– Ayana - 14m Planing Hull Powercat –
Designed by Roger Hill • Built by Noosa Marine • images James Dumergue
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This project began with a call from the client enquiring about a 14m semi displacement alloy/composite (composite fly bridge) RHYD power cat that was for sale. He needed to confirm the overall dimensions as it was critical for fitting into their berth, the beam was about 50mm too wide, Murphy’s Law. They were very disappointed as the boat ticked most of the boxes for what they were looking for to take long range cruising holidays out of Perth, WA.
Not thinking too much about it I suggested they take a look at an existing 14m design I had that did fit their berth, emailed the study plans, next minute we had a client for a new build, too easy.
The original 14m was built in Noosa by Julian Griffiths and his team at Noosa Marine (reviewed in this magazine mid 2018) so it was a simple process of introducing the clients to Julian and letting them get on with sorting out pricing, contracts, etc.
As is reasonably normal, the new 14m was to be changed a bit from the original design so we got on with the re-design process, in the end there was very little of the original design that we used again, perhaps the hull bottom shape! Outwardly the two boats do look similar, not difficult to see their parentage, but when you examine things more closely there is nothing throughout the boat that has not been modified, moved a little bit, re-shaped, transformed into a new ‘one off’ that was to be the least compromised solution.
After settling on a build price and contract and getting on with the new design work the clients changed course a bit, the boat was now to be built in survey, to comply with the NSCV code 2B, non- passenger vessel (less than 12 people over night). This is a high standard, full commercial rules and regs, up to 200nm offshore, etc, quite different to the original plan! Fortunately we had not finalised the cut files and no panels had been made and Julian had not started building the boat but we were now having to deal with making the design comply structurally and the fit-out to meet this commercial standard and get on with it as the builder was standing there with tools and labour poised to make a start.
The Noosa Marine preferred building material and methodology is the ATL Composites ‘Duflex’ system, pre-made, CNC router cut composite panels, ourselves and Julian have had a long association with ATL. Nick Cossich, ATL’s chief engineer worked closely with us and re-calculated the panel laminates to comply with the DNV-GL class rules and handled the plan approval process with DNV. The DNV-GL rule is recognised to be a better fit for foam cored structures than the other rules used such as the LSSC (Lloyds Special Service Craft for high speed vessels), the main requirement is a minimum skin thickness to the outer surface laminate and some areas of higher density cores. Keeping this to a minimum for compliance still added something like 800kgs of additional weight to the boat. Other structural factors included a bow collision zone, buoyancy foam under the cabin sole fwd of the built in fuel tanks, water tight doors mid-ships, minimum bulwark and rail heights, stability requirements, safety equipment, etc.
All up we ended up with a loaded displacement of 16,747kgs compared to the original 14m design which was 14,701kgs, over two tonne heavier. Remember that this is a planing hull form and as such needs to get on the plane to function properly. The 14m had the 480hp Yanmars and ended up with a top speed of 33kts, to make matters more concerning with the new boat, that model Yanmar was no longer available and we had to work with the 440hp rated model, so 80hp down! The boat is getting heavier and the available power less, not an ideal direction to be heading and caused a reasonable amount of concern. Thankfully it is a reasonably forgiving hull shape and in a fully loaded conditions went through her sea trials in very good shape.
Performance comparisons with the original 14m are interesting.
Original 14m – At 2500 rpm, 22kts, 50% engine loading, 40 L/H, 3.64L/NM. New 14m – At 2500rpm, 19kts, 58% engine loading, 46 L/H, 4.84 L/NM.
A good comparison example, and a good reason to build the boat as light as possible. The original 14m is, I think, and exceptional boat from a performance point of view, a very good result. The new 14m is still a very good performing boat considering the commercial classification it complies with. It still has nearly 800nm range at that speed starting off in a fully loaded condition (3100L of fuel, 600L of water). I doubt if there is a comparable 14m/15m planing hull mono built to the same level of survey that would get close.
The boat also looks stunning, such a high standard of finish and fit out detailing, the clients have ended up with a full live aboard, long range cruising yacht, fully capable of being autonomous for three or four weeks with four to six people on board, no need to be looking for the next fuel dock every two or 300 miles.
Coastal cruising up the West Coast from Perth the sea state can be challenging so the boat is fitted with a Humphrey ride control interceptor system. This cat has a special custom built unit over each prop tunnel mounted directly to the transom, the standard interceptors come in a range of straight lengths but if mounting over a prop tunnel is required then a custom made curved unit is called for. Interceptor systems are not very commonly used yet on planing and displacement hull cats and monos, most people are familiar with the trim tab systems which are useful in most conditions for changing the running trim and helping in a side sea state but the active ride control system of the interceptor is far superior for improving the boat’s motion in a seaway and controlling the fore and aft trim.
Another detail that is a little bit different to your average planing hull power cat is the full depth fin keel forward of the running gear. Part of the intended cruising area is in and around the Abrolhos Islands which has large areas of shoal draft coral and sand and the clients wanted some prop and rudder protection when they were in this area and other coral reef cruising grounds. This fin keel looks a bit like something off a sailing yacht, it has the same low drag aerofoil shape and needs to be deep enough to be effective in a grounding situation. The added wetted surface area and appendage drag did nothing to improve our performance but is one of the compromises that has to be accepted and the design optimised for minimal impact.
The survey work for the build was handled by Terry Davis of TD Marine Surveyors Pty Ltd. Terry was a delight to work with, very sympathetic towards what we were trying to achieve and very helpful with information and rule requirements. This was the first full commercial survey vessel built by Noosa Marine which can be a bit challenging compared to the more usual light weight, high performance sailing cats, and other non-rule compliant power boats previously built. Julian and his team were up for it and the final result bares testimony to their high standard of workmanship, strict adherence to weight control, and build quality.
Other notable contributors to the project include Brad Stack of ‘Edge Marine & Auto Electrical’ who was responsible for the electrical design, procurement and installation. Andy from Coastal Marine Trimmers for the upholstery and linings, Richard from Australian Marine Windows, the exhaust system was designed and supplied by Braden of Foreshore Marine, and Andy from ‘Creative Stainless’ produced all of the shiny bits.
Full credit also to our clients who had the courage of their convictions, not happy to put up with the status quo and settle for an off the peg polyester production boat. They now have an outstanding power cat that will provide many adventures cruising the coast and further afield with their friends and family, keeping them safe in the most adverse conditions and opening up a commercial charter opportunities that will augment their existing marine business and lifestyle.
