Looking for a long range expedition aluminum power catamaran design

Hey! I'm new to the forum but I've been lurking for a while as I've been searching for something suitable, so I figured I might ask you all to maybe point me in the right direction.

My partner and I are planning early retirement, and we've always shared a passion for adventure and traveling so we wanted to segue into seafaring and exploration of the world through our own eyes. To this end we were looking to find a go anywhere long-range fuel-efficient cruiser that would serve as a platform to do everything out of. It seems a lot of production vessels focus on things we frankly don't care about, so we figure that going for something custom for our needs is a reasonable strategy.

To begin with we don't care about luxury finishes or 15 different ways to entertain or host parties or rely on a bunch of crew. We want an owner-operator focused vessel that leans more towards commercial/military ruggedness and utilitarian interiors and emphasizes ease of maintenance and access to systems and operability. We're both tech savvy engineers (albeit from fields not directly related to the marine industry) and part of the appeal for us is to learning to maintain and work on our ship as necessary, as well as DIY systems and integrations. We want excellent seakeeping and safety for ocean crossings, and the capacity for redundant systems. We intend to spend most of our time cruising or at anchor, with minimal time at marinas.

We want a high degree of autonomy and would like to be able to go months without needing to resupply. We also (more so me than her) have a bit of prepper tendencies and would like this to feel more of a home base or moving fortress rather than a luxury yacht, which means no real need for a sun decks or open spaces, let alone dozens, or huge windows everywhere or a flybridge. I'd rather have solar power generation instead. One of our goals is to optimize fuel efficiency and fuel capacity alongside weight in order to maximize operational range, so while we want and are open to springing for as much space as possible, we want to keep it manageable by the two of us. We don't want to dedicate a lot of resources to guests seeing as how we will be traveling alone most of the time so our spaces would always the be the priority, and we'd just have nominal accommodation for maybe 4 other guests.

We opted for a catamaran due to their speed, stability and fuel efficiency compared to monohull displacement trawler, which we've considered but sacrifices too much efficiency to space.

We do want the ability to store and launch some toys, like an amphibious gyrocopter, a mini submarine, kayaks, etc. aside from the usual tender.

I'm sure more specifics escape me right now, but I hope that gives a general idea of what we have in mind. Ideally we'd like to find some designs or a designer/NA that closely aligns with these goals so we can work with them to bring about this vision as quickly and as efficiently as possible, since it's something we've been wanting to do for some time now and would love to see it realized. If this is something you all could help us with, or if there's something else we should be doing, please let us know!

 

Welcome to the Forum Silvard.

That is a pretty detailed Statement of Requirements you have outlined above - but there is no mention of budget, or what sort of size vessel you are thinking of. Bear in mind that once the loadline length of a vessel is more than 24 metres then the rules become much more strict, including the need for having professional crew to operate the vessel for you.
There are naval architects on this forum who have considerable experience in the design of aluminium power catamarans, and I am sure that one of them would be able to design a vessel for you to suit your specific needs.

Re the monohulls, have you considered the FPB range designed by Steve Dashew?
There are a couple of secondhand vessels for sale on the Berthon website -
FPB Motor Yachts For Sale - Berthon International https://www.berthoninternational.com/yacht-sales-brokerage/fpb-motor-yachts/

You might even be able to talk Sue Grant at Berthon into letting you build another new FPB - if your budget will allow for this, there is no harm in asking.
As the FPB range does seem to cover most of your requirements fairly well.

 

I think you need to define your needs with dimensions. For example, what kind of food do you require for months on end? Water is what takes most of the volume and weight. Watermakers are fine and if only for drinking use a moderate amount of energy. Are you two OK with salt water showers? Refrigeration also uses a lot of energy. Dehydrated food last a long time, but K-rations are not the most palatable. Fuel efficient is a goal, but what does it mean in MPG, and at what speed. Commercial/Military rugedness comes at the cost of more weight and less fuel efficiency. The military do not pay for their own fuel. When you start answering all these questions and more, the design will decide whether a multi or mono hull is better. Aluminum may sound good, but steel is easier to repair and modify in remote areas. I have worked on steel trawlers where we were stick welding with rain and salt water splashing. It didn't look pretty though.

 

With this in mind, as your main Design driver, you need to accept the comprises needed to achieve this objective.
That being, a "light" hull for its length.
This is the length-displacement ratio (LD).

So if you had, for example, a 19m hull and if you kept everything the same, but only extended the ends of the hull at the fore end and aft end...so hulls that are longer than you think you need, you are increasing the LD ratio, positively. So of that hull is extend by say 5m either end, your power requirement comes down by 50%:



So, if you wish to have a vessel with as least resistance as possible, you need a long slender hull for your design with the weights to support it.
Also, luckily a hull with a higher LD ratio is also better in seakeeping too.

But to create a design that utilises this simple hydrodynamic relationship....aaahh...that's where the fun starts and the compromises become....'difficult' to accept for many.

 

Thanks a lot!

I was hesitant to throw hard numbers around because I am not an expert, and we figured more knowledgeable people would be able to more accurately spec out something suitable for that mission. That said we had been thinking somewhere between 60 ft and 70 ft long. We want space, we don't want to feel cramped (especially if we have to work on the boat ourselves) and we're not overly concerned about marina costs, but we don't want a boat that is t00 big for the two of us to maintain (including cleaning) on our own or so big that it cuts down on fuel efficiency unnecessarily.

