penberth3
Well-Known Member
As high as possible means your props become close to vertical, assuming the same footprint. The props then take bending load instead of axial load, so you need heavier props or more bracing.
Boat fall tragedy in Weymouth
- Thread starter Dipper
- Start date
As high as possible means your props become close to vertical, assuming the same footprint. The props then take bending load instead of axial load, so you need heavier props or more bracing.
Seajet
...
May I suggest, with such a simple thing as a boat cradle one should just ' Over-Engineer The **** Out Of It ' !
While still keeping the thing vaguely liftable by the local crane - IF that is suitable - seems the only design constraint.
When one gets to calculating forces and loads this way and that,
A, it's pretentious
B, something's wrong
While still keeping the thing vaguely liftable by the local crane - IF that is suitable - seems the only design constraint.
When one gets to calculating forces and loads this way and that,
A, it's pretentious
B, something's wrong
lpdsn
Well-Known Member
How would you know you'd over-engineered it if you can't do the calculations. Better to engineer it properly and specify a higher safety factor to allow for misuse if that's deemed appropriate.
The calculations are ones that blokes in top hats and frock coats were able to do with pencil and paper.
Keith 66
Well-Known Member
Very sad story. It should be a wake up call for the rest of us.
I was taught how to lift & block boats by an old school shipwright, each boat is different but they are all heavy & out of their element add in inexperience & no training & accidents will happen.
DJE will remember when our mutual father in law's contessa 32 fell over 25 years ago. That was a case of a fine yacht sitting on £50 worth of rusty scrap iron & it nearly killed him.
Many yachts have rounded or short dimensions fore & aft on their keels, The contessa 32's Centre of gravity is actually slightly fwd of the front edge of the keel, Twisters are the same. They tend to go light on the aft pads & roll forwards. They can then twist in the cradle. A recent haul out at our club saw a Sparkman & stevens yacht gently go nose down when it was hauled. Prompt action saved an accident. Some yachts may be stern heavy. I have no idea where this yachts Cof G was but wouldnt be the least surprised if something similar occurred. Be interesting to see what the HSE says.
I was taught how to lift & block boats by an old school shipwright, each boat is different but they are all heavy & out of their element add in inexperience & no training & accidents will happen.
DJE will remember when our mutual father in law's contessa 32 fell over 25 years ago. That was a case of a fine yacht sitting on £50 worth of rusty scrap iron & it nearly killed him.
Many yachts have rounded or short dimensions fore & aft on their keels, The contessa 32's Centre of gravity is actually slightly fwd of the front edge of the keel, Twisters are the same. They tend to go light on the aft pads & roll forwards. They can then twist in the cradle. A recent haul out at our club saw a Sparkman & stevens yacht gently go nose down when it was hauled. Prompt action saved an accident. Some yachts may be stern heavy. I have no idea where this yachts Cof G was but wouldnt be the least surprised if something similar occurred. Be interesting to see what the HSE says.
zoidberg
Well-Known Member
In helping antifoul friends' boats from time to time I've seen plenty of boats propped-up on timber shores with wedges driven under the feet of the shores..... on relatively soft ground beyond the tarmac hardstanding of several pro boatyards. Many of those wooden wedges had worked loose and some were 'adjacent' to the props they supplemented. I've tapped quite a few back in with my foot....
I gained the view that the boats rock slightly when the wind gusts, putting a cyclic load/unload onto those unfixed supports. Naturally, some work loose over time. Not all yard foremen were swift to address the issues when mentioned....
I gained the view that the boats rock slightly when the wind gusts, putting a cyclic load/unload onto those unfixed supports. Naturally, some work loose over time. Not all yard foremen were swift to address the issues when mentioned....
Motor_Sailor
Well-Known Member
Really? The longitudinal centre of gravity of nearly all yachts is just aft of the halfway point on its waterline length. Boats don't sail very well if their Longitudinal Centre of Buoyancy is more than a very few percentage points from here. The centre of gravity has to in exactly the same longitudinal position or else they will trim down by the head or stern. All boats that float to their lines have the two in perfect correlation.
I bet every S&S design in Olin Stephen's tenure had the CofG between 52 and 54% aft of the forward cutwater.
penberth3
Well-Known Member
Er, hang on, that isn't what Engineers do.
ShinyShoe
Well-Known Member
HSE is rarely persausive. HSE rarely mandates extra requirements.
What it does do, is prosecute people for breaches of (mostly) old(ish) legislation. That then ripples through into (over)interpretation of the issue and so insurers and Health and Safety Officers in companies then respond with excessive application of the rules to try and keep them from paying out...
I believe its a Club, But as I understand the rules - if a Club employs someone, then all its volunteers automatically are covered by the H&S at Work Act.
