QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

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I have started a project on a boat that should end up similar to this Dipper 17, although with a wider and longer cabin space

I have done a lot of fiberglass and epoxy work, and re-tabbed or repaired loose or rotting bulkheads, but I have never done cabin construction with plywood... (Ive done it with aluminum, but not plywood)

so the questions are.....
1...... I will be using 1/4"plywood.... if it is all going to be covered and sealed with fiberglass, does the plywood need to be marine grade, or just a good finish on both sides?... i have seen the plywood that OEM used on their boats for bulkheads and floors and it seems to be a fairly low grade of plywood.... i want something better than this, but dont really see the need for the premium marine grade....

2..... when building with light plywood like this, would it be reasonable to paint the plywood with resin to seal it and keep it from warping while working with it... and maybe a layer of cloth on each side? this project will NOT be done in a heated shop and it will take a few months rather than weeks, so after cutting the panels i dont want it to warp out of shape as it sits waiting to be assembled.
I know it will cost more to cover plywood that is going to be cut off and thrown away, but my thoughts are is that i would rather it cost a bit more money than have it all cut out and ready to assemble and have the panels warped beyond usage.

3.... IF the panels have ALREADY been covered with cloth/resin, and the shapes all cut to size and the edges sealed, will that make it easier to tab it all together and do the finish work on it, and make ready for paint?..... I still have not decided if it is going to be tabbed to the boat, or attached with fastners so that it could be removable... but either way, I want the weather sealed out.

4.... is one layer of cloth/resin on the exterior side of the plywood adequate to insure it weathers well?.... although on the top of the cabin roof I plan to have more, as it may be used to carry a crab pot or two..

5.... is coating only the exterior side of the plywood better for cabin construction?.... maybe the outside with cloth and the inside with a only a coating of resin? I want it light, but I also want longevity.....

6.... I would like suggestions to help me decide on the best way to do this...... also, are there any good books you could recommend that shows how to construct the proper joints when doing this kind of work? thank you........

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

its hard to imagine that with all the people who are doing a restoration on a boat, that there arent more people who have worked with plywood and fiberglass that has any opinions that would help get me started in the right direction here...

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

You will be using epoxy & fiberglass? Not polyester resin & glass, correct?

On this boat:

From here:
can anyone identify this old boat?

I suspect that 1/4" is going to be a bit thin for use to support crab boats, unless you use quite a few layers of epoxy & glass.

SeaStomper has done a hardtop addition to his rig:
1977 Orrion becoming an ocean animal

I don't think it's 1/4" ply

No, you don't 'have' to use marine grade. No the OEM plywood used on your boat probably isn't marine grade. An ACX plywod would likely be sufficient, but if your going to use thinner then 1/2", and can find the thickness you want in marine grade, I would at least price it.

Better wood used for laminations, fewer edge/core voids, and better face veneers, for $20/sheet would likely be worth it to me.....

Try the advanced search function from the resto forum homepage. Here's 2 that the iboats server put at the very bottom of your thread:
Building a cabin

Building a Hardtop ?

But as you can see, not many add a hardtop/cabin to their boat, so there's only 6 posts total in those 2 threads.

Coating the panels in resin & glass, and storing them for extended periods of time is certainly better then storing them un-sealed. But in a non-temp controlled environment, they could distort some even after sealing & glassing...

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

BTW: Dry dock isn't as busy as it sometimes is this time of year. Got to give anyone interested enough to open your thread, time to comment on your thread. 240+/- views & no replies, YET...

It's nearly the end or at the end of the boating season for much of the US. Some are frantically trying to get the last use or last fair weather project complete on their own rigs.....

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

jbcurt00, thank you for the reply.

