UK-Cherub Forum
Cherub Chat => Tech Chat => Topic started by: Jimmy Rudd on June 15, 2017, 12:26:12 PM
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Squid work is coming along nicely, its now time to stump and I need some advice.
I have some large diameter carbon tube for the main stump, and two lengths of smaller diameter for the arms.
My plan is to cut the stump to the length so it goes from floor to gooseneck, maximising mast height. Cut a rectangle slot vertically out of the bottom of the stump to slot over the box the mast currently sits on(seen in photo, tunnel has since been removed), then fix this to the floor with some carbon. The arms would then be put on going from stump to shroud points.
My main concern is the bottom of the stump and what to do with it? A) As described above, slot in the tube over the old mast foot area? Or B) Putting a mast foot on the bottom of the stump, and simply put that in the current mast base?
Any advice or thoughts appreciated on this? and the whole stumping thing?
Thanks guys
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Could you take the current box out so you can mount it directly to the bottom of the hull?
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Directly to the bottom of the hull would be best, but would involve some proper boat surgery to attach it there.
Mine terminates at the cockpit floor in a similar way to what you're suggesting, and is now stiff. I wouldn't want to use the existing mast base, as the kicker load (as this will presumably be anchored on the stump) will be putting a lot of force directly into that fitting, and if it were to break, it would be a pain to replace. Likewise, you'll need a very strong joint between the floor and the vertical stump tube: mine is a piece of 20mm thick Utile (hardwood) with a 55mm hole cut in the middle. this was glued to the floor of the boat, then 2 larger layers of carbon placed over the top and vac bagged down to hold it well. The stump then just sat in the 55mm hole in the utile, and was filleted in.
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Do you know what is inside the composite part of the current mast step? If it is solid then you could slot your tube and fit over the top, then bond to it with lots of 45's.
I have had to chop rotten wood out of every old glass boat I have ever had to fix so I would use either some HD foam or G10 to spread the load if you could not keep the load transfer through the fibers.
You also need to think what you want the side supports to be doing. Structurally the joints at the boat and stump they won't be much stiffer than pinned joints so you need to think about the angle of the strmp and what the rig tension is going to do. Also the angle of the stump affects what happens with the kicker when the boom goes out.
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Mines like this:
(http://i271.photobucket.com/albums/jj143/kerrgreg2111/Madge%20-%20Cherub%20-%20GBR2646/DSC_0432_zpss3yqzxmv.jpg) (http://s271.photobucket.com/user/kerrgreg2111/media/Madge%20-%20Cherub%20-%20GBR2646/DSC_0432_zpss3yqzxmv.jpg.html)
so not slotted but bonded in 4 directions everything meets flush and then is bogged into place followed by bi-ax tape everwhere i can get it.
This is designed to be the same sort of setup with the gooseneck and kicker attaching to the stump, the top of the stump will have some wires coming down to the shroud base to help with gooseneck loading and the bow section has been stepped up to provide additional bonding surface. Hopefully its strong enough. (tube is 75mm dia - yep! )
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I put in a new mast step when I rebuilt 2648 a few years ago. It did have a gooseneck high stump, but I found that it was flexing too much under kicker loads as it was unsupported and I didn't really want to put in additional tubes to support it. Also, I was aware that the stump was made of a very heavy piece of tube which seemed to not be attached to the floor very well. The mast was also a classic Angel 600 job and the ally sleeve was expanding and causing the laminate to crack (and was also incredibly heavy at the sleeved bit. )
Long story short... I replaced the stump with a shorter 'deck stepped' arrangement, and then extended the mast.
Picture attached of what my stump looked like when I put it in. From memory, I placed a few layers of weave under where the mast was to sit to form a plate to spread the load, and then I tied the stump in to the UD's which were spread across the floor and also the foredeck support bulkheads in all directions. I had also replaced a large proportion of the floor under the foredeck, so when that was off I also reinforced the main bulkhead underneath the stump.
As Phil has mentioned, it's totally worth thinking about the angle of the stump in relation to the rig before you put it in as it's a lot better if it's in line. I got a mast foot machined which fits together really nicely, but it does have it's drawbacks. In hindsight, although I set stump in an angled position, it's not angled far enough back. The mast foot fits so well that it doesn't allow the rig to pivot back and so when you pull the rig tension on, it actually ends up pulling it straight in relation to the stump (which in turn actually has the effect of putting a lot of pre bend into the lower mast) which isn't very flash for powering the rig up. To counteract this, I then have to put a metric sh!t tonne of tension on the lowers to pull the mast straight enough.
I plan to machine a new mast fitting to sit on the stump which is angled in relation to the stump so that there is no bend induced by the stump.
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Thank you all for your help and advice. I think stumping squid may take too long this year if I still want to make it to nationals, so.....
I am thinking of extending the mast and having a deck stepped mast as per original. I don't need to extend the mast all that much, I think its about 500mm, so planned to use a carbon tube of the same OD as the mast to the length of the extension, then put a tube with the same OD as the ID of the mast inside the mast and the extension. If I put the inner tube from the bottom of the extension and then inside the mast by the same length, so 500mm extension and 1000mm inner sleeve, bond them together, will this be enough strength? and not simply explode as soon as I pull rig tension or kicker on.
