Wanting to build a ~50ft aluminium power catamaran, and looking for others who'd like to build in parallel

[Rycochet]

Forming large pieces of sheet metal is no easy task. Welding them is even worse.

Why are you insisting on an aluminum hull?

Personal opinion.

I've looked at 4 different materials - GRP, Steel, Aluminium, Ferrocement.

Ferrocement I've sort of discounted due to the insurance issue. There's various alternatives including carbon fibre instead of iron for the reinforcement, and it would be very strong and easy to get cement almost everywhere for repairs, but weight is the worst of all of them, so far more suited to a monohull than a multihull.

GRP shatters on an impact that would bounce off steel and dent / bounce aluminium - I'm not willing to risk that (even if I went full resin). It also has far greater maintenance costs and time requirements - I could get a world record barnacle on GRP and need to do a repair, with a metal hull I could hit the thing with a hammer to remove it (although it could also lead to rust on steel).

Both steel and aluminium are easy to access and repair. Weight between the two is very similar (stronger vs thicker) - in fact the weight is also similar for GRP too, coming within 10-20% for all of them (assuming similar structural strengths etc).

Total price is also very similar for the raw materials too (5083 aluminium against 316L stainless steel).

Stainless steel is very good, but if there's any trapped water anywhere (yes, there really shouldn't be) then it can still corrode more easily.

Both types of hull benefit from a sacrificial anode, so there's very little difference between the two in any practical terms.

My biggest decision weight turned into insurance again - aluminium leisure boats are becoming more popular, and while you need to document everything and get both inspected, I feel that sticking to something "better known" will make the entire experience "safer" (even if only in a financial sense for this one).

 

[bajansailor]

If laser welding is so amazingly good for welding aluminium boats, why isn't everybody using it?
How long do you think it will take you to get up to speed on welding proficiently?
After the naval architect reviews the design, will you get a kit supplied where every bit of aluminium plate is already cut, and then you just assemble it like a 3-D jigsaw?

 

[Rycochet]

If laser welding is so amazingly good for welding aluminium boats, why isn't everybody using it?

People and companies *are* using it - the difference with "normal" welding is that the safety equipment can't be half-assed... With any other welding you need something to protect yourself from very bright light, and there are people and places that will macguyver something - with laser welding you're probably going to lose your eyesight if you don't use the right eye protection. It's used a lot in automotive and other CNC based welding situations (since the 80s) where humans never need to look (and I watched some videos where they're being used by large ship manufacturers for multiple reasons). A quick search says roughly half a million laser welders are sold in a year, compared to millions of mig & tig welders - for "home" use it's only very recently that we've had the materials required to really start using it - When Was Laser Welding Invented? A Complete Historical Overview https://dynalaserstech.com/when-was-laser-welding-invented/

How long do you think it will take you to get up to speed on welding proficiently?

With laser welding - maybe a couple of hours... Seriously... Go look at videos of people using them for the first time!

With traditional MIG welding I'd probably take days to weeks, and TIG welding would be weeks to months.

After the naval architect reviews the design, will you get a kit supplied where every bit of aluminium plate is already cut, and then you just assemble it like a 3-D jigsaw?

More like one of those 3d metal models, except you need to tack weld every join - then come back later to do the length of everything needed. Laser welding has a huge benefit here with less indirect heat, so you have less risk of distortion (from what I've seen / read you need to be careful not to let things twist with traditional welding, and while I don't think that would go entirely with laser welding, I feel the risks / time goes down significantly). I'd recommend watching the 1 year timelapse for SV Delos (I've included the playlist link so it's easier to see their weekly updates) -

SV Delos 2.0 is entirely the reason why I've gone from "this is my dream" to "I can see what they're doing and actually this is entirely possible" - in the full videos they also go into bending / shaping the plates (I vaguely remember them calling it an Oxford Wheel, but it's an English Wheel they use). Brian is about my age (there's a couple of months between us), and also learnt to weld (traditionally) during this, I'd also estimate that they have 2-4 people (including Brian) working on it most of the time (plus external contractors for fitting out etc).

