Thread: GIS Build in Queenstown New Zealand

Hi MIK

OK, if you're in the ACT let me know what day you can make it during that week (if any) and I'll see if I can take a day off

I think the Moths would be great to see because they are right at the pinnacle of development. I have also read that there will be at least two boats sporting wing masts for the first time at a Worlds, so it would be special to to see them.

Will be interesting to see if they can make the wing masts light enough to be competitive. I suspect that they might not be quite so effective on hydrofoil boats because their big advantage is that the boat can point infinitely high in a gust without sails flapping and causing drag.

With a Hydrofoil boat the speed to angle curves (polars) keep pushing you further off the wind in a gust - bear off a bit and double speed.

But if anyone can make them work the Moths can.

MIK

I'll be on the Central Coast on holiday from tomorrow, if people are going to see the moths it would be nice to catch up.

Robin

Will let you know what days we're planning to be there Robin! It would be great to catch up.

I really hope the wing guys arrive. We can probably expect that they won't be as fast as the sails yet, but I have a hunch it might not be long because the Moths develop things very quickly.

You up there on the weekend Robin?

MIK

Well, I finally got on to measuring out the big bits, and I discovered my 6mm ply is metric size 2400x1200 mm. Hmm, I'm sure I ordered 2440x1220...

So, I'll be 55mm too short on the sides. I'm figuring I'll scarf on another bit, probably at the bow end on both sides as it will be hidden under / supported by the stem piece on the inside and the paint on the outside.

Another way I'm thinking is I could butt strap the join if I angle the join so it is parallel to the stem line and the right distance so the front edge of the butt strap butts against the back edge of the stem piece.

How close are the tolerances fitting the two side panels across the width of the ply? (The metric ply is only 20mm narrower, but over the 2 sheet length I lose 80mm of length)

I'll be cutting exactly to the line with a 0.5 mm kerf Japanese saw.

If necessary, I could move all the side offsets 8 mm or so closer to the edge to make a little more room - I see the plan offsets don't go closer to the edge than 10 mm.

Ian

Sheesh, that's a curve ball that I think is pretty unique as I can't recall anyone else in the spot you're in!

I think MIK's expertise is needed here. My immediate thoughts are not to join a piece on at the bow, but to do it at the transom end instead. Also, I'd use a butt strap join because it's strong and you can keep it fair and flat. The join at the transom end will almost disappear under the knees and won't look out of place, especially because only a small bit of the strap will be visible.

However, the main reason I wouldn't consider the join at the bow is because I fear that you will have problems due to the considerable twist there, and there is a risk that you won't get a nice fair twist into the stem. Also, everybody's gaze is more fixed on the bow area than the transom, so it will be more invisible back there.

Anyway, MIK will be along soon and is far more qualified to comment on what's best.

Bummer!

Hi Bruce, some good points, thanks.

Probably better to do it at the stern as I guess there is less pressure/twist there. (Although I think the radius of curvature of the side panel is greater at the stern than the front, I'll do some reverse engineering when I get the chance and see)

Reason I was figuring on needing to scarf is the join would overlap the join with the stem (at the front) or the side cleat of the transom (at the back), and the extra thickness of a buttstrap would get in the way of this.

I think I've figured a way to do the buttstrap, keeping the join line vertical but angling the buttstrap so it is parallel to the rake of the transom so the butt strap also butts against the side cleats of the transom.

Will wait to hear what Mik says, issues could be doing a join right in the area where the panel is supported, which may help, but which can concentrate bending forces, though it will also be supported by the knees, gunwale structure and seat cleats along the sides.

Ian

Howdy,

What sort of ply was it? I have never seen 2400 x 1200 ply made anywhere but Australia.

My feeling is that you can drop the sheer a little bit - but you have to preserve the length of the panels using scarfs to join the extra length if needed.

It is a real curve ball.

Happily having no foredeck and sidedecks makes this a lot easier to accommodate. I would be nervous about suggesting it to a first time builder, but i know you have the skills to work it out and work it through.

MIK

Thanks, Mik.

