Want to design only a top part of catamaran, looking of plans for hulls 14m, aluminum

[Daniel Mazurkiewicz]

2012 Custom Aluminum Catamaran sailboat for sale in Texas https://www.sailboatlistings.com/view/94066

If it was somewhere in Europe I would be seriously looking at it already. Unfortunately can not move to States to finish it up there. I think.

For a build that size and your planned use, I would seriously consider using second hand Nissan Leaf power plants. They are affordable, compact, and powerful with an integrated gearbox and inverter, and there are experts out there offering stand alone control interfaces making them easy to adapt to builds like yours. They are a power plant you can grow into, and as batteries and solar get better, you can operate them at a higher voltage.

Didn't think of used Nissan Leaf electric motors, but that is actually interesting option and within planned budget (just checked prices). Instead of 2x10kW could have 2x40kW. I guess that makes a difference. Aldo wondering what is the difference in efficiency of motor with propeller on shaft immersed in the water and efficiency of onboard motor with that water resistant bearing (what is the name of it in English???)

Regarding using forward and reverse independent thrust of each motor for steering, yes it can be done but as others have pointed out if you lose propulsion from one motor you won’t be able to steer or even keep a course without a rudder. I use this method on my catamaran and keep a rudder onboard that can be center mounted for steering in case of emergency.

Detachable emergency rudder sounds good to me too.

Also keep in mind using the motor propulsion for steering is great for slow speed maneuverability, but is more inefficient at higher speeds and less responsive than a properly designed rudder.
On my boat, I tend to drop the throttle of one motor to allow the opposite to overtake in order to steer in a direction, rather than throttling one up to overtake the other.

That is definitely power saving approach and looks to me like you won't need anything else at high speed in 99% of cases. Am I right?

 

[Daniel Mazurkiewicz]

Daniel, have you had a look at Bruce Roberts' webpage re his aluminium power catamaran designs?
https://www.bruceroberts.com/public/HTML/CATS.htm

Using the Cat400 as an example -
https://www.bruceroberts.com/public/HTML/descriptions/cat39_description.htm

They mention that the study plans cost US$95 and that
"Each STUDY PLAN contains ALL the construction drawings for each material - ALUMINUM & FIBERGLASS as applicable to the particular boat plan - with up to 25 sheets per plan!
Lists of materials - Technical information - Numerous construction drawings are all included."

It could be worthwhile investing $95 in a set of plans so that you can get a rough idea of what you will be up against re the design of your vessel.

Edit - for general reference, you could also have a look at the aluminium power (and sailing) cats built by GHI Yachts in South Korea.
https://www.ghiyachts.com/복제-products

But I will again agree with the others above, re how US$150,000 is only going to be a fraction of the cost to build your cat, and that 2 x 10 kw electric motors are not going to be enough power for it to operate effectively. What happens when you have to motor into a 20 knot (or more) head wind and a rough sea?
Your vessel is not going to be very seaworthy if it cannot do this, as you might have to motor off a lee shore in anger sometime.

Looked already at Bruce Roberts plans, and still considering it, but for now will follow advice from @Rumars to do some basic design and give it to some professional NA to polish it up.
As it comes to motors, yes, I might reconsider to get a bigger ones. Just for the sake of safety.

 

[kerosene]

the 2x 10kw might be ok for calm water and even have reserve but as mentioned earlier in tough conditions you might need plenty more excess. Windage on a 45ft boat is no small thing and lets say you have to put 2x15kW to engines to beat the wind. Suddenly 60kWh battery starts top look very small in that storm at night.

Solar looks limiting too.
You'll be getting maybe 6 peak sun hours - rarely less I'd guess. On the sea it might be bit better than 6h of peak sun but unlikely more than 7h and your panels are not going to be aligned to south so I think 6 is not pessimistic at all (might be optimistic). This all would mean that each kWp of panels would generate 6 kWh per day so 20kW solar array times 6h = 120kWh per day. Divide by 24 and you are at 5kW average constant output. I think even for the 2x10kW you need more batteries and more panels.
Panels themselves are not terribly pricey. I would only consider LFP (LiFePO4) batteries for sea for their safety. Battery fire on sea would likely be a fatal incident.

