Little Rascal
Well-Known Member
PS were you able to pump out while still afloat and get back into anything like normal trim?
Making a Hunter Europa Unsinkable
- Thread starter Little Rascal
- Start date
Bajansailor
Well-Known Member
Re the discussions above about stability, here is an excellent article on the subject for general background reference - http://www.rogerlongboats.com/Stability.htm
Even Chance
Well-Known Member
The lower washboard was glassed in place, which allowed pumping out to normal bouyancy. They pulled a halyard to capsize her and did a normal dingy righting routine to get her up again with no problems. This proves that foam does indeed work.
Ecosse120
Well-Known Member
Totally agree with Even Chance but then us e boaters need to stick together! My e-boat has also had most of the buoyancy changes made and another important one is that my four bunk cushions have all been wrapped in cling film otherwise they are just big sponges !!
Even Chance
Well-Known Member
Well said Ecosse!
Wee things like that can all play a part in providing positive bouyancy. Sealing the lazarette locker with foam round the coaming, and locking it closed is another idea/tip. (as long as it is also sealed/ isolated from the main hull) Keeping big fenders on board is another that most of us would forget in our bouyancy calculations!
Most boats can be made unsinkable, its just that us E-Boaters have been at the forefront of the DIY unsinkable mods for a long time now. Who needs a liferaft on a wee yacht!? (well me if I could afford one!!)
Wee things like that can all play a part in providing positive bouyancy. Sealing the lazarette locker with foam round the coaming, and locking it closed is another idea/tip. (as long as it is also sealed/ isolated from the main hull) Keeping big fenders on board is another that most of us would forget in our bouyancy calculations!
Most boats can be made unsinkable, its just that us E-Boaters have been at the forefront of the DIY unsinkable mods for a long time now. Who needs a liferaft on a wee yacht!? (well me if I could afford one!!)
Little Rascal
Well-Known Member
Unsinkability
Firstly, why bother? (For the doubters): Although this was not the question asked in the original post - some thoughts:
- Most small boaters can’t carry a liferaft on size or cost grounds.
- Small boats are in a better position to benefit from unsinkability because of the scale effect mentioned in previous posts.
- In my view, a boat able to make some way even though flooded is preferable to a liferaft which is a passive tactic. The ability to get yourself out of trouble is preferable, especially in remote waters - but only if the damaged boat is ‘survivable’ i.e. will support life and be inhabitable. Just not sinking is not enough.
Positioning of buoyancy and stability: Having thought a bit about it, here goes...
In my opinion there are two factors that need to be balanced. One is he need for stability when flooded and second is the survivability of the flooded boat.
As Rob (fae Stornaway) was saying buoyancy in the form of added foam, bags or watertight compartments (should call this flotation really) only comes into play when submerged. So it makes sense that flotation should be placed below the level of hatches to enable you to pump out the flooded cabin. So in a flat calm the optimum position for flotation would be under the sole, in the bilges etc.
Unfortunately this is the worst place to put for stability in 'real' conditions. For maximum stability the flotation should be placed as high as possible. (A huge flotation bag at the masthead or a sunken yacht would be ultimately stable!)
Obviously the two factors conflict: a hull with flotation on the deckhead only will float with the entire cabin submerged - not only unsurvivable but how do you get to the pumps or to repair any damage?
The stability issue is complex because unlike in ‘normal’ stability calculations a flooded hull acts differently - think of the water as shifting ballast.
Also where you position any added flotation changes the position of the centre of buoyancy of the hull as a whole when flooded. If floatation is in the bilges it becomes a de-stabilizing factor as the boat heels: it actually begins to provide a capsizing couple to the point where the flooded boat is most stable inverted!
So a solution for me would be:
- Place flotation around the gunwale level, as far outboard as possible. This would ensure that as the boat heeled the flotation on the ‘down’ side is progressively immersed and provides a righting couple. It also would help to keep the flooded water towards the centre of the boat to reduce destabilising sloshing. Buoyancy concentrated at this level should at least not reduce stability.
- A good size bow and stern tank/bag would be needed for pitch stability.
- Place reserve floatation on the deck head that would only come into play if knocked down.
- Raise up my bridgedeck by glassing in lower washboards.
- Make sure I had enough floatation to give access to the cabin and forepeak.
And test it. Somewhere warm .... and bring some mates to pump!
Firstly, why bother? (For the doubters): Although this was not the question asked in the original post - some thoughts:
- Most small boaters can’t carry a liferaft on size or cost grounds.
- Small boats are in a better position to benefit from unsinkability because of the scale effect mentioned in previous posts.
- In my view, a boat able to make some way even though flooded is preferable to a liferaft which is a passive tactic. The ability to get yourself out of trouble is preferable, especially in remote waters - but only if the damaged boat is ‘survivable’ i.e. will support life and be inhabitable. Just not sinking is not enough.
Positioning of buoyancy and stability: Having thought a bit about it, here goes...
In my opinion there are two factors that need to be balanced. One is he need for stability when flooded and second is the survivability of the flooded boat.
As Rob (fae Stornaway) was saying buoyancy in the form of added foam, bags or watertight compartments (should call this flotation really) only comes into play when submerged. So it makes sense that flotation should be placed below the level of hatches to enable you to pump out the flooded cabin. So in a flat calm the optimum position for flotation would be under the sole, in the bilges etc.
