What is the 'pull' on an anchor bollard?

[NPMR]

We have a need to reduce the height of the stainless bollard in the anchor well of our Jeanneau S.O. 33i

The lid of the anchor well doesn't shut properly, as it fouls the top of the factory fitted bollard! The current bollard is 125mm high with a 90mm base.

I can buy a 109mm high version but it has a 600kgf rating, whilst the taller ones have a higher rating.

a) what is this rating?
b) what do I need for my boat?

or c) shall I get the existing unit cut and re-welded, so it's shorter?

We have a swinging mooring so it is 'in use' most of the time, not just occasionally.

Or, cut a hole in the anchor well lid!!???

 

[silver-fox]

If you are serious about finding out, then you could do worse than have a look at this site which has all the information you could need. Part way down page 1 is a calculator where you can enter the boat length and wind speed which will then calculate the "pull"

http://alain.fraysse.free.fr/sail/rode/forces/forces.htm

 

[simonfraser]

Appears to greatly overestimate the force.
20 knots on 7m give 90 kg, I can hand pull my boat into that no problem.

 

[chinita]

Or leave the lid open.

Do you not have a drain in the anchor chain locker?

 

[chinita]

Or leave the lid open.

Do you not have a drain in the anchor chain locker?

 

[J Neeves]

Appears to greatly overestimate the force.
20 knots on 7m give 90 kg, I can hand pull my boat into that no problem.

I suspect the data is for maximum loads which will include snatch loading (caused by shearing - do not recall did he include waves?), hence the 90kg. If the yacht was veering around you would not pull into it if your yacht was at 45 degrees to the wind - you would wait till you could pull it in a straight line forward. We did some measurements on a 38' cat, 6t (its about the same windage as a 45' Bav and this is 30% bigger, surface area, than a 35' Bav). Max loads at 17 knots were about 80kg (which meant all the chain was off the seabed). We had 600kg snatch loads - but only at 3:1 scope. Most snatch loads and damage caused by same is when you are retrieving the anchor (and I guess not using the bollard).

The bollard needs to be rated for the maximum plus something for a safety factor.

Given that they installed a bollard that is too big for the lid I'd be checking to see the reinforcing they used, if they made one mistake they might have made others.

Jonathan

 

[ff_nick]

Is the bollard too big, or has it moved already?

 

[William_H]

I find it strange that the bollard is inside the anchor locker. Yes the end of the chgain or rope should be attached to the boat but this is often easiet doine with a large saddle bolted down with the rode shackled onto it..
The bollard for mooring and for anchoring is usually on the deck enabling the anchor line or mooring line to go straight to the bollard via a fair lead or anchor roller.
Now I may be completely confused on your arrangement. I would say however that a higher bollard must have less load capability than a lower one of material is just as thick and mountings the same. In any case I would always advocate an alternative mooring rope and attachment for swing mooring. This reduces concern on bollard strength.
I would say however that loads aree likely to be greatest ina an emergncy when and if you are towed off a sand bank or similar by a powerful tug boat. especially snatch loads.
good luck olewill

 

[lustyd]

with the rode shackled onto it..

Don't use a shackle! the end of the chain or rope should be tied with cord to the boat which will allow you to cut loose in an emergency. You should never just heave the lot over the side and rely on the end of the rode to hold the boat either.

 

[sailorman]

We have a need to reduce the height of the stainless bollard in the anchor well of our Jeanneau S.O. 33i

The lid of the anchor well doesn't shut properly, as it fouls the top of the factory fitted bollard! The current bollard is 125mm high with a 90mm base.

I can buy a 109mm high version but it has a 600kgf rating, whilst the taller ones have a higher rating.

a) what is this rating?
b) what do I need for my boat?

or c) shall I get the existing unit cut and re-welded, so it's shorter?

We have a swinging mooring so it is 'in use' most of the time, not just occasionally.

Or, cut a hole in the anchor well lid!!???

How do the fixings differ between the two bollards, this will give some idea of strength

 

[Seajet]

I wonder if Jeannau were counting on the boat having a windlass or deck cleat / post fitted, and this bollard of the wrong size in the locker was a rushed answer ?

I agree with J Neeves, check the reinforcing as they may have bodged that as well !

Probably not practical to leave the lid open even on the mooring as it would be subjected to high loads in gales, and anyway what about going forward when sailing ?

I think I'd fit a jolly big cleat on deck - or ideally two, so as to leave the central foredeck clear - with Brunel style large wood & stainless backing pads, leaving unused chain in the locker; this may require a protected channel through the edge of the lid for the slack chain.

 

[reeac]

Maybe I don't understand the geometry but it sounds as if the anchor chain will exert a vertical pull on the bollard rather than shear in a horizontal direction and that sounds wrong. Far better to use a deck cleat.

