Omra News

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Pic 1, Pic 2, Pic 3, Pic 4, Pic 5,

Pic 1: Gary Pope’s new for 2007, Sikk powered Sigma 51. Picture courtesy of Mike Luxton. Pic 2: Robin Butler’s C class CMB91 RS powered Apache in fine form at Telford. Pic 3: Another line up waiting for the start hooter, this time the D class at Telford. Phil Hatcher’s Phase Two, Phil Dakin’s Avenger Cat and in the background Sean Tubby’s G.P.1 Bat type boat. Picture courtesy of Mike Luxton. Pic 4: The Thompson’s new boats for the season. Alan’s Valvola powered Challenger 43 (AA112) and Geoff’s CMB67 powered Donzi (B113) with Geoff’s 2006 C class championship winning Giant Apache (C113). Pic 5: Geoff Thompson’s brand new Donzi after a crash at Telford. Believe it or not, it was back racing at Stevenage the following weekend!

Telford AA-D Classes April 29th 2007 by Stewart Rae

After several weeks of warm sunny weather, today was overcast with a very cold north easterly wind blowing towards us at the lakeside. Weather forecasts promised warmer weather by the afternoon and I’m glad to say they were spot on. O.O.D. Phil Dakin announced two twenty minute races in each class, the entry in D class was quite large, so this was to be split into two groups. Unusually (and it caught a few competitors out) the mill time was two and a half minutes with a ‘No Launch’ announcement after two minutes. Normal mill time is two minutes.

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AA class boats were the first out of the pits and all competitors got off to a good start, but bad luck befell Danny Bell’s CMB21 RS Challenger after just one lap, with stripped gears putting him out of the race. Alan Thompson’s new CMB21 Valvola Red Head Challenger 43 got a bit too warm for Alan’s liking during the race and he sensibly decided not to run the second race to conserve his engine, no doubt any cooling problems it was suffering would be sorted for the following event at Stevenage. Mark Beesley’s nicely prepared Bat boat was giving him a few problems and did not do as well as it normally does. Gary Wilkinson’s CMB21 Aasvogel was in close contention with Dave Clay’s NovaRossi 21 powered Crusader 3, as were two other Crusaders driven by Bernard Holder and Robin Butler.

Just a few minutes into the first A class race three blasts were sounded on the start hooter (the equivalent of a red flag in F1 racing) bringing the race to an abrupt halt – the rescue boat had lost its steering! New member for 2007 Kurt Cave, quickly came to the rescue with his battery drill and within five minutes racing resumed, producing some good close racing. Alan Thompson did a bit better in the A class race with his CMB45 RS Challenger 48 managing to stay ahead of Danny Bell’s CMB45 Challenger 48 who was just, and only just, in front of Bernard Holder’s Crusader 2, again running a CMB45.

Racing order was changed after the A class race when group one of D class was brought forward, catching out a few drivers who were still fuelling their boats. Extra time was allocated to allow everyone to make the start, but it was still a bit frantic for some. Kurt Cave brought along his well sorted Sikk powered Apache and had an excellent first race. Gary Pope had entered his brand new designed Sikk powered Sigma 51 and when I say brand new it was literally that, having left the mould just eight days previously. With no testing, Dave Marles from Prestwich Model Boat Centre who designed and produced the hull gave Gary some advice on the set up and the boat ran straight out of the box, so to speak, without any problems.

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Mark Beesley did very well with his Zenoah 23 powered Pipedream in this first race for group one, taking first place as did Robin Butler who followed close behind with his submerged drive Magnum. With only four minutes to race end Gary Pope’s Sigma was in collision with another boat putting him out of the first race.

Next out of the pits came B class or should I say ‘B’ crash as Geoff Thompson’s brand new CMB67 Donzi spun out just in front of Jason Barrett’s Apache 50. Jason had absolutely nowhere to go, resulting in a demolition job on the Donzi (see photo) as it was struck broadside, I had a look at the fibreglass lay up and it did seem to be a bit on the thin side. Also in this race Gary Pope’s Donzi was grabbed by a clump of weed sitting just under the surface at the turning point for buoy two. The weed was quickly removed from the prop, rudder and cooling system by pitman Stewart Rae and the Donzi was soon back on the water. Number 13 was unlucky for Nigel Bedford as that was how many laps he managed in the first of the C class races with his CMB90 Stealth when the prop shaft bearing overheated. This left Geoff Thompson, Tony Ellis and Bernard Holder to battle it out for the top three places followed by Jason Barrett and Robin Butler.

