UK-Cherub Class

Get Your Heart Racing


Top Cherub Designers/Sailors talk about their boats.

(Interview by Jim Champ in 2002)

The Cherub Class had some rule changes in 1997 which have had a significant effect on performance. The changes enabled the newer boats to be rather quicker in the lighter winds that have traditionally been the Achilles heel of the Cherub, without compromising the superb performance in sea breeze conditions. That this has been achieved is obvious in the recent drop in the PY number. Traditionally with a Cherub you won in a breeze and were last in F1, but the newer boats are proving competitive in moderate conditions too.

Gathered here are Andy Paterson, of Bloodaxe Boats, 2002 National Champion, in a series that ended up with a light airs bias, Robin Russell, last years winner in a fresh breeze series, together with his boat's designer Simon Roberts, and Gavin Sims, runner up this year in his new boat, exhibited at Sailboat in 2002, which was particularly strong in the mid wind range. They're talking about their own and each other's boats. Doing the interviewing is Class president Jim Champ.

JC Gavin, tell us about your boat

GS - The design is my own called “ButtPlug.” I built spars, foils, hull and cut the sails. Crew weight is towards the heavy end of the Cherub spectrum, 150kg (70kg crew, 80kg helm) Hull wise it has flat U-sections forward, going to very flat at the back. The chines are minimum length (2m), so the floor merges into the topsides almost back to the mast. The maximum chine beam is about 800mm from the transom I think but they hardly tuck in that much after that. There's very little rocker it's made to be flat for high planing speeds and very little rise of floor, again for top speed in flat water. It's not down to the minimum waterline beam though, when I drew it I didn't like the way a narrower boat would float with our crew weight. The U-sections forward are for light(non-trapezing) conditions as they should give slightly less wetted surface than carrying chines forward. The rudder gantry, well something different was nice!

Graphic One - Line Drawing of ButtPlus (Sims) Design.

Above the deck the carbon mast is evenly prebent throughout its length, with the bottom locked through the use of D2's (Check stays to the root of the lower spreaders). The mast is stepped at gooseneck height and the gooseneck mounted on an extended kingpost so the kicker has very little effect on mast bend. The rig is very rigid. The jib is cut quite flat, with a wider sheeting angle than most, and is self tacking with the sail leech roach giving minimal overlap.. The main is quite full for its chord but because it has a higher aspect than most it looks slightly flatter the luff is about 5.8m. The main is cut with a very straight exit at the leech. The rig has considerable rake, this coupled with the prebend makes the mast seem hooked to windward when viewed from apparent wind angle (as discussed in Bethwaite). It seems exceedingly quick and powered up on a 2-sailer, with no real gap between wiring with 2 sails quite deep and being able to hold the kite. The kite is masthead, and so with that tall mast it is very high aspect ratio. Basically I went for luff length (see Bethwaite again), and it seems to work all right, although it looks small. The rig doesn't seem very effective with the apparent wind aft of the beam, due to the rake and the fact that, because of the prebend, the upper part of the main tends to stay centrelined when the wind gets down towards the 5 knot region.

JC When you designed/setup your boat what were the major considerations?

GS Well it needed to be faster than my last boat (Dangerous Strawberry)! Simon (my crew) said to me whilst I was designing “make it as extreme as you want, we can always find a way to sail it.” But I chickened out from my first try and made it tamer. The rig is slightly further aft than the norm (I think), again this coupled with the rake and prebend is what I think makes it a demon on a 2 sailer. Also putting the mast back allowed me to keep the bow entry angle down whilst achieving a reasonable beam where the cockpit starts/chine starts. This also allowed for a slightly longer kite pole (as it's on the centreline it can only go as far back as mast) and a longer kite luff, which should make downwind quicker. Structurally it's fairly standard (same as the Slug I think) but thinner foam was used (cheaper). I decided to build an extended kingpost with integral lower shrouds primarily to lower the all up weight. This could be included in the hull weight and so a lighter mast would be required. It also stiffened up the hull considerably it's effectively twice as deep in that area as a conventional boat. With the rig I wanted to keep with what I had started with Dangerous Strawberry (Dangerous Strawberry has a very radical tall rig with around a 6.1m luff). But Strawberry had a drawback in the medium wind strengths, the short chord on the main (and very flat cut) meant that it was impossible to get the leech to stand firm, so upwind pointing and speed was lost. Therefore I shortened the mast by about 30cm to give more chord (foot is also slightly higher inboard) and made sure the sails were full enough. Looking down the mast of a prebent rig compared to a straight one, the main looks more right without having to pile on the sheet and kicker (only if the sail's luff is cut for that curve). I used monofilm to make the sails because it is cheap. It seems to have lasted a season fine. The jib is probably too flat as it stalls out in the very light stuff (i.e. end of nationals).

