installing bunks

[slowpoke]

I'm at that point where the plans and instructions stop and "personal preferences," i.e. "figure it out for yourself", is coming into play. How did everyone do their bunks? I was thinking of putting support blocks and screwing them down, but then I realized I couldn't really put support along the ouside hull? so then I thought I'd just glass them in, but if i do that, should I install limber holes first? I don't know, so I come to those who have gone before on hands and knees begging for knowledge....O Great Masters, edify me!!!!

In other words, how did you do it?

[jray]

For what it is worth, I sealed the bunk areas and made them floatation voids. I installed deck access plates as I hate having a void that I can't inspect and open up for winter storage.

[slowpoke]

Thanks Jon, I think that's the way I'm going to go also...

[Mist]

Rocky,

I feel water and moisture always make their way to places that I can't reach. Water intrusion is just destructible to wood boats. I firmly believe one needs to allow air to reach the voids of a wooden boat to allow nature to dry them out as often as possible. Below is a photo of Mist's bunk arrangement. I doubled the ply thickness in the area where I removed the triangular cut-outs. I beveled the outboard edge of the bunk to closely match the hull curvature. After wetting out both surfaces (the hull and the bunk) I applied a generous fillet with 6 oz tape on top. Once cured I thought the 6 oz tape was insufficient so I added another layer. I hindsight I'd used some 10 oz. Oh-well!

[Mist]

I intend to tackle the floatation issue with airbags, two aft of fr 169 and one forward of fr 53.

[Chad]

I don't believe the bunks achieve anything structural in these boats, except around the keel area, especially in long cabin jobbies where the trunk doesn't reach the cockpit diaphragm. They can be used to create a sort of I-beam across the boat's bottom under the compression post (the hull bottom will be in tension laterally), but that area of bunk is omitted in the plan. I recall DBSS had some compression post step/hull bottom issues when they first launched, so it's an area that should be reinforced somewhat beyond the plans, IMO.

Like Mist, I just filleted and taped my (much smaller than the plans) bunks to the hull sides. I cut in fairly large access holes so that just a couple inch border is remaining, though- I need to fit the covers for those holes once the boat goes back upright.

[lohwaikin]

And install the compression post before installing forward bunks.

I could never see tomorrow. I was never told about the sorrows...

[ryderp]

I glued triangular strips along the inside of the hull and along the inside of the bunk supports as additional attachment surfaces for the bunks. My original thought was to fasten the bunks with screws so that they could be removed at any time, but I changed my mind on that and just epoxied them in place. I did not tape the edges of the bunks but instead just glued them in place. I do have large rectangular holes in the bunk supports to allow for air circulation in that area (I'm using a combination of expanded polyurethane foam under a couple areas of the deck and airbags for flotation).

Actually, I still have not installed the compression post and I'm quite happy that I've put this off. Getting in and out of the cabin of a long cockpit boat is hard enough without the compression post being right there. Access is even harder for me now that the keel foil sticks up right behind the hatch. I'm going to put the compression post in place this week, but looking at the structure of the boat, I have often wondered if the post is necessary with the hull, cabin-top, deck and frames all being glued into a single structure (I also doubled-up all of the frames in the middle of the boat). I wonder if the cabin-top/frame would be strong enough to support the rig if simple steel (or maybe carbon fiber) plates were attached in front of, and behind the top of frame 89 under the mast. This would keep the cabin and the top of frame 89 from deflecting and would transfer the stress to the rest of the boat. Maybe one of you guys with the CAD programs could run a finite element analysis on that one (hint to Chad).

[Chad]

I'm not shmart enough (nor do I have the tools) to do an FEA of the deck structure, but my eyeballs tell me it's not at all strong enough to omit the compression post. Evidence so far is DBSS' problems at the bottom of their compression post and Ron's compression post failure- if the deck was strong enough, why's the stuff underneath failing? If you did strengthen the deck a bunch, it's still going to deflect and lack stiffness, and that's never good- rig tuning depends on the geometry between mast step and chainplates remaining very rigid.

The beam needed to support the mast "rigidly enough" would be pretty hefty I would guess, and would need to span from sheer to sheer- in the middle it would be maybe 2-3x as tall as the mast is wide, and have at least as much carbon in it. I recall the Lido 14 that I had 20 years ago had such a beam, spanning about 4', and it was a 2x6 cut with a radius crown on top to fit the underside of the deck. Multiply the span by two, the loads by about 10, and you see the beam gets a lot bigger...

My compression post removes with 4 nuts, so I can slacken the rig and remove the post if I go boat camping, or need to work on the interior.

[ryderp]

I'm also going with the removable post. I was only kidding about the FEA ( I just don't like putting in those smiley faces)

Phil

[Kevin]

My post is pretty fix and I find that it helps more than it hinders usually. Just part of the boat imho.

And you really need something. Ron's (lunatic fringe) home made one gave way with his m20 kite up in 20+ knots and the whole cabin top just ripped apart. The pdx guys have some kind of cross beam that they are using to avoid the post but I don't have the details but as I recall it was a rather large laminated beam. I'd take AL tube vertically over all that mass up high any day.

Kevin.

[Big_Dog]

When I read the earlier posts, I was also thinking of what happened to Ron’s boat. Thanks Kevin for filling the details. The issue I see, that would make this a very complex FEA, is the different skill level of builders and range of materials used. I think Chad’s eyeballs are calibrated right and just add the post. I do like his idea on making it removable.

The Portland boats do not have a big cross beam that supports the mast. They have a compression post that can be seen in the photos when they flip the boats. I only know of one boat without a post, but that mast is keel stepped.

[Kevin]

To follow up on Ron's initial compression post. He has made a carbon tube using sleeves from soller composites. It was an experiment that he initially was going to use for his prod. He went a different route on the prod and then used it for the compression post. I don't know the full lamination and Ron may not remember it any more either. The flaw in the plan was a dry spot in his lamination towards the top of the post. Gust, huge kite and bow in wave = crushed post = no more cabin top. All reports are that the ride up until the failure was absolutely fantastic.