Adventure 40—Engine and Drive Train


I have to admit, I have been procrastinating about writing posts about the Adventure 40 systems because this is the area where we will have to make some of the hardest and most unpopular decisions if we are going to produce a viable, reliable, fast, strong and comfortable offshore voyaging sailboat for less than US$200,000, ready to sail around the world. But, I procrastinate no longer, here goes.

Things to Keep in Mind

Before we start, if you have not read it already, or even if you have and the memory is fuzzy, please reread the first few paragraphs of this post, in which I explain the goals and limitations of this specification.

For those who may be wondering why I’m writing about the engine before discussing the interior it will need to fit into, I need to explain a fundamental Adventure 40 concept:

Unlike most production boats, where an interior that will sell at a boat show is designed first and the systems are then fitted into the space left over, the Adventure 40 design team will focus on the systems that make the boat a fun, safe and easy to maintain offshore sailboat first, and then fit a functional interior into the space that’s left. A radical concept, but a totally right one.

And, if you are wondering why I am putting so much effort into the engine for a boat that is primarily designed to sail, Colin does a great job of explaining here.


The engine will be about 35 HP, relatively low revving and high torque, based on an industrial block. A good choice would be the Beta 35 based on a Kubota block.

Yes, I know the horsepower sounds low, but I assure you it’s not. As I have written before, many, perhaps most, modern sailboats are ridiculously overpowered, which results in poor fuel economy and premature engine failure due to under loading—diesels, particularly industrial ones, like to work hard.

Also, keep in mind that the Adventure 40 will be a long waterline comparatively light hull form that will be much easier to drive through the water than most modern production boats, which need more power because their hull forms are fundamentally inefficient.

Finally, if I’m wrong about the engine size, always a possibility, we will find that out in the prototype phase and we can always go up one model. Rest assured that the engine we end up with will be able to drive the boat to a speed to length ratio of 1.25 (about 7 knots) into 20 knots of wind and a 3 foot (1 meter) chop—when the wind and waves get higher than that, no amount of power will drive you any faster, or even that fast, without cracking off and putting some sail up.


ZF15M (HBW150) Hurth Marine TransmissionThe transmission will be a mechanically activated unit such as the ZF/Hurth  ZF15, because this will allow for locking the propeller shaft without use of a separate shaft lock.

The gear will be fitted with a heat exchanger oil cooler, which, along with oversizing the transmission, as I have done, is one of the best things you can do to guarantee that the Adventure 40 will not be plagued by the transmission problems so common on sailing yachts.

Running Gear

The propeller shaft will be of high quality stainless steel (Aquamet 22, or equivalent) that will be at least one size over standard practice for an engine this size. It’s amazing how often sailboat propeller shafts bend or break due to something fouling the propeller—an event that should be a minor irritation, not the start of a major repair job.

split-coupling_mediumThe shaft will be coupled to the engine with a clamp-on split-coupling, with set screws screwed into dimples in the shaft and then wired. The coupling will be faced on a lathe to insure accuracy after it is fitted to the shaft. A DriveSaver will be fitted between the transmission and coupling to act as a fuse in the event of a severe prop fouling event.

The boat will come standard with a two blade fixed propeller but the shaft will be machined to accept a MaxProp, for owners who wish to add one and keep the fixed prop as a spare.

There will be enough bare shaft between the front face of the propeller face and the aft face of the strut to accommodate an owner-fitted line-cutter device.

If there is any doubt about properly supporting the shaft run, two cutless bearings will be fitted, one in the stern tube and the other in the strut—many sailboats have inadequate shaft support.

product_beauty_shotThe shaft will enter the boat via a PSS dripless shaft seal, rather than a stuffing box.

The shaft will be fitted with a clamped collar just forward of the shaft seal boss to insure that the shaft will not foul the rudder or exit the boat in the event of the coupling coming loose; and so that the boat won’t leak catastrophically in the event of the shaft seal rot0r coming loose.

Fuel System

The boat will be fitted with a single high quality aluminum tank with baffles and large inspection ports so that all parts of the tank can be reached for cleaning.

I am hoping that this tank will fit in the bilge, and given the hull form that I favour, I think this is likely. Fuel tank size can’t be specified until the boat is drawn, but I am aiming for minimum flat water range under power of 400 miles at six knots. Because of the extremely efficient hull and relatively small engine, I’m guessing that this will equate to about 50 US gallons (190 liters).

racor 500A Racor 500 primary off engine fuel filter will be fitted. This filter is huge overkill for such a small engine, but it is the smallest one I know of that does not have a spin-on element—an invention of the devil.


The engine will be fitted with a single 80 amp alternator driven by a serpentine belt. The mounting points and belt system will be robust enough to take a 150 amp large case alternator for those owners that wish to fit one and keep the old alternator as a spare.


The instrument panel will be supplied with oil pressure and water temperature gauges, not just indicator lights. Loud alarms that can be easily heard in the cockpit will be fitted for low oil pressure or high water temperature.

Oil Change

A permanently mounted oil change pump will be provided.


A standard water lift muffler will be used, but particular attention will be paid to insuring that water can’t back-flood the engine. Precautions may include:

  • Center-line U-bend to deck height.
  • Surge tube fitted to exhaust outlet.
  • Telltale water flow into aft end of cockpit, rather than siphon break.


In order to avoid the use of a V drive, it is likely that the front of the engine will protrude under the companionway steps. These steps will be completely removable.

