Twin Engines/Twin Rudders on a Mono?

[poiu]

How about adapting a bowthruster? You've probably planned to have one anyway. Why not make it rotate too. Just rotate through 90 deg and it can be an auxiliary prop able to push forwards or reverse. Use a hydraulic pump on the genset to drive it and it could be designed for continuous duty.

A bowthruster normally will not have a huge amount of power, but you don't need much to limp home. As said above, you will be using this in calm conditions most likely and it will not take much power to push you at 4 kt. 15hp maybe.

You may have to locate the bowthruster a little further aft than usual to avoid sucking air in as you motor forwards.

Now you have gone for a rotatable bowthruster, why not take another step and make it rotate through say 270 deg and control its angle. Just another control motor will be needed, or even use a cable control. This gives you redundancy for the rudder. You can loose both your main prop/engine and/or your rudder and still get home.

The dinghy with a largish engine as a tug alongside is a good back up, but I reckon on it only being good for getting the last few miles into harbour as you will need an unfeasible amount of fuel to go a serious distance.

[boom23]

I stumbled on another twin engine monohull, Feeling 55.

https://www.youtube.com/watch?v=TTAEdWxtICA

[Dockhead]

Originally Posted by boom23

I stumbled on another twin engine monohull, Feeling 55.

A monomaran!

Love the anchor arm.

Note that it's CE Class "B" - unusual for a boat that size not to make "A"

[Dockhead]

Originally Posted by poiu

How about adapting a bowthruster? You've probably planned to have one anyway. Why not make it rotate too. Just rotate through 90 deg and it can be an auxiliary prop able to push forwards or reverse. Use a hydraulic pump on the genset to drive it and it could be designed for continuous duty.

A bowthruster normally will not have a huge amount of power, but you don't need much to limp home. As said above, you will be using this in calm conditions most likely and it will not take much power to push you at 4 kt. 15hp maybe.

You may have to locate the bowthruster a little further aft than usual to avoid sucking air in as you motor forwards.

Now you have gone for a rotatable bowthruster, why not take another step and make it rotate through say 270 deg and control its angle. Just another control motor will be needed, or even use a cable control. This gives you redundancy for the rudder. You can loose both your main prop/engine and/or your rudder and still get home.

The dinghy with a largish engine as a tug alongside is a good back up, but I reckon on it only being good for getting the last few miles into harbour as you will need an unfeasible amount of fuel to go a serious distance.

Interesting, but can you buy such a thruster?

[poiu]

Originally Posted by Dockhead

Interesting, but can you buy such a thruster?

Your next boat is a one off, so just invent a bit more. It can't be too hard if you start with a stock thruster.

Vitters make one, a retractable pod.

Hundested make a unit for Baltic yachts that might be adaptable. See a write up here on all products I mention as the article addresses this subject really well:
http://shipmotiongroup.com/module/Pr...%20systems.pdf

Or just buy the Ship Motion retractable unit and fit it with an electric or hydraulic motor for redundancy, powered off the genset. As it is retractable you don't need so much redundancy for the prop and shaft; they are protected by the hull most of the time, plus you benefit from drag reduction.

[poiu]

Originally Posted by Dockhead

A monomaran!

Love the anchor arm.

It is nice to watch. There's lots of leverage on that long arm, wouldn't it bend or break?

[PeterBernard]

We have a twin engined mono, and it's hard to describe just how significant the positive impact on my psyche is to have this kind of redundancy.

It's a one-off Bill Dixon designed 50 foot cutter rigged ketch built in steel and launched in 1994.

She's already circumnavigated twice with previous owners, and we're half way through our own circumnavigation in her.

The engines are identical Ford Lehman SP90's, each with around 5,500 hours on them. We only run them both together in tight marinas or on a couple of occasions in big seas on the nose, but 99% of the time we're motoring, it's with just one.

At 32 tonnes fully laden, 90hp is a little undersized (I've read somewhere that 4hp per tonne is a good rule of thumb for most boats), but we cruise at 5.5 knots at 1,600 rpm with one engine, 7.0 knots at WOT (2,500), and only 8.5 knots with both engines at WOT, which is hull speed. As others have noted, the fuel consumption increase running two engines is simply not justified by the extra speed.

Given that we're steel, the weight penalty of twin engines is less significant, but it's definitely still a factor. The feathering props are MaxProp, hung off mini skegs, with a single skeg mounted rudder, and the extra drag of the second prop doubtless contributes to what I feel is a hull speed which is a little low for our size. Having the two engines side by side also entails the beam extending a fair way below the water line - we definitely do not have a slippery underwater profile.

Having said that, we comfortably make 50% of apparent wind speed under sail at all times (up to hull speed of course), which is fine for me given the type of sailing we're doing.

We also have a 7.5 kVA generator on board but that's more a product of the thinking at the time the boat was built - the alternators on the engines are relatively undersized and internally regulated, and there was negligible solar on board when we bought the boat. That, coupled with significant AC systems (fridge/freezer, watermaker, water heaters, chargers etc) meant that we needed to run the generator for 3-4 hours per day.

Slowly, we've been upgrading, and now with 1,200w of solar and a big inverter, plus a huge Lifeline AGM bank, we're down to running the generator for 2 hours every 3-4 days. When we next replace the batteries we'll move to lithium, at which point the generator would be superfluous and will probably be removed.

If I could have a generator and one engine, or no generator and two engines, it would be the latter every time. Not only do we have optimum redundancy on a boat designed with that in mind (two masts, two headsails, two autopilots etc etc), it also means we have a complete set of engine spares at all times, making repairs in remote places straightforward.

i don't know how to place a value on that kind of peace of mind.

