fairing the sheer question

[stevenj]

I'm working on a gardner flatiron skiff, 14'4". I've attached the ply sides over the frames.

Looking at the sheer from the side appears to be fair. But looking at the sheer from a vertical position the frames appear to be pushing out. I'm probably not describing this as well as I could. I think the picture speaks for itself.
http://www.stripersonline.com/ubb547/image_uploads5/DSC01731.JPG

I faired the frames with a batten. I think the problem is the ply isn't ridgid enough to hold a smooth shape between the frames. It's doing this only between the transom and 2 frames up.

I'm going to sheath with fiberglass (not per instructions, I know). So I was thinking of attaching the gunwale prior to glassing, to get the sides back in shape, then glass the sides. Or should I glass, then hope the gunwales pull it back into shape.

I'm really not sure what to do. Any suggestions would be appreciated.

thanks,
stevenj

[Bob Smalser]

From what I can see, I wouldn't do anything. I suspect it'll straighten itself out once those spalls are removed and their function taken over by thwarts.

If it doesn't, the plywood is thin enuf that the inwales and guards may also iron it out.

[Stephen Hutchins]

It may be an illusion that can be caused by by having the lowest point of the the sheer (in profile view) too far away from the widest point in beam. (as seen in plan view.) in such cases, the further the model is turned over, the more wavy the sheer can apear.

[JimD]

So I was thinking of attaching the gunwale prior to glassing, to get the sides back in shape, then glass the sides. Or should I glass, then hope the gunwales pull it back into shape.
It would be nice to have the gunwale (or sheer clamp, or an inwale, even temporary, if there's a convenient way to install it. A temporary inwale to coax the plywood into shape might not be as in the way) on first so the plywood bends as fairly as possible before the glass goes on.

Edited to add: On my most recent kayak I had both an inner and outter. The inner went on permanently to the side panel which was then fitted and glued to the bulkheads. The outter went on last, after the deck.

[ 12-28-2005, 03:11 PM: Message edited by: JimD ]

[Billy Bones]

Putting the gunwale on before glassing will present you with a whole new set of nightmares. The glass will not contribute significantly to the stiffness of the panel, so when you take it off the molds it should straighten out with or without the glass, as has been said by others. If it still bothers you, you could go through the tedium of installing an inwale to smooth out the bend, but doing so at this stage would be quite difficult as well as unnecessary.

Good luck.

[JimD]

Putting the gunwale on before glassing will present you with a whole new set of nightmares. True, it's much less trouble to be able to run the cloth off the edge of the plywood panel and trim it after it cures than to have get the cloth to reach a nice tidy conclusion up against the rail.

[stevenj]

thanks for the replies.

I had briefly though about the boat springing into it's 'natural' shape once removed from the spalls. The more I looked at the dips and humps the more concerned I became.

Installing the gunwale at this stage is something I really didn't want to do for the reasons others have stated. I cringed at the thought of instaling a inwale, while the boat is upside down.

I took another picture of the hump on the last frame, as the previous picture isn't from the best angle. This is from directly overhead and shows a more pronounced hump.

http://www.stripersonline.com/ubb547/image_uploads5/DSC01730.JPG

regards,
stevenj

[Mike Vogdes]

It can be a little un-nerving at times but it will go away once you have the gunwale, thwarts and decking in place.
Sometimes gets a little wobbly...

[JimD]

Yeah, looking at the photos again I agree, just glass it as is.

[pcford]

Well, I'm sorry, and I'm not being contrary....it sure looks like a dog leg to me. (hump or kink) After section is flat. Frame seems out of fair.

If you don't fix it you will see it every time you look at the boat...

Maybe run a batten along the sheer to check fairness?

Get more opinions and decide for yourself...but I think there is a problem.

[JimD]

Originally posted by pcford:
Well, I'm sorry, and I'm not being contrary....it sure looks like a dog leg to me. (hump or kink) After section is flat. Frame seems out of fair.

If you don't fix it you will see it every time you look at the boat...

Maybe run a batten along the sheer to check fairness?

Get more opinions and decide for yourself...but I think there is a problem.Looks to me like the panel was wrapped a little too tightly around around the frames, creating the flat spots and hard bends at the point of contact with the frames (dog legs). If they were temporary moulds then the panel would be allowed to bend fairly once the hull is lifted off. But if the panels are presently bent over the permanent frames then there is possibly a permanent problem as the panels are not long enough to bend fairly. Shaving the frames narrower to make the hull a little narrower toward the stern might be necessary. Another reason to have either a sheer clamp on the frames to guide the panel in a fair bend or have a stringer of some sort such as the gunwale attatched to the outside of the panel before it is bent over the frames and attatched. :(

[ 12-29-2005, 02:11 AM: Message edited by: JimD ]

[ishmael]

Frame seems out of fair.

Yup. As said, when you remove it it will probably wiggle enough to be fair again. The chine looks fair, and that's good.