Last race before lunch break was the group two D class. Sean Tubby put down some very fast laps with his Quickdraw 26 powered G.P.1 to claim his place as one of the contenders for the trophies. Dave Hole had a big spin in the pit straight with his Apache, causing much damage and putting him out of the competition. After lunch came the second of the races in each class, quite a few of the drivers had put in good lap scores in the morning session and consistency was going to play its part in the proceedings.

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The wind had picked up and was causing quite a few problems as boats approached and rounded buoy three. Racing in both AA and A classes was very close with little attrition, giving the rescue crew a bit of a rest.

It was a nail biting finish in B class for second, third and fourth places which were eventually sorted out on countback, all having scored 117 laps.

In C class both Tony Ellis and Bernard Holder raised their game increasing their race one lap scores considerably to take second and third places overall, with Geoff Thompson putting in consistent laps of 61 and 62 to give him an easy first place.

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Kurt Cave had a bit of bad luck in his last race of the day, when his D class Apache was upended at buoy two after hitting an under surface obstruction. With an engine full of water and refusing the restart he decided to call it a day, but still he can be proud of his lap scores from race one. Gary Pope set the pace with his Sigma 51 with a two race total of 113 laps. As with the AA and A class races, both the second B and C classes saw the rescue boat maintain its mooring for most of the time, leaving the drivers with only the wind and waves to contend with.

In the last race of the day, group two D class Sean Tubby took up the challenge set by Gary Pope’s Sigma. Sean’s G.P.1 put in some very fast laps and at one stage he was covering over four laps per minute, slowing for the rescue and rough water took its toll, with him ending up one lap down on Gary’s total. Two twenty minute races certainly add to the excitement of racing – a pity it’s not done more often. Slowing for the rescue and blustery conditions in the afternoon played their part in all the races and it was the competitors who put in consistent lap scores who found themselves taking home the trophies.

Our thanks to O.O.D Phil Dakin assisted by lapscorers John Wright and Peter Kelly. Richard Wright, Neil Evans and John Nightingale found themselves manning the rescue boat with the barbeque and refreshments in the care of Geoff Dakin. As ever, OMRA were made very welcome at Priorslee Lake, thanks chaps.

Results in laps

AA Class

1 G. Wilkinson 113
2 D. Clay 104
3 B. Holder 89
4 R. Butler 84
5 A. Thompson 42
6 M. Beasley 15
7 D. Bell 1

A Class

1 A. Thompson 111
2 D. Bell 101
3 B. Holder 98
4 N. Bedford 83
5 I. Hayward 80
6 R. Butler 79
7 T. Ellis 77
8 J. Barrett 74
9 S. Wilkinson 73

B class

1 D. Clay 131
2 B. Holder 117
3 A. Rennie 117
4 T. Ellis 117
5 G. Pope 105
6 J. Barrett 104
7 G. Thompson 48

C class

1 G. Thompson 123
2 T. Ellis 104
3 B. Holder 91
4 J. Barrett 62
5 R. Butler 60
6 N. Bedford 13

D class

1 G. Pope 113
2 S. Tubby 112
3 R. Butler 104
4 M. Beesley 96
5 P. Hatcher 78
6 K. Cave 53
7 P. Dakin 48
8 A. Rennie 39
9 D. Hole 9
10 D. Wherlock 1

Highest laps of the day: Dave Clay with 131 in B class, CMB67 Apache. B class second, third and fourth places were awarded on countback.

Stevenage AA-D Classes May 6th 2007 by Stewart Rae

Like Telford the previous week, the weather at Stevenage was dull, overcast and cold, however it did brighten up a bit later on. This year saw the return to the larger of the lakes after its leak had been repaired. A row of marker buoys strung together had been floated across the lake to mark the sailing limits, not only for the OMRA racers but also the full size dinghy sailors using the other section of the lake.

O.O.D. Syd McGoun announced 30 minute race times and went on to explain that people spend a lot of time and money on their boats and he would like to see everyone take them home in one piece. A polite but firm and fair way of warning drivers that he did not expect to see aggressive driving.

