Building an 8' Nesting/Mirage drive "Optimist"

[Sven Heesterman]

Last year we brought a Mirage drive kayak with us on sailing holiday.
I thoroughly enjoyed having it with us, but I almost hated taking it with us.
It is so heavy that lifting it on deck while underway is not very pleasurable so I decided to tow it instead.

I made a triangle from pvc pipe and rope from the rear of the boat to the nose of the kayak which made towing it a lot easier than using just a bit of rope, this way we could gently reverse when maneuvering and it could not try and overtake us in wavy conditions.

But it was clear I wanted something that is easier to take with us.
And since our daughter is almost at an age where she can start sailing lessons and do other kinds of boating by herself, it would be nice if she could use the mirage dinghy too (she's too short for really pedaling the hobie).
And if she were to eventually like sailing, there would need to be a boat for that too.

So I started planning a dinghy that we could take along easily, use with the mirage drive, go out together with the little one, and eventually let her go out by herself, maybe even under sail.

After considering the options, I decided on a nesting dinghy.
I looked at converting an optimist but that would require a short bow section and a long rear section, and the same goes for the dutch "Piraat" dinghy. Too large a nested package for my taste.

So I started designing my own.

After some modeling in Inkscape and paper models I started a 1:2 scale model:
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This is currently being refined and additional bulkhead being tried.

Today I started making the first parts for the real thing.
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Here is the rudder profile being cut in to blade.

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Ready for shaping, with a sample on top.

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Darn, why is this rotated?
Anyway, roughly shaped with the hungry disk in the angle grinder and RO sander with 80 grit.

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First part of shaping is done, with a nice crisp trailing edge.
If needed I'll extend the profile, depending on the transom height later on.

[pez_leon]

Looks great! I think I see a CNC router cutting those long kerfs into the rudder blade to lay out the profile. If so, why switch to the angle grinder- why not have the CNC cut the whole thing? I ask from a perspective of great ignorance.
I'm excited to see it all come together. Thanks for posting the photos.

- James

[Sven Heesterman]

It's a good question The profile is part of a kit I sell, which is aimed at reducing cost as much as possible.

I could machine the entire profile no problem but that would require the customer to pay for the machining time. (And the ones that are willing to pay for that get a composite blade ; )
Because of this I do not have that profile available as code but I did have the kerfs, and those could easily be adapted to an 18 mm thick blade, where the one in the kit is 36 mm.

[John Meachen]

Respect! Anybody who can create stuff in Inkscape is on a different level to we mere mortals.It appears that you are machining on a mill rather than a router and if this is so it might be a factor in the time taken.What feed rate are you using?

[sp_clark]

IMG_20220204_155421.jpg

Darn, why is this rotated?

You using an iPhone for these pics? They do that sometimes...

Flip_This'n.jpg

Fixed that for yah.

Nice work BTW with the CNC thing.

[Sven Heesterman]

Thanks guys!
The cnc is a router. I think the feed was 2000 mm a minute but for this job feed was not that important, setup time was.

All in all, it took an hour or so from board to profile, it would not be very different if I had machined the profile completely.

This boat is the first time I could have done with a 4x8 size router, for most of my work the 4x4 size is plenty.

@ sp_clark What did you do to change the rotation? It shows the right way up on both the (android) phone and the laptop...


Here are some additional pics of the process so far.

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Earlier models

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Bulkheads in the bow section as a practice run/design excercise.

[sp_clark]

[QUOTE=Sven Heesterman;6607309@ sp_clark What did you do to change the rotation? It shows the right way up on both the (android) phone and the laptop...[/QUOTE]

Hmmm... interesting.

First time I encountered this with files of mine own I found that e-mailing myself the image somehow turned it 90° clockwise. No idea why but it worked. I'm using Apple stuff 100%.

For your image (and others similarly afflicted here) I simply download a copy, open & rotate in Photoshop, save & upload. Takes less time to do that than key in this explanation. Probably other apps on every platform that'd effect a similar result? Interested parties will have to search 'em out, I have enough tools already.

Nice project BTW. Following your thread with interest. You gonna fit oars too or just the Mirage & sail?

[Sven Heesterman]

Made the second trial version of the cartridge for the mirage drive:
IMG_20220208_195111.jpg

This cartridge can be replaced if I were to need a different design interior at some point, for the center board for instance.

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The drive is a difficult thing to get the dimensions for, but that may be because of my lack of understanding imperial?....

[sp_clark]

The drive is a difficult thing to get the dimensions for, but that may be because of my lack of understanding imperial?....

