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Old 30-11-2019, 03:09   #16
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Re: crash bulkheads on production boats?

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Originally Posted by funjohnson View Post
Every Hunter over 33' has Kevlar forward too They don't define how far back the Kevlar goes, but even if it's an inch, they can add it to the advertisement.

If I remember correctly, the Moody has it back to the keel stub.. is that right? Is it on the inner or outer side of the coring?

Matt

Correct. The Kevlar is the outermost layer of the layup (naturally), and goes to the keel stub, so covering all the forward sections. This greatly increases the impact resistance of the forward sections. Kevlar is very weak in compression so it has a weird effect on the structure, increasing stiffness in tension but not compression.



Concerning watertight compartments: I think people are underestimating how difficult it is to build a boat with them. It requires a lot more than watertight doors. The bilges have to separated, it requires separate bilge pump pickups (better, entirely separate bilge pump systems) for each compartment, and it is the very devil to seal the various cables and pipes passing through all these bulkheads. I admire the Amel very much, and I would prefer that approach to what I have, but I like the Sundeer approach even much better. With no penetrations in the main hull volume, the boat becomes practically unsinkable with substantial watertight compartments fore and aft of the main hull volume. The after part of the boat is a large volume including not only lazarette but large volume engine room and technical space. It would suck of course to have this space flooded, but the boat would not sink, and you could work on dewatering it from a safe place. This is really good design.



I hate the fact that the lazarette of my boat communicates with the main hull volume. There is already a substantial structural bulkhead between the laz and aft cabin and the bilge is very shallow there. There are few pipes and cables. It would have been pretty simple to make that bulkhead watertight, requiring one bilge pump and sealing up a pretty small space. The volume of that space is quite substantial.
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Old 30-11-2019, 05:28   #17
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Re: crash bulkheads on production boats?

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Correct. The Kevlar is the outermost layer of the layup (naturally), and goes to the keel stub, so covering all the forward sections. This greatly increases the impact resistance of the forward sections. Kevlar is very weak in compression so it has a weird effect on the structure, increasing stiffness in tension but not compression.

.
In an impact, the outer layer is in compression and the inner is in tension. That's why I've always been confused as to where this laminate layer goes in a build. Seeing Lyman-Morse build Kiwi Spirit, the outer hull was carbon/core/carbon/kevlar/carbon which seems to reinforce the idea that the inner laminate is in tension and where the kevlar works best. But a lot of other builders are outer of glass/kevlar/glass/core/glass.

I'm just slightly confused and no amount of Googling seems to clear this up.

Matt
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Old 30-11-2019, 06:28   #18
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Re: crash bulkheads on production boats?

We have Kevlar on the outer layer of the laminate in the turn of the bilge. This is not so much for collisions as it is for grinding on a reef, i.e. for abrasion resistance
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Old 30-11-2019, 06:51   #19
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Re: crash bulkheads on production boats?

Quote:
Originally Posted by funjohnson View Post
In an impact, the outer layer is in compression and the inner is in tension. That's why I've always been confused as to where this laminate layer goes in a build. Seeing Lyman-Morse build Kiwi Spirit, the outer hull was carbon/core/carbon/kevlar/carbon which seems to reinforce the idea that the inner laminate is in tension and where the kevlar works best. But a lot of other builders are outer of glass/kevlar/glass/core/glass.

I'm just slightly confused and no amount of Googling seems to clear this up.

Matt

If you wanted the Kevlar for its structural properties, then perhaps it would make sense to put it in an inside layer. But remember resisting an impact may also involve preventing PENETRATION and a hull breach, and that is what the Kevlar is for, at least on my boat.
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Old 30-11-2019, 08:46   #20
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Re: crash bulkheads on production boats?

Our boat has 5 watertight areas separated with either watertight doors or bulkheads.

It is an expensive way to build a boat, proper watertight doors are not cheap.

This would be overkill for most production boats, but I think they could do a better job in some common areas of water intrusion, such as around the rudder area. As this is close to the waterline a simple coffer dam could provide very effective protection. Some boats have this, but not many.

This is our watertight bulkhead and door separating the owners’ cabin from the rest of the interior, taken during construction:
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Old 30-11-2019, 09:20   #21
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Re: crash bulkheads on production boats?

Catalina's newer models have crash bulkheads and foam for impact in the bow below waterline.
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Old 30-11-2019, 09:20   #22
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Re: crash bulkheads on production boats?

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Originally Posted by noelex 77 View Post
Our boat has 5 watertight areas separated with either watertight doors or bulkheads.

It is an expensive way to build a boat, proper watertight doors are not cheap.