One thing that their videos did make me realise is how many changes they had to make after getting the plates and welding them together - even in that timelapse you saw then cutting a vent hole - it's where I want to have that full 3d model where everything is already included, and then even the bulkheads and cabinets can be CNC cut so the majority of the work will be putting together the 3d jigsaw with an integrated cheat sheet

 

[Rumars]

Oh boy, where should I begin.
Maybe with the welding issue. What you certainly don't want is an inexperienced welder working on structural stuff. You can certainly weld your cabinets but please hire someone to do the important things. As for laser, I'm going to say this, the machines you typically see on youtube aren't going to cut it. You need at least a 2kW laser to weld 3mm Al, more for thicker plates. Plus there's fit, sequence and intersections etc. You want to weld your own hull take a class and start practicing now. Laser welding isn't a magic bullet. The safety precautions are also at another level, think no windows and nobody else around when you're firing up that big laser.

Boat plans come in different complexity levels. 3D modeling the hull to the last bit is certainly done, but it's expensive for a one off. It's the old tradeoff between time at the computer vs. time in the shop and who's more expensive. For the amateur it comes down to what skills he already has. If you can already do modeling go for it, otherwise you need to pay by the hour.
Al has its own pitfalls as a boatbuilding material, just like anything else. You make your choices and you live with them.
For an amateur buildt boat that bounces of rocks I would favor a thick plate multichine design in order to avoid english wheels and minimize welding. The other way around (thin round plate with lots of stiffeners) is also possible but there's more skilled work involved and the "bounces off rocks" part might not prove as true as you think.

A solar electric boat lives and dies by energy budget. Electric hot water isn't going to happen underway, only at anchor. You want to offset the rig weight with batteries, but solar panels and their supporting structure have their own weight. Lighter panels have durability issues, the good ones are significantly more expensive and even those don't achieve the lifespan of glass panels. If you cover the entire boat in the best panels you can probably do 20kWp, plenty for living at anchor in luxury, not a lot for moving the boat in the same style.
Take a look at existing designs like the Silent yachts 60, they can't achieve a positive balance. Of course it's a much heavier boat, but their cabins aren't broom closets. OTOH they do save massive amounts of diesel fuel over a comparable conventional boat, so maybe this should be your goal. I think you need to remain realistic, a comfortable Al cruising boat isn't going to make net positive on solar underway over 24h. Something with a single carbon fiber bucket serving as the whole crew toilet will, but that's a different style of cruising and it certainly won't "bounce off rocks".

 

[Rycochet]

Oh boy, where should I begin.
Maybe with the welding issue. What you certainly don't want is an inexperienced welder working on structural stuff. You can certainly weld your cabinets but please hire someone to do the important things. As for laser, I'm going to say this, the machines you typically see on youtube aren't going to cut it. You need at least a 2kW laser to weld 3mm Al, more for thicker plates. Plus there's fit, sequence and intersections etc. You want to weld your own hull take a class and start practicing now. Laser welding isn't a magic bullet. The safety precautions are also at another level, think no windows and nobody else around when you're firing up that big laser.

- looking at a 3-5kw laser for it, and like several videos of people testing laser welders I'll be budgeting some time for testing strengths and techniques - plus putting together the framework pieces is definitely not a 1-person job. The area I'm looking at does have plenty of skilled welders available outside of normal job times - so I'm planning for fallback. Renting an enclosed space, and making sure that anyone else there while doing the laser welding has eye protection isn't something I'll risk either - at least with normal welding you get that bright flash of light that says "don't look this way" - lasers do the damage without even noticing it

Boat plans come in different complexity levels. 3D modeling the hull to the last bit is certainly done, but it's expensive for a one off. It's the old tradeoff between time at the computer vs. time in the shop and who's more expensive. For the amateur it comes down to what skills he already has. If you can already do modeling go for it, otherwise you need to pay by the hour.