Nah, it's 'cause there's no reference surfaces to measure against! I had the same problem when fitting mine.

Clever approach using particle board to make mock-ups of the drive well. Dimensions were lacking in the build manual for my Waterlust kit, I had to query the designer for details to have any confidence mine'd fit. Even with that, after putting her into winter storage I noted a coupe of spots on the hull opening that have some wear spots I'll need to attend to before launching this year.

Imperial's harder to grasp than Metric I agree. Tenths is easy compared to fractions. I can work either side with confidence 'cause I started back then with using both.

Would that the US had gone Metric back 60 years ago we'd all be better off I think.

[Sven Heesterman]

Even then, the tab in the front (that has to fit in a slot) is on a different height than the one in the rear, if you reference it to the axis the flippers swing round. And that is just by a few mm, and I cannot figure out why, the only reason I could think of is that drive well dimensions got there first and the drive hat to be fitted to that somehow.

Anyway, in trying to do a tiny bit every day before leaving the workshop, I did a bit of mocking up and it looks like I came up with a good locking solution to secure the drive in the well, an excenter lever:

IMG_20220211_161541.jpg

Now I have to figure out where to point the lever...

[sp_clark]

Where'd you source your Mirage drive from? I recognize it for what it is but mine looks somewhat different, and those two tabs (front & back) to my mind are the same 'depth' from the center axle upon which the entire contraption locks into place. CLC's instructions specified 3/4" square blocks epoxied into the drive well where the tabs are to rest so the drive itself is parallel to the Waterlust's hull.

Making everything from scratch is certainly more of an endeavor than simply buying the mounts Hobie makes available! If memory serves they were close to US $70 each & I left the included plastic shroud parts off entirely to allow bolting the clamps to the drive shelves I made out of 1" Delrin. CLC somehow forgot to include the factory plywood parts in my kit so I had to fabricate my own. First attempt from 6mm marine ply epoxied together failed when I first mounted my drive during assembly.

[Sven Heesterman]

I bought the drive for next to nothing and got a leaking kayak as an extra. (I welded the leaks) According to the serial number it's from 2006, maybe it has been changed since,the flippers are very different now, and I'd prefer to have the larger flippers.

[Loose Moose]

Wooden Widget has a nice Mirage drive dinghy plan which has a very simple Mirage drive mount with the design. Might want to check it out.

https://www.woodenwidget.com/deckster.htm

[Todd Bradshaw]

the flippers are very different now, and I'd prefer to have the larger flippers.

These are the current standard fin size in the kick-up variety from our Hobie Lynx boats, which came out last summer. I actually tried switching mine to the longer "Turbo Fins" which are a couple of inches longer, and after trying the bigger fins, I went back to my standard fins. The speed difference is typically on the order of maybe one knot or slightly more. The main real difference, which we could clearly feel, was the cadence that you find comfortable to pedal at. We ride recumbent trikes and usually pedal at a reasonably fast cadence. We both tried them and found that at our typical cadence, the Turbos were substantially less comfortable and more tiring. If there was a speed advantage, it didn't last for long once you started getting tired. So my initial thought that I could change the fins out and simply go faster didn't pan out the way I thought it would.

DSCF3750.jpg

[Sven Heesterman]

The bigger fins are probably just like a smaller rear sprocket on a bike, a change in gears. Maybe you can shorten the larger flipper, so to change to "a larger sprocket" I also found the cadence on my current drive in the kayak to be slightly too high. But I expect the dinghy to be slower than the kayak so maybe the current size fits well.

[Sven Heesterman]

Until I have time to get a week available for non stop building I do jobs that do not require much space.

The cartrige for the drive is taking shape:

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[sp_clark]

Todd that appears to be one of the newer 'reversing' Mirage rigs? That looks nothing like the unit I bought ("NIB" pre-owned but never used) for my Waterlust a couple of years ago... fins mount differently, look different too. I'll try to get it out of storage, take a pic to add here.

Friend w/ Waterlust mounted the longer fins on his device, says they work very nicely over the shorter stock fins. I'd have to think it's like gears onna bike too in that more surface area on larger fins is gonna take more effort to push water about with 'em, everything else being unchanged on the drive itself.

[Todd Bradshaw]

Yes, we have the new/current 180 degree reversing rigs. The two cables sticking out the back side with the finger loops flip the fins 180 degrees and add reverse gear to the picture. The fins also automatically kick up upon impact and re-deploy automatically once clear. That grey block just above the rubber is the kick-up mechanism. It's pretty amazing technology and I can't believe how well they move the boat, despite the fact that the hull shape is not particularly sleek. Our boats are the new "Mirage Lynx" model - kind of like a Stand-up paddleboard (foam block, fiberglass wrapped with a light plastic shell over that) with what is kind of like a lawn chair mounted on it. Very comfortable, fast, stable and somewhat embarrassingly easy to operate.