Point taken on having patience... and thank you for the links.

as for putting a hard top on the boat, i want a fully enclosed, dry and heatable boat... like a mini cruiser. a full canvas top and hardware, with a backdrop will cost more than the materials for a hardtop, and when i get the hardtop on, I plan to modify or possibly delete the existing bulkhead between the deck and cabin space to make for a more open area inside... more room. i know it isnt for everyone, but here in the northwest, us old folks like our comfort:joyous:

I will be using polyester resin and fiberglass cloth and mat where applicable. im not sure if roving has any place in what im doing.
I will check the pricing in my area on the marine grade ply... at $20 per sheet, its within my budget.

the cabin top will be rounded and with runners for support. the design will strengthen it a lot, but the thoughts you shared about possibly using thicker plywood is the kind of input I need.
I planned at least 2 layers of cloth on the outside and one layer over the runners to strengthen and seal it on the inside. (insulation between and a headliner over the runners) it would be easy to add another layer to the top or even the inside if i think its necessary at the time of glassing.
the crabpots weigh about 16lbs each, X 6 pots, and would be mostly over, and supported by the rear bulkhead, but I will give some thought to going with 3/8 ply. it only makes the rounded shape harder to build into it.

any more thoughts here, let me know, thanks....

 

[chriscraft254]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Is the boat that is posted the one you are trying to build an enclosure for? If so I would recommend you do a sketch on your computer and post it here to give everyone an idea of what you want it to look like. I think you will find it is easier to use a thicker material like 1/2 inch ply to form this. even then you will have to make sure it is dried out and laid flat for some time before using it so it doesn't warp.

You will notice on some of the rebuild threads even with transoms, it is usually weighted down when the lay up process is done. I think it would be a good thing if you built the entire thing on the boat and then glassed it in. You will want to encapsulate it in glass so there is no water intrusion from anywhere.

Here is a very good read and a boat that had a hardtop already and was completely redone to be a hard inclosure/cabin. I'm not saying you will go to this extreme, but it might give you some ideas. http://www.thehulltruth.com/boating-forum/340930-new-boat.html

 

[chriscraft254]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

I will check the pricing in my area on the marine grade ply... at $20 per sheet, its within my budget.

I meant the marine plywood might be $20 MORE per sheet then ACX plywood.

If I can find it ACX is $30 +/- per sheet for 1/2"
If I can find it Arauco is @$40/sheet for 1/2"
If I order it MDO is @$48/sheet for 1/2"
If I can find it Marine is @$70/sheet for 1/2"

Never priced 1/4" or 3/8" of any, but based on those #'s ^^^, I guessed 1/4" or 3/8" marine could be about $20 more then ACX.

Price MDO, I like working w/ it. Depending on what you're using it for, MDO is available in 1 or 2 'good' sides. For most of what I'll be using it for in a boat, 1 sided will be more then sufficient. It's a bit cheaper then 2 sided, and should be plenty for your purposes too.

Be very conscious of how much weight you add above the cabin. Since you didn't answer my question about what boat, I'm still guessing it's the Glasspar you want to add an enclosure to.

If you haven't gone thru the entire boat yet, and closely examined the transom, stringers & deck, starting the enclosure 1st might not be a great plan.

Per your layup schedule:

the cabin top will be rounded and with runners for support. the design will strengthen it a lot, but the thoughts you shared about possibly using thicker plywood is the kind of input I need.
I planned at least 2 layers of cloth on the outside and one layer over the runners to strengthen and seal it on the inside. (insulation between and a headliner over the runners) it would be easy to add another layer to the top or even the inside if i think its necessary at the time of glassing.
the crabpots weigh about 16lbs each, X 6 pots, and would be mostly over, and supported by the rear bulkhead, but I will give some thought to going with 3/8 ply. it only makes the rounded shape harder to build into it.

Depending on the glass weight you choose, IMHO 2 layers on the top & 1 below may not be sufficient in heavy seas. The cabin, it's corners & attachment points on the boat will see LOTS of stress.

Even at 16lbs per, 6 pots up high could make the boat even more top heavy then it'll be w/ just the cabin addition. I'd also recommend using some sort of skid to protect the cabin roof from the metal pots. Gelcoat might not be up to that task. Starboard comes to mind. You can get cut off scraps on ebay fairly reasonably, and cut them to suit your application.

If you're not going to use gelcoat as a final finish on the cabin addition's roof (I wouldn't) I don't think I'd use it at all on the addition. If you're not going to use gelcoat, I would consider using epoxy instead of polyester, and paint it as needed at the end of each season.

Using epoxy would give you a stronger structure at about the same weight as a poly structure when the layup schedule for both is the same. Or more importantly, save some weight for the same strength structure by using fewer layups.

