Hard top conversion

[sogood]

Despite not having even gotten my new to me boat into the water yet, (it will be happening soon) I'm thinking ahead to next winter when it will probably come out for a once over. As part of that, I'm playing with the idea of making a hard top for it, to replace the windscreen and side windows up on deck.

I'm happy and confident with my woodworking skills and have all the necessary tools etc. so that doesn't bother me. My plan would be to use 1/2" plywood for the general construction and it's just in regard to the finish that I have some questions.

With the hard top made up and prior to fitting, I would intend to paint the entire thing with two or three coats of fibreglass resin, sanding lightly between coats. Then I have the option of fibreglassing it all with woven mat, sanding, filling, sanding again etc. and finally painting it with a 2 pack marine paint. Or would it be possible to just paint over the resin without the need for any matting? I've used this 2 pack paint in the past with very good results.

I know matting would add to the strength, but is it needed? It would also add to the weight, making it more top heavy. As mentioned, I would be happy with my construction skills etc. but I wouldn't want to over do it.

Any thoughts welcome and thanks in advance.

 

[Pete7]

Can't help but think that is going to be very heavy in 12mm ply. Why not use 6mm ply plus re-inforcement and then give it two layers of cloth each side. Sand smooth and paint. How are you going to attach the windows?

Pete

 

[sogood]

Thanks for the response. The "top heavy" factor is a consideration and that's why I'd like to avoid using fibreglass as the combined weight of resin and matting might negate the use of 6mm as opposed to 12mm plywood. The 12mm plywood can be constructed using less in the way for bracing and fixing. I would be jointing the panels together, like a mortice and tenon, which I've always found to be very strong in the past. Perhaps the actual roof panel could be made using 6mm?

As for the windows, I haven't thought too far ahead just yet. There's still the actual design and aesthetics to be worked out along with the actual size. I'd like it to be tall enough to be able to stand under, while at the wheel. Windows would probably be "Perspex", flush mounted into a recessed channel, which is another good reason to use 12mm.

As to the finish, would you think the resin/epoxy and paint approach work well enough.

Thanks again.

 

[lw395]

I think unreinforced polyester resin would likely crack or craze. If weight is a concern, consider using epoxy and maybe a layer of glass cloth.
How strong do you envisage this structure being? Strong enough to stand on? Survive atlantic seas? Or just to keep the rain off?
Another possibility is to make the panels GRP/foam/GRP sandwich.

 

[PowerSlapper]

Another possibility is to make the panels GRP/foam/GRP sandwich.

+1 Will curve in one direction only without lots of cutting and shaping but one direction is fine for a simple curved roof. Lighter and cheaper than marine ply (and rot proof)

 

[prv]

What sort of boat are we talking about here? Pootling day motorboat, 30' sailing yacht, wooden, GRP, old, new?

Pete

 

[sogood]

Thanks for the input guys. As for the boat, it's a fibreglass 25' Wellcraft Sportsman 250, powered by a Mercruiser 5.7. My boating would be mostly confined to the South West coast of Ireland and despite having made a folding Bimini type top for it, I would like something a little more permanent to protect against the ever changeable weather here in Ireland. I've included a "mock up" picture of the sort of thing I'd like to do. Be advised, this is very rough!
I don't envisage ever walking about on top of this, but I'd like it to be strong and sturdy enough to do so anyway. It might also be a good place to relocate my solar panel to.

 

[Neeves]

I'd use glass and foam. If you use thick enough foam you can bend it in one direction and grind it down in the other to give a more pleasing profile. We built a helm station using this technique and it has been robust based on 750gm glass each side and 20mm foam. It is not particularly heavy. You can cut out the window holes and then rout the edges so as to take acrylic which, if the foam is of a compatible thickness and you glass where you rout you can introduce flush windows - and hinge the acrylic (and foam) if you so desire. We also have grab rails and we bonded in 5mm aluminium plate as reinforcement and double layers of glass and then tapped into the aluminium. We built ours with a flange where it joins the original deck/superstructure and simply used Sika and screw to bond. To get the junction perfect, when we had 'finished' we simply covered the original deck with removalists tape, dropped a layer of bog on the tape, dropped the god pod onto and then when the bog had set off, lifted the hole thing, ground off the excess and put on a layer of glass.

