how strong are my frames?

Ok, total beginner here. I'm building frames and just need to know if i'm on the right track and what my next step should be. Even if this means starting over.

After a little life-changing experience i made my bucket-list and a building a wooden boat topped the list (improving my english is also on it, please give me some time for that) Short story, i picked up a big load of african mahogany planks, about 80 years old, as dry as they get but only 20-21mm thick.
I wanted to learn so i started lofting a Hacker. The plans call for 1 inch thick frames. So i made each frame twice in 15mm with the pieces joining in different places so i get 2 overlaps on each corner, then i put the two frames on top op eachother with 4 brass screws in each corner (and a few more on long parts) with Poxy-grip from Glen-L. The 15mm pieces are about 3 inches wide.
Question; do i bolt through the two frames instead of the screws, do i put extra pieces over the corners, or am i good to go?

Thanks!
Joris

 

Laminating frames is an acceptable way to get the strength you need, but it is not clear to me what exactly you are doing. Are the planks you have all so short you are actually splicing the frames? how is that splice made? Please provide a sketch or picture of the configuration, it does not sound like what you are doing is the correct way to go about it, but it is not clear exactly how you are building up the frames.

Do not use brass screws, they will corrode away, you want to use silicon-bronze or stainless fasteners.

 

Petros,
Looks like i made a small mistake in the message there, the screws i'm using are the silicone bronze (also from Glen-L) not brass as i wrote.

Here is a picture of one of the frames during fitting of the pieces. In this picture i'm building the frame in 15mm with every overlap as big as possible. I then fit the "missing" pieces to end up with a double frame and take it apart to reassemble it with the Poxy-Grip.

To get everything fitted as tight as possible all edges are made as straight and square as possible to get the least possible play between the pieces that will go in the gaps. In this picture i'm making the two pieces that will go in the bottom.
They are made a few mm's to long so i can run a router through the connecting spots to get a perfect fit. On the two top pieces that make the arch for the deck (backside on picture) i wait until everything is epoxied and cured, then run the router with a 8mm cutter between the pieces that dont connect so i can fit a 8mm piece with epoxy.
My idea was to get frames where there are no gaps to make the frames as strong as possible without the need for fasteners. Relying on the epoxy for strength, not the screws who are basically only there to aid in fitting everything correctly.
Hope this picture is more understandable then my explanation?
Thanks,
Joris

 

Joris,

Unfortunately what you have done so far is not very good, sorry about that. The joints you are making at the centerline, chine, and sheer are in English called "half-lapped". While the lapped part is strong, the other half (butt joint) does nothing. The problem is that the butt joint between the end grain of one piece and the side grain of it's partner adds no strength to the structure.

You can add plywood "gussets" over the joint area (both sides and through bolted) which I think is standard with these Glen-L boats....

 

Right or wrong, it appears that you are doing work at a good standard of craftsmanship.

As a wild guess, it appears that the boat might be an old time "gentlemans runabout" of the Century, Chris-Craft, Riva variety.

 

Tad,
Thanks for the clear answer! I was hoping gussets would be the answer so that was good news Any advice on thickness for those gussets?

Messabout,
Thank you and good guess btw! It is "Gladys" the 20' Hacker from the runabout book.

 

There are few different ways to do gussets, but the general rule is they should equal the strength and stiffness of the frame futtocks. Metal is the least offending, in regard to the amount of space they can rob from the interior, though usually more expensive and often heavier then other options. Plywood, sandwiching each side of the frame is the most common, but usually also the most intrusive into interior spaces, plus they don't look so good. If the plywood gussets are "let" into the futtocks, this decreases their impact a bit. Lastly is a filler piece, which in your case would be a triangular hunk of wood, fitted to the inside of the joint. These too are intrusive, but if made from the same material can look nice, especially with the fine fitting you're employing on these frames.

If it was me, I'd use a combination, with fitted filler "knees" where they'll be easily seen and need to look good, but in locations where no one's going to see them, plywood or metal gussets.

If using plywood, half the thickness of the frame on each side of the joints is the rule. So if you have 1 3/16" frames (which is what it appears you have), you'll want a minimum of 1/2", preferably 5/8" plywood on each side of the frame. If you use the 3:1 rule, you can get by with 1/2" plywood. The 3:1 rule means the "reach" or breadth of the gusset should be 3 times the depth of the frame. So, if your frames are 3" deep, you'll want a gusset that spans at least 9" on each side of the bisect line. If you want smaller dimension "bridging" in the gussets, use thicker stock.

Attached is a typical gusseted frame. The lower gusset is short on the bottom, but is supported by a structural floors. The upper gusset bridges two joints, but you can see the "reach" it has, relative to the frame.

The photo is again another view, of appropriately sized plywood gussets on frames. The vast majority of these gussets (in the photo) are out of sight, so stylized shaping wasn't necessary. These are 7 ply BS-6566 meranti, 1/2" gussets over 4/4th's frame stock. There are no lap joints withing the frame assemblies, just butt joints under each gusset sandwich. Epoxy is the primary fastening system, though a few screws and through bolts are employed in high load areas.

 

Joris,

looks like nice work, but as noted the butt joints are not strong enough. But it can be reinforced so you can use what you have built. On the deck beam if you add another full length curved piece to the other side of the center butt joint it would likely be strong enough. the Plywood gussets are a good choice for the corners, but the deck beam should get another full length splice piece.
You need the total thickness of specified lumber along each length, when you butt splice it there is only half the thickness, so another layer will provide the necessary strength. IOW, you must resume the full thickness of solid lumber even at the splice. the cut wood at the butt splice adds no strength at that spot.

You can correct it by adding another layer of wood overlapping the splice. this adds some weight, but if you are determined to build with the wood you have than this would be acceptable, and it would not add too much weight I suspect. Just resist the erg to make everything stronger than the plans indicated.

 

Before i forget; I didn't mention this boat will be cold mold. From what i've read this is the best method for newbies?

Par,
that for all that information! You made me curious about the filler pieces, there is one frame that will be visible in this boat, the others will be under the seats or under the closed deck so invisible. So on one frame it could be a nice solution. Are these filler pieces laminated on the inside straight to the frame? Or are the frames gapped and the piece fitted inside these gaps?

I'm sorry for all these beginnerquestions, it's been a steep learning curve the last 5 weeks

btw, your second picture goes funny when i open it...and i have a feeling i really need to see it

Petros, i was so focused on reinforcing the chine-sheer-etcetera i didn't think about the top-piece any further. Thanks for reminding me, i think you're right the easiest solution is to fit an extra arc. Possibly the pretiest solution too.