MirageDrive position fore/aft

[Richard]

Hi, does anyone know, for the MirageDrive to work efficiently, must it be forward like in the Hobie kayak, or could it be aft in the cockpit of a little cruiser?

[Jeremy]

The drive will work with the same efficiency anywhere in the boat, as it doesn't depend on the hull in any way.  The only reason for mounting it forward in small boats is so that the boat remains balanced, with the pedallers weight near the centre of the boat.  Putting the drive at the rear of a small boat might present some challenges with getting enough room to pedal it effectively whilst still keeping the boat well balanced, but other than that it should work OK.

Jeremy

[Richard]

Thanks that's great news! The boat will be about 14' LOA with 5' of cockpit
so should be ok. Although I assume the MirageDrive will work best under the
deepest part of the hull, so that might be an issue?

Sorry for abrupt question, I spent half an hour writing an intro to my
project but my battery died just before I posted it! Will post it again
later

[Timmo]

Only issue might be with directional stability. The further back it is the more the bow could be blown about. If you have a boat that is already 'sorted' directionally (keel/rudder etc. all in balance) then I see no problem at all. After all, the alternative is an outboard and that goes right on the stern!

Tim.

From: "Richard [via UK HBBR Forum]" <[hidden email]>
Date: Tue, 13 Sep 2011 01:02:06 -0700 (PDT)
To: Tim O'Connor <[hidden email]>
Subject: MirageDrive position fore/aft

Hi, does anyone know, for the MirageDrive to work efficiently, must it be forward like in the Hobie kayak, or could it be aft in the cockpit of a little cruiser?

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[Richard]

Thanks Tim, the boat will have Chine runners and a healthy sized rudder so
it might be alright there.

Does the MirageDrive need to be removeable, or can it be glued and sealed
permanently as part of the hull?

[Timmo]

The 'box' in which it sits (bit like a wide centreboard case) that you'll
have to create will have to be a permanent part of the hull. The Mirage
Drive does need to be removable, it does need occasional maintenance and the
pedals sticking up could be in the way at times. There are also moving parts
at the junction with the hull that can't be sealed.

If you plan to be underway with the drive removed (it does create some drag
even when flippers are up under the hull) I'd recommend creating a plate
that fits the hole in the hull and clamps in place using the clamps that
hold the drive. That will stop water swirling up and filling the box. If you
don't make it watertight a small amount of water will sit in the boxŠ great
for cooling cans of beer

Tim.


From:  "Richard [via UK HBBR Forum]"

Thanks Tim, the boat will have Chine runners and a healthy sized rudder so
it might be alright there.

Does the MirageDrive need to be removeable, or can it be glued and sealed
permanently as part of the hull?

[Richard]

Thanks Timmo! How the piano sounding?

[Timmo]

Sounding really good, Kate and Ruth love how it feels even more. You made a
real difference!

Tim.

From:  "Richard [via UK HBBR Forum]"
<[e-mail]>
Date:  Tue, 13 Sep 2011 02:48:52 -0700 (PDT)
To:  Tim O'Connor <[e-mail]>
Subject:  Re: MirageDrive position fore/aft


Thanks Timmo! How the piano sounding?

[Richard]

Glad to hear it!

Not sure about the MirageDrive, not keen on having holes in the hull - it's
meant to be a warm, dry and  and cozy liveaboard.

Is there any such thing as a pedal-powered outboard that'll hang off the
transom?

On Sep 13, 2011 11:19 AM, "Timmo [via UK HBBR Forum]"  wrote:
>
>
> Sounding really good, Kate and Ruth love how it feels even more. You made
a
> real difference!
>
> Tim.

[Jeremy]

Richard wrote

Glad to hear it!

Not sure about the MirageDrive, not keen on having holes in the hull - it's
meant to be a warm, dry and  and cozy liveaboard.

Is there any such thing as a pedal-powered outboard that'll hang off the
transom?

There are pedal drives available that look a bit like an outboard, but they still usually have the pedals mounted on the top, so would need to fit in a case like the Mirage drive.

You could, however, perhaps adapt one of these so that you pedalled it facing aft.  The most available one I've heard of is one made in China (or maybe Taiwan), but it is a bit crude and I can't find a link for it at the moment.  It uses the same twisted chain system as this, much more elegant unit: http://microship.com/bobstuart/spinfin.html, as, I believe, does this unit from the US: http://www.nativewatercraft.com/video.cfm?id=73

Here's an article on how such drive units work: http://www.recumbents.com/wisil/hpb/compact_drive.htm

There are other options for pedal drive, like this one on a Paul Gartside design: http://www.gartsideboats.com/custom-boatbuilding/20ft-pedal-boat-blue-skies-design-92.html or this neat twisted toothed belt drive from Nauticraft: http://nauticraft.com/downloads/nauticraft_drive_system.pdf

Jeremy

[Richard]

Thanks Jeremy, that's pretty much all I've seen on the internet - clearly
it's not possible to incorporate pedal drive/MirageDrive without either
making a hole in the hull or facing aft (for which I can scull the
traditional way anyway). Unless of course I get really creative with some
very long bicycle chain like a rear-drive recumbent, but I doubt that would
be efficient or tidy.

I think I'll have to stick with sculling and punting to keep my design
simple. Thanks for all the advice.

It's for a sort of liveaboard punt/microcruiser - I'll post some drawings up
when I've honed the design a bit more - right now I'm still doing some
punting on the river and thinking about the size and weight.

[Jeremy]

Richard wrote

Thanks Jeremy, that's pretty much all I've seen on the internet - clearly
it's not possible to incorporate pedal drive/MirageDrive without either
making a hole in the hull or facing aft (for which I can scull the
traditional way anyway). Unless of course I get really creative with some
very long bicycle chain like a rear-drive recumbent, but I doubt that would
be efficient or tidy.