I've had a little play with the side panel offsets on the spreadsheet and I'm pretty sure the 1200 mm width is enough to fit the two panels on. I'll move the offsets over by 9mm so the sheer comes within 1mm of the sheet edge rather than 10mm, which will give me a little more space and cut right on the line with the Japanese saw.

I'll need 55 mm more length, so I think I'll just join a bit on the stern end of each side with a buttstrap. I think I'll just keep the joint and buttstrap vertical, think I've figured how to integrate it with the join of the transom and the knee / gunwale structure in the corner, and it will be hidden under the knee in any case.

Not sure how I ended up with 2400 x 1200 mm sheets, I guess the ply (Gaboon) is some of the Chinese stuff (stamped BS1088). Quality is a little variable, some sheets have a good side and a not quite so good side, but as I had an extra sheet of 4 mm I could cut to get all panels with the best side where it will show. If the supplier was around the corner I'd march in and make a fuss, but sorting it out from 600km away is more trouble than it's worth at the moment. I've gone back and inspected each and every edge I've cut, including all the scraps, and to my relief haven't found any voids, and cosmetically everything that will be clear finished looks OK, but I'll know to make sure I go to the Joubert stuff for another build, I've since found someone who imports that to NZ (though it's at least half as much again per sheet).

Ian

Hi Ian, just make sure you have enough on the edges that need to be bevelled. The plans are pretty clear on this though so you should know which edges are the critical ones.

The Joubert ply will pay you back for the extra cost. It is very high quality, both sides are of equal quality, and importantly is also very light weight.

Hi Bruce, do you have a weight per sheet value for your Joubert ply?

Just curious, I don't have the dollars to buy more at the moment, had to upgrade the car last week after the previous one was rear ended / written off on New Years Eve. On the plus side, we now have one with a tow bar so once I can sort out a trailer getting further afield will be much easier.

Ian

Howdy Ian,

While sailing with Bruce we talked about your ply and were happy it looks like it will work out.

However our talk made me remember one shipment of Chinese ply that came to Duckflat back two years ago when nothing else was available.

The quality European Gaboon/Okoume sheet is 2500 x 1220 - 4ft by a bit longer than 8ft. The chinese don't have their own standard for plywood so just copy everyone elses sizes - probably your manufacturer had a contact in OZ or looked at an OZ website and found 1200 x 2400 was "standard" here - even though no other country in the world manufactures that size - as far as I know.

Anyway ... this shipment was 8ft by 4ft compared to the slightly longer European sheet. On closer inspection we noticed that the sheets had all been docked on one end by a different saw. That might be worth checking on your sheets to make sure all the sides are straight and square. Possible that only two of them could be original manufactured sides.

Also thinking about this ... I would be inclined to do a boil test of a corner of the ply to make sure everything is kosher in the gluing. I wouldn't expect any problems - but cut off a small corner sample and boil it for 20 mins and then allow it to completely dry. See what happens. And do it again.

I really don't expect any problems - but good to be sure - the odd size makes me wonder a bit - and seeing it is easy to confirm ...!

Best wishes
MIK

Hi, thanks Mik, yes, what you describe above is exactly what I have - some of the edges are cut with a different saw than the original manufactured sides, though they appear to be straight and square to within a millimeter. I've just boiled a piece for about 40 minutes and it seems OK, so that's a relief!

If I'd found five little individual veneers floating in the saucepan, it would have been quite tragic, although not quite on the scale of Charlie Whipple's boat building tragedy.

I'm in the middle of doing the buttstraps on the side panels, I'm adding the extra 55 mm with buttstraps at the stern, it will look OK and be hidden under the knees anyway.

Once I had to do an extra buttstrap, I felt a strong urge to add another 750mm on at the back of the side panels and bottom, continue the lines with a fairing batten and take the boat out to 17ft, but managed to (just) restrain myself!

I'm happy enough with how the boat will come out with the best sides of the ply in the right places, only one sheet has one particularly poor side, so that will go into the seat tops and centreboard case with good side out. Hassle I could have done without and a warning to check origin of ply when ordering.

Bruce - I understand your brother in New Plymouth is building a boat, these people (Plytech) seem to have the real stuff from Joubert.

Ian