Before I go cutting some holes in my boat...

I would appreciate your views on the following beaching leg design before I start. The boat is 3tonnes displacement with a draft of 1m:-
1) The legs will be splayed out by 10degrees and will be 100mm shorter than the keel to ensure the keel touches first which will mean that if on a very hard surface the boat will heel by 10degrees before a leg touches the ground. In most cases the keel will settle slightly so the heel could be less.

2) The legs will have 125mm square feet (don’t want them to resist sinking too much otherwise they will take undue load if the keel sinks more)

3) They will be made from 48mm diameter, 4mm wall thickness, galvanised steel tube (scaffold!) with a total length from hull attachment point to foot of 1.5m

Many thanks..

Colin solocoastalsailing.co.uk
 
I'm not qualified to answer your questions, but 48mm is considerably narrower than the yachtlegs that I have. It would be interesting to calculate the resistance to bending of each design.

I wouldn't underestimate how robust the legs have to be- they are not simply in compression. For example, I was aboard whilst she floated off one time. The wind had veered ninety degrees, and strengthened. When she started to lift, the loaded leg and keel together bounced and dragged across the bottom as she swung, imposing all sorts of loads on the leg.
 
1). I normally set my adjustable length legs to be pretty much the same depth as the keel. Although people who keep their boats on legs on drying moorings seem to allow a generous amount of heel to avoid any possible tripping over the leg I think this might be uncomfortable if on board.

2). 125 mm square is far lower than the Yacht Legs design although I appreciate that yachts with timber legs are probably even less than that. My Yacht Legs feet are about 8 x 10 inches.

3). I agree with Kelpie that 48 mm seems low. Buckling resistance of tubes is highly dependent upon diameter and I a larger diameter, with the same wall thickness, would be desirable. I made some additional 'legs' to fit the YL sockets for winter use with the boat in a cradle. These were in galvanised pipe of more like 3 inches diameter and around the same wall thickness, a far more robust design. I think you will find that this size is widely available.
 
Kelpie said:
I'm not qualified to answer your questions, but 48mm is considerably narrower than the yachtlegs that I have. It would be interesting to calculate the resistance to bending of each design.

I wouldn't underestimate how robust the legs have to be- they are not simply in compression. For example, I was aboard whilst she floated off one time. The wind had veered ninety degrees, and strengthened. When she started to lift, the loaded leg and keel together bounced and dragged across the bottom as she swung, imposing all sorts of loads on the leg.
Click to expand...

Wow. Thanks for sharing your scary experience! Will take your views into account.......
 
vyv_cox said:
1). I normally set my adjustable length legs to be pretty much the same depth as the keel. Although people who keep their boats on legs on drying moorings seem to allow a generous amount of heel to avoid any possible tripping over the leg I think this might be uncomfortable if on board.

2). 125 mm square is far lower than the Yacht Legs design although I appreciate that yachts with timber legs are probably even less than that. My Yacht Legs feet are about 8 x 10 inches.

3). I agree with Kelpie that 48 mm seems low. Buckling resistance of tubes is highly dependent upon diameter and I a larger diameter, with the same wall thickness, would be desirable. I made some additional 'legs' to fit the YL sockets for winter use with the boat in a cradle. These were in galvanised pipe of more like 3 inches diameter and around the same wall thickness, a far more robust design. I think you will find that this size is widely available.
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Thanks for your advice Viv. I have no plan to stay on board so I can live with a 10 degree heel in return for the significantly reduced risk of tripping up a leg during the grounding/floating transitions.

Wow, you have got big feet! :-) of all the breeching legs I have studied I have never seen any that big yet. Obviously you don't want the feet to start sinking in soft ground but you also do not want them to sink less than the keel so the legs start to take the whole boat mass. My other boat is a 5 tonne Falmouth Working Boat that has the original timber legs from the Cornish builder (Martin Heard) which only have 150mm square on 100mm square timber legs.

The boat for this project is shallower, beamier and lighter and was going to use steel tube legs to take less stowage space. And use an articulated joint to the hull like the principle of the YL design with a standoff support to the hull 500mm below the mounting point giving me 10 ddegrees of splay with just 1m of leg below that standoff which will be the only bending moment when the load from the foot is in the direction towards the keel. Trying to establish that bending load is near impossible without a strain gauge!

I will try to find the compression load that a 1.5m length of steel scaffold can sustain before buckling.

Your variable length legs obviously are the best idea allowing you to make realtime adjustments during grounding and raising them the moment she starts to refloat but not everyone can justify the cost.

Thanks again for your views and experience.

Colin. solocoastalsailing.co.uk
 
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Plum said:
Wow. Thanks for sharing your scary experience! Will take your views into account.......
Click to expand...
It wasn't actually scary at all, the boat could not have fallen over as she was on the point of floating anyway, it was just a bit bumpy as the leg kept digging in. Maybe if I put up with a greater angle of heel whilst grounded, she would have levelled up fully before being able to start floating.
 
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