New Islay Ferry – part 2. The ferry that CMAL designed to fail.

April 2022

From the outset of the New Islay Ferry (NIF) project, catamarans were ruled out of consideration. In CMAL’s public Q&A documents of July and November 2020 a catamaran design was firmly deemed “not feasible”.

CMAL’s public Q&A document of November 2nd 2020. Can be viewed in full here.

At the same time, we on Mull were campaigning to persuade CMAL to buy a second-hand (but newly built) catamaran for Mull that was available in Indonesia. (see more here). Catamarans were therefore a relatively ‘hot’ topic at the time. We were publicly questioning why CMAL seemed to have an aversion to them, despite their proven reliability, weather-resilience, suitability to west coast ports and piers, their low running costs – and particularly their low build cost. (Download a factsheet on the benefits of medium-speed catamaran ferries here.)

So CMAL’s rejection of catamarans appeared absolute, and certainly no investigation of a catamaran solution for Islay had been undertaken. However, early in November 2020, Mull & Iona Ferry Committee held a public online webinar entitled ‘Catamarans – Future Ferries for Mull?’. In it, we laid out the benefits of medium-speed catamarans. Our webinar appears to have provoked a reaction within CMAL.

Catamarans suddenly back in contention for Islay – apparently

Just ten weeks after our webinar on January 14th 2021, CMAL held their own webinar ‘consultation’ on the Islay ferry options, still available to view here. Rather than a ‘consultation’ it appeared to us to be more of a presentation, justifying a decision already made. It contained a series of errors, omissions, assumptions and judgements that favoured the largest vessel choice. Part one critiques that presentation, but on this page we look at a specific element – the misrepresentation of the catamaran option.

A table was included that compared CMAL’s ‘preferred’ monohull solution with an unnamed catamaran. Despite the previous statements that a catamaran was ‘operationally unfeasible’ as little as ten weeks previously, CMAL appeared to now be introducing a catamaran for consideration. Below is the table:

Side note – Islay’s ferries are Islay’s business, and we have no desire to interfere with the wishes of the Islay community on this. They are having much-needed new ferries delivered, and that is to be welcomed. It is for that reason that we have witheld from publishing this piece until the NIF contract was awarded.

The slide caught the interest not just of MIFC, but of many other informed and professional people from the ferry industry. To our and their surprise, the catamaran was deemed to be worse than the monohull on every key metric. It appeared to contradict every known natural advantage of good medium-speed catamaran ferry designs.

Catamarans have two inherent natural advantages when compared to monohulls – a) shallower draught, and b) improved fuel efficiency. These two advantages are demonstrated by proven catamaran designs, like for example Pentland Ferries’ MV Alfred, which has a draught of just 2.75m and is the only UK ferry to receive a Green Tourism Award in recognition of its fuel efficiency.

Pentland Ferries’ MV Alfred, that operates services to Orkney

By contrast, CMAL presented an anonymous catamaran that would consume more fuel than the monohull, and have exactly the same draught. It was a highly surprising set of numbers. The draught figure was particularly notable. CMAL’s monohull requires to have nearly £17 million spent in three different ports, much of it for dredging and rock removal to accommodate the deep draught of the new monohull (4 metres). One of the first and largest cost savings for a catamaran (of normal design, with a draught similar to Alfred’s 2.75m) is that it would not require these large sums to be spent on port deepening. It was very strange indeed for CMAL to have designed a catamaran that did not display their ususal natural advantage – shallow draught.

We tried to ask questions

Immediately after the presentation, we wrote to the Head of Vessels at CMAL. We asked for more details about the catamaran in his presentation.

A sporadic correspondence over the course of several months then ensued, but CMAL refused to release many further details, citing commercial confidentiality. We found this refusal to provide basic information about the un-named catamaran to be completely unjustified.

Of particular interest was the general arrangement (GA) drawing – we wanted to see how well developed the design was, and how it compared with proven (ie built and operational) catamaran designs. CMAL steadfastly refused to give it to us.

There is nothing of unique commercial value in a GA drawing – they are often freely provided by vessel designers and builders, as a sales tool. We have freely been given many of them by a variety of shipyards and designers – yet CMAL were insistent that this particular GA should remain secret.

