cep32 4 Posted November 20, 2015 Share Posted November 20, 2015 I've just got hold of my next Javelin and want to open the cockpit up by removing the traveller shown in the attached photo. As far as I can tell the lateral rig loads are carried by the aluminium frame at the front of the cockpit so the traveller structure only carries crew loads. On the other hand, the traveller structure is only attached to the side tanks with four very short screws so I'm not sure it's actually contributing anything anyway. Am I correct in thinking that that the box beam shape of the side tanks held together by the 25mm thick cedar/glass transom and the front bulkhead is enough on its own and the traveller structure is only there for the traveller function? Any advice would be greatly appreciated. Cheers, Chris Quote Link to post Share on other sites
erice 732 Posted November 20, 2015 Share Posted November 20, 2015 if you remove the traveller where will the loads from the mainsheet be going? as shown we can imagine the loads from a hiking crew to be shared between both hulls at; fwd bar 10%?, mid beam 40%?, transom, 50%? if you remove the traveller beam the loads could be something like fwd bar 20%? transom 80%?... the length of screws doesn't really effect how much load they can take more the number, spacing and type of mounting there are 8 of them meaning they could be taking substantial loads are they coarse tapered screws that go straight into glass or screw headed fine pitch bolts going into a metal plate? gets pretty windy in nelson do you intend to just potter about in light air for a few years or thrash it in big air for eons? Quote Link to post Share on other sites
cep32 4 Posted November 20, 2015 Author Share Posted November 20, 2015 Sorry, I should have mentioned. The mainsheet wil lget transferred to the transom on a bridle then dropped to the floor at the back of the cockpit then forward along the floor to a sensible position. At the moment half of the screws go through a 10mm stringer and 4mm ply and the other half just go through 4mm ply. The plan is to thrash the boat for the rest of my natural life (40 years or so) so it has to be strong. Back to the drawing board. Quote Link to post Share on other sites
RushMan 31 Posted November 20, 2015 Share Posted November 20, 2015 Erice... Not following your point about the hiking loads from the crew, how is this affected by the removal of the traveller? Bridle on the transom, lead forward along the boom and sheet from the boom might work better than across the floor. If extra strength is required perhaps glass in an angled wooden brace between the side tanks and the floor. Quote Link to post Share on other sites
cep32 4 Posted November 21, 2015 Author Share Posted November 21, 2015 I like the idea of the simplicity of the boom sheeting and have tried on a couple of boats now. The last one I kept at it for a couple of months and just couldn't get comfortable. I think it is something to do with me being a fat bastard that relies on locking my arm on the mainsheet to help me hike. I'll try it again and see how I get on. As far as the traveller goes, me and a mate (combined weight 220kg) are going to site either side and hike hard to see if we can get the boat to flex without the traveller in. Quote Link to post Share on other sites
Romany 162 Posted November 21, 2015 Share Posted November 21, 2015 I sense a minties moment approaching. Pictures or it never happened. Quote Link to post Share on other sites
erice 732 Posted November 21, 2015 Share Posted November 21, 2015 i'm no structural engineer but it seems to me that with a fully powered up rig there are going to be BIG loads on the windward stay trying to pull the windward side of the boat up and towards the leeward side putting the; fwd bar, the traveller beam and the transom under considerable compression loads those loads can be greatly reduced by correct positioning of the crew weight but it is not a static environment, there are going to be large pulses? of compression loads as the boat; hits waves, flys off them, gets hit by unexpected gusts etc and then there'll be times someone falls off the boat or onto the leeward side of it meaning the counter acting crew force is completely lost this isn't even an frp boat but tortured ply i would be worried that removing the central structural beam that absorbs these loads would place too much strain on the transom area and that's before the extra loads of transferring the main-sheet loads there too... but again i know nothing of how javelins and their transoms are built, or even this boat's age are they considered bullet-proof brick sh*t-houses or fragile egg shell constructions? Quote Link to post Share on other sites
erice 732 Posted November 21, 2015 Share Posted November 21, 2015 As far as the traveller goes, me and a mate (combined weight 220kg) are going to site either side and hike hard to see if we can get the boat to flex without the traveller in. here's an idea if you're going to take the traveller off anyway cut a bit of thin 10x10mm? or 6mm dowel (thin enough to flex) long enough to sit about where the traveller beam would be but touching both hulls, pencil marks under where it supports itself then try both of you hiking off the sides, first gently then with more vigor to see if the hulls spring open a little and drop 1 side of the dowel below the pencil marks just be careful not to use a 4' x 2' instead of thin dowel cause if the hull does flex and drops something that doesn't flex down when you stop hiking the point loads of the ends might do bad things to the thin ply... Quote Link to post Share on other sites
cep32 4 Posted November 23, 2015 Author Share Posted November 23, 2015 Sounds like a plan. I was going to set something up to measure the deflection but the dowel idea sounds good to me. Quote Link to post Share on other sites
