Flex in cabin roof (563)

[Steve]

Hi Guys,
I have a question regarding Flex in the cabin roof of the Investigator, When I stand the mast up and grab the forestay and draw it like a bow string with little effort, there is or what appears to me, to be quite allot of compression in the cabin roof just forward of the mast plate. I can change the angle of the mast with this flex, if I tighten the aft stay, it preloads the cabin roof until the mast starts to flex, also there is a slight depression in this area without much tension on the stays.
I'm unsure if it goes away when I drop the mast but I will find that out shortly. A close inspection of the arch way inside the cabin under the mast reviles cracks in the jelcoat along the top of the arch and along the base of the arch on the port side forward bunk (down at your feet if you where laying in that forward port bunk)
My question to the forum is:
Is this flex normal, do others see flex in that same area and has any one else noticed or repaired gel coat cracks around the arch way on their 563.
I'm just having a little trouble getting my head around what parts of the rigging are taking the most load under sail.
Also, I'm so glad I found this Forum , have spent a few enjoyable hours of reading and many thanks to all the contributors

Steve

[Yara50]

Welcome Steve.
You have picked on one of the few weak points in the design, however you may also be having a problem with the plywood laminate in the cabin top rotting. Check all penetrations, like bolt holes, in the cabin top, and see if there was maybe some water leakage which could have caused rot.

In any case, deflection of the cabin top under the mast is a known problem. See http://www.investigator563.com/forum/vi ... p?f=4&t=84
It is reasonably easy to make a brace beam as described in my post. Next time I am inside the boat I will try to take a picture of the beam from the other side, so that you can see it.

[Steve]

Thanks for your reply Ian and pointing out your modification, I don't feel quite as worried now knowing it has been a common concern amongst other 563 skippers.
The ply in the roof seems free of rot (determined from inspections as you suggested) but the fiberglass and resin may have fatigued at that stress point."I can't believe how much it flexes"??
Seeing that I haven't entered her in the boxing day Sydney to Hobart, no need to panic and charge into a modification, instead I will enjoy sailing Christmas day and boxing day on Geographe Bay with my Wife, only a bit more mindful of the mast mount. Sounds like modifying it will be my first project for 2013 though. In the mean time I will get a few snap shots of the arch and post them up for you guys to see.
Thanks again..

Steve

[Yara50]

So you are a WA sailor! If you are based in Perth, I would have a good look at the trailer bearings before starting a 200k hike. We have some comments on this site,- IMHO the standard so-called marine bearing seals are hopeless, and you are better off with normal 'terrestrial" seals changed regularly, or the best, Durahub oil filled hubs.

Back to the cabin top. All of the stay tensions result in a compression of the mast, and a lifting force on the shroud mountings. When the boat heels, more tension goes on one side, but in addition, the healing force adds more tension in the windward shroud, and more compression in the mast and hence down-force on the cabin.

The brace beam under the mast is easy to make if you can do woodwork, and I think the support posts are just standard table legs. Also make sure you have tapered large pads and large washers under the shroud U bolt nuts.

Suggest you reef early, so you dont load the components until you have time to do the mods.

[Yara50]

Have now added some more pics to my original post on mast compression support, so you can see how it is made.

[Steve]

Here are a couple of pictures of the cracks on the arch. Had a bit more of a look today and it looks like a filler or bog of some sort has cracked/de-bonded and broken away.

[Yara50]

Mmm, the cracks in the top section are easy to explain, high load, insufficient strength in bond. However, no worries once you build the support frame under the mast, and have a new way of getting the compression forces down to the hull. The bottom cracks are a bit of a mystery. My guess is that the tensions of the shrouds may have been transmitted to the arch, and then lifted the joint. However, normally those tensions go from the deck into the hull, via the hull /deck joint. By tapering the pads under the u-bolt shroud bolt nuts, it should spread this force without causing a high stress point. How does the hull/ deck joint look like in the vicinity of those bolts? Have you got tapered pads?

[Steve]

Hi Ian,
Thanks for your replies, I don't think it is going to be too difficult to repair and reinforce if needed, I was more curios to know if it was a common problem. The crack along the bottom of the arch has stumped me a bit. The shrouds attachment point has been modified and now attaches directly to the side of the hull on a glassed reinforced pad, no u-bolts through the deck, instead a s/steel strap through the lip of the deck and onto the side of the hull, looks good to me though.
Anyway , I will gouge out the filler along the crack till I can see day light under it right along it then fill it with West Systems epoxy.
There have been a few other mods done to this 563, One that is playing on me a bit is that the compartment to access the swing keel plate pivot has been glassed over. I noticed the keel clanging a bit so I had a look at it on the trailer and it is in need of a couple of thrust washers. In the mean time I will cut some big washers out of a sheet of nylon, slit them and force them over the pivot from the outside.
Also what type of s/steel rigging cable do you guys use? Alot of the rigging on this 563 is 1/8" -19, I like the 1/8" 7 - 19, I know it has a lower breaking strain but it is allot more flexible.

Steve

[Yara50]

1x19 is standard for standing rigging and 7x19 for running rigging. As long as you are careful in mast raising, the 1x19 is fine. If you have the standard single shroud per side design, I would stick with the 1x19.

[geoffr]

Hi Steve:

In Ian's post on mast compression issues you will also notice the laminated ply 'post and lintel' system I added on the inside of my cabin arch support.

Like you, I noticed a bit of flex in the cabin top on my boat too when I bought it, even just by standing on it (85kg body weight -- then add weight of upright mast). I also noticed significant cracking in the fibreglass around the inside of the arch, no doubt caused by 30+ years of flexing under various loads.

However, having added the ply supports (glued in with glass resin, then screwed through with SS self-tapers) I can report the cabin top is now rock solid, as all the downward forces are shared more evenly down through the 'posts' to the cabin berths below.

I did consider Ian's more obvious post supports, but wanted a system that was less 'visible', and did not encroach on the circular inner berth area of the cabin.

Good luck with whatever system you decide on.

Cheers,