how to extend hard top?

[realslimshady]

My brother wants to extend the hardtop on his boat-



All the way to the stern. What's there at the moment is GRP-would it be practical to make a new roof out of marine ply?

 

[Jabs]

Think about how strong you want it. Do you want/need to walk on it?

How will you support the aft end?

Fibreglass would look super but a mould would be needed.

I have a friend who did exactly that and it looks great but cost loads.

Tony

 

[prv]

Proceed very carefully, amateur additions like this generally end up looking like sheds!

I think if I was determined to do it, I would put a very slight curve in the roof by making shaped ribs out of 12 or 18mm ply and screwing down 6mm (or maybe even thinner) over them. Hopefully the existing roof already has a curve to it, which should be matched. Then I would lay a layer of GRP and white gelcoat over the top to match the existing. Depending on what the after edge of the existing looks like, I might even decide to make a seamless join between the two, grinding a step into the existing surface to take a layer or two of cloth overlapping without ending up with a raised ridge. Obviously by using a GRP top we avoid too much dependence on the waterproofness of the ply, which can be problematic nowadays as so much "marine ply", even stamped and labelled, is nothing of the sort.

He will need some uprights to support the thing; if he's not intending any solid "walls" then stainless tubing would probably look best. You can get fittings that clamp into position with grub screws to avoid the need for TIG welding.

Pete

 

[realslimshady]

Yes, very determined that it won't end up looking like it should be at the bottom of the garden! My brother tells me there is no curve in the existing roof, and I don't expect there will be any need to walk on it, though I think a slight curve would be essential-if only so the water runs off. Intending to ultimately completely enclose the cockpit, so will be supported by wooden uprights at the rear corners.

 

[prv]

determined that it won't end up looking like it should be at the bottom of the garden!
[...]
will be supported by wooden uprights at the rear corners.

So what form will these wooden uprights take?

Do you have access to a large wood lathe, to turn some decorative shape into them?


Or will they just be plain and square?



And perhaps about 4" wide?





Looking like...







Fence posts!

Pete

 

[realslimshady]

I did say 'at the bottom of the garden' not 'down the side of the garden...'



This is how we want it to look

 

[Rigger Mortice]

Mmmm. Making an 18ft(?) look like a 30(?) footer is a design challenge. The proportions are totally different.
Get it wrong and you end up with this http://smg.photobucket.com/user/Dr59Elky/media/Pictures/7.jpg.html

 

[realslimshady]

Not sure where you got your dimensions. Same boat- Project 31- only the other one is a 'sedan'

 

[Rigger Mortice]

Not sure where you got your dimensions. Same boat- Project 31- only the other one is a 'sedan'

Blimey. Deceptive photos.
Is it worth spending the money to make that conversion?

 

[realslimshady]

It's primary function is as accommodation, hence the desire to make the cockpit area more weatherproof. A professional boatbuilder just quoted 8k to do it, which is a bit steep when boat only cost 6....
My brother is proposing that we do it ourselves, but I only see a whole heap of pain coming...making a roof is simple enough, but when you get into windows and sliding doors etc, hmmmm.

 

[Tranona]

£8k sound pretty reasonable if it looks like the one in your second picture. Whether it is worth doing depends on the alternatives. Can you get what you want buying another boat for 14k? in a way the £6k cost of the current boat is irrelevant. If you are keeping the boat a long time and it does what you want it is the overall cost of the boat against alternatives that is important.

 

[Rigger Mortice]

It's primary function is as accommodation, hence the desire to make the cockpit area more weatherproof. A professional boatbuilder just quoted 8k to do it, which is a bit steep when boat only cost 6....
My brother is proposing that we do it ourselves, but I only see a whole heap of pain coming...making a roof is simple enough, but when you get into windows and sliding doors etc, hmmmm.

It might be better to sell the boat and buy another which is more suitable? A conversion will rarely increase the value of a boat and may even reduce it.

 

[cliff]

All depends on how good you or your brother is at Joinery, Carpentry and Cabinet making.

 

[oldsaltoz]

Not too difficult, we replaced the original fabric cover with fibreglass and includes cabling for lights, speakers antennas as well as overhead life jacket storage.

The process:

Sheet of 3 mm ply temporarily fixed to 2 lengths of timber one each side to produce the required curve. seal the ply with almost anything handy that will give you a smooth finish.

Coat with a good release agent and lay up the glass for what will end up as the top side. You should stiffen the structure using foam around the edges, nicely rounded on the under side and slightly raised in the top side to form gutters thus avoiding the waterfall effect in heavy rain/seas. You can also include some rounded stiffeners athwart ship on the underside.

Cables can be included under the foam for stern light and general lighting and anything else you might like to power up.

Tip: Take a few pictures of her side on with a tallish person standing in the area to be covered. Lay some trasparent material over the pictures and draw what you think you want her look like.

The tall person will indicate height required, also draw in some angled posts and or panels at the back for support and select the look your after.

Good luck and fair winds.

 

[rob2]

There's been quite a jump from "Can I nail some plywood on?" to "Will I end up with a coachbuilt finish?" The answer is no. If you really want to achieve the same finish as an original, you'll have to rip off the existing doghouse and start again with heavy, hardwood framing - nothing else will support a sliding door! Take your brother to look at an original and if he still wants to go ahead, agree the conditions under which you will bail out of the project!

Rob (too many failed projects)

 

[realslimshady]

He's going to get another quote....
Yes, the original stuff needs to come off (needs attention anyway) and a whole new superstructure built, but that's a bit much for me, on further reflection.
Not sure if I got an answer to my original question i.e. 'will marine ply do the job?' (of a roof, not the whole thing)

 

[Rigger Mortice]

. Not sure if I got an answer to my original question i.e. 'will marine ply do the job?' (of a roof, not the whole thing)

Yes it will. Getting decent marine ply seems to be a bit of a gamble though.

 

[Tranona]

Not sure if I got an answer to my original question i.e. 'will marine ply do the job?' (of a roof, not the whole thing)

Yes. Marine ply will do the job, but best if then covered with glass cloth and epoxy taking care to seal all the end grain and any joints between sheets.

 

[prv]

Yes. Marine ply will do the job, but best if then covered with glass cloth and epoxy taking care to seal all the end grain and any joints between sheets.

If you're doing that (which I agree I would) then the expense of true marine ply seems a bit unnecessary, versus decent WBP.

Pete

 

[realslimshady]

Yes. Marine ply will do the job, but best if then covered with glass cloth and epoxy taking care to seal all the end grain and any joints between sheets.

Seems like the answer is 'yes-if you get a good bit' or 'yes-if you turn it into a fibreglassing exercise'...which I can see being a laugh over a 10'x8' or so area....
Let's hope we can find someone to do it for us (him)