3 layups of epoxy using 1708 glass could be as strong as 4 layups of poly & 1708, but weigh about 3/4 as much....

Using some 1/2 deep kerfs in the 1/2" ply and skimming them w/ resin filler would be less stress & probably be easier to work with then 1/4" ply bent into a curved roof.

You could make a buck (form) on top of the existing cabin roof, so the new roof matches the profile of the existing.

 

[ondarvr]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

As others have alluded to, the combination of products you asked about may not yield the best results.

Polyester resin, cloth, and wood aren’t really what you want to use, the three of them combine for the perfect storm (premature failure).

Epoxy, cloth and wood work very well together though, so I would advise going that direction. The next part is to build the entire structure and then glass it, this will be much easier. If you build a frame and wrap it with ? ply it will most likely work fine, it just depends on the bracing and the curvature of the load bearing surface. Without a frame you would need to use thicker ply.

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Is the boat that is posted the one you are trying to build an enclosure for?

If so I would recommend you do a sketch on your computer and post it here to give everyone an idea of what you want it to look like.

You will notice on some of the rebuild threads even with transoms, it is usually weighted down when the lay up process is done. I think it would be a good thing if you built the entire thing on the boat and then glassed it in. You will want to encapsulate it in glass so there is no water intrusion from anywhere.

Here is a very good read and a boat that had a hardtop already and was completely redone to be a hard inclosure/cabin. I'm not saying you will go to this extreme, but it might give you some ideas. New boat - The Hull Truth - Boating and Fishing Forum

oh how I wish i could make a sketch on the computer..... if only i knew someone savvy enough to show me what program to use and how to do it.... but anyway, Yes. I want to enclose the Glassply.... I have decided to go with 3/8 ply and leaning towards the epoxy. the existing top windshield will be discarded and the proposed enclosure will be about 6ft long, 5ft wide, and about 24 inches above the existing cabin roof. it will begin at the rear of the side windows and run rearward and will drop down and attach to the gunnel about 8" aft of where the existing cabin roof terminates with it. I hope to have a forward sloping windshield. the roof will supported on the 5x6 footprint of the walls, and have an additional 4 stringers(3/4" wide x 1-1/4" tall) glassed to the underside of it for strength
at every joint where the walls meet in the corners, and the roof meets the walls, and the front window panels meet the walls and roof, I was planning to use a 1x2 with glue and fasteners to make the connections, so that it has a frame to stiffen all the corners. then cover it all with cloth and resin to seal and strengthen it....

I have a sketch that I will see if I can scan in and attach, but a computer aided sketch would be better... thanks

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

CC254 meant a rough sketch on a pix of your Glassply. Just to mock-up what your plan is. Use MS Paint if on a windows pc.

We are NOT expecting a graphic~CAD rendering:

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

I hope this attaches correctly.

this is the look im going for, but it may be a bit out of proportion in the sketch.... I dont see any reason why I cant achieve something similar to it.

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

That rendering attached, but it has to be opened, let me drop it here:

Minimizing the amount of weight added up high & making it sufficiently sturdy may be a bit of a guessing game.

Having to use more epoxy resin & cloth to use thinner substrait material (1/4" or 3/8" ply) or building a mold/frame that you use to build a epoxy & glass only shell isn't something I can help you decide how to proceed.

If I had to start this project, I'd probably start w/ the hardtop portion & build it as you describe. Then set it across 2 saw horses to see how rigid it is. If it's not rigid enough, add another layer of glass & epoxy. See what that assembly weighs.

Don't forget adding structure to the existing hull where your superstructure attaches.

What's the beam on your Glasspar? Adding weight up high could make it unstable, esp in rough seas.

