Please select your home edition
RS Sailing 2021 - LEADERBOARD

Off Kilter - Part II

by John Curnow, Global Editor, Powerboat.World 14 Sep 2022 13:00 PDT
Invincible 46 underway - bow out, steps for lift, and asymmetric hull design for turn in. Cool © Invincible Boats

Thank you very much to all of you, the readers of Off Kilter - Part I. The response has been fantastic, and all of the team here are very appreciative. Cheers. Also, a big shout out to our friends at Invincible for all their help, Ian Birdsall and Oliver Huntsman.

In the first instalment, we began our investigation into why Invincible cats turn in, not heel out, and many more aspects of the design, build, and ethos that is Invincible. Now if have not read said epistle, please do so before taking on Part II here. We have more to get through, and some additional treats as well, so now is very much time to go WOT.

Staying very much on the grid

One of the things not mentioned too much around cats is that they can end up porky pig pretty quickly, especially cruising power cats. At 20 plus metric tonnes and 40 odd feet, the latter can be substantial, whereas the Invincible is more like 6.5-7 metric tonnes (for the 37), and you need to be light if you're going to be fast. So learning that Invincibles are wet lay up with core in places was a little bit of surprise. I had almost been expecting to learn it was E-glass, actually.

So what's the key? Ian Birdsall explains, "One of the things that differentiates the way an Invincible is constructed to a lot of the other catamarans, or even monos out there, is the liner grid system that we use. Liners are common, but they are predominantly using longitudinal stringers."

"With catamarans, particularly, it's very difficult to get a grid stringer system. You just don't have the space. We do have a grid stringer system. It's a complex mould, beyond words actually, and very expensive to maintain. However, the result is that we cut down an awful lot of weight by having a grid stringer system."

"We've got longitudinal and midships bracing, and it's solid glass; there's no core in that. Also bear in mind that we although we do use core around the vessel, in certain areas it's solid glass. So we will lose the core where we need to get additional strength, without worrying about the weight. For instance, midway where we can expect an awful lot of stresses to be put on the hull, we get rid of the core."

Can you open it?

A lot of fishos like gunwale doors. Does this mean that it is not possible with an Invincible then? "A portside gunwale door is an option on every model except the 33."

Now if you've got solid glass in certain parts, a gunwale door is not really your friend. "On the 37, 40, 46, we don't just cut a hull in the side; it's a totally different mould. The actual structural integrity of the boat isn't compromised at all. The liner is changed to suit, with additional strength added to take into account the fact that you've chopped a hole in the side of the boat." Just like you do with a good convertible...

"You're not even talking about the same animal. The liner creates a huge amount of the strength, by being a box section, and it is below the sill of the door anyway."

Power on, dude

Everyone has a mild fetish at the moment with outboards, and large numbers on the cowling of those outboards, combined with an extensive array of outboards along the transom. Yet the numbers mean different things. For instance, an Invincible 35 with a pair of 600s will go better than a 35 with quad 300s. Same horsepower, delivered totally differently, and the same fuel burn on the whole. So it's not a fuel scenario, and probably weight is going to favour the quad application, because the V12 is a very heavy beast, but yet the performance would be very different.

Birdsall elaborated, "I would say that we don't have enough actual hours on that V12 right now in real world situations ourselves, to be able to pass what I would say to be a valid comment on its long-term durability. There's enough out there now that have verified that, however. Really, it's a cost/benefit issue. Amazingly, you can put 4x300s on there cheaper than 2xV12s. Significantly cheaper than 2xV12s. Yes the performance of the V12s on the 35, for instance, is quite phenomenal. That boat will plane easily on one motor. You don't find many cats that will do that. You can kill a motor, and the thing will run at 35 knots, and just laugh at you." That makes me think of a passenger jetliner, BTW.

"That's always been my issue with a twin-engined cat. You're 100 miles offshore, one motor fails, and it's a long way home in circles at five knots. So we get through to that issue and that's why on a boat of that size, quads have always been the way to go. Also, bear in mind also that by putting quads on a cat, in particular, it creates a huge amount of lift at the transom, which cats love. So it does actually increase the performance of the boat dramatically over twins. Having said that, those V12s have got a massive amount of lift anyway, due to the duo prop and huge torque."

"So they'll lift the back end of that boat, no problem, whereas your twin 400s won't do it at all. They haven't got the lift; the props will not lift the hull at the transom and they create a bit of a slug really. You're better off putting on quad 300s. Our 35 with quad 300s is an absolute peach of a boat. It's beautiful. But money no object, I'd probably put twin V12s on it", and so the debate continues... (and of course they look cool!)

What's the essence?

Ian, would you say that pace, apart from toughness, is sort of the key requirement of buyers? "I think it's cruise speed that people are looking for. I mean that top speed number looks great, but is it realistic? Our customers are looking for a boat that will cruise easily, comfortably, all day long in the mid-40s. Our sweet spot for most models is about 42-45 knots, depending on the boat length."

You're going to get to a lot of places very quickly. "Yes, and you're going to get maximum efficiency too unless you're talking trolling speeds. For instance, on the 33 its sweet spot for range and endurance is 42 knots. That's really what is the selling point, I think. If I'm looking at what I'm going to do with a boat, I want to get somewhere quickly, and I want to get there as efficiently as I can. Now okay if I had a displacement hull and I was happy to sit there at six knots, it would cost me a lot less, but it would cost me much more in time that I just don't have."

