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 Post subject: Soloing the Oasis Tandem
PostPosted: Sun Sep 23, 2007 11:31 pm 
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We tend to think of tandems as two person machines, but, in fact, they also make an excellent solo kayak, with good performance and tons of room for just about anything.

Saturday I used the Oasis on an annual trash pick-up excursion at a local wildlife estuary on one of the coastal lagoons. The tandem worked out perfectly as a trash barge. Here, assigned as a rear guide, the Oasis is hauling some of our "loot" while also towing a straggling paddler.
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For this, I was using 15 lb. of ballast in the bow and (borrowing Stringy's idea) a well plug filled with 12 lb. of lead and sand. Keeping the ballast low and forward as much as possible requires a lot less, so I used the front hatch to slide it all the way forward.
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I've had the tandem out many times solo, but today for a change of pace, I took the Oasis out just to see how it performs solo compared with some of the other single Hobie kayaks. I added another 28 lb. of ballast that sits in the front drivewell (no trash this time). The three weights, totaling 55 lb, look like this:
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This gives the boat a reasonable compromise between pushing a lot of dead weight and having the bow sky high. There seems to be a point of diminishing returns.
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So, what kind of performance does the Oasis provide solo? Primary stability is about the same, but with the ballast low, secondary stability is outstanding. Turning (using the sailing rudder with winglet) is crisp and tight, especially with the fins down. Acceleration is somewhat slower with the extra weight, but cruising speed is quite good. This has to be the driest ride in the Hobie fleet!

Using turbofins (naturally), in exactly one hour, the ballasted Oasis went 5.01 (GPS) miles. For me, this is almost as fast (within .1 mph) as the Revo and about .2 mph faster than the new Outback (in comparable one hour cruises), and is actually faster than when my wife and I go out together. Not bad at all! This goes to show that while weight may be a big deal on land, it doesn't really mean much on the water in actual use (within reason). Having the boat sitting well on the water is much more important.

Sprinting, the Oasis got to 6.6 mph solo. Paddling with the rudder down, tracking was very good and speed maxed out at 5.0 mph. With the extra weight, acceleration for boat wakes was a little slower, but once aboard the wakes, the rides were excellent. In two rides today I got up to 7.5 and 8.6 mph (GPS).
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The Oasis is just as much fun to operate solo as the singles. It's reasonably fast and agile, yet it has gobs of space forward for kids, dogs, trash, gear, or even a large custom fish storage well for Aloha Dan's pelagics!

Tandem or solo, if you're looking for just one boat that can do everything well, the Oasis is as versatile a kayak as you'll find!

PS: Regarding ballast, Stringy reports using about a 70 lb. bag of water (doesn't have to be carried, just dumped out) and an additional 20 lb. in his well plug, so there's lots of other great ideas. There's also some variation in thought as to what constitutes adequate ballast. In any event, the use of ballast brings out the excellent solo performance in the Oasis.


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 Post subject:
PostPosted: Mon Sep 24, 2007 8:36 pm 
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Posts: 2007
Location: Central Coast NSW Australia
RR-Thanks for the great review. It was interesting to hear from someone with so much experience with the other Hobie's. My only experience has been with the tandem, which I have had for 7 months now, and I regularly use it solo. I can support all that you have stated. When properly ballasted the tandem makes a great single kayak. The difference is especially noticed when conditions get rough. It cuts through chop and even waves so much better with much less hull slap. The stability is excellent.
Here is a picture of my mod to the drivewell plug. A 10kg (22lb?) bag of lead shot fits almost perfectly in the plug.
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The 40 litre dry bag when filled with water sits snug in the front footwell. It is easy to fill at the boatramp and empty at my destination.
Image

I have to wheel the kayak about 600m to get to work so I need the cart. The disadvantage of the tandem is that it has no dedicated storage for it. I used to carry it behind me but it interferes with the sail. I have found the following works well and can even be used with a front passenger pedalling.
Image
I cut a padeye in half and fitted both halves under the front hatch screws for the bungee cord which goes through an eye fitted to the bottom mounting screw. The long bungee is great for keeping hold of the cart when launching.
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I actually used an eye bolt with an eye nut to replace the lower hatch screw. The internal eye gives you something to clip things to preventing them from getting lost in the hull! I have added these eyes to the other two hatches as well.
Ultimately I would like to add more ballast into the front hatch. Getting the weight further forward does mean having to use less to keep the hull in the water. It is difficult to get it in there though. The water ballast is great for me as I can empty it easily. Maybe a bladder with a pump system for easy filling/draining!!!!


Last edited by stringy on Wed Oct 10, 2007 10:21 pm, edited 1 time in total.

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 Post subject:
PostPosted: Wed Sep 26, 2007 7:41 am 
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Location: sacramento california
Hi-ya going Roadie ! :)
Kepnutz


Last edited by kepnutz on Tue Sep 16, 2008 4:05 pm, edited 1 time in total.

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 Post subject:
PostPosted: Wed Oct 10, 2007 8:41 am 
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I'm reading this thread with great interest, as I have an Outfitter rigged for fishing and 90% of my trips are solo. I regularly range a mile or two off the coast here in Santa Barbara, CA and have had problems with the "hull slap" mentioned in this thread.