Crewing was a cut-and-paste assumption

However, we were able to get somewhere with the crewing figure of 27, which was curiously identical across all monohull options, as well as the catamaran. During our email exchange, CMAL told us that “CalMac assessed the crew level on the proposed design…”

So we contacted CalMac, asking them how the crew requirement of 27 had been arrived at. However, they replied that “…CalMac never provided an assessment for a catamaran design…. The crewing figures included under the catamaran option are an indication and are aligned to the crew requirements of the preferred [monohull] option. No other assessments of crewing levels for the catamaran, or other vessel options have been carried out.”

So “CalMac never provided an assessment for a catamaran design” yet CMAL presented the crewing figures as fact. The crewing figure was a copy-and-paste assumption from the preferred monohull design. Rather than investigating a design option and considering how the crewing level could be optimised around it, CMAL had assumed that the crewing figure would be the same, and offered it as established fact to the public without any qualification. (The same crewing assumptions also applied to ALL the monohull options under consideration. For more on that, see part one.)

Even our MSP and cabinet member was denied the data.

We were quite shocked to find that CMAL were prepared to present this blind assumption as fact in a public presentation, and it made us more intent to be provided with the full details of their un-named catamaran. By this stage we had formally submitted our request for the data as a Freedom of Information Request.

We also received help from our MSP (and Cabinet member) Michael Russell, who made the same requests for the vessel information on our behalf. Even he, our elected MSP and cabinet member, was refused the catamaran data by CMAL. They did finally relent after he persisted, and gave us most of the figures we asked for by May of ’21, five months after initially asking. However, CMAL continued to refuse to release the general arrangement drawing or the calculations behind the fuel consumption figures. The exact shape and design of the catamaran was stubbornly being kept a secret, for reasons we could not comprehend. We therefore lodged an appeal with the Information Commissioner. We’ll come back to that later.

How does CMAL’s catamaran compare, and why is this important?

We were persisting with our enquiries, not just because tens of millions of pounds of taxpayer’s money is at stake, but because ferry design choices are at the heart of the unfolding crisis of ferry provision in the Hebrides. CMAL and Scottish Government have a track record of buying complex, one-off, over-large, heavily-crewed, thirsty and expensive vessels. Poor vessel choices not only result in a poor service (notably the huge superstructures making vessels vulnerable to wind when berthing), but they make each new vessel more and more expensive. This is not just a waste of public funds, but it slows down vessel replacement – the government simply cannot afford to build many of these hugely expensive vessels, and the pace of renewal slows. So expensive vessel choices on one route impacts on the entire network.

CMAL’s Islay catamaran (above) and STS’s 85m catamaran referenced below.

Even without the general arrangement drawing, we had enough key information to produce a comparison of CMAL’s catamaran with known, proven catamaran designs. Medium-speed catamarans are becoming increasingly popular with operators of small to medium sized ferries, particularly at sizes of 100m and below where their efficiency advantages are pronounced. For an operating area with relatively shallow ports and high winds like the West of Scotland, they could be particularly well suited. Sea Transport Solutions (STS) of Australia are the market leaders in the design of these ferries (distinct from high-speed catamarans). STS invented this class of vessel. Others including BMT have entered the market, notably designing the Alfred which was built for Pentland Ferries in 2019.

Both STS and BMT have provided us with GA drawings and key specifications of their designs, and this allows us to compare CMAL’s design with these proven (ie built and operational) designs from the established specialists:

CMAL 94.8m monohull ‘option 2’CMAL 90m catamaranSTS 85m catamaranBMT 84.5m catamaran ‘Alfred’
Car Capacity1079810098
HGV capacity14 x 18 metres12 x 18 metres12 x 15 metres12 x 15 metres
Passenger Capacity350350387430
Speed16.5 knts16 knts16 knts16 knts
PropulsionHybrid diesel-electricHybrid diesel-electricDieselDiesel
Fuel Consumption*760-857 litres/hour794-888 litres/hour541-730 litres/hour630-760 litres/hour
Draught*3.8-4.0 metres3.8 – 4.0 metres2.8 metres2.75 metres
Block coefficient*0.5740.590.360.55
Port Dredging Costs£8 million£8 million£0£0
Pier upgrade Costs£9 millionunknown£0£0
Build Costs£52.5 million**unknown, but assumed to be very similar to CMAL monohull costcirca £20 million, European shipyardcirca £20 million, European shipyard***
How many could be delivered for the £122m total NIF budget? *2266
* These are the main points on which a well-designed catamaran normally has a natural advantage, but CMAL’s catamaran does not. Block co-efficient is one measure of how much resistance a hull will have being pushed through the water. The lower the number, the better. **Taken from news release, March ’22. More recently CMAL state £44.5m ‘excluding spares’, but total contract still £105 million. ***Built in Vietnam for £14 million, 2019. Large 50% uplift for European build

