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Old 07-12-2007, 07:24   #46
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Kanani..perhaps I shouldn't be too concerned then, as there are actually 4 small cockpit drains, but they carry down to "T" connections branching in from galley sink, drains, etc. before continuing on to "thru-hulls".
Shutoff valves at the sink, prevent intrusion from the deckwaters, as long as someone remembers to close them in heavy seas.
As I write this, perhaps I should just enlarge the existing 4 since they are less than 3/4 inch I.D? (tend to clog)
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Old 07-12-2007, 09:30   #47
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Cockpit drain through-hulls should serve no other purpose. Sink drains & etc should NOT be TEE’d into them.
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Old 07-12-2007, 10:24   #48
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Cockpit drain through-hulls should serve no other purpose. Sink drains & etc should NOT be TEE’d into them.
Gord,
I don't know why, but I thought the boat was built with the "T's" installed. DoH!

Stupid me, that is why they tend to clog..
I'll be changing them immediately.
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Old 01-08-2012, 22:55   #49
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Re: Storm Management for Cruisers

In the interests of balance for anyone (like me) who comes on this discussion too late to participate, I'd like to put another point of dissenting view to the OP's central assertion.

My objection is very broadly similar to one raised in post 38, although he's making a somewhat different point to mine (but valid too, it seems to me)

The OP talks of decoupling the vessel from the energy of the waves, which is an admirable aim, but then commits a logical non sequitur by talking as though this can best be achieved by reducing the speed of the vessel through the water to zero.

This makes sense to me in the situation where the waves are not breaking forwards, so I have no trouble with it in that circumstance.

And I freely admit that even in storms, this covers the situation almost all of the time - very few of us will ever see more than a handful, at most, of deep ocean waves breaking entirely down their front face, as opposed to spilling some or all of the crest down the back, which is what 99% or more of so called "breaking" waves are really doing when you pay close attention.
[Of course there is an exception for waves which hit something, such as your boat. Then the crests routinely detach and travel forwards.]

I say this because it's well known that there is no mass transfer horizontally in an ordinary wave train. The particles of water, viewed side on, orbit back to their starting point each wave, unless there's an underlying current.

This all changes when the wave front becomes so steep that the crest can 'exit the system' and fall under the influence of gravity down the fast-moving face of the wave. At this point there can be collossal horizontal mass translation, and sitting there stationary is not an optimum way of 'decoupling the energy of the storm from your yacht'. In fact, it's almost the opposite. The only way you could do worse would be to motor rapidly towards it (and even this might be better, if you made it over the top before it broke!)

Certainly it is better to be anchored to the body of water by the bow (or even the stern) than to be anchored side on, or in almost all cases than to be drifting side on, as you can well imagine with the thought experiment of anchoring in a surf break. But such anchoring will take massively strong gear if the wave is very large, with a significant crest.

If the aim is to avoid coupling to the kinetic energy of the avalanche of water coming down the flank towards the yacht, it is (at least in theory) necessary to travel in the same direction at the same speed as the avalanche.

This is not literally practicable because the speed is unrealistically high. The ramp down which the avalanche is travelling is itself moving at maybe 40 knots, and the water tumbling down it is effectively in freefall.

However if the vessel is designed to be able to skid off at considerable speed down the face of such waves without tripping over its own appendages or bow (and ideally in such a way that, if caught beam on, it will tend to bear away so as to run away end-on) then we are a lot closer to the ideal the OP sets up, of NOT coupling to the kinetic energy.

Imagine a surfboard plonked in mid ocean in such conditions. Even one not strong enough to survive your weight in the middle with both ends on blocks, will survive the worst a breaking wave can do, and it may even stay sunny side up.

Adding a ballasted keel would NOT improve its chances, in fact, I would venture, quite the opposite. I can't say for sure that internal ballast would not be an improvement, however.

I'm straying from the topic, which is that it's the speed Delta, or difference, between the mass translation of the wave and that of the vessel, which causes energy coupling (which is a Bad Thing, when there's lots of energy on tap).

