Any ideas on materials for a coach roof?

[meekumslr]

My cousin and I are about to cover the large hold of a Larch on Oak MFV/ trawler liveaboard with a coach roof with side windows.
The hold beams are Oak and the deck is pitch pine.
The wheelhouse is aluminium and I would like to link the wheelhouse with the hold.
This job is a large and daunting one and i'd be very thankful for views on materials and structure of both the frame and sides/roof.
We've thought about an aluminium set of sides and roof to blend with the wheelhouse but will the joints expand with heat?
Is wood for the frame ok or could there be problems?
Thank you. Neil.

 

[bilbobaggins]

You could give some thought to laminating beams, knees, ribs and so on from marine ply and epoxy resin. The book 'Gougeon Brothers On Boat Construction' is a must-read and a must-have.

The use of wood - especially laminated as above and in the form of marine ply skins ( cold moulded ) - is immensely versatile, economic, relatively undemanding of skills ( compared to working in aluminium ), requires simple tools, and is both easy and cheap to repair.

And you can get epoxy formulations to work with 'oily' oak - read the book, then ask the West System people.

 

[boatmike]

Aluminium would be fine but unless you are an expert welder difficult to do. Frankly I would make a framework out of a good hardwood like iroko (teak is great but very expensive) and clad it in a good quality marine ply. If you make shaped beams the ply (9mm max) will bend around the shape. One good tip however is to buy quadrant for the edges and seal with liberal amounts of adhesive to avoid exposing the end grain of the plywood.

 

[Blueboatman]

Basically maybe think along the lines of building a 'box'(ply,alloy,grp,ply+grp)that is then set over the hold and OUTSIDE of longitudinal timbers'carlings'set along the edge of the deck and themselves throughbolted to the existing carlings below-this way you are in with a chance that as the hull flexes at sea no leaks will develop around the sides..
Well worth visiting other mfvs first and standing inside to determine the 'right'height for the coachroof,the camber on the top,what height to set the portholes or windows vis -a-vis height of gunwales,how it will look when viewed from afar,etc.
Peruse a couple of good woodworking books to decide if you really want to laminate curved beams etc,or maybe get a quote to fabricate an alloy 'box' that you can insulate ,line and finish off...

 

[Lakesailor]

I'd go with Blueboatman on the research side of things. You will, without doubt, come across all manner of things which hadn't occurred to you, and may save money and time.
I'm sure most MFV owners would be delighted to help a fellow convertor in that way.

 

[meekumslr]

Thanks very much for all ther information.
I'll try and get a copy of that book Bilbo and am very attracted to ply/ GRP.
Thanks for the reminder to cover the grain in edging too as I know this will cause problems if not carried out.
Thanks again.

 

[DoubleEnder]

I think the biggest quetsion to reolve is: will you be going to sea? I know of MFVs with very good accomodation built over the hold - in some cases they even support a boat deck above. But they dont go 'seriously' to sea, just occasional short hops from harbour to harbour in flat water/settled weather. These superstructures are built on substantial steel angle, bolted to deck beams and clad with exterior ply. They work very well, but Id be dubious about the effect of taking a substantial wave on baord

 

[meekumslr]

I'll most definately be going to sea Graham.
I'm not a fair weather person so it does need to be practical too.
Thats why I wonder about ply. I enjoy watching the waves hit the wheelhouse, so need it to be robust.
Thank you for that view. Its worth thinking about.

 

[Stemar]

Ply of the right thickness, well supported, will be extremely strong and long lasting. Here are a few basic thoughts, in no particular order:

Curved ply is more rigid than flat ply, and sheds water better. If you can't get the curve you want using the thickness you need, laminate two or more sheets. Just make sure any joins don't coincide.

Laminated beams will almost always be stronger than sawn solid beams of similar size and you can make any shape you want

Avoid places where water can run down into a join.

Avoid leaving end grain exposed to the elements.

Slather everything with epoxy to keep the water out - consider a layer of glass fibre epoxied over the top. It'll protect against dings and dinghies.

Epoxy doesn't resist ultraviolet, so put a UV resistant barrier over it.

 

[meekumslr]

Steve.
Thank you for your reply and I definately think thats the way we'll go forward.
I like the cheap and robust option of ply with ply carlings coated in epoxy/GRP.
The materials are easy to work with and will give more insulation.
Thanks.
Neil.