Access to the side of the engine, transmission and drive train will be from the “utility cabin” on one side of the boat and from a large cockpit locker on the other side. This will result in 360 degree access without too much disassembly. Grubby engine jobs will be doable from the utility cabin with all tools, parts, and a small work bench to hand.

The decision of which side of the boat the utility cabin will be sited will be, at least partly, based on the location of the service points on the engine selected—an example of the ease of maintenance driven holistic design that will go into the boat.

The Budget

Although this is a relatively simple propulsion system, there is no question that I have gone for a significantly more expensive solution than that proposed by Richard originally. And yes, it is possible that this could push us a bit above the budget number, although I think not since I plan to pay for this by being ruthless in the specification of other systems.

Even if this engine does push us over our original goal of US$175,000, I really can’t see the amount of overrun exceeding US$5000. And since our primary goal is a low ten year cost of ownership, this is worth it when measured against the cost and aggravation of, for example, replacing a defective Saildrive in some out of the way place.


If you have suggestions to improve this engine specification or questions about it, please leave a comment.

Like what you just read? Get lots more:

Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

191 comments… add one
  • Charles R Jun 15, 2013, 6:06 pm

    My comment got ridiculously long. I moved to it its own post at my boat blog.

    The post pertains to engine space and makes an argument in favor of outboards. Advantages and disadvantages are mentioned. I don’t recall outboard powering being discussed as an option for Adventure40, but I think it’s worthy of discussion, especially if you want to fit in your target price.

    • John Jun 16, 2013, 2:41 pm

      Hi Charles

      I took the liberty of moving you comment here, where I think it more properly belongs—a new power we have here at AAC world headquarters.

      Well you are certainly thinking outside the box. However I really can’t see an out board for several reasons, the most important being exposure to the ocean just when you need it most: clawing off a lee shore.

      Also in my some 55 years of messing around in boat the outboard engine has caused me more aggravation and expense than just about any other device.

      • Charles R Jun 16, 2013, 3:05 pm

        For those who won’t read the article at my blog, I am NOT talking about hanging an outboard on the transom. That’s an invitation to disaster to have your primary mechanical thrust system wide open to the sea. I’m talking about neatly tucking it into a well-designed engine well where it would be [relatively] protected.

        And, frankly, I don’t consider those little kicker motors hanging on brackets to be anything other than a hail mary when all else fails; or a trolling motor for fishing, in which case, why not use the dinghy? Those little bitty things will always be as finicky as lawn mowers. I think it’s just the nature of trying to shrink the IC process into such a miniscule package and then pushing the power envelope. I’m not sure exactly where the first reliability leap is, but I suspect it’s somewhere in the neighborhood of 20hp. The bigger motors always seem to be more reliable.

        John, of course you are right. Even a well designed to be nearly-sealed with the motor in its various positions cannot altogether stop water getting in and possibly up to the cowling. That said, it seems to be increasingly common for boat designs meant for the home builder (Selway-Fisher, Phil Bolger, a few others.) Some long-range commercial fishing boats are even being designed in this way, too, where the sole thrust comes from outboards tucked away in a well. This would never have happened much less than 20 years ago. Is this simply a demand-response thing, or is there some fundamental change in the product that makes them somehow worthy where they never were before?

        • Eric Klem Jun 16, 2013, 5:27 pm


          This is certainly an interesting idea for a way to go on propulsion. Everyone has their own set of requirements but lets pretend that the requirements for this propulsion system are: ~35 hp, >10% drivetrain efficiency (there are many other ways to state this), sailing efficiency (needs some quantification, >5000 hour service life, >100 hours service interval, reliable (I am not going to quantify this but it should be), easy to work on (again, it should be quantified), size, weight, max operating heel angle 45 degrees, max survival heel angle 120 degrees, maximum operating pitch angle 30 degrees, maximum g force, we need something about wave size but that is hard to state, something about drivetrain efficiency when the weather gets really rough, fuel safety, cost, and there are undoubtedly many that I am forgetting. Then, we would need to put weights on all of the requirements and decide which ones were absolute and which ones were squishy so that we could pick the “optimal” drivetrain. There are a few areas where a gas outboard and a diesel inboard would differ a lot.

          Efficiency is the first that I listed that I could see there being a major difference. In general, diesel engines will get 30-50% better fuel efficiency than their gas counterparts. This depends a lot on the operating point being discussed but it is safe to assume that a diesel engine will burn less gallons of fuel to do the same amount of useable work from idle to WOT. From there, you have to look at your drivetrain efficiency. Traditional inboard shafts are not the most efficient but they are not bad. Outboards and I/O’s do pretty well at high speeds but not nearly as well at low speeds. This is largely due to gearing as these are developed for high rpm with relatively small propellers. A diesel outboard (not yet widely available) with different gearing could compete on efficiency but today’s gas outboards won’t. It is worth noting that the sailing efficiency should be better with an outboard that is retracted.

          In general, outboards are designed for much shorter service lives than inboard diesel engines. Some of this has to do with the fact that they are gas versus diesel but a lot of this comes down to the tradeoffs made in design as they are designing to a different set of requirements than we will likely have.

          Outboards are the clear winners on power and size to weight ratios. This is really important for their target market but is likely much less so for a boat like the Adventure 40.

          Ease of service really depends on the design of the boat around it. An outboard that is fixed down in a well with only top access would be a complete nightmare but one that could be lifted would be great in a harbor and a nightmare at sea. The inboard will really depend on access and the layout of the engine. Modern gas engines have gotten pretty good but they still have more maintenance items than diesels.

