Helical mooring

[miracze]

Hi,

does anybody have any experience with helical screws for mooring? I'm considering to create permanent mooring in a bay and helical screws such as helixmooring – helixmooring looks like much better solution then concrete blocks.
Is there a chance to install them only on scuba (for 38ft boat) or is heavy machinery necessary? Any tips for EU based manufacturer I can get in touch with?

Thanks

 

[LittleSister]

I would imagine it would depend very much on the nature of the bottom where you are laying the mooring, and likely to be unreliable or impossible in some areas.

I wouldn't know whether they are any good elsewhere.

In what way are they 'better' than concrete blocks?

 

[Boathook]

On the faq bit of the website it mentions installed by hand but I suspect that is when you can stand on the dry seabed. It does mention scuba plus a support vessel to install as well.
I would suspect that other manufactures wouldn't be much different in the installation.

 

[Tranona]

Suggest you talk to Boatfolk who have installed the new moorings in Studland Bay and I believe there are some in Cawsand in Cornwall. They are controversial for a variety of reasons related to the types of seabeds they are suitable for and how they deal with varying water depths particularly in shallow water. I don't think anybody makes them in Europe (which might tell you something!) and from memory I think the ones in Studland came from Australia.

 

[Neeves]

The advantage of the block is - you can lift it for servicing. You can of course lift a helical screw - with some effort and then more effort to re-instal. Concrete blocks have a proven track record over decades. We have an annexe to the Australian Navy dive school at the bottom of the hill on which we live - the navy use concrete blocks for their vessels.

Helical screws maybe used for moorings around the Barrier Reef (don't know) but in Pittwater we use, exclusively, concrete blocks and for exceptional installations 3 opposing Danforths. If Australia is the location of manufacture - they are not actually common place here - acceptance is, very, limited.

Jonathan

 

[William_H]

Th advantage of concrete blocks or similar mass is that worse case of the boat starts to lift the mass and drag it if goes towards shallow water it will reset itself. if it goes to deeper water well.... ol'will

 

[AntarcticPilot]

Hi,

does anybody have any experience with helical screws for mooring? I'm considering to create permanent mooring in a bay and helical screws such as helixmooring – helixmooring looks like much better solution then concrete blocks.
Is there a chance to install them only on scuba (for 38ft boat) or is heavy machinery necessary? Any tips for EU based manufacturer I can get in touch with?

Thanks

If you're in the UK, bear in mind that you will need permission from the body that has rights to the sea-bed. In almost all parts of the UK, that's the Crown Commissioners, but there are places where ancient rights mean that other bodies are involved. You can't just install a mooring without asking someone! If you don't have a license, your mooring can be removed at any time by the agents of the sea-bed owner.

As others have noted, the suitability of helical screws depends very strongly on the nature of the sea-bed, and they are NOT suitable for some substrates such as soft mud.

 

[emmalina]

SE Asia I put some screw moorings into sand. Can be done using a long bar and 2-3 divers

 

[thinwater]

In the US they have been VERY successful, including a number of direct huricane strikes. Irma was catagory 4 at landfall, which is beyond most people's comprehension. Peak windspeeds reach 280 KPH.

Hurricane Irma Boot Key
PS Magazine Hurricane Irma moorings

If you read them through, you will find that in virtually every case, it was the owner pendant that failed. The only screw moorings that failed were impacted by multiple dragging boats before they failed.

Yes, they must be selected to suit the bottom, but even mud typically works by using a larger, longer screw that reaches the firm material under the ooze.

 

[Daydream believer]

The actual screw may last some years, but one must accept that the riser chain will need replacement. That will need a diver if the screw is not in a tidal area & exposed at LW. With a concrete block the forces to move it are pretty much known from local exoerience. How does one know if the screw has a good fixing. In our area the sea bed can be scoured by 18 inches. This is evident from the sand on top of the sinker sometimes when it is raised, or the bright chain from gravel scouring even after 3 years in the water. Would such scouring expose a section of the thread? Alternatively, if it was covered, how would one undo the old chain & fit a new one every 3 years? With a concrete sinker one just raises it, services the mooring & re lays .
If the screw were left standing up above the bed,( so the eye was accessible) would that lead to it being levered back & forth, thus making it lose grip or bend?