"Now there are a lot of boats that I look at and check out their performance. They'll say it is 60 knots all day long, but the actual sweet spot is probably 30. That's not what we're looking for; we're looking for something that I want significantly faster than that, and be at its maximum efficiency. So in terms of range on this 37, unless you're running it idle or at trolling speeds, your maximum range is going to be achieved at around 40 knots."

You will be able to do that in a one and half metre seaway too, and backing off at about two and half metres. Of course it all depends on period, and every sea state is different, but you get the idea.

"Sure. You've got to know how to drive it, and being able to read the water conditions. I'm a big believer in that. People ask me, 'Will your boat run in two metre seas?' Absolutely. No problem. But you've got to know how to drive it. You don't take these things lightly. People take the sea and go, 'oh you know it's all about the boat'. It's not all about the boat. It's about being able to read the sea state, and being able to handle it, to know to judge properly, correctly. That's what makes it. It's a combination of the boat and the driver, that makes a boat safe and comfortable to run."

"An Invincible will take anything you can throw at it. But if you want to be comfortable you've got to know what you're doing and that goes for any boat. Too many people just do not take that into account at all. You need to have the capabilities equal to those of the boat that you're driving. You should have. That way you'll get the maximum out of it."

"Invest time in learning as well as buying the product. And it's money and time well spent. It really is. It absolutely makes a massive difference to your enjoyment on the water. I believe. I've spent thousands of hours on the water, and still get caught out occasionally. Just sometimes you think: 'really? Didn't expect that! That wasn't in the forecast. I don't remember seeing that on any forecast I looked at.' So the sea is a very unforgiving partner.

"We take a lot of pride in the fact that we do build a product which is different, which is have a huge amount of research and development into it over a long period of time."

Parting Gift

We have seen monohull CCs go out to 75 feet, so are we likely to see Invincible with a 55 powercat or something, maybe 60. "You're likely to see Invincible with additional catamarans in the range, in a certain size bracket, let's say." Given they go down to 33 feet presently, you'd have to think the next one will be upscale, but just how soon? "We're not about to stop, let's put it that way. We're moving on as we speak, in fact," said Birdsall in closing.

Given I saw the look on Ian's face, I have a feeling that project may be closer than what we imagine. "It could well be," was the closing remark.

Watch this unique way of seeing an Invincible 46 get underway.

OK. Today you will find that the website has an abundance of material from right across the globe, and if you cannot find something, just try the search button right up the top of the landing page, above our logo. If you cannot find what you want or wish to want to add to that, then please make contact with us via email.

Happy boating,

John Curnow
Global Editor, Powerboat.World

Related Articles

Taking a closer look at the Switch
We spoke to Simon Hiscocks to find out more about the one design foiler There are many dinghies throughout the years which have taken their inspiration from the International Moth and become one design. The Europe and the British Moth are two, and now there's the Switch. Posted on 28 Feb
Celebrating offshore accomplishments
Global Solo Challenge and the Arkéa Ultim Challenge endgames Back in January, I wrote about 2024 having an embarrassment of riches, and the first of these dividends have arrived, courtesy of the Global Solo Challenge and the Arkéa Ultim Challenge. Posted on 27 Feb
Back with a vengeance
Categorically been on the Mixed two-handed offshore bandwagon from the beginning Categorically been on this bandwagon from the beginning. Flag bearing, card-carrying, full-blown trumpeter. Mixed two-handed offshore. You might argue it had a wee false start, but it just was a bridge too far at the time Posted on 26 Feb
We chat with Tom Morris on the Allen stand
At the RYA Dinghy & Watersports Show Tom Morris of the Youtube channel Mozzy Sails talks to us at the RYA Dinghy & Watersports Show 2024 about developing fittings with Allen for his RS800, his favourite block, the America's Cup and more! Posted on 26 Feb
Celebrating 25 years of Rooster!
We speak with founder Steve Cockerill at the RYA Dinghy & Watersports Show Mark Jardine speaks with Steve Cockerill, founder of Rooster, on the 25th Anniversary of the innovative sailing clothing and chandlery company. Posted on 25 Feb
1948 Olympic Firefly wins Concours d'Elegance
At the RYA Dinghy and Watersports Show For the judging of the Concours d'Elegance, Mark Jardine, Editor of, was joined this year by the British Sailing Team 49er crew Fynn Sterritt, who has been selected for the Paris 2024 Olympics. Posted on 24 Feb
Oldest video footage of 18ft Skiffs
A look back into our video archive, from 1939 to 1987 With the JJ Giltinan 18ft Skiff Championships starting next week, it's a great time to look back into our video archive, from 1939 to 1987, to see some of the oldest footage of skiff sailing in Australia. There are some gems! Posted on 23 Feb
2024 505 Midwinter Championship interview
We talk with Ethan Bixby about the 2024 505 Midwinters Sail-World checked in with Ethan Bixby, event chair of the 2024 505 Midwinter Championship, to learn more about this competitive, warm-water One Design regatta. Posted on 20 Feb
It's a wrap!
In sailing we have a lot of plain white hulls In sailing we have a lot of plain white hulls. Let's face it, when everything looks the same, it does make things a bit dull. The end of February is a dreary time, so it's time to talk about boats which brighten things up. Posted on 19 Feb
Small Packages
You know? It is all about really good things You know? It is all about really good things. In sailing, two of the best attributes have always been fun and participation. Some would argue that these may have slipped off of late, but perhaps, it is more about finding a suitable offering. Posted on 13 Feb
North Sails Performance 2023 - FOOTERArmstrong 728x90 - MA Foil Range - BOTTOMJ Composites 2022 - J45 v4 FOOTER