UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: Torchy on March 05, 2012, 05:43:07 PM
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Hi,
Picked up Loco Perro from Tom the other day.
When screwing into a block of epoxy (which might be a bit brittle)...any tips? Jib track has come free IMO because under-engineered. Held by a single screw at centre and this has pulled right through the laminated wooden stringer.
Does anyone have any sections of C Tech sail track or know a UK source? NZ is quite a long way for a bit of plastic :) (short section around centre of mast has lost edges in 2 places - might be OK/might not)
Otherwise it's just minor re-roping
A few queries:
* What purchase do people use on cunningham?
* Ditto kicker
..a long shot - has anyone got a C Tech sheave box tucked away anywhere?...old boom kept for spares?
Has anyone got a trapeze harness they want to part with?
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If I remember from the day that the track broke, It is held in the middle by a screw, but the ends take most of the stress and I think these were held on with some loops of Carbon tow. (- Put some pictures up and someone will be advise you on the best way to mend, also I can't remember the details..)
As for the mast track, I sailed her with it and had no problem, but getting the main on/off can be a bit tricky. It won't be c-tech track but I am sure there is an easier supply somewhere here in the Uk.
Kicker purchase will be a little different as Loco is one of only a few Cherubs to have a Gnav.. Again, when I sailed her I didn't have a problem.
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Hi Andrew,
Forgot about G Nav. What purchase were you using with the G Nav?...and Cunningham...it's just a mass of ropes and mixed up blocks, so I can't easily tell and it doesn't look like an original set up. There's a massive Barton block and jammer that looks out of place.
I'll measure the track and see if Purple can match the dimensions...low priority following your reassurance but I may as well get her back to full spec.
Jib track...it looks like the breakage was caused by the centre (single) screw pulling through which caused the ends to fail...or did one end fail and the others go in sequence? It is easy to put 3 screws back where the one failed, which is prudent because the wood laminate needs putting back together and strengthening. Long screws right through from the track will naturally and very easily do this. Previously the screw only held the laminate, with the track bolted to the laminate (which will remain unchanged).
At the outer ends I am planning to sand back to carbon then re-epoxy with new carbon bands over all...hopefully under the track, if I can get it off. I'll at least match the previous bands and possibly beef it up, especially if you think one of the ends failed first.
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I have some spare track here. We order it in bulk from Bainbridge. Then you need some Plexus to stick it on with. I've just ordered 5 tubes, but at the price it's now at I'd suggest you buy half a tube (i.e. send ti back to me after using some).
Is the track white or black....
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Ta Slippy...it's white and count me in for half a tube and some track.
Hope to have Loco ready in a couple of weeks and then we can give the folks at Bartley a larf or two...they already think we're nuts after my single handed asymmetric antics in the Tres recently
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I seem to remember the track came off at one end; we were two sail reaching, it pinged off the starboard side and the diagonal load just popped the other two points. (Sorry this didn't get fixed before.. My crw and I were fairly tired after trollying the boat 1/2 mile down the beach, and Tom had just returned from kenya.. must have forgotten it after putting her away, we had to help recover the SK4 after a fairly swift (20kt) grounding)
I understand that this repair has been done before on loco, so may be worth adding a little more strength this time round..
(Could be that the plywood is breathing?)
Wrt to gnav - There is a 6:1 in the boom, which does something.. Nearest guess is that it goes from one end (Tail leading out the boom>cleat), through a cheek block at the gooseneck and onto the gnav. (I only sailed this boat one weekend in Tom's absence, so didn't figure out all her rigging exactly, but she worked well)
The cunningham - From memory these are the two 4:1 pulleys on the deck below the mast. A piece of yellow dyneema should be kicking about; this goes through the Tack-eye and each end hooks onto one of those pulleys. This means you can play with the cunningham from either side.
I was just going to point you towards BS and his magical Plexus.. :D
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Thanks Andy and don't worry about the track damage...I wouldn't be surprised if it had happened before and otherwise it might have happened again on the last beat with us leading at the nationals (dream on). All 3 points of breakage have gone straight through materials (epoxy or wood laminate, not carbon) and there's no sign of prior delamination. It needs a once-for-all fix and I will post photos and get the gurus on it.