          Finally, there is the nasty issue of which one you would want in a storm. First, the engine needs to survive which means dealing with heal, g force, water intrusion, etc. The major differentiation will be with water intrusion through an outboard well. In truth, an outboard could be totally sealed except for an air intake and the exhaust. If the air intake is the only concern, you could route it somewhere else as they do on race boats. At this point though, you basically have a saildrive except for the possible ability to lift the engine. In practice, it is really hard to seal an engine up tight and maintain serviceability so it is much easier to seal the space that it is in.

          If I were asked to weigh all of the requirements, I believe that I would weight them in a way that the diesel would come out on top. The major differentiators for me would be efficiency and rough weather including maintenance during rough weather.

          Sorry, this one got a bit long. I guess your idea of putting it on your own blog was a good one.


    • Marc Dacey Jun 16, 2013, 3:38 pm

      Charles, this is an interesting set of proposals you make. I have both a diesel inboard on a steel cutter, and a gas inboard (Atomic 4) on an F/G boat, along with various outboards. In addition, I am familiar with the still-extant series of ’60s and ’70s sub-30 foot fibreglass boats that sport “outboards in a well” of much the type you discuss, such as the Viking 28, Sharks and some others.

      I would say that your proposal is valid as far as it goes for coastal boats, but is impractical for offshore on the following basis: 1) Gasoline engines do not, in fact, yield the same kind of range as diesel, pound for pound. I downsized my Atomic 4’s fuel tank from 12 Imperial gallons to 10 U.S. and my “cruise speed” of five knots on engine alone in calm seas gives a measly 75 NM of range per tank. Ten gallons of fuel on a diesel of 60 HP (three times the power) on a steel boat four times the displacement at the same speed gives about 80-90 NM of range, a significantly better “energy density”.

      2) The second problem, to which many outboard owners can attest, is related to the volatility of modern gasolines, particularly those cut with ethanol. Not only does ethanol weaken certain types of gaskets and seals inside engines, but it attracts water to itself, creating issues of water separation and filtering. Related “performance-enhancing” chemicals in modern gas, such as xylene and tolulene, a solvent and octane-booster, seem to me to reduce the time in which gas is stable, meaning it’s fine if you run it daily or weekly, but doesn’t last a whole season or over winter without stability issues.

      It’s why, despite the fact I have difficulty running through even two 10-gallon tanks on my Atomic 4, I’ve switched to the no-ethanol premium grades of gas…it’s chemically easier to manage. I have a Honda 2 outboard with a gummed carb awaiting me because I chose regular gas.

      I think your idea, which has some merit in other regards, particularly if the outboard could be raised clear of the water when not in use, awaits a reliable diesel outboard of 30-50 HP, one specifically engineered to provide the torquey and relatively slow output best suited to a displacement hull. Certainly, the idea of a tight, vertical hole from which a 140-kilo outboard could be hydraulically lifted into the sunlight for service has great appeal over working on one’s hands and knees through access panels on a bolted-down engine. My steel boat has a 360 degree engine bay reached from a big hatch in the pilothouse floor, because (I presume) the original owner and his designer decided access trumped living space and wanted all water tanks, mechanicals and engine in the same metre and a half-tall by four metre “box”. There are few people for which this set-up would have appeal, although I’ve found it’s the single most appealing aspect for those who’ve had to fix more traditionally situated sailboat engine a thousand NM offshore!

  • Ed Seling Jun 17, 2013, 1:07 pm

    Why has no one mentioned the problem of keeping an outboard prop immersed in the water in large seas rather than just screaming uselessly in the air?

    • Charles R Jun 17, 2013, 3:29 pm

      Ed, it hasn’t been mentioned because its no different than keeping an inboard prop in the water in similar circumstances if the outboard is mounted as I proposed – in a well forward of the sternpost or transom in approximately the same location an inboard prop would be.

  • Neil McCubbin Sep 5, 2013, 2:14 pm

    This is a request for feedback, as well as a comment
    I am researching a replacement engine for a 43 HP Volvo 2003T, which has failed every year but one since launching in 2004. Each failure lost a week or so of sailing, and some were expensive. About 5 other failures that I fixed in an hour or so.
    Surprise! We will not buy a Volvo at any price.
    We have looked at a lot of info, and have pretty much narrowed down to a Yanmar 53 HP , a Beta 50 or a Beta 60. We have feedback from a number of friends with years of cruising experience, and most recommend Yanmar, some Beta and some say equal. Those that have Beta all refer to zero failures
    So far, we are put off by Yanmar insisting that warranty will depend on a 76 mm exhaust system, despite the fact that back-pressure measurements on our existing 60 mm system show that it will develop only about half the back pressure that Yanmar specifies as maximum. The cost and work to change to 76mm dia is one issue, but more disconcerting to me is Yanmar’s unwillingness to let customers discuss technical issues with engineers or technicians, and being faced with salesmen who act like lawyers.
    Beta are more approachable, but we are not done yet.
    The SSCA gear survey shows the Yanmar breakdown rate to be about half that of Volvo. It also shows Beta breakdown rate at zero, but based on only about 40 engines, whereas the Volvo/Yanmar data is based on hundreds of engines and longer installed time
    I like the availability of Kubota industrial engine parts, and the fact that Beta gives customers a Kubota parts book, instead of trying got sell marked up parts, as I am told Universal does.
    Questions for readers of this board
    1) Any opinions on reliability of Beta (Kubota based) vs Yanmar?
    2) Any comments on the level of mechanical noise (not exhaust) of Beta vs Yanmar
    3) Any comments on Nanni, or other Kubota based engines vs Beta?

