht?

Thanks for all the replies,

Quote:
Originally Posted by S/V Alchemy View Post
A one-inch shaft turning a 23 inch wheel? That seems quite large to me. You will want to do the math on pitching the prop in order to avoid both lugging or not being able to wring out every rev. It sounds as if you want torque power as opposed to speed while motoring in the flat stuff. Prop pitch will therefore play a role for you.
According to the paperwork that is the prop, I haven't actually measured it, it does seem excessively huge, although it is only a two blader.

I am not interested in lugging the engine, had problems with a boat I delivered that was overproped, great for motorsailing or in light air, but hopeless punching into anything. The motor and prob both stalled, best we could get was about two knots with the reefed main up helping, painfull. The owner has since cut it back a bit and reports it's much better all around (except when motorsailing). I will slightly optimise it for flat water fuel efficiently, but not much.

Yes the shaft seems light, but a freind has been using a 1 inch on a Perkins 4108. as far as I know standard 316 not fancy duplex. So at least torque wise it should be OK? need to run some figures and see if I need to go duplex or upsize the shaft to 1 1/4, providing the stern tube will take it.

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Old 04-03-2013, 04:19   #14
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Re: repower engine size and type for 40 foot yacht?

Quote:
Originally Posted by banjoship View Post
You might want to include WM Diesel in your research
Thanks Lee, I have already emailed them for a quote, they look very good and it is great to get positive feedback from someone who has used them.

Cheers
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Old 04-03-2013, 04:36   #15
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Re: repower engine size and type for 40 foot yacht?

Quote:
Originally Posted by Jim Cate View Post
Ben, it might be helpful to know a bit more about the yacht...

And FWIW, Insatiable II, 46 ft LOA, 44 ft LWL, light ship 9.5 tonnes, estimated cruising weight around 12 tonnes with full tanks, easily driven hull shape, low wetted area. Engine is a Nanni 43 which is based on a 2 litre Kubota tractor engine.
Ha, well if you look out to the north as you come into Kettering you will see her on one of the outer moorings, called Sunburst, white with red/orange stripes. She is a peterson 40, 12.9 foot wide, aluminium, big masthead rig with lots of rake and prebend. Short waterline (33 foot?) and very low wetted surface, slight bustle aft and narrow stern, but not a pintail. She has a spade rudder. According to the paperwork her IRC weight is 7 tonnes and another racing cert says 8 tonnes.

I noticed bringing her back from Adelaide that she sat on 5.5-6 knots with hardly any sail up, and hardly any heel, seeming very easily driven at loww speeds. I don't think she would have a high top speed (we never pushed her). Although my brother reckoned he had a steady 9-9.5 for a while off Tasman island. I was asleep so it must have been very smooth otherwise I would have woken up and put a reef in!

Very interesting to hear you payload is about 2.5 tonnes, I guess I should use about 10 tonnes as my cruising weight! I have considered Nanni's as well. Rumors were that they had heat exchanger corrosion issues, and no anodes, but Rumors are only rumors. And the new ones I saw had anodes and looked sturdy.

Cheers

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