tag:blogger.com,1999:blog-3580987459140037495.post6199915378843662065..comments2024-03-18T10:29:20.125-08:00Comments on TriloBoat Talk: Mast Overboard!Dave Zhttp://www.blogger.com/profile/13241033623115158564noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-3580987459140037495.post-68646203541936872812013-11-12T15:13:02.935-09:002013-11-12T15:13:02.935-09:00(Conversation with JOHN, continued):
J: A count...(Conversation with JOHN, continued):<br /><br />J: A counter argument to catamarans needing stronger masts was made by Pete Hill, who has now made two junk-rigged catamarans. He noted that monohulls are just as stiff fore-and-aft as catamarans are stiff amidships, so if a free-standing monohull mast can withstand a wind blast from astern, then certainly that same mast will be sufficient on a similarly-sized catamaran. The only question I had to that argument was the fact that both cats and monos are made to slide forwards relatively easily (and thus may relieve some of the wind pressure), but only monos can easily heel to relieve wind pressure. So it still may be true that cats need stronger free-standing masts than monos?<br /><br />D: Interesting hypothesis from Pete (who has vastly more experience than I), but I'd agree with your analysis.<br /><br />Anything that 'gives' before a force absorbs some of it. Quite a lot of it, actually. A boxer who merely ticks his opponent's glove on it's way in has robbed it of its heavy hitting power.<br /><br /> It's one of the main arguments for free standing rig that it can absorb so much energy by flexing. A stayed rig transmits nearly the full force to much more localized points (e.g., chainplates and mast-step).<br /><br />So I'd think that accelerating the boat forward would be quite a cushion, whereas heeling mounts tremendous righting arm in opposition.<br /><br />Dave ZDave Zhttps://www.blogger.com/profile/13241033623115158564noreply@blogger.comtag:blogger.com,1999:blog-3580987459140037495.post-74863154734181420552013-11-12T15:11:58.511-09:002013-11-12T15:11:58.511-09:00(Conversation with JOHN):
Hi John,
J: I'm ...(Conversation with JOHN):<br /><br />Hi John,<br /><br />J: I'm trying to understand how you sailed SLACKTIDE backwards using just the mizzen sail. Did you twist the sail around the mast such that the luff was again the leading edge of the sail (with the stern now the bow)?<br /><br />D: Yes, this is the way we did it. The extra line (single) was lead to the the end of the boom as a sheet, since the real sheets would have taken too long to shift. As we sailed deep reefed, we didn't need the extra purchase.<br /><br />If we would have had to 'jibe', we would have let it stream down wind (normal position, and back around the 'forward' side of the mast. If we jibed normally (relative to our 'bow'), we'd end up wraping the haulyard tight around the mast, going the wrong way.<br /><br /> <br /><br />J: Or did you attach a (single?) line to the lowest batten at the luff end, and call the previous luff edge the new leech?<br /><br />D: This wouldn't work out... the proportion of sail on each side of the mast is very unequal (85%/15%, in our case). Off the wind you'd have to sheet the larger portion, or it would stream downwind, levering the other upwind (against the sheet, which goes slack in compression).<br /><br />If one were sailing ON the wind, it would be possible, but inadvisable. The sheet would be working in tension, but the leverage of the unsheeted portion would set up large stresses in the battens.<br /> <br /><br />J: How did you control the sheet in the new location? Threaded through blocks to winches?<br /><br />D: We just lead it straight aft and tied off on one of the tabernacle struts. It didn't take any tending until we were clear. Then we fooled around a little bit, experimenting, but with the mast and sail still dragging, it was hard to tell what worked well. May try it again, down the road, under more controlled circumstances!<br /><br /> <br />J: Some say that a free-standing mast on a catamaran needs to be stronger than a free-standing mast on a monohull, because a catamaran won't heel (very much) and spill hard wind gusts like a monohull will. Since your Triloboats (and maybe LUNA too) are initially stiffer than many monohulls do you think that SLACKTIDE needs a stronger mast than a similarly-sized round-bilged keeled monohull?<br /><br />D: Definitely yes, though Van Loan's formula for calculating mast diameter factors in beam. In otherwords, both types would use the same formula, but generate different numbers.<br /><br />Still, with any rule-of-thumb, debriefing is important in the attempt to learn how that rule applies to specific situations.<br /><br />The rule seems to have been adequate so long as the mast is in good condition.