small boat self righting

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finbarr

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How do you know if your boat is self righting from a 90degree knockdown or 180degree knockdown etc?
I was looking at the small craft advisor sea worthiness test
http://smallcraftadvisor.com/sca-seaworthiness-test
and it is one of the questions.

I know newer boats have a rating but for my 1960's mirror offshore is there anyway of knowing for sure without it getting knocked over and either recovering or not :eek:
 
Haul it down with a halyard and then let go. Do this from a dock or another boat alongside. It's a good idea to secure everthing in the boat first, and put the washboards in.
 
Salty John said:
Haul it down with a halyard and then let go. Do this from a dock or another boat alongside. It's a good idea to secure everthing in the boat first, and put the washboards in.
Click to expand...

Even with quite a small cruising boat you might be surprised just how difficult some are to haul down with a halliard from the masthead. I'm sure a Mirror Offshore should right from 90 degrees - she was a van de Stadt design after all.

As a comparison I KNOW a 17 ft Seahawk can right from having the spreader tip in the water, which is at least 90 degrees, with very little water coming aboard. This is from two wind-induced (big downdraughts or williwaws from cliffs ).

Only wave-induced knockdowns will go much past 90 degrees.

Theoretically nothing will self-right from exactly 180 degrees, but in the conditions that will produce a 180 degree inversion the boat will be chucked around enough upside down to depart from the 180 degrees. Many large modern beamy cruising boats will stay upside down for quite a long time, till enough water gets inside to destabilise them, at which point they will right. The danger there is to crew tapeed in the now underwater cockpit. Many older boats will right much faster.
 
If you do the halyard test and the boat just lies down or fully inverts what happens then? How do you bring it back, the same as you would a dinghy by hanging of the keel? Would you do it in deeper water then the mast is long in case it does invert? To be honest the thought of doing this scares me though the peace of mind you would have knowing the boat will come back up / around would be great when the going gets rough.
 
If you measure the pull on the halyard during the test, the righting force will be apparent. It is not unusual for small cruisers to be capsized by someone climbing the mast....

Have a look at the Swallow Boats vids of testing their BayRaider.

http://www.swallowboats.com/ and scroll down for a vid on the Baycruiser 20
 
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finbarr said:
If you do the halyard test and the boat just lies down or fully inverts what happens then? How do you bring it back, the same as you would a dinghy by hanging of the keel? Would you do it in deeper water then the mast is long in case it does invert? To be honest the thought of doing this scares me though the peace of mind you would have knowing the boat will come back up / around would be great when the going gets rough.
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I'd imagine that since you have hold of a halyard, you have good control - when you get towards inversion, you'd be paying out rope, rather than pulling it in/down. To get it back would therefore just be a simple matter of pulling up, rather than down. Health warning - I have never, and don't intend to ever try it out!
 
I like Mukti Mitchell's demonstration-

http://www.mitchellyachts.co.uk/photos/capsize.html

Nice little photo sequence. But, hmmm, only see it going down...

I remember somewhere seeing similar of Miss E Macs open 60 getting it's righting test done, but that's not the chat here, sorry.

Just did a google images search of yacht righting test, and there's a lot of interesting pics.

Oooh, nice powerpoint (the link in google just downloads this, not send you to a website, so not sure it'll work)-
academic.amc.edu.au/~gthomas/yacht/yacht_lec2_stability.ppt
 
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Anything with a ballast keel should be self-righting, even with it up. Water ballasted (Mac26 et al) is less likely to be so if tanks are empty or only part filled. Dinghies & most open boats with centreboards, lee boards, dagger boards etc probably are not. Motor boats probably are not.

Some day boats are & some aren't, deep keel ones like Flying Fifteen et al are, others with metal boards may not be.

But yer average plastic cabin yacht should always be self-righting. Mirror offshore certainly will be.
 
Mine has the standard 380lb ballast in stub keel, then it has two steel plate bilge keels (maybe 100 - 200lb) and the md1b 300lb inboard. so the ballast ratio is a little better, though I don't know how much the inboard is in these calculations as the weight may be to near the centre?

I noticed the open companionway in the Swallowboat video, they must have been pretty confident :cool:
 
jwilson said:
Theoretically nothing will self-right from exactly 180 degrees
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I've read about small boat designs which have a space on one side only that is designed to fill with water when inverted, while the same space on the other has sealed buoyancy. So after a couple of seconds upside down their buoyancy becomes asymmetric, they roll over a little way, and then the ballast pops them back upright.

Pete
 
The problem about boats remaining inverted was mostly about extreme IOR racers that had high CofGs and flat wide sections (and some RTW jobs that lose their keels). Most normal designs, if tempted to stay wrong side up, will be tipped back by wave action that gets the CofG and centre of buoyancy back out of line.
In the BayCruiser vid, it was not mentioned if the water ballast was full. He was not useing much force to hold it down.

If you really want to read up on this: Tony Marchaj's 'Seaworthiness- The forgotten factor' is the tome. Might put you off going offshore though......
 
Tried to pull over my 1980 Barbican 33, not as a test but to change the bog seacock, (didnt want to risk the 'bung' method in case the skin fitting moved).
the yard said a lift was 300 euros, and as you might expect waiting for the tide was pointless in Italy.

Anyway, three strong blokes using a 2 to 1 block on the spinnaker halyard couldnt get her past 40 degrees! we were so knackered that we tied it off and went for lunch (Italian style) When we returned there was a crowd of incredulous spectators.

Heated the cock up with a Hot air stripper gun, came off easy.


I have on several occasions broached in our other boat, a 1960 Wing25, mast in the water with the sails up, as a result of huge gusts or sudden catabatic winds, and we have never shipped any water in the cockpit, let alone needed washboards.

Have confidence, but beware that bilge keelers and cats dont behave the same way.
 
jwilson said:
Theoretically nothing will self-right from exactly 180 degrees
Click to expand...

Some older vessels with deep keel and narrow beam have positive righting moment all the way to 180°. In theory the 180° position in any boat will have zero righting moment but that is the same as saying a pencil stood on its point is stable.
 
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