erice 732 Posted November 23, 2015 Share Posted November 23, 2015 Sounds like a plan. I was going to set something up to measure the deflection but the dowel idea sounds good to me. once you've tried your traveller on traveller off flex tests with the mast on think about carefully trying them again with the mast off without the stays and mast absorbing your flex loadings you'll get a better idea of the "naked" load paths across the deck Quote Link to post Share on other sites
ScottiE 174 Posted November 23, 2015 Share Posted November 23, 2015 cep32, here's a basic sketch of the sorts of things to look at, really as outlined by erice. It's rough, NTS and really just an indication. 1. where on plan is the side stay attachments - if close to the rig frame then most of the load will be transmitted there - i suspect that it will be but can't make it out from your image. If not consider the flex tests per erice. The line of action of force is the trajectory of the stay so a much bigger component of the load is actually orthogonal to the deck which the hull will already (hopefully!) be capable of withstanding. Probably less of an issue. 2. Hiking loads on the other hand have quite a bit more component of force in the plane of the deck and as erice points out "give it areseholes" to satisfy your self that its capable of withstanding a launch and land at 20kts of those narly waves in Wellywood!. The side of the hull should be very well taped already and hopefuly has a few internal bulkheads to stop the box shape warping but if you were concerned you could always lay up some carbon unis and db for a bit of extra stiffness. 20151124103811.pdf Quote Link to post Share on other sites
cep32 4 Posted November 24, 2015 Author Share Posted November 24, 2015 Thanks for the drawing ScottiE. The side stays attach about 100mm back from the forward alloy frame so I'm pretty confident the compression loads of the rig are handled OK. I have just finished sanding the side decks and haven't found any fibreglass or carbon tape although it it all holding together well with the traveller in. The budget won't stretch to carbon tape of any sort unfortunately. Do you think some 400gm fibreglass double bias would be worth a try? Alternatively I have some spare carbon tube so could put two lengths from the side deck down to the middle of the cockpit. This way there would be a couple of large rigid triangles stopping the side tanks from sagging outwards. Quote Link to post Share on other sites
madyottie 82 Posted December 1, 2015 Share Posted December 1, 2015 I know I'm a week late, but just thinking back to Fireballs, with 400lb static tension on the forestay, the WINDWARD shroud would go loose with the crew on the wire. because you have 100kg pulling the rig over. Digression...It was commonplace to get the crew out in under 10 knots, even if the helm was sitting to leeward, because the tension imbalance would cause the mid mast area to push to windward, opening the slot slightly. Back on topic... Looking at the pic, I think that traveller is just to take sheeting loads. It's a pretty old looking Jav, (Farr mk1?) and back then everyone used lots of mainsheet tension. Now it's a lot more vang. Running a split mainsheet from the stern shouldn't cause any problems back there, as the loads at the end of the boom aren't high. Indicated by fb's having a straight split sheet with no purchase. Just hooked into both corners (rope outer going to one side, core going to other) then up to the boom, forward, and down to the ratchet block. I'm slightly inclined to think it's been over-thought, but I'm not a marine engineer, just a guy with 30 odd years of dinghy racing memories to call on. Although I did once drive the mast right through the bottom of the hull on a windy day! The conversation went something like... "Forestays sagging a bit" (pulling on the tensioner) "Something must have slipped, we're still on the right settings" "Still too loose" "Ok, now I've run out of adjustment, and it does look a bit loose still." "Oh, never mind, we're so far ahead now it won't matter, the race is almost done" Then later, when lifting the mast out "can you see what's catching down there? I cant lift it" "I'm not suprised, it's sticking out the bottom!" Oops! Quote Link to post Share on other sites
Ed 143 Posted December 1, 2015 Share Posted December 1, 2015 I remember one fireball where the correct amount of rig tension was that which would just still allow the center board to be moved Quote Link to post Share on other sites
cep32 4 Posted December 6, 2015 Author Share Posted December 6, 2015 So test number one took place last night. With the hull on the beach trolley I hung off one side (120kg) and a 70kg body bounced up and down on the other side. Without the traveller bar in the width of the boat changed by around halfa milimetre. To measure it I laid a aluminium box section accross the decks and taped one side down. When we leant on the boat, one side of the bar stayed attached and the other moved to show the deflection. I marked up mm measurements on the side that moved and then videoed the movement. The question now is whether the beach trolley provides more support than the water that will be under the hull. The beach trolley supports the hull out to around 200mm short of the chine. I think given the result that the side tanks can be considered to be pretty stiff and strong so I'm going to sail it for a while without the traveller bar. If any cracks open up I'll look at solutions then. Quote Link to post Share on other sites
erice 732 Posted December 6, 2015 Share Posted December 6, 2015 good work on the testing looks like the hull is structurally sound enough to move from static land testing to dynamic water tests Quote Link to post Share on other sites
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