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Old 02-12-2011, 08:55   #1
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Improving Cabin Top Stiffeners

Well its too late to turn back on this project if people here see a huge flaw in my process, but I figure I'd share. I know I write long posts, but I feel some people appreciate the detail of my thought process. If you take the time to read this, you will notice that they aren't yet finished, and I will update when they are. Too many times on this forum people skim through a post, write up a critique and fail to realize half the things they are commenting on were covered in the original post. So this is just a pre-amble to someone coming in and saying something like "you should glass those in if you want them to be strong!"



The project that has been keeping me busy lately has been designing and making the cabin top stiffeners for Windsong. This project has been one of the most difficult ones for me, mostly out of indecision on which option I wanted to take but also with plenty of setbacks.

The original stiffeners are molded fiberglass and were attached to the cabin top with screws and a weak chopped fiberglass and resin mixture. They did an adequate job of keeping the cabin top from flexing, but never appeared to be that strong.






I didn't realize just how much they were holding the cabin top shape until I began to remove them and saw the cabin top begin to sag. Before I removed the bulkheads I am replacing, I had to prop the top up with beams. As described in this post, I raised the top when installing the beams. Not very much, but enough to make it a stronger, more convex shape (it was sagging/concave in areas otherwise).



I was originally planning on reusing the original stiffeners and improving their purpose by heavily glassing them onto the cabintop. Unfortunately, when I started to consider many of the modifications I plan on making to the interior I began to see limitations with using the old stiffeners.

The first problem was the molded light bases. I didn't want to be forced to place lights where those are, or have the bases bare and ugly. If I really wanted to reuse the original stiffeners, I considered cutting the light bases out and glassing them in flush.

Furthermore, I am changing the original vinyl headliner to hard panels screwed into furring strips. The end points of the original stiffeners extended about 1.5 inches, where I only want 1/4" furring strips. I began to modify the stiffeners to have 1/4" ends, but soon realized I would have to lengthen each stiffener to compensate for the ends I cut off:









I figured out a decent way of adding length to the stiffeners, it would just require some crafty epoxy and fiberglass work...something I am feeling confident in.

But then I brought a couple of the stiffeners back to the boat to get some measurements on length, and the final straw broke on using the original stiffeners. I tried to fit one in position and the curve of the cabin top was now changed due to the support beams and the original stiffeners didn't have the correct shape. They are hard fiberglass and not very flexible, so fitting them now seemed more trouble than it was worth.

Therefore, I concluded making new stiffeners would be necessary. I mused for many weeks over the decisions leading up to this, and continued for many more trying to figure out the best way to make them. Originally I decided on using some pre-formed foam to glass in, such as these. Unfortunately these would cost nearly $40 per stiffener (6 total, 7 maybe) and that seemed ridiculous to me.

After much contemplation, I decided to use strips of plywood laminated together and heavily glassed in. Once glassed, they would be faired and painted; with the original teak trim installed. At first I figured that I would rip 1/4" ply into strips and laminate them together. I wanted to make them approximately 2"H x 1.5W" x whatever the length is of each stiffener. This would require about 8 - 1/4" ply strips each. I had a sheet of 1/2" ply that I wasn't using yet, and decided to experiment with it first. If the 1/2" strips were flexible enough to conform to the cabin top, it would take only 1 sheet of ply for all of them and would make this project a lot faster.

I took the ply over to a friends table saw and we ripped it into 2" strips. I then took the strips to the boat to make some test bends, and it all worked out well. I had my materials, my design, and I finally got on with the construction.

The process started by grinding the cabin top where the old stiffeners were in preparation for epoxy/glass. Of course, it was a dusty mess and it was awful having all of the at fiberglass flying around inside. But good glassing technique requires it. I found the spots on the cabin sides where the stiffeners would end, and glued on a plate of 1/4" ply that will be part of the furring strips:



I then measured and cut the first of three layers for each stiffener. The first layer is then screwed into the cabin top, forming the proper curve of the stiffener. Before screwed in, the beam and cabin top is wetted out with epoxy, then the beam is slathered with cabosil thickened epoxy. When screwed in, the glue squeezes out and I create a filet:







I repeat this process for each stiffener two more times, waiting a day in between each layer for the glue to dry (so screws can be removed). The final beam is rounded on the edge for easier fiberglass layout (same with the filet). I made sure to form a thick and solid filet on the end pieces.

