UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: roland_trim on July 25, 2008, 09:54:52 AM
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All those who I've bored in boat parks will not be suprised that we are not planning on adding a self tacker. But after last weekend's antics we need to address a couple of things:
1) The jib furls around the forstay during big stacks.
2) The jib furls around the forestay when three-sailing if I forget to cleat it.
3) Finding the jib sheet when twinning is an ar$e.
4) When it is ballistic excess sheet spins around the taught sheet and stops the jib being pulled in.
To this end I'm planning on trying the attached sketch - appologies as once again it is a bit poor. To explain we intend to:
a) Put a stopper knot in each sheet, set so the clew cannoth go around the forestay (1 inch inboard). This allows the jib to set downhill, although not perfectly.
b) Set length of sheet so when both sheets are on the stopper knots the jib sheet is tight between the cleats.
c) Tie the dead end of the main to the join between the jib sheets.
Any thoughts appreciated.
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We used to tie the jib sheets to the crew trapeze elastic when sailing the laser 2 and the 4000. This means that they are always easily accesable. With the twisting issue, could tapered jib sheets help?
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I tie the stopper knot at about the furthest out I want the sail to set at, the clew is still quite a way from the forestay(I think), this also helps a bit with the twisting thing.
for the length you still need to be able to play the jib sheet on the wire at the back of the boat which might work with the mainsheet tail, just not sure.
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Even with our self tacker we have had 1/3 of the jib twisted around the luff. The battens make it harder to untangle. The main and jib sheet on Slippery are one continuous rope. We get additional purchase on the jib via a 2:1 between the clew and the self tacker car. This means we can let a lot of jib out following a capsize.
You may want to stop the jib going out so far. I agree once the clew has got forward of the luff it can be difficult to recover unless you are on a dead run. in last weeks reported conditions I doubt that would be a favoured point of sail.
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the jib on atum was twisting last weekend even though its self tacking.....only problem with stopper knots is, it will stop the lower half of the sail twisting, but the head prob will still twist a bit. will still take a bit of pulling to get it un twisted. we have tried a system on our jib wire to help it un twist, but thats more before going sailing - stop twists being in the wire in the first place.
Kevan suggests a jib boom ;D his other suggestion is a thin carbon batten down the leech.... (or think windsurfer sail with a thin batten down the leech and round the clew)
hows that for some crazy suggestions :D
edit: forgot to ask, does your jib have any battens in it??
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Ours twisted on the forestay too even with the knot such that the clew was quite a way behind the forestay. Our solution to this is to notice that it has happened before bringing the boat upright and sheeting the jib in hard in the water. Remember to release it as the boat comes up though or it's a cheap day supersaver to Swimsville Tennessee.
I wouldn't recommend knotting the sheets such that the clew can't go in front of the forestay. There are times when you'll want to dump it off miles. A neat way to sort out the twisting issue is for the helm when on the board to use a jib sheet to balance with, and then drop it (assuming it is uncleated) when the boat comes up.
The windward jib sheet tangling issue can be sorted out if you see it start to happen soon enough by pulling the windward sheet. Otherwise its a job to be done in the water!
Finding the jib sheet when twinning: Try dropping the end over the windward gunwhale in front of your front foot before you go out. That way it may well be there when you want it a bit later. Alternatively, when Hayley and you swap sheets after the tack, keep hold of the jib sheet.
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Thanks for all the suggestions. As there was no wind at our end of the country I have verry little to add at them moment. The plan for next weekend is to try the system above, but without the stopper knots. This gives the jib a bit more fly awayability (Dr. Lee) and still reduces the ammount of rope in the boat.
For now Born Slippy is in a garage having her nails extended - we tried this one two weeks ago but snagged one on a groin so are going for some stronger ones.
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up to the Draycote practice week our righting from a capsize technique was for the helm standing on the centreboard to lean back on the jib sheet as per standard RYA technique. We discovered in strong winds it is impossible to fully right the boat. We now uncleat the jib before recovery and I lean back on the tail of the trapeeze line. The jib only seems to twist if it is out when you go in or if you are over for a long time. At BALA when I broke Sarah we had to untwist the jib in the water. Simply pulling on the sheet did not work.
A jib boom would make the sail more efficient off wind as it controls twist and is used a lot on Radio model yachts. You would have to have it semi ballanced so that the rig loads are shared between the luff and leach in a 6:1 ish ratio. The boom is then under severe bending loads and will probably catch the kite more often during hoists and drops.
The other downside is the jib boom makes it harder for the crew to stay on the foredeck during tacks. The second plus point is that the jib sheet loads are lower because the leach tension is being controlled by the rig tension and you don't need a self tacker track.
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I have long thought this may work but never had the bottle to try it!
N12 designers have moaned to me in the past that their rules forbid it.
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I have long thought this may work but never had the bottle to try it!
I understand that the boomed jib has been done on Canoes quite a few times with no huge improvement and is not on any current boats to my knowledge. One possible disadvantage is that the slot is narrower because the jib luff winds up to windward of the centreline. Also you can't get the jib foot to close the slot on the foredeck, which is supposed to have a big efficiency gain. n the other hand I've sailed with one on 30ft Norfolk Broads cruisers, and it is really convenient ...
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I think the achilies heel would be the kite tangling round the fwd end of the boom on hoists and drops. My prefference would be to have a very deep boom 150-200mm tapered towards the aft end. This could be fitted with a flat plate on the upper surface to give an end plate to the jib and miantain efficiency.
The luff of the jib could be set in front of the snout if the ballancing point was at the end of the snout. This would potentially allow a larger jib but with reduced aspect area. To work well the pivot would have to work under high load and may be prone to failure.
