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PostPosted: Fri Jan 25, 2013 9:51 am 
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Joined: Tue May 18, 2010 10:34 am
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Location: Portland, Texas
Yesterday I was sailing the Oasis from St. Charles Bay to Goose Island in Texas. It was a perfect day with the wind at about 10 to 15 mph out of the S.E. On the return trip to the launch site I had been on a starboard tack run. As I eased the kayak into a direct downwind run the Oasis started rocking violently back and forth. I thought I was going to get bucked out of the boat. It had been a while but I had forgotten a basic rule about downwind sailing in a small boat with only one sail. The rule is : Don't sail directly down wind(DDW) in a small single sail boat. (I don't think this rule is written anywhere). Always keep the boat on a little bit on a tack to prevent this type of violent rocking. This type of behavior doesn't happen in all boats. I've never had it happen in a Sunfish or a Snark with their lateen sails nor have I had it happen in sloop rigged boats or keel boats. I have however had it happen in single sail Lasers, my old Cape Dory cat boat and as of yesterday my Oasis.
What occurs is this; in a DDW situation the sail wants to act like a flag flapping in the breeze. Since the outside of the sail is basically held in place by the mainsheet, the energy is transferred to the mast in a lateral fashion pulling the boat to leeward. When the sail is far enough over it dumps the force and the boat responds by rocking to windward. Then the sail fills up with pressure and the event repeats itself. This happens really fast and if you're like me you feel like you might do you know what in your pants. Don't do that. You have two options. The first is to turn the boat back into a slight tack and the rocking will stop. A second option is to complete a jive by pulling in on the sheet and changing the tack to the other side of the stern. I usually take the first option to allow time to get my bearings and then complete the jive. By the way the rest of my trip was uneventful and wonderful. This I can tell you as I get well into my sixties, I'm getting too old for white knuckle sailing. I'll try to play it safer in the future so I don't self induce a heart attack.

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Roger
2010 Oasis
Lucie Belle


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PostPosted: Fri Jan 25, 2013 10:22 am 
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Joined: Tue May 27, 2003 12:44 pm
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Location: Oceanside, California
Yep... commonly called a "Death Roll". :)

That is associated to single hull craft with soft sails... mostly related to spinnaker use where the sail is not fully supported.

Oscillation... starts slowly and increases with each roll if corrective measures are not taken. Usually heading up just a bit or using the paddle to hold the sail out will stop it.

Normally only an issue when you are trying to maintain a specific downwind course... like when racing or following a narrow channel or avoiding obstacles. It's easy to correct by course changes.

Note: The downwind turn across the wind direction is called "Gybe" or "Jibe". http://en.wikipedia.org/wiki/Jibe

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Matt Miller
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PostPosted: Fri Jan 25, 2013 12:02 pm 
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Joined: Tue May 18, 2010 10:34 am
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Location: Portland, Texas
Thanks for the correction, Matt. After all when you get old and deaf like me a b or a v they all sound about the same. By the way, that was a great article reference you included. Should be must reading for all of us. :)

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Roger
2010 Oasis
Lucie Belle


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PostPosted: Sat Feb 02, 2013 7:28 pm 
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Joined: Sun Aug 12, 2007 5:17 pm
Posts: 519
Location: Auckland NZ
There is a solution which can be easily and cheaply implemented on Hobie kayaks and that is to add a "boom batten" to the foot of the sail (this idea has been well-documented on this forum). This has the effect of converting the sail from completely loose footed (which has a tendency to fill and collapse, fill and collapse when sailing due downwind - thus causing the rolling) to a sail which has enough stiffness in its foot to hold the sail open and prevent the sail from collapsing.

Following the advice of others my boom batten is a length of fibreglass rod taken from a Roman blind (I think that is what they call them - anyway it is a circular fibreglass rod a few mm in diameter and very flexible). I cut it to the right length and glued an end cap to one end.

The boom batten is then inserted in the sleeve along the bottom of the sail window. To do this you have to make a small hole in the sleeve material in the vicinity of the clew to allow you to poke the batten in, then it will slide all the way into the sleeve right the way down to the tack of the sail beside the mast (with the end-cap preventing the batten from becoming completely inserted and 'lost' inside the sleeve). I made the hole in the sleeve of my sail with the tip of a small hot soldering iron - just enough to make a hole of the right size and melt the fibres to prevent further fraying (and the hole in no way detracts from the sail's structural integrity or performance - you would hardly know it is there)

I keep the boom batten inside the boat and accessible through the centre hatch. When I want to sail dead down wind I get the batten out of the and slide it into the (already deployed) sail. In fact the batten works well for all near down wind sailing as well as dead downwind sailing, all you have to do is remember to take it out & stow it before you try rolling the sail up !