With large entries for the A and D classes, these were split into two heats with one B class driver mixing it with the C class entry due to a clash of frequencies. Mark Copley having missed the previous week’s racing at Telford was back in fine form in AA class taking his Rossi 21 Evo powered Challenger 43 to first place nine laps ahead of Dave Clay running his NovaRossi 21 Crusader 3, which crossed the finish line just one lap ahead of Gary Wilkinson’s Aasvogel. Bernard Holder failed to make the start with his Force 21 Crusader 3 after stripping the gear during testing.

Consolation for Bernard though, as he took first place in A class when his CMB 45 Crusader 2 crossed the finish three laps ahead of a second placed Alan Thompson driving his overheating CMB 45 powered Challenger. Jason Barrett followed Alan over the line, six laps behind with his CMB 45 Challenger to take third place. Young lady driver Shannen Wilkinson landed in fourth place with her Protech 27 Avalanche, one lap in front of her dad Gary. With a clash of frequencies, Andy Uttley ran his B class CMB 45 Challenger in amongst the C class entries and managed to clock up a B class winning score of 83 laps. Bernard Holder was out on his own in second place while third, fourth, fifth and sixth places were all separated on countback.

Richard Haydock’s very strong run in C class saw him going home with first place and 15 points in the bag, six laps ahead of Bernard Holder’s second placed Magnum. Most unusual for Mark Copley’s CMB 90 Evo powered Giant Apache was a couple of trips back to the pits in the rescue boat but he still managed to clock up enough laps to take third place from last year’s C class champion Geoff Thompson, whose Giant Apache’s CMB 91 RS engine was well down on power. After just 37 laps Nigel Bedford retired his Stealth. With steering problems it was becoming a bit of a mobile chicane for the other drivers, a good decision from this gentleman driver.

Next out of the pits roared the first heat in D class. Steve Whenham took the heat win (second overall) with his new Trident hull powered by one of the new 35cc S.G. Racing engines imported from Italy. I had a feeling that the uninterrupted second place in this heat would give John Smith his first trophy win for his own design Zenoah 26 powered Stealth. Last race of the day, D class heat two, saw relatively new drivers to D class racing Kurt Cave and Sean Tubby racing for the same space at buoy two resulting in the inevitable clash. Kurt had some rudder damage and a bent propeller on his Sikk powered Apache. This was soon repaired and he was back in the race. Sean retired his G.P.1 Bat boat unable to carry on with severe damage to the hull and drive shaft. Gary Pope drove a tight uninterrupted race with his Sikk powered Sigma 51 finishing two laps ahead of Steve Whenham’s first heat score to take first place.

Members of the Stevenage club were kept busy all day rescuing drivers’ boats which had strayed just a bit to close to the marker buoys and their tethers. Wave and wind action also caused quite a few boats to turn turtle, mainly around buoys three and four, the pit straight between buoys four and one also became unusually rough on occasions, catching a few drivers unaware.

Thanks to O.O.D. Syd McGoun, ably assisted by OMRA secretary Alan Baldry whose wife Lesley shared lapscoring duties with Syd’s wife Pauline. New driver Simon Beament was awarded the Concours d’Elegance trophy for his Zenoah 26 Makara and highest laps of the day went to Richard Haydock, C class with 89 laps. If you would like to see some fantastic and quality action photos not only of racing boats but other subjects as well, can I suggest you pay a visit to Mike Luxton’s website www.MikeLuxtonPhotography.com.

Another place to visit for boat bits is Prestwich Models Ltd, run by Dave Marles who can be contacted on 07842 634090 or www.prestwich.ndirect.co.uk, or you can email: [email protected].

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Pic 6, Pic 7, Pic 8, Pic 9, Pic 10,

Pic 6: Kurt Cave comes over from car racing, in at the deep end so to speak with his very fast and well sorted Sikk powered Apache. It did very well in the first race, but then hit something in the water at buoy one, putting him out of the second race at Telford. Pic 7: Some of the winners at Telford went home with prizes consisting of clamps, screwdrivers and digital multimeters instead of the usual trophies. Pic 8: C class boats line up ready for the start hooter at Stevenage. Pic 9: Simon Beament with his Zenoah 26 powered Makara took Concours d’Elegance trophy at Stevenage. Pic 10: I spotted this unfinished in-line twin Zenoah powered Apache in the Gilder camp at Stevenage. Must keep an eye on this one – it looks interesting.