 

[AntarcticPilot]

The actual screw may last some years, but one must accept that the riser chain will need replacement. That will need a diver if the screw is not in a tidal area & exposed at LW. With a concrete block the forces to move it are pretty much known from local exoerience. How does one know if the screw has a good fixing. In our area the sea bed can be scoured by 18 inches. This is evident from the sand on top of the sinker sometimes when it is raised, or the bright chain from gravel scouring even after 3 years in the water. Would such scouring expose a section of the thread? Alternatively, if it was covered, how would one undo the old chain & fit a new one every 3 years? With a concrete sinker one just raises it, services the mooring & re lays .
If the screw were left standing up above the bed,( so the eye was accessible) would that lead to it being levered back & forth, thus making it lose grip or bend?

@Daydream believer hits the nail on its head. Many popular areas for moorings in the UK have very mobile substrates; if you could screw into a firm substrate (doubtful in many areas) the mobile material above it would shift over time.

 

[Daydream believer]

@Daydream believer hits the nail on its head.

I think the idea is that you do not just hit it on the head. You have to screw it in. ?

 

[miracze]

I would imagine it would depend very much on the nature of the bottom where you are laying the mooring, and likely to be unreliable or impossible in some areas.

I wouldn't know whether they are any good elsewhere.

In what way are they 'better' than concrete blocks?

I mainly like the "easy installation" - or so I imagine, because you don't need a crane and working ship to move the concrete blocks.

@Daydream believer hits the nail on its head. Many popular areas for moorings in the UK have very mobile substrates; if you could screw into a firm substrate (doubtful in many areas) the mobile material above it would shift over time.

fortunately I'm based in Med, so no tides and the bottom should be much more stable I hope.

 

[Daydream believer]

I mainly like the "easy installation" - or so I imagine, because you don't need a crane and working ship to move the concrete blocks.

In our area I place concrete sinkers around the 1 tonne mark ( but up to 2.5 tonnes in 1 case) with a tractor to carry the mooring to the waters edge then a 20 ft launch with the mooring undr an air bag. I can place 10 race marks in a day over our race area with the assistance of 3 & a RIB & 4 boat moorings in a day with 2 helpers. No crane needed to place. A tug is employed to lift 30 in one go every 3 years but I have now developed a way to lift individual moorings up to 1 tonne. with no crane. Just using the tide. However, no good on a lake or the med with no tide range of course. But it can still be placed Ok.

 

[LittleSister]

If the area has other moorings, there is almost certainly a local operator with the kit to safely and efficiently lift concrete blocks. If the are does not have other moorings one has to wonder why that is.

FRED DRIFT ALERT! The references to how far down one has to go to find 'solid' underlying ground reminds me of the history of the Acle Straight, a road in Norfolk, UK, that was built across very extensive marshes to provide a much more direct route than previously between Great Yarmouth and Norwich. The road is dead straight for miles except for one sharp bend about halfway along. It is barely above sea level, with very little change in elevation along its length.

It was constructed circa 1800 IIRC, by laying faggots of wood on the road alignment, digging a trench either side and piling up the excavated material on top, plus probably more wood on top of that. Willows were planted continuously either side along its length to stabilise the road edges and provide some protection from the wind, etc. (sadly only short stretches of the willows remain). All the work involved would at that time, of course, have been done using only men and horses .

By around the early 1900s the road was, unsurprisingly, in a poor condition due to subsidence etc. The engineer responsible for the renovation dug down to find firm ground, but even at a depth of IIRC 15 foot it was still just wet mud. He therefore just piled up more wood and mud, and thus, except for a surfacing of tarmac etc., it has survived to this day.

Originally it would have carried only people and goods on foot, on horse, or in horse or ox carts. Today it forms part of the A47 trunk road, and carries a very heavy traffic of cars and lorries of all weights. Amazing!