    • Ed Seling Sep 6, 2013, 1:31 pm

      Just a data point for Beta 50: 800 hours so far on engine I installed in 2010. (Engine layed up for 2 seasons.) No mechanical issues except for Balmar alternator which heated up more than I was comfortable with. Not a Beta problem Extremely helpful staff at the North Carolina US center has quickly answered any questions I have had in any amount of detail desired. They also list common auto store filters etc that can be used instead of oem parts.

      The custom mounts they made for me were exactly as I had ordered. The engine is leak free and the noise level is not out of line for a small diesel engine. I think it is also important that it is naturally aspirated. It starts easily in temps down to 50F with no heaters. All in all I am extremely pleased with this engine.

      BTW I opted for a Borg Warner transmission which I would recommend for durability but not for weight!

    • Eric Klem Sep 6, 2013, 1:52 pm


      Here is my take on the decision that you are facing.

      1) From a very high level engineering standpoint, I slightly prefer the Yanmar. From a practical execution standpoint, my personal opinion is that Kubota has slightly more reliable engines than Yanmar. Yanmar engines are decent but most models seem to have common failure modes. The Kubota engines that make up the base of the Beta package are very well executed, they are extremely durable but not overweight. I have only worked on a few betas but have several friends who have them and I have worked on the same engines in tractors and they take very little to keep them going well. Beta service is very good and Yanmar service is very much a function of your dealer. I would recommend researching the specific engine models you are looking at for known problems instead of just the makes and look into your local dealer. If you are going to be traveling abroad a lot, think about availability of parts there. Think about ease of service with each engine in your specific installation, sometimes locations of things like water pumps and oil fills can be a real nightmare for a specific boat. If I had no experience with either one and only looked at spec sheets, I would choose Yanmar but in the real world, I would probably choose a Beta.

      2) I don’t feel that I can say this as I have never had a true apples to apples comparison, there have always been other factors involved.

      3) Nanni engines seem to be much less popular around here but I do know of a few boats running them. I have not heard any complaints which is a good thing but my sample size is too small to draw any conclusions. Talking to a Nanni rep, he made several claims about why their engines were better than Beta but with everything that he mentioned, I felt like Beta did it just fine so I was wondering if this was just a sales pitch or whether they were fixing problems that don’t exist.


      • Marc Dacey Sep 6, 2013, 2:15 pm

        Eric, very good points and essentially lists why I went with a Beta-marinized Kubota (the 60 hp, 2403 cc model). Correct me if I’m wrong, but are not Nannis simply Kubota diesels marinized in France? Unless Beta has some as-yet unknown shortcomings in this area, they couldn’t really be “better”, unless they are supposed to have some sort of extra-special heat exchanger…

        As we are discussing good ideas for the Adventure 40, whatever engine is determined to be best should have as standard equipment a remote oil filter. Too many engines “feature” horizontally installed filters, which invariably spill oil during a swap-out whether one has drained the sump or not. Vertically mounted ones can be taken off and set in a margarine tub or something without spilling a drop. Care has to be taken to use hoses good to 300 PSI (or even hydraulic hoses crimped on), but I have found it odd that fuel filters are (usually) orientated vertically, while oil filters sit sideways, way down on the block, within a penny’s thickness of the engine stringers.

        • neil Sep 6, 2013, 3:29 pm

          Remote oil filters
          Agreed that oil filters are often poorly located. Our Volvo is one of the worst, since it is immediately over the water pump/alternator drive belt, with no room to catch the drips except what can be done with paper towels. DUMB engineering, and one reason I will NEVER buy a Volvo again. Any company who will sell such an abomination does not take maintenance seriously.
          While a remote, vertical, filter in a good location to catch the drips in a bucket is an asset, it is also one more thing to go wrong.
          In the Beta engines we are looking at, the filter is on the side, near the front, and it will be easy to slip a small container under the drippy part.
          If we buy Yanmar, then we will buy a remote filter kit, since the Yanmar filter will be hard to get at in our boat.
          One trick we find useful with horizontal oil filters it to drill or punch a small hole on the top, then do something else for an hour or so. Almost all the oil drains to the sump, so the filter is much less messy.

  • Neil McCubbin Sep 5, 2013, 2:24 pm

    Permanent oil change pump
    We added on years ago, and are pleased with the results. A few ideas:
    Best with an electric pump, reversible, and mounted beside the engine. That lets you fill without pouring.
    Our pump (West Marine) has a built in switch, which moves in the direction I want the oil to flow. .
    We have a 1/2″ ball valve in the hose from the engine to the pump, reducing the chance of accidental emptying of the engine.
    On simple way to avoid mess is have the discharge UP into a host a foot or so long. When finished with the change, point it up and secure it, and run the pump in reverse to empty the hose. No drips.
    I would post a photo, but do not know how