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PostPosted: Sun Feb 03, 2013 12:57 pm 
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Joined: Fri Sep 21, 2012 4:55 pm
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Location: Virginia - USA
I have a Oasis I bought last fall and plan on getting the sail in April and trying it out. What are the general characteristics of sailing an Oasis with two people...should I get the stabilizers before I try it for the first time with my wife? :shock: Bob Northern VA

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Bob
2013 Oasis w/ Sail
Virginia


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PostPosted: Sun Feb 03, 2013 3:58 pm 
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Location: Auckland NZ
Bob,

kinda depends what wind strength (and water temperature) you intend to go out in. Personally I dislike the 'locked flat' feeling of a trimaran and really enjoy the heeling and the challenge of sailing a miniature keelboat to its best. So if I were you I would try without the outriggers first.

HOWEVER! I only sail in light to moderate wind conditions in relatively flat water and the water here in Auckland is never excruciatingly cold (in the event that I take an unexpected ducking).

I sail an Adventure and it is a somewhat different sailing proposition than a fully loaded Oasis - basically you have a lot more weight and resistance to overcome with an Oasis with 2 on board so for a given wind speed the sailing performance will be less than for an Adventure. Given this fact the sailing performance in light winds may feel rather pedestrian - which may tempt you to go out in stronger breezes so as to get a more enjoyable sailing experience.

2-up the Oasis has substantially more ballast than the Adventure so it should be able to cope perfectly OK with greater wind strengths but of course this depends on exactly how strong the wind is, exactly how well the crew can sail the boat, and, I guess, exactly what the implications of getting it wrong are. It is all about risk profile: if t'wife has a sense of humour then she might be OK about getting her hair wet unexpectedly; if not then you might be willing to give her the required listening to in the event that you tip her in; on the other hand if the pair of you are likely to freeze to death or get eaten by sharks that is altogether a different set of risks (or maybe it is not :lol: ).

Subject to the above observations I would give it a go w/o stabilisers (betcha don't still have them on your bike!) and take it gently as you learn the ropes before you make up your mind. You should be able to single-hand it quite effectively too if you add some ballast up front.


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PostPosted: Thu Feb 07, 2013 8:36 am 
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Location: Portland, Texas
Sorry that it took me so long to respond guys, I haven't gotton into this site much over the past few days.

1st - Stobbo, I really like your idea about the plastic rod adding a flexible boom in the sleeve in the bottom of the sail. You got me thinking. Since there is a grommet for the sheet and one for the downhaul bungee at the luff side of the foot one could easily use an expanding shower curtain rod with small holes drilled in it at each end. Then a small diameter cord could be run through the holes and the grommets to hold the rod in place while sailing downwind. There must be a million ways to simply create a temporary boom for this purpose. You could also create something that would act like a whisker pole for a jib. Hmmmmmmmmmm! It's just a matter of putting one's brain in gear.

2nd - Bob, I'm with Stobbo on this one. I'd start without the Amas first. I had been contemplating getting a set for my Oasis until I went out with a guy who had purchased a set for his Revolution. They were OK until we went into shallow water where he had to paddle. At that point they were really in the way. In sailing my Oasis when I get to the point where the wind is so strong that sailing becomes dangerous I usually furl the sail and head for shore. By that time even being in the boat has ceased to be fun so I just call it quits. But then again I'm really just an overgrown wimp. :oops:

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Roger
2010 Oasis
Lucie Belle


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PostPosted: Thu Feb 07, 2013 4:16 pm 
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Joined: Fri Sep 21, 2012 4:55 pm
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Location: Virginia - USA
Good advice from both of you and yes, I plan a very small start...warm day, warm water ,calm lake, light winds, No SHARKS...just to try it out. So I will not buy the akas to start out and go from there. This will be my first sailing adventure... :-) And yes, we both have a sense of humor and can survive a dunking! Bob

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Bob
2013 Oasis w/ Sail
Virginia


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PostPosted: Fri Feb 08, 2013 12:26 pm 
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Joined: Sun Aug 12, 2007 5:17 pm
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Location: Auckland NZ
RPL

research the boom batten on these forums before cutting any holes!

The solution I implemented (on the advice of others here) is dead simple, really non-invasive, dead cheap and really effective.

The rod can be obtained from blind/curtain stores I believe (I found mine lying on top of a curtain fitting in my house where someone had fitted a blind and it is the same as what has been sewn into the blind to hold its shape) - it is whitish, only a few mm in diameter and highly flexible. To make the end cap I glued a short length of plastic tubing onto the end of the rod.

Personally I don't think you really need much more than this.


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PostPosted: Sun Feb 10, 2013 7:26 am 
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Location: Portland, Texas
Stobbo,
I definately agree! Although there can be many solutions to any single issue, generally speaking simplicity is beauty and the right way to go. This is especially true with anything dealing with sailing. Complexity creates more problems than it solves! Happy Sunday to you! Or is it Monday over there? :?

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Roger
2010 Oasis
Lucie Belle


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