Downflooding

[[194497]]

It's too late when the blipper is wet.....

It's the weight up the mast that counts in stability measurements.

And I guess for knockdowns primarily driven by wind rather than wave action, windage above deck height is also worth considering - roller reefing foresails, radar reflectors, spinnaker poles, fat mast sections to accommodate in-mast reefing, etc, all add windage and make a boat more vulnerable.

 

[Chiara’s slave]

And I guess for knockdowns primarily driven by wind rather than wave action, windage above deck height is also worth considering - roller reefing foresails, radar reflectors, spinnaker poles, fat mast sections to accommodate in-mast reefing, etc, all add windage and make a boat more vulnerable.

And yet it’s more complicated. Without making any of that incorrect. Mass in the mast gives inertia, resistance to sudden forces. I’ve had a demo of this, having been in a dismasted boat. It was barely possible to stand up. Windage, apart from sails is obviously all bad, no upside at all. Not just in extreme circumstances, but day to day sailing.

And radar reflectors, having their fair share of windage, could indeed be a contributor to downflooding.

 

[zoidberg]

Here's a thought.

Some years ago I acquired and sailed a quite well-known 26' conventional sailboat a few hundred miles here and there.

It had your standard pair of 1½" cockpit drains and I noticed that, even when sailing along fairly normally, water would bubble/surge up a little from one or other of those drains. That suggested the actual height of the cockpit floor was rather close to the laden waterline. Thinking about that, I reasoned that in stormy sea states, any one of many boisterous waves could/would leap into the cockpit and the ton or more of extra water would weigh down the rear end such that the cockpit would not drain, but would continue to fill up through the drains.

There would be plenty of other similar wave-tops trying to do the same.... which could swiftly lead to a 'downflooding' risk when the bridgedeck top was reached.

Later, with the boat out of the water and suspecting a part-blockage somewhere, I explored the cockpit drain tubing. I was more than a little surprised to discover that the two drain tubes from the two cockpit drains were actually 'siamesed' under the floor into just one tube - leading to a single through-hull.

A hidden cost-saver by the boatbuilder that could have had lethal consequences.

 

[Tranona]

Funny things cockpits, at least in relation to flooding. For 30 years I sailed my Eventide, sometimes in lively but not extreme conditions and never had any water other than rain enter the non selfdraining cockpit. MG the designer was very keen on buoyant boats that bobbed around on top of the seas.

At the other end of the spectrum my modern Bavarias had cockpits well above the waterline and open transoms and likewise never took any water on board.

 

[[194497]]

And yet it’s more complicated. Without making any of that incorrect. Mass in the mast gives inertia, resistance to sudden forces. I’ve had a demo of this, having been in a dismasted boat. It was barely possible to stand up. Windage, apart from sails is obviously all bad, no upside at all. Not just in extreme circumstances, but day to day sailing.

And radar reflectors, having their fair share of windage, could indeed be a contributor to downflooding.

Yes - I had a gaff-rigged Tahitiana for a while, which had a massively heavy solid wood pole mast. I think that contributed a lot to the motion of the boat, which was more smooth and comfortable than any other boat I've been on.
I sold it because its exceptional resistance to uncomfortable motion included a great deal of resistance to forward motion... But I think it was as safe as any 30' boat could be.

 

[Chiara’s slave]

Yes - I had a gaff-rigged Tahitiana for a while, which had a massively heavy solid wood pole mast. I think that contributed a lot to the motion of the boat, which was more smooth and comfortable than any other boat I've been on.
I sold it because its exceptional resistance to uncomfortable motion included a great deal of resistance to forward motion... But I think it was as safe as any 30' boat could be.

That is my experience too, heavy wooden masts contribute greatly to comfort, and not so much to speed We have a light boat, and a carbon mast that I can carry on my own, fully dressed. Again, results exactly as you’d expect. I daresay it helps your AVS in a multi, having a very light rig. Not that it’s a limit anyone wants to explore.

Low cockpits and slow drains, that was probably a big contributor to the incident with the classic that sank that I referred to. In fact I seem to recall that it’s cockpit drains led to the bilge, then relied on the pump to get rid of it. Luckily, design has moved on.

 

[Stemar]

it’s cockpit drains led to the bilge, then relied on the pump to get rid of it.

How could any sailor think that's a good idea? It sounds like something an accountant might dream up.

 

[capnsensible]

That is my experience too, heavy wooden masts contribute greatly to comfort, and not so much to speed We have a light boat, and a carbon mast that I can carry on my own, fully dressed. Again, results exactly as you’d expect. I daresay it helps your AVS in a multi, having a very light rig. Not that it’s a limit anyone wants to explore.

Low cockpits and slow drains, that was probably a big contributor to the incident with the classic that sank that I referred to. In fact I seem to recall that it’s cockpit drains led to the bilge, then relied on the pump to get rid of it. Luckily, design has moved on.

Carrying your mast fully dressed is a good plan. The alternative needs mind bleach......

 

[Chiara’s slave]

Carrying your mast fully dressed is a good plan. The alternative needs mind bleach......

Unless you’re James Wharram

 

[Chiara’s slave]

How could any sailor think that's a good idea? It sounds like something an accountant might dream up.

Late 40s/early 50s Robert Clarke design. I think many were like that in those days. It had low freeboard and quite a deep cockpit, maybe the floor was below the waterline. Anyway, to prove all us armchair experts right, she sank. Tragically with the loss of one of her 4 crew. The skipper has never been quite right since.