I guess this points inexorably towards some sort of skimming dish, with appendages retractable except at the stern, buoyant, high lift in the forebody, low freeboard, and (when keel is retracted) with the centre of mass at about mid height relative to the side profile (not the underwater profile)

There needs to be some way of ensuring this vessel can reright if the attempt to decouple is - or more accurately: the attempt to AVOID tripping, is unsuccessful, but the mast is not likely to survive if it inverts in such circumstances. *

For a small deep sea vessel, this implies to me the whole design of the vessel would have to prioritise the hypothetical encounter with this (very unlikely) circumstance: either a (very strongly built) catamaran - but I don't know pretend to know much about this option ... or a strong but relatively light monohull, with a lifting ballast keel independent from deep appendages aft. (The latter acting like the fletches of an arrow)

Ideally the ballast keel would be hydraulically operable, using an accumulator. This would enable the ballast keel to be immediately deployed if the vessel should invert. Would probably have to be a swing rather than a dagger so the center of mass did not rise too high, because a skimming dish needs a minimal draft in the canoe body.

This all hardly seems worth doing, except in the specific case of sailing in the few parts of the world where such waves are --let's say, while still infrequent, not unheard of.

*Possibly for a small vessel, say 10 to 11m, with a short rig, given that we can now look, via satellite, at wave heights in developing systems which have not reached us, it might be feasible to engineer a rig which could preemptively be dropped and secured at sea. You'd only do this if a sufficiently ugly system was in the offing - but you'd have to made a decision early, when the motion of the boat was still moderate, and this seems unlikely in practice.
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Old 03-08-2012, 20:35   #50
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Re: Storm Management for Cruisers

Interesting discussion.

Nothing has changed in the way I manage storms on board Exit Only. It's either the Abbott Drogue, Gale Rider Drogue, Series Drogue or the eighteen foot diameter parachute. They all do a good job of controlling the energy on board Exit Only when we are in storm conditions on our circumnavigation.

Your mileage may differ.
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Old 03-08-2012, 21:40   #51
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Re: Storm Management for Cruisers

As the old fella who taught me to sail 50 + years ago told me, make the boat as comfortable for your body as you can, and she will safe, cus she's tougher then you!! so ya use a drogue, or a chute or as i like to do keep sail on and drag a heavy long warp behind the boat !! keep steering and run slow down hill, its always worked for me !
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Old 04-08-2012, 00:04   #52
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Re: Storm Management for Cruisers

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Originally Posted by bobconnie View Post
As the old fella who taught me to sail 50 + years ago told me, make the boat as comfortable for your body as you can, and she will safe, cus she's tougher then you!! so ya use a drogue, or a chute or as i like to do keep sail on and drag a heavy long warp behind the boat !! keep steering and run slow down hill, its always worked for me !
I wouldn't hand steer in the waves with a following sea like that. Super hard on the mind.
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Old 22-08-2012, 07:23   #53
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Re: Storm Management for Cruisers

Great thread!. I was caught by NE front in a Gulfstream crossing in November years ago with 10-15' breaking seas. We were on a 31' monohull (Allamand 31') and choose to run before it. We took the breakers on the port quarter and even with her considerable freeboard got pooped twice. Should I have handled this differently and used a parachute, drogue or warps?

Right now I own a 37' double ender thinking she would have handled this situation a lot better considering her full keel, added size, displacement, 6' as opposed to 4' draft and off course the canoe stern. How would any of you handle 30+ knots of wind and short confused 10-15' breaking seas with this boat?

Any advice would be appreciated since the Gulfstream is my backyard...

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Old 22-08-2012, 08:45   #54
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Re: Storm Management for Cruisers

The issue is not to necessarily avoid being pooped but to avoid being rolled. The deployment of a series drogue seems to be one of the better strategies to control the boat speed in steep breaking seas. When the seas are large enough and steep enought the boat has the potential to surf out of control down the wave face and pitchpole or be tripped by the keel and roll. The series drogue serves to maintain a downwind heading and as a speed brake. The series drogue is a speed dependent brake in that the faster the boat goes the more the drag force increases.
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Old 22-08-2012, 09:05   #55
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Re: Storm Management for Cruisers

I can't wait to read your article.