I have plenty of time to get this right - and I'll always go with the old "measure twice and cut once" - my hope is to be building next year, but if that has to wait another year then that's what I'll do (especially as next year in Kenya is a political year...)

Al has its own pitfalls as a boatbuilding material, just like anything else. You make your choices and you live with them.
For an amateur buildt boat that bounces of rocks I would favor a thick plate multichine design in order to avoid english wheels and minimize welding. The other way around (thin round plate with lots of stiffeners) is also possible but there's more skilled work involved and the "bounces off rocks" part might not prove as true as you think.

The "bounces off rocks" was a bit tongue in cheek - and making sure the plates are strong enough even before bracing is important. The hull shape itself isn't set in my mind, so multichine feels like a good call (easier to laser cut the pieces) - but they'll still want at least a gentle curve in them to sit in place and not have any spring forces working against the welds. Even for the very prow of the boat I want to have an angled stem `__/` - then weld a solid sort of triangular plate to turn that into a vertical `__/|` - so it'll not only be better for cutting the water, and stronger for head-on impacts, but also less curved for easier finishing

A solar electric boat lives and dies by energy budget. Electric hot water isn't going to happen underway, only at anchor. You want to offset the rig weight with batteries, but solar panels and their supporting structure have their own weight. Lighter panels have durability issues, the good ones are significantly more expensive and even those don't achieve the lifespan of glass panels. If you cover the entire boat in the best panels you can probably do 20kWp, plenty for living at anchor in luxury, not a lot for moving the boat in the same style.
Take a look at existing designs like the Silent yachts 60, they can't achieve a positive balance. Of course it's a much heavier boat, but their cabins aren't broom closets. OTOH they do save massive amounts of diesel fuel over a comparable conventional boat, so maybe this should be your goal. I think you need to remain realistic, a comfortable Al cruising boat isn't going to make net positive on solar underway over 24h. Something with a single carbon fiber bucket serving as the whole crew toilet will, but that's a different style of cruising and it certainly won't "bounce off rocks".

Yeah - the energy budget, especially if that's the only source of propulsion, is the big question. It's all well and good having 100kwh of batteries - if the motors are running at ~6kwh for 24 hours that's totally drained, but if the solar / wind can't recharge them enough then eventually you're going to be doing nothing while waiting for some power (I've seen some people with conversions that do that - or switch between sail and solar). Sea trials will definitely give those answers - as long as it can be safe and go to nice places I'll be happy, even if the average speed becomes sloth-like (they're average speed when moving, but have long rests lol).

Definitely not planning to use any buckets for necessities - that's not the type of life we want on there - nor do I want to be running my ~250w server rack on it and wasting energy that way

 

[montero]

I'm a boat lunatic here on the forum. I don't write much about my ideas because I've devoted some time to them and I don't want to be perceived as an even bigger boat lunatic. But I respect other boat lunatics.

Getting back to your project:

You have zero welding experience, yet you choose a laser.
I wanted to find a YouTube video where one man welds an aluminum Shinkansen cabin from start to finish with a MIG machine, manually aligning the frames on the plane.
It's a quick and relatively inexpensive welding method. Besides, it would be good to have a welder on board when sailing.
So, I think that with an aluminum cruiser, welding skills are essential.

This is supposed to be a boat with a global reach, and the engine power seems too low to me.

Using kites is possible, but requires special solutions. How do you see this?

Kites will wear out, and you'll need a sewing machine on board and a large supply of fabric. How do you see this? Are you good at sewing?

What sailing experience do you have, if I may ask?

 

[Rycochet]

I'm a boat lunatic here on the forum. I don't write much about my ideas because I've devoted some time to them and I don't want to be perceived as an even bigger boat lunatic. But I respect other boat lunatics.

I have a feeling we're fellow lunatics with some crossovers here

Getting back to your project:

You have zero welding experience, yet you choose a laser.
I wanted to find a YouTube video where one man welds an aluminum Shinkansen cabin from start to finish with a MIG machine, manually aligning the frames on the plane.
It's a quick and relatively inexpensive welding method. Besides, it would be good to have a welder on board when sailing.
So, I think that with an aluminum cruiser, welding skills are essential.

