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| Mast Support Fail http://www.hobie.com/forums/viewtopic.php?f=71&t=44081 |
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| Author: | Drewyaker [ Fri Aug 03, 2012 8:41 pm ] |
| Post subject: | Re: Mast Support Fail |
Just so happens I had my v brace out today for cleaning off salt corrosion. I see what people are talking about when putting it back getting the studs to line up. Trying to put the bottom on first, then on the 2 top studs was not the way to go. I can see how someone might get it in a bind that way. What I found is to first expand the turn buckles until the 2 top studs line up, then they will slip right on when bases are parallel. Turn both sides evenly, not just one. Once the 2 top holes line up, they slide right on. Then place on the nuts but don't tighten, just get them started so the brace doesn't fall back down. I found it easier to put one side on the stud, just start the nut to hold it up, then place the other side near the stud working both couplings until there was line up, then slip on and start this nut. Now turn the brass coupling to draw up the bottom base plate up and over the bottom stud. will have to alternate turning each coupling until the bottom plate is over the stud and the hole lines up as it will go to one side or the other as a result of turning the couplings. Now once the bottom stud lines up with the bottom plate hole, turn the couplings the other way, again both sides the same amount, to expand the brace evenly until all bases are seated on the studs. This looks to to be the way to go so nothing is in a bind. Then turn by hand a little more so that there is no play and just a little tension. (That was how I found it) Then tighten down all nuts. I assume there is not much preload on this brace other then what it takes to snug it into place before tightening the nuts, but if there is some spec about this, I would like to know. Just my 2 cents from my piddling today. |
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| Author: | Tom Kirkman [ Sat Aug 04, 2012 1:31 pm ] |
| Post subject: | Re: Mast Support Fail |
The mounting studs aren't in the exact same place on every boat due to variances in the manufacturing (cooling, etc.) process. On some boats, the truss will have to be forced into position, or modified slightly to accommodate these slight variances. Mine was forced on during initial assembly. I modified it so that it could go on without any force after I repaired my hull. But, having said that, you certainly installed yours the right way. |
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| Author: | Drewyaker [ Sun Aug 05, 2012 5:44 am ] |
| Post subject: | Re: Mast Support Fail |
Im glad to know it will be ok. I didn't want to over or under tighten it. I can see how binding can come from a slight stud shift when the hull is cooling off. I wonder why hobie didn't have another brace like that on the other side of the mast base complete with another mast base tab, studs, etc. for even more support even though it would be hard to reach. Any way, I got it all back together and look foward to having fun with it and hopefully not have to deal with it again. |
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| Author: | SailScott [ Thu Aug 09, 2012 9:31 am ] |
| Post subject: | Re: Mast Support Fail |
Ok... The replacement main hull is on its way, and I think I will have to use the crossbeams from the defective hull. So, when I re-bolt the crossbeams, what do you recommend for lube on the crossbeam bolts? (WD-40? Marine axle grease?) Also, how much torque? And, related to this topic, what are some steps that I can take to tune the mast support system so that I don't have "slop" and/or another broken nut (bolt) in the future? Thanks for all the info, all! Scott |
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| Author: | Tom Kirkman [ Thu Aug 09, 2012 10:12 am ] |
| Post subject: | Re: Mast Support Fail |
If you're going to put anything on the bolts I would choose Permatex anti-seize. This is the sort of thing it's specifically made for. When I reinstalled the V-Truss, I simply brought the pieces into firm contact and used the turnbuckles, moving each one equally a half turn at a time, until everything was very snug. You can exert a great deal of pressure with the truss, so don't overdo things. If you simply keep turning things until they get really "tight" you may find you've deformed or blown something out. Hobie could tell you more in terms of the proper torque value (I assume) but in the interim I simply hand tightened the turnbuckles. The point beyond where you can hand tighten them would seem, to me, to be much too much. |
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| Author: | kayakman7 [ Thu Aug 09, 2012 10:40 am ] |
| Post subject: | Re: Mast Support Fail |
Tom, I think I read somewhere that the v-brace should be tightened until the furling drum of the mast is about 1/8" above the deck. When my boat was new I tightened these up to reduce the space and after installing a new x-bar I had to loosen them to increase the space. J |
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| Author: | Tom Kirkman [ Thu Aug 09, 2012 11:44 am ] |
| Post subject: | Re: Mast Support Fail |
Something isn't right about that. The V-Truss doesn't push that center area upwards - it pushes from the center bottom of the hull to the inner outside (gunwales) of the hull. Even if you could raise the center of the hull via the gunwale attachment points of the Aka, the mast tube support is a fixed length and is bolted to the Aka. It's attached to the bottom, and the top, of the hull. I see no way you can raise something that's also fastened at the bottom, not to mention that even if you could, as the top is raised, so is the bottom, so the furling drum would remain the same height above the support top no matter what. |
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| Author: | kayakman7 [ Thu Aug 09, 2012 12:31 pm ] |
| Post subject: | Re: Mast Support Fail |
I absolutely agree with your statement; but what I did worked. |
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| Author: | Tom Kirkman [ Thu Aug 09, 2012 1:49 pm ] |
| Post subject: | Re: Mast Support Fail |
Maybe the mast support/Aka arm is different between an AI and a TI. If I simply continued to spin the turnbuckle, I'd likely just break something but the distance between the top support and the mast furling drum wouldn't change at all. I haven't taken a close look at the TI assembly so again, perhaps it's different than what's on an AI. |
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| Author: | fusioneng [ Thu Aug 09, 2012 5:16 pm ] |