Cheers mate
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ill give you some helpo if you need it, just give me a call and i can come over
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It may be worth bolting the track on. 1 at either end and 2 between them either side of the centre. The chunky I track on the e5's doesn't need much support because it is a large section. If self tapping into carbon, fibre glass or epoxy i would always drill a pilot hole first so that only the thread of the screw has to cut through the material.
Purchases either a 4:1 or 8:1.
Normal kicker needs a 16:1 purchase.
For a Gnav you can use a 2:1 or 3:1 from the bit that slides along the boom or mast and then another 2:1 after that. I do recall that loco has some part of the system in the boom that you don't want to let go of but never rigged it myself. i would look at a similarly GNav rigged boat and work out the purchase used on them.
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Yes Phil, there is a substantial purchase inside the boom. I'll have a close look but I think the 2:1 routed either side will be enough hooked onto this.
Thanks for the info on likely purchase needed.
Would bolting through foam/carbon hold? I'll post photos...it can be done but I'm concerned about crushing the (undamaged) supports...the angle isn't right.
...I'm considering supporting the track with dyneema strops under tension (to the deck behind the track at either end) and using the supports as 'stops' rather than 'anchors'. Might be too Heath Robinson...but it would be bomb proof and light.
..and thanks John HH...might well ask for help with carbon/epoxy stuff. Have you done much of that? I'll need to reinstate what was there even if on its own it is weak.
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Would bolting through foam/carbon hold? I'll post photos...it can be done but I'm concerned about crushing the (undamaged) supports...the angle isn't right.
I would expect bolting through the composite with a massive "penny" washer on the back to be fine.
However, if you are concerned about crushing you could make an insert of a higher density material where the bolt goes through:
- stick in a piece of plastic tube
- cut a piece of foam out and replace it with HD foam or wood
- make a plug of epoxy
This is probably how I would do it:
1. Sand the area you will laminate in step 7, make sure you take off all the paint, undercoat and filler. It doesn't matter if you go through the laminate as you will replace it later.
2. Measure the diameter of the nut, add 2mm and choose that drill bit. Drill a hole all the way through where the bolt will go.
3. Mix about 10ml of epoxy resin with glass microfibres at about 1 teaspoon at a time until it is the thickness of toothpaste and doesn't run.
4. Pack the hole with resin/fibres mix then tape up the ends with brown parcel tape. This will stop the resin seeping out and epoxy doesnt stick to parcel tape.
5. Wait for your epoxy to set, probably 24hrs.
6. Take off the parcel tape and sand any proud bits. If there are hollows repeat steps 3, 4 and 5 until it is completely flush.
7. Laminate over the top of everything. I would probably use s-glass. It will have about 25% less tensile strength but it will be see-through so you can see where your plug is when re-drilling.
8. Drill the hole again and bolt through.
This means that when you tighten the nut you will be pushing against a very hard lump of epoxy, and you won't crush that.
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The plastic tube idea makes the most sense as if I leave some sticking out the back it will deform as the bolt (with largish washer) is tightened and transfer the load more evenly to the composite (see photos)
It should be a neat, simple and strong solution
Thanks guys
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yeh, i built a boat with phil
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Of course!...in the kitchen!
Sorry we didn't get to see you at Boat Show....did you have a kite for me to look at?
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yeh, just didnt bump into each other i guess!
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you can bolt through carbon foam plate but you need 2 layers of carbon or glass in the area you are bolting through and a reasonable sized backing washer. The best solution is to combine this with an epoxy insert through the thickness of the foam but this takes longer.
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Generally I would not put self tappers into anything that might see tension loading, and would avoid for anything other than light side loading, they will come out it is just a matter of time.
For bolting through foam you can also use an allan key to breakup the foam around the hole and then fill with bog. Carbon plate, or penny washers work well.
A track supported at the middle and ends does work as the normal high load is when the cark is at the end, the problem is if the car is in the middle and the sheet loads up e.g. in a capsize with crew landing in jib, then it will break. Your cats cradle idea may help with that, longer term I would put a foam-carbon strip from deck to track to give more support.
