• … can I get a 5.3-tonne unstepped diesel pleasure boat with full weekend accommodation to run 80mph plus while still giving amazing fuel economy?
• Starting with a clean sheet of paper enabled me to reduce the engine centres from 950mm to 800mm, allowing a higher X dimension and lower centre of gravity.
• Many weekends were spent with an angle grinder and various other power tools, cutting out all the damaged areas.
• At the end of 2013, the engines had completed around 1000 hours of very spirited use. It was time for a rebuild.

Unwin’s Odyssey

Peter Unwin is an unusual powerboat enthusiast. His heritage may hail back to the swinging 60s but his passion for performance propels his continuing exploits firmly into the future. This is the first part of Peter’s story …

In 1958, my late father Ken Unwin took the whole family to a boat show in Birmingham, where he purchased a raffle ticket and was fortunate enough to win the first prize of a small boat with an outboard motor. After the show he was able to do a deal with the manufacturers whereby he added some money and purchased one of their larger runabouts. He then bought an old Ariel Square Four as a donor for its engine and built a very primitive form of outdrive to transfer the power to the water. It took about a year of working in his spare time to get the boat ready for its first trials, and although there were lots of teething troubles, he didn’t let them put him off.

All early testing was done with the landowners’ permission on old gravel pits or deserted parts of the River Trent. During this time he met a few other people with a similar interest in boats and they decided to form the Burton Speed Boat Club at Drakelow Deeps near Burton-Upon-Trent. It wasn’t long before they had a considerable number of members and a variety of boats, and racing took place on an almost weekly basis during the summer.

In 1960, he bought a Healey Sprite and fitted it with a 45hp Mercury outboard; however, he soon part-exchanged it for a 65hp to make the boat faster. Never one to stand still, the next modification was a completely home-made power trim system that enabled trimming out on the straights and in for the sharp U-turns, giving a much faster lap time. During this period my dad made his fellow members trailers for their boats, which were custom-built and tailored to each different craft.

Dad was now commodore of the club and things were going really well until British Waterways decided to dredge the river. Unfortunately they removed a weir downstream, which dropped the level to such an extent that racing had to be halted. Dad and a few of his friends joined Chasewater Speedboat Club so that they could continue with their passion. The Healey, however, proved to be unsuitable for the wide-open fairly rough waters of Chasewater.

Family holidays were taken at Exmouth in Devon, where we met Chris Tremlett from Topsham and soon became friends. Dad ordered one of the first 14ft deep Vs that Chris built and outfitted it himself, including manufacturing the deck. He raced it for several seasons in the ET class, and by now I was old enough to help with the builds.

In 1966, Ford introduced the Escort and Dad ordered a 1300 GT engine for the basis of the next project. This time the hull was supplied in two separate parts, which enabled us to reduce the weight and have a steeper V. A lightweight outdrive was fabricated from scratch and fitted into the boat ready for the Chasewater 50-mile endurance race. Practice went extremely well – the boat was far quicker than the opposition and went on to win first time out.

In 1967, I started my apprenticeship at Rawdon Foundry Ltd as a fitter machinist, and what a fantastic place to learn a trade it was. In the following year the boat took part in the Chasewater 24-hour race, where it finished first in class and won numerous other trophies. Over the next couple of years the boat had extensive modifications, each of which made the boat quicker.

Dad’s last racing season was 1970 as he had such a good offer for the boat he decided to sell it on the spot. The next four years were spent building motor caravans and also pleasure boats for our own use – we still had a huge interest in powerboat racing and visited Bristol Docks and Windermere for the speed trials every year, as well as any offshore powerboat racing we could find.

By 1975, my interest had moved towards custom vans and we started making parts in our spare time to earn a few pounds. It wasn’t long before the Ford Motor Company spotted our efforts and commissioned us to build the 2001 Space Odyssey six-wheel transit. What a break! On the back of this, we decided to form Unwin Engineering Ltd.