As can be seen from this summary table, on the key points that a ferry operator should be concerned with, the CMAL catamaran is particularly uncompetitive. It has more than double the crew ‘requirement’, consumes considerably more fuel and needs expensive port dredging to enable its deep draught to enter. What completely rules it out as a competitive design is the huge cost. Recent bids for both the STS and BMT comparator designs have come in at well under £20 million from far-eastern yards. We have added a large 50% premium for a European build in the figures above, yet still both of these alternatives would have been around one third of the total cost of either CMAL’s monohull or catamaran design (including the port upgrades required to accommodate them).

STS and BMT are known to CMAL. In the relatively specialist area of medium-speed catamarans, these are the only companies who have had their designs deployed and proven by UK ferry operators. We now know that the company CMAL chose to create their catamaran design was naValue, the same German firm of Naval Architects who created the NIF monohull proposals. naValue are a team of monohull ferry designers, and we can find no evidence that they have ever designed or built a roll-on roll-off catamaran previously.

So why would CMAL commission a hurried catamaran design from a company who have no experience in designing them?
The obvious conclusion is that the decision to choose a monohull was taken from the outset.
A catamaran was never in contention. This catamaran ‘design’ was not a serious exploration of a catamaran option; it was a late and scant addition to the comparison, and it’s apparent purpose was to discredit catamarans and justify the monohull decision already taken.

CMAL have done this before

This is not the first time that CMAL have publicly mis-represented the capabilities of a medium-speed catamaran. We can go back to the last major procurement – the ill-fated hulls 801 and 802. The 801/802 project began as the ‘MARS’ (Mull & Arran Replacement Ships) program back in 2012. (it later moved focus to Arran and the Uig triangle instead).

A public review of the vessel options being considered is still available to view here. In the presentation, a catamaran proposal from STS of Australia is presented:

Extract from CMAL presentation of 2012

As noted above, the capacity of this catamaran was under-stated by 275 tonnes (68%), asserting that it could only carry 4 x 44t trucks, and little else. We have examined the GA drawings and the tender submission from STS, and it is clear from those documents that the real capacity was 475 tonnes. Since CMAL’s assertion was taken at face-value, the catamaran was of course discounted. And ten years later, we are still waiting for the 801 and 802 to be delivered.

So how bad is CMAL’s catamaran?

Finally more than a year after the presentation, the Information Commissioner upheld our appeal and the GA drawing and other technical detail was released to us. It was immediately apparent that this was an immature and very flawed design. We can take a few extracts from the GA drawing of CMAL’s catamaran and compare it with examples from STS –

In this section across the ship, we can see several failings of the unrefined CMAL catamaran:

  • The superstructure is much larger – both taller and with a much larger cross-section. This indicates a much heavier design with more cost, windage and weight to push around.
  • An entire deck (plus other space) is taken over by the 31 crew cabins. The STS design requires a crew of just 12-14, which in this design do not live onboard the vessel, so their cabins are smaller and below decks. (If ‘live aboard’ cabins were required these could be re-located, but it would be much easier to accommodate 12 cabins rather than 31. If live-ashore crewing were chosen – which is arguably preferable on such a short crossing – the construction burden on the vessel would be significantly less).
  • Because it is so much heavier, the CMAL catamaran sits low in the water, with a draft of 4m, whilst the lightly-constructed and simple STS catamaran has a draught of just 2.8m – ideal for accessing the typically shallow ports of the West Coast.
  • The tunnel between the two hulls is just 1.55m high, and has a large flat upper surface. This will result in water slamming in even moderate seas. Compare with the STS tunnel, which is both much higher and with a gentle curved shape to minimise slamming. This is a key indicator that this is a very immature design.

In these two car deck plans, the superior arrangement of the STS catamaran results in exactly the same number of cars on a vessel around 16 metres shorter than the CMAL vessel. The CMAL catamaran has only six lanes of cars, whilst the STS cat has eight. STS minimise the ancilliary space, and move it to the corners so that the area remaining for cars is maximised. Shorter vessels = cheaper to build = lighter = more fuel efficient = can berth at shorter piers.