I like this idea of adding shot to the front Mirage Plug, but I am concerned about the extra stress this might put on the front drive well. It looks like the mirage plug rests its weight entirely on the two "pins" that locate in the locking mechanisms. This means that the mass of 10kgs of shot in the drive plug is being "focused" on two relatively tiny mounting points, which were certainly not designed for this purpose... Just wondering if anyone has had problems with this snapping off, or any other sorts of deformation of the mounting points...


Thanks in advance

-Brent

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 Post subject:
PostPosted: Wed Oct 10, 2007 6:19 pm 
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Location: Central Coast NSW Australia
I like this idea of adding shot to the front Mirage Plug, but I am concerned about the extra stress this might put on the front drive well. It looks like the mirage plug rests its weight entirely on the two "pins" that locate in the locking mechanisms.

I actually came up with the idea of filling the drivewell plug for ballast after finding one had filled up with water when we were on our first shallow freshwater creek trip without the mirage drives in. One of the locating side 'pins' had been split- probably from new. Anyway I was surprised to find how heavy it was when removing it. Because I use my tandem solo I added a bung plug to the drivewell plug and filled it with water. I realised more weight was needed and used the lead shot. I have beeen using the weighted driveplug for 5 months now and there is no stress to the drivewell. The weight is actually carried by the front and rear slots which are designed to handle the stress of pedaling. The locating pins don't bear much of the weight at all. As the plug is submerged it's not really subject to much stress anyway. I have had no problems so far- apart from distorting the hollow plastic pins by overtightening the cam bolts the first couple of times. The plug only needs to be snug under the cambolts- not tight like the drive. It would be interesting to know what pressures a tightened down mirage drive is exerting on the drivewell. I reckon it would be a lot more than 10kg.


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 Post subject:
PostPosted: Thu Oct 11, 2007 10:24 pm 
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Stringy, nice pics -- I especially like your cart storage idea.

After seeing how much weight you were packing into that well plug, I became inspired to make my weights more efficient. I went to lead shot also for the plug and was able to double the previous weight to 24 lb. (including a slurry of tile "thin-set" to fill the tiny gaps and bind the contents). Then I melted up some old lead wheel weights into 3 1/2 empty vegetable cans, cut the cans away, and dropped the lead into a 15" length of 3" drain pipe. This pipe, 3" shorter than the older one, was now 31 lb. instead of 15.

Image

Thus, with just two weights now totaling 55 lb, this would move the center of gravity lower and more forward while eliminating the 3rd ballast.. I also streamlined the hull bottom some and re-tested for speed. In both measures, I picked up about .1 MPH (mostly due to streamlining I suspect).

I dug up some pics for comparison. Here's what a similar Oasis looks like solo with no ballast:
Image

Here's how it looks with two passengers:
Image


And here it is solo with my newest ballast:
Image

Sbsyncro, I agree with stringy that the plug and drive well should handle the weight. Here, the well is supporting all 55 lb. of ballast. Considering the punishment it takes from the legs, it's got to be quite strong.
Image

Kep, you might want to try this for when your wife's out of town! 8)


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 Post subject:
PostPosted: Fri Oct 12, 2007 8:16 am 
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Great posts and great ideas - I think I might have to try this out. Now the only remaining problem is how to transport all this weight to the beach. The Outfitter is already a monster to handle solo, and I often launch from beaches where a 100 yard scramble down goat paths to the beach is not uncommon. Looks like instead of two or three trips down, it will now be three or four! ;-)

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 Post subject:
PostPosted: Fri Oct 12, 2007 5:16 pm 
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Location: Central Coast NSW Australia
RR- Using the tile set to fill the spaces between the shot is a great idea and would prevent water leaking in from any damaged pins. I originally thought of using the plastic plug to make a plaster mould for casting lead with a stainless tube for the locating pins but decided the lead on plastic may damage the drivewell.
Your pics clearly show the difference that ballast makes when soloing the tandem.

These pics from Hobie reinforce that:
Image

Image
With this much boat out of the water all you really have is a sport or outback with terrible hull slap and windage!

Here is how my tandem sits in the water with the lead plug and water (dry) bag:
Image

And here with added organic ballast:
Image


I'd better stop. If I use the words wife and ballast in the same sentence I'll be in serious trouble!

SBSYNCRO-If you have a difficult launch site you may be better off exploring the drybag filled with water option. I use the lead plug to counterbalance the tandem when wheeling it on the cart. I sit it on the rear seat. 10kg's though is about the limit I would like to wheel.

PS. RR you mentioned streamlining the hull. What does this involve?


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 Post subject:
PostPosted: Fri Oct 12, 2007 9:29 pm 
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stringy wrote:
... streamlining the hull. What does this involve?

I like the use of packaging tape on the hull. For the current "streamlining" effort, I covered the front drive well:
Image
Image

the front 2/3rds of both seat scuppers:
Image

and the mast button:
Image

The well plug does not protrude beyond the hull bottom, so a smooth surface results. I think this is the biggest help in terms of speed improvement.

