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Re: UK Zip Build

Posted: Tue Aug 13, 2019 8:32 am
by sproggy
It's an interesting idea. And would be more viable if I had a thicknesser! I've got one on my shopping list but for later in the project - I could bring it forward. I would have to test to see whether stripping the outer ply (or two) off caused any cracking issues when bending but it's supposed to be high quality ply so it should cope.

Thanks for the suggestion - definitely worth considering.

Re: UK Zip Build

Posted: Tue Aug 13, 2019 6:23 pm
by BarnacleMike
If you have the patience, you can always sand it to match.

Re: UK Zip Build

Posted: Wed Aug 14, 2019 1:43 am
by sproggy
My first thought when I read that was "I don't have the patience"!

But using a belt sander with a fairly aggressive grit could do the job in an acceptable amount of time, I guess. And the advantage of sanding ply is that it's quite easy to see how far through you're going. It would be feasible.

But having given it some more thought last night it seems to me the easiest method would be to bond 2mm shims to the sheer, chine and stringers (after they have been faired) to bring the 6mm ply out to meet the 8mm. Then fair the shims back into the stem. It would make a few challenges in terms of the butt blocks but I think I can do something about that. Perhaps it's not as much of a problem as it seemed! Sleeping on a problem usually brings perspective.

Re: UK Zip Build

Posted: Wed Nov 27, 2019 7:32 am
by sproggy
It's a year and a day since I last posted a photo. So probably time for another one. Having spent a very long time fairing (and I'm still not done aft, where I have to work upside down) I reached the point where I was ready to stick some skin on the frame. I expect starting in the middle of the boat is somewhat unconventional but these are 'transition' panels in 4mm ply (was supposed to be 3mm) between the single layer of 6mm (1/4") forward and a double layer of 4mm strips aft.

First one with lots of staples holding it in place:

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and then I realised how much effort it took to remove staples so on the next one I used more clamps and fewer staples:

Image

The next job was to bond 2mm shims to the sheer, chine and stringers, which were then thinned out towards the forward frame to blend back to the original profile:

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Explanation for the shims - 2mm shim + 6mm ply is the same thickness as two layers of 4mm ply.

The first forward panel is about ready to go on. I used a router to thin it from 6mm to 4mm for an approximately 6" overlap with the transition panel. This leaves it proud of the transition panel by exactly the thickness of the ply for the second cold moulded layer and the shim on the frames makes up the difference.

I intended to use 6" wide strips of ply aft but realised that squeezing the transition from flare forward to the barrel transom into a Zip length and low freeboard (a proper Barrelback has an extra 5' or so of length and greater freeboard to achieve this) meant I needed narrower strips to accommodate the fairly extreme twist. I'm working with 5" width at the moment although that may still be pushing my luck. There's more fairing to do before I explore that further.

Re: UK Zip Build

Posted: Thu Jan 02, 2020 7:33 am
by sproggy
First forward, topside ply panel fitted over the Christmas break:

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The clamps are because I decided to use screws only every 6" rather than the 3" recommended - the epoxy is strong enough once hardened. For the first time I experimented with a mix of hardeners - 50% slow and 50% fast. It worked out perfectly in the cold conditions - enough working time to do the whole panel but it went off a lot quicker than it would with all slow hardener. I'll definitely do the same again depending upon the weather.

I can't remember where I read the tip to do trial assembly with stainless screws (probably on here somewhere) but I'll repeat it for the benefit of others. I lost track of the number of times I fitted and removed that sheet of ply until everything was just right and was happy to be using hard (and disposable) stainless screws instead of the soft silicone bronze ones. Got it all right and then used the silicone bronze screws only for final assembly with the epoxy. The stainless screws are still good for dry assembly of the other side.

Detail of the bow - it'll be rounded over with a solid timber 'nose' and a split cutwater like Garwood used on some of their boats. Final deck edge will be 2" higher than the sheer.

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You can see that I misjudged the position of the screws along the sheer and had to re-drill. Not the end of the world but I won't make the same mistake on the other side!

My family is getting bored with buying me clamps for Christmas but I did get some deep throat clamps this time which I'll use for the cold-moulded strips to avoid using staples for the first layer. That's the next job which will keep me busy well into the spring at the rate I'm working.

Can't diagonal cold mould

Posted: Sun Jan 19, 2020 5:01 am
by sproggy
I've hit a problem. Although the boat is faired I can't get 5.5" wide okoume ply to wrap around it. Not at 45 degrees. I've tried a couple of strips:

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but other than looking like a dogs dinner, what the photo doesn't show is the ripples in the ply between the stringers. If I faired this layer I'd go right through the ply - the distortions are bigger than the ply is thick (4mm). The more I do to try to force the new strip to confirm to the previous one (the edge has been profiled to fit properly against the previous one) the worse the ripples are. If I try to fit a strip away from previous work it's the same. I figure the change in profile of the topsides, although fair, is simply too extreme for 5.5" strips to wrap around. So I tried 2.75" strips instead and that's nearly as bad. If I go any narrower I might as well strip plank it....

I tried reducing the angle so rather than being at 45 degrees the strips are more vertical. The closer they get to vertical the better they work. Vertical is perfect, with successive strips providing a smooth surface. So..... Unless anyone can suggest something I might be missing or doing wrong I'm going to cut vertically through what I've done so far and adopt the Ashcroft method from there back - vertical strips with the two layers overlapping. An advantage of this is that I can do both layers at once, negating the need to fair the first layer before applying the second.

Any suggestions or words of wisdom before I get the circular saw out?

Re: UK Zip Build

Posted: Thu Jan 23, 2020 1:16 am
by sproggy
I took the plunge and set the circular saw on the boat:

Image

The vertical cuts still visible are through the ply layer only, not through the longitudinals themselves. Next job is to take that ply off completely, then I'm ready to start again with vertical strips. This is the second significant setback (first was having to cut off the original stem and fit a new one) but as my wife pointed out it's a learning exercise - it won't always go right first time.