  • Dick Stevenson Sep 6, 2013, 7:21 am

    Neil, We have been doing the same dance over the last couple of years. I wrote my reasons for choosing a Yanmar over a Beta on this site a while back. With Yanmars dealing with the company is the pits (my experience and unlike dealing with Beta which was a joy) so I have gravitated to only dealing with dealers. My dealer/installer received permission for a smaller exhaust hose, 2.5 inches, from Yanmar, so the warranty will be intact. I will test the back pressure after installation (this winter I expect), but I can’t imagine their being a problem.
    Dick Stevenson, s/v Alchemy, Vlieland, The Netherlands

  • Gene Gruender Dec 30, 2013, 12:46 pm

    You mention two cutlass bearings. We have a problem with our Cheoy Lee 40 Midshipman with an 11′ long 1 1/4″ dia shaft. It bangs and clatters around in the long tube under the floor. A new shaft, removing the flexible coupler and a very precise alignment helped, but at some RPMs it still gets pretty bad. I’d thought it needed a bearing in the middle but cutting open the tube, building a mount and re-sealing seemed pretty radical. I’d never heard of it being done.

    Now that you’ve mentioned it I don’t feel quite so crazy to consider it. Boat yards around here struggle to do a decent bottom job, this would be a different planet for them. If anyone reading this has a link to this being done or info that might help I’m all ears.

    • John Dec 30, 2013, 3:12 pm

      Hi Gene,

      First off, there are a lot of things that can cause the noise and vibration you speak of, including: a bent shaft, out of true coupling, worn out engine mounts, and worn thrust damper plate. Don’t assume that all or the above are right, just because they are new. The only way to be sure on the first two is to take the shaft out and have it checked by a competent machinist, ditto the coupling, which should be faced while on the shaft. I’m assuming you have checked the existing cutlass bearing.

      An 11′ unsupported span on a 1-1/4″ does sound long, but don’t assume that is the problem. There are standard specifications for the amount of allowable span for a given shaft diameter.

      If you were in Maine, I would say go to Billings Diesel and they would sort this out for sure. As you say, boatyards that actually know what they are doing in this kind of situation are few and far between. So your best, and cheapest, bet might be to enlist the help of a good commercial machinist. Even if he knows nothing about boats, he will know how to get a shaft true. Also, if he is competent, he will know where to look to determine if that shaft length is unacceptable.

  • Everett Woodworth Jan 12, 2014, 6:19 am

    As a live aboard cruiser repowering my Whitby 42 with a Beta 50 your site answered so many questions. Oversizing the gear is my choice for reliability. Cruisers motor much more than most admit. Pegging the gear ratio is the mystery I need to solve. Also I want to freewheel the prop but what about bearing wear?
    My favorite tip is a bilge pump counter. If you find counts you have a problem Houston. If you have been away or motoring there is no way to know if the bilge pump is cycling. The more visible the location the better.

    • Skeeter Sep 17, 2014, 8:05 pm

      I am also re-powering my Whitby 42 with a Beta 50. May I ask, what did you do for your engine bed mounts? I’d love to know what you think of it, if you have it completed.

  • Bill Attwood Jan 12, 2014, 11:46 am

    As usual, the comments are worth as much (sonetimes more, sorry John) as the original post. Almost a primer on marine engineering. Re suggestion of an outboard as a solution for the A40, I suspect that this would move the weight of the engine significantly towards the stern which would not be a good idea. Some (all?) of the French alu boats have their engines in the saloon, which is great for weight distribution, and gives fantastic access.

  • Bill Attwood Feb 8, 2014, 3:10 am

    Hi Matt.
    A brief follow up on your post re PEX. I replaced all 3 stainless tanks on Kinsa. All were corroded on their base, and showed signs of corrosion on the welds. I have replaced with high density PE. the new tanks are approx 30% lighter, corrosion resistant, and have increased capacity – they fit their spaces better. Internal baffles also help to prevent flexing. I had to accept the disadvantage of PE (thermoplastic) for the diesel tank (I believe the melting point for HDPE is about 135°C). Although PEX is not thermoplastic I believe tanks in this material can only be produced using spin molding? Do you think that the potential production volumes would make this an option for the A40 tanks?
    Yours aye,

  • Rob B Feb 28, 2014, 1:57 pm

    Amazing that I made it to bottom of this chapter’s comments! This book is a virtual course in marine technology & testament to the depth’s of John’s & other AAC member’s patience & knowledge.

    Credits to all who were concise, a few others could do better, please! Anticipate that newcomers considering A40 purchase will try to wade through this discourse so worth keeping that in mind. Impressive debate though may need some future editing. Most important, the completed A40 I hope to buy should have excellent odds of meeting it’s goals due to all the effort, knowledge, & care invested here.

  • Neil McCubbin Sep 18, 2014, 3:43 am

    We replaced a troublesome Volvo with a Beta 60 in May.
    300 hours on it this summer with no problems
    Even in Spitsbergen in water at 0 degrees and air temp about – 1 it always started first bang without using the glow plugs.
    It is mechanically quieter than the Volvo.
    We had to redrill the aluminium engine beds and block it up a bit, using the standard Beta mounts

  • Emilios P. Sep 20, 2014, 4:20 pm

    On the drive train, has there been any thought of fitting an Aquadrive (or similar) system that pushes the boat rather than the engine that then pushes the boat ? seems a better way of doing things…

    • Laurent Sep 20, 2014, 5:30 pm

      Its about 1,500$ + taxes and it does not reduce noises very much on new composite sailboats aux. engines, unless engine is not correctly installed.

      Often quite effective on metal boats with old diesels, shafts misalignment and/or antiquated silent-blocks….