Ever since the day that I took my Cape Dory 25D out in 45 kts to practice heavy weather tactics and heaving to I've been amassed at how well our small 25D can be de-powered. I've always been concerned with being over powered and not able to reduce the effect on our vessel...
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Old 22-08-2012, 10:29   #56
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Re: Storm Management for Cruisers

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Originally Posted by vtcapo View Post
Great thread!. I was caught by NE front in a Gulfstream crossing in November years ago with 10-15' breaking seas. We were on a 31' monohull (Allamand 31') and choose to run before it. We took the breakers on the port quarter and even with her considerable freeboard got pooped twice. Should I have handled this differently and used a parachute, drogue or warps?

Right now I own a 37' double ender thinking she would have handled this situation a lot better considering her full keel, added size, displacement, 6' as opposed to 4' draft and off course the canoe stern. How would any of you handle 30+ knots of wind and short confused 10-15' breaking seas with this boat?

Any advice would be appreciated since the Gulfstream is my backyard...

RT

It's what you can expect when the Gulfstream meets a strong wind from any northerly point. In some parts of Florida you'll also have a hard time pulling in in many places, especially if the tide is going out.
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Old 22-08-2012, 11:54   #57
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Re: Storm Management for Cruisers

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Thanks for the EXCELLENT article Dave.

Although you emphasize reducing the Kinetic Energy (momentuum) imparted on a boat, and the importance of minimizing (decoupling) it’s effects - it could be noted that the same square relationship applies to Wind Pressure, and Displacement vs Load relationships (which explains why loads & costs increase exponentially with boat size), and etc.

Wind Pressure can be approximated by:
Pressure = ˝ Density of air x Wind Speed Squared x Shape Factor
The shape factor (drag coefficient) depends on the shape of the body it impacts upon.

Simplified:
Wind Pressure is proportional to;
- wind velocity squared
- exposed area squared
Hence:
Doubling the sail Area will quadruple the wind force acting upon it.
Doubling the Wind Velocity will quadruple the wind force acting upon the same sail.

The chart shows approximate relationship between wind speed and wind force developed on one square foot of flat area set perpendicular to wind direction.
Very important and often poorly understood point about wind pressure and wind speed.

The wind force doesn't go with the square of sail area, though. Double the sail area and you get double the pressure.
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Old 23-08-2012, 00:18   #58
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Re: Storm Management for Cruisers

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Very important and often poorly understood point about wind pressure and wind speed.

The wind force doesn't go with the square of sail area, though. Double the sail area and you get double the pressure.
You're right to pick up on that, but you've fallen into another trap set up by the post you're amending.

"Pressure" means force per unit area.

In the post you're referring to, it's used in a different and incorrect way, to denote force alone.

So your correction should ideally read "Double the sail area and you get double the force"

The pressure does not double when you change sail area; it remains the same (In the simplified context under discussion, it's a function of wind speed and density)

Might seem like a quibble, but any discussion using formulae needs to plug in terms according to their agreed definition, or confusion and errors are inevitable.
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Old 23-08-2012, 00:44   #59
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Re: Storm Management for Cruisers

Fitzroy, the original weather forecaster that travelled with Darwin, was also involved with Admiral Beaufort creating the wind pressure system. Each increase of 1 is a doubling of the pressure, which is why a progression during the day from f3 to f5 seems so great, you've got four times the force on the sail area!
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Old 23-08-2012, 07:26   #60
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Quote:
Originally Posted by Andrew Troup

You're right to pick up on that, but you've fallen into another trap set up by the post you're amending.

"Pressure" means force per unit area.

In the post you're referring to, it's used in a different and incorrect way, to denote force alone.

So your correction should ideally read "Double the sail area and you get double the force"

The pressure does not double when you change sail area; it remains the same (In the simplified context under discussion, it's a function of wind speed and density)

Might seem like a quibble, but any discussion using formulae needs to plug in terms according to their agreed definition, or confusion and errors are inevitable.
Nice catch! Sorry about that. I use the right word at the start of the sentence, the screw up at the end. Doh!
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