Archimedes screw / Helical embedded screw anchor

[Tom]

I'm wondering if anyone has experience with embedded mooring systems, and/or knows how to weld bronze to iron, or bronze to stainless steel, if that is possible.

 

I would like to make a helical type screw to embed in soft sand, and am thinking of fixing some old propellers onto a shaft in order to create a segmented archimedes screw which will then be wound down into the substrate.

 

Old parts inventory...a 100 kilo engine block, some rebar, a few old propellers, some chain, some discarded anchors of various types.  A pile of mixed metals.  I suppose I could scrounge a stainless shaft.

 

I want the old propellers affixed to the rod/shaft which is fixed to the block.  I'm thinking that the block would reduce wiggle in the shaft, while the shaft would prevent the block from dragging.  The chains would go from the block to the anchors, as backup.

 

Sorry to ramble.  I guess the question is:  What is the best way to affix bronze propellers to a shaft of a dissimilar metal?

 

Thanks in advance for your ideas.  And, Cheers!

 

 

[boatsmith]

Helix mooring screws are fairly inexpensive. Welfing dissimalar metals and the droppng them into saltwater makes my bones shiver, SS starts deteriorating as soon as it's made. It looks fine right up until it breaks JMT

[Tom]

Thanks for the reply JMT.

[sam]

i have heard of people using screw anchors here in nz .they are fairly easy to get the power & telephone companys use them to stay poles with

[boatsmith]

Tom ,the photos of your boat look great. Must fell terrific to launch even with violated savings. JMT was meant to mean just my thoughts. David

[Tom]

Well I found one made of stainless, but it looked kind of like some kid had made it in his high school welding class.  Didn't have the helix right and the welds weren't worth...anyway, it was a waste of time on somebody's part.

 

I did find a company that seems to make them properly at http://www.helicalanchorsinc.com/ but that's a lot of weight to be sending overland.

 

Sam, thanks for the idea of checking with the local power company.  They are used locally to anchor the posts that the electrical lines are run on.

 

David, please excuse my poor memory for names, and thanks for enlightening me as to JMT.  Yes launch was fun, great to be in the water :)  Still have a lot of work to do though.

 

Meanwhile, I'm going to go find a couple more small engine blocks.  Hate to be getting a bigger hammer when I could just use my brain and others to create a more elegant solution, but unfortunately I lack the welding skills.  Definitely a project for later though :)

[Trevor Lowmass]

In the Arabian Gulf we used to chain 2 or 3 engine bocks together, float them out with a couple of of oil drums before dropping them to the bottom.  Didn't move much and seemed to be enough to hold 30feet monohulls. Cheap and cheerful but it was in relatively sheltered water.

[vern]

A friend used one from the power poles that hydro uses, it's been there for 4 years. holds a 36' steel boat works great! only problem was with the tides and boat swinging it unscrewed it some, so he put a small anchor with a chain attached to the eye and that stopped it from turning. there galvanized so will last for many years.

[Geminidawn]

Hi Tom,

The simple system we use here is old tyres with a galvanized steel hoop, filled with concrete, Ideal for sandy bottoms, simple, cheap and secure. The size of the tyre denotes the size of the boat you want to secure. For a Pahi 63 you'd be looking a an old large tractor tyre at the very least.

[Ann and Neville Clement]

We got a galvi well made helix mooring purpose built at a hardware store in Florida.  It wasn't much money and it was easy to install either by hand using the strength of two young men who wanted bottles of rum as their thanks or else a simple type of reverse bilge type pump that blew sand away as it drilled a hole into which we simply dropped the 6 foot long inch and a quarter thick shaft with its 10 inch wheel helix screw.  Next day we had a 40 knot wind and the helix just stayed in the hole and gradually the hole has filled in nicely.  The entire helix is under the sand now and only a very heavy mooring chain is seen going down there.  Likely the cement for that tractor tire would cost more than we paid and weigh more too.   

[Geminidawn]

A tractor tyre full of concrete will weigh about two tonne but that's the idea. We get the tyres for free and sometimes the concrete too or get it cheap. We wait for a delivery or pouring at a construction site near by and offer to take the dregs. We make up the mooring between the tidelines at a low tide, this gives the concrete just enough time to kick off before the tide comes in and covers it. When the tide is high we float a raft over it with a gantry fitted with a chain block and tackle and lift it just enough to clear the sea bed and move it into place.

[Tom]

Thanks for all the good ideas.  I'll be sure to post some pics of whatever system we cobble together :)

[alex]

try this

 

http://www.youtube.com/watch?v=HPAMUEAAMII

http://en.wikipedia.org/wiki/Screwpiles  more information

http://www.screwpile.com.au/Moorings-Marine/applications/38

 

i hope this could help

alex