[NSboatman]

Originally Posted by estarzinger

mmmm . . . . I am trying (and failing occasionally, like now) to avoid commenting on your 'dream vessel'. It is very personal, and my perspective is so very different.

But I can't resist today

If your objective is either/both (1) a good sailing boat, and (2) a high latitude boat . . . . just dont think about two props, two struts, two shafts, two stuffing boxes. In order of priority . . . That is a huge amount of underwater drag. It is extra weight (down low yes, but still sinking the boat). And it is extra complexity (for haul outs, for annual maintenance, for the design and build). In the incident investigation team, I saw an interesting comparison of the Bounty in original configuration (as a pure sailing vessel), and in 'modern configuration' with two props. It was a massive hit to sailing.

Diesel engines are enormously reliable AND they are super easy for even an idiot to work on. Don't waste even a single neuron to thinking about 'engine redundancy'. This all true also of the electronic common rail systems - although there part of the process can be the idiot simply swapping in a spare black box.

Following that up - personally I believe in (a) simplicity, (b) best gear, (c) correct and super accessible installation, (d) spare parts and tools . . . . rather than redundancy. Eg do it right.

That broker boat morning star - I look at it and very honestly my initial gut reaction is 'what a nightmare'. That hard Bimini in a storm at sea . Trying to short tack in light winds . Trying to get upwind in a gale . Trying to troubleshoot a problem, when there is most probably a forest of black boxes, pumps and motors hidden in pretty much ever corner of the boat . I doubt she sails on her design lines . It may well be someone else's dream boat, but not mine (and obviously also not the guy who commissioned her).

I really dislike the 60-65' size range. Owners think they are getting a 'big' boat and cram way too much stuff into it. And they become too big for the owner and too small for pro crew. Dashew's personal boats were 80' for a reason, and it was not big crews (their layouts were really designed for two people), that 20' buys you a lot in terms of space to lay out mechanical equipment. The above boat might work at 80' but would be better at 100' - honestly it looks to me like the guy chartered a bunch of big boats and made long lists of clever things (or things that looked clever sitting in an anchorage) and then hired a NA with the mission to 'cram all this in the smallest possible boat'.

I have rarely seen a 'motor sailor' that sailed well. If they get big enough a sailing focused boat can motor well, but, at least in my experience, that is more like in the +72' range (the oyster 72 motors pretty well . . . but as an aside their machinery space is way way too small).

edit - oh, btw, there are pretty good reasons for integral tanks on aluminum boats (except black tanks). For water tanks you do need to be a bit careful with coatings. And while most NA's prefer bare aluminum in the diesel tanks, I prefer coatings (different than for water) in there also. For both you want to design good access, which includes easy access thru the interior that is placed on top (for some reason, the NA's so often put good aluminum access ports/plates, but forget about all the interior built on top of the tanks).

And yes, it is your dream . . . .so you can file this in the circular file - lol

This is good advice, well delivered (as usual from the starzingers!).

Having looked after smaller nordhavns and a number of other similar motor and sailing yachts with wing/get home engines, I am no longer a big fan. THey are perpetually under-run, under-maintained, squeezed in at weird angles and with difficult access; and even when new, they barely get the job done (usually woefully undersized). Forget making way against 20kts of wind, and since they are weak and off center, even picking up a mooring is a trial that requires calm conditions and good practice (btw- don't suck the mooring pendants into the bow thruster as you try to compensate for crazy wing engine thrust... ask me how I know this...).

They ARE pot line catchers, they DO complicate haul outs and bottom maintenance, because they are put in as a 'back-up', they are usually noisy, rattle and are another series of holes in your boat. The added complication just doesn't add up in all of the boats I've been on.

I agree that (for me anyway) it's better to maintain the main engine well and not compromise on sailing ability wherever possible. No engine Get home? Sail!

If it's flat calm and you can't sail, then I'd much rather have a decent rib with a good O/B to tow from ahead or push on the stern when offshore, and on the hip when approaching moorings or docks. I've moved lots of heavy boats very easily with a good 25hp rib. Easy and safe, and on a 60' boat, you should have room for a good tender- which has multiple uses. 5 knots is doable. Just stow away another 5 gals of gas somewhere...

The hydraulic thing is interesting. We've looked at it for other power conversion devices extensively (wave and tidal energy converters). The tech is becoming very smart now with electronically variable displacement, high speed valve switching and stroke adjustments. This can result in very good power matching, very high efficiencies, in the same way that electronics and smart integration have increased common rail diesel efficiencies. But, like crd it is quite finicky, sensitive to dirt, and requires highly trained designers and techs to implement. It's NOT a bunch of hoses, pumps and a few fittings anymore. Not if you want better than 80% efficiencies. Hydraulics can also be quite noisy - depending on valves and motors chosen.

On the plus side, it is wonderfully power dense- you can deliver a whack of power thru a small pair of hoses. And there is a real sense of satisfaction when you lean on your hydraulic thruster handle or windlass control and know that you can run that sucker full-out for as long as you like, and no thermal cut out is going to foil your plans. There's a reason it's used everywhere in commercial operations. It works.

Of course, converting energy from one form to another always has losses. You're already converting twice- chemical/thermal to mechanical (in the ICE); and from mechanical to electrical (alternator or generator head to charge the batteries on the boat); and you are always going to have backups for that charging (solar, stand alone gen).

In my opinion, I'd avoid yet another conversion and associated losses, and stick with electrical options (Dashew approach with FPB's). But also- stick to the ability to sail, and sail well.