Open Source Anchor Project

[Delancey]

Here's some prior art on the bridle thing. All of these and the Vryhof use a four point attachment (except for dredge3). Note the angle on the teeth up front to aid in penetration.

Maybe our pipe anchor could have one attachment point up front and two points in the back? Couple feet of pipe and some chain? Anywhere, anytime, anyplace. One piece of pipe is enough for two anchors. Prolly could cut the bottle opener somewhere along the back edge of the roll bar.

Maybe manufacturer's thought of this one already and killed it because it would put them out of business?




I like how in the upper right corner of dredge3 there is a plan view of the boat with four little anchors holding it in position.

[Cormorant]

My thought on the shankless pipe anchor is it will have trouble holding in rock and weed. Just a first reaction -- anyone else share that concern?

The OSA anchor project may need to make a few prototypes and test 'em all.

[Delancey]

Might not want it hanging off your bow but the 55 gallon drum could be a good option for the advancing furrycame scenario. Anytime, anywhere, anybody.

700 square inches of fluke area, weighs about 25lbs not including chain. Comes in stainless steel for about $750, that's two giant stainless anchors for three hundred and twenty five bucks a piece! Sweet. Variable geometry. Needs bottle opener.

I think you would need a concave profile on the edges to aid in orientation and penetration, maybe we could throw some angle at it to make winglets, ha ha!

I think you're prolly right about weeds. Maybe not quite what we're looking for in a general purpose OSA.

[foolishsailor]

No reason you cant make the tip narrower so that it has a greater opportunity to penetrate weed - but then it becomes weaker when dealing with hard substrates and rock...

[foolishsailor]

Originally Posted by Delancey

Might not want it hanging off your bow but the 55 gallon drum could be a good option for the advancing furrycame scenario. Anytime, anywhere, anybody. 700 square inches of fluke area, weighs about 25lbs not including chain. Comes in stainless steel for about $750, that's two giant stainless anchors for three hundred and twenty five bucks a piece! Sweet. Variable geometry. Needs bottle opener. I think you would need a concave profile on the edges to aid in orientation and penetration, maybe we could throw some angle at it to make winglets, ha ha! I think you're prolly right about weeds. Maybe not quite what we're looking for in a general purpose OSA.

Brilliant imagery, exactly what I had in my minds eye...

...but has it been made?

...has it been tested?

As has been said, real world copies will have to be made and evaluated. As great as this forum is at some point it has to be brought to the real world.

That takes real time and real money, and if a boat is hanging off the end it also involves real risk.

Once the rubber meets the road it becomes apparent why developing new anchors is difficult.

Im all for this, but we once we have all the ideas collated we can only narrow it down with real world testing and data.

[Shawn67]

Originally Posted by Delancey

Different attachment points on the shank is interesting idea, have to look at that more closely.

It altered the angle from 32 degrees to 40 degrees if you used the other point.



The idea was you used a second shackle to attach the chain to the 40 degree point as needed.

Shawn

[Delancey]

I couldn't help myself. You can see on the second image why the edge needs to be concave so that the tip enters first. I supposed you could call it a scalloped edge as well.

[Bestathook]

How about a barrel/plate hybrid, with a hard point to get it digging in, and to pull the barrel section into the bottom?

[Delancey]

First thing, I'm making one of these things.

Second thing, lazy barrel get to work!

Third thing, before you decide I am totally out to lunch, hear me out.

I considered the barrel as a resource early on. The third world is littered with them. The problem with them, or so I thought, was that the thickness was too thin for them to be of much use.

So when someone suggested them I thought "yeah right, nice try".

But I was wrong.

Now here's the catch, 700 square inches is a freakin lot of area for 25lbs of anchor (nimblemotors wants a super light anchor right?) It's like what? At least what 3 or 4 times the fluke area on a typical 20kg/44lb anchor right? Probably more.

Well if I am only pulling a third or a fourth of the load on those 700 square inches, it only has to be a third or fourth as strong as what I need for the 20kg/44lb anchor with smaller area to spread the load now doesn't it?

Makes me think of time I went sailing on a Santz Cruz 70, a classic Ultra Light Displacement Boat design. You take a relatively short mast and a modest amount of sail area and you put it on a big long waterline and watch it go!

Those things are so much fun to sail, and you look around at the hardware and everything is tiny. The size of the hardware, it's all for a boat twenty feet shorter because everything is so lightweight the loads are so low.

