Making a bridle to moor a trimaran

[Rum_Pirate]

How do you make a mooring bridle for a 27'0" trimaran?

Size of rope?

Length of rope? Overall width is 19'0".

Knot/thimble or attachment at centre to connect to the mooring bouy line?

Any other tips or suggestions?

 

[Neeves]

How do you make a mooring bridle for a 27'0" trimaran?

Size of rope?

Length of rope? Overall width is 19'0".

Knot/thimble or attachment at centre to connect to the mooring bouy line?

Any other tips or suggestions?

The snatch loads should be managed by the mooring itself, not by the mooring bridle. The mooring bridle thus does not need to contribute any elasticity and simply holds the tri to the mooring line and needs to be sufficiently strong to accept whatever weather is thrown at it and stop the tri shearing or yawing.

Our mooring has chain on the seabed that manages the snatch load and the mooring rope from the chain on the seabed to, in our case, the surface 10m above is simply 1" 3 ply spliced at top and bottom with hose pipe to protect the points of contact. The bridle is simply spliced (each arm has a splice) to the central riser. Tte bridle arms are short, not much longer than half the beam. The eyes that attach to the cat are again spliced with hose pipe protection.

Our mooring has 1.5 t of concrete on the bottom and the pennant and bridle need to lift this concrete and the chain when the mooring is serviced. The size of the pennant and bridle is dictated by the loads necessary to lift the whole assembly to the surface for annual servicing. In effect the lines are specified for the mooring not the vessel.

The degradation of our mooring is to the steel components on the seabed - the bridle and mooring pennant (from the seabed) last for years but the steel components need replacement maybe every 3 years, abrasion and corrosion.

This is our mooring block, since increased to have another block half the size of the one in the picture. The big chain offers some reduction in snatch loading and this chain and a smaller chain, a sweep chain, sits on the seabed. The rope in the man's hand is the riser and needs to be strong enough to lift the 2 blocks and the chain.


This not our mooring but one that had not been serviced - and you can see how the steel wears, rather than the cordage.



Mooring design varies round the world. I note many UK moorings have a chain pennant from seabed to a floating buoy. Ours are totally different. Designs seem to evolve to meet local demands. If you define what the tackle is like to the sea bed you might get more focussed replies that are eminently sensible - but totally different to what we do in Sydney.

Jonathan

 

[AngusMcDoon]

I had a DF920 for 20 years and never bothered. Centreboard (or in your boat, dagger board) up, rudder down and lashed, and the boat sits quietly, much less swinging around than a similar sized mono.

 

[Chiara’s slave]

I had a DF920 for 20 years and never bothered. Centreboard (or in your boat, dagger board) up, rudder down and lashed, and the boat sits quietly, much less swinging around than a similar sized mono.

Same, though we had our F27 on a swinging mooring, a DF800 prior to that. Our 920 is moored to a pontoon. The trouble with a bridle for a tri is how to get to the float tips. Some F boats have front nets, but they don’t usually go that far forward. Therefore a spliced loop around each front cleat on either side of the main hull is what you use. Pick it up and attach one side, relax before passing the other uder the bobstay to the other cleat. The biggest line that sits comfortably on the cleat is what you want. Centreboard up, rudder down, as you say.

 

[Neeves]

We have a bridle but both arms of the bridle are easy to access and we have horn cleats on each bow.

We find that even though we have easy access to both sides of the bridle when we let go of one arm the cat then swings and lies partially side on to the wind, If you have the mainsail up she then sails forward (and you are still on the bow). This matters not if there is more than you on board but for single handed, depends on how close other yachts are, it might be anxious. We thus have a centre pennant that we attach to a horn cleat amidships. Normally the centre line is slack, when we leave we take tension in the centre line, release both sides of the bridle and we then lie into the wind - it makes for a much more relaxed procedure. When we return to the swing mooring we do the reverse - use the centre line as the pick up line, with a dan buoy type pole that can be reached from the bow deck/crossbeam.

