steerable saildrive

Happy Wolf

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does anyone have experience with a combination of steerable saildrive plus bowthruster instead of the standard twin fixed saildrives on catamarans ?
what are the cons ?
 
I'm afraid the anarchists here don't give much thought to the extra features of a spare propulsion system, such as a spinning saildrive, which probably has a special place for owners of heavy cruising catamarans equipped with thrusters.

I am more than sure that many of the inhabitants of this forum do not need anything at all but sails to moor their boat.

Sorry for that... :confused:
 

CapDave

Anarchist
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Fort Lauderdale
does anyone have experience with a combination of steerable saildrive plus bowthruster instead of the standard twin fixed saildrives on catamarans ?
what are the cons ?
I have experience with them in larger sizes. I didn’t know anybody was making pod drives in the 40-100HP range? The drawbacks are more complexity, more moving parts submerged, more drag, and to really extract the benefit from twin pod & thruster you really need a fly by wire joystick system
 

Happy Wolf

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Actually my interest might be well aligned with the sailors. I never use the second engine except for manouvering, so why not do without and add a retractable bowthruster to help in tight places ? Catamaran size is 60’ for 18 tons fully loaded.
Less weight, less drag, less maintenance.
I am just concerned I might be overlooking some cons …
 

vokstar

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Tasmania
Actually my interest might be well aligned with the sailors. I never use the second engine except for manouvering, so why not do without and add a retractable bowthruster to help in tight places ? Catamaran size is 60’ for 18 tons fully loaded.
Less weight, less drag, less maintenance.
I am just concerned I might be overlooking some cons …
What happens if the singular pod/engine fails?
 

Happy Wolf

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the same that happens to a monohull; they do not consider this risk high enough to carry a back-up engine all the time
 

Happy Wolf

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talk to your local tug boat Captain
actually I did and he could not come up with cons except for the fact that you need qualified dealers for maintenance/repairs (which is not readily available in all the 4 corners of the world).
I would love to have qualified feedback from the pro sailor on this forum to make sure I am not overlooking other cons.
 
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vokstar

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Tasmania
the same that happens to a monohull; they do not consider this risk high enough to carry a back-up engine all the time
I think the point I was trying to make (poorly) is that one of the pro's for a cat in my eyes is the inbuilt redundancy in cat's of having two engines.

I also thing there is good weight and bad weight. The bow thruster is going to be up front where you don't want weight. More often than not you won't need it for docking anyway so it is dead weight.

Looking at Cat Greatcircle's vids with their Outremer, they initially planned on having a bow thruster but after being taught how to use the engines to manoeuvre in port they ditched it. I think this is the vid where they are being taught how to use the engines to move the boat in pretty tight confines.

 

Zonker

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Our 40' cat had a single 27 HP diesel in 1 hull, and a Yamaha 9.9 high thrust outboard against the back beam on the other hull. Worked very well for tight quarters movements. Except for our life (99% at anchor where we didn't use the outboard for anchoring) - the outboard suffered from lack of use. The outboard was a good backup and would push the boat at ~ 5 knots in calm weather. And at about $4000 it's about the same price as a bow thruster. It's not for everybody. Lots of people like 2 x diesels.

You're not going to fit a 10HP bow thruster in a typical 40' cat so the outboard gives you better performance and no hole in the bow.
 

Happy Wolf

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Docking with 2 engines is absolutely ok, couldn’t agree more.
But the second engine adds more than 500 lbs and contributes to drag. A retractable bowthruster in the needed power range will weigh approximately 100 lbs and will basically be drag-free.
 

Happy Wolf

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Our 40' cat had a single 27 HP diesel in 1 hull, and a Yamaha 9.9 high thrust outboard against the back beam on the other hull. Worked very well for tight quarters movements. Except for our life (99% at anchor where we didn't use the outboard for anchoring) - the outboard suffered from lack of use. The outboard was a good backup and would push the boat at ~ 5 knots in calm weather. And at about $4000 it's about the same price as a bow thruster. It's not for everybody. Lots of people like 2 x diesels.

You're not going to fit a 10HP bow thruster in a typical 40' cat so the outboard gives you better performance and no hole in the bow.
I was hoping you’d chime in … read a lot of good posts from you.
The cat is 60’ so no space issue with the bowthruster.
As an alternative I was considering a pod (like Oceanvolt that can also double as hydrogenerator) instead of the second ICE. As far as I know not retractable though. This would be more in line with your solution.
 