I think I'll have to stick with sculling and punting to keep my design
simple. Thanks for all the advice.

It's for a sort of liveaboard punt/microcruiser - I'll post some drawings up
when I've honed the design a bit more - right now I'm still doing some
punting on the river and thinking about the size and weight.

You could take a look at Rick Willoughby's pedal drive system.  He uses a flexible shaft off the side of the boat (no holes through the hull) and gets some pretty good performance figures from his boats.  This one shows the basic layout of his drive system: http://www.rickwill.bigpondhosting.com/V11.htm

There is an extremely long thread on Boat Design detailing how Rick arrived at the final design for his drives, starting here (Rick has left that forum, so his name shows as "Guest625101138"): http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345.html

Jeremy

[Timmo]

Certainly a variety of pedal powered gizmos but as soon as you put the prop
at the back and the pedals in front you create a pretty complex mechanism.

You may be better checking out CeeDubbs yuloh rig. Very effective, cheaper
than a mirage drive and hangs off the back the way you want it.

Tim.

[Chris Waite]

Thanks for the vote of confidence TimmO

In fact, I've now managed to cobble up a (few) frame(s) that fit on 'Octavia' and having learnt a little more about gearing and leverage and such, I was going to ask you to come and pace me on the Hamble, not because I think I can out-do the Mirage drive, but by default you are the 'Gold Standard' for forward facing propulsion.

'Octavia' and frames?  Well, I didn't want to make ugly, temporary holes in her relatively beautiful hull, so I came up with a frame over the stern deck and there was a period when she rather looked as if she might have decided to take up a second career as a beam trawler:
 






 There is another for the pedals and the 'frame' that takes my nethers - commonly known as a seat:





Once I realized that the length of the Yuloh handle needs to be inversely proportional to the waterline, then we were getting somewhere

Chris W

[Timmo]

Looking very good! A day out on the Hamble would be good before winter settles in properly!

From: "Chris Waite [via UK HBBR Forum]" <[hidden email]>

In fact, I've now managed to cobble up a (few) frame(s) that fit on 'Octavia' and having learnt a little more about gearing and leverage and such, I was going to ask you to come and pace me on the Hamble, not because I think I can out-do the Mirage drive, but by default you are the 'Gold Standard' for forward facing propulsion. 

[Richard]

A flexible prop shaft! well I never! The thread in Rick Willoughby's pedal drive is 70 pages long I'll read more of it later, but I like the idea.

Do let me know if you go out on the Hamble to compare yuloh and MirageDrive, I'd be very interested to observe.

[Richard]

Just looking at close up photos of the mirage drive - I love the simplicity of the design. It looks like the pedals and flippers are just connected with bicycle brake/gear cable and chain. Perhaps its possible to split the unit into pedalset and flippers, and fit longer cables so that only the cables need pass through the hull.

The chain looks a bit wider than my bike chain, I wonder if it's a standard size. Otherwise it might be modded with spare parts from Hobie.

[Timmo]

Possible? Probably. 

Easy? I doubt!

Complexities involve:

- sealing holes through the hull with moving cables inside. Can be done using tubes that come above waterline level, but you're back to holes in the hull again, this time four of them. 

- splitting the casting that is the central frame of the drive, or recreating elements of it so the two parts can operate independently.

- fixing each half in place sufficiently rigidly to survive the stresses (complex; pedals go back and forth, flippers go side to side) when all you have to fix each to is the wooden hull. As a single unit those stresses are all absorbed within it but the robustness of the casting Hobie uses suggests they may be significant.

I'd love to see it done, but I think there could be a lot of experimentation before it could work.

Why are you so against holes in the hull? Sailing dinghies have had them for years (dagger and centre board slots,) there are boats with outboard wells based on the same principle and over reefs in sunny parts of the world there are the ubiquitous 'glass bottom' boats which have a similar 'box' to keep the boat afloat should the glass seal fail.

Having said all that, the flexible prop shaft is a fascinating thing too. A wider boat with twin props could be interesting. Main problem with a Mirage drive is it's propensity to pick up weed. On canals that could be an issue. A folding prop might work better there.

There's still the yuloh. All the elegance of a traditional solution and the simplicity of having no engineering that requires a specialist machine shop or forge to create it.

Tim.

From: "Richard [via UK HBBR Forum]" <[hidden email]>
Subject: Re: MirageDrive position fore/aft

Just looking at close up photos of the mirage drive; Perhaps its possible to split the unit into pedalset and flippers, and fit longer cables so that only the cables need pass through the hull.

[Richard]

Thanks, yes four little holes in the hull, and looking more closely at the MirageDrive perhaps not so little holes because it appears the chains also need to come up through the hull some distance on part of the stroke, if the flippers are to rest flush with the hull. Oh well...

My allergy to making a hole in the hull (especially a big one like for a centreboard) is because this boat will be my home in the winter as well. The other reason is to keep the boat simple. I want a warm, dry, heavily insulated, albeit extremely small living space. Eccentric, I know, but as you noted when I was in Banbury, it might be very small but a definite upgrade from my Laser Photon tent that I live in now!

Interesting what you say about picking up weeds, I thought one of the main attractions of the MirageDrive is that it sheds weeds much better than a propeller.

I'm definitely having a yuloh, and a punt pole. Also thinking if my cockpit's long enough to operate a yuloh efficiently, I might as well have a fold-out sliding seat and rollocks for sculling with two oars. I read about Matt Layden's sore wrists from sculling long distances and I think the more different options I have for human power the merrier, hence my interest in the MirageDrive but that might be over-complicating my boat.