I can (and possibly will) pick them up - all 3 types of welding have strengths and weaknesses (although the main weaknesses for the traditional forms are power usage and skills) - the learning curve for laser is significantly lower, and it will give an almost perfect weld every time *provided* you follow the instructions and have the right settings for the thickness of material - but it's not going to be able to fit into every hole so I'm not discounting the other types, just planning for the majority to be laser (and if MIG / TIG is barely needed I'd rather get an expert in for a couple of days - and watch and learn so I can practice on scraps etc).

This is supposed to be a boat with a global reach, and the engine power seems too low to me.

This I really don't know - I need to run some scale tests and do some maths, then figure out how much energy *should* be required for various speeds (once the hull design is at least partially there to figure out drag etc) - the different propulsion system will likely make a difference in many ways (not least by becoming the rudder when not providing power) so prop drag should be even less than a folding prop. Currently I'm going by feel, and if I'm within 50% of the true figure I'll be surprised! Not going for speed - as I'm happy to sit at 6kts or so (power curves will give useful numbers etc)

Using kites is possible, but requires special solutions. How do you see this?

Kites will wear out, and you'll need a sewing machine on board and a large supply of fabric. How do you see this? Are you good at sewing?

I've seen one boat that went fully electric and started using a kite - from memory he had to charge the batteries and not go anywhere every other day - but it was a conversion he was having fun with rather than something designed that way originally. There's a couple of companies that sell them - and without a mast in the way it is another potential way to get from A to B - or at least part of the way. Currently it's a "probably" - but I want to actually see how the boat performs (ie, battery usage against distance) - kites are a lot less "work" than sails, but ideally I'd want to be fully electric and not needing to do anything manual at any point.

On top of designing and building furniture in the past (commercially), I also designed and sold costumes and props for larp - so while I hope that I'd not need to repair anything important, I'm almost definitely going to have a sewing machine on board anyway - AuDHD career paths gave me a *lot* of skills

What sailing experience do you have, if I may ask?

Almost none - the last time I sailed (ie, wind) was nearly 40 years ago on inland lochs in Scotland, and more than a decade since I last powered anywhere (inland rivers in England) - it's not the worst, but definitely not that good - getting blue water experience before I take my own helm is on the todo list, and while there's no certification requirements for that situation, I'm also not going to go unprepared (I'm also certified for first aid, mhfa, fire marshal, etc - you get the idea)

 

[comfisherman]

Read the post from the 7th regarding the materials. Let's call it three as ferro cement is or should be relegated to the dustbin of history.

Ive owned both fiberglass, aluminun and steel boats around the size of this project as well as worked as shipyard worker on all three types. Because of the odd way we do permiting for about half a decade I owned near identical size boats in glass and aluminum and had them operating next to eachother. Logged 13k engine hrs as a crewman on an aluminum boat and 11k engine hrs on my own in addition to living aboard it for two years. Have also worked seasonally repairing as well as in new construction of aluminum boats, wont call myself a pro but "aggressive hobbiest" is fair. So have a bit of an idea of what it takes to build as well as own and operate aluminum boats. Pacific nw has also been the type of the spear in aluminum boats since shore and matsumoto started dominating in the 70s and it spread down the coast.

Aluminum is just another material, its not better or worse than the other just a different set of trade offs. Its the current flavor of the month in the online space but that doesnt automatically make it the best material. If those trade offs work, then wonderful... but there are downsides.

Aluminum still can be defeated by water obstacles. Years back we had a big storm tear up a cargo boat and we had a fall of being plagued by semi submerged 40 foot vans. Had friend on plastic boats holed as well as the bow of a partner boat get holed by one and it was over 6mm plate that was perfed. It does survive a bit better on rock impacts but sticks worse to sand.

