Took the Java out for a paddle with my girlfriend last week. We put-in on the slipway at the fishing harbour in Hermanus, Western Cape (South Africa) - whale country. A 15-knot south-easter was blowing and there was quite a bit of chop beyond the breakwater. A couple of strokes beyond the breakwater, we decided that conditions were not great for a continued coastal paddle and turned about to head back to the harbour. A few strokes downwind and turning slightly abeam a following sea, we went over, easy as pie. The nice thing about the Java is that it is a doddle to get back on (very much unlike a waterlogged Klepper double), so we were back on board in a few seconds. But it was a salient lesson in boat stability and usability. While the Java can take a second paddler comfortably (and I'm 6'3"), it alters the stability of the sit-on-top quite dramatically. My question: is this purely a function of waterline length coupled with a high centre of gravity? I would guess that Feathercraft's Gemini (a proper double) would be a more stable boat given its greater waterline length, but I would appreciate any thoughts on this issue. Wishing you all a paddle-happy 2012! Paul This message may contain information which is confidential, private or privileged in nature and subject to legal privilege. If you are not the intended recipient, you may not peruse, use, disseminate, distribute or copy this message or file which is attached to this message. If you have received this message in error, please notify the sender immediately by e-mail, facsimile or telephone and thereafter return and/or destroy the original message. The sender cannot assure that the integrity of this communication has been maintained nor that it is free of errors, viruses, interception or interference. The sender accepts no liability of whatever nature for any loss, liability, damage or expense resulting directly or indirectly from the access of any files which are attached to this message. For a detailed disclaimer please visit <http://www.avusa.co.za/AvusaEmailDisclaimer.pdf> *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Interesting question Paul. I've paddled a Feathercraft Java for years and had the same sensation, but until your note I thought it was just my imagination. I believe it has to do with changing the rocker of the hull by distributing the weight closer to both ends. I noticed that if I inflate it with more pressure for a more rigid and stable shape, it seems to stabilize it a little. Overall I still love the Java and think its particular quick-assembly hybrid inflatable over durable frame design coupled with its single-double flexibility was of the great steps in collapsible kayak design. Happy New Year, Al Vazquez KayakGuide.com Places to Paddle Closewaters LLC SKYPE: KayakGuide.com Florida, USA On Dec 30, 2011, at 3:46 AM, Paul Ash wrote: > But it was a salient lesson in boat stability and usability. While the Java can take a second paddler comfortably (and I'm 6'3"), it alters the stability of the sit-on-top quite dramatically. > > My question: is this purely a function of waterline length coupled with a high centre of gravity? I would guess that Feathercraft's Gemini (a proper double) would be a more stable boat given its greater waterline length, but I would appreciate any thoughts on this issue. > > Wishing you all a paddle-happy 2012! > > Paul *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Paul Ash AshP_at_sundaytimes.co.za asked: >>>>>But it was a salient lesson in boat stability and usability. While the Java can take a second paddler comfortably (and I'm 6'3"), it alters the stability of the sit-on-top quite dramatically. My question: is this purely a function of waterline length coupled with a high centre of gravity? I would guess that Feathercraft's Gemini (a proper double) would be a more stable boat given its greater waterline length, but I would appreciate any thoughts on this issue.<<<<<< As long as the center of buoyancy moves to the side further than the center of gravity the kayak will right itself. Once the center of gravity moves out further to the side than the center of buoyancy the kayak capsizes. Therefore, hull width and center of gravity height are the main factors determining a hulls stability. The shape of the hull underwater and the length of the kayak that the kayak's maximum width is carried along the length of the hull are also factors. The longer the kayak's width stays near maximum the more the center of buoyancy will shift when leaned. The relatively blunt ended Java benefits from this factor. More rounded hulls are less stable because they don't move the center of buoyancy of the leaned hull to the side as quickly as a flatter hull does. In fact, a perfectly cylindrical hull shape (sunk to half its width) would have no static stability at all because no buoyancy shifts to the side when it is being leaned. There is another reason that double kayaks are usually much wider than single kayaks. That is because doubles have two independent paddlers so it is much harder to anticipate what you need to do next to make compensations to actively keep that center of gravity inside the cone of stability because you can't always anticipate just how and when the other paddler will react. Sometimes the two paddlers balance each other out, but it is also likely they will sometimes move together in the wrong way, or even fight each other unknowingly, thus intensifying the other paddler's reaction. More paddling time together with your paddling partner will help here. So with the Java you have a kayak that already has a relatively high center of gravity (like other sit-on-tops, in order to make it self-draining). As a single its 27.5" width is adequate for normal sized paddlers. Even though a big paddler would sink the kayak deeper in the water (lowering the CG some), unless their body weight is carried very low, the center of gravity will still likely be higher when compared a lighter single paddler aboard the same kayak (and any weight shift the same distance to the side will have more effect on the kayak's stability when the weight shifted that distance is larger). Two paddlers paddling in the same kayak will have about the same effect on stability as putting a bigger paddler in it that weighs as much as both the paddlers (given their centers of gravity work out the same). However, the double paddlers aren't likely to be as coordinated in actively keeping their center of gravity inside the cone of stability as the heavy single paddler will be. The smaller Feathercraft Uno sit-on-top is 30" wide. It floated so high that I felt I had to reach way down to the water to paddle it and it also emphasized initial stability so much I found it hard to lean to turn (and therefore also much harder to balance it when I had it leaned because I had to move my center of gravity over so far to one side to get it up on edge I was teetering on the brink). The 2.5" narrower Java leaned to turn rather nicely so was the only sit-on-top Feathercraft we sold. Although I don't think I ever paddled one, the 30" wide Feathercraft Gemini sit-on-top double is going to be much more stable as a double than the Java is unless the CG is way higher. A three inch difference in a kayak's width is huge when considering stability. So is a 1" change in CG. I suspect having the Java as fully inflated as possible will help with the stability because it will act more as a unit (like a hard shell kayak). But mainly it will shift the center of buoyancy over better than with a softer side tube (that is being collapsed some by the water pressure it is being pushed into when leaned). *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt, thank you very much for the detailed reply. I had never given much thought to the science of paddling. Which, you could say, is one reason for the unexpected swims. Still hot here (35 degrees C most days) so aim to do 20 days on the water before the leaves turn. Cheers and thanks, Paul >>>>>>I suspect having the Java as fully inflated as possible will help with the stability because it will act more as a unit (like a hard shell kayak). But mainly it will shift the center of buoyancy over better than with a softer side tube (that is being collapsed some by the water pressure it is being pushed into when leaned). This message may contain information which is confidential, private or privileged in nature and subject to legal privilege. If you are not the intended recipient, you may not peruse, use, disseminate, distribute or copy this message or file which is attached to this message. If you have received this message in error, please notify the sender immediately by e-mail, facsimile or telephone and thereafter return and/or destroy the original message. The sender cannot assure that the integrity of this communication has been maintained nor that it is free of errors, viruses, interception or interference. The sender accepts no liability of whatever nature for any loss, liability, damage or expense resulting directly or indirectly from the access of any files which are attached to this message. For a detailed disclaimer please visit <http://www.avusa.co.za/AvusaEmailDisclaimer.pdf> *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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