The early 80s saw the business focus more on engineering. We also became agents for Mosselman turbo systems, supercharging and turbocharging high-end performance cars. However, the mainstay of the business became the design and manufacture of small hydraulic drill rigs.

The next progression was to change the company name to Unwin Hydraulic Engineering Ltd. Manufacturing continued but we also became a cash-and-carry for anything hydraulic, including a full diagnostic and repair department. My main hobby at the time was track days with supercars; however, always being one to want to go as fast as possible, this turned into track days with race cars. I did all my own preparation and even designed and manufactured suspension components and aerodynamic aids. Then, on a day out to Wales with my new girlfriend Carolyn, we saw lots of people enjoying their powerboats, which started the cogs turning once again. Wouldn’t it be nice to have a boat large enough to live on at weekends?

So we did lots of research, arranged a shortlist, conducted some tests and finally decided on a Hunton XRS 37. We visited the factory every couple of weeks during the construction period and she was eventually launched in March 2007. The engines were Volvo D6 350s with DPR drives. The boat ran at 62mph with a very comfortable dry ride; however, once the running-in period was over, the engineer in me started to think of ways of making her quicker. The first modification was cupping the propellers to allow more trim and bow lift, which raised the speed to 66mph. This was pretty good, but I now needed more power, so I built a set of through-transom free-breathing exhausts, and this, along with an ECU remap, saw the speed rise to around 70mph.

The next few years saw numerous other modifications mainly focused on making the engines and drives reliable at higher HP. At the end of 2013, the engines had completed around 1000 hours of very spirited use. It was time for a rebuild. The first job was to remove the engines, followed by the drives and transom shields. During this process I noticed that water had penetrated some areas of the transom and engine bearers. This was not a good sign, so I took the decision that the transom engine bearers and inner skin had to be cut out. Many weekends were spent with an angle grinder and various other power tools, cutting out all the damaged areas. During this process I came to the conclusion I could save a huge amount of weight by changing the materials and design of the transom and engine bearers. They are now high-density foam with Kevlar and carbon overlay, all bonded together with epoxy resins.

Starting with a clean sheet of paper enabled me to reduce the engine centres from 950mm to 800mm, allowing a higher X dimension and lower centre of gravity. Having priced up the parts to convert the 350s to 435s, the spec plus full rebuild kits and labour came to more than buying a pair of brand-new 435 bobtails, so the old engines were sold off and a new pair of 435 bobtails ordered. I also ordered the extended bell housings from the 400 sterndrive package to move the engines forward by about 5.2 inches. This makes maintenance much easier, and also, along with the reduction in the weight of the back of the boat, moves the longitudinal centre of gravity forward by about 15 inches, making the boat fly much more level and more comfortably in rough water.

The downside is that unstepped V hulls need the smallest contact area possible if you want to run fast, so my thoughts are turning to the aero package on race cars. Could I use a wing flipped upside down on the bow to get back the lift lost by the high X dimension and move the centre of gravity forward? So I designed and built a bow-mounted wing – it has linear actuators on the trailing edge so I can change the angle of attack very easily while moving. The calculated lift at 75mph is 250lb, and it also has a good damping effect, making the boat even more stable. The engines are standard at the moment, and when I repitched the propellers I allowed for more power. Even though the engines aren’t pulling full revs, she still managed a very credible 76mph.

Now, during the winter, I am doing lots more modifications: 1. more engine bay ventilation and a cold-air induction system; 2. completely redesigning the cooling system to allow for an HP increase; 3. remapping the ECUs to increase the RPM range and HP; 4. reworking the steering pumps to give even quicker, more responsive steering.

So the question is: can I get a 5.3-tonne unstepped diesel pleasure boat with full weekend accommodation to run 80mph plus while still giving amazing fuel economy?

Peter Unwin

Join us in the further issues to learn more about Peter’s exploits and the customisation of his Hunton and other craft.