deck to hull mounting flanges ?

[pescaloco]

hello, looking for suggstions, this is a new construction 27ft deep v hull boat will have a mid cockpit v-drive single diesel ............. integeral fuel tanks in a saddle configuration and fish boxes/wet boxes also intergral to the hull.

so the question is having a 10 ft x 9.5ft aft deck that has no bulk running at 90 degress to the stringers, what would be recommended to support the center span of the decking ? ...........what would be recommended to support the outer edges of the decking?.............it should not be the top of the integral (core and glass fuel tanks) should it? ......or is that ok?

how does one install a flange or ledger to the hull sides with out mechanical fastening?

thanks, mark

[SamSam]

I put the decks in 10 or so 30' boats with 12' beam at a place I worked at. First I would grind a 12" wide stripe where I was going to work, then I would mark a line along the insides of the hull, close to the center of the grinding. A 2x4 would get all four corners rounded over with a 1/4" roundover bit, then cut down the center at an angle that corresponded to the angle of the sides' flare, ending up with two pieces with an angle cut on one edge and the other two corners rounded over. The pieces were only 2-3' long or so, and the angle of cut varied in each piece to match the varying angles of the side as it went forward. It wasn't a precise thing. Every 3-6" a kerf was made in the outside of the sticks to allow them to bend and conform to the curvature of the hull. The cut left a 1/4" or less of wood so you ended up with a flexible string of blocks that sometimes broke. That was OK as it wasn't a precise thing. These were buttered with Bondo and stuck to the hull below the line, a few feet at at time, held in place by hand for a few seconds until the Bondo set and so on until they were all affixed. Excess Bondo squeezeout was trimmed off while the stuff was still semi soft. Two layers of 1-1/2 oz mat were then put on, the first layer 12" wide and the second 14" so the edges were staggered and tapered somewhat. The first piece was a full length 12" wide one, the second was a 14" one applied over that with a short piece ripped off the end so you could just keep going around putting both layers on at once and the ends would be staggered so you didn't end up with multiple layers and bumps. No attempt was made to fillet between the hull and blocks before lamination.
After that set up, upright 2x4's every 12" were laid from side to side, the ends held back from the hull 1/8" or so to prevent hard spots, a 1/4" hole drilled through the 2x4 and the ledge and everything bolted together with 1/4 X 6" carriage bolts. There were two stringers about 3-4' apart, on both sides of the centerline with the engine in between. 2x2 legs were run from the bottom of every 2x4 deck joist (?) to the top of the stringers, attached with gussets.
Centered two foot on each side of the fore and aft centerline, a 1x2 was let into the tops of the joists to support the edges of the plywood sheets.
To finish the deck, full width 1/2"plywood was applied up the middle, glued with resourcinal glue and fastened with bronze ringshank nails. The ouside sheets were then scribed and cut 1/8"or more short of the hull to eliminate hardspots, glued and fastened.
After that the fiberglass maniac would take over and fill in stuff and then put on a layer of 1 1/2 oz mat and a layer of 10 oz cloth, both lapped up the hull sides a little and maybe even a little extra at that junction.
Sometimes regular manufactured hatches would be put in and sometimes I would mark them out on the ply deck, using a quarter for the corners as a template, cut that out and put a lip on the underside of the deck. The deck and cutout piece would be glassed, a handle put on the cutout piece and that was the hatch. Sam

[pescaloco]

Sam Sam

thanks for the very complete explanation, that is exactly what I was looking for - that is what I was thinking, but wasn't sure how to go about it.

lets modify just a bit what if I want to use wood for flange and joists, but foam core for decks (would you 5200 and s/s screw to joists ???)

thanks, mark

[SamSam]

Mark,
I haven't worked with foam much. I would be suspicious of screws working around and wallowing out holes and would be tempted to just use 5200 or something on that order. Screws from above through both skins and the foam into the wood, would probably tend to crush the foam. Screws from below through just one skin might pull the skin away from the core, eventually. Sam

[BTScow]

Screws have a fraction of the holding power of wood. Use wood. I have seen a lot of deck repairs - and I would have say Sam's methodology is about the most complete and well thought out I have heard.

[pescaloco]

thanks, I known what you are saying - looking to save some weight but it is not absolutely necessary that the decking be foam core.

I do have concern about any penetrationions into foam core - may be time for a new thread..........but the pilot house for sure is foam core and it will have grab handles / rocket launchers (rod holders) / antennas - radar mounts etc. all with penetrationions into a pvc foam core. in the past with wood I would just float a hot coat of poly resin or feed smith's penetrating epoxy into the penetrations before assembly then use a polysulfide sealer.
with open cell structure of the foam and lack of stregenth with out glass skin
I am wondering how this can be done with good long term results.

thanks, mark

[BTScow]

Mark,
I have two words - G-10 fiberglass rod. It is actually garolite, but it is a hollow tube we have installed on all of our high-load penatrations as it has a compressive strength of what I consider infinity. I have gotton it at McMaster Carr - argably the most complete hardware store in the world. Back to the point, you can get it in a varity of diameters. We used it when mounting outboards as our transoms were foam (albeit high density). Another consideration in pre-determining where all of the penatrations are and omitting the core in those areas. This is by far the more economical way to go especally if you are building/rigging more than one. We did this with great success on our decks for handrails and other hardware. By core omision you have addressed the majority of problems associated with core penatrations, water ingress, holding power, sealer, and open cell structure.

Hope this helps,

Crayke

[pescaloco]

BTScow, g-10 sounds interesting - in your example of hanging an outboard on a cored transom how do you apply the g-10 ? remove core and use as a sleeve that becomes non compressive due to it stregenth properties and bed in with epoxy ?............ does it have any application where some thing is screwed in instead of bolted or just for bolted on parts ?

thanks, mark

[BTScow]

Mark,

You are correct. We oversized the hole to about a 16th over the O.D. (with a hole saw) of the rod, cut the necessary thickness with just a fuzz sticking out on either side of the transom, goo-ed the snot out of the rod, and put r' in. We set ours in caulk (5200 or the like) - for no particular reason other than it was the closest to grab. Epoxy is great. I can not speak the the holding power of self-tappers. Perhaps a more economical way would be to just oversize the hole and fill it with thickened epoxy, wait until it drys and drill a pilot hole for your screw....just a thought.

[SamSam]

Another way of handling core penetrations is, if you know where bolts are going to be and where you need the compressive strength or where you need something for screws to bite into, cut away the foam and put in blocks of plywood, before laminating. Sam

[pescaloco]

thanks, guys

this is a custom so there are no set locations at this point I have a pretty good general idea.................. but not for sure on some things. will have to figure out when things come together more.

thanks, mark