We built a polythene tent to spray paint.

But be warned I might suggest I built a helm station - most of the time you actually spend sanding! though it will depend on the quality of finish you will accept.

You need to think through exactly what you want and what you want to achieve - as adding grab rails later, for example, will still need the reinforcing - do it as you build is so much neater. For example we have solar panels on the roof and recessed the cabling into the foam.

Its a good winter project.

Jonathan

 

[sogood]

Many thanks guys, although now I'm getting confused. GRP/Foam/GRP sandwich, Glass and Foam? Can anyone elaborate or point me towards some youtube videos?

I'm leaning towards ply as it's a material I'm very familiar with and I could make up the hardtop as a complete unit in my workshop, right down to the finished product. Then it would just be a case of fitting it.

If I was to go with ply, what would the recommended route be? I'm talking primarily about protection, and finish, with an eye to minimising top heaviness.

Thanks again.

 

[prv]

an eye to minimising top heaviness.

A half-sheet or more of 12mm ply above head height on a relatively small boat doesn't strike me as a good way to minimise top-heaviness.

Pete

 

[sogood]

A half-sheet or more of 12mm ply above head height on a relatively small boat doesn't strike me as a good way to minimise top-heaviness.

Pete

Thanks for that. But seriously, what would you suggest, in laymans terms if possible. I can do lots of different things, just unsure of what many of those things are called.

 

[prv]

Thanks for that. But seriously, what would you suggest, in laymans terms if possible. I can do lots of different things, just unsure of what many of those things are called.

Well, if I was going to use ply I'd use something much thinner than 12mm, put a bit of a curve in it to give strength in one direction and some stiffening ribs to give strength in the other without adding too much weight. But I think the suggestions of using lighter foam core material of some kind are on the right track.

Pete

 

[Neeves]

No idea about YouTubes of foam glass construction - but I assure you its not rocket science. Have a quick word with a distributor of foam, resin and glass - they will point you in the right direction (for background) and if they are professional they will advise the thickness of foam, weight of glass and resins.

We built our Godpod at home, though we took panels to the yacht to check for size. When we 'built' we joined one panel at a time and checked for fit. When it was finished we tied to the roof rack, it was a bit high (but we have no bridges nor power cables ) and its only 500m from home to dinghy. The biggest issue was moving it in the dinghy - but we could have moved the yacht closer if it had been insurmountable.

Don't think its difficult. Don't be intimidated. You could train monkeys to work with fibreglass, well almost!

Jonathan

Edit We did not use it but you can buy pre glassed foam - which you might find suitable. I don't know anything about it - other than it exists (and it might only be glassed on one side and the glassing might be a bit lightweight). It will be more expensive but might cut out a step of glassing and a lot of fairing. Worth asking about. Just go speak to one of the foam, resin, glass distributors.

 

[sogood]

No idea about YouTubes of foam glass construction - but I assure you its not rocket science. Have a quick word with a distributor of foam, resin and glass - they will point you in the right direction (for background) and if they are professional they will advise the thickness of foam, weight of glass and resins.

We built our Godpod at home, though we took panels to the yacht to check for size. When we 'built' we joined one panel at a time and checked for fit. When it was finished we tied to the roof rack, it was a bit high (but we have no bridges nor power cables ) and its only 500m from home to dinghy. The biggest issue was moving it in the dinghy - but we could have moved the yacht closer if it had been insurmountable.

Don't think its difficult. Don't be intimidated. You could train monkeys to work with fibreglass, well almost!

Jonathan

Edit We did not use it but you can buy pre glassed foam - which you might find suitable. I don't know anything about it - other than it exists (and it might only be glassed on one side and the glassing might be a bit lightweight). It will be more expensive but might cut out a step of glassing and a lot of fairing. Worth asking about. Just go speak to one of the foam, resin, glass distributors.