Tri's seem to behave differently to cats and seem to have different procedures. Much will also depend on where and what are your strong points for attachment of the bridle, pick up line.

I assume when you will have 'weather' you will take her ashore.

Jonathan

 

[Chiara’s slave]

Tris need mooring like monohulls in the main. Don’t tie up anywhere by the amas, except maybe an extra spring. Tris lie best, swinging, pontoon or finger berth, with all lines to the main hull. Dragonflys don‘t have cleats on the amas. Newbies and mono owners have been known to ask why not. Even tie lines to the u bolts on the ama bows. That’s not what they are for.

 

[Neeves]

Its good to have owners with real experiences, all power to you and Angus.

Jonathan

 

[Bajansailor]

I know a trimaran here that has been on a mooring for at least 50 years (doing regular coastal cruises with passengers all this time), and has never had any form of bridle, just a rope cable coming up to the mooring cleat.

Re your mooring, I would agree absolutely with @Neeves re a rope riser rather than chain - initially we had a couple (in succession) of 3/8" chain risers to the buoy from the heavy ground chain, but I found that these would wear fairly quickly, especially closer to the surface (more oxygen perhaps for corrosion?).
Instead of replacing the riser chain for the third time, I then used a 1" diameter 3 strand nylon riser, and this lasted much longer!
Just make sure that the ground chain is still off the bottom by at least a foot or two at low tide, especially if there are any rocks or coral nearby that could possibly chafe the rope.

Our riser rope was a continuous rope from the thimble eye joined by a shackle to the ground chain, to the eye splice at the top on the mooring cleat.
The mooring buoy was simply attached to the riser rope with a rope strop using a rolling hitch, and this worked well.
It also meant that the position of the buoy on the riser could be easily adjusted after you have laid the mooring, by sliding the rolling hitch up or down the riser as required to suit the water depth.

If you have a nice sandy bottom, I would suggest using proper anchors rather than a concrete block - an anchor (or two) is much easier to transport, and drop overboard / set than a very heavy block. And it has much more holding power than a block, unless the block is completely buried in the sand.
Our mooring for a 35' sailing boat was two 35 lb anchors on the bottom, in a bridle laid in an east - west direction, and this lasted well for 15 years.
I would go scuba diving on the mooring every 6 months or so, and I invariably had to do some maintenance each time, such as replacing shackles that were getting worn, even adding chain doublers as back up when required - I would take various bits of chain, shackles, pliers, a big adjustable spanner and a screw driver (for un-doing shackles) and cable ties (many!) for seizing shackles.

Oh, and our boat sat happily on her mooring during Tropical Storm Tomas in 2010 - the winds were predominantly easterly (as he went south of us) so the boat was on the lee side of the island - it would have been very different if Tomas had passed just north of us, and we would have then had westerlys instead, with a lee shore not far away.
One of the anchors (a 35 lb CQR - this was the easterly anchor) had a 12 lb Danforth attached to the ring on the plough in tandem fashion - I had added this some years previously.
I went diving on the mooring soon after Tomas had passed - ok, he was not a full hurricane, but the boat probably experienced 60 - 70 knot gusts - and I found that something had happened to the CQR, and it was just lying on the sea bed, tangled up in it's chain. The other anchor (a Danforth) to the west did not contribute anything (re the easterly winds) and the flukes were not even buried. But the 12 lb Danforth was nowhere to be seen - it and its chain had buried itself deeply, and I think it is probably still down there. So I think I can say that this 12 lb Danforth held the boat in 60 knots of wind quite happily, and in tandem fashion to boot, which most folk say will not work. But it definitely did work for us on this occasion.

