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bhackford
02-02-2010, 08:33 PM
I am building a Nina - stitch and glue and reading the designers website, they recommend fiberglass scrafs. I am all for it because it saves time and is easier than 8 to 1 cut scrafs but will there be lumps or weakness? Thanks

Hwyl
02-02-2010, 08:46 PM
In general I'd do what the plans say and because it's a 22' boat, the fiberglass scarphs are going to save you a scarph on each side.

JimD
02-02-2010, 09:33 PM
Do you mean a butt joint with fiberglass cloth on either side as in this illustration?

http://www.boatbuilding-links.de/Jim-Michalak/gif/plyjnt5.gif

If so, you will definitely have an ugly lump of fiberglass that will be very noticable. If you want to glass a butt joint then sand a trough or router a rabet in the plywood for the cloth to sit in so that the cloth is flush with the plywood as in this second illustration:

http://www.boatbuilding-links.de/Jim-Michalak/gif/plyjnt6.gif

Read the full article here: http://images.google.ca/imgres?imgurl=http://www.boatbuilding-links.de/Jim-Michalak/gif/plyjnt5.gif&imgrefurl=http://www.boatbuilding-links.de/Jim-Michalak/joining-plywood-sheets.html&usg=__aJSIO4QU6esVbIGhiou9FCsO-nk=&h=242&w=476&sz=3&hl=en&start=42&itbs=1&tbnid=NCe5OsDCL4hjVM:&tbnh=66&tbnw=129&prev=/images%3Fq%3Dfiberglass%2Bscarf%2Bplywood%26gbv%3D 2%26ndsp%3D20%26hl%3Den%26sa%3DN%26start%3D40

john welsford
02-02-2010, 09:41 PM
I am building a Nina - stitch and glue and reading the designers website, they recommend fiberglass scrafs. I am all for it because it saves time and is easier than 8 to 1 cut scrafs but will there be lumps or weakness? Thanks

In general its only the people who have not done slope scarfs who think they are hard work or time consuming, those who have done a few know that they are in fact easy and the best way to do it.

A fiberglass scarf without lumps of unfairness is much harder to achieve.

John Welsford

BBSebens
02-02-2010, 09:46 PM
Indeed, if the plan tells you one way, then you can rest easy that it ought to be sufficient.

never-the-less, there's room for artistic license. Its your boat, and the plans are only plans, and plans change. I agree, you will find scarfs not difficult to do. Not as easy as the glass, but i dare say the end result will be better.

spirit
02-02-2010, 10:11 PM
Bolger liked butt blocks.
They are easy to do.
And strong.

JimD
02-02-2010, 10:16 PM
Bolger liked butt blocks.
They are easy to do.
And strong.

I like butt blocks, too. Aesthetically there are some boats where they will just look wrong and ruin the appearance, but in many cases the block won't appear out of place at all. Just part of the construction and often can be strategically placed where they are not seen at all.

wizbang 13
02-02-2010, 10:30 PM
If you have a planer and a good disc sander then scarph it. If you don't have the right tools there are still a thousand ways to do it right.

BobW
02-03-2010, 12:02 AM
Scarphs used to intimidate me...

8 months ago I was convinced I couldn't make a scarph join...

Of course, I hadn't actually tried to make one, but I knew I couldn't...

But I tried... didn't work the first time...

Built a jig for the router and it worked great...

Bought in to trying to cut scarphs with a plane... didn't work so well...

But - in my own words to my sons when they were young and playing sports - practice, practice, practice...

I have scarphed the gunwales, inwales and gunwale caps for my Goat Island Skiff - and the sun keeps coming up in the east...

The hull panels and bottom of the Goat are butt strapped together... This did not intimidate me. I just figured this is what the designer called for. the butt straps worked and now I've got a Goat Island Skiff...

http://farm5.static.flickr.com/4020/4327023692_112f8f8d67_o.jpg

Follow the plans... trust in the designer... get that boat built!

Bob

David G
02-03-2010, 12:14 AM
Lets just get the terminology straight. If we're talking about the kind of joint that Jim D so beautifully illustrates in post #3... it's not any kind of scarph. It's a modified butt joint. I've most often heard it referred to as a Payson Butt, after Dynamite Payson, who is said to be the originator.

I've used this joint several times now, and have done a bit of informal testing. Seems plenty strong to me. However, a scarph will bend to a fairer curve, and will look better under a bright finish. It takes as much practice to learn to make a clean Payson Butt as it takes to learn to make scarph joints. The one clear advantage the PB has is if you absolutely don't have the length of material for a scarph. It's also a bit quicker... but only a bit.

Typhoon
02-03-2010, 03:38 AM
Anyone ever scarfed plywood with a router by cutting each laminate back say a few inches then stepping to the next laminate? Sort of like a step pattern viewed in section.
Would be dead easy to jig up and would yield a nice finish on the face laminates if done well.
I agree with a butt strap joint though, I've seen those fibreglass joins, they're as ugly raw as they are finished....

Regards, Andrew.

Brian Palmer
02-