JC Robin, what about your boat? The Slug's a bit older I guess, 1998 wasn't it?

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Photo 2 Green Slug (Robin Russel & Will Lee) Photo © Jim Champ

RR I suppose but it's on no way obsolescent, just a slightly different approach, but I'd better let Simon talk about the hull shape. The boat is home built by me, with a Proctor/Batt sails rig, and we're right at the top of the weight range with around 160kg between us. On the rig I've gone for a fair amount of rake, max. width shroud base with long spreaders, and moderate rig tension compared to some. The mainsail profile is a moderate (by Cherub standards) elliptical profile, with plenty of roach but not as fat at the top as some of the more extreme rigs. The luff is around 5.4m going to 5.49m with the cunningham right down. The chord is greater at the foot than the narrower sails favoured by Andy and Gavin. The rig is basically a logical development of the rigs on my previous boats, with some observations from others. Apart from the long spreaders the “solid lowers” are one of the more distinctive features. This locks the mast up at gooseneck level in the same way as Gavin's post does, but with more scope for changes of course.

The hull – well, low but some rocker, minimum width @ about 7-8ft, fair amount of curvature across deadrise, fairly parallel running aft compared to other boats.

Graphic 2 - Slug (Roberts mk3) Design

JC - Simon, what are your thoughts on the shape? It was a development of my previous design, the Dog. The main aim was to keep the same basic form but remove some of the volume around the 3 to 4 ft station. This was an attempt to improve its upwind performance in chop, where the Dog tended to slam too much. The changes in chine beam measurement allowed the max. beam to move aft and allow the volume to be removed from the front sections.

JC and you Andy. This is the fourth year for your Mk 7, and it's probably the most numerous of the 97 rules shapes there's even one being built in the States.

AP Two being built in the US in fact, with plans having gone to Croatia and Holland too! Yes, there are more of these than any of my other Cherub designs, although there are a lot more Axeman Moths. The hull and foils are Bloodaxe carbon of course, the mast is Superspars and the sails are from Caws. We had 135kg on board in the Nationals 75+60 respectively, which is middle to light end of the range for Cherubs.

The hull is boxy, with low chines carried through to the bottom of the stem and low rise of floor. It's got more vertical topsides than the other boats, high freeboard and a moderate even rocker line. The entry is fine with a constant entry angle from the base to the top of the stem, it's not flared at all above the waterline. The transom is narrow with the chines curving inwards in plan view. It's also much simpler in construction. By doing away with sidedecks, only having transverse frames and the crew working on the inner skin of the hull above the false floor there's am awful lot less structure, although what there is has to be beefed up with thicker foam and all carbon skins to keep the stiffness in the boat. Graphic 3 Paterson mk7 Design

JC and the rig?

AP It's very much a development of the rig on my previous boat, but lighter with the carbon mast. There are no check stays, I've found them unnecessary as the mid spreaders are set up with forward deflection to keep the lower mast straight. The upper spreaders on the other hand are raked back about 45 degrees to induce plenty of topmast pre-bend. The caps come through the upper spreaders, the mid spreaders about halfway along and then down to the gooseneck to keep the mast stiff sideways. The mainsail luff is longer than average at about 5.5m, and the mainsail is virtually flat topped with plenty of roach. The masthead kite is fairly narrow. This rig (combined with hull shape) gives the advantage of sailing deeper downwind than the rest of the fleet, but at the same boat speed. The disadvantage of the high rig/ flat hull shape and low crew weight combination is that it is very difficult to tight 3-sail-reach in any breeze with the kite up. 2676-xxxxxxxx.jpg Shiny Beast 2676-20000905d.jpg Shiny Beast (Andy Paterson & Ross Clark) Photo © Castle Photography.

The Cherub Class does not own rights for this far superior photo of Shiny Beast beyond the Class Website

JC What were your thoughts when you designed the boat? It's certainly been the most successful of your Cherubs.

