Get-Home Backup for Offshore Motorboats—Part 1, Is It Even a Thing?

As those of you who have been members a while know, I have been writing about safe and efficient offshore motorboats for a couple of years now in this Online Book, and working with two designers on satisfying that design criteria at a price that's a little less stratospheric than Steve Dashew's wonderful boats, albeit with less capability too.

Right now, there is only one new boat available that even comes close to meeting that criteria: the Artnautica LRC 58 (picktured above).  So far two have been launched, one of which has crossed the Pacific, with two more in-build.

With the exception of the designer Dennis' boat, all were selected by their owners as a result of exposure here at AAC, so it does seem as if we are making progress toward our goal of a motorboat that solves the weaknesses of the trawlers currently on offer.

And early last winter I wrote about an AAC Adventure version of the Artnautica 58 that Dennis and I had come up with for those who want to get a bit more aggressive with their cruising.

I'm also thinking about traveling to test one of the Artnauticas in the water, particularly in big breeze and waves, and writing about that, although funding will need to come from somewhere other than my pocket or AAC to make that happen.

In addition, Boréal have asked me to provide input on an offshore motorboat that they are considering adding to their incredibly well-thought-out and successful line of offshore expedition sailboats.

During all of this, two questions keep coming to the fore:

  • What to do about backup or get-home power in case the main engine fails?
  • Which of several stabilization options are the best for a boat of this type?

And Steve Dashew, who knows more about the type of boat I envision than anyone, has confirmed in one of our telephone chats that these two questions should be settled very early on in the design process. An assertion confirmed by the amount of push back from the market against the first Artnautica LRC 58s launched that have neither a viable get-home or stabilization.

So I have been thinking about these two challenges for the last couple of years, as well as discussing them with motorboat experts.

In this chapter and the next, I'm going to look at the options for get-home power in case the main engine fails.

Subscribe
Notify of
39 Comments
Oldest
Newest
Inline Feedbacks
View all comments
Alan Bradley

Hi John,
Great topic as always. One word, Catamaran, sail or power.
Thanks, Alan

marcus petraska

i think i am coming around to the same realisation – a powercat – not needing a remedial stabilising system – either active or passive – is very appealing

Stein Varjord

Hi John.

Being a sailing fanatic, 🙂 I shouldn’t think this topic is interesting, but I still do. I guess I should punish myself by flogging my back, like a good monk(ey). 😀 Or maybe I I’ll just indulge in pondering this just for fun? Flogging or fun. What should I choose? 🙂

I think a possible catamaran version of this motorboat concept was mentioned in a previous post, but either way, here goes: A sailing and multihull fanatic talking about motor boats, (mostly). I know catamarans are not what you (and many others) feel attracted to, but it does have some big advantages. One of them is the redundancy of the double set of main engines, including two totally independent fuel systems, battery charging systems, heat source and propeller, which is nice when the other has got a rope wrapped around it. Two rudders can also be handy. The extra cost of two main engines will be partly offset by needing considerably smaller engines and no need for a bow thruster. For complicated manoeuvres, two main engines beat single engine with bow thruster hands down. As I’m now a professional skipper on a lot of different tourist boats on the Amsterdam canals, I’ve tested it quite a bit. 🙂

The smaller engines can also run on a proper high load, keeping it efficient and healthy, without going ridiculously fast all the time. One of them is off to save fuel. In the rare situations when max power is needed to get out of trouble, twin engines and props make a difference on the “grip” in the water. A cat will also have a significantly higher max speed and cruising speed with the same fuel consumption. That’s true even for a shorter one with the same interior space.

Stabilization is also mentioned in this post. A catamaran, of course, doesn’t need that. It will be more pleasant to be on in a seaway, either at anchor or on the move. Monohulls exaggerate the waves as a pendulum. The motion is not in synch with the wave pattern and frequently a wave hits at the worst time and place to increase the move rather than dampen it. That never happens on a cat, which will synchronize, even out and move less than the actual wave pattern. Many anchorages are intolerable or even unsafe in a mono due to swell while being not even unpleasant on a cat.

Capsize is an issue on this type of motorboats, intended for use in severe weather. A monohull is fairly easy to make self righting. Actually easier than a sailing mono, despite the deep keel of the sailing boat. A similar motor catamaran will be probably be much narrower than a typical sailing cat and have a bigger superstructure. It should be fairly easy to make completely self righting too, but that claim would need checking with an actual design.

