Twin Engines/Twin Rudders on a Mono?

[navy davy]

I like the seaward 48 retractable keel and retractable twin rudders also twin engines ! A Bahama liveabord for sure ! I don't have the links but there are YouTube videos reviewing this exceptional monohull

[Dockhead]

Originally Posted by KP44

There were some monohulls made with twin keels. They are especially useful for grounding the boat and safely doing a bottom job during low tide.
Other than that, far increased wetted surface. ballast not centered but shared on two sides. Such ballast probably makes a tender boat. That is, reduced initial stability.

I personally don't see any advantage to a second engine. But to each his own. But why the twin rudders? Just a complex system with more that can go awry, and one rudder or the other will always be nearly unusable unless you are motoring. Again, much more wetted surface which is drag. If you really want the advantages of twin screws for maneuvering, I'd opt for a bow thruster instead of a second engine.
There is a reason there are so few twin engine, twin rudder, and twin keel boats. All decent ideas for certain issues but a disadvantage for most sailors.

Well, it's a fair question, but most of the answers are in the original post.

Twin engines does not increase the number of engines. I have two engines already now. The only difference in this is getting both of them to drive propellers somehow.

This is not a coastal or tropical cruiser -- it's for high latitudes and remote places, including perhaps the Northwest Passage. In those latitudes, you can have dead calms lasting for weeks or months. So mechanical propulsion needs to be as reliable as an ocean-going motorboat.

Twin rudders would be in case there are twin engines and twin normal shaft drives. So that the rudders are behind the props. Twin rudders have a lot of advantages and are becoming more and more common on normal sailing yachts. A really big advantage is that they don't have to be as long, so they are less exposed, and it's easier to make them really strong. Another advantage is that on a heel, one rudder is always well under water without aeration. Properly designed, twin rudders don't add much if any wetted surface compared to a single rudder.

Twin keels is a bit of a wacky idea which I can't think through without a NA on board. There are, however, high performance twin keel boats -- check out RM Yachts in France. More likely for this boat is a lifting keel of some kind.

[Dockhead]

Originally Posted by a64pilot

I'm being argumentative, but a second motor is a get home motor. Good thing to have, no doubt, second source of battery charging etc.
However if you look at the BSFC which is brake specific fuel consumption of our little Diesels, you'll find it pretty flat, meaning that to make half as much power pretty much takes half as much fuel. There is no point to where you cut power in half, but fuel consumption only by 10% or so. Yes there is a point of max efficiency, but the graph is a gentle curve, not a pyramid.
If your after range, take the space and weight that a second motor takes up and put in an extra fuel tank, that will take you way further.
But you don't have a get home motor of course.

It's a good point. And I don't think you can justify a second motor just to improve fuel efficiency by running a single at a better load -- for the reason you showed. But it is pleasant to be able to run your diesels at loads which are healthy for them. Especially if the main engine is oversized. We have such a huge range of power demand on a sailing boat, compared to a motor boat. On my present boat, from probably 5 hp when lightly motorsailing to 150 horsepower (which I don't have) for motoring against a strong wind and head seas. I don't think any diesel engine can operate in a healthy way over such a range of output. Twin engines would make that a lot easier. By the way, turbos really help with this issue too.

[K_V_B]

Originally Posted by Dockhead

4. Props not protected by the keel

You could have a small skeg protecting the prop. Look at how the propulsion on this design:

Berckemeyer Yacht Design | plans for modern and classic sailing yachts

[Dockhead]

Originally Posted by K_V_B

You could have a small skeg protecting the prop. Look at how the propulsion on this design:

Berckemeyer Yacht Design | plans for modern and classic sailing yachts

That's an interesting boat, actually.

[N1EYO]

Vertical and retractable? I looked at that page and I’m still scratching my dome. When retracted, does the whole tunnel prop clear the hull or does it stick out waiting for snags?

[K_V_B]

Originally Posted by Dockhead

That's an interesting boat, actually.

Was even on the market half a year ago. Now if only I had the money...

[boom23]

I am not sure if this boat came up in this discussion, but here it is:

https://www.youtube.com/watch?v=Cga9g7z4t_o

I do not know the boat or owner. I have no connection whatsoever.