    • John Sep 21, 2014, 2:23 pm

      Hi Emilios,

      No, no plans for an Aquadrive. They are good pieces of kit, no doubt about it. In fact we have one on our boat. But as Laurent points out, they are expensive and his estimate is just the parts. Installation is not trivial either. Also, it’s another thing to maintain since he small ones need to be serviced every 1500 hours. In summary, just not worth it with such a small engine.

      On an engine this size, it’s really not worth it.

  • Gerben SYD Nov 16, 2015, 9:01 am

    Now, please don’t bite my head off for asking this question: Can we have an electric engine in the Adventure 40? Considering one of the key objectives of the A40: bringing in first time, younger buyers into the world of cruising, at a budget they can afford (such as myself), the requirement of becoming a part-time diesel mechanic is something I can do without. Too much ‘regular’ maintenance, noise, smell, big tanks full of diesel, even this website has plenty of articles of things that go wrong with diesel engines. I’d rather have a clean, green, silent, easy to maintain, no-smell, electric motor. Coupled with a hydro-generation function of the prop/shaft, all you need to do is keep those batteries topped up: solar, wind and hydro generation is the way of the future. That younger audience the Adventure 40 targets would most certainly appreciate these benefits.

    • Jo Nov 16, 2015, 12:42 pm

      Given this article from two years ago, I don’t think any kind of electric drive is viable for cruising today. Today electric seems to work best for day-sailors on the weekend, where the batteries can either recharge at the dock or during the whole week from other sources.

      • John Nov 17, 2015, 9:07 am

        Hi Jo,

        You got it.

    • John Nov 17, 2015, 9:10 am

      Hi Gerben SYD,

      No one would be happier than me, for all the reasons you mention, if electric drive was a practical alternative for the A40. However, for the usage profiles of most cruisers it simply isn’t.

      See the posts I linked to in my comment below for why.

  • Simon Wirth Nov 16, 2015, 10:28 am

    Hei Gerben
    As one of the younger adience and as an engineer, I have to say that I wouldn’t like to go this way. The energy density is to low for my liking in current day batteries. You’re right, becoming a part time diesel mechanic isn’t too high on things I like to do, the safety of mind a full diesel tank gives me just can’t be reached with batteries and regeneration at this time
    Regards, Simon

    • Marc Dacey Nov 16, 2015, 1:28 pm

      Even though with a steel full-keeler, I had the option to carry half a tonne (or more) of batteries, I came to a similar conclusion regarding electric motor systems. The closest thing that makes sense is a diesel-electric hybrid setup, but that just adds complexity without any real benefit in my view. So I put in a diesel. I have renewables sufficient to charge without running it (unless I’m already moving under power), and that at least avoids the “run the diesel to make the ice cubes” equation.

  • RDE Nov 16, 2015, 1:57 pm

    One of the objections raised to electric motor drive systems in the discussion a couple of years ago was the lack of fully engineered and integrated systems in the marketplace. Here is a company that offers that type of system :

    • Jo Nov 16, 2015, 2:48 pm

      Going by the Oceanvolt FAQ, the batterypack gives 4-6 hours cruising and take 5-10 recharging from shore power. Definitively an attractive proposition for many uses, but will that work for cruising?

      • RDE Nov 16, 2015, 10:01 pm

        Hi Jo,
        In order to answer that question you need to analyze the actual full cycle utilization pattern for the particular style of cruising anticipated. For example, if you were cruising in the Caribbean on a catamaran with the cabin top covered with solar panels, two wind generators and regen capabilities under sail, and typically spent a week at anchorage followed by a brisk tradewind passage to a new anchorage you would never need to use diesel or shore power charging.

        Analyzing the system solely on the basis of energy conversion losses when motoring in diesel electric mode is something like describing an elephant by feeling its trunk.

        “I can see no way an electric drive system of any practical weight and physical size will push a boat into a 20 knot headwind and a 4 foot chop.” Did you happen to look at OceanVolt’s video of a pull test between a sailboat equipped with a 20 hp diesel and a similar sized boat equipped with a similar rated small electric drive? I think that answers your question. And if it is a diesel electric drive system there is no limit to the size of boat or its ability to power compared to a conventional ICE drive.

        I for one cannot predict the future price or charging efficiency of Li or other batteries under intensive development for land transportation, so I would never say “never”. I do know that an electric motor is inherently more reliable and less expensive than an internal combustion engine, and from that fact would predict that at some point their cost benefit curves will cross.

        I’d be the last to argue that in the year 2015 electric drive systems are as highly developed or as cost effective as a Basic Beta, especially for a price conscious 42′ monohull project. But at some point the cost benefit curves may shift for even this limited application.

        • Jo Nov 17, 2015, 4:09 am

          So in the end, if one sails a lot and motors only a little, the electric drive and a backup-generator like many sailors have anyway might do. It’ll be interesting how attractive this will be on the market.

          On a related note, the french yacht Amasia has shown, that an electric yacht can cross the Panama channel. That’s often cited as a most severe limitation of electric motors.

    • John Nov 17, 2015, 9:00 am

      Hi Richard,

      Actually, that’s not so. The posts we did on that subject dealt with the fundamentals that are not changed by a new product.

      Bottom line, the practicality of electric or diesel/electric or electric drive depends on the usage profile.

      • RDE Nov 17, 2015, 11:47 am

        Agree totally: The usage profile plus the cost/benefit.