 

[lustyd]

I wonder if Jeannau were counting on the boat having a windlass or deck cleat / post fitted, and this bollard of the wrong size in the locker was a rushed answer ?

I agree with J Neeves, check the reinforcing as they may have bodged that as well !

Probably not practical to leave the lid open even on the mooring as it would be subjected to high loads in gales, and anyway what about going forward when sailing ?

I think I'd fit a jolly big cleat on deck - or ideally two, so as to leave the central foredeck clear - with Brunel style large wood & stainless backing pads, leaving unused chain in the locker; this may require a protected channel through the edge of the lid for the slack chain.

How does fitting a deck cleat make the deck more clear than a bollard in the chain locker and the lid closed?

 

[reeac]

How does fitting a deck cleat make the deck more clear than a bollard in the chain locker and the lid closed?

It doesn't but I was objecting to the concept of a vertical component of chain tension on a bollard [cleat?] and that will be the case with a lower bollard as much as with the present one.

 

[NPMR]

The chain locker has a lid over a well, built into the deck moulding, with enough space for chain, rope and anchor (The anchor does not live in the bow roller as this is also needed for cruising chute ropes etc. The bow roller is like a small bowsprit)

The mooring/anchor chain comes over the bow roller and horizontally to the bollard which sits on its own platform at the rear of the space. The 'pull' would always be in one direction, towards the bow, as the bow roller takes the initial shear and changes the direction towards the bollard.

I cannot understand why a bollard that does not fit was chosen but do feel the shelf/space might have been designed for a winch, which might have less height. Incidentally, the bollard is also too close to the rear bulkhead, making it very difficult to put chain round it anyway! The original plan was to move it away from the bulkhead but as the platform slopes upwards, this will exacerbate the height problem! (Well done Jeanneau!)

Hence the need to reduce the height and I don't care to fit a winch at present.

 

[GrahamM376]

Appears to greatly overestimate the force.
20 knots on 7m give 90 kg, I can hand pull my boat into that no problem.

Don't underestimate forces, I've seen a windlass with the mounting studs torn out of it with snatch loads, the owner had never heard of a snubber.

 

[lustyd]

The chain locker has a lid over a well, built into the deck moulding, with enough space for chain, rope and anchor (The anchor does not live in the bow roller as this is also needed for cruising chute ropes etc. The bow roller is like a small bowsprit)

The mooring/anchor chain comes over the bow roller and horizontally to the bollard which sits on its own platform at the rear of the space. The 'pull' would always be in one direction, towards the bow, as the bow roller takes the initial shear and changes the direction towards the bollard.

I cannot understand why a bollard that does not fit was chosen but do feel the shelf/space might have been designed for a winch, which might have less height. Incidentally, the bollard is also too close to the rear bulkhead, making it very difficult to put chain round it anyway! The original plan was to move it away from the bulkhead but as the platform slopes upwards, this will exacerbate the height problem! (Well done Jeanneau!)

Hence the need to reduce the height and I don't care to fit a winch at present.

I'd ask Jeanneau, they could probably tell you what was designed to go in there and then see how much that would cost to fit.

 

[john_morris_uk]

Don't underestimate forces, I've seen a windlass with the mounting studs torn out of it with snatch loads, the owner had never heard of a snubber.

The smarty pants reply would be that windlasses should never be used as mooring points and the load should always be transferred to a bollard or cleat... I know some people do leave their chain on the windlass but it's not very kind to the bearings, gears and mechanism.

Regards the table which allegedly calculates loads; I'm not sure that load is as easily proportional to LOA as the author claims. The real answer is found in the windage which is much more proportionate to front cross sectional area if I remember my physics correctly. Even that is an approximations as the real figure depends on some coefficients of drag which are nigh on impossible to calculate and need to be measured... The table will give only an approximate figure...

I remember a car advert of some family car that said it had a lower drag factor than some supercar. What it conveniently forgot to say was that the cross sectional area was four times that of the supercar. The actual drag was therefore much bigger. (Or something along those lines; no doubt a more up to date physicist than me will correct me if necessary?)

 

[NPMR]

Update on conversations:

Bollard manufacturer advised using a cleat instead, as it is stronger and also lower.
Jeanneau say that they do not fit a bollard but either leave the plate blank or install a windlass. They also advise putting a bridle on the mooring chain and attaching the end(s) to the two cleats on the deck.

 

[sailorman]

Update on conversations:

Bollard manufacturer advised using a cleat instead, as it is stronger and also lower.
Jeanneau say that they do not fit a bollard but either leave the plate blank or install a windlass. They also advise putting a bridle on the mooring chain and attaching the end(s) to the two cleats on the deck.

All normal seamanship stuff then