I always cover seat scuppers -- in boats with lower, wetter seating positions like the Adventure, it siphons water away as the boat moves forward. But in the Oasis, it also keeps the occasional splash from washing into the seat area while reducing drag. The tape keeps its adhesion when wet and is easy to remove and replace when appropriate. It's pretty tough, and can help protect your keel line from light abrasion.



Solo sailing the Oasis without ballast is neither fun nor easy, but the picture changes dramatically with ballast, especially placed low -- she becomes very stable, and there are no problems with weather helm (using the large sailing rudder). Upwind there is some slide-slip, and chop slows it down some, but it gets there eventually. On reaches, it was easy to stay in the 4 to 5 MPH range with a moderate breeze. The boat topped out the other day at 5.8 MPH (GPS), but mostly ran in the threes and fours.
Image

Sailing this way, the Oasis is stable enough to enjoy the use of a cam cleat arrangement, although with the gusty and variable winds, it's wise to keep a hand near the sheet at all times. I couldn't get away with this in the Adventure except in light winds. I borrowed this rigging arrangement from Kepnutz (with an additional block at the aft pad-eye, not shown):
Image 8)


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 Post subject:
PostPosted: Sat Oct 13, 2007 3:48 am 
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Location: Central Coast NSW Australia
Many thanks for the very useful hints Roadrunner.


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 Post subject: faster than that
PostPosted: Sat Oct 13, 2007 8:38 am 
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Location: sacramento california
Hey


Last edited by kepnutz on Tue Sep 16, 2008 4:06 pm, edited 1 time in total.

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 Post subject:
PostPosted: Sat Oct 13, 2007 9:13 am 
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Some interesting thoughts there. I have noticed that when the wind gets "fresh" and things start getting fun, the side-slip is so bad that probably 20 to 30% of the wind energy is being deflected into sideways motion. I'm not sure a surfboard fin would do much more than just installing the forward mirage drive and making sure the fins were both in the "down" position (which I have done). Even with that arrangement the side-slip is pretty bad. I think that it would take a lot more area on a daggerboard to cure this problem. I wonder if something could be arranged that could be dropped over one side, much like some of the old sabots I remember sailing as a kid...

Also, I'm intringued about a couple of things mentioned here - what is this "boombatten" you talk about, and also this larger sailing rudder - is it universally adaptable to all the newer (twist & flip) rudders?

Thanks

-Brent

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 Post subject:
PostPosted: Sat Oct 13, 2007 5:49 pm 
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Location: Central Coast NSW Australia
I agree with you Kepnutz about the mast being the weak link in stronger winds. It bends like spaghetti. Anything above 12 knots and it is uncontrollable. That is why I made the roller furler seen here:
http://www.hobiecat.com/community/viewtopic.php?t=7740
This allows me to get home when conditions get rough using sail power as an assist to pedalling. In fact I am now confident I could handle conditions of around 25 knots and still have some sail out. I haven't found slippage to be a problem because I am still pedalling the Turbo's at a slow cadence.
I also haven't felt as if the boat would tip either. It heels over but pedalling to provide forward motion must add to the stability. I have mentioned before that Hobie should come out with a stiffer mast and larger furling sail option as I know the tandem could handle it. The mast tube may need to be strengthened though. In lighter winds the larger sail would be a bonus and you could furl it to what you are comfortable with as conditions pick up. The problem I see with stays is that they would make furling difficult.

SB- You can find info on the boombatten here:
http://www.hobiecat.com/community/viewtopic.php?t=7158
http://www.hobiecat.com/community/viewtopic.php?t=7439
I have made one out of a tent pole repair kit and it works great in lighter winds and is a huge improvement downwind.

After reading about the improvements a larger sailing rudder makes here:
http://www.hobiecat.com/community/viewt ... highlight=
and here:
http://www.hobiecat.com/community/viewtopic.php?t=7935
I knew it was just what I needed to stop the "weather helm" I was experiencing ( I think that's what it's called?) -when a gust overpowers the rudder and turns you into the wind.
Unfortunately I have the tandem with the old style flip up rudder. Kepnutz made a very nice rudder sleeve but I am always banging the standard rudder into things and a larger one would be worse.I ended up purchasing the newer twist-n-stow mechanism and large sailing rudder and adapted it to the older system. I agree with the other positive comments and can report that it makes a huge difference. I will post a how to soon.


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 Post subject:
PostPosted: Wed Oct 17, 2007 7:50 pm 
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Location: sacramento california
Hey Ya.Stringy. :wink:


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PostPosted: Wed Apr 18, 2012 7:56 pm 
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I have a question about ballast on a Oasis. I filled the drivewell plug with about 23 lbs. of lead shot. I have a 3" diameter by 15" long drain pipe also filled with lead shot (approx. 30 lbs.) (thx Roadrunner for the idea :) which I would like to put in the front hatch and hold it in place with velcro. I was wondering if the bottom of the front hull is strong enough to handle it? It would be nice to leave the front passenger area open for ice chest, supplies, etc. when I take it out solo and not use water bags for ballast all the time.

Do you think it will handle it, or will it deform the hull?
Thanks in advance!

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