As for budget it's a bit more open ended. We don't want to waste a lot of money on luxuries we don't want, let alone need, but we know it's a big project regardless. We wanted to leverage lower cost of labor wherever possible as well as getting ABYC certs ourselves and do as much of the systems and interiors on our own, with supervision and double checking, so we were hoping for something between $500,000 and $1,000,000.

I have, in fact, considered the FPB range! And similar suggestions from other threads on this forum. They do come very close to what we wanted overall, but they seemed just a tad too cramped (I know I know, ironic) and too expensive. In the research we did they stood out among monohulls because most power cruisers seem designed for people who want to maximize space at the cost of efficiency since liveaboards don't seem move that often. Multihull seemed to afford a bit more space without sacrificing that much efficiency.

We don't want saltwater showers, but we're fine with dehydrated food (and all that prepper cuisine). We intend to have a hydroponics set up and a stock of nutrients (as well as recycling organic waste like food scraps) to produce, well, produce, and herbs. We're counting on having a sizeable battery bank (200kwh+) and maximizing solar generation (as many as a designer can fit, hopefully 20kw+ with the highest density panels) in order to run house loads like refrigeration and HVAC and desalination and the aforementioned hydroponics, though we would of course try to be as efficient as possible with our energy consumption.

As I said above I was hesitant to set a hard target when it comes to numbers. We want to optimize fuel efficiency within the other set of constraints. I'm not sure what's a realistic expectation but if we can get 3+ nautical miles per gallon at 8-9 knots, and enough top speed to be able to get out of trouble, that would be good. With ruggedness I mean more about the finish (or lack thereof) and practicality/utility rather than combat readiness. And we're not opposed to steel, but it seems like it would be heavier than it needs to be, but again, we're not experts.

That's what we've been picking up, which led us to search for narrow long vessels like the FPB. We want to see what compromises it would lead to for a multihull.

 

Is there room for a case of rum?

 

I think that even US$ 1,000,000 is a very optimistic (and unrealistic) budget for what you want - this link popped up in my IN box yesterday :
2024 Regal 43 SAV Boat Test, Pricing, Specs | Boating Mag https://www.boatingmag.com/boats/2025-regal-43-sav-boat-test/
Here we have a production 43' fibreglass motorboat with outboard engines selling for US$ 1.5 million.....

 

I think there's a good chance that it's optimistic regardless, but this budget is for the hull, propulsion and essential systems, and not for luxury fit and finish and fancy amenities. We've no doubt overlooked and/or underestimated certain expenses, but we've been looking at and asking for quotes for many different things and it seems that it's within reason. As I mentioned we intend to go where costs are the lowest and we want to handle a lot of the work ourselves (mostly installations and interior finish), not just to save money but to be intimately familiar with the ship and make it our own. But ultimately I guess it's going to come down to the actual design.

 

That is absolutely unrealistic for the high end technology you require.

 

Consider that a 200KWh battery bank cost about $90,000. That does not include the power management and cooling system.

 

60 to 70 feet might get you base hull mechanicals and some generators, oddly enough that's much cheaper these days than labor for fit out.

Outfit local to me is cranking out similar sized cats for whale charters and they break well into the mid 2 million category with an interior of an aluminun box with basic panels and bench seats. My guess is you'd hit 3 in a fit out even spartan finished for liveaboard. With labor what it is in the trades it could easily double that, although that has definitely slowed in the last year.

Your location is set to US, if it were me I'd probably spend a bit of time hitting up some of the yards making the bigger cats right now. Mavrik was the most well oiled outfit a decade ago, but others make a good product as well. Heck even bayweld up in homer has scaled up to make 60 to 70 foot cats.

Over the years I've watched several Builders form relationships with naval architect's. A poor design usually lands on the builder as remedies as well as bad p.r. usually land on them first. From my vantage point the builder to NA method is better than the NA to builder.

 

I don't mean to dispute that because I'm here asking about it for a reason. Can you please specify to which high end technology you refer?

I understand the costs involved with most of these systems (in particular energy) and I'm familiar with them, albeit not in a marine environment (it looks to me that even at something of a premium you might be able to get 200kwh of marine rated batteries for closer to 60k, and that isn't the cheapest). I'm less familiar with the marine specifics aspects such as hull and propulsion and what not. Could you please elaborate so I can adjust accordingly, either our budget or our goals? I don't know what eats up the costs in these projects. For instance we've been quoted 250k for propulsion, batteries, inverters, power management, etc. Which seems doable, but that's based on a rough idea, not a concrete design.

The design, hull and essential work (like mounting the propulsion and such) and equipment is our primary concern budgetwise, at this juncture anyway, which is why we are looking to take the design to cheaper regions to get that done. The fit out labor is less relevant as this is something we intend to do largely ourselves. We are both trained engineers who like tinkering and learning, and we're still both young and fit so part of the appeal was to DIO as much as possible according to ABYC and all applicable standards, alongisde proper inspections, and we intend to do this full time. Insurance would be a concern in general, but not enough to dissuade us from trying to work it out.

 

Why does it have to be an expedition / aluminum boat .Where you want to sail?

 

Everywhere. I'm sorry for the vague and semi-useless answer, but we want to spend the rest of our able lives cruising and getting to know places. From Alaska to Ushuaia, Bahamas and Galapagos, we'd like to circumnavigate, SCUBA and fly all over the other continents and islands as well. I know it's a romantic idea that smacks of wide-eyed naivete, but it's a dream that motivates us. And I'm here to see how we can make it happen.

 

Have you given consideration to a second hand sailing catamaran? There are so many for sale nowadays, of all shapes, sizes and prices.
Alaska to Ushuaia in a motor boat is going to cost a lot in diesel, even if the boat is fairly efficient re miles per gallon.