There you go, super big fluke area with low loading per square inch. Now let's consider this lazy barrel a little closer.

It's a cylinder which is great for stiffness along the axis. It's got formed frames which are super super stiff to resist the thing spreading apart. It's very thin which means you have a knife edge much like a shovel purpose built for digging in the dirt. This knife edge presents like zero resistance to penetration.

Now how do we put it together to make an anchor? Well, our problem there is load distribution from the bridle attachment points. No big deal, you take flat bar stock of whatever thickness you like. Bend it to the diameter of the OD of the barrel and place the bent bar on the outside of the barrel. Cut a hole in the barrel and shackle your bridle chain though the barrel to the bar on the outside.

The key to making it work will be the scallop edge and the tip. If anything we have too much area, cutting away the sides will bring it down by maybe a third. I think the way to go on the tip is a bird's beak like you see on some of the big oil rig anchors. The prior art for that one is the Star fort - Wikipedia, the free encyclopedia

The way the fort works is there are overlapping fields of fire from the adjacent walls and no blind spot on any outside corner like you would if the fort was square.

For us this no blind spot geometry means that when the anchor is on its side, as it rotates in to position it will present a good attitude for the off-axis angle of the median line of point of the relevant side of the bird'd beak to stick in the ground. Once you get it to bite a little bit you are home free.

I'll draw it up tomorrow so you can see what I mean. Also, I have a little trick up my sleeves for winglets that doesn't require getting that lazy angle out of bed, maybe she gets a day off after all.

As far as execution goes, hell yes I am making one. So so so easy! Take a barrel cut it. Bend some bar. Cut some holes. Link up some chain. Take it out to the canal and have some fun! All my friends are sailors but I might know a guy who knows a guy with a powerboat. Downside to the canal is the PCB sludge on the bottom of the canal. We'll bring a bucket to wash it off!

BTW, yes you can get 55 gallon drum in 304 stainless for about $750. U-Line for example carries them.

[Shawn67]

"it only has to be a third or fourth as strong as what I need for the 20kg/44lb anchor with smaller area to spread the load now doesn't it?"

Only if the whole anchor is buried. Is it going to be strong enough to fully bury the anchor?

Shawn

[Delancey]

You don't even need shackles to connect the chain to the bars. You pull your chain through the holes, thread your bent bars (solid round bar stock, whatever size is the biggest size you can fit through your chain) through the chain then pull the chain tight.

Fix the bar however you like so it doesn't slide out. Then all you have to do is join the bridle legs together at the rode.

On the other hand, if the point doesn't stick because there is no shank to leverage the tip in, maybe it just drags across the bottom sideways.

Could be the forward leg of the bridle is a bar that acts in compression to push the tip down when the two back legs of the bridle are pulled on. Can't push on a rope. Have to think it through.

[marujo.sortudo]

Excuse me if I misunderstand you, but isn't your 1/3 force based on a straight line pull on the bridle? When a wind shift or even yawing presents a shock load to the anchor won't the force often be transferred to 1 or 2 attachment points?

[roland stockham]

Originally Posted by Delancey

Hey LibreCAD looks pretty neat, does it have good curves/splines? I looked it up on Wikipedia and found a link to this one that looks pretty cool too, QCad, it's also free. It's about time for this stuff to be available.

QCAD - What is QCAD?

I looked at lots of free CAD software and LibraCAD looked much better than the others. This may be because I was used to AutoCAD and it was nearest to it so someone with different training might prefer the others. Yes it does the full range of basic CAD functions and I have used it for hull lofting. There are some more specialist programs out there if you are doing hull design from scratch and some have 'free' student versions which can be fun to play with.
The other one I use is sailcut CAD which, as the mame says is a specialist sail design program. Alows basic sail shape development and does all the panel development very well. Does not do any aerodynamic modeling so you cant use it for force calculations, not seen anything that does but would be interested if you found one! The other limitation is that it is not setup for spinnakers and assumes a leading edge but you can get round this buy altering the profiles to make the symetrical.

[roland stockham]

Really like the idea of a barrel anchor. If in testing the tip proves to weak it should be simple to add a piece of thick plate and some rods to strengthen it, the extra tip weight might help it set as well. Even if this does not get used by sailors it could be very useful for fishermen etc in parts of the world where they can't afford commercial anchors. Some of the NGO providing alternative technology input might be interested in distributing the design. The other thing I am thinking is that this could be a very good way of setting up a temporary mooring.

[Delancey]

Meh, bit of a mess with all that chain.