| Post subject: | Re: Mast Support Fail |
SailScott: One thing I discovered on my TI's that may relate to your situation. If you open the front hatch and look inside you will see the metal triangle brace setup is very strong to prevent side to side movement (you shouldn't have problems with that as long as you check it "often"). However if you study where the stresses are exerted from while the sails are propelling the boat "forward" you will discover the mast reciever acts just like a giant lever for the forward and backward forces. The pivot point is about a foot up from the bottom of the mast, you then have a 17 foot lever pushing forward (the sail). This create a backwards force at the base of the mast cup that is huge (could be several thousands pounds of force). Think about it, if you took an 18 ft pole and put a brick under it 1 ft up from the end, when you push down on the long end you can probably lift your car easily with the short end (17 to 1 ratio 200* 17 = 3400 lbs lifting force if I stand on the end ). Now if you look at what is holding the mast cup from forward to back movement you will see a tiny 1/4" stud that is all that holds the mast cup, and thats it.... If the stud breaks the hull bottom just pushes out of the way as it rises up and over the tapered pyramids with the brass insert inside. above is a (slightly modified) excerpt plagiazed from a previous "kind of related" thread ( viewtopic.php?f=69&t=44169) I realize my TI is not normal with 265sq ft of sail, but alot of the same forces apply regardless how much sail you are flying. This video shows how I re-enforced the bottom of my mast cup to help counteract some of the extreme backward force going on down there. I have way over 2000 sailing miles with all my custom mods and extra sails installed (really hard miles at times (over 18mph)), and have never broken a 1/4 inch stud. I laid in a 1/8" x 2" x 7 1/2" piece of aluminum behind the mast cup. I then built a dam with clay and filled in and around the aluminum piece with West Epoxy. The front of the mirage drive pocket is probably one of the strongest points on the boat. Of course the Epoxy does not stick to the plastic hull, so if you ever want to remove the brace, you just pop it out. I'm not suggesting anyone re-enforce their mast recievers, I'm just describing what has worked well for me, and more importantly try to explain why those darn studs break, and the forces involved. PS Pulling the sail really tight (like when sailing directly into the wind) can also snap that stud (in the forward direction)... (my fix doesn't help with that) Hope all this helps... Fusioneng [youtube]http://www.youtube.com/watch?v=jU4paaX3lzU&feature=plcp[/youtube] |
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| Author: | Tom Kirkman [ Thu Aug 09, 2012 5:26 pm ] |
| Post subject: | Re: Mast Support Fail |
One thing to remember in terms of the force that can be applied - our boats aren't bolted down. They move upon the water. Not to say that such forces aren't present, just that it's difficult to apply a great deal of force to something that just moves when you push it. |
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| Author: | SailScott [ Thu Aug 09, 2012 8:53 pm ] |
| Post subject: | Re: Mast Support Fail |
Thanks, guys, for all of the input. It really is a helpful discussion... I like the idea of adding some sort of aluminum mast brace to control fore/aft pressure at the bottom of the mast cup. (Any free-standing mast base MUST be strong enough to handle significant loads... as was noted above regarding the power of levers.) In my case, after the nut failed, the bottom of the mast popped forward a couple inches (bringing the mast tip back a foot or so and flexing the deck area around the mast cup, and signaling me immediately to reef before further damage was suffered). A piece of aluminum yoked into the forward mirage well and the mast cup could add a lot to fore/aft loads... I'll work on this concept when the new hull arrives. (I would love to see what the inside of the hull on a free-standing, stay-less boat like a Laser looks like around its mast cup.... There must be substantial material involved...?) Thanks, again, for helping me work through this issue... to make sure that it does NOT happen again. Scott |
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| Author: | tonystott [ Thu Aug 09, 2012 9:19 pm ] |
| Post subject: | Re: Mast Support Fail |
Maybe it is because I am in the Southern Hemisphere (but I doubt it LOL), but aren't the forces on the base of the mast FORWARD? In that case, any reinforcement would logically consist of some kind of strapping from the >rear< of the Miragedrive well, around the base of the mast to prevent it being pushed forward??? Humour me here please! |
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| Author: | SailScott [ Thu Aug 09, 2012 9:28 pm ] |
| Post subject: | Re: Mast Support Fail |
Hey, that just gave me an idea: Use a cargo/ratchet tie-down strap around the Mirage well and the mast cup with an aluminum brace/yoke sandwiched between...? Let the brainstorming continue, kids! Grateful again, Scott |
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| Author: | fusioneng [ Fri Aug 10, 2012 2:50 am ] |
| Post subject: | Re: Mast Support Fail |
guys : That is a great idea, I have an extra hold down strap from my boat racks that I will wrap around the drive well and around the front of the mast reciever. The way I realized that force is when I first rigged my TI's with all the extra sails I had a braided nylon rear stay line attached to the top of the mast. I snapped that line right away second time out flying my 130 sq ft Spinnaker, that line was I think 750 lb break. I upgraded to a 1/4 inch nylon stay line. The force was forward at the top of the mast, so in turn (because of the lever action) becomes rearward force ( times 17) down below (on the stud), Like Tom says all that force is not all realized because it is distributed all over the place, and the boat is propelled. When I snapped my stay line the winds were 20mph gusting over 30mph, and I was going down wind. ( I think I was tipping 20mph+ when the line broke but didn't have the GPS on). I no longer push the boat that hard. Like I said that line broke when I first made the spinnaker back in 2010 and was testing everything out. Bob My aluminum bracket or my rear stay line don't prevent me from breaking the stud if I pull hard on the sheet line and pull the sail tight (like when going up wind), the strap I think will help with that. Great idea.... |
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