In what is perhaps another indication that CMAL’s designers are more used to designing monohulls, they have lined both sides of the car deck with ancillary rooms. This is common on monohull car ferries, because the primary function of these spaces is to provide bouyancy if the vessel is flooded. Catamaran car ferries achieve the same resilience and ‘damage stability’ by virtue of having two hulls. The result on the CMAL design is a lot of wasted space, needless additional length, added weight, and cost.

After examining the contract tender for the Islay vessel design work, we could see there was no mention of a catamaran design option. This confirms that a catamaran was not in contention from the outset.

We sent CMAL’s drawings to retired naval architect Euan Haig (C Eng, FRINA, RCNC), who worked for many years for the MOD, overseeing the construction of a series of different military vessels. He summarises the design as a “catamaranised version of a CalMac monohull” and “a pig in a poke”. Of the low height of the tunnel between the hulls (referred to above) Mr Haig said “…this alone makes CMAL’s design unfit for purpose and unworthy of development.” You can read his full and damning opinion here.
The full GA drawing can be seen here, and the power/speed calculation here.

Why are CMAL so opposed to catamarans?

This is a question that has perplexed us and others for years. In great part, we think it is down to dogma and pride. We experienced first-hand how determined CMAL was to obstruct the Indonesian catamaran we advocated for in 2020/21, and there seems to be similar determination to discredit catamarans here. But the benefits of medium-speed catamaran designs are clear and convincing. They demonstrate how poorly many CalMac/CMAL monohulls perform. And this is perhaps the problem – if introduced, a catamaran could demonstrate the repeated errors of past procurement and design decisions.

But that then raises a more fundamental question – how can such personal subjective preference apparently be playing any part in public procurement decisions worth hundreds of millions of pounds?

It also seems that ‘process’ overwhelms economics. For example – CMAL have a ‘process’ for achieving ‘value for money’ – they put all vessel builds out for competitive tender, and can therefore claim to have fairly picked the best-value bid. But there are two fatal flaws with this process:

  • CMAL and Transport Scotland publish what they expect to pay well in advance – just look at the CMAL corporate plan for evidence of this. A year ahead of selecting a winning bid, they had already published what they expected to pay. This doesn’t indicate that CMAL’s estimate was accurate, so much as the bidders can read what’s on the internet.
Extract from CMAL’s corporate plan, published April 2021, 11 months before contract award
  • The design specification process is completely topsy-turvey. CMAL and Transport Scotland seem to start by specifying a ship solution, rather than identifying a transport requirement. There are many different ways of providing transport to an island; many different combinations of ship, timetable and route. If Transport Scotland specified the requirement in terms of vehicles/passengers/trucks to be carried each day, month and year; minimum operating hours and any other service requirements, competing designers and shipyards could then propose solutions, in the shape of different types, sizes and number of vessels. That would encourage a true competition of ideas and design.
    Instead, CMAL task a single designer to produce options within a restrictive and limiting ‘vessel requirement’ with little opportunity for innovation or competing ideas. For example, the ‘requirement’ that all vessels should have a crew of 27 regardless of ferry size or type is as absurd as it might be to specify the same engine size, regardless of how large the ferry is. One of the key objectives of good vessel design is to optimise crewing requirement (by for example keeping all passenger spaces on one deck to make emergency mustering easier; or choosing evacuation equipment that can be operated by fewer crew members). It is truly baffling that instead, CMAL/CalMac make a particular crew number a ‘design requirement’, when the ‘requirement’ should instead be to optimise crewing around the design and operational needs of the vessel.

What could catamarans have delivered to Islay and the taxpayer?

Had a more open design competition been carried out as suggested above, a medium-speed catamaran solution could well have won out. Better-designed monohulls could also have been contenders – see part one for more on that.)

