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Old 04-03-2016, 03:09   #16
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Re: Moisture in Hull

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Originally Posted by boatman61 View Post
Don't tell Wharram that. he's been calling his boats Catamarans for years.. the shock of finding out he's not a Multi-huller could kill the old buga..

I would not want to harm that old bon vivant. How old is he now, around 90?


Thats why I said "fairly unlikely to find anything but fibreglass" and not "there is only fibreglas hulls in multis".
The vast majority of cruising multis will be cored / undcored fibreglass.

There are of course some plywood boats and very few aluminium cats but thats a rare thing compared to the number of production cats out there.
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Old 04-03-2016, 03:15   #17
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pirate Re: Moisture in Hull

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Originally Posted by rabbi View Post

I would not want to harm that old bon vivant. How old is he now, around 90?


Thats why I said "fairly unlikely to find anything but fibreglass" and not "there is only fibreglas hulls in multis".
The vast majority of cruising multis will be cored / undcored fibreglass.

There are of course some plywood boats and very few aluminium cats but thats a rare thing compared to the number of production cats out there.
Getting on for sure and an excellent example of the benefits of a sailing life.. even if he is more fragile these days.
Just could not resist tugging some tails..
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Old 04-03-2016, 04:28   #18
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Re: Moisture in Hull

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.... polyester.....
Cheers


Yeloya
Why on earth would a large scale production builder use polyester. I do not get why they don't use Vinylester.
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Old 04-03-2016, 04:31   #19
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Re: Moisture in Hull

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Originally Posted by rabbi View Post

I would not want to harm that old bon vivant. How old is he now, around 90?


Thats why I said "fairly unlikely to find anything but fibreglass" and not "there is only fibreglas hulls in multis".
The vast majority of cruising multis will be cored / undcored fibreglass.

There are of course some plywood boats and very few aluminium cats but thats a rare thing compared to the number of production cats out there.
There is shed loads of WRC strip, and duflex and duracore boats as well.
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Old 04-03-2016, 04:49   #20
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Re: Moisture in Hull

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Originally Posted by HankOnthewater View Post
Boatpoker:
Thank you that link, interesting read, although I still don't understand why the author uses 'capacitance', instead of 'resistance'. Although I have limited knowledge of these meters, I think he makes some good points.

It can be confusing and thats why right at the beginning of that article I say ...

There are a different types of meters and several brands and detailed discussion would include terms like impedance, dielectric constant, capacitance, RF, resistance and conductance but basically they measure how much electricity a material can conduct, so for the purposes of this article we will say they measure something most of us understand.........."conductivity".


Some of the differences in these terms may appear subtle but are fundamental. Here is an explanation of the difference between capacitance and resistance that is better than anything I could put together
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Old 04-03-2016, 04:55   #21
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Re: Moisture in Hull

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Why on earth would a large scale production builder use polyester. I do not get why they don't use Vinylester.
I'm sure you know the reason is poly resin costs much less than vinylester resin.
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Old 04-03-2016, 05:07   #22
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Re: Moisture in Hull

Capacitance is used for moisture detection because Fiberglas is non-conductive and therefore would prevent a resistance meter from working at all. Air has a dielectric constant of 1, Fiberglas is between 2-3 and water is 80. Therefore, it is possible to detect the presence of water because the capacitance will be many times more when water is mixed with the Fiberglas. But it is a myth that any moisture meter for fiberglass can tell the exact amount of water because the change in capacitance depends on the physical shape, thickness and original properties of the Fiberglas. Metal embedded in the fiberglass will change the capacitance too. So at best a moisture meter can only compare one area of the hull to another similar area and it will give totally wrong results when there is a metal part nearby. So when someone using a moisture meter says with confidence that a hull has 8, 10, 25 or 50% moisture content you know they do not understand how the meter works. It is a bit sad that manufacturers of meters put a % scale on the meter because there is no way they can prove it is accurate in most cases. Taking relative readings in different areas can tell something about moisture if there is no metal nearby but no one can tell the exact amount of water with these meters.
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Old 04-03-2016, 05:14   #23
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Re: Moisture in Hull