(There have been plans for years for a dual carriageway replacement of the Acle Straight, but the exceptional construction costs and environmental complications (including that those marshes are now part of the Broads designated area - a national park in all but name - and support a lot of wildlife, some it rare), plus the limitations of the current junction and bridges at the Great Yarmouth end, raise doubt about when, if ever, this will actually go ahead.)

 

[AntarcticPilot]

If the area has other moorings, there is almost certainly a local operator with the kit to safely and efficiently lift concrete blocks. If the are does not have other moorings one has to wonder why that is.

FRED DRIFT ALERT! The references to how far down one has to go to find 'solid' underlying ground reminds me of the history of the Acle Straight, a road in Norfolk, UK, that was built across very extensive marshes to provide a much more direct route than previously between Great Yarmouth and Norwich. The road is dead straight for miles except for one sharp bend about halfway along. It is barely above sea level, with very little change in elevation along its length.

It was constructed circa 1800 IIRC, by laying faggots of wood on the road alignment, digging a trench either side and piling up the excavated material on top, plus probably more wood on top of that. Willows were planted continuously either side along its length to stabilise the road edges and provide some protection from the wind, etc. (sadly only short stretches of the willows remain). All the work involved would at that time, of course, have been done using only men and horses .

By around the early 1900s the road was, unsurprisingly, in a poor condition due to subsidence etc. The engineer responsible for the renovation dug down to find firm ground, but even at a depth of IIRC 15 foot it was still just wet mud. He therefore just piled up more wood and mud, and thus, except for a surfacing of tarmac etc., it has survived to this day.

Originally it would have carried only people and goods on foot, on horse, or in horse or ox carts. Today it forms part of the A47 trunk road, and carries a very heavy traffic of cars and lorries of all weights. Amazing!

(There have been plans for years for a dual carriageway replacement of the Acle Straight, but the exceptional construction costs and environmental complications (including that those marshes are now part of the Broads designated area - a national park in all but name - and support a lot of wildlife, some it rare), plus the limitations of the current junction and bridges at the Great Yarmouth end, raise doubt about when, if ever, this will actually go ahead.)

Many minor roads in the Fens suffer from there being no firm ground for many metres; they slowly subside and every now and again they get smoothed and resurfaced! But there isn't anything solid for a long way down.

 

[thinwater]

Change is hard.

I'm not sure how using a crane is harder than diving. I've watched both operations. I'm pretty sure concrete blocks would have moved in Irma. In areas with sensitive sea beds a screw causes less disruption.

A screw that is well sunk is below the sea floor; nothing for the boat to land on at low tide.

As for the base of expereince, given the number of screws that have been used by power companies to brace power poles and oil companies to secure pipes and floating docks, the experience with screws is probably much greater than with concrete blocks ... because they offer high, reliable holding.

 

[Daydream believer]

As for the base of expereince, given the number of screws that have been used by power companies to brace power poles and oil companies to secure pipes and floating docks, the experience with screws is probably much greater than with concrete blocks ... because they offer high, reliable holding.

I would imagine that the screws that you refer to, for commercial purposes, ,go many feet into the sea bed & need specialist equipment. Far beyond the earlier suggestion of using a couple of divers to screw them into the bed for more "domestic" moorings. I think this thread is meant for the more usual boat mooring, is it not? Whilst the data may be available for the holding power of such a fitting I would suggest that data for a unit in a shallower, ill defined ,bed, may be less accurate. Particularly because it may be liable to movement for starters.
If one has ever tried inserting a screwed post hole borer into the ground one will know how awkward it can be. A different application I agree but when Our club wanted to put ground anchors down for chains to tie down dinghies. They did an experiment with 2 spiral ones & the idea was soon dropped on the grounds of cost -£ 15-00 ea for about 2 ft long- & difficulty. How long would one expect screwed mooring anchors to be & how much would each one cost to buy.?

 

[thinwater]

Sometimes it's DIY (best in shallow water and smaller sizes). Mooring fields are a commercial installation, but lots of big concrete boats for big boats requires equipment too.
DIY or commercial (DIY is for smaller boats in shallow water)
Commercial installation, such as mooring fields