Floor/Frame Fasteners

[gmeadows]

Hi all,

I am building a carvel planked round-bottomed boat with 3/4" white cedar planking over 7/8" square white oak frames. My keel is 2 3/4" thick white oak with an external lead ballast. My floors are 2" white oak and my question is what would be an appropriate fastener to tie the floor and frame together.

I am planning to use #10 x 2 1/2" silicon bronze screws that will be pre-drilled with a tapered bit and countersunk for the screw head. I will space them 6" apart along the frame and leave a minimum 2" edge distance from the screw to the edge of the floor. The screw head will be on the face of the frame once the screw is finally set (i.e. I will screw through the frame and then into the floor).

With a 7/8" frame, I will be left with only 7/16" above the planking to set my screw and this will make it difficult to place the screw parallel to the plank.

I welcome your thoughts on how to set the screw with a standard size screw gun along with the fastener size and spacing. The floor will attached to the keel with through-bolts that will ride down into the dead wood and the lead ballast.

[gmeadows]

seayou7,

Yes. I think that makes more sense. This way you attach the floor to the frame prior to planking and use bolts that are nice and straight through the frames in lieu of screws that would be difficult to place once the planking is on. Makes perfect sense. Why didn't I think of that. So goes the rooky I guess. Thanks.

[wizbang 13]

ya, bolts, or rivets, scantlings are kinna small.
Might be able to lock up the frames with the floors by filling in between the frame ends, against the floors.

[hanleyclifford]

Thru bolt is definitely the way to go. 2" floors are hefty for 7/8" square frames but beefy. I have 1 1/2" frames and floors and I used 5/16" bolts but you might be better off with 1/4" bolts in view of the smaller frames.

[Cogeniac]

How many bolts do you put into each frame (I assume at least 2), and how do you avoid hitting the plank fasteners if you are doing this in an existing boat?

[hanleyclifford]

This can get tricky in a cross-planked boat unless it is fastened with rivets. Usually when you are putting in a new floor you are also doing frame work. Before installing the frame (heel or sister) I predrill the hull and mark each hole on the inside with a pencil line running fore and aft. On new construction you would have to mark as you plank.

[seo]

I have seen a lot of boats with frames neatly broken right where the floor/frame bolts pass through them.
Also not that Herreshof's rules of construction call for the frames to not touch the keel, so the end grain isn't in bilge water.
My idea of best practice is to fasten the lower planks into both the frame and into the end of the floors. I fasten the floors with screws an inch longer and a size larger than the plank/frame screws. So, 2 1/4" X 14 plank, 3 1/4" X 16 floor fastening. This compensates for the slightly less good holding in the nearly end-grain floor timer.
In this scheme, the planks act as cleats holding the floors and frames in alignment with each other, and transfer the loads on the keel/floor assembly to the frame/plank/deck assembly.
It's a critical joint.
Several times I've been able to stop sailboats leaking at the garboard near the mast step by simply adding fastenings through the planks into the floor timbers.
The problem with this is that it adds a step in construction. Bolts are nice because they hold the frames in place with the floors until the planking is installed.

[wizbang 13]

...fastening planking to floors means screwing into end grain,no?
Not my idea of beat practice!

[seo]

That's why I use longer, bigger screws, first thing. Second, the screws are usually oblique to the grain, not parallel to it. Third, Plank fastenings are primarily in shear, not in tension, and end-grain fastenings in hardwood are pretty good in shear.
I made several tests by running large screws into the oak and yellow pine that I have used for floor timbers, and then tried to pull them out with a crowbar. They're not as strong as screws running square to the grain, but if you want to pull out a 3 1/2 X 16 screw that's driven in about 15º oblique to the grain, you'd better have a four foot crowbar and the wood mounted in a very firmly mounted vice.
With bronze screws, the heads broke off before the screws pulled off, which suggests that the screw has enough traction to pull the head right through the planking, if it comes to that.

[hanleyclifford]

While I have no problem with fastening thru planks into the end grain of a floor, there is no substitute for bolts holding frames to floors. Careful drilling and size selection are involved. I also agree that frames should not be extended to keel and definitely not let in. I dislike pitch pockets and prefer limber rabbets.

[seo]

The whole train of thought behind this odd fastening scheme originated when I was working around a schooner hull being built, double-sawn frame, oak planking, the whole gizmo. The futtocks of the frames were fastened together with treenails, and I commented to the designer and master builder that there weren't many treenails, I wondered if they were strong enough. His answer was that they were really only there to hold the futtocks in alignment while standing up the frames. The real work of making the multiple parts of the two futtocks work together as a single frame would be done by the plank fastenings, with the planks acting as cleats that connected the futtocks in each frame, and the numerous frames, together into one hull.
This was a revelation to me. I'd always thought of the frames as being the strength members, and planks as being just the waterproof skin.
The reason I was given for using treenails to fasten the futtocks together was that if you hit one with a drill while boring for plank fastening nails, it wouldn't hurt the drill. (I wondered then why don't they treenail fasten the hull too. I still don't know the answer to that.)
Anyway, I began to think that it would be reasonable to think of the steamed frames and the floors in a bent-frame boat as being like futtocks in sawn frame construction. I still think that, and I'm stickin' to it.
SEO

[boattruck]

Certainly out of my league, put the chances of getting a meaninfull fastening in a 7/8 x7/8 are pretty limited, might be one of those boats where the floors and the frames should act independantly of each other, but that info would be in you building specs if you have them. Cheers, BT

[floatingkiwi]

...fastening planking to floors means screwing into end grain,no?
Not my idea of beat practice!

I screwed the floor timbers into the hull,( or the other way around), with a screw through each plank. Man did it stiffen up the hull noticeably, when walking around in there. Thinking about the screw going into end grain, it all depends on how the floors were made in relation to how they grew. A grown crook would curve around the form of the hulls interior in a U shape. Kinda. No screwing into end grain there. In fact, to get straight into the end grain, one would have to invert that floor to do so.