Before someone points out that sun shines for more than 6h/day the term peak sun hours means total output measured in hours that is equivalent to 100% output from panels. ie. 6h of mid day sun equivalent.

And it si cool that you can handle the electronics (Leaf motors was a good idea btw) but what you listed is basically like a traditional powerboat having a crankcase and a gas tank. The rest of the powertrain, chargers and inverters etc. all add up a fair amount. 30kWh (still small) array needs a serious frame to not get blown away in bad weather.
Powerboats, even slow ones, need a lot of juice so the setup needs to be quite heavy duty - ocean crossing? even more so.

And you should listen to other people's experiences. We get quite a few posts here who have invented new way to create a hull and think they will save a ton by making it bit cheaper. Still rule of thumb seems to be that hull is 1/3 of the cost. I get that on home build a more utilitarian and more modest equipment might satisfy compared to commercial counterparts but if it costs 500k for everyone else to make, I think you should not bypass that very lightly.

I think the Ocean crossing part makes everything significantly more challenging as the level of autonomy and ruggedness and inability to stay in harbor changes quite a bit. Do you have mulit-day sailing experience?

If you were looking for a boat to coastal hop around Europe the plan would be much more feasible imo.

 

[bajansailor]

Looked already at Bruce Roberts plans, and still considering it, but for now will follow advice from @Rumars to do some basic design and give it to some professional NA to polish it up.

If you can essentially buy a full set of construction plans for $95 for a 'typical' aluminium power cat in the size range that you are interested in, then I think this would be an excellent investment for minimal cost - it would certainly help you with your initial basic design.
I think that Bruce Roberts puts this out to help tempt folk into buying the full set of plans, including the lines.

And I do think that you need to have some reserve power available, for that inevitable time when you need to make progress to windward in rough conditions.
And it would be prudent to have a diesel generator on board for emergencies - you are still being very 'green' if you don't use it, but it will be reassuring to have in case you do need it.

 

[Daniel Mazurkiewicz]

If you can essentially buy a full set of construction plans for $95 for a 'typical' aluminium power cat in the size range that you are interested in, then I think this would be an excellent investment for minimal cost - it would certainly help you with your initial basic design.
I think that Bruce Roberts puts this out to help tempt folk into buying the full set of plans, including the lines.

And I do think that you need to have some reserve power available, for that inevitable time when you need to make progress to windward in rough conditions.
And it would be prudent to have a diesel generator on board for emergencies - you are still being very 'green' if you don't use it, but it will be reassuring to have in case you do need it.

$95 is just for some intro information. Construction plans cost there 1200USD if I remember correctly
Yup, a diesel generator is in my plan as safety option

 

[bajansailor]

Oh dear. I am just trying to help you Daniel.
On the Bruce Roberts site they specifically say this -
"Each STUDY PLAN contains ALL the construction drawings for each material - ALUMINUM & FIBERGLASS as applicable to the particular boat plan - with up to 25 sheets per plan!"
If you pay them the full $1,200 then you get the full works hull lines plan drawings as well.
And the odds are good that your method of construction would be similar to these cats, hence why I think that if you had something like this it would be a good introduction for you to the basics of hull structure design.
And $95 is a drop in the ocean compared to a few hundred thousand $$'s to build your cat.

 

[Daniel Mazurkiewicz]

the 2x 10kw might be ok for calm water and even have reserve but as mentioned earlier in tough conditions you might need plenty more excess. Windage on a 45ft boat is no small thing and lets say you have to put 2x15kW to engines to beat the wind. Suddenly 60kWh battery starts top look very small in that storm at night.

Solar looks limiting too.
You'll be getting maybe 6 peak sun hours - rarely less I'd guess. On the sea it might be bit better than 6h of peak sun but unlikely more than 7h and your panels are not going to be aligned to south so I think 6 is not pessimistic at all (might be optimistic). This all would mean that each kWp of panels would generate 6 kWh per day so 20kW solar array times 6h = 120kWh per day. Divide by 24 and you are at 5kW average constant output. I think even for the 2x10kW you need more batteries and more panels.
Panels themselves are not terribly pricey. I would only consider LFP (LiFePO4) batteries for sea for their safety. Battery fire on sea would likely be a fatal incident.