As I see it the advantages would be:
Better control of jib twist when close to beam reaching,
Reduced complexity of jib sheeting system and lighter sheet loads.
Since we don't do much 2 sail reaching the main advantage would be the second point. If the jib boom is not included in the hull weight you would have lost out on overal weight.
remember that radio yachts don't have spinnakers and need the simple sheeting system to keep the no. of servos down.
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Is it possible for a self tacking jib to be trackless? Like this chap has done with the traveler thing? I'm still toying with the idea of a new boat but the cost of sails and fit out seems prohibitive.
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Many people have tried this and failed. Basically, even with a v tight rope, the functioning track could only ever be straight. If there is the slightest stretch or slack (and don't forget that at high forces even the boat distorts) then the effective track shape is a curve the wrong way, so the leech and foot are too loose and the sheeting angle is too tight in because it will not go to the end.
Many many people have trod this path before and it did not work for any of them. Scumbag had one for a period, and one of the Dogs too. Take my advice and don't go there!
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Nice to know there is a reason. It's a shame there is no budget (not bodged) alternative to a hugely expensive track/car. Maybe buy the track only and get on the lathe/mill!
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They seems expensive, but its not so many blocks etc to end up with the same cost.
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I don't know - 200 quid will buy you a few blocks! or 30kg of resin!
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One of the reasons Stanley is sailable in mental breeze is because it hasn't got a self tacker. Less to go wrong and means you can just let it go and just sit there and wonder why everyone else is capsizing. A self tacker will always be powered up which is fine if you're completely amazing but for most people it's a pain in the arse if it's 'SMODs are scared' weather.
Why reinvent the wheel if the wheel works fine?
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If you go for a regular profile track you can buy a self tacking system for a lot ( half ) the cost of a low profile one. The difference is a couple of centimeters extra between the track car and the jib tack.
If you go RWO which is even cheaper than Ronstan it comes in at about £25 for a track and £30 for a car.
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http://www.49eronline.co.uk/acatalog/ronstan-blocks-parts.html
£164 is a lot, so go without.
It was £110 all in for Atums, and I though less for Antidotes.
It's funny, lots of people think a self tacker is the answer to their worries. Actually they are expensive, fragile, difficult to make work, and probably not worth it as a retrofit.
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This isn't for Stanley! More as part of a feasibility study for a new build, and jib hardware seems to be a fair bulk of the cost!
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Hulls are the cheapest part of the build as far as I can tell. Glass is basically free and foam and epoxy look dirt cheap compared to the cost of a full harken fit out. Getting sails and fittings/hardware by far cost the most if your going to be making all your own spars and foils.
Getting a bit off topic....Check PM
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Nice to know there is a reason. It's a shame there is no budget (not bodged) alternative to a hugely expensive track/car. Maybe buy the track only and get on the lathe/mill!
There is always a bodge
(http://www.sailingsource.com/cherub/test/lib/exe/fetch.php/boats/2681-20030801.jpg?cache=)
This was done using a bent bit of curtain rail and the bow fitting from a Laser II.
It could however be turned into a budget method. If you make a curved track from either glass or carbon, sized so that a block can run along it in place of the crappy U bolt above, you have your track and slider.
It has to be very strongly fixed at each end as there is no support along the length or in the middle but it could be made to work
I think that for a budget build there is potential in bying an old boat like a 14 and stripping it for parts, for £1000-£1500 you should be able to get a 14 with loads of blocks and string, foils, potentially a carbon mast, pole and boom maybe even a road trailer. The Sails could be converted or you could probably get £200 selling them back to a budget 14 team.
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I did consider (for a few seconds) making a carbon curved track similar to the ronstan track but looking at the posts above having the sheet car bearing on the rear of the track would ease the complexity of the track.
We bought a ronstan track and car having sailed with one on Slippery with no complaints.
The jib boom that ends at the luff with a jib Kicker or Vang would allow a very simple sheet system.
But you would have to make the other two components for less cost than the track for it to be viable.
To go upwind efficiently you need a good jib system that sets the sail right. without this you wont either point well or go fast.
I'm now thinking that it is a neccesary evil.
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Any recommendations on where to source a track/car from?
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We got ours from ovingtons. The ronstan track is a 49er track.
Ronstan may deal direct.
you could try RS because I think the same track is on the 800.
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To go upwind efficiently you need a good jib system that sets the sail right. without this you wont either point well or go fast.
In single string days I was convinced that the superior performance gained from having better control of the jib slot/twist relationship upwind was easily worth the cost of the extra hassle gybing downwind. I suspect the importance of this is often underestimated - I think the jib settings are the single most impotrant factor in upwind speed tuning. However with the bigger sails and two strings the balance *may* have changed.
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Any recommendations on where to source a track/car from?
Jason Belben works for Ronstan UK - Kevin has his number.
W
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Any recommendations on where to source a track/car from?
I have been pleased by Trident UK's service and discount levels so I would recommend them every time.
Ronstan don't deal direct.
but you can always go to sailboats.co.uk or any other, I just wouldn't ever recommend P&B.
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Any recommendations on where to source a track/car from?
Jason Belben works for Ronstan UK - Kevin has his number.
W
If he does supply i would be interested to know. As it will have a barring on a 'Trading Standards' complaint I have outstanding concerning price fixing between P&B and Ronstan UK.
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Ian "bov" turnbull is quite good for bits and peices, including rope and Harken hardware.
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Bov is good for bits phil he is however still in New Zealand think he is due home soon might be june but not totally sure.
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If you have the part numbers i can probably source the fittings direct from the manufacturer. let me know the best price you've been given (via pm please) and the part number and i'll try to better the quote. :)