New Hard Top

[tego]

Ambler, That's a common affliction here. Ben '87 27FC

[WillieC]

"but I like to build stuff for no good reason."

That should be on the AOG masthead somewhere...

[DesertAlbin736]

Ambler, is that dock on one of the creeks around Solomons? Back Creek, Mill Creek, etc?

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[DesertAlbin736]

"but I like to build stuff for no good reason."

“Believe me, my young friend, there is nothing–absolutely nothing–half so much worth doing as simply messing about in boats.”
Kenneth Grahame, Wind In The Willows

[Ambler27FC]

DA - near Solomon's, but I mostly only go there for Diesel and to cruise around.

I am neck deep into building a mold. Most fun I've had with boat work, and probably the easiest part of the project. Everything else involves a respirator. I've saw that the West System works down to 40 degrees with the fast hardener, so hoping to make periodic progress through the winter.

MottheDiesel - thanks for the video reference. Some great ideas, especially with the cloth. Wish they would emphasize safety in these types of those posts. I'm not a fanatic, but first time I opened a canister of thickener (in the wind) I imagined it was like smoking a pack of Marlboros all at once.

My last questions are difficult, and I'm not expecting a great response. This structure is about 7' x 8'. It will be integrally attached to the forward cabin and supported in the back by two canted verticals - about in line with the hand-holds on top of the aft cabin. I have a philosophy than anything that can be walked on will be walked on. These structures are really judged on stiffness, not strength. I am thinking 1/8" fiberglass top and bottom, with a 3/4 core.
1) Is the 1/8" fiberglass thickness (top and bottom) excessive?
2) Is a 3/4" core sufficient for this size? Up it to 1"?
3) Best core material? Currently leaning honeycomb, balsa, then foam.

I've been surveying the boat yards. You can guess at thicknesses, but not construction.

[WillieC]

1/8-3/4-1/8 is almost exactly how the WillieC FG top was laid up. The core is mostly some kind of pink foam. The edges are wood, I think some kind of hardwood plank, not balsa. The pink foam is easy to remove for fastener reinforcement with the dremel. Not so easy at the solid wood edges.

Note from earlier pictures, our top has a Gentle Ben(d) to it which I am sure gives it lots of walk on strength. (We regularly walk on it with no worries, other than breaking your neck.)

These are my observations of an older top. Actual builders of such tops will add more to clarify.

[DesertAlbin736]

Nice job with the mold! What's happening in the bottom picture? Is that the finished surface of the mold? In my experience masonite works well to line the mold.

Here's an interesting Practical Sailor treatise on mold release techniques & agents.

https://www.practical-sailor.com/boat-m ... king-molds

On my hard top project the finished layup is about 3/4" thick. But it's not one outer and one inner layer of f/g sandwiching a single layer of coring like the cabin top & deck is, but instead three alternating layers of of 1/8" diviny cell foam coring & wetted chopped strand mat. Since I used isothalic resin, which is a type of polyester resin, the issues of epoxy being adversely affected by binders in chopped strand aren't there. Except for the outer layer of cloth on top & around the hatch opening frames all the rest is chopped mat. However the only sharp curves involved were the rounded edges. I'm pretty sure it's strong enough to walk on, although there's never been reason to do so in my case.

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Plywood backing was used where the hatch hinges & corners of the solar panel were through bolted. Note the thermometer for checking temperature.

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"What is isophthalic resin?
Isophthalic Resin is a medium viscocity, Unsaturated Polyester Resin based on Isophthalic acid. It is specially designed for corrosion resistant applications. It exhibits excellent mechanical properties along with good chemical resistance compared with other isopthalates and orthophthalates."

https://www.youtube.com/watch?v=7h4fIcjeibQ

[dkirsop]

Just make sure no one wears stiletto heels while dancing on top!

[DCatSea]

Ambler, Love your top, especially the canvas, very trim. If I were not such a sunseeker I would be looking out for your "Offering up", and about making some serious changes to my old and hard to navigate Bimini. Another "Inshallah Plan" to add to the list, which is, I think, is slightly less ambitious this year anyway.

[Ambler27FC]

Thanks, this is helpful. I’m feeling good about 1/8” fiberglass skins. I kind of like the idea of building up the core in layers with a layer in glass between. The thing I am wrestling with is the size - about 7’ x 7’ - and what happens when you put weight in the center of that span. I’m trying to avoid beams across the center. When you follow the lines of existing top, beams are head-knockers for taller people. I did add a 2” tapered bump up to increase curvature and push water to the sides and aft.

That second picture is the skinned mold, which took 2.3 sheets of 4x8 plywood. Adding backer blocks behind the joints. The curves use thin strips, so I am filling in the gaps in the back with thickend epoxy and adding a layer of FG to strengthen. Then a lot of fairing and sanding.

Because of the size of this thing, I’m looking for the very best mold release coating.

I don’t even allow hard sole dress shoes on my boat! Enough to do w/o wiping off stuff marks.

[dkirsop]

I did a non-boat FRP project 2 years ago. The trick to getting a good release is paying attention to the fairing, smoothing and polishing of the mould surface. You cannot be too meticulous when it comes to finishing the interior surface of the mould. Then give it several coats of PVA release agent (I ended up using seven coats). It will still take an effort to pop the finished shell out of the mould as atmospheric pressure will fight you in breaking the air seal. You might want to leave a lip that you can fasten a clamp to give a purchase point for levering the shell out of the mould from various points around the perimeter. Once you start to get release it will come free quickly but take your time working from several points in turn around the perimeter.

[SalishAire]

My only experience with working fiberglass I used Coosa Board from Fisheries Supply - I just have to say it was easy to work with (respirator highly recommended when cutting) and is designed to adhere to the resin (but expensive). I haven't used a mold but wondered if it would be possible to plan an air injection hole/fitting in the mold so that an air pump could be used to help pop it free - just my mind playing with ideas. As to the stiletto's - darn I forgot to consider that as I really wanted to dance the flamenco on the roof - I guess that will need to wait for the next boat when I'm 90 years old or so.

[asuydam]

Ambler,
Do you think your present hardtop would fit my 27SC? I would be interested in your “old” hardtop if you are not going to cut it up for a pattern.
Alan

[Ambler27FC]

Asuydam, my current hardtop certainly would fit an SC. I am pretty sure the lines on the back of the cockpit for both the SC and FC are identical. I think I read that some of the later models had an extended overhang, but not by much. This overhead is slightly more rounded than the cabin overhead (which is very flat), so a PVC backer board was used at the junction. The back is held up by a bimini frame. If you have a bimini frame, it might be a simple matter of adjusting the height/angles. Otherwise some simple stainless tube supports. Hate to throw the thing away - it is a smart system. Would probably be available between May and July, depending on the weather.

[Ambler27FC]

50 hours into an ~80 hour mold build. As expected, most of the work is filler and sanding to get the complex curves just right. Will likely need to make a long and slightly curved sanding tool for the final layers of filler.

After doing some research I am thinking 3 layers of 10oz bi-axial weave, then matt, and then two more layers of bi-axial. Top and bottom with all seams staggered. I will likely go polyester or vinylelester so that I can use matt, and because I am apparently allergic to epoxy even wearing a good respirator and with the garage door open. Sites like Total Boat seem to have polyester resins with measurable amounts of hardener. If polyester can be used without some guesswork (counting drops), I am on board. Also currently liking end-grain balsa as a core material, which seems superior if you can keep it dry.

Any corrections to my thinking would be much appreciated.