Any advice or ideas or mast extending appreciated.
Cheers
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Depends entirely on what your tubes are made of.
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I think I have the bottom 500mm of a rs800 mast from before my boat was stumped if you are looking for bits of mast.
Can dig it out if you want to know the diameter and length?
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I think I have the bottom 500mm of a rs800 mast from before my boat was stumped if you are looking for bits of mast.
Can dig it out if you want to know the diameter and length?
Think I might have that? - Jimmy is welcome to it if its of use, Im sure i can get it up to him.
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Depends entirely on what your tubes are made of.
Should have said carbon tubes......
As for the bottom of an 800 mast, that sounds perfect. Kerrgreg, I'll message you.
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glad unused bits of eva being put to good use, happy carboning.
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I think I have the bottom 500mm of a rs800 mast from before my boat was stumped if you are looking for bits of mast.
Can dig it out if you want to know the diameter and length?
Just tried to send a personal message, but not sure it has worked. Would be really interested in the bottom the 800 mast if you have it. If my message hasn't come through, can you PM me?
Cheers
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I think I have the bottom 500mm of a rs800 mast from before my boat was stumped if you are looking for bits of mast.
Can dig it out if you want to know the diameter and length?
Just tried to send a personal message, but not sure it has worked. Would be really interested in the bottom the 800 mast if you have it. If my message hasn't come through, can you PM me?
Cheers
Happy to be transport from south to midlands for it if I can be of any use.
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Have found the rs800 mast bit, it is longer than I remembered it being.
It is in two sections with a sleeved sliding top section, the sizes are as below.
Total length : 101cm
Bottom section length : 82cm
ID : 56mm
OD : 60mm
PM me if you are interested.
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I am thinking of extending the mast and having a deck stepped mast as per original. I don't need to extend the mast all that much, I think its about 500mm, so planned to use a carbon tube of the same OD as the mast to the length of the extension, then put a tube with the same OD as the ID of the mast inside the mast and the extension. If I put the inner tube from the bottom of the extension and then inside the mast by the same length, so 500mm extension and 1000mm inner sleeve, bond them together, will this be enough strength? and not simply explode as soon as I pull rig tension or kicker on.
I've broken a few masts in my time and so have had the pleasure of fixing them too. I am almost certain that I wrote a post at some point regarding the fixing method so I'll try and dig it out for you as it'll also be suitable in this instance!
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Ok, I can't find it!
Unless you have a piece of carbon tube that is the perfect fit for the sleeve, then I'd not worry about that too much. What I have done previously is to laminate up a single layer sheet of glass weave (Peelply, Glass, Peelply on something flat). Make it large enough so that the width is around 1.5 times the circumference of the mast and perhaps half a metre in length. Sand up both sides of it so that it's keyed up nicely for bonding. Take both ends of your mast (the mast, and the new stump) and then sand up the inside of the tube for around 30cm each end and clean it up.
If you take the piece of glass and roll it up into a tube and then insert it into one end of the mast, when you let go of it, it'll obviously unroll itself to fit the internal diameter of the tube nicely. With luck, both of your tubes will have a similar ID, but the sprung tube method will hopefully take a bit of the slack out and fit snugly in both sides. Have a test fit and make the 'join' in the tubes nice. You can just but them up with a straight cut, or if you are feeling keen you can perhaps put a tapered cut in so that you don't have an obvious line. It'll probably spread the load better and be a better join (but I've done 3 with a straight butt joint and they're all still ok, so not essential).
Now is the key bit, you need to try and remove some carbon from the tubes that you are going to join together as you want to taper the outside of the tubes. This is essential for making a really nice and clean looking mast join. The aim is to replicate the mast laminate that already exists, but in the join. If you're feeling lazy, then you can just 'bandage' the carbon around the outside which will leave you with a 'lump' at the join, but as we all strive for composite perfection I know that you are going to taper the outside! I normally try and make my laminates cover around a 60cm area from memory. So you want to sand the carbon off from around 30cm from the join, so that you take enough carbon off so that when you replace it across the join, it is replacing what you are now sanding off. *See sexy diagram*. This sanding is easier to do now, before you have made your mast into one piece rather than 2.
Mix up a nice thick blend of epoxy and fillers. Coat up the inside of each of the pieces of tube with the bog so that when you insert the glass 'tube' it will spring out and stick to the inside wall. If you work out where the tube will overlap on itself, it's worth perhaps putting some bog on there as well so that the end is contained. Also, lastly, if you're being keen, you could align the overlap of the glass tube with the back of the mast as it might add a little stiffness (although this is unlikely to make much difference as that is what the carbon will do) You'll have a bit of time to work with this so spend time making sure it is straight. When I've done this, I've used some long lengths of wood and strapped them to the mast to make sure that it is in line, and not going to get knocked before the epoxy has gone off. Ok. Go and have a beer, you're done for the day!