Incidentally I had a survey job after Tomas on a 40' Fountaine Pajot cat that had been on a mooring in Carlisle bay - this mooring had been professionally laid by a diving contractor a few weeks earlier, and the ground weights comprised two big and heavy steel cog wheels that had come from a sugar factory.
The cat proceeded to happily drag this mooring until she came into contact with another cat called Heatwave (which had been designed and built here in the 80's). This contact resulted in Heatwave breaking her mooring, and coming ashore, and the Fountaine Pajot cat capsizing. There are some photos in this thread I posted on here afterwards -
Some photos from Tomas' recent visit to Barbados

I will add a couple of proper photos of the FP cat and Heatwave, as I had posted photos in Photobucket in the above thread, and they are watermarked.

The FP cat was subsequently sold to a chap who righted her, hauled her ashore and rebuilt her totally, and she is sailing again now.

In the photo below you can just see a huge hole (from the deck to below the waterline) in the side of the port hull of the FP cat, caused I think by impact from one of Heatwave's bows.

 

[Neeves]

To underline what Bejansailor says

Our moorings and all the other moorings, 100s of them, where we moor Josepheline are concrete blocks. About 1nm north of us are moorings for super yachts, when they wait to go down to The Harbour for a Jolie. One of the moorings was specifically installed for Southern Cloud, SOUTHERN CLOUD Yacht | Fraser and are 3 x 1.75t Danforth anchors set at 120 degrees to each other with a central riser. The mooring is Classification Society certificated.

The issue is - concrete is cheaper than approved anchors and easier (think cheaper) to service.

As Bejan intimates a Danforth given time and use will simply bury itself and continue to bury itself. The constant worrying of the anchor by moored yachts (and no retrieval) simply encourages the Danforth to bury more deeply - and its retrieval requirements simply increase. Fine for the owners of Southern Cloud - but not something a private owner needs to encounter.

I am sure that there is a means to calculate the holds that might develop on day 1 when the mooring is installed and how the hold increases with use - concrete blocks are easier

Jonathan

 

[NormanS]

Remember that concrete loses approximately half of its weight once submerged in sea water. When I laid moorings for my 60' ex fishing boat, it was three 150kg Danforth (type) anchors at roughly 120°, each on 45' of 32mm studlink chain, connected to a central ring, and then a riser chain to a buoy. Although these are heavy items, they are individually manageable, whereas the concrete block with equivalent holding ability, would have been massively heavy.

 

[Neeves]

Picking up on Bejansailor's post and that of NormanS.

When our mooring is serviced I attend the work (and one of the few. apparently, who show any interest). Its part of my continuing education.

Often when our concrete block is retrieved the top of the block has a pile of sand on the flat top surface. Nothing massive but - loose sand. Our mooring is around 10m deep, 2m tides, no current and in terms of other reports - well sheltered.

No sand on top of the block here (but you don't make this sort of thing up - I'm human - did not have any means to take a picture . The block is quite big and sand on top of the block surface cannot develop through current, there is none. The sand is non cohesive (and may wash off easily, on retrieval).



My analysis is that over the year the block sits on the seabed it settles into the sand, and settles sufficient to allow sand to creep over the the top surface. I cannot believe that simply sitting on the seabed without any external influence, this gravity alone, allows the block to sink in the seabed. The only external influence is the mooring tackle and gravity and my conclusion is that the constant movement of the heavy duty chain (which I would have thought was minimal movement) encourages the block to accept the twitching and slowly buries itself, gravity, in the sand (largely clean silica sand).

When the blocks are retrieved, for servicing of the tackle, the mooring pennant is tensioned and then 'left' allowing the movement of the barge to break the suction and accept the weight of the block.

Two factors:

Bejansailor's comment that his 'inadequate' (too small) Danforth device developed hold to secure an 'oversize' yacht and NormanS comment that a 1t block loses 'weight' when submerged. Bejansailor's Danforth was being constantly 'worried' which allowed it to develop hold well beyond 'expectation' and the tension needed to release a buried block might be higher than theory suggests.

