[MHml] Advice please

[Diane Selkirk]

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