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

the boat hull, inner and outer, is solid and sound in every respect. except for the lower portion of the bulkhead where it meets the tabbing at the floor. it is delaminated and is soft. the floor is solid and the transom seems good without any cracks, swelling or soft spots. all the aluminum trim and trim wood is tight. and the glass is all good and does not leak around the channels or frames. it impressed me that a hull this old could be so sound and tight... if only someone wouldnt have painted the latex on it to cover the mildewed hull, it would not seem like such a big project. woodworking and glassing is easy compared to paint removing and prepping for new paint....

because of where the proposed front windows will be positioned over the existing cabintop, AND in addition, i plan to remove the existing bulkhead and cutaway the cabintop inside the structure to make an open floor plan, I will construct a stainless steel "bridge" support on the inner portion of the existing cabin under the proposed forward windows, to replace the structural strength that was removed with the deleted bulkhead and to prevent the weight of the new structure from ripping the rest of it loose from the hull when the boat rocks side to side....

the beam is 7'-1"... I will be removing about 70lbs of existing material as I go (upper windshields, trim, bulkhead and cutaway fiberglass), and depending on the type of 3/8" plywood I use (doug fir or mahogany, which equates to weight), and the amount of resin and window glass, I can see less than 200lbs of weight added to the boat. closer to 160lbs by my calculations and it wont all be up high.... (about 2 sheets of plywood and windows above 4ft)
and I know from experience that 200lbs (one mans weight) that high up will have some effect on that size of boat in a wild sea, but it will have to be exceptionally rough with high winds before it is the cause of being hazardous to ones health... and, as the boat was never originally designed to take gale force weather offshore, neither am i trying to make it so with my design...
so in any kind of weather, the weight that will be added during the reconstruction will be a minimal factor in the safety of the boat and crew in contrast to the competence factor of the skipper....

I think everyone for their input... it is helping me understand the different angles of view from a design standpoint....

 

[chriscraft254]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Ok buddy, did as well as I could on short notice,lol What do you think? Your going to have to follow the lines of that boat if you want it to look like anything close to right. The rendition I gave should be fairly easy to build and can be tabbed in using the existing structure. I personally would use 1/2 inch ply because it is basically 3/8 of an inch these days anyway. Built right, this thing can be strong as an Ox. Using 1/2 inch will give you a good frame for windows to be installed as well. You might consider using Lexon glass as it is lighter weight than glass and just as clear, its actually a lot stronger to.

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Perfect. I like that... the front window need to come forward more. the outer front corner of the proposed cabin will begin over the rear of the lower windows. it will be a two window design that is sloped forward and will be swept rearward from the center to the outer edges on the same lines as the lower windows...

what program do you use to draw that?...

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Google Sketch-up is free online, and many use it. I found it difficult to use, but many @iboats have, w/ exceptional results.

CC254 is in the building trade so he may have another program.

 

[chriscraft254]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Depending on where your bulkhead inside is, that would be the determining factor for me if it were my boat on where to start the cabin. I don't think you don't want a lot of extra weight coming down on your front window frames.

I simply used windows paint, almost every computer has it already on it.

Can you post up some pics of the interior/layout?

Is this better?

 

[centerline]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

Depending on where your bulkhead inside is, that would be the determining factor for me if it were my boat on where to start the cabin. I don't think you don't want a lot of extra weight coming down on your front window frames.

I simply used windows paint, almost every computer has it already on it.

Can you post up some pics of the interior/layout?

I will build a stainless steel "Bridged" truss, inside, bolted to the existing cabin top and coming down and attaching to the hull to support the cabin roof and to prevent any side to side thrust when the boat rocks hard... as I have said, i plan to remove the bulkhead entirely from the boat.

I do have a plan for the interior, but right now all that is there is the cushions on the v-berth, the bulkhead and the helm.

Ive tried to snap lines with the paint program, but have never figured it out... and cant figure out how to erase when i make a mistake.... i always closed the program without saving, and then reopened it.
i will try again now that i see it can be done... i will also check out google sketch....

 

[jbcurt00]

Re: QUESTIONS, when building an enclosed hardtop cabin to replace canvas...

There should be a reverse arrow up along the top of the paint window, it's an 'undo last step' button. Use that to remove any work you've done, 1 step at a time, until you move back to the stage you want to re-start from.

Every time you hit save, the undo step resets, and no more go backs.

As you make additional changes, any step forward from the save can be undone, but anything prior to the save is now permanent. I tend to use 'save as' & add sequential #'s to the end of the file name. I might end up w/ 12 verisons, but can re-start from any of those saved end points.