  • Neil Nov 16, 2015, 4:27 pm

    I am a mechanical engineer by profession, and I think I understand the basic laws of physics as applied to propulsion quite well, both on a theoretical and practical basis.
    The only type of cruising sailing where I can see an electric drive being satisfactory is for the sailor who wants to sail engineless, like our grandfathers, or the Pardey’s, but wants a little power for flat calms, manoeuvring in dock etc. He could realistically charge his batteries by wind and solar, or while dockside, and thus avoid having a diesel, while accepting the constraints on performance under power.
    I can see no way an electric drive system of any practical weight and physical size will push a boat into a 20 know headwind and a 4 foot chop.
    In addition to this basic performance issue, the reality is that companies offering electric propulsion systems are experimenting, so regardless of how clever they are, they cannot possibly sell a systems as reliable as something like a Beta diesel with many years of engineering experience making millions of small diesel engines behind it.

  • Neil Nov 17, 2015, 1:40 am

    The video of the electric powered boat towing the diesel one backward is indeed impressive. I am old enough to have seen lots of promotional videos for various products produced by competent engineers. Some were grossly misleading.
    When Oceanvolt shows an 8kW (=10.7HP ) having more pulling power than a 20 HP boat of similar size and type, all it means that the Oceanvolt boat has a well selected propeller for slow speed pulling while the diesel has poorly selected prop. Notice the lack of propwash from the diesel boat. Of course the electric motor has better torque at low revs, but that does not explain the difference in propwash. Our 53 HP diesel on a 47 foot boat make a LOT more propwash when gunned at a standstill.

    The video of hoists all by itself. Feeling mentions 4 hours cruising range at 4 knots with a Honda generator. Being gasoline or propane, it has an ignition system. Not very seaworthy.
    Now we have an ICE to maintain. This also confirms that the electric system is for short term use only, unless an ICE generator is added. Also, when I see claims that some new, complex, and innovative system is “maintenance free” my BS flag rises.

  • John Nov 17, 2015, 9:04 am

    Hi All,

    We have already published posts on electric and diesel electric drive options and then debated them at length.

    Bottom line, neither technology is practical for most offshore cruising usage profiles.

    Those interested in getting a better understand of the fundamentals will find this this post helpful:

    Those who would like to see if their planned usage profile would be well served by electric or diesel electric drive can experiment, without spending tens of thousands on the wrong alternative, here:

  • John Nov 17, 2015, 9:13 am

    Hi All,

    If we really must go through the whole electric drive thing yet again, please make your comments to the posts I have linked to above, not here.

    And please read the posts before you comment.

  • Terry Mason Dec 10, 2015, 1:41 pm

    I see you are planning to use the PSS shaft seal, is it really as reliable and bulletproof as a stuffing box with PTFE packing? My Beta dealer would not sell me anything other than the stuffing box for offshore, but I like the idea of totally no drips, although the PTFE comes close. Pros and cons?

    • John Dec 11, 2015, 9:19 am

      Hi Terry,

      I agree with Neil. We have been using PSS shaft seals for just on 20 years without problems. I also like them for the A40 because they are not dependant on a tricky adjustment (the amount to screw the packing nut down) like a stuffing box is.

      • Terry Mason Dec 11, 2015, 11:07 am

        Hi john,
        It’s time to change my packing, a tricky job and I always wonder if it will leak when the boat is launched, I will make the change to the P.S.S. this year. Thanks for you input.

        P.S. any news on the A40’s progress?

  • Neil Dec 10, 2015, 3:01 pm

    I think your Beta dealer is rather out-of-date.
    I was suspicious, but bought one for our then new Garcia Passoa 47 in 2004. (We had a stuffing box on our previous boat)
    We have had the PSS seal for 30,000 miles, including Caribbean, trans-Atlantic and up to 80 North, spread over 11 years.
    No problems other than having to push the collar back once to tighten the pressure to stop a TINY drip.
    We replaced the bellows a year or so ago on the standard PSS recommendation, but the old one still seems to be OK

    • Terry Mason Dec 10, 2015, 7:53 pm

      Thanks Neil, good to have some real world feedback.

  • Dick Stevenson Dec 11, 2015, 12:17 pm

    Hi Terry,
    I echo others advice about the PSS Shaft seal. I have over 30 years on 2 boats. A quite wonderful pictorial installation essay can be had at (along with many other very helpful essays).
    My best, Dick Stevenson, s/v Alchemy

  • Bill Attwood Dec 11, 2015, 12:43 pm

    Kinsa has a Manecraft (a subsidiary of Wärtsilä) shaft seal, the same basic design as the PSS, and I believe just as good – their main customers are the RN and other navies. The seals should be good for 10,000 hours of service, or 100,000 sea miles, but they do recommend a new shaft seal every 5 years.
    When I bought Kinsa in Falmouth and sailed her back to the Baltic, the seal started to leak off the Dutch coast, and we had to divert, haul out and change it. The date stamped on the old seal was 11 years earlier! I am really happy with the performance of the seal, but I do now carry a spare.