Of course, the poor guy involved might not be covered - he wasn't volunteering at the time to move boats etc (I assume) - rather was working on his own boat.
Even if the club doesn't employ anyone, I'd be surprised if their insurers would allow them for instance to lift boats without complying with LOLER regs.
Actually - virtually none of the existing regulations requires that. Its the systems around it that create such circumstances. Regulations would likely say things like "the individual must be competent" - it is unlikely they will define competence. Some body will decide to produce a 2 day course that they declare will demonstrate competence. But rarely will the rule state you must do the 2 day course. You could self certify as competent... ...the challenge will be ensuring everyone else is happy with your self certification... ...Alternatively you don't state anything about competence, you simply use legislation to control certain aspects - so you prevent discharge, including sanding down, spillages / splashes that can wash into the sea for instance. The course would teach you everything about how to control those measures. But you'd be better taking a train a local lead approach for that - as it will need local interpretation.
Now if you are a commercial yard... you might decide to control the activity. It wouldn't be the first time something like that was done in a way that brought financial reward. So the yard might employ its own anti-foulers or have a list of approved anti-foulers who might have to pay to be on the list...
Unless I'm wrong, the rules are probably 80% there already - its just no-one is enforcing them... and it may take a "major incident" to make something happen. The day a yard accidentally washes 10litres of spilled antifoul down a drain into a harbour and causes harm... ...expect every other yard to get twitched.
JumbleDuck
Well-Known Member
It really doesn't matter all that much. Resistance to bending and buckling (you can forget compressive failure of the material) both depend on a suitable second moment of area: anything which resists one will resist the other.
JumbleDuck
Well-Known Member
And as you move them higher they only have to take lateral wind loadings and not a share of the weight, so the loads become less ...
Keith 66
Well-Known Member
Out of the water the base of the keel carries the load, if the C of G is biased fwd or aft of the centre of the keel base it will result in unequal pressure on each end. Anyone who has ever hauled one of these out should have seen this.
steve350
Well-Known Member
The cradle seems to be designed for a smaller yacht. The acrows are fully extended, webbing appears very light weight. A terribly sad event.
Firefly625
Well-Known Member
only just seen this. Dreadfully sad. I know how much I love working on my boat, most people who have a love for their boat quite enjoy the maintenance part so I imagine he was having a nice time tinkering until whatever happened happened...that is so tragic.
Norman_E
Well-Known Member
Very true, The guys at Marmaris Yacht Marine are really good at propping boats, they not only choose prop lengths carefully, they sound the hull to determine where the internal stringers are and place the props accordingly. The boat feels very secure on them. The cradles used there are designed for ease of moving boats around, and can be picked up complete with boat on a special trailer that slides underneath projecting pads on each side, and is raised hydraulically. I don't like them because I consider them too narrow.
Seajet
...
Fierfly625,
your empathy does you credit, I don't often hear mobo owners loving their boats as much as I towards my saily job !
I hope the poor bloke concerned is looking at blue horizons now.
Firefly625
Well-Known Member
Seajet, once a sailor always a sailor..
KREW2
Well-Known Member
Did it go nose down whilst being put on the ground, or was it when being lifted out of the water?
If it was when lifting the boat out of the water it generally means, the slings are not positioned correctly, or the forward chains have not been shortened enough.
We find relaunching a boat that is not level is not too much of a problem.
Lift out is much different, if a boat starts to lift too unevenly, either for and aft, or a list to one side it is lowered back into the water and adjustments made.
Keith 66
Well-Known Member
The S&S was coming up the slipway on its own heavy yard trolley as she came up over the top of the slip she rolled gently fwd as the trolley became horizontal.
Just because the bottom of a keel is flat is no guarantee that weight is evenly distributed. Many keels sweep up at the front & extend forwards (Twister)& the cof g of the yacht may be biased one way or the other. My Sabre 27 is fairly stable but the C of G is not dead centre of the keel base, rather a bit further fwd.
Just because the bottom of a keel is flat is no guarantee that weight is evenly distributed. Many keels sweep up at the front & extend forwards (Twister)& the cof g of the yacht may be biased one way or the other. My Sabre 27 is fairly stable but the C of G is not dead centre of the keel base, rather a bit further fwd.
Elessar
Well-Known Member
The only benefit of steel cradles is they are quicker for the boatyard and allow the boat to be moved, chocked, in the boat mover.
Well done wooden props have more redundancy and are arguably safer.
chewi
Well-Known Member
apart from...
being predictable
can be designed to prop in the right places on the intended boat
avoid props being put to weak parts of the hull
puts the responsibility in the owners hands...(not the clubs... each owner provides his own cradle for 6 months).