AP Light weather performance was top of the pile traditionally a Cherub weakness. I was looking to increase power in the rig in light/moderate conditions, but still be able to flatten off the rig and depower without flapping the main when it's windy. The long luff masthead kite is intended to increase downwind power and allow lower angles to be sailed at top speed. The hull is developed from Mk 6, but the '97 rule change gave freedom to reduce the chine beam, and to move the position of max. chine beam aft to make the entry finer. The shape is designed to plane early, with large flat areas under the mast. The moderate rocker and curvy chines aid control at high speed and avoid nosediving. Its narrow forward so that hull doesn't slow in a nosedive. The narrow entry and high freeboard at the bow allow the boat to be driven hard upwind and downwind in waves. The hull was designed to be sailed in the (home club) Solent waves, where steep wind over tide waves can catch out the fuller bow designs. The simplistic hull construction enabled me to reduce hull weight and carry max. correctors to reduce inertia and weight in the bow.

JC So much for your own boats, how do you rate them against each other?

GS Well, Andy P is good when its light, but Patrick [also with a Paterson 7 and a similar rig] has the ability to go faster I think. But AquaMarina [another Paterson 7 owned by Phil Alderson] was going fast enough when it was windier. He has a different rig which is more like Robins and is a bit heavier crew as well. In all though I think the Paterson is more suited to the lighter stuff.

I was pleased with my boat. It's definitely fast in the moderate wind range, from semi trapezing up to flat out, but it is very sensitive to heel. Gybing is a dream, especially with the high aspect ratio kite and clean cockpit. It's better than my previous boat, a Bistro, which is not regarded as a tricky Cherub design to sail. The Slug now looks fairly moderate compared to other 97 rules designs, probably because it has a wide foredeck. The relatively high rise of floor makes it quite tolerant of heel and waves and therefore it's probably the easiest to sail when the wind is up, therefore enabling the crew to push harder.

RR - Really they're all much of a muchness I don't think you can put the differences all down to the boats. The Patersons seem to fare well in light stuff, Gavin's seems OK in all conditions and I wouldn't write the Slug off in light airs in the right hands.

JC yes, we haven't really seen a Slug with a light crew have we?

SR The Paterson seems OK. Goes well in light wind but I think that may be strongly aided by the crews. fairly average in winds over 10/12 knots. The Sims seems fine, but I haven't really seen it in many conditions. I think the Slug is good except in light wind where the transom sinks too much to be quick. It seems to plane fairly early and fairly fast and upwind it is significantly better than Dog especially in choppy water. I would guess it's the fastest design around with the possible exception of Mango Jam.

AP My boat is hard to sail. It has to be sailed very flat. It's excellent in light winds and also in moderate conditions (but we had no nice moderate races this year)! With more crew weight, and less falling in, it would be more competitive in strong winds. Gavin's boat was good in all conditions, and of course Robin goes very well in a breeze.

JC so what would you put the performance differences down to?

RR Crew, crew crew!

AP The light crews are at disadvantage in strong winds compared to the heavies, but in light winds the heavies/wide boats are at a BIG disadvantage. e.g. Robin and Dave [Roe] 1st/2nd in windy races, then barely top ten in the light stuff, but we and Patrick were 1st/2nd in light races, but only down to 4th ish places in the windy stuff. The tall rig that I (and Patrick) use with a square top main, large roach, masthead kite, flat sails was significant.. Phil Alderson performed best in moderate winds with a different rig (which in many ways is more like Robin's rig in concept). Hull shape has got a lot to do with it too, and low all up weight. Gavin's boat seems basically similar to Pat7 in concept, while the Slug gains in a breeze from being easier to sail, the lower aspect rig and high crew weight.

SR – On the P7 the heavy U bow combined with very little curvature. Should have very straight water planes and low wetted surface. Probably makes it a hand full in strong winds and unlikely to be quick when it starts to pop out of the water upwind. I'm not really familiar enough with Gavin's boat to comment too much. As for the Slug, well it's not very radical in any way. There is enough curvature to make it fairly manageable in most wind but still flat enough to plane early. The thinner bows make it much easier to drive up wind through slop and so it doesn't slow down in the same way as a Dog/Bistro/Frenzy etc.

GS Andy and Patrick's light weight both contribute to their light airs performance. Their Caws rigs are very flat which I reckon also helps. But the hull is the major factor I think, the maximum chine beam nearer to the centreline, with the even rocker throughout and the narrow transom coupled with a mast relatively far forward in the boat enable the crew to get forward and sail with a clean wake in non planing conditions. My rig I think seems to get powered up sooner than the rest, and the hull seems to plane nicely. It suits flat water (i.e. Bala and the second day of Nationals). Robin and Will's available righting moment allow them to power away from everyone when the breeze is up. They just drive hard and go.