If even more propulsion backup is wanted, a cat version would be a more capable sailing boat too. The much better stability would provide the extra upwind ability in heavy conditions. A daggerboard swinging down between the hulls would ensure superior windward VMG. Most here probably know this, but just for the record: The usual belief, that multihulls don’t go well to windward, is false, (unless there is almost no wind). Reality is that they outperform any similar type of mono to windward, especially in stronger winds. This is because of issues with hull efficiency versus stability/power. Several multihulls are lousy sailboats. Same with monohulls. Those designs are flawed, not the boat types. Most of the present day cruising cats are totally motor sailors, prioritizing motor and harbour, overly heavy with ridiculous rigs, but still they sail acceptably.

Then it’s the building and running cost plus docking space issue. For a given length, a cat will be wider and cost more in harbour, be more complicated to build, meaning a significantly more expensive boat. However, for a given length, a cat is normally a much bigger boat. It has much more space inside and outside, it’s faster. It has more comfort features. In sailing versions, I normally say that it’s fair to compare a 40 foot cruising cat to a similar mono of about 55 foot. Then the building price, running cost, harbour troubles etc will be more than the cat with the same interior space, speed, etc. Boat length is a bad criterion to compare cats and monos. I think that in a motor version, this issue is definitely still valid but less significant due to the smaller width needed.

The last issue I’ll mention is aesthetics. Even most monohull sailors think extreme racing multihulls can be beautiful, but that most cruising multihulls totally lack the ability to create a spark to make us love them. Many of them look expensive, but beautiful? Mostly not at all. Even a fanatic like me will totally agree on that. To be willing to go for a motor cat that I mention here, one needs to make a design that looks properly attractive. That’s a challenge, but definitely possible. Probably most readers here will just not consider a cat version of the long distance adventure motor boat. I strongly believe that’s because of this last issue: Aesthetics. Feelings. If Boreal looks at making a motor boat and treats this last issue well, I think they will have a winner.

Stein Varjord

Hi John.

I never thought of you as a multihull hater. Such an emotional position would be impossible to combine with the analytic nature of your efforts here. When I assume “most people here” have a preference for monohulls or opinions about catamaran aesthetics, I actually mean the readers, not you. I judge the readers as members of the general sailing population, albeit on the experienced side of the spectrum. Since the majority of sailors are monohull sailors, and sailors in general may be a bit more conservative than the average man in the street, I generalize, which is always problematic, of course.

RDE

Hi Stein,
I’m with you 100%. Its been fifteen years since I developed and built production tooling for a sailing catamaran that would exceed 20 knots under power and under sail. Not what the market wanted*, although I did have deposits on three boats before the first hulls came out of the mold. (* what the market wanted was a floating condo/drinking platform)

And by the way, the Lightspeed 58 was one of the few catamarans that is actually beautiful, so it can be done. (no bias here since I did the styling) LOL Of course that involved compromises in build cost and control of solar overheating, but compromises are always the case! And the fact that the one in the pictures was built by a fly-by-night builder using cheap polyester resin and two tons overweight did it no favors.

As for the esthetic of power catamaran design , my friend Kurt Hughes hit the sweet spot with his 50′ design that has trawler references in the house styling but sits on a very efficient pair of narrow beam hulls with high bridge deck clearance. (http://multihulldesigns.com/designs_stock/50pwrcruisingcat.htm) Not a boat to push through pack ice near Greenland, but rather for the ICW and on down the Bahamas & Caribbean or from Puget Sound up to Alaska.

RDE

John,, sorry for going off topic, but you know what happens when I get started on the topic of efficient power cat hulls!

RDE

re: “get home”
Five months adrift in the Atlantic winter and still the best lifeboat!
http://sailinganarchy.com/wp-content/uploads/2017/05/upside-down.jpg

Chris Groobey

Hi John, first-time commenter here, so first let me say thanks for the site, enjoy it greatly and recently relied on your experience with Lifeline batteries in replacing the batteries in our FPB 64.

Speaking as the second owners of an FPB64, I’ll contribute that in the 1600 hours (roughly 15,000 miles) we have used our boat so far, we have suffered two main-engine impeller failures while exiting harbors via narrow channels, both caused by foreign objects being sucked up into the sea chest intake pipe (one a fish, the other a large chunk of sea grass). In both of these situations, it was very important for us to be able to start the back-up engine immediately and continue out the channel before finding a safe place to change the impeller on the main engine. The concept of back-up propulsion is most definitely not an “emotional crutch,” nor (obviously) would a back-up sail plan help in these situations. There are soft spots to all engines, they are usually made of rubber, whether impeller, hose or otherwise, and the assumption needs to be that they will always fail when most dangerous to do so, not necessarily mid-passage in a wide open environment.

