Boat hull formula

We used G and M a lot at sea

The weights on the ship were put into average distance boxes from the centreline and keel if memory serves, it was a long time ago...

So the engine room was a fixed weight with a low centre of gravity on the centreline

The accommodation had a high centre of gravity

There was a lot of guesswork, but it was well informed average guesswork

Then it all got checked manually via the fore and aft drafts to check there wasn't anything badly amiss

Only material weights were relevant, cargo placement, large tanks of fuel or water, even the 25ton swimming pool on one 5000t ship since it was only just below the bridge deck so a long way above the centre of gravity

You will have to do the same sort of thing, then trim your creation with "ballast" as required to get the best result once it has been launched

Model sailing yachts are simple since you put a big fat bit of shaped wood on the surface then hang a stonking bit of lead at the bottom of the keel, change the depth of the keel, change the righting moment lever

Edited By Ady1 on 09/12/2020 01:20:32

That's exactly as I understand loadings - vital to put weight in the right places! What I don't understand is how the stability of container ships are managed:

There's a lot of weight stacked high on the deck. Presumably heavy containers full of Chinese lathes are loaded first deep in the holds, and only light containers full of bubble wrap go on the top layer. Although the pictured ship is carrying a full load of containers, it appears to be running light - the red bottom and bow bulb are both above the water line. I don't recall any container ship capsizes so it must be safe. Unlike badly loaded aircraft, and roll-on, roll-off, roll-over car ferries!

Dave

Following my post about using the Trace function in Alibre someone on MEM queried it and I went looking for an answer. I mentioned using CAD to model the hull early on and if you look here at the third row down, left hand video "Trace images in 3D" it starts with how a boat hull can be drawn from the profiles on the plans

Container weights are declared in advance for the loading plan

Containers are pulled by a tug onto a weighbridge before loading, weight is checked, then tug moves under crane

Light ones go up top

Can be a pain if they are last off at the last port of call, nowadays I would reckon the loading plan is 95% computerised with a few PITA containers in a dedicated couple of slots which are faster to load/unload

edit: I always avoided maersk. Lovely ships, awful wages.

Edited By Ady1 on 09/12/2020 10:30:23

Great replies thanks all. The Maersk ship showing the load line you can just see the top of the bow bulge, how much of the ship hull is in the water in depth, say fifteen feet for example. Looks like a good storm would roll the ship over, as stated light loads on top.

Bob

Bob, I intended to say this on my last post but for some reason it got ommitted!

Your idea to mock the hull up and test is a good one. Hope it provides the answer you are looking for and allows you to go ahead.

Good luck with your build whatever way you choose.

Regards - Tug

Reminds me of my steplad explaining how he calculated the loading of mail planes for DHL. Basically you start with the heavy ones at the middle and work outwards balancing as best you can.

He got a worksheet and had to work it out with a pen or pencil, multiplying each cage's weight with the distance of its loading bay from the CofG IIRC.

The pilot then had to check his workings before takeoff.

Neil

With regards to the container ship loading. Anyone who has been in a rowing boat ( or kayak) will have first hand knowledge of just how high the c of g can be with what seems like very little under water and still be perfectly stable. But as we all know stand up in either and it's a different matter.

Yep, it changes the name to paddle board