• Announcements

    • Zapata

      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  

kubark42

Members
  • Content count

    35
  • Joined

  • Last visited

About kubark42

  • Rank
    Member

Profile Information

  • Location
    Boston, MA

Recent Profile Visitors

131 profile views
  1. Sidestay tension, why does it matter?

    Thanks, guys, I appreciate the insight. Coming from the world of multihulls, what I typically see is a rotating mast with a slack leeward shroud, so this has been very educational. I think I can conclude that in typical boats first-order mast tuning can be done to "just snug to leeward in a blow", and that second-order tuning needs to be done if looking to eek the most out of the sail.
  2. Sidestay tension, why does it matter?

    Thanks, I appreciate the input. I had thought that most of the fore-aft tension was controlled by the forestay, the baby stay, and the backstay. Is it fair to say that sidestay tension can only affect fore-aft bend when the mast has raked spreaders?
  3. Sidestay tension, why does it matter?

    Here's the part I'm not getting. How does it help to tune? Either the spreaders are in column or they're not. And either it's enough to keep tension on or it's not. Tuning it implies analog decisions. I'm not arguing they're not being made, just that I'm not understanding the considerations because they're something else going on. @Raz'r hints at it when he mentions mast compression, but I don't follow what that impacts and how. I would think, naively, that-- ignoring fore-aft bend and prebend-- this mast compression is a result of the sidestay tension, which itself is designed to keep the mast upright. Put differently, I am currently thinking of side-stay-induced mast compression as an undesirable after-effect, not a sought-after feature.
  4. Sidestay tension, why does it matter?

    @DSE, that's not quite correct. We can see this with the simple Hooke's Law, F = k*x. If we want to look at how much change in force gives us how much change in elongation, then we simply take the derivative: dF = k*dx. So in other words, additional force dF makes the same additional stretch, dx. Neglecting second-order effects, no matter how much you preload the rigging, an additional force will always make the mast bend the same amount for the same rigging. Regarding bolt preload, it's purpose is to ensure the bolt always stays under tension, which is very important for fastener and joint life-cycle, and that there is sufficient compression to transfer shear loads. I don't think this principle applies here, unless it's to prevent the leeward rigging from slackening. But if that's the only reason for rigging tension, then I don't understand what the value is of the Loos gauge, as @MidPack mentions. You don't need precise measurements to ensure that in a huge blow the lateral tension never goes to zero, it's enough to tighten the turnbuckles to "snug and sturdy" when beating to windward, all while ensuring the mast stays in column. EDIT: Submitted just seconds after @longy's comment. So can I conclude that "tight enough not to flop or unduly vibrate" is fine?
  5. I'm looking for insight into understanding why the rigging needs to be a certain tension. The sidestay rigging is designed to prevent the mast from coming out of column, and how much it comes out of column is purely a question of how much load is applied, not how much preload there is. This is because wire/rope strain is a linear deformation, which means that doubling the load doubles the stretch. The upshot is that when looking at elastic deformation it doesn't matter how much preload exists. For 1kN of load the rigging will stretch a distance Y, no matter if there were 1kN of preload or 100kN. If you want to reduce the distance Y, you have to increase the elasticity, i.e. move to a stiffer material or increase the material diameter. All I can think is that tension can help increase pressure on parts which might move in shear, such as rigging fittings. Or that sufficient tension means that the leeward rigging is stretched to the point that it never goes slack. But that second case only seems useful to prevent chafe or fittings wobbling loose. What am I missing?
  6. Cool place! I'll definitely keep them in mind for any major repairs. But I think that for just a simple gasket replacement I can do that at home. Nothing is broken, and the window comes out of the frame just fine. All I need to do is decide if I want to use some marine sealant or a weatherstripping gasket.
  7. 4" Carbon Fiber Tube as Boom

    @mowgli, that's a really neat solution. I'd want to find something with more squarish edges in order to properly contain the rope as the mast rolls. A triangular shape which could give me a V-groove would be even better. Short of trying to lasercut laminations out of balsa, I'm not sure how to get a profile made which will slide onto the boom. P.S. I was onboard my boat today and indeed, the boom is 4" tall. It's a teardrop profile so not as wide, though. It's fair to say that there is very little aerodynamic difference between the two. Jackpot!
  8. According to the Lewmar website, I've got Trimline hatches. On these particular hatches, the window is held in place by two seals. One is a rubber gasket around the perimeter of the acrylic, and seems to be in good shape. The other is a foam weatherstripping seal along the inner edge, which can be seen in the upper left side of the picture: https://photos.app.goo.gl/6aa9mMQxFHcsYxTk1. This weatherstripping has completely dried up and turned to dust and I now need to replace it. The hatches are potentially 25 years old, so I don't know if this is standard, or someone has replaced stuff in their own way. I can't find any diagrams for Trimline hatches (which Lewmar stopped producing in 1999). For all I know, the weatherstripping was just there to mechanically hold in the window, while the thick rubber seal did the sealing work. So what should I use to restick the hatch? Some convenient weatherstripping, some marine weatherstripping, or proper marine sealant? My concern with sealant is that it will be very hard to mechanically separate the hatch. I've not seen salt deposits on the inside of the hatch so I don't suspect that the rubber gasket is leaking, and thus I don't want to overbuild the mechanical attachment.
  9. 4" Carbon Fiber Tube as Boom