Unfortunately this is the worst place to put for stability in 'real' conditions. For maximum stability the flotation should be placed as high as possible. (A huge flotation bag at the masthead or a sunken yacht would be ultimately stable!)
Obviously the two factors conflict: a hull with flotation on the deckhead only will float with the entire cabin submerged - not only unsurvivable but how do you get to the pumps or to repair any damage?
The stability issue is complex because unlike in ‘normal’ stability calculations a flooded hull acts differently - think of the water as shifting ballast.
Also where you position any added flotation changes the position of the centre of buoyancy of the hull as a whole when flooded. If floatation is in the bilges it becomes a de-stabilizing factor as the boat heels: it actually begins to provide a capsizing couple to the point where the flooded boat is most stable inverted!
So a solution for me would be:
- Place flotation around the gunwale level, as far outboard as possible. This would ensure that as the boat heeled the flotation on the ‘down’ side is progressively immersed and provides a righting couple. It also would help to keep the flooded water towards the centre of the boat to reduce destabilising sloshing. Buoyancy concentrated at this level should at least not reduce stability.
- A good size bow and stern tank/bag would be needed for pitch stability.
- Place reserve floatation on the deck head that would only come into play if knocked down.
- Raise up my bridgedeck by glassing in lower washboards.
- Make sure I had enough floatation to give access to the cabin and forepeak.
And test it. Somewhere warm .... and bring some mates to pump!
bbg
Well-Known Member
I agree that the risk is extremely small. But for anyone who can read French, here is an article reporting on someone who survived because he did have a boat with positivie bouyancy (I don't like the word "unsinkable").
The cause of the problem was downflooding due to being pooped. It is sobering reading and highlights the fact that, in large waves, the instability and sloshing around of water inside the cabin makes being down below a very hazardous place.
Even if this yacht had not been dismasted, it is clear to me that continuing on and "helping yourself" back to shore is unlikely to be a real option, except in very calm waters and for a short distance only. A yacht with positive bouyancy might be better than a liferaft, but I don't think it should be thought of as a means of transport. In almost all conditions it would be a platform for rescue at best.
The other thing it highlights is that anyone aboard is - in terms of warmth - little better than being in the water. If the idea is to use a +ve bouyancy yacht instead of a liferaft, I think a survival suit would be essential. And those - like liferafts - don't come cheap.
Happy ending - he was picked up safe and sound, and the boat recovered. He still sails her.
Kelpie
Well-Known Member
When all is considered, it's pretty clear that by far the best method of providing buoyancy is by dividing the boat up into sealed watertight compartments. Lockers underneath the bunks will, as suggested, provide some lateral stability. Cockpit lockers provide stability aft. Perhaps the only real 'compromise' would be the space under the forward berths- in most boats this means losing your watertank, chain locker, or heads- but I think it would be essential for stability reasons.
If all of these areas were portioned off, of course, you would find that any puncture/impact damage on the hull would very likely only flood one of the compartments itself. So it's a double win situation!
Further, all of these spaces remain available for storage.
The practical difficulty would lie in making the hatches and seals properly watertight. I've encountered this problem with the buoyancy compartments on my Wayfarer- what appears to be a perfect seal will actually leak enough to flood in a short period of time. But if you are thorough enough with your construction, use good soft rubber seals and positive locking catches, it is doable. Once built, stick a smoke pellet inside the locker and see where the leaks are... and seal them up... and try again... and again...
You may find that you'd rather just go for a sail, of course
If all of these areas were portioned off, of course, you would find that any puncture/impact damage on the hull would very likely only flood one of the compartments itself. So it's a double win situation!
Further, all of these spaces remain available for storage.
The practical difficulty would lie in making the hatches and seals properly watertight. I've encountered this problem with the buoyancy compartments on my Wayfarer- what appears to be a perfect seal will actually leak enough to flood in a short period of time. But if you are thorough enough with your construction, use good soft rubber seals and positive locking catches, it is doable. Once built, stick a smoke pellet inside the locker and see where the leaks are... and seal them up... and try again... and again...
You may find that you'd rather just go for a sail, of course
bbg
Well-Known Member
I would suggest that there is an additional practical difficulty - ensuring that the structure itself is strong enough to withstand the water pressure.
It is one thing to make a watertight seal on - for example - a storage space under the fo'csle bunks. It is something else for that space to withstand the force of a couple of tons of water on top of it.
Sealing a space and making it watertight doesn't necessarily mean it is strong enough to act as a flotation chamber.
Little Rascal
Well-Known Member
You may find that you'd rather just go for a sail, of course
Hehe - yup, preferably on a reservoir in less than a F3
Kelpie
Well-Known Member
I hadn't really thought about it in terms of tonnes of water on top of the hatch. If you envisage taking the buoyancy chamber and forcing it underwater to a certain depth, that would be more like it. An even load spread over the whole area. But you're probably right to bring it up as an issue.
Little Rascal
Well-Known Member
And don't forget the massive forces associated with water moving/sloshing inside. The inertia of water running forward into the foreparts has been known to spring planks 