In my estimation I used LiFePO4 prices.
Also was assuming that I'm not gonna go full throttle 24h a day. So the matter is more of what is the distance you can make on solar panels a day at what speed. (in my opinion)

And it si cool that you can handle the electronics (Leaf motors was a good idea btw) but what you listed is basically like a traditional powerboat having a crankcase and a gas tank. The rest of the powertrain, chargers and inverters etc. all add up a fair amount. 30kWh (still small) array needs a serious frame to not get blown away in bad weather.
Powerboats, even slow ones, need a lot of juice so the setup needs to be quite heavy duty - ocean crossing? even more so.

Had a second thought on Leaf motors - there are really high voltages involved. Not sure it it is best idea on the sea to use them.

And you should listen to other people's experiences. We get quite a few posts here who have invented new way to create a hull and think they will save a ton by making it bit cheaper. Still rule of thumb seems to be that hull is 1/3 of the cost. I get that on home build a more utilitarian and more modest equipment might satisfy compared to commercial counterparts but if it costs 500k for everyone else to make, I think you should not bypass that very lightly.

Not expecting magic, before I start throwing money on that I'll make sure I'll have enough of them. Not trying to reinvent a wheel here too. Just trying to gather knowledge and experience of others who actually did something, not only talked about it ;-)

I think the Ocean crossing part makes everything significantly more challenging as the level of autonomy and ruggedness and inability to stay in harbor changes quite a bit. Do you have mulit-day sailing experience?

I think so too, it is gonna be challenging. Yes, been sailing already a bit.

 

[Daniel Mazurkiewicz]

Oh dear. I am just trying to help you Daniel.
On the Bruce Roberts site they specifically say this -
"Each STUDY PLAN contains ALL the construction drawings for each material - ALUMINUM & FIBERGLASS as applicable to the particular boat plan - with up to 25 sheets per plan!"
If you pay them the full $1,200 then you get the full works hull lines plan drawings as well.
And the odds are good that your method of construction would be similar to these cats, hence why I think that if you had something like this it would be a good introduction for you to the basics of hull structure design.
And $95 is a drop in the ocean compared to a few hundred thousand $$'s to build your cat.

Sorry, mea culpa, just trying to answer to everyone, and with all the information I'm gathering with my research I missed the details. But you're right. That might be worth looking at just to learn something. Did you see something from them already? That page looks pretty "fishy" actually.

 

[bajansailor]

The only time I ever bought anything from Bruce Roberts was a paper catalogue of his designs 40 odd years ago, long before the days of the internet.
Re 'fishy', I think that Google will bring up lots of hits about Bruce Roberts, with people for and against his designs and philosophy.
However if he is supplying construction drawings, then they must have been designed 'properly' - and for $95 they would help to give you an idea as to what the construction plans are about (if you do not have any prior experience of metal boat plans).

 

[gonzo]

3 hours of reserve power on the batteries is really low. That will mean spending several hours a day floating with no available power. That is not even considering the house loads. Also, the budget will barely cover the batteries, engine, controllers, solar panels, wiring, etc. I doubt you could even build the hulls and deck for that money.

 

[Rumars]

Superstructure is anything above deck level, in your case the whole bridgedeck cabin. For example you could have Al hulls and a fiberglass or plywood cabin. It's debatable if that makes sense (technical or financial), but that is a problem for you to solve.

As kerosene has so nicely explained, solar is better for coastal cruising. As for maintaining speed in rough weather, forget about it, you should be happy if you can maintain steerage.
To understand what's needed for more than fair weather power, let's look at the Lagoon 45. It has 2x33kW diesels for a 15t boat and 1040l of fuel (plus the sails). You can of course install bigger electric motors, but batteries are finite, you would need a diesel generator capable of sustaining them. For example 2x25kW electric motors with 60kW diesel generator, plus fuel. The generator will not be "emergency power" but a normal component of your energy budget.

This is why a statement of requirements (SOR) is so important, the boat adapts to you.

