[Public-List] Strength of Mazonite

mahseer at kos.net mahseer at kos.net
Mon Jul 26 14:21:01 PDT 2010


When I did my fittings through the balsa core I drilled the deck hole of
the fitting with a 3/8 in drill bit making sure you do not drill the inner
hole.  Then using a demmel 3/8in  saw blade I routed out the core all
arround the hole.  This gives I believe a 3/4 dia cavity that after taping
the inner hole closed filled with epoxy through a needle syringe to make
sure there is no air trapped inside.  When cured I drilled right through
with a 1/4 in drill, beveled the top and reinstalled the fittings.

John Boor
MAHSEER #380

>
>
> Roger,
>
> I am not an expert but have the same vintage boat.  What I plan to do on
> rebedding my deck hardware is to fashion some type of tool to remove that
> material, what ever it is, between the upper and lower skins outward
> perhaps a quarter inch around each fastener hole. Clean surfaces with
> acetone and then tape the bottom of the hole and fill with Epoxy, keep
> filling until the hole is completely filled. After curing redrill the hole
> to the fastener size using each piece of hardware as a template. If I plan
> to increase the fastener size then I would use the hardware as a template
> and drill the larger hole prior to removing the 1/4" of core material
> around each hole. I would use this same process to fill unused holes and
> for new mounting holes.
>
>
>
> Where ever possible I plan to use a single solid backing plate, made from
> either Coosa Board or Star board of a foot print large enough to encompass
> all of the fasteners and extend beyond them an inch.  If clearance is an
> issue I still plan to use a single backing board rather than fender
> washers around each fastener, even if I need to make it some strange shape
> to fit.
>
>
>
> We are fortunate to have no liners in our boats so this system is more
> possible to accomplish. I believe that the Masonite composite cores have
> substantial compression strength, assuming that they are not severely
> delaminated or deteriorated by advanced wetting rot. 
>
>
>
> The donuts of Epoxy around each fastener hole should accomplish several
> tasks, consolidate the edge of the skins of fibreglass, adhear them to the
> core, seal the core from the fastener hole and provide some measure of
> compressive resistance to the fasteners.  On the early boats with
> Masonite coring I would not go to the work to remove and replace bits of
> core where the fastener holes are to increase compressive strength.  If
> you inspect our early boats as they came from Whitby.....you will realize
> that the above proceedure is many degrees better than the factory mounting
> which in most cases has lasted forty plus years with a few but not too
> many problems.
>
>
>
> Now on my Cape Dory Typhoon, with 3/8" balsa core.................I plan
> to recore the deck and use 3/8" Coosa board anywhere there is a planned
> deck penetration for a fastener, hatch opening.etc.
>
> The Coosa board will be laid up at the same time as the new balsa core and
> then a new upper skin laid on top of that.
>
>
>
> Hope this helps.
>
>
>
> Michael #133
> ----- Original Message -----
> From: "Roger L. Kingsland" <r.kingsland at ksba.com>
> To: "Alberg 30 Public List -- open to all"
> <public-list at lists.alberg30.org>
> Sent: Monday, July 26, 2010 1:06:55 PM
> Subject: [Public-List] Strength of Mazonite
>
> Hi Folks,
>  
> I will soon be installing the deck cleats on good old #148 and noticed in
> the current issue of Sail Magazine (pg 66) is a description of cleat
> mounting that recommends, with cored decks, cutting out the core around
> the
> bolt holes and filling w/ epoxy to avoid crushing the core when tightening
> the fasteners.  I am wondering if the Masonite core on our boats is
> strong
> enough in compression make the epoxy unnecessary?  What do the experts
> think?
>  
> Thanks,
>  
> Roger 148
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