<br /><br />In both our dismastings, there were problems with the masts. The first was undersized (didn't comply with the rules) and had poor annular ring pattern (wide spacing = lowered strength). The second had rot.<br /><br />Nevertheless, both had sailed stoutly through many heavy blows, despite our tendency to reef late. I believe this confirms the rule.<br /><br />Going heavier would grant an extra margin of safety, but would be heavier and stiffer (less able to flex before a gust). Masts in good condition, sized according to a successful formula would still be my choice.<br /> <br /><br />Continued below...<br /><br />Dave Zhttps://www.blogger.com/profile/13241033623115158564noreply@blogger.comtag:blogger.com,1999:blog-3580987459140037495.post-27388632153734549362013-11-11T14:27:06.761-09:002013-11-11T14:27:06.761-09:00One of the things this episode illustrates is the ...One of the things this episode illustrates is the benefits of the fail-safer rule-of-thumb.<br /><br />Free standing rig may have gone down a bit sooner, in these instances, than stayed rig, but this one was an accident-in-wait. Sooner or later (unless the rot began to show itself), it was going down.<br /><br />A (fully) stayed rig would have gone down harder, and likely on-board (dangerous). Response would have been much harder, both initially, for 'jury rig' (loss of only one panel's sail area) and replacement. We sailed about another 100n.miles, upwind and down, blow high blow low under jury before replacing (admittedly reefing quite a bit early to spare the suspect mast)!<br /><br />Free standing rig also allowed the aft sail to be used as a foresail. We were able to work slightly to windward (close reach) under it. Though that ability wasn't crucial in this situation, it's fine to know that it's in the bag of tricks!<br /><br />Split rig (sails set on two masts) affords the redundancy that let us sail off the wind WITHOUT a jury rig. This kept us off a lee shore, and even allowed us to relocate to a calm anchorage for jury rigging.<br /><br />Off-centerboards (leeboard-like) help keep our underwater shape nearly symmetrical (vs say, a 3/4, deep keel). This makes it relatively easy to reverse sail, and even abetted that close reach I mentioned.<br /><br />Our kick-up rudder and yuloh didn't play a part this time, but when sailing reversed, one could pull up the rudder and move the yuloh 'aft' to the true bow... using a corner post for a fulcrum, one could steer from there.<br /><br />If we'd not managed to clear the shore, shoal draft keeps the bottom clear longer (increasing chances of hooking a shoaling bottom without grounding). In case of contact, our copper plate bottom holds damage at bay, to some extent. In a worst case, we're likely able to jump or wade ashore, rather than swim.<br /><br />All these features contribute to a fail-safer approach that increases options and confidence in times of trouble.<br /><br />Dave Z<br /><br />Dave Zhttps://www.blogger.com/profile/13241033623115158564noreply@blogger.comtag:blogger.com,1999:blog-3580987459140037495.post-68090927150366293802013-11-11T02:18:49.497-09:002013-11-11T02:18:49.497-09:00Oh indeed! It's easy to sound brave after the ...Oh indeed! It's easy to sound brave after the event. When my boat decided to move down and sideways (only a couple of inches) the other day when I was lowering it, it nevertheless made a great thumping noise...I went weak at the knees, even though I was nowhere too close for danger. So yes, I learned something else at that moment... I hope I'll remember it. Don't tell my wife though... :)Joelhttps://www.blogger.com/profile/10844967794207697583noreply@blogger.comtag:blogger.com,1999:blog-3580987459140037495.post-36803805442712855362013-11-10T13:59:09.301-09:002013-11-10T13:59:09.301-09:00Hi Joel,
You SAID it! Reading back over the post,...Hi Joel,<br /><br />You SAID it! Reading back over the post, I see I neglected to mention the shaky knees and cotton mouth.<br /><br />There are times and places this event would have been very bad, indeed. Losing a mast is no inconsiderable accident. The domino effect could take that all the way to catastrophic.<br /><br />In emergencies, it's important to remain calm, alert and flexible. Panic lurks around the corners. It's a fine line between down-playing the real dangers (mis-assessing the situation), and losing one's self in them.<br /><br />But all's well that ends well... and hopefully we learned something that'll help us avoid another one!<br /><br />Dave ZDave Zhttps://www.blogger.com/profile/13241033623115158564noreply@blogger.comtag:blogger.com,1999:blog-3580987459140037495.post-40491621309781861192013-11-09T23:17:50.919-09:002013-11-09T23:17:50.919-09:00Only a temporary delay, no-one hurt, that's th...Only a temporary delay, no-one hurt, that's the main thing. Joelhttps://www.blogger.com/profile/10844967794207697583noreply@blogger.com