The previous owner of our boat had the back-up engine added by the builder after an initial period of use and I believe all but one of the other owners (11 FPB64s now built) have also either spec’d or retrofitted back-up power as well. Note that all other FPB designs are twin-engine, so the problem is less of an issue for all designs after the 64.

Without knowing how detailed you plan to get in your future examinations, one question that crosses my mind is just how separate the backup propulsion needs to be. In the FPB, we have an entirely separate engine and drivetrain, which I generally think is correct, but it shares the seachest with all other raw water consumers. This is fine unless, as in our situations, the reason for main-engine failure is raw water starvation at the sea chest, in which case the back-up engine is not getting raw water either. This has not been a problem for us, as it’s easy to manage the coolant temp of the back-up engine and if needed we would just run it hot until failure, but I think in a perfect world I would rather have a separate/dedicated raw water source for the back-up engine as well.

Looking forward to the next posts.

marcus petraska

thank you for sharing your experience with us Chris – some valuable insights here

RDE

Since “all” motor yachts already have generators, why not install an inexpensive AC motor (perhaps with a toothed belt reduction system) along with a feathering prop as the back up drive. No worries about conversion efficiency or battery capacity— just run the motor directly off the generator.

Conor Smith

RDE,
Yeah, I agree that is a really elegant, simple setup. I am curious to hear the discussion on this seemingly (to me) great solution. Using a online source(psychosnail) to calculate the HP requirement, I see that a boat like the Artnautica, would need 9.6 hp, to attain 4 knots. With inefficiencies, and pessimistic rounding, I think a 9-10kw genset would be able to provide this power. A bit bigger of a generator than ideal, but maybe you could have a quick adjust rpm selector, and when only battery charging is necessary, you could bring the unit to 50 hz, and a corresponding drop to to 7-9kw. I think most battery chargers can handle an array of power inputs pretty easily, and I think most of the large battery banks on a cruising boat could soak up the corresponding 400 amps dc (approximately) (at 12v) that 90% electrically efficient chargers would create putting 80% load on a 8kw generator.

Dick Stevenson

Hi John,
Fun topic, although all the boats seem to be out of my range for the size/money I may have when it comes to be that time.
While not a fan of external strainer/screens (many I see in boatyards are installed backwards), I have been pleased that the previous owner installed 2 intakes to the raw water manifold: on either side of the keel sump. He said this was because he moored crosswise to a river current and the refrigeration was left on. It needed water and plastic bags would float down on the upriver side into the intake and stop flow into the boat in a previous boat. I have never worried about there being an extra hole as I consider sea-cocks now-a-days pretty bulletproof with adequate inspection and maintenance.
My best, Dick Stevenson, s/v Alchemy

Doug

Every addition, second engine, stabilizers, tankage… will add to the waterline to maintain efficiency, pretty soon you end up with a yacht much longer than you wanted. All things considered, might be better off going with something like the Hallberg-Rassy, push buttons and all.
http://www.hallberg-rassy.com/

Doug

Yes, the larger HR’s (example yacht) wouldn’t fit the kind of budget or needs we’re talking about here, so I was thinking a downsize to the 40-45″ would be in order.

Hans

Hi Chris and John,
raw water intake cloggings can’t happen if you don’t have them. I think that serious thought should be given to a system that uses part of the underwater surface of the hull as a heat exchanger, at least in metal boats its a very sound alternative. A system like that does away with raw water in the engine and all associated problems. No corrosion in the engine, no thru-hull, no seacock, no impeller, no raw water filter, no worries about debris or mud in the water, good working temperature for the engine. Yes, you have a dry exhaust that has to be insulated with care and that takes up some more space. But that is the only drawback, if you can call it that.