    @mowgli, thanks for the dimensions. I'll assume that as long as I meet or exceed, it will be okay for an F-27, even if the weave isn't optimal. I really liked the detailed pics, http://members.ziggo.nl/arno.molenaar/thrillseeker/fotos/giek14.jpg gives me an idea for how to do the end with a dyneema strop, instead of installing a rotating joint. I think it would be cool if I could just put a dyneema loop around the boom and let it slide as the boom spins. Maybe have it in some kind of built up "groove", so it can't slide forwards or backwards. Or maybe instead of a loop, I could just use a really long soft-shackle. @tomtriad, I already have an aluminum bowsprit, as well as a handy supply of smaller CF tubes which I think could be (mis)appropriated for a replacement bowsprit. In a similar vein to the boom, not for speed so much as for fun.
  10. 4" Carbon Fiber Tube as Boom

    @Mizzmo, thanks for the input. Since you've got an F-boat, you probably have the same tear-drop shaped boom as I do, which could be that shape because of aerodynamics, or simply because that's the right way to make a groove for a bolt-footed sail. I suspect it's the latter, and I'm happy to see that you agree it's not the former. Class legality isn't a particular motivator. PHRF seems to be the rule up here with NEMA, and I prefer to use my boat for weekend destination sails. Regarding the outhaul, I was very impressed with the simple outhaul system in the RS400. The sail is held to the boom with velcro (for the F27 I might have to up the spec to a dyneema strop). The outhaul line comes out of a sheeve on the end of the boom, goes through the clew, and then goes to a notch on the opposite side of the boom. A button knot keeps the end of the outhaul wedged firmly in the notch, giving a nice 2:1 ratio before starting with the internals. Which is good, because I always wished I had more leverage on my outhaul, I can only ever tighten it when directly head to wind. I'll build a cascaded purchase system out of aluminum climbing rings and dyneema. This worked incredibly well on my sidestay tensioners, which I increased to 16:1 (I know that friction takes a chunk, but it still works out well) and can now adjust from the cockpit with a simple pull, instead of needing beefy ropes leading up to the winch. I'll hold the tack to the main in a similar way to the outhaul, with a velcro (or dyneema) strap. I might use an additional velcro strap to hold the tack to the mast as well. For the gooseneck, I will visit a local boat scrapyard to get some donor parts so that I don't have to take apart my main boom (hey, maybe the next guy after me *does* want the boat to be class legal!). If it works easily, I'll just stick with it. And if it doesn't, there are several 3D printing companies around here where I can go to get the right part made. But I think the gooseneck will be pretty easy. As you point out, the boom end-fitting is similar. In fact, that one should be even easier, because it'll be enough to lathe up a shouldered UHMWPE and then plate it with a bit of CF for toughness.
  11. 4" Carbon Fiber Tube as Boom

    Fair questions. I guess in the interest of brevity, I didn't go into the full details. My background is in mechanical engineering, and I work in drones/aviation so am used to CF and its failure modes. But making CF sailboat parts is new to me and I want to be alert to the things that one just don't think about when starting something new. I think the unresolved question in my mind is aerodynamics and windage. Answering your questions for completeness: The CF tube is the good section from a broken research boat. I don't know much about the CF tube's construction, and I haven't measured the wall thickness. But you can look at it and tell right away it's "waaaay too strong". If I were doing racing parts, or even marginally optimized parts, I would go for much smaller. Glowboat, an F24, is very happy with a reinforced windsurfing mast as a boom. And the extra sail area on the F27 is very small in comparison to the extra CF vs windsurfing masts, so the anecdotal experience points toward likelihood of success. How are the coordinate axes defined? Is x forward (aviation) or athwarships? I suspect it's athwartships, but it's good to confirm. The mainsheet on an F27 is at the end of the boom. Totally okay with possibly blowing up. I've still got a jib, right?
  12. 4" Carbon Fiber Tube as Boom

    I have the opportunity to get a 4" x 15' CF tube and I'm contemplating replacing my stock F27 boom with it. For really no good reason, other than that it will be a fun project. I can sell it as worthwhile because it will save some weight on the trimaran, but really I just want to have some fun and learn something in the process. I know that a 4" tube would absolutely ruin the airflow if it were used in a vertical part, e.g. the mast, but does it make a big difference if used for the boom? Since its horizontal it would only marginally increase the wetted area for airflow in a part of the boat which sees relatively low wind velocities. I can't think of any big reason why this would be a bad idea, but maybe I'm missing something?
  13. Gear Bags for Carry On

    Realizing I'm hijacking @sadug's thread here a little, but here goes... I roll it up from toe to head. I have the Stohlquist Shift, http://www.stohlquist.com/apparel/drysuits/shift.html, which I'm really happy with. It's much easier to get into and out of than others I've tried. The only thing I don't quite like about it is that the elastic waistband makes whatever I'm wearing underneath hike up, and of course there's no easy way to pull it back down once you're cocooned up. But the zipper runs a very different route from a typical suit, so I've never it get in the way when rolling.
  14. Gear Bags for Carry On

    Just stepped off the delivery yesterday; I had my drysuit, my SeaRacer boots, neoprene pants, neoprene jacket, hoodie, thermal underwear, changes of day clothes, plus some elex. Still had space left for more, although by then it was getting pretty heavy. It's also brilliant for airplanes, where you can either choose to jam the whole thing in to the overhead bin, or unzip bit by bit to fit in whatever bin compartments are free.
  15. Gear Bags for Carry On

    The straps aren't detachable, but they do nestle in between the red backpack and the blue central bag. The backpack is too on the small size to be comfortable for long walks, but it definitely serves in a pinch. The fanny pack is a great place for keys, wallet, phone, and passport as well, and it's very nice to be able to detach it from the main bag when I go offboard and not worry if I'm forgetting anything, and to know when I get back that it goes in its place and isn't getting forgotten when I leave.