"Vic Smith" wrote in message
...
Of course the first "prevention" is to avoid getting knocked down.
Now you don't have to say that.
This discusses a inflated masthead bag for the F-27, and also examples
of righting procedures for the F-27.
The F-27 is a trimaran, which affords it huge advantages for righting.
Maybe my favorite boat.
Right up there with the Mac 26X/M, but for different reasons.
http://www.f-boat.com/pages/backgrou...zearticle.html

Monohulls can be so equipped too, but if hatches aren't sealed, most
will just sink like a rock when knocked down unless equipped with
positive buoyancy foam.
Like the Mac 26M/X is.

Don't know if anyone else has pitched in on this. A ballasted keel mono hull
sail boat wants to right itself the more it heels due to the ballast and
leverage. Monohulls get knocked down at sea and stand back up on thier own,
unlike thier multihull counterparts. I guess if a sailor is real lucky and
the hull is lying across the wind and you get a good gust it could push the
boat upright but if the sails are still set, it might just keep going over
and back into the same predicament.
The flotation at the masthead is an idea that Hobie came out with way back
when, necessary to keep the boat from "turtling" when the mast fills with
water. With a Hobie, turtling would be a huge PITA, with a larger multi
nothing short of a crane is going to make things right (or upright haha).
There's a thing called "righting moment" when talking about mono hulls which
is the point the hull has to attain in order for the boat to recover from
turtling. On my Traveler 32' the righting moment was 165 degrees, meaning if
the boat completely capsized, it would recover on its own once the hull
rotated 16 degrees from exactly upside down. Like when the next wave pushed
the boat sideways and the resistance offered by the rig caused the hull to
rotate on it's long axis.
"Righting moment" is a good button to push when talking to a multi sailor
with an attitude. The argument over comfort and speed (multi) vs. crappy
weather survivability (mono) is an old one.
Thanks for a boat related post Vic!

Sure, some owners have retro-fitted their boats with foam, but those
aren't properly engineered and tank-tested.
Amateur stuff and probably just more food for Davy Jones.
But it's skiffs that got me thinking about this, because open boats
are easily swamped, whereupon they are prone to rolling over
Sure, a bit of hull sticks out of the water when the boat is
constructed with positive buoyancy.
Doesn't mean you can roll it back over, or that it's a good platform
for survival.
The NFL players lost off Tampa a while back are a good example.
Four very strong men couldn't right that boat, which was well
designed, and level floating when capsized. They tried.
Had they been able to, they could have bailed and survived.
So for typical open powerboats which might be subject to swamping and
capsize, I'm thinking inflatable airbags on both gunnels..
Activation could be manual and/or automatic upon immersion.
Keep that boat from rolling over when swamped.
The engineering is straightforward and easily accomplished.
The system would be lightweight and not affect boat performance.
What's the problem? A number.
1. Cost. Might add a couple/few grand to the boat cost.
2. Cosmetics - some bulkiness or bumps on the gunnels.
3. Liability - if you sell it, it has to work - every time.
Maybe there's disclaimers for that - I'm not a lawyer.
4. Safety ain't no fun.
5. But the biggest problem by far - I don't have my own boat
manufacturing company.
Somebody could market these systems to clamp onto the gunnels
of any boat. Add some cupholders to ensure sales. Maybe an iPod
option. Be creative.

--Vic

On Sun, 18 Oct 2009 20:05:02 -0400, "mmc" wrote:

On my Traveler 32' the righting moment was 165 degrees, meaning if
the boat completely capsized, it would recover on its own once the hull
rotated 16 degrees from exactly upside down. Like when the next wave pushed
the boat sideways and the resistance offered by the rig caused the hull to
rotate on it's long axis.

Once the mast of a monohull gets rotated past horizontal, i.e. well
into the water, it usually breaks.

"Wayne.B" wrote in message
...
On Sun, 18 Oct 2009 20:05:02 -0400, "mmc" wrote:

On my Traveler 32' the righting moment was 165 degrees, meaning if
the boat completely capsized, it would recover on its own once the hull
rotated 16 degrees from exactly upside down. Like when the next wave
pushed
the boat sideways and the resistance offered by the rig caused the hull to
rotate on it's long axis.

Once the mast of a monohull gets rotated past horizontal, i.e. well
into the water, it usually breaks.

I'd think that would depend on the mast configuration and rig strength,
right? For instance, a Westsail 32 would probably come through something
like this in a lot better shape than a Hunter 30.

In article m, mmc wrote:

Don't know if anyone else has pitched in on this. A ballasted keel mono hull
sail boat wants to right itself the more it heels due to the ballast and
leverage. Monohulls get knocked down at sea and stand back up on thier own,
unlike thier multihull counterparts. I guess if a sailor is real lucky and
the hull is lying across the wind and you get a good gust it could push the
boat upright but if the sails are still set, it might just keep going over
and back into the same predicament.

Wind doesn't capsize keelboats, waves do. Wind may knock it flat, but
nowhere near enough to capsize. Once the boat has been knocked flat the
wind no longer has any effect, as soon as the gust has passed the boat
comes back up-righ.

If a keelboat does capsize, and, as I think you're saying, the wind
against the keel is enough to right the boat, all a strong wind can
do is knock the boat down again, not capsize it.

Of course, anything that's not ballasted is a going to experience
things differently.


The flotation at the masthead is an idea that Hobie came out with way back
when, necessary to keep the boat from "turtling" when the mast fills with
water. With a Hobie, turtling would be a huge PITA, with a larger multi
nothing short of a crane is going to make things right (or upright haha).
There's a thing called "righting moment" when talking about mono hulls which
is the point the hull has to attain in order for the boat to recover from
turtling. On my Traveler 32' the righting moment was 165 degrees,

I think you mean the angle of vanishing stability. The "righting moment"
is completely different, it isn't a point, it's a measure of force that
is calculated by multiplying the distance between the centre of gravity
and centre of buoyancy by the boat mass.

Your AVS may be 165 degrees (that's very high). What that means is that
when the boat is tipped that far from upright it is as likely to fully
capsize as it is likely to come back upright. The correlation of this is
that, as you say, tipping from inverted by more than 15 degrees would
cause your boat to right.

meaning if
the boat completely capsized, it would recover on its own once the hull
rotated 16 degrees from exactly upside down. Like when the next wave pushed
the boat sideways and the resistance offered by the rig caused the hull to
rotate on it's long axis.

Justin.

--
Justin C, by the sea.