[fallingeggs]

Originally Posted by boom23

I am not sure if this boat came up in this discussion, but here it is:

I do not know the boat or owner. I have no connection whatsoever.

Impressive.

She is for sale: http://www.davidwaltersyachts.com/ya....cfm?y=6313041

Cost EUR 3 million to make in 2015 and is now selling for $1.9 million. A bit of a hair cut for just sailing across the Atlantic once...

But on the topic at hand, she does have twin 65hp diesels with a possible range of 2k nm. Doesn't discuss how the prop is connected, so perhaps one should assume via a shaft.

And to the dismay of DH, she has a generator and that hard dodger is huge! Not sure what the keel is.

[poiu]

Originally Posted by fallingeggs

Impressive.

She is for sale: 2015 Custom Morning Star | David Walters Yachts

Cost EUR 3 million to make in 2015 and is now selling for $1.9 million. A bit of a hair cut for just sailing across the Atlantic once...

But on the topic at hand, she does have twin 65hp diesels with a possible range of 2k nm. Doesn't discuss how the prop is connected, so perhaps one should assume via a shaft.

And to the dismay of DH, she has a generator and that hard dodger is huge! Not sure what the keel is.

The salesman actually said she was appraised at EUR3m. She would have cost less than that.

[Dockhead]

Originally Posted by fallingeggs

Impressive.

She is for sale: 2015 Custom Morning Star | David Walters Yachts

Cost EUR 3 million to make in 2015 and is now selling for $1.9 million. A bit of a hair cut for just sailing across the Atlantic once...

But on the topic at hand, she does have twin 65hp diesels with a possible range of 2k nm. Doesn't discuss how the prop is connected, so perhaps one should assume via a shaft.

And to the dismay of DH, she has a generator and that hard dodger is huge! Not sure what the keel is.

Ticks a lot of my boxes. The people who ordered her obviously had very similar priorities to mine.

There's no accommodation plan (unbelievable that someone would be trying to sell a $2 million yacht and not even post accommodation plans, line drawings, any photo of the underbody and keel, etc.) but as far as I understand there is really just one sleeping cabin plus a kind of quarter berth -- I like to sail with bigger crews and that wouldn't be enough for me.

Nor do I like the integral tanks -- in alu, that seems like asking for trouble.

Underpowered for a twin weighing 25 metric tons light ship.

No permanently rigged staysail.


But there are a whole lot of things I like, including:

1. General approach to systems design -- lots of redundancy everywhere.

2. Whole aft section of the boat devoted to technical space a la Sundeer

3. Good pilothouse (but that narrow helm station is weird -- no room to do any kind of navigation, and I don't like the steeply slanted front windows -- can we say "solar gain"?).


I could live with the ordinary generator. The electrical system seems excellent. And I laughed when the broker apologized for no propane stove!

[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

[Dockhead]

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

Circular file?? Extremely interesting and extremely valuable commentary. Please don't be shy, in the future!

[LoudMusic]

Originally Posted by Dockhead

Yes, I think about lifting keels.

And I think about twin keels also.

This is getting into the territory where the NA is already needed -- it's getting over my head technically.


I like all the stuff Beta make, and I am familiar with their hybrid gear.

Attaching a DC generator is not rocket science. A big question is belts? Or layshaft?

Is there an arrangement where the leeward keel can be lifted in order to combat heel? What if, rather than lifting or swinging, they could independently be canted toward the center (windward)? Since the keel doesn't provide the same function as the rudder, ballast rather than directional control, the keel doesn't need to be on the low side for optimal function. Get'cha some goofy relative of a Volvo Ocean Race boat keel.

[Pete7]

Originally Posted by Dockhead

Circular file??

Looks like one of these:

https://www.google.co.uk/search?q=of...IbxTvNxADE7iM:

Knowing the way you like to sail I have agree, I can't see you getting on with all that stuff hanging underneath, but does it need to?

This is now 5 years old but some of the figures they give then are quite interesting. I am not sure about an outboard but how about a stern drive or surface drive.

https://www.youtube.com/watch?v=_EV2qq2-Lck