Comments on: Auto-drogue & T-rudder

By: Jason

Jason — Mon, 28 Jun 2010 17:09:59 +0000

I’ll echo what’s been said before… in any kind of storm conditions that drogue line is going to chafe through in no time on the edge of the pipe it’s exiting from. You can “trumpet” the end of the pipe, or have a toroidal piece of HDPE machined, and attach that to the end of the pipe. If you have the rope contacting a large-ish radius piece of low-friction high-density plastic, it’s much less likely to chafe.

As for the drogue itself, I’d be concerned that it might be so light that it would just skip across the surface. When sailboats put out sea anchors, they often weigh them down to make sure they stay in the water, and below the level of surface waves. Were it me, I would go with a heavily-constructed cone-shaped cloth drogue, with some sort of weight added to it to make it both self-deploying and to keep it uner the waves… something along the lines of this http://www.smartmarine.co.nz/easy-stow-25-drogue-sea-anchor-boats-to-7mtr-p-5586.html

Have you had anyone calculate what the forces on the “T” of the rudder would be if you broach and are pushed sideways through the water? Is your rudder assembly strong enough to take those forces without warping or breaking?

I don’t know if you’re dead set on running downwind in storm conditions, but have you considered pointing upwind instead? With as light as WiTHiN must be, it probably wouldn’t take much of a “fin” sticking up into the wind to weathercock her around to pointing upwind… I’m picturing something like the dorsal fin of a fish, set well aft, that you could raise in storm conditions.

Cheers!
Jason
Calgary, Alberta

By: Jarl

Jarl — Thu, 17 Jun 2010 14:00:32 +0000

Apart from that drogue likely being wobbly in water, it will also be a unwelcome wind resistance if pedaling against the wind. (And of course a welcome micro-sail if going down-wind, but this is not a sail boat so..).

Hopefully the rudder mechanism is strong enough to cope with the increased area and grip of the rudder. Possible to bend/break the rudder axle if under harsh conditions? (And btw, what is your plan if the rudder break? Abandon ship or is there some backup solution? I’ve seen that you have a backup drivetrain, but rudder failure would likely also be a major problem?)

I still think you will need a keel with more area to reduce side-to-side movements and a bow with more volume to improve the boats ability to handle big waves, but hopefully I’m wrong.

By: Bruce Bolster

Bruce Bolster — Thu, 17 Jun 2010 12:10:42 +0000

Patrick Egan’s suggestions are good ones. I agree with Russel Moore’s comments about the shape of the drone – a flat one will likely flutter and precess like a fishing lure – it will want to gyrate in circles.

By: Xabier

Xabier — Mon, 14 Jun 2010 04:01:54 +0000

Greg, have you seen this website?:
http://www.expedition360.com/reference/design.htm
STEVE SMITH and JASON LEWIS set off from the Greenwich Meridian on the 12th July 1994 to attempt one of the last great firsts for circumnavigation of the World. Steve decided to leave the expedition upon reaching Hawaii in 1999. Jason carried on solo and is still on course to complete the circumnavigation in October 2007.

By: David Tangye

David Tangye — Sun, 13 Jun 2010 10:54:38 +0000

Good comments.

Also, a Kevlar line should go through the skin fitting OK, as long as the outer braid is not a soft weave. Whip it onto a small ss rigging thimble so it wont get abrasion and break at the end fitting. It will draw a bit of water inside on retrieval, and perhaps at other times too, so have an absorbent cloth nearby to mop it up. Perhaps mount the retractor winch in a shallow plastic pan? Ignore my earlier comment about a cone shaped drogue: I thought it was retracted onto the bow .

By: Russell Moore

Russell Moore — Sun, 13 Jun 2010 05:22:18 +0000

Perhaps a slightly cone shaped drogue would work better, and would be more stable in the water with the ‘point’ facing forward.
I concur with patrick egan concerning the pipe and drogue rope.
Also a swivel in the rope may prevent line twist, as no matter how symetrical you make the drogue, it will twist.

By: patrick egan

patrick egan — Sun, 13 Jun 2010 03:03:37 +0000

Where the rope connects to the sea anchor, back splice the line around a grommet so that it does not wear on the anchor, trumpet the end of the pipe and vary the length of the rope every so often, also some kind of mechanical connection on the sea anchor so that when it draws into the hull that you could replace the sea anchor line with out it falling off… Just my 2 cents.. Not that anyone asked.

By: Pete Hoffmann

Pete Hoffmann — Sun, 13 Jun 2010 02:46:35 +0000

Jason is right the mouth of the pipe is a sever chafe point.

By: Mitch Flanagan

Mitch Flanagan — Sun, 13 Jun 2010 02:44:13 +0000

Hey, The T-rudder looks and sounds like a good idea! But…it looks kinda small? I sure hope it works for you. as for the drogue….I hope you’re using some really good quality rope for it! I’d be worried about it breaking off in rough water. But, I’m sure you’ve got that covered.
I’m looking forward to hearing about the sea trials with the new mods. I sure hope you have favourable conditions for the trials, a little bit of the nasty stuff and whole bunch of calm sea’s.
Have a safe trip!

By: Elrey

Elrey — Sun, 13 Jun 2010 02:35:48 +0000

You need a bombproof line. Kevlar? Spider silk. Greg, get the spiders on board as sponsors. Have ‘em get to work.