Results in laps

AA Class

1 M. Copley 82
2 D. Clay 73
3 M G. Wilkinson 72
4 A. Thompson 59
5 A. Payne 46
6 D. Bell 45
7 A. Rennie 44
8 I. Searle 30
9 R. Butler 29
10 G. Sadler 14

A Class

1 B. Holder 76
2 A. Thompson 73
3 J. Barrett 67
4 S. Wilkinson 56
5 G. Wilkinson 55
6 A. Preou 53
7 L. Copley 47
8 D. Bell 41
9 N. Bedford 38
10 R. Butler 34

B Class

1 A. Uttley 83
2 B. Holder 77
3 G. Thompson 69.1
4 A. Payne 69.4
5 D. Clay 59.2
6 G. Pope 59.5
7 J. Barrett 28
8 A. Rennie 23
9 I. Kotarski 4
10 A. Preou 2

C Class

1 R. Haydock 89
2 B. Holder 83
3 M. Copley 75
4 G. Thompson 53
5 N. Bedford 37
6= J. Barrett 7
6= I. Searle 7

D Class

1 G. Pope 88
2 S. Whenham 86
3 J. Smith 79
4 G. Darch 78
5 T. Gilder 66
6 R. Butler 64
7 S. Tubby 63
8 Kurt Cave 47
9 P. Hatcher 45
10 D. Wherlock 36

The ABC of powerboat bits – ‘S’ continued

The propeller shaft is either a solid steel bar or a length of flexible cable attached to a shorter steel bar. The torque of the engine is transmitted down the shaft and it is important that the shaft should be strong enough to withstand the propeller striking objects in the water. Fitting a reduction gearbox to the engine has the effect of increasing the torque and reducing the revs, just like using an electric drill. As a guide, a 4mm shaft is fine for a 0.12 engine without a gearbox. For geared 0.12 up to 0.45 cu.in. without gears, 3/16in flexi or 5mm solid shaft should be ok. Above this engine size, I would recommend 1/4in shafts. Ideally the shaft should not be threaded, so that the coupling at the front and the propeller at the back are more likely to be true. However, many of the propellers used for submerged drive are threaded. Flexible shafts are made of several layers of spring steel coiled in opposite directions. They are normally brazed to a solid shaft at the propeller end, which runs in two bearings. The flexible part of the shaft runs in a brass tube, which can be bent to suit the boat and may have a Teflon liner. Flexi shafts need to be dried and sprayed with WD 40 after use and kept oily to prevent rusting. Although needle roller bearings, running on hardened shafts, and thrust races are available, I do not recommend their use for offshore racing as they rust too easily. Solid shafts usually have a ballrace bearing at the front and a lead Teflon bearing at the back end. The straight outer tube can be stainless steel to withstand knocks better than brass. A grease nipple on the tube is used to expel any water from around a solid shaft and the bearings. In both types, the thread or hole in the propeller will determine the size of shaft at that point. A 1/4in shaft often has a 3/16in insert in the end to take the smaller propellers. Be aware that 3/16in bore propellers will not quite fit on a 5mm shaft, but M5 threaded props will fit on an appropriately threaded 3/16in shaft.

A silencer operates by attempting to smooth out the short high-pressure wave travelling down an exhaust system into a constant stream of lower-pressure exhaust. This is often achieved by disrupting the flow of the gasses using baffles to allow some gas to pass and some to be delayed. A tuned pipe alone can have some silencing effect as part of the pulse is reflected back toward the engine, but it is unlikely to provide effective silencing on its own. Most tuned pipes therefore have a silencing ‘can’ on the end containing several baffles, each one helping to even out the flow. Given sufficient space for the exhaust to wait in, delaying some of the exhaust pulse in this way is unlikely to have any noticeable effect on engine performance. Water can be added, but only after the tuned pipe section, to further help disrupt the wave and to cool the exhaust gasses, thereby reducing their volume. It is by using an appropriate combination of expansion box and silencer that has reduced road car exhaust noise to barely audible. The use of underwater exhaust outlets to bury the exhaust noise has not been very successful. Unlike most full sized craft, model boats often completely leave the water, generating random changes in exhaust pressure that can severely upset the engine settings.