But since we know a fair bit about medium-speed catamarans and have access to proven, built, UK-spec designs and their designers, we can outline what a catamaran-based service would have looked like. And we can compare it to the solution that CMAL ultimately chose in early March ’22 – , two 95 metre ‘option 2’ monohulls:

2 x ‘Option 2’ monohulls3 x 85m catamarans
Length94.8 metres85 metres
Draught4.0 metres2.8 metres
Car capacity2 x 107 = 2143 x 100 = 294
HGV capacity (44t)2 x 11 = 223 x 9 = 27
Speed*16 knts14 knts
Turnaround time25 minutes15 minutes
Passengers2 x 350 = 7003 x 387 = 1161
Crew**2 x (27 x 2.2) = 1203 x (2.2 x 12) = 80
Sailings per day2 x 5 = 103 x 5 = 15
Total HGV capacity / day110135
Total car capacity / day10701500
Fuel consumption***2 x 857 = 1714 litres / hour3 x 541 = 1623 litres / hour
Fuel consumption / car space / hr***8 litres5.5 litres
CO2 emissions / car space / hr21 kg14.5 kg
Pier upgrade cost£17 million£0
Build cost£105 million3 x £20 m = £60 million
Total cost£122 million£60 million
Annual crew costs (est)£5.4 million£3.6 million
Annual Fuel costs (est)£5.2 million£4.97 million
Total 25 year cost£387 million£274 million
RedundancyMEDIUM. 50% loss of service from one breakdownHIGH. 33% loss of service from one breakdown
Interoperability with other portsMEDIUM. Restricted by both draught and beam to limited range of ports.HIGH. No draught or beam restrictions (twin vehicle ramps aligned as per 14m wide monohull)
Timetable frequencyMEDIUM. Maintains existing TTHIGH. Increases frequency by 33%, or five additional sailings per day.
Wind resilienceHIGH. Highly powered vessel with rotating azipods.HIGH. very low windage and high turning torque from widely separated props.
* catamaran service speed is 16 knots, but reduced to 14 in this example for fuel savings. Time made up by quicker turnaround (no mezzanine decks) ** 2.2 complete crews needed for shifts and holiday cover. ***A crude measure that takes no account of the more demand-responsive timetable that three vessels can offer, that would likely increase the catamaran advantage.

So there it is – by persisting with the ‘option 2’ monohulls over catamarans, Islay have missed out on a 33% increase in service frequency; 25% increase in HGV capacity; and 50% increase in car capacity.
Taxpayers will be spending £113 million more than they would have over the next 25 years – enough to build another five catamarans.

And that, in a nutshell, goes a long way to explaining why the whole network has such an ageing, expensive and increasingly incapable fleet.


Acknowledgements and sources
We are grateful for the expertise and advice of many industry experts in creating these pages. We have also had essential contributions from practicing, retired and teaching naval architects in the UK and abroad; ship brokers, financiers, ferry operators, and numerous Scots close to the subject. Thank you to all of them.

If you have any questions on the subject, would like to see our source material or have any contribtions of your own, please do get in touch by emailing us.

Further reading:

Comparison of catamaran and monohull ferry efficiency and operations:

Baird, A. J. (2012) Comparing the efficiency of public and private ferry services between mainland Scotland and the Orkney Islands. Research in Transportation Business & Management, Vol. 4, pp. 79-89. [PDF] Comparing the efficiency of public and private ferry services on the Pentland Firth between mainland Scotland and the Orkney Islands | Semantic Scholar

Comparison of small catamaran and monohull hybrid ferries efficiency/emissions:

Baird, A. J. (2012) An evaluation of the benefits of CMAL’s Hybrid Ferry. Scottish Transport Review, 55, November, p. 10-11. str55.pdf (

Baird A. J. and Pedersen, R. (2013) Analysis of CO2 emissions for island ferry services. Journal of Transport Geography, Vol 32, pp. 77-85. Analysis of CO2 emissions for island ferry services – ScienceDirect

Baird, A. J. (2018) “Monohull versus catamaran: analysis of efficiency and operability in the small and medium-sized, medium-speed ferry sector.” Shippax Info, Jan/Feb, pp. 70-76 Shippax Info – The complete ferry information source | Shippax

Comparison of catamaran and high displacement monohull costs and efficiency:

Baird, A. J. (2018) Submission to the Rural Economy and Connectivity Committee Ferry Inquiry. Dr._Alfred_J._Baird submission REC Sept2018.pdf

Ferry design and procurement, comparison of catamarans and monohulls:

Baird, A. J. (2020) Submission to the Rural Economy and Connectivity Committee Ferry Inquiry. RECC_Dr Alf Baird_FI (1).pdf

MIFC, submission to Rural Economy and Connectivity Committee Inquiry 2020

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