  • Leif Drabløs Dec 11, 2015, 7:26 pm

    I really like the comments on Adventure 40 and the knowledge that are behind them. I also like the design ,even if i belong to the heavy brigade, long keel enthusiast, provided it is designed as a sailing boat ,not a barge.
    I like the fine ends, the proclaimed soft movements in heavy seas(even if i am not completely convinced on this yet, as the boat is very light). But most of all i like the aft hung rudder, doing away with the shaft and the problems associated with that. The main thing is that it is planned to have like a weak point, like a bolt that will shear if the rudder is hitting anything, like f. ex a timber log.Then You can Just push the rudder down again and put in a new bolt. I would never have accepted an unsupported spade rudder without such a feature.
    However, I have two suggestions for improvements , on the equipment of the Adventure 40. Have You ever looked into a propellar shaft called the Rodahl shaft. it is a shaft with an outer pipe ,and in the inboard end there is a SKF crossbearing, axial and radial bearing and in the other end a glide bearing, seals in both ends. It will be filled with gear oil. The thrust from the propellar will be taken up by the x bearing, so it is possible to fit a doubble cvt joint between the Rodahl shaft and the gearbox, making it possible to have soft motor beds. The Rodahl shaft were developed in Sweden in mid sixties and have a reputation of very high reliabilty, the bearings and seals beeing protected by oil. It was quite popular in the 70ties and 80ties, but after that the more conventional equipment have taken over. I have never understood why it is not more popular, as 20 years or more of troublefree operation is not uncommon. But I have bought one for my boat, and then i probably understood why. This part of their buisness is run buy the invenor himself, i suppose he is in his late 80ies and want to run it at his pace. I will attach a photo of my new shaft if i can. They are still making it and the price of this, at least bought from Norway, is lower that the alternative standard seawatercooled bearing, shaft, pipe and seals, when i checked it up.
    Another proposal for improovement ,that i got from some motorboat friends of me from west coast of Norway is about diesel fuel security.
    Filters is ok, but if You get diesel bugs ,and discover it when You comes out in the high seas(which is when You will discover it), You can hardly filter You away from the problem. You need to get to a harbour or inlet ,empty and clean the tank(s). The idea is to have an extra smallish tank, about the volume of 10 hours running in cruising speed ,installed not far away from the engine. Then lead the return diesel from the diesel pump into the bottom of this tank. Out from the top of the tank the diesel goes to your usage tank. In normal mode the return diesel goes via this tank that is kept completely filled all the time, securing that water cannot condensate. Then from the pipe entering the bottom of this tank You take off a pipe with a valve to go to enter the normal diesel line to the engine in between the prefilter and the filter on the engine. So if You get problems with dirt or bugs in the diesel when you come out in more rough conditions, You only have to open one valve ,and then You have 10 hours of troublefree running, hopefully enough to get You to a place You can clean your tanks.
    With best regards , Leif.

    • John Dec 13, 2015, 10:37 am

      Hi Leif,

      Interesting ideas, although I’m not sure we will be able to afford them. To meet the price point and still have a strong safe boat, we must prioritize the budget toward structure rather than gear. So, while I agree that day tanks, for example, are a good idea in some ways, an A40 with a relatively small tank and very large primary filter (in relation to engine size) should not have many problems with fuel bugs.

  • Kit Laughlin Aug 23, 2018, 6:34 am

    What a wonderful thread. Two questions, if I may:

    Would the designers consider a power-only version of the A40 (if this has been canvassed, please delete!) and can John point to the design rationale behind the aft-hung rudder; we hit logs and containers around here from time to time, and that’s the only part of the design that raises a flag, for me. I did read the notes in
    on this.

    • John Aug 23, 2018, 6:56 am

      Hi Kit,

      I have thought from time to time about a simple motor boat. See this series:

      As to the rudder on the A40, I can’t see why being on the transom would make it any more vulnerable, unless you are comparing to a skeg hung rudder. If so, yes, it’s a trade off. That said a transom hung rudder can be made to kick up and/or have a blade that can be replaced at sea.

  • Kit Laughlin Aug 23, 2018, 7:05 am

    Hello John; thanks for responding. I had read the linked posts—but could the A40 be repurposed to this end? If it could, it would be competitive with the Sea Piper being discussed, and would be a much better long-distance power boat, too, IMHO.

    I am working in the UK for the next month; many yachts here have twin bilge keels, and that’s the direction a power-only A40 could go, perhaps.

    I was thinking skeg-hung rudder initially, but the arguments in favour of a transom-hung rudder are convincing, too. This is such an interesting project!

    • John Aug 23, 2018, 9:45 am

      Hi Kit,

      I would start with a blank sheet if doing a motorboat, not repurpose. Motorboats have completely different hull forms because they don’t need large ballast ratios to balance the rig. Therefore starting with a sailboat hull to design a motorboat is fundamentally wrong.

  • Kit Laughlin Aug 23, 2018, 11:07 am

    Excellent point, John.

  • Mike Feb 25, 2019, 7:07 pm

    So I noticed you don’t like spin on filters? Why not? I find the bowl is much easier to clean if needed, and mine has an integral priming pump so after I spin on new filter I can pump the filter full of fuel and bleed out air. With my prior racor 500 i had to keep a separate can of diesel fuel to fill the bowl after filter change.

    • John Feb 26, 2019, 10:38 am

      Hi Mike,

      Each to their own, I find the 500 series much easier to deal with and less messy, but then I always keep a small jug of clean diesel available.

  • ric Moore Mar 9, 2019, 12:23 pm

    Where can I get the permanently mounted oil change pump?

    • John Mar 10, 2019, 9:35 am

      Hi Ric,

      I’m sorry, I don’t know, our Perkins came with it already mounted. That said, there are aftermarket oil change systems. I found a bunch of options with a quick Google search. Here’s one example:

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