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building frame with only screws?

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Forgive me for asking, but it seems the options most people use to attach stringers are either lashing or epoxy and screws. Has anyone tried just using stainless steel deck screws without epoxy? I was thinking of trying 3/4" plywood for the frames, then being very careful with drilling and screwing. But before I try this, has anyone else? Stories or advice? Thanks so much

 

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Let me preface this by saying that I have not yet built a fuselage style kayak. I do have lots of woodworking experience though.

 

Drilling a hole and putting a screw in the already very thin framing members, will weeken them significantly. Lashing does not affect the integrity of the wood. Lashing also allows a permanent flexability that won't deteroirate the wood too much over time (screw holes get looser and looser with flexing)

 

Because the skin of the kayak tends to hold the frame together, you probably wouldn't have any problems for a while. But, lashing will tend to keep the frames from cracking and make your kayak last much longer.

 

Glue of any kind will eventually crack because of the flexibility of the overall design. So, there's not much point in using epoxy.

 

This is just my opinion of course. Hopefully, experienced buildiers will chime in and add to this or correct me...  :unsure:

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Always the contrarian, I prefer epoxy with stainless screws. I dislike epoxy, but it works and lasts well. I'm not that big a fan of a flexible frame and the epoxy with screws produces a very rigid structure that hold its shape very well. I've heard the flexible frame will resist damage, but my boat survived without damage when it fell off a rack and landed on an air conditioner; the boat was unscathed, but the A/C didn't.

 

Your boat, your choice.

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I would never put a structural screw into the edge of a piece of plywood.

That's like screwing into the end grain of a natural board.

If you are building a Kudzu boat, I wouldn't stray too far from the designer's specs, the methods are clearly tested and succesful.

Otherwise, do whatever the designer says, especially if the designer is you.

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I have just finished the frame of a fuselage style Disko Bay kayak.  

 

I was surprised how many minor adjustments are needed to be made to complete a kayak that is straight and true.   Altering things is so easy with a lashed joint and the frame and stringers are not damaged in any way.    Whereas a glued and screwed joint would difficult to pull apart and the integrity of the timber has been compromised.

 

Lashing is so easy once you have done a few joints and I actually learnt to enjoy the process.   Lashing is the way to go and any future repairs will be so easy.

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What about cable ties, I think you guys call them zip ties. They would work, but not look so pretty.

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It's hard to pull them tight enough. I have looked at using them in a kids boat. One where it was built cheap and didn't expect a long life. The goal was to let young kids build a small their own canoe in 3-4 day class.Cable ties would allow for quick assembly. I can't see  young kids lashing for 3 days! But playing the cable ties I was not impressed and wouldn't want them on a serious boat. Can not pull them tight like you can sinew. Always have play in the joints. It would be OK on the kids boats assuming they would never be out on big water and rough conditions.

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There is a tool made for bicycle repair called a fourth hand. It is made to hold a brake cable, while closing the caliper so you can adjust the brake's tension.

They are also stellar at pulling tension on zip ties...pull till the break!

Zip ties would still be iffy though, because there is no frapping to really snug them down...

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I have a number of skin on frame boats. The oldest of these is a Percy Blandford design that I built 35 years ago, and another PB design that I purchased from someone which was built about 45 years ago. They ( and all of my other SOF boats) are screwed and glued. I have re-skinned these two oldest ones this past year and had a good chance to look at the frame structure. They were both in great shape and showed no signs of cracking or undue wear and tear and I re-skinned them confident that they will provide several more decades of similar use. The oldest boat 's frame is varnished throughout, the next oldest is epoxy encapsulated throughout ( an early generation product called chem tech t88) and my other boats are epoxy encapsulated. For those of you wondering if screw and glue is acceptable I offer this only to show that I am having good results this way. I am not finding it difficult to build straight frame structures this way. For the "glue" I would use epoxy. 

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What plywood are you using? 35 year old plywood is a better product than what you typically get now. Unless you are buying the good imported plywood, what I have seen won't hold a screw. A screw will often wedge the plys apart.

 

But if you are gluing the joints, the screw is no longer doing much if anything structurally.

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I thought of including this in my original post but left it out in order to be brief. The 35 year old boat in question has some plywood bulkheads and stems, but is largely constructed using bent ribs. The 45 year old boat was built from a kit produced in England and then shipped to Canada for assembly. Yes the plywood seems different than your usual big box store grade. This construction also uses a  number of ribs instead of cross frames. These 45 year old ribs are quite interesting. They are made up of 5-7 layers of wood and look almost like plywood that has been steam bent or formed during construction into a curve. So when you screw into it you don't separate the layers, you screw through them. My own ribs are composed of 1 and at the most so far, 2 , layers of wood. I have questioned the structural usefulness of the screws in the past and decided I was pretty much using them to hold the stringers in place until the epoxy cured. So about 10 years ago I started leaving the screws out and just epoxying the stringers in place using clamps. My oldest boat using this technique is 10 years old now and holding up just great with no problems. So to sum up....

I am not trying to talk anybody out of lashing, I may make a boat this way someday, it is just not my first choice right now. I build my boats using marine plywood for stems and sterns and some cross frames and also steam bend ash or fir for many of the ribs. I epoxy encapsulate the frame. I am not trying to say this is the best or only way to do things, it is just a system that appeals to me and has worked well in my experience in craft up to 45 years of age. There are many reasons for not going this route. (I would assume perhaps cost, also if you only have say, 3 ply plywood that can't be edge screwed, although epoxy alone might work here, etc) I offer my experiences only for those debating doing the same thing as me. Allan Brown

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