You may want to look at this website for an explanation of the differences
between polyurethane (MasterSeal NP-1) and silicone sealants.
https://www.directsealants.com/difference-between-silicone-sealant-polyurethane-sealant/

Key difference is breaking down under UV exposure.  Rummy used it for the
deck joint which should not have much (or any) exposure to UV.  The ports,
however, would have a lot of UV exposure.

Hank

On Thu, Jan 10, 2019 at 6:25 PM <mweisner at ebsmed.com> wrote:

> The problem with the silicone sealant is that it is meant to used as a
> compression gasket material.  The port light plastic tends to pull away
> from
> the complex curves of the fiberglass surface since the materials expand and
> contract at different rates.  The plastic fails to compress the silicone
> over time and the seal fails.  The silicone material may last 50 years but,
> in my experience, the seal fails in 3 to 4 years.
>
>
>
> An alternative sealant suggested by Rummy for the hull joint but may work
> fine here is as follows (thank you Graham):
>
>
>
> For those who want more information on the sealant Rummy used for his deck
>
> hull join now called Master Seal NP-1 (formerly Sonolastic NP 1) the spec
>
> sheet is available here:
>
>
> http://assets.master-builders-solutions.basf.com/Shared%20Documents/EB%20Con
>
>
> struction%20Chemcials%20-%20US/Construction%20Systems/Data%20Guides/MasterSe
>
> al/basf-masterseal-np-1-tds.pdf .   (Note: The link is still valid on
> 1-10-19, copy attached)
>
>
>
> The sealant seems to have all of the properties that would be advisable for
>
> such an application such as high flexibility, can be immersed in water,
>
> tenacious, sticks to anything and is available in a range of colours such
> as
>
> off white. It appears to be available at Home Depot and is much cheaper
> than
>
> the traditional marine sealants.
>
>
>
> It is not clear that Beckson Marine would recommend it but it probably
> wouldn't hurt the plastic.
>
>
>
> Mike
>
> s/v Wind Lass ('91)
>
> Nissequogue River, NY
>
>
>
>
>
>
>
> -----Original Message-----
> From: Rhodes22-list <rhodes22-list-bounces at rhodes22.org> On Behalf Of Cary
> Tolbert
> Sent: Thursday, January 10, 2019 5:41 PM
> To: Art Czerwonky <a_czerwonky at yahoo.com>; The Rhodes 22 Email List
> <rhodes22-list at rhodes22.org>
> Subject: Re: [Rhodes22-list] Silicone sealant used on cabin windows
>
>
>
> Art, Beckson Marine who makes port lights says to use ONLY 100% silicone
> sealant. On my '86, Beckson is the name on the frames. Their think (as
> posted) says most sealants will only last 10 years and that silicone should
> last over 50 years. This is their business, so my guess would be to follow
> their advice.
>
> Cary
>
> S/V Whisper '86
>
>
>
> On Thu, Jan 10, 2019 at 4:41 PM Art Czerwonky via Rhodes22-list <
> <mailto:rhodes22-list at rhodes22.org> rhodes22-list at rhodes22.org> wrote:
>
>
>
> > Guys,One of our veteran skippers may know the special sealant which is
>
> > used on the windows on our boat. It is unique because of the material
>
> > used to make the window frame. Anyone recall?Art
>
> >
>
> >
>
> >
>
> >
>
> >
>
> >
>
> > Sent from Yahoo Mail on Android
>
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>
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>
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