With my Gnav I have 3:1 on the boom, and 4:1 going down the mast.
You need to be careful where you attach the turning blocks on the boom for the gnav, if they are on the boom then there will be a high load pulling the gooseneck apart. This can be OK but the gooseneck-boom attachment must be very strong.
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Thanks Phil
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If you are coming to the Sheppey blast I should be able to help with any rigging problems, unless Tom made any major changes most was put in or modified by us.
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Thanks Simon...Sheppey is a bit far for us just now and actually having had a bit of a closer look I think the rigging is more straightforward than it looked - the oddly cobbled together ropes and massive Barton block which confused me are for tensioning the rig prior to attachment of the jib...I think.
Rigging tomorrow morning...will post photos.
Track is 'mended' (bolted - worked fine) but awaits wraparound and over the top carbon bands, then re-bolting, which I'll contact John HH about and see if he can help. Should get the preparation work done this week.
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Getting there...learnt what a boat breaker is (thenks Andy) and now I need a Loos gauge
Here's a go at putting up pictures
(http://www.sailingsource.com/Users/nigelgillmodern/Desktop/rigged)
(http://www.sailingsource.com/Users/nigelgillmodern/Desktop/Kite)
(http://www.sailingsource.com/Users/nigelgillmodern/Desktop/First stage)
Not working...scratches head...
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Torchy,
You are trying to link to a file on your desktop, they have to be somewhere on the web for that to work. if you click on Additional Options, and then upload the image files, they will display.
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Not getting an 'upload file' option...do I need to be an association member?...some other admin fix?
Cheque for association is in post btw
My additional options say:
Notify me of replies. Lock this topic.
Return to this topic.
Don't use smileys.
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and now I need a Loos gauge
Hmm this sounds seriously technical. There are two other options for this:
1) Twang shroud. if it is a musical note a bit like a guitar - you have enough tension to go sailing.
2) Ask the previous owners (Dan/Dean/Si are regular readers adn I'm sure they'll be along on this thread soon enough).
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Not getting an 'upload file' option...do I need to be an association member?...some other admin fix?
Cheque for association is in post btw
My additional options say:
Notify me of replies. Lock this topic.
Return to this topic.
Don't use smileys.
Hi it would be a non member thing that is stopping you uploading the pictures, I will get that sorted for you.
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Thanks guys...yes Loos gauge may be a bit technical just yet so I'll go for the D 2 octaves below middle C and see how it goes :O)
...is that Modern or baroque pitch?
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IIRC Loco's shrouds do not go through the spreader ends. This makes the pitch of the shrouds twang v low, even with good tension.
Fret it at the spreader and twang it above that. If it is definitely a note, then that's about right.
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Thanks Will...it really is like playing a guitar
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With her final C-tech rig the right rigging tension on Halo was a bass guitar A string on the shroud. I don't have perfect pitch, but I found I was close enough for adequate consistency...
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:O)
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I use a loose gauge, particularly for setting the uppers, as it is hard to get repeat settings with the lashings. I am not at all musical so would not get anywhere twanging.
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and now I need a Loos gauge
Hmm this sounds seriously technical. There are two other options for this:
1) Twang shroud. if it is a musical note a bit like a guitar - you have enough tension to go sailing.
2) Ask the previous owners (Dan/Dean/Si are regular readers adn I'm sure they'll be along on this thread soon enough).
Not forgetting the first owners / builders... Ben & Daryl
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Hi Daryl,
Glad to hear of any tuning tips...latest thing exercising my mind is jib sheeting angle.
There seem to be 2 holes for stops - one almost at end of track and another quite a lot finer.
Photo of Loco with Fyfes and the jib track repair (awaiting clipping of bolts and cosmetic finish) - in the end I used a plastic pipe to feed the bolt through, epoxied into the foam and extending out as a bed for the penny washer.
(http://2685-2012xxxx.jpg)
(http://2685-2012xxxxrepair.jpg)
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PS Hope you don't mind the cheap sniping at your Spanish grammar on the boat page :)