This would be overkill for most production boats, but I think they could do a better job in some common areas of water intrusion, such as around the rudder area. As this is close to the waterline a simple coffer dam could provide very effective protection. Some boats have this, but not many.

This is our watertight bulkhead and door separating the owners’ cabin from the rest of the interior, taken during construction:

And the galley standpipes! I love the dogs for the door top and bottom.... all very proper.

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Old 30-11-2019, 09:28   #23
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Re: crash bulkheads on production boats?

Our boat has a watertight, isolated lazzarette . Sort of like an airbag on a tricycle.
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Old 30-11-2019, 10:29   #24
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Re: crash bulkheads on production boats?

I don't think I've ever seen a production boat make the v-berth bed into a double bottom.

Matt[/QUOTE]


My old Beneteau 38 under the V berth was the forward integral water tank and I have to think if I hit something in the first 7 feet of the boat at water line I would loose most of my fresh water (I have two tanks) but not take on any salt water
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Old 30-11-2019, 10:45   #25
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Re: crash bulkheads on production boats?

I might follow a wider field of sailing news than the average cruiser here, and whilst there have been some noted and publicised events of cruising boats hitting objects at sea that caused sufficient damage to be of major concern, including the boat sinking, I would like to highlight some other events.

In pretty much every single major offshore racing event for the last few years competitors have hit objects at sea and caused serious damage.

This year, I think (I didn't make a spreadsheet, sorry) every single offshore event that I followed the news for had serious collisions resulting in at least one boat (from a relatively small entry list) retiring or returning to port for repairs.

Whilst I appreciate that a lot of these were high speed yachts possibly resulting in higher collision damage, the real point that I wanted to make was from a statistical point of view.

It seems that there is SO MUCH stuff floating around out there now that the odds of hitting something at some stage seem to be quite high these days.

So it seems that positive buoyancy (however you want to achieve that) would be a sensible item to have on the wish list for a future offshore cruising boat purchase.

Because unfortunately the issue of floating debris at sea will only get worse for the foreseeable future.

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Old 30-11-2019, 10:59   #26
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Re: crash bulkheads on production boats?

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Because unfortunately the issue of floating debris at sea will only get worse for the foreseeable future.

That's a good point. More commerce equals more cast-offs.

AIS and radar may be getting better, but half-submerged objects may be getting worse.
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Old 30-11-2019, 11:12   #27
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Re: crash bulkheads on production boats?

https://www.sailmagazine.com/cruisin...ision-offshore
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Old 30-11-2019, 11:25   #28
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Re: crash bulkheads on production boats?

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The real odds of hitting anything while on passage are, however, vanishingly small.

Recent surveys by the World Shipping Council meanwhile suggest that somewhere between 300-700 containers are also lost overboard worldwide each year, excluding unusual catastrophic events. These numbers may seem large, but you must also consider the incredibly vast area over which these potential threats are deployed.
Despite the warm fuzzies that author Charles J. Doane wishes to bestow on us (which mostly seems to be along the lines of 'ah, don't worry about it...') the anecdotal evidence seems to suggest (to me at least) that the odds are changing, quite rapidly...

One can even see it, by the much larger amount of 'stuff' - be that rubbish, junk, debris, etc, that now floats by us much more regularly at sea

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Old 30-11-2019, 11:44   #29
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Re: crash bulkheads on production boats?

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Despite the warm fuzzies that author Charles J. Doane wishes to bestow on us (which mostly seems to be along the lines of 'ah, don't worry about it...') the anecdotal evidence seems to suggest (to me at least) that the odds are changing, quite rapidly...

One can even see it, by the much larger amount of 'stuff' - be that rubbish, junk, debris, etc, that now floats by us much more regularly at sea

But of those 300-700, how many remain on the surface after falling in? I'm sure it depends on what they are carrying, and if it's a insulated container, but it's got to be rare that they stay on the surface for long.

We've seen a massive steel off station Super Buoy (unlit), a few 55 gallon drums and a bunch of wooden shipping in the mid Atlantic... the super buoy would be bad if you hit it, but the other stuff shouldn't cause severe damage if sailing at cruising speed.

Has anyone seen much else?

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Old 30-11-2019, 12:16   #30
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Re: crash bulkheads on production boats?

Yeah containers issue seems to be somewhat of a constant, probably just more reported these days.

But the amount of other debris seems to be on the increase.

I also think that cruising boats hit objects more often than they realise especially in rough weather when the object couldn't be seen and there is a lot of noise anyway.

I for one have found scratch/abrasion type marks on the hull after passages that weren't there before. Plain old sea water doesn't do that...

But I'm also not trying to start a panic here, only just trying to reinforce the notion that the amount of debris is getting worse and boats are starting to hit objects much more often.

I think it should be a consideration for the future.

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