Zonker

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Bow thruster installation: You want the tunnel at LEAST 1 tunnel diameter below the waterline.

The static bollard pull (zero speed thrust) of a Yanmar 9.9 high thrust is ~ 250 lbs. To get that in a bow thruster let's consider this Vetus https://webshop.vetus.com/en/product/bow12524d-bow-thruster-125kgf

125 kg = 275 lbs thrust so close enough.

Tunnel diameter is 250mm. 24V / 450 Amps so a few very big cables or dedicated battery.

(Vetus says only 1/2 tunnel diameter which IMO will allow a bit of air being sucked in.)

But the dimension you need to notice is "B" tunnel length - 500-1000mm.
1675837091246.png


Your average performance catamaran hull isn't wide or deep enough at the bow!

Here's a Crowther 47 lines. Red = my best guess where you'd put a bow thruster. Green is bow thruster. Just can't get a big thruster there. The beam at the waterline is about 1500mm. That tunnel is MAYBE 500mm.

1675837412437.png


If you are considering a 150 HP engine in a cat you're in a different world. I doubt you'd find a yard willing to sell you a single engine + bow thruster with a big cat.

Driving a cat with twin engines is the easiest thing ever
 

Zonker

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If you're considering a 60' cat I think folding 3 blade props get you most of the way there and go with twin diesels. Able to be fixed anywhere in the world with a guy in a greasy shirt and box of rusty tools.

I did consider electric drive as my second engine. But at the time wasn't enough electric propulsion to buy. And in our boat we'd need to go with 48V to give me enough thrust/small enough cables to matter.

I did like the backup small outboard engine for the 2 bad times the main engine died (starter issues both times) and I really wanted to get to anchor before the sun went down.
 
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vokstar

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Tasmania
Just to muddy the waters even more how about hybrid? There is quite a bit of info on the GB60 Moonwave site.


Zonker makes a great point though, having something that has parts that are generally available around the world that can be fixed easily by someone who isn't a specialist would be a huge benefit if you are planning on doing big cruising miles.

The KISS principle is often overlooked in design.
 

Happy Wolf

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If you're considering a 60' cat I think folding 3 blade props get you most of the way there and go with twin diesels. Able to be fixed anywhere in the world with a guy in a greasy shirt and box of rusty tools.

I did consider electric drive as my second engine. But at the time wasn't enough electric propulsion to buy. And in our boat we'd need to go with 48V to give me enough thrust/small enough cables to matter.

I did like the backup small outboard engine for the 2 bad times the main engine died (starter issues both times) and I really wanted to get to anchor before the sun went down.
The twin diesel is my current solution and as y’all point out, it works well. No problems with maintenance, either (no fly-by-wire).
What really nags me is the fact that I use the two engines simultaneously only when manoeuvring, i.e. 1% of the engine ON time. With one D2-75HP at 2000 rpm I achieve a motoring speed of 6 kn which is good enough for me.
That’s why I it would be nice to come up with a more elegant solution where you use the ICE for motoring and something else for docking.
 

Happy Wolf

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Just to muddy the waters even more how about hybrid? There is quite a bit of info on the GB60 Moonwave site.


Zonker makes a great point though, having something that has parts that are generally available around the world that can be fixed easily by someone who isn't a specialist would be a huge benefit if you are planning on doing big cruising miles.

The KISS principle is often overlooked in design.
Hybrid (generator plus e-propulsion) is heavier in total weight, riskier (lightning apparently can take out both e-drives) and more difficult to mantain. Plus either less HP or less range when motoring.
Looked into it and ruled it out but am happy to get wiser …
 

Happy Wolf

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Our 40' cat had a single 27 HP diesel in 1 hull, and a Yamaha 9.9 high thrust outboard against the back beam on the other hull. Worked very well for tight quarters movements. Except for our life (99% at anchor where we didn't use the outboard for anchoring) - the outboard suffered from lack of use. The outboard was a good backup and would push the boat at ~ 5 knots in calm weather. And at about $4000 it's about the same price as a bow thruster. It's not for everybody. Lots of people like 2 x diesels.

You're not going to fit a 10HP bow thruster in a typical 40' cat so the outboard gives you better performance and no hole in the bow.
Could you dock with the outboard only ?
In other words, do you think that a single steerable saildrive would be sufficient for docking ?
 
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