Para drogues in large seas

"Joe" <steelredcloudm> wrote
>
> I'd wait till they got close to twice the beam size...heck we raced
> with full sails downwind with 12 ft seas..
>

That's reasonable. There is a lot more to it than just size. Wave equal to
the beam can result in capsize breaking in shoal water. You are unlikely to
get a deep water wave breaking that hard in a developing near coastal
depression. A long set of swells running under waves of that size could
cause a problem but you might not see it in a lifetime.

It's out in the long fetch areas of the world where systems can blow for
long periods in the same direction that the swells can combine with local
wind driven waves such that you should just start thinking about it when the
waves get to about equal to your beam. I'm talking about really being equal
to the beam as opposed to just looking like it. I wouldn't put a drogue out
at that point but, it the barometer or weather report indicated that
conditions could worsen, I'd probably look and make sure it was ready to go.

--
Roger Long

> "Joe" <steelredcloudm> wrote
>>
>>...heck we raced with full sails downwind with 12 ft seas..
>>

Joe, which wave measurement are you using here, the "looks like 12 feet", in
which case they would be 6, or height of eye from waterline when sighting
across the crests with the boat in the trough?

Back when I was researching sailing vessel losses, accuracy of reported wave
height was an important question. I got out on professionally crewed boats
a lot more in those days and would ask experienced mariners how high they
thought the waves were whenever I got a chance. Then, I would go and check
carefully. They were almost universally half as high, even when asking
very experience people. To this day, I estimate wave height by taking my
best visual guess and then just cutting it in half.

I still check wave height occasionally the careful way and it always
surprises me how low they actually are. The 50% rule always works. There
is a solid physical reason for this which is rooted in the dynamics of the
water motion and has nothing to do with inexperience or being frightened.

--
Roger Long

On Mon, 22 Oct 2007 21:20:16 -0400, "Roger Long"
<strider@maine.> wrote:

>I still check wave height occasionally the careful way and it always
>surprises me how low they actually are. The 50% rule always works. There
>is a solid physical reason for this which is rooted in the dynamics of the
>water motion and has nothing to do with inexperience or being frightened.

If a large sportfishing boat with a 30 ft tuna tower, 1/2 mile away,
disappears behind a nearby wave, how big is the wave?

I estimated 12 ft from my perch on the flybridge about 15 ft above the
water. My experience is that waves look a lot larger from deck level
than they do from the flybridge, probably an optical effect.

On Tue, 23 Oct 2007 05:41:08 -0400, "Roger Long"
<strider@maine.> wrote:

>Heel angles are also overestimated by prominent amounts.

Used to be you could buy a heel and pitch indicator cheap. Guys put
them on their jeeps.

The Queen Mary was in routine [for it] 30 to 40 foot waves when a
breaking wave took out the windows of the pilothouse. That was not
estimated to be 93 feet above sea level, there was no guesswork there.
The heel was not measured, but there was general agreement that it was
near the point of no return. More than fifty degrees. Bit more and she
would have just disappeared.

Casady

"Richard Casady" <richardcasady@> wrote
>
>>Heel angles are also overestimated by prominent amounts.
>

Yes, but "down" is hard to establish in waves. Mount a tripod on a life
ring and hang a plumb bob in it. As the tube goes up on a wave, it will
point perpendicular to the surface. It can even go up inside the tube of a
breaking sea and be pointing straight up for a moment. The life ring
follows the surface of the wave so is subject to the pure dynamics. Add in
the rolling of a boat that doesn't follow the surface and "down" can be all
over the place.

--
Roger Long

On Oct 23, 3:02 am, Goofball_star_dot_etal <w...@needs.email.anyhow>
wrote:
> On Mon, 22 Oct 2007 17:25:39 -0700, Joe <steelredcl...m>
> wrote:
>
> >What is the depth of the diminishing factors. ie: say a 20 ft wave,
> >how deep would your drouge need to be to avoid any wave action?
>
> Good question! Zero at precisely half the wave's length, independent
> of height.

Problem is, takes lots of weight and line length to get a chute off
the surface under load..and in heavy loads even harder if not
impossiable, lots of catenary with a mid line chain sinker would help
more than anything IMO.

Joe

On Oct 22, 11:41 pm, "Roger Long" <stri...@maine.> wrote:
> > Interesting. How did you check carefully?
>
> You adjust your height of eye by climbing superstructure or rigging
> (actually, in most cases you bend over or lie on the deck) until you see
> most of the wave tops lined up when the vessel is in the trough. Your
> height of eye is then the wave height. It's quite striking when you see it
> because your height of eye is so seldom equal to the wave height. ...

I think your method will tend to underestimate the wave height. As
you have mentioned elsewhere it is very hard to estimate when you are
in the trough because "down" for you depends on your movement. That
is the explanation given for why we all tend to overestimate wave
height when we look a wave faces in the first place. In your case, it
is likely that you will have some heal relative to the "real" local
gravity as opposed to having some heal on your clinometer when you
take your observation. This will add two types of error. First, you
will be on the wave face rather than in the trough and second you need
to correct for the vessel's heal relative to local gravity by
multiplying your height of eye by the cosine of that heal. Those
errors will both subtract from the apparent wave height. Taking
these issues into account might bring your observations into agreement
with what I've been told which is that we tend to overestimate wave
height by 30%. My rule of thumb is to take my best guess at wave
height and remove a third...


-- Tom.

On Oct 23, 11:11 am, "Roger Long" <stri...@maine.> wrote:
> "Joe" <steelredcl...m> wrote

> I was out for a sail this morning not far from the buoy and the 50% rule
> still works.

> Roger Long


Hi Roger:

I was heading south a few miles off the mid WA coast in early August.
Had a following sea. I have a 12m boat. So Im on top of this crest and
look down to this hole. I eye estimated two more boat lengths to the
bottom of the trough. In other words, three boat lengths (3x12m) to
the bottom.

What would the wave height be on that one?
I used the hypotenuse of a right triangle calculation......... Eeks!
Would that be an accurate estimate?
Your thoughts?
Bob

"Bob" <freya2gom>
>
> What would the wave height be on that one?
> I used the hypotenuse of a right triangle calculation......... Eeks!
> Would that be an accurate estimate?

No. But a typical length to height ratio is 20:1 for a well developed sea
with a long fetch. If your crest to trough estimate is correct, that would
put the wave height at about 12 feet where Joe is still racing along with
full sail:)

--
Roger Long

"Joe" <steelredcloudm> wrote
>
> That looks pretty choppy for your boat Roger..isn't perception a
> funny thing?
>
No, she's a remarkably good rough water boat. I didn't even put on my foul
weather gear. It would have been hard work if I needed to be anywhere dead
to windward in a hurry but she's good for a lot more. Close reaching at 5.5
knots was dry and comfortable. Went a bit over 7 on the beam reach back in.

--
Roger Long