After two layers:



All three layers glued in:









As of now I have all of the stiffeners glued into place, and they appear to be quite strong as is. But with a couple layers of bi-axial cloth layered over them will really make them tough and the cabin top should be much improved. After laying down the glass, I will fair and prep for paint. Once these are finished I will finalize the installation of the bulkheads, and be ready to focus on the deck paint prep. I have decided to hold off paint prep on the interior until I finish the decks. Too many leaks make keeping the interior clean a difficult task. For a preview, here is the new main bulkhead being fitted:

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Old 02-12-2011, 09:33   #2
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Re: Improving Cabin Top Stiffeners

So far so good. I would add several gussets as well (roof to cabin side) between the port holes. The stronger you can make your cabin, the better.
I am contemplating the same thing only I will fabricate my gussets out of bronze. I will also install a few bronze rod bolts while Im at it.
Have fun!
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Old 02-12-2011, 11:22   #3
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Re: Improving Cabin Top Stiffeners

Quote:
Originally Posted by Beersmith View Post
Well its too late to turn back on this project if people here see a huge flaw in my process, but I figure I'd share. I know I write long posts, but I feel some people appreciate the detail of my thought process. If you take the time to read this, you will notice that they aren't yet finished, and I will update when they are. Too many times on this forum people skim through a post, write up a critique and fail to realize half the things they are commenting on were covered in the original post. So this is just a pre-amble to someone coming in and saying something like "!"

you should glass those in if you want them to be strong.

Until I got to the end pictures (and saw that the cross beams were back - and of a design I had not seen before (sitting proud of the panels) was going to suggest adding a couple more crossbeams (and spaced out according. Man ) Cound still do that of course, but hard to tell (for me) whether it would look odd.



Is that you? and if so, are you height "Challenged" or simply wear a top hat? Masses of headroom

Given where you are (and the past problems) I would be tempted to add a couple of layers of Fibreglass sheet to the underside between each cross beam. You may also want to look on deck and see whether anything is attached - and consider beefing up the underside accordingly.

Not seeking to worry you, but if she has a cored deck that degree of flex might indicate a wet core .........I would sleep happier at night if I had opened up a decent sized hole to have a looksee - easy to reglass back in place. and even if you decide that it's a job for another day, you will at least know where you are.........and if replacing wet core would do one panel at a time - just in case



Quote:
Furthermore, I am changing the original vinyl headliner to hard panels screwed into furring strips. The end points of the original stiffeners extended about 1.5 inches, where I only want 1/4" furring strips. I began to modify the stiffeners to have 1/4" ends, but soon realized I would have to lengthen each stiffener to compensate for the ends I cut off:
I see your panels are also full width, same as mine. What I have done is cut the panels in two (centreline of the boat, going from stern to bow ) as makes effing around with 'em a lot easier. also allows a bit of wiggle room on fit. (I will admit that I have not yet refitted mine yet, so no photos - but done same before). To hide the join simply use DIY shop quality hardwood batten. I would also do the same for the cabin edges (if you don't have already) - visually makes a big difference

A tidy Seadog 30 (not same as mine, at present - but she will look similar




How wide depends on how good you were with the tapemeasuring / sawing............
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Old 02-12-2011, 12:02   #4
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Re: Improving Cabin Top Stiffeners

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Originally Posted by Beersmith View Post
Furthermore, I am changing the original vinyl headliner to hard panels
I wish I had done that but job part done (my speciality ) already and I have a large roll of vinyl to use up...........

If you have not already cut the panels, consider dropping them to fix on top of the newly fitted cross beams. Will save some finishing and provide lots of insulation room - good for keeping out heat as well as cold. A Trim piece again to hide the join.
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