[MHml] Advice please

[Michael Conley]

Hi there
     Not to dampen your project but I have been there. I sawed down each side horizontally until I got to the aft part of the centerboard case and then dipped down towards the keel the front of the case being the lowest part of the profile. I left about three inches intact where the cuts bisected to act as a hinge. I then let the sterns sag open 7" clamped every thing in line and filled in the dart. Then I added 6' to the new sterns. While the results were excellent,it would have been less work if I bought some plans and and built from scratch.
  Mike

Allied <allied at clear.net.nz> wrote:
  Thanks Evan

After a night on the web yesterday, I could see that I don't just get my 
fore - aft profile, with my extension keel, then get great hunks of foam, 
glue them on some how and sculpture them to shape, before glassing over. My 
first imagination of how to do this.

I think I will need to get this fore - aft profile fitted and shaped, then 
make foam ribs at 200 mm apart? Which will give me a frame, much like 
building a hull from scratch. Then using foam with groves to allow bending 
to cover these ribs. Do I make these ribs wide enough for butt joints, of 
the outer foam, to go over them? Do I need to do one section at a time, so I 
can glass inside as I move aft? What about areas impossible to get to? What 
happens about the void space left behind, leave void, or fill with expanding 
foam?

With the flat panels, it seems that best, is to make the basic shape out of 
say 20 mm foam and butt join where necessary, putting a complete skin over 
this first, then add a flange round the outer edge and ribs, glassing these 
first, then gluing on and glassing again. Am I on the right track?

For all my previous boat building and repairs, I have used a general purpose 
epoxy, currently West Z105 resin and Z206 hardener, for gluing and filling. 
Do I need to change this to anything else, for use on foam?

I read 'Foam sandwich construction' on the net last night and it is very 
informative, but obviously, can not answer each persons particular query. I 
will need some hands on help when I actually start, but I'm sure most of you 
have in the past, put together as much information as you can from forums 
and friends, before starting a project. So I am most grateful for everything 
that can be offered here.

Colin


> Allied wrote:
>> I have a 40 foot glass over ply, bridgedeck, catamaran and I am about to
>> start work on extending my hulls by about 600 mm, changing the transom's 
>> to
>> scoops and deepening the draft aft, to make up for diesel engine, fridge,
>> freezer and various other creature comforts, which have sunk me by the
>> stern.
>>
>> My thought is, to make new, extension keels, from 40 mm wide, laminated,
>> timber, glued and screwed to the existing hulls aft, giving the extra 
>> length
>> and depth. Then filling in the depth and some extra width, with foam and
>> then glassing over. Cutting out the transoms, filling between the frames 
>> and
>> generally faring with foam and again glassing over. Fitting light weight
>> steps (yet to be designed).
>>
There's an online foam boat building book here:
>
> http://bateau2.com/content/view/160/28/ links to the following pages
> on the bottom of each page...
>
> (disclaimer - I get royalties for some of the plans on this site and
> helped proof read the foam boat building guide)
>> I have never worked with foam and would appreciate a 'beginners guide', 
>> in
>> the form of advice, pointing to a web site, or printed material. I also 
>> want
>> to make a light weight flat deck, for behind my afterbeam and between the
>> hulls. Do I use foam glassed over, how can I make it strong yet light 
>> (build
>> in ribs)? I will probably make the boarding steps as open style, with a 
>> flat
>> board, how best do I make these flat steps?
>>
>>
For bridgedeck / cockpit soles the default solution is usually some ribs
to get enough stiffness. It's much easier to built a flat panel with
foam/glass on both sides and then mold the ribs separately. I moulded
my ribs in a female mould and made them single skin with carbon top
flanges to get them as light as possible. It is easier to glue on foam
ribs shapes, round the corners, and glass over them. The biggest
problem with bridgedeck soles is the large spans. Thicker foam does
better here, though I used 3/4" foam because I had bought a case of it
for a bridgedeck cabin.

Evan Gatehouse

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