Chris Groobey

Well now we are getting deep in the weeds, and in a part of the discussion where hopefully a Nordhavn person will chime in, as my understanding is many of their models can be ordered with either wet or dry exhaust (neither side ever wins the day, it’s kind of like arguing about how to load the TP on the holder). I vaguely recall a Dashew posting on the topic on SetSail as well, and there are relatively constant threads on the topic on the Nordhavn Dreamers listserv. Umstot’s Voyaging Under Power devotes some time to the topic and references a Gilkes Series M raw water pump with bronze impeller that I thought interesting. FPB64s use hull cooling for the hydraulic fluid, some or all of the AC units (depends on the boat), the fridge and two freezers. At some point you run out of cooling capacity, especially when the vast majority of the FPB64 hull is the bottom of the four fuel and two water tanks. I don’t mean to harp on the 64, it’s just what I know, completely understand that the purpose of this thread is a bottom-up design.

Hans

Hi John and Chris,
uhuu, I wasn’t aware that there had been a discussion over that topic (although I could have guessed). All I can say is that on my -admittedly small at 33 ft- sailboat the dry system serves me extremely well. When I come to think of it: On big ships they don’t use a dry system, so there definitely has to be a limit for the feasibility of hull cooling.

Mark

There is a thing called an anti-roll tank (ART) – passive, works at anchor. Ping Dave Cooper over on the passagemaking under power email list, has had one for > a decade. Spend a bit of $ on design, and the incremental cost per build is very low.

http://lists.trawlering.com/pipermail/passagemaking_lists.trawlering.com/2017-May/006031.html

Stedem Wood

Lot of moving pieces to this conversation.

Addressing only the need for get-home solutions and their redundancy, here.

I too have burned up an impeller and am convinced that using a “get-home” solution was a lot more than an emotional convenience. I’m happier describing my experience as a “down payment” on an expensive second drive system; one that is mostly unused and a serious piece on the list of annual maintenance items.

We should consider causes for failure AND the list of what goes down with the main engine when considering back up.

Stabilizers are hydraulic off the main engine.
Flotsam hitting the drive system.
Loosing main engine charging capacity and its effect on ship’s systems.
fuel problems usually affect the whole boat
Common raw-water problems (in my case, I have to add they guy in the mirror who left the valve turned the wrong way while working on the engine, so lock-out, tag- out procedures are on the list, as well.
Separate propeller/shaft
Speed and the ability to go to weather with a much smaller drive system
Degraded weather avoidance capability
Engine electronics (get home doesn’t have any, but you need to start it. I.E., lightning, etc.)
Reduced range (efficiency) under “get-home”
Maneuvering with an offset drive.
Fire in the engine room

That gets me to minutia, but my point is that a far-ranging boat will need to consider what can be relied upon as truly redundant and what is truly compromised in different failure modes.

Stedem Wood
M/V Atlantis

Marc Dacey

Ah, now we reach the reason why I learned how to rebuild an engine….alas.

Marc Dacey

Actually, John, I was referring to the wrong-way inlet. I’ve done it too, and it led to a rebuild (on land).

Doug

There is a semi-production yacht built today that at first look meets the requirements, but you’re not going to like it.
https://www.chriswhitedesigns.com/a47-mastfoil

Scott

Wow, that’s a really interesting rig for shorthanded cruising. Thanks for posting it!

Doug

An unproven design, would make for an interesting sail plan on a trawler.

RDE

Hi John,
Chris White specifies 31″ underwing clearance in lightship condition, which translates to +-28″ in cruising trim. If it were mine I’d want a full meter for this size boat.

I must admit to being a skeptic about his schooner rig. First consideration— cost of two carbon masts and associated deck reinforcements vs. one conventional mast. That said, lower sail height and eliminating the huge & powerful main from conventional cat rigs is certainly desirable for a cruising cat. If it helps avoid the fate of this sister ship any skepticism would fall by the wayside! http://sailinganarchy.com/wp-content/uploads/2017/05/upside-down.jpg

Doug

Two Chris White designed cats have flipped, both are 57′ and have conventional rigs. The cause for both was determined to be a sudden spike in windspeed (water spout). A cat will flip and a mono would broach. I would also note that Mr. Whites cats are high-performance boats.
http://wavetrain.net/news-a-views/764-atlantic-57-capsize-more-details-on-the-fate-of-leopard
I have heard that one of these MastFoil rigs have come down.
The downside to cats is by design they have no give like a monohull (heal), so the sails and rig need to absorb the load.
http://myboatsgear.com/2017/01/12/upside-up-anticapsize/

Marc Dacey

This is rather odd. I was discussing a Chris White cat design (Atlantic 55) just this afternoon. A guy from my club is completing a circ in one of them and the fellow I was talking to crewed for him on the Africa to Caribbean leg. Just the adjectives I heard made it sound fast as hell.