Next session, you can remove all the wood and check that your join is good and the mast is straight. It's pretty solid at this stage and should be ok to move about without too much worry. Get your old friend the sandpaper out again and clean up the join ready for your next exciting laminating task! The key to the join, as mentioned earlier, is to place as much laminate into the join as is in the mast. I can't exactly tell you how much this will be, but from memory (which isn't quite what it used to be) I did a layer of weave, then maybe 5 layers of UD with a final layer of weave over the top. These layers need to be tapered across the join to spread the load, so these should match the tapering of the mast that you have removed by sanding. when I've done it before the first layer of weave was perhaps 10cm over the join, then steadily make the layers longer as you go over. So if the first one was 10cm, make the next layers of UD 20cm, 30cm, 40cm, 50cm and 60cm. Finally, you will want a nice layer of weave over the top. (You can decide whether or not you want to do this now, or if you want a clear laquer, it might be best to cure this lot and then do the final weave as a second process over the top). I normally wet out these cloths off the mast and really work the epoxy into them, and then transfer them onto the mast. I'd also work the cloths onto the tube with a foam roller to make sure that they are all flat and nicely bedded in. Peel ply is essential next so up to you how you do this. I like to cut some long strips, say 10cm wide, and then coil and wrap them around the mast from top to bottom. You can pull it nice and tight to get some good compression on the laminate BUT you need to be really careful that you aren't twisting the layup! Hold the laminate firm in one hand, and then carefully wrap and pull tight the peelply. I personally, then get the roller again and keep rolling the laminate till all of the peelply is thoroughly wet out with the excess coming through, you can do a secondary layer of peeply on top of this if you want (leave the ends of both of the wraps available and not stuck down so that you can pull the peelply off again!) I'd now re attach your wooden sticks just to ensure that it all goes off straight. Yay, it's beer time again.
Remove the peel ply and admire your handiwork. Sand it all back nice and smooth. If you didn't put the weave on in the first laminate, then you can do that now. It's only one layer, so it's easier to consolidate and you'll find it easier to get it really neat. Once that has been sanded then you can obviously lacquer or paint it.
Other notes... If this is up to or below the gooseneck, then you can't really make this bit of the mast too stiff. So if you don't think the 5 layers of UD is enough, then just do more.
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Hi Tim,
thank you for all this advise and step by step guide, its fantastic, and I'm sure will be very handy for a newbie like me.
I'll try to keep you all posted as I do this, and touch wood, though I am running out of time, Squid will be at Nationals.......
Cheers
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No worries. Feel free to add me on FB and ping me a message if you need any help if and when you do the job rather than having to wait a few days for me to reply on here!
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Well what a bit of luck. Thanks to Amusing Outrigger and the bottom section of mast he had, it looks like the mast might be even easier than 1st thought.
The bottom section already has a sleeve sticking out (male) and as luck has it, it is a perfect fit for my existing mast.
I plan to take a small amount off the mast (approx. 250mm), then simply pop the new bottom section in to the mast, put a bolt through, mast foot on and pop it back on the original mast base area.
Do I need to bolt, or will this all hold together under rig tension?
Is there anything else I need to do or may have over looked?
Thanking you all muchly for the advice and help thus far, I'm sure more questions will arise.
Jimmy
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Unless you really want to be able to remove the bottom section then I'd be inclined to bog it together I think.
Bear in mind that the sleeve arrangement is a lot of excess weight over a conventional mast, especially if you are not going to take any performance or practical benefit from it. I agree though, certainly makes the job easier!
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Based on lots of experience of 2-piece windsurfing masts, I would say that, provided there is a decent length of sleeve, your proposed bolt won't do anything once rigged. It would keep the two sections together while travelling and rigging - which you may see as good or bad!
So there are some critical differences:
- when rigging the windsurfer, the joint is in compression as you feed the mast up the luff sleeve, whereas when you lift your mast into place the bottom section will tend to fall off
- the bending load on the windsurfer mast is much more even than you will have with the gooseneck quite close to the sleeved section.
That all seems to support Tim's approach of sticking it together. But if you see the sleeve approach as a purely temporary route to get you through the nationals it would be so much easier to be able to just slip it out at the end of the event.
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When it was on Eva before I stumped her it just slightly in and stayed there no problem getting it out could be a problem though if salt water evaporated in there.
Cheers Andy
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Glad it fits, looks like it is far more useful on squid than in my garage.
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Slips in there a treat. As the actress said to the bishop!
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Given your experience at the Nationals, would now be a good time to resurrect this project?!
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Certainly thinking about the stump again, though as a quick fix with the hope of attending Queen Mary we have made a carbon top hat section to put over the offending mast step and plan to bog it down this week. Over the winter I may consider the stump again.
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jimmy give me a bell or FB me and if I can be of any helpAndy ex EVa
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The stump on Eva is going well, apart from the plastic locator pin that was one the top. That snapped off very quickly, but a bolt and a tap it was quickly sorted out.
Carwyn