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Pic 11, Pic 12, Pic 13, Pic 14, Pic 15, Pic 16, Pic 17,

Pic 11: Andy Payne makes a welcome return to offshore racing at Stevenage. Pic 12: John ‘Kiwi’ Smith fresh back from his holiday in New Zealand prepares his own design Stealth, for the D class Stevenage race, assisted by Dennis Wherlock. John went on to take a well deserved third place. Pic 13: Steve Whenham with his new Trident boat at Stevenage. Steve is running a very quick S.G. Racing 35cc motor imported from Italy. Pic 14: Tony Gilder has a choice of two D class boats set up for different weather conditions. The white one is a tuned Zenoah 26 powered Spirit of Oslo. The yellow one is a Sonic, powered by a 35cc S.G. Racing motor from Italy. Pic 15: Trophy winners at Stevenage, not all Pictured as some had left early for a long drive home. Pic 16: The baffled silencing can forms the end part of this Irvine tuned pipe. Pic 17: Not quite all the colours in all the sizes. Heat resistant silicone tubing comes in all sizes.

Silicone tubing is used for the water-cooling pipes and also for exhaust and fuel pipes on glow engines. Ideally silicone should not be used with petrol. Silicone rubber has a good resistance to heat but will still char and split if subjected to direct contact with the hottest exhaust gasses near the engine. The manifold to tuned pipe joint should therefore overlap to shield the rubber which is only used to seal over the join. Silicone tube can split fairly easily so the ends need to be cut smoothly and it should not be stretched too far over nipples etc. To prevent pipes coming off, use another short piece of tube over the outside. This can be stretched over the inner pipe using the outside of a pair of long nose pliers. Silicone rubber also comes in liquid form and is good for sealing the exhaust manifold to engine joint and around through-hull exhaust outlets. Some waterjackets leak unless a thin film of silicone is applied during assembly, but allow plenty of time for it to dry before testing.

Each form of powerboat racing has its own engine classes. The size of boat is not really limited, but the size most suited to the engine depends on its potential use. It will have to be large enough to float, but beyond that the water conditions will determine its optimum size. The ratio of length to beam of a model powerboat is usually between three and four. Full-sized offshore boats are long and thin for straight-line speed and have very poor turning characteristics as the turns form such a small part of their race. Model offshore boats have to turn much more frequently, so tend to be wider and also have to be quite tall to prevent submarining in the comparatively large waves. There is an OMRA rule that chine to deck distance must be at least 50mm at some point for the AA-D classes. Multi racing boats rarely have to deal with such extreme waves and are very flat to keep the centre of gravity low, giving excellent stability and spectacular turning ability. Circuit racing boats are somewhere between the two. The Aeromarine Challenger 43 is used successfully in the 3.5cc class for offshore racing, but the manufacturer intended it for 7.5 to 15cc circuit racing. The largest D class (petrol) offshore boats can be nearly two metres in length and weigh over 20kgs. Boats this large are spectacular and keep going in all conditions, but you must also consider the size of your car and the state of your back! As a guide, most C and D class (50cc) boats are nearer 1.5 metres long. B class (11cc) around 1.3 metres, A class (7.5cc) 1.2 metres, AA class (3.5cc) 1.1 metres and Z class (2.11cc) under one metre in length.

Strictly speaking a skeg is a small fixed fin by the rudder on yachts or the fin that provides directional stability to surfboards. In powerboats such a separate fin is usually known as a turn fin. The propeller end of a submerged drive propeller shaft is however supported by a flat strut, which also performs the stabilising function of a skeg. Some strut units for surface drive also have a skeg below the shaft to help prevent spins and protect the propeller. Much more on struts and turn fins later when considering the trim of the boat. More on ‘S’ next month.

Come racing and you could be a national champion!

To take part in OMRA races you have to be a member. All the information and membership forms come from the website www.omra-uk.org or just contact one of the committee: Chairman, Kevin Jones, 5 Kenrick Square, Bletchingley, Surrey RH1 4PU; 01883 743477; [email protected]: Secretary, Alan Baldry, 7 Hyde Way, Wickford, Essex SS12 9BH; 01268 462640; [email protected]: Treasurer, Martin Golder, 12 Norfolk Way, Canvey Island, Essex SS8 9TJ; 01268 449246; [email protected].


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