bad roll with following sea

[cpthook]

hi there

My wooden Nicholson 31 which threw us about something rotten
with a 3 to 6 foot swell on the quarter. The stern would rise then
then the bow seemed to dig in at an angle and the whole thing
would wallow disturbingly from toe-rail to toe-rail, almost like
a "death roll" despite tiller adjustment.

We pumped quite a bit of water out of the blige which helped a
little but about 5 inches remained and I suppose this could have
sloshed about increasing the roll. Also had 70 litres of diesel
strapped to the starboard side of the pulpit.

Are long keel narrow beam boats prone to this kind of roll with
a sea on the quarter? The boat has a new mast and it has been
suggested that it has been cut too long...

Many thanks

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[Peterduck]

All boats are going to roll under the right conditions, and the right conditions vary from boat to boat. You just struck the "right conditions " for your boat. I don't think that there would be anything inherently wrong with a Nic 31, although most British boats are too narrow for my taste. Having the diesel drums up at the pulpit would not have helped; it always pays to keep weight out of the ends of a boat. Extra weight in the bow could make her cranky and hard to steer, too much aft will make her sluggish. If the same thing happens again, and it gets too much to cope with, heave to and have a rest until the sea goes down a bit.
Peter.

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[Mirelle]

I agree with that.

Very broadly, Ancient British designs with narrow beam and heavy, deep lead keels are somewhat more prone to be champion downwind rollers, and, notoriously, one of the very worst is the legendary "Wanderer III"; roll period two seconds, roll amplitude up to 40 degrees! - which has not stopped her going round the world four times, downwind each time, so far!

All vessels suffer this - recently there has been a spate of cases of very large container ships shedding deck containers due to "parametric rolling"!

A seemingly-drastic course alteration can often stop the trouble without adding much to the distance - coming off by 40 degrees or so can make all the difference and add little to a passage, but of course if you are running into a harbour on a fixed bearing (which is when it always seems to happen to me!) there is not much you can do!



<hr width=100% size=1>Que scais-je?

 

[cpthook]

cheers all

So is it possible for the boat to broach under these conditions?
It certainly felt like it.....

Nick

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[ongolo]

Hi Mirelle,

Ancient british designs...

What would be the typical beam to length ratio?

There was (a few are still around) a plywood design RCOD a narrow 30 footer. They used to go like hell. In one race from durban to east london, skipper and crew arrived at night, but the harbour lights were all wrong.

It turned out, they sailed an extra 400km or so without realizing how well they did.
Forgot who the skipper was.

I like a narrow design, smaller engine, smaller sails and usable size depends more on the length of the boat than the beam in my opinion.

Regards Ongolo


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[Mirelle]

Typical sort of boat built in Britain up to around 1970, particularly under the old RORC Rule for offshore racing, would be narrow, long keel, heavy. LOA = 3.5 x B, with ballast ratio around 40% and draft about 60 - 70% of B.

These boats go to windward in our home waters very well; they are however prone to dramatic "pendulum" rolling!

<hr width=100% size=1>Que scais-je?

 

[Mirelle]

Dunno...

I never have broached in any of my boats, although I have certainly capsized in a dinghy that developed a "death roll"!

I suspect that in the case of a normal cruising boat the feel of the helm makes you think that a broach is imminent some time before the broach becomes reality.

<hr width=100% size=1>Que scais-je?

 

[mikesharp]

Were you sailing or motoring? Our boat is 58ft overall with an 11ft beam and can roll in those circumstances (although with a much bigger sea). Under sail she is a lot better, especially if you can get her speed up to slow the catch up of the swell. Under motor we would put up a steadying sail, normally the mizzen but if you are a sloop the main, perhaps reefed and as central as possible may damp the roll.

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[cpthook]

hi there

We were motor sailing with little wind and only a relatively small swell.

With the swell dead astern she was fine and surfed down at speed.
However with the sea slightly on the quarter she would dig in, twist and
end up at least 20 or 30 degrees off course. I dread to think what it
would have been like in a bigger sea.

She has a narrow beam.

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[halcyon]

Our Hurley 27 did just the same, simple cure, don't sail that way, move the sea more to the beam and she was happy.

Brian

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