The aluminum boat was hotter in summer, colder in winter and was perceptibly louder even with more insulation. Wone spring we had my boats next to eachother on anchor even with more foam and a bigger heater it had more temperature swings than the glass boat. The most notable was on the fish refrigeration side, both boats had roughly the same hold capacity (within 10%) and similar hold insulation and liners. On a 5 hr night the glass boat could hold fish in the chill range but the aluminum could not, crew on the aluminum boat would have to cycle the refrigeration during the night to maintain temp. Hard to shake the reality of being a boat built out of a great conductor of noise and heat.

Upside is rapid one off construction, its so fast to build an aluminum one off. Especially now that we have broad adoption of cnc router and plasma tables, from design to cut to assembly is a short and so much easier to adapt than glass. When my new glass boat was built a guy from my group built an aluminum boat that's nearly identical to mine, he beat me to the water by months with more custom features.

Another thing to be mindful of is electrolysis, it shows up under generators in the laz, and near battery boxes almost without fail. Its also more money to do hull penetrations. For all the aluminum building we have on the us west coast there is only one outfit casting marine grade thru hulls. Even then they still can fail. I keep a baby multimatic machine with a tank and a spool gun aboard. Got to weld in a new fitting on an aluminum boat built in 2012 that had a 1.5 inch thru hull corrode through. Was an exiting day for the owner and a miserable night on the beach welding in a new backing and thru hull... lots of hull perfs to worry about on a big aluminum boat.

Once again its a trade off, the previously mentioned friend who built a new aluminum boat had all manner of new plate on his previous boat from trapped water near some stringers. Most aluminum boats don't seem to start showing those problems until year 15... he figures he'll be 5 years retired before he has to start cutting bad alloy out.

On the welding side, its hard to bear the 255 pulse mig with the air cooled spool gun. Duty cycle is good enough for even a hard-core home builder and its a shocking amount of production capacity. I just bought a new setup as there was a gap between my baby mig multimatic and my now 20 year old xmt 350 with wire feeder. It was under 9k usd with the rebates for the push pull and welder, add in a tank and consumables its hard to beat dollar for dollar. The pulse function is the heat management easy button, have used a few and its awesome. Know a few shops that operated for years on just that before stepping up to the big systems. Lasers may have their place, but Id wager youtube university and a bit of practice and most people could build a lot of boat with a 255 and a push pull gun.

 

[Calafatus_LAB]

About 5–6 years ago I worked on a similar aluminium catamaran project in a professional setting. The concept had good potential, but the company stopped it purely for financial reasons.

One thing I learned: aluminium and aluminium welding are not trivial. Even professional yards have lost aluminium boats to galvanic currents. It’s rarely talked about, but it’s a real risk if materials, isolation, electrical bonding and anodes aren’t engineered as one system. A single wrong fastener or poorly isolated joint can cause serious damage.

Here’s one image from that project. If useful, I can share more sketches and technical notes.

 

[leecallen]

I've looked at 4 different materials - GRP, Steel, Aluminium, Ferrocement.

A few thoughts from an avid reader & researcher - with no relevant skills

I find your plan very intriguing. I am planning to build a boat in the near future but this is far larger than I have in mind.

I have been keeping up with solar + battery electric power and, as others have pointed out, I don't think it's there yet - and it may never be. Currently it only works on a very narrow and light craft that's completely covered with solar panels and travels slowly. But I do like the idea of building a foundation that works now and leverages the improvements that are on (or over) the horizon.

So if it were me, I would add a diesel generator capable of driving the boat at your desired speed. Consider it backup or supplemental power. And set aside the wind generators and kite.

Missing from the above list of materials: plywood + fiberglass + epoxy. Have you considered it? The plywood provides the stiffness, the GRP provides the strength, and the combination is very light weight. And the skills and equipment required are more within reach of 'us regular folk'.

Richard Woods has designed several power catamarans up to 36 feet long. His designs are built in (plywood or foam sandwich) + fiberglass + epoxy. He is an extremely experienced and competent naval architect. You might consider engaging him for your design effort.

 

[BoatBuildLog]

A 50ft build in parallel with others would be a huge project. Are you planning to document the design changes and construction stages somewhere as the builds progress ?