I have mentioned that if you touch your anchor when the chain is off the seabed that it 'twitches' - it all seems to be the same mechanism - movement of the rode/pennant (which might seem imperceptible and unremarkable) does reduce the shear strength of the seabed, allowing a concrete block to sink, and anchor to bury further - and maybe (and conversely) allow a poorly set (oversize) anchor to lose its hold and.......drag.

My and Bejansailor's observation is of anchors (and concrete blocks) not overstressed - but allowed to soak, over a period of time. Most anchors that drag are recently deployed, or recently set. Members have been know to mention that 'soaking' of older style anchors is advantageous to their performance. Noting that some anchors may not have sufficient soak time, nor an 'appropriate' tension (lower shear strength and gentle tension - to encourage deeper diving - before a catastrophic tension + hobby horsing is applied)

Now there may be other mechanisms - that I'm unaware of (or minimising)......? And I may be accused of a fertile imagination (to suit my arguments ).

Jonathan

Sincere apologies Rum Pirate - I've hijacked your thread on moorings and relied on lateral thinking to move to forbidden territory. Hopefully developments on Admiralty pattern anchors will keep them occupied (which reminds me of the lyrics in an early Stones song, viz 19th nervous break down, and mention of development in sealing wax ).

 

[kleppar]

Same, though we had our F27 on a swinging mooring, a DF800 prior to that. Our 920 is moored to a pontoon. The trouble with a bridle for a tri is how to get to the float tips. Some F boats have front nets, but they don’t usually go that far forward. Therefore a spliced loop around each front cleat on either side of the main hull is what you use. Pick it up and attach one side, relax before passing the other uder the bobstay to the other cleat. The biggest line that sits comfortably on the cleat is what you want. Centreboard up, rudder down, as you say.

I am the owner of a Corsair Dash 750, and also plan to make bridle for a mooring (mooring ball and lines to jetty). There are starboard and port cleats on main hull, but only two small eyes on float bows. I guess I could have slings around beams. Or is a bridle necessary? Maybe a small one attached to main hull is acceptable; as indicated below?

 

[Chiara’s slave]

We used just the small sort on our F boat, and would again on the current beastie.

 

[Stemar]

I have an 8m cat with a 4m beam. My mooring is a 4' railway wagon wheel, buried 4' into gloopy mud, with a chain riser and a bridle made of 18mm polysteel rope with a Brummel splice making an eye with a steel thimble in the middle and eye splices at each end. One end goes to each hull, giving a roughly right angled isosceles triangle. We find the boat sits better than with a single line, with less tendency to sail around the mooring.

We had the same setup on our previous Snapdragon 24 monohull, taking a line though each of the bow fairleads. She also sat better, so I could well imagine a tri being happier doing the same thing. The ideal would be to spread the lines out to each ama, but they'd obviously have to be designed to take mooring loads, which many aren't.

The reason for doing this instead of the previous single chain strop was the rate of wear on the chain. The polysteel's been there for three years now, and is still going strong, while a three year old chain strop would definitely have had me worried in the recent blow. An additional advantage of polysteel over chain is that the polysteel floats, and is a lot lighter to pick up. A disadvantage is that, because it floats, it gathers weed, so it often looks like something out the creepier bits of the Pirates of the Caribbean movies.

 

[kleppar]

We used just the small sort on our F boat, and would again on the current beastie.

Centreboard up I understand, but why rudder down at mooring?

 

[Chiara’s slave]

Centreboard up I understand, but why rudder down at mooring?

It’s lateral area at the back, it helps the boat point into any current like the monos around you, and damps the tendency to swing. Makes it easier to get on from your tender too, along with not scaring your neighbours and not chafing the gear.

 

[simonfraser]

grainger 6.5m trimaran on swinging mooring, had two strops to the bow, plastic pipe to protect the strops, tied the loops to the cleat (two strops not needed, made me sleep better)
had her on the mooring for 5 years summer and winter time in the UK east coast, never saw any wear or other issues with the mooring