Many thanks for that. I have used fibreglass long before I ever got into boats and am happy using it. I've also made moulds for making unusual and irregular fibreglass shapes so that's another plus. What would you think of making a mould of the hard top, complete and using it to make a fibreglass hard top shell, with some stiffeners glassed in for strength?

Hard to explain, but there are various lips/steps on the part of the boat where the hard top would sit and I'd like to marry into these to make things more streamlined and also eliminate area which at present serve no purpose and are only dirt traps.

The notion of using ply lighter than 12mm and then adding framing/bracing might be possible but would the addition of stiffening material not negate the idea of using lighter ply? 12mm can be worked and jointed very easily without a whole lot of extra bracing. And back to my original thought, if I use plywood as the finished product, what's the best way to protect it, without using fibreglass matting? Would fibreglass resin and a two pack marine paint do the job? I've used 2 pack in the past with very good results. Thanks again.

 

[Tranona]

A common way to sheath ply is to use glass cloth and epoxy, applying peel ply over it while it cures. This gives a pretty clean surface that can be painted with normal one pack paint.

If you want to use GRP/foam then make a female hardboard mould to the correct curvature and just lay it up as normal, probably with a couple of foam stiffening ribs. A but more work than ply but lighter and potentially more durable.

However, suspect your biggest problem will be mating it securely and neatly to the existing structure. The boat you have is not designed for a solid top. Many years ago I worked for a yard that made a similar type of boat and for a hard top version for a commercial client we bolted a GRP mould onto the normal deck bedded on sealant because we found the pounding caused any rigid mounting to fracture.

 

[sogood]

A common way to sheath ply is to use glass cloth and epoxy, applying peel ply over it while it cures. This gives a pretty clean surface that can be painted with normal one pack paint.

If you want to use GRP/foam then make a female hardboard mould to the correct curvature and just lay it up as normal, probably with a couple of foam stiffening ribs. A but more work than ply but lighter and potentially more durable.

However, suspect your biggest problem will be mating it securely and neatly to the existing structure. The boat you have is not designed for a solid top. Many years ago I worked for a yard that made a similar type of boat and for a hard top version for a commercial client we bolted a GRP mould onto the normal deck bedded on sealant because we found the pounding caused any rigid mounting to fracture.

I'm not so worried about mating the top to the boat as I'd be removing the current windscreen and side windows completely. These are sitting on a sort of lip or ledge all around the existing cabin roof, so the permanent hard top would occupy the existing site. I'm leaning towards the female mould, gel coat and glass. The interior finish would be lined anyway, so that would cover a multitude of sins. I doubt that I'd have as many of these "sins" as my boat had when I stripped the old lining from the cabin. It was as rough as you could imagine!
However, in the meantime I have a first splash to look forward to and a season of boating and fishing. Next winter I can hibernate to the workshop again and give this further thought.
Thanks for the input.

 

[PCUK]

Just finished a hardtop for my Reinell 26. Two layers of 4mm ply bonded together for the top to maintain the curve. Inside reinforced with 4mm ply stringers to give 'egg-box' construction and internally covered with 6mm ply bonded internally to the stringers. Outside covered with one layer of epoxy and bi-axial cloth with Inside sheathed with polyester and chopped strand mat. All outside corners routed back to allow another layer of bi-axial cloth below the surrounding level. Then filled and faired with thickened epoxy. All outside finish faired with epoxy fine filler. Then sprayed with Jotun Anti-Pest primer and finished with Jotun Mega-Yacht. Massively strong (I can stand right on the aft edge with no flexing) and not unduly heavy. (Sunroof is the new BlueSky from Webasto).
View attachment 68994View attachment 68998View attachment 69000

 

[sogood]

Thanks very much for that PCUK. Very nice job! A difference in my approach would be that I would be removing the existing windscreen and side windows completely. These just screw down onto the boat and would leave me with a clean surface to mate the hard top onto. It also means that I would be working with a simpler shape, not having to marry into or connect onto the current aluminium frames. This would also make the hard top much sturdier.

