Design help for self righting catamaran wanted

[jimi]

I am the the process of designing a self righting catamaran. This will involve a masthead duogen with reverse egineering as well as normal. The question is what power will I need to spin the prop sufficiently to generate enough speed to shoot the mast back in the air?

 

[Superstrath]

I can smell alcohol on your breath, and you're slurring your worms.

 

[jimi]

Mock if you wish ... they all laughed at Christopher Columbus ...

 

[cgull]

Didnt Donald Crowhurst sort this one out with TEIGNMOUTH ELECTRON?

 

[BrendanS]

Why not just attach a large hot air or helium balloon to the mast, then it will never capsise in the first place. This might be a little awkward when trying to sail in normal conditions, so should be deployable in bad conditions - actually you could deploy it when the boat is capsized so bringing the boat upright if required.

 

[Sybarite]

Especially the Irish. They got there a 1000 years before he did...

John

 

[BrendanS]

It was a hell of a voyage in my curragh, and I did have my doubts on occasion, but we got there eventually! /forums/images/graemlins/wink.gif

 

[Guest]

Assuming you want a serious answer

The minimum thrust required would be:-

Displacement times half the beam divided by the height of the mast.

This assumes that the boat would be rotated about one hull; it would need to be restrained from moving sideways.

Clearly, as a method to right a free floating boat, it would not work.

 

[graham]

Attach a large heavy appendage to the bottom of one hull(cast iron or lead)should look something like this: :

then cut off and discard the other hull and any bits now surplus to requirements.

/forums/images/graemlins/grin.gif

 

[Rum_Pirate]

For a Catamaran to be truly self righting (ie righting without external help) then you have to in essence flood one hull; float the masthead (winch a float to the top); inflate (large) floats on the deck of the submerged hull; then inflate floats IN the now semi-submerged hull; pump the water out of the semi-submerged hull; deflate all the floats you inflated; mop up the water left in the hull, replace all the electrics, fuel, drinking water, stores and rebuild the sail drive engine and you are on your way. SIMPLE.

PS if your compressor is knackered from being submerged then it is going to take you a little while to inflate those floats by mouth. /forums/images/graemlins/grin.gif

 

[claymore]

Jamesie
I see true potential in your design but might I put it to you that it is the conversion into energy of the stopping moment of the propellor that first you need to address.
If the prop is spinning, then any fool knows that if you stop it something has to continue - this in the case of the src would be the catamaran itself so get the prop bazzing around then stop it - momentum runs along propshaft, spins something else and up comes the boat - simple really - anything else?

 

[Jeannius]

[ QUOTE ]
Lifting Keelers can allways get it up.

[/ QUOTE ]
Doesn't Mirabella have a lifting keel?

 

[michael_99]

Lifting Keelers can allways get it up.


Because, they don't go deep in. /forums/images/graemlins/grin.gif

 

[Aardee]

Not sure DC ever got around to wiring his system up. I believe he'd planned on finishing it during the voyage (obviously hadn't planned on capsizing for the first few weeks...).

Didn't his scheme involve airbags, gas and some kind of float switch??

 

[snowleopard]

Re: Assuming you want a serious answer

Self-righting of cats has been demonstrated. The surprise is that it is not done by rotating about one hull but by sinking one end, usually the stern, until a masthead buoyancy bag can get enough leverage to bring the mast horizontal. By shifting buoyancy the stern is then persuaded to float again, this time the right way up.

With a small amount of outside assistance the effect can be achieved by attaching a bridle to the bows and leading it aft between the hulls to a towing vessel which pulls the boat backward. The drag of the rig causes the sterns to dig in and the boat rotates. The required force is small and can be provided by another yacht.

So why hasn't a lot more research been done on this? Answer: because capsizes are so rare.

In 1976 an Italian entered a C class cat with a cut-down rig for the OSTAR. The committee agreed to allow it to enter provided the skipper could right it unaided. In the Millbay dock a crane tipped the boat over until the masthead float was in the water and the skipper extended a short spar sticking out from the underside opposite the mast. He hung a large canvas bag from the spar and bailed it full of water so its weight pulled the boat upright. Unfortunately he hadn't allowed for the fact that as the mast rose and the bag sank, the bag went into the water and lost its weight. The attempt ended with the mast horizontal and the committee concluded that wave action would probably flip it upright from there. They allowed the entry which didn't capsize - it broke up!! The boat was called Spirit of Surprise.