 

[[194497]]

How could any sailor think that's a good idea? It sounds like something an accountant might dream up.

Reading older yachting books, it's clear that self-draining cockpits were far from standard in the pre-GRP era, I suppose due to a mix of materials issues and low freeboard. Some writers also mention the idea that a deep cockpit is safer and more sheltered for the crew.

 

[jwilson]

Reading older yachting books, it's clear that self-draining cockpits were far from standard in the pre-GRP era, I suppose due to a mix of materials issues and low freeboard. Some writers also mention the idea that a deep cockpit is safer and more sheltered for the crew.

Owned a boat like that once, deep non-draining cockpit where water slowly went through to bilges. When in use, big bilge pump in cockpit. Once had a lot of water arrive in a lump, boat heeled a lot and most went over the sides. Bilge pump sorted the rest.

When moored unattended had to visit regularly to pump out rainwater, and chuck some salt in the bilges to minimise wood rot. It's how life used to be.....

 

[Tranona]

When moored unattended had to visit regularly to pump out rainwater, and chuck some salt in the bilges to minimise wood rot. It's how life used to be.....

That is why a cockpit cover pays off. A typical pleasure boat is in use underway for somewhere between zero and maybe 10% of its life during which the crew can deal with any water that comes aboard. Of course you can fit an automatic bilge pump for when the boat is unattended, but much better to stop the water from getting on board in the first place. Another side benefit is that the woodwork stays pristine. Phot shows the cockpit of my Eventide over 20 years after the teak was laid and the varnish applied.

 

[Chiara’s slave]

That is why a cockpit cover pays off. A typical pleasure boat is in use underway for somewhere between zero and maybe 10% of its life during which the crew can deal with any water that comes aboard. Of course you can fit an automatic bilge pump for when the boat is unattended, but much better to stop the water from getting on board in the first place. Another side benefit is that the woodwork stays pristine. Phot shows the cockpit of my Eventide over 20 years after the teak was laid and the varnish applied.

The boat I referred to certainly had covers. A fitted cockpit over, which really kept the rain out, and an over boom cover for the sun protection. Plus a winter cover that was too hard to remove to be fitted after every sail.

The owner was convinced that boats like thst are better in every way than their modern counterparts. That it was intrinsically more seaworthy, and more comfortable. I begged to differ, though I’ll sail anything. It was hideously wet, an order of magnitude worse than a Dragonfly.

 

[Supertramp]

I reread Maurice Griffiths book "Ten Small Yachts" over Xmas and it was a great reminder of how much things have progressed (he was buying boats for £40!). He explains that no boat is perfect for everything but some excel (and fail) in certain areas. One of his boats had no cockpit so nothing to fill up (but perhaps a bit exposed), others had self draining, others bilge draining. None of it seemed to hold him back and his later designs embody a lot of the features he respected.

Very interesting reading about the differences in rig and sail handling - like the difficulty handling bermudan sails versus gaff and the use of bowsprits. Not much help with downflooding though.....

 

[doug748]

I reread Maurice Griffiths book "Ten Small Yachts" over Xmas and it was a great reminder of how much things have progressed (he was buying boats for £40!). He explains that no boat is perfect for everything but some excel (and fail) in certain areas. One of his boats had no cockpit so nothing to fill up (but perhaps a bit exposed), others had self draining, others bilge draining. None of it seemed to hold him back and his later designs embody a lot of the features he respected.

Very interesting reading about the differences in rig and sail handling - like the difficulty handling bermudan sails versus gaff and the use of bowsprits. Not much help with downflooding though.....

Have you still got the book, was one of the boats "Pochard"? I think he described it as a Victorian duck punt to which someone had added accommodation.

.

 

[Supertramp]

Have you still got the book, was one of the boats "Pochard"? I think he described it as a Victorian duck punt to which someone had added accommodation.

I have the book but not to hand. I will check when I'm with it next, a couple of weeks.

I do recall he had several Broads type yachts one of which needed the mast lowering system removed for sea use! "Dabchick" was famous as he wrote Magic of the Swatchways with it but I would need to check if he refers to its history and if it started life as something simpler.

 

[TLouth7]

It had your standard pair of 1½" cockpit drains and I noticed that, even when sailing along fairly normally, water would bubble/surge up a little from one or other of those drains. That suggested the actual height of the cockpit floor was rather close to the laden waterline. Thinking about that, I reasoned that in stormy sea states, any one of many boisterous waves could/would leap into the cockpit and the ton or more of extra water would weigh down the rear end such that the cockpit would not drain, but would continue to fill up through the drains.

If the surface of the water inside the cockpit is higher than that outside then water *should* flow out through the drains. Even with a flooded cockpit the stern should have buoyancy which will keep the water surface inside higher than outside. Of course in the period immediately after being pooped it is recognised that lower freeboard makes subsequent pooping more likely; minimum cockpit drain size is driven by the time taken to empty the cockpit for this reason.

 

[zoidberg]

Carrying your mast fully dressed is a good plan. The alternative needs mind bleach......

Unless you’re James Wharram

... Or Hanneke Boon.

 

[lustyd]

We sail with all port lights closed and locked and the main hatch closed when away from shore.
My main concern is that the “locks” are 25 year old plastic. Realistically even if they failed the boat would be back upright quite quickly following a knockdown. I’ve experienced a knockdown with spreaders in the water and while scary it was faster than expected.