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I'm sure you know the reason is poly resin costs much less than vinylester resin.
Not that much less and certainly when you factor in warranty claims for osmosis, which occur not infrequently in Poly and rarely in Vinyl - A large volume manufacturer using poly under the waterline smacks of taking the easy way - and if they do that there, where else do they do it.
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Old 04-03-2016, 05:20   #24
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Re: Moisture in Hull

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Capacitance is used for moisture detection because Fiberglas is non-conductive and therefore would prevent a resistance meter from working at all. Air has a dielectric constant of 1, Fiberglas is between 2-3 and water is 80. Therefore, it is possible to detect the presence of water because the capacitance will be many times more when water is mixed with the Fiberglas. But it is a myth that any moisture meter for fiberglass can tell the exact amount of water because the change in capacitance depends on the physical shape, thickness and original properties of the Fiberglas. Metal embedded in the fiberglass will change the capacitance too. So at best a moisture meter can only compare one area of the hull to another similar area and it will give totally wrong results when there is a metal part nearby. So when someone using a moisture meter says with confidence that a hull has 8, 10, 25 or 50% moisture content you know they do not understand how the meter works. It is a bit sad that manufacturers of meters put a % scale on the meter because there is no way they can prove it is accurate in most cases. Taking relative readings in different areas can tell something about moisture if there is no metal nearby but no one can tell the exact amount of water with these meters.
A terrific explanation, better than mine. Would you mind f I pasted that into my article (with attribution of course)?
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Old 04-03-2016, 05:58   #25
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Re: Moisture in Hull

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There is shed loads of WRC strip, and duflex and duracore boats as well.
Doesn't WRC, duflex, duracore and all that fit into the cored fibreglass category?
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Old 04-03-2016, 07:34   #26
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Re: Moisture in Hull

Originally Posted by rabbi View Post
"capacitance is what these meters measure, not resistance
resistance is only used by those cheap meters which have spikes to press into wood. they don't work on hulls


as for hull material.. this is the mulltihull forum so it's fairly unlikely to find anything but fibreglass."


so you never met any one with a cross trimaran.. wood with glass.. or a piver tri..wood with glass.... horstmann tri-- ditto-- wharram, ditto--- man, you gotta research before ye spew....
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Old 04-03-2016, 07:46   #27
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Re: Moisture in Hull

Yes.

b.
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Old 04-03-2016, 07:58   #28
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Re: Moisture in Hull

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Originally Posted by rabbi View Post
"capacitance is what these meters measure, not resistance
resistance is only used by those cheap meters which have spikes to press into wood. they don't work on hulls


as for hull material.. this is the mulltihull forum so it's fairly unlikely to find anything but fibreglass."


so you never met any one with a cross trimaran.. wood with glass.. or a piver tri..wood with glass.... horstmann tri-- ditto-- wharram, ditto--- man, you gotta research before ye spew....
I said "fairly unlikely" and not " impossible"

I am sure that with the hundrets of cats produced each year over the last decades that 95% of all average sized cruising multis currently on the market are cored / uncored fibreglass.
Some markets may be different, of course. If one concentrates on trimarans of the 60s or 70s for example, or maybe Australia with a more active homebuilding scene.
But the current global market of multihulls is for sure fibreglass, and any other hull material is an exception.

A 5% chance of finding something different than fibreglass is what I call unlikely. And nothing else I said.


Disclaimer:
These 95% are just my guess. May be wrong, but not by far. If you questions this figure, please provide better ones.

EDIT: Yes, I met a few Wharrams, and I saw Pivers in the junk yard. They are a very tiny little fraction of the market.
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Old 04-03-2016, 10:15   #29
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Re: Moisture in Hull

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A terrific explanation, better than mine. Would you mind f I pasted that into my article (with attribution of course)?
Yes, no attribution required. I give this speech a couple times a year when a surveyor tells some newbie at the marina their would-be boat has 20% moisture content in the hull.
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