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Old 24-01-2016, 04:02   #1
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Flex to the fore?

Dear contributors,


Yacht category: 48ft to 55ft. Modern volume European manufacturer, non bespoke. Deck construction: injection moulded.

Are fore decks designed to flex?

Should there be some flex or no flex?

If yes or some;

Is the the amount of flex measurable?

Should you feel the flex when you walk on it?

Should the flex be visible to the naked eye?

What could be the possible effects of a flexing foredeck?
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Old 24-01-2016, 04:12   #2
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pirate Re: Flex to the fore?

Quote:
Originally Posted by Dumbstruck View Post
Dear contributors,


Yacht category: 48ft to 55ft. Modern volume European manufacturer, non bespoke. Deck construction: injection moulded.

Are fore decks designed to flex?
NO

Should there be some flex or no flex?

If yes or some; NO

Is the the amount of flex measurable?

Should you feel the flex when you walk on it?


Should the flex be visible to the naked eye?

What could be the possible effects of a flexing foredeck?
A flexing mid and aft deck over time...
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Old 24-01-2016, 05:00   #3
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Re: Flex to the fore?

Scary!

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Old 24-01-2016, 05:00   #4
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Re: Flex to the fore?

Greetings and welcome aboard the CF, Dumbstruck.

There should be no discernible deck flex.
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Old 24-01-2016, 05:55   #5
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Re: Flex to the fore?

I think it depends, decks of lighter vessels of newer construction methods flex a little, geminis, Fountain pajots, lagoons etc have a tiny bit of give, so do some heavier mono cruisers ive been on made of solid glass.

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Old 24-01-2016, 08:33   #6
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Re: Flex to the fore?

On a monohull, none
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Old 24-01-2016, 08:43   #7
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Re: Flex to the fore?

GRP is an inherently flexible material, it is the core that creates rigidity. So if it is a solid uncored deck it will have some give which you may feel. If it is enough to see I would be worried. If the deck has no core I would want to know why, the deck takes the lateral compression loads from the rig so normally wants to be very stiff. If it has a core then it is either shot or so badly build it might as well be, repairing a failed core is virtually impossible
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Old 24-01-2016, 09:10   #8
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Re: Flex to the fore?

Quote:
Originally Posted by Dulcesuenos View Post
I think it depends, decks of lighter vessels of newer construction methods flex a little, geminis, Fountain pajots, lagoons etc have a tiny bit of give, so do some heavier mono cruisers ive been on made of solid glass.

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There is no flex on our L400. I think that there should be no flex on any deck.
Check for liquid intrusion.
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Old 24-01-2016, 09:22   #9
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Re: Flex to the fore?

I would t think much flex is desirable. The main downside will be detachment of gel coat, fissures, fractures etc in the short term. Long term probably more damage from cycling, leaks around fittings etc. Some lighter weight racers are designed with flex in mind but that doesn't fit the description of your yacht. If it's a volume builder I guess you can find another of the same model to compare and see if it's 'normal'
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Old 24-01-2016, 09:37   #10
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Re: Flex to the fore?

I am too in the band crying no flex. It IS a big boat.

I have seen small amt of flex in older, smaller boats. The bigger the boat, the less flex (as our body weight becomes inconsequential to the scantlings).

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Old 24-01-2016, 09:39   #11
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Re: Flex to the fore?

Quote:
Originally Posted by Dumbstruck View Post
Dear contributors,


Yacht category: 48ft to 55ft. Modern volume European manufacturer, non bespoke. Deck construction: injection moulded.

Are fore decks designed to flex?

Should there be some flex or no flex?

If yes or some;

Is the the amount of flex measurable?

Should you feel the flex when you walk on it?

Should the flex be visible to the naked eye?

What could be the possible effects of a flexing foredeck?
Technically, an entire vessel flexes to some degree, but it should not be discernible just walking on deck... Given that the deck is injection molded, it is always possible to have a resin starved area.

If you have found specific deck areas on a particular vessel you are interested in that flexes just from your weight, I recommend you find a sister ship manufactured around the same time and see if those same areas [or worse, different areas] on deck exhibit the same flexing.

You might also peruse relevant online Owner's Groups for information.

I know several of the popular French production boat manufacturers went to injection molded decks about 10-15 years ago in an attempt to reduce labor [injection molded vs. hand lay-up.] The premise is good if the appropriate structural reinforcement is properly placed within the mold before the resin is injected- as long as there are no resin starved areas...

I'm not a boat designer or builder, but have some experience with the materials and processes involved.

If you are focused on this particular vessel and the relevant Owner's Groups don't reveal any similar issues with the make and model you have your eyes on, you might consider having a preliminary survey performed [one with no report- just providing an educated opinion...]

Best wishes with your endeavor.

Cheers!

Bill
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Old 24-01-2016, 10:07   #12
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Re: Flex to the fore?

I agree with Bill, "it depends". Most fiberglass boats flex more than you might imagine, but it should also be very predictable across all of the same models if they are built the same. I am assuming that if it is resin infused? (not "injection"?) it is also very probably cored with something. (What?)
I also have to ask the obvious- how much weight is making it flex, did/does the boat have a very large crew that might have damaged it? Many common lay-ups can not support a barefoot 250lbs person without damage to the core. Deck shoes help distribute the load. I realize that may sound bad, but it is reality. I many cases, some flex is quite acceptable in flat panels. Eliminating "all" flex would weigh too much. That said, finding very much movement on an over 40' cruising boat would at least justify some research.
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Old 24-01-2016, 10:39   #13
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Re: Flex to the fore?

NOOOOO to all questions.


is this a french boat?
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Old 24-01-2016, 11:19   #14
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Re: Flex to the fore?

Quote:
Originally Posted by meirriba View Post
There is no flex on our L400. I think that there should be no flex on any deck.
Check for liquid intrusion.
I have yet to see a french or SA cat whose deck doesnt give a tiny bit, stanchions wiggle or shake a hair when walking down the walk ways

The lighter ones tend to have more not as much as a gemini would, but some
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Old 24-01-2016, 13:08   #15
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Re: Flex to the fore?

The cross member dividing the forward deck hatches appears to deflect under a weight of less than 70 kilos / 130lbs.

There is movement under foot in all directions forward of these hatches.

The deck is covered in teak which I thought would have the effect of strengthening the area.

Thank you all.
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