JC so what's most significant? What should someone planning a new boat concentrate on?

GS I would say the hull is a big decision, as that is what makes these three different. The rigs aren't that different, but crew weight is. Andy's boat is optimised for the light stuff at least in Cherub terms , mine is for when as soon as there is enough wind to wire, and the Slug is the all-rounder. It's just that coupled with the crew weight of Robin and Will the Slug needs wind.

AP There's no doubt that in light winds the Paterson 7 hull shape is faster… in the light last race, Pat7's were 1,2,3 on the water. The crew weight on the Slug gave them significant advantage in strong winds, but also the crew ability! They were the only boat not fall in the windy races.

SR – Certainly the Paterson 7 seem to be a hull shape that suits light breeze, but on the other hand most of the people sailing them are light and seem to be good light winds sailors. I don't think the shape will work well in any wind though. The Sims looks like a good shape, and I think it should go well in the medium stuff as it looks flat, but I've not really studied it much. My guess is it should go in a breeze as it seems like a flatter Slug. Could be slightly harder to sail though. The Slug is fairly easy to sail in a breeze so you can push it quite hard. I think it should go well in medium breeze though given the right crew. At the moment both Robin/Will and Andy/Me go well in strong wind but that is largely down to lard and enjoyment. The Dog was a good medium wind boat and I would expect the Slug to be similar. Gavin's boat may have the edge in medium but I don't think that it will be by much if any.

JC Where do you see us going from here? Where do you think the next big gains will come?

GS - I think rigs. Plenty more playing to be done. Wing masts. Hulls will get faster, but only in incremental steps, unless there is a change to the minimum weight. Foils, hmm not gonna make that much difference unless someone discovers something new. I don't think hydrofoils will find their way in, not the t-foil type things the 14's have. The thing is that Cherubs are heavily optimised for flat out planing speeds. I have wondered what a National Twelve style hull would go like in the sub 10 knot wind range, but all the F4, 5 and 6 jumping is too much to miss out on.

RR Wing masts, tall rigs for light airs. Weight.

AP less weight!!

JC at this point I guess I should note for readers that there's a general acceptance that the minimum weight for the Cherub, which has been much the same at 110lbs/50kg for the last 50 years, is due to drop. The majority of new boats are carrying lead, which is hardly in the spirit of the class. The concern is at what point the technology and skills out there will progress so that a first time builder will normally get within a few pounds of the new minimum.

AP And more rig development e.g. your rig seems the best new 'thing'. [The president's boat has just been upgraded with a New Zealand made C-tech/Fyfe Sails rig with a 5.9m luff. It's straight up to the hounds with plenty of prebend above.] More hull designs along the lines of Pat 7 and Sims (and, sort of, Squid) to refine the performance We need more boats to tell if it's hull, rig or crew.

Its interesting to note that versus “conventional” boats like the RS and Laser products our light wind speed is poor, and our outstanding performance comes in at F2/3, when we are full powered up upwind and downwind, and are planing along, apparent wind sailing, whilst the heavier boats are still not powered or fast. (exception of course is RS 700 which has more sail, more length and less all up weight when you include the crew! My design/rig/crew weight is optimised for these 'average' conditions, but this seems to make it a light wind flyer vs. other cherubs.

SR Rig changes. I think the Slug/Sims hulls are moving towards a good all round shape though there a bound to be some improvements which can be made. Also there will be more extreme shapes which suit certain conditions but a slightly flatter Slug or tweaked Sims seems a logical conclusion to me. Rigs are much more open to exploit. Maybe wing masts but certainly there should be room to improve the current rigs. Still much variation in luff length roach & ellipse/square plan form within the fleet`. My guess is we will move towards rigs similar in plan to Fyfe and maybe sleeve luff/wing mast.

JC - Thanks all. One interesting point is on optimising boats for conditions Andy, you seem to me to have designed his boat as much as anything to be competitive in handicap club racing. You've dropped a bit of performance from the top end (winning races by 10 minutes is over the top if 5 minutes will do). The result is a boat which by Cherub standards is somewhat polarised to light airs, but in terms of a handicap event like Cowes Dinghy Week is strong in medium and heavy winds. In a fleet which notoriously likes to do multi-class events it will be interesting to see what decisions others make. We're in for an interesting few year's development (as usual)!.

Credit

Words: Jim Champ


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