As mentioned, woodworking would be one of my strengths and the notion of making a complete female mould wouldn't cause me any issues. I thought of maybe using MDF as it gives a lovely clean, smooth surface for the gel coat. All internal corners would be filled and rounded off.

Follow the gel coat with chopped mat, reinforced with hardwood laths, especially in the roof section and around the base to stiffen up the mating surfaces where it joins onto the boat. I would also envisage incorporating a lip or corner all around the rear, open end of the hard top to help provide more strength and rigidity.

Openings for windows would be incorporated into the mould, possibly with a raised edge on the inside of the mould, which would translate into a recessed lip on the finished shell. This would create a more flush fitting when it comes to installing windows. These could be "Perspex" or similar, fitted using automotive rubber windscreen moulding.

I thought that where the hardtop is mated to the boat, it could be bolted on, using a rub rail as a decorative feature, which would hide the bolts at the same time, similar to how a cap is fitted to a hull. ( If you can't disguise something, then make a feature of it!)

I think this would be the best compromise for weight versus strength, without the need for a load of filling/rubbing etc. I have to take some measurements to see how tall the top would be, but I can't see the boat being top heavy with the extra weight, given the weight of the boat and the fact that I've seen many flybridges, complete with seating etc. and these don't seem to suffer as a result. And while I appreciate that the height plays an important part in stability, I would be reducing the top weight considerably by removing the existing screens and ( glass ) windows, which in themselves are quite heavy.

If push came to shove and it presented problems with stability or otherwise, it can be simply unbolted, removed and the original windscreen set up could be reinstated, as there would be no structural changes made to the boat itself. In essence, it would be like one of those removable tops you see on some pick up trucks.

Thanks again for taking the time to post, especially the pictures!!

 

[Neeves]

When we built ours I did think of using a mould, or making one. I decided this was simply too complex.

I used quite thick foam, 20mm, which bends relatively easily in one direction, so you can bend to form a part of a cylinder. Basically I had a batten down the middle and bent the 2 sides. I then glassed the top surface and once the resin had set (it held shape) I glassed the other side, the interior. I made over size, so that I could tension down the sides, and then cut the oversize off.

Once the roof was roughly made, so still oversized but the curve fixed, we took it to the yacht and mocked it up using various scraps and poles and made formers, initially from corrugated cardboard, then thin MDF (becoming more accurate each time). The space we had was complex. We then used the MDF to cut out the foam for the sides. There was a decent amount of toing and froing to get it all right

The sides were made out of flat panels, but because we were using thick foam we could bulk out the corners and then grind back. Once the sides were completed I then glassed the whole thing.

Foam is 'nice' to work with as it carves (and curves) well. So it is a bit like working with balsa wood. It has enough strength to work with but is easy to cut and shape - the strength comes from glassing it. If you make a mistake its easy to glue in another priece or simply fill.

The time comes from fairing - and Wests have lots of instructions - but don't underestimate the fairing - nor the dust it creates.

20mm might seem thick, but we cut much of it away for the windows and door and I used 20mm so that I could make decent curves for the corners to try to make a more pleasing shape. I knew how big the windows were roughly to be and I only glassed the parts that were to remain.

I found it quite satisfying but it did discourage me from thinking we would build a complete cruising cat - a one off project (to prove I could do it) was enough, though I forgot about the fairing and did some further work later!

 

[sogood]

Many thanks for that. When you say "fairing" are you talking about the finished outer surface, as in gel coat or what. If not, what finish did you put on the outside? This is why a mould/ gel coat approach appeals to me, as it gives you a clean, durable finished exterior, with no real filling or sanding.

Using 1/2" MDF would allow plenty of curve to soften the lines and create a curve on the roof section.

I don't know if you saw the mock up picture in one of my previous posts, illustrating the sort of thing I'm proposing. This would be open at the rear, with no doors.

Thanks for the input.