One thing which may also enter into the fin length equation is the weight of the hull. Our boats are only about 46 lbs. for the hull alone and about 60 lbs. with the drive, rudder and seat added. It doesn't take an awful lot of "push" to get them going and keep them going. A rigged rotomolded fishing Hobie can often weigh well over 100 lbs. and may need more brute force to get it moving. I think folks just need to experiment a bit to find the fin length and peddling cadence that feels comfortable for them. The bad news is that the price to try a set of the longer Turbo fins to see if they're right for you is about $200. The good news is that if you are careful, they can be installed and field tested in clean water and not show it. I'd buy them from a dealer that will let you return them if you don't like them.

Marite in/on her Hobie Lynx:

fd.jpg

The Lynx is actually faster with less effort, more comfortable and more stable than her 22" wide sea kayak.

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[Sven Heesterman]

After rounding over the edges that would benefit from it, I did the first epoxy work today:

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Pocket to later drill the hole for the excenter lever in filled with goop just before glassing over, and some glass added to the holder for the axle

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[Sven Heesterman]

Family matters suddenly brought all work (in the shop) to a stop.
The only thing I could still do was to finalize the design for the final boat.

I wanted to make the boat slightly longer as the standard sheets are not 2440 mm (8') but 2500 mm long, and the transom might benefit from slightly steeper sides.
And finally, I wanted to see if I could make the design stand on its transom.

I'm not sure if this works with fitted rudder hardware but at least the model does stand vertically now:

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I have taken all coordinates from inkscape and put them in a spreadsheet, which allows changing the scale easily, to fit larger cardboard. The small model is 1:10, the larger 1:5.

[Sven Heesterman]

Well, that took a while...

Finally got started on the full scale build. All tywrapt together:

IMG_20220520_130355.jpg
Now the hard work starts!

[Sven Heesterman]

Parting bulkhead is ready for epoxy.

with-bulkhead.jpg

[Sven Heesterman]

Double post.

[Sven Heesterman]

Wow. After pointing some people to this thread I just found out they cannot see the images.
Forum owners probably think that people will then make an account to view but I think it will drive posters away...

[sp_clark]

Wow. After pointing some people to this thread I just found out they cannot see the images.
Forum owners probably think that people will then make an account to view but I think it will drive posters away...

Yep. No account, no seeum pics. See links but w/no account you get a message about 'insufficient permissions' or some such for viewing.

Why this would drive posters away I can't fathom as they typically would already have accounts to be able to post in the first place. Casual readers are those most affected. Accounts are free for the simple act of registration, enabling both the viewing of posted images as well as the ability to post/reply.

This is one of two forums I frequent that permits easy posting of images. No limit here, t'other has a 40mb total. There's a third that I find inscrutably difficult to post to, that doesn't 'host' image files, permitting only those that are stored elsewhere. Spend not much time nor effort there.

[Sven Heesterman]

I guess it is a valid reason not to show pics to random visitors.
But I post my work to be seen. For me it is a lot less interesting to post because of this..

[Sven Heesterman]

Finally, the cut has been made!
4 weeks to the holidays, it has to be usable then.IMG_20220610_122037.jpg

I really enjoy being able to have it stand up on its transom, did not expect it would make such a difference.

I did not expect how much time it takes to have each and every surface coated in epoxy. It means you cannot use a screw or nail to fix things, which would save a lot of time.

[sp_clark]

I did not expect how much time it takes to have each and every surface coated in epoxy. It means you cannot use a screw or nail to fix things, which would save a lot of time.

True, yet the purported benefit of encapsulating the wood against inevitable intrusion by water is the price paid for a (hopefully) longer usable lifespan.

Doing what you're attempting I think would be pretty tricky using 'traditional' methods & materials.

[Sven Heesterman]

Another big step, cutting the big hole for the drive cartrige:

IMG_20220614_143818648_HDR.jpg

I still have to connect it al but so far, so good.

[Sven Heesterman]

After a day of waiting for epoxy to cure (and doing other things at the time) the front water tight compartments are ready to be templated and the rudder is ready to be coated.

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rudder.jpg
I glue carbon fiber bushings in the holes against water intrusion.

[Sven Heesterman]

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Different phone, same rotation...
One step away from finishing.