 

[Daniel Mazurkiewicz]

Superstructure is anything above deck level, in your case the whole bridgedeck cabin. For example you could have Al hulls and a fiberglass or plywood cabin. It's debatable if that makes sense (technical or financial), but that is a problem for you to solve.

As kerosene has so nicely explained, solar is better for coastal cruising. As for maintaining speed in rough weather, forget about it, you should be happy if you can maintain steerage.
To understand what's needed for more than fair weather power, let's look at the Lagoon 45. It has 2x33kW diesels for a 15t boat and 1040l of fuel (plus the sails). You can of course install bigger electric motors, but batteries are finite, you would need a diesel generator capable of sustaining them. For example 2x25kW electric motors with 60kW diesel generator, plus fuel. The generator will not be "emergency power" but a normal component of your energy budget.

This is why a statement of requirements (SOR) is so important, the boat adapts to you.

I guess my mind got polluted with things like from this article: https://electrek.co/2020/05/25/aquanima-40-series-electric-yacht-battery-solar-power/
And that is not a first one with such 2x10kW claiming to be ocean crossing capable. But that is why I came to this forum. Looking for all the details.

 

[bajansailor]

Here is a quote from the Electrek article -
'According to the company, the Aquanima 40 series can travel “more than 100 nautical miles (185 km) in a single day without stopping.”

How much 'more than' 100 nautical miles?
They have to potter along at 4 knots to do this - presumably in calm seas.
What happens when they have 20 knots on the nose?
I am thinking that if they want to use the same amount of power, their speed will be dramatically reduced.

Pretty much most 'conventional' motor boats with diesel engines can also cross the Atlantic (theoretically) with the engine running at idle speed (perhaps 800 rpm) if you look at the fuel consumption figures in the reports on www.boattest.com
But how many people would want to do this?

 

[kerosene]

Well that is a good benchmark to reflect against.
https://www.azura-marine.com/aquanima-40
It is CAT A CE meaning ocean voyaging. That should mean that the structures for solar arrays etc. are designed with thti sin mind and could be used as models/inspiration.

Battery is 60kWh but motors are indeed just 2x 10kW.

They advertise "Unlimited" range at 4 knots, but I have to warn that marketing lingo is not accounting for headwind or waves.

(my earlier comment about driving through the night, and having capacity to do so, wasn't about wanting to maximize distance made good but a situation where wind is pushing you towards lee shore and you _have to_ keep powering. or Crazy weather that needs constant active powering and steering. Maybe the generator will provide this ability in a dire need)

Also: Base boat €523,000

 

[Rumars]

Ocean crossing is simple as long as you don't go against the prevailing wind and have time. People regularly cross the Atlantic on rowboats, and a fit human can't make more then 250W if he has to do it for hours, plus a human can't row 24h a day, therefore such crossings usually take two months.

The first solar catamaran to cross the Atlantic (29 days from Canary Islands to Martinique) was the sun21 in 2007. Their data might be surprising to some, 14x6,6m, displacement 12t, 2x8kW motors, 10kWp solar panels and 24,9kWh of lead acid battery. transatlantic21: The world's first crossing of the Atlantic on a solar boat http://www.transatlantic21.org/
So yes, your proposed vessel will cross without problems, even on your initial design parameters.
In really bad weather you simply stop motoring, put out drouges or sea anchors to keep you from loosing to much ground in an unwanted direction, or get broached, and enjoy the ride. It's safe, there is nothing you can hit out there, close the hatches and go to sleep. The storm usually goes into the direction you want, it's free travel.
If your battery is low after several cloudy days, in the first day of sunshine you simply drift and wait to charge. The wind and sea push you to the destination anyway, just slower then you want to go. Or you motor just fast enough to keep the bows pointed in the right direction, it's not a race.

The problems are in coastal waters, when you want to go somewhere against the wind and waves, where you don't have searoom to simply drift around, etc. This ca all be avoided by good planing and waiting for suitable weather.

But, all of the above might collide with your expectations, that's why the SOR is important. You have to have a good ideea about what the boat should be capable to do, how it is going to be used, in order to be able to design it. The sun21, while a proven transatlantic and coastal sailor is not a comfortable cruiser, and it will not be able to go around Cape Horn east to west.