This is the reason to run battens and look at fairness before you plank. Given this boats materials and lack of topside shape it will work out, most of it anyway. If it were planked with solid wood it might be a slightly different conundrum, but even that would likely wiggle fair, since it's a flat panel. A Swampscot's shape would be a different matter.

I don't think glassing it as it sits is going to have much impact, though it's tempting to get it off the spalls and onto horses, just to see what happens.

Good luck, and keep remembering the boat's working heritage. They weren't meant to be "perfect."

[ 12-29-2005, 06:38 AM: Message edited by: ishmael ]

[Mike Vogdes]

If those are permanant frames, then you should be able to locate a fore and aft center line on your building form, then pull a string line taunt so you can check for center at all your stations along the sheer.

[ishmael]

No need to measure, it's clearly out of fair. Have faith brother, and keep going! smile.gif

[Vince Hoffmann]

It appears to me that the angle of the transom is too shallow when compared to the much steeper angle of the former which is causing the side to not form correctly. The side pieces are being forced to twist as they are being bent around toward the stem causing the flat spot in front of the transom.

I realized this while building my boat and shaped the bottom panels to create a proper curvature, eliminating the 'dog leg' appearance.

[Billy Bones]

I don't think we're in a position to critique your building form with only two awkwardly angled photos. String, ruler and lofting should be your guides at this point. If you want to test our approach, you can temporarily remove that spall after temporarily clamping a outwale-sized piece of lumber along the sheer. I think you'll be pleasantly surprised.

Just out of curiosity, does the same thing occur on the opposite side?

[ishmael]

The first frame foward of the transom is clearly too wide at the gunnel. Or the other's too narrow.

No biggie. I think it will wiggle and fair quite accepably.

Take it as a lesson. It's part of the reason a simple skiff is such a good teaching tool; they are forgiving when we forget to run fairing battens over the frames.

Here in Maine there is a thing called skiff boards. White Pine, Pinus Strobus, wide enough for a single plank to make a side. Rare today. Someone who wanted a skiff would take a transom and a stem and fashion a midship section out of scrap. Run it all together, nail on a bottom, maybe some chines, definately a wale and a thwart, and you've got yourself a boat. All by guess and by gawd. Throw in centuries of experience.

So relax, and keep going! smile.gif

[stevenj]

thanks for the input.

As to whether or not the last frame or all of them are fair, my battan tells me they're fair. Though the way the panel's laid across the last frame it may not look it. I think the panel is not stiff enough, or perhaps on too tight as JimD mentioned.

I'm gonna glass it as is, take it off the spalls, install the gunwale, and hope it takes the proper shape. If it doesn't, well, my first boat will be lumpy... Things can always be better, but they could be worse too.

BillyB, the other side is nearly identical. I did the other side first, and noticed the lump. I figured I didn't get it fair enough, though the battan did lay flat across the frames. I took an extra hard look at the fairing on the other second side before doing the panel, shown above. So when that one came out lumpy too, I wanted to hear from experienced builders.

Many thanks.

stevenj

[Boatmik]

faired the frames with a batten. I think the problem is the ply isn't ridgid enough to hold a smooth shape between the frames. It's doing this only between the transom and 2 frames up. If the framing has been faired with the batten the framing IS fair.

If you look carefully the ply bends sharply over the frame and runs straight to the transom. If you clamp a batten to the sheer edge that sharp curve, instead of being at one point - will be distributed forward to the next frame and aft to the transom.

This can only happen because the frame has been already checked by the batten.

The best thing to do would have been to put a temporary batten along the sheer to make it fair while the side panel was being bonded to the transom and the bottom panel.

That would have made it entirely fair.
________________________________________

The situation now in my opinion is not a big problem - when the sheer is properly supported by gunwales etc it will go to a fair curve.

However because all the panels have been bonded with the hard spot in there the angles they have been bonded at are subtly wrong. So even when the sheer clamp/gunwale etc goes on the side panel it won't be able to fair the side panel where it contacts the other panels - thus leaving a very slight hollow in the side panel within a couple of inches of both the transom and the side panel.

With a fair sheerline and the boat upright I don't think it will be very noticeably unless you are looking for it.

If it stil bugs you would be able to fill it and use a torture board to fair - my feeling is the hollow will be less than 1/4 inch - but I really think that you will be the only one who notices it.

Michael Storer
Michael Storer Boat Design (http://www.ozemail.com.au/~storerm)

[JimD]

If you look carefully the ply bends sharply over the frame and runs straight to the transom. If you clamp a batten to the sheer edge that sharp curve, instead of being at one point - will be distributed forward to the next frame and aft to the transom. At the risk of beating the dead horse I still disagree. You're still talking about a straight line (the plywood) being a shorter distance between points A and B (the frames and transom)than the curved line we are after. Using a batten of some sort to properly distribute the bend around the frame to form a fair curve won't work effectively without narrowing the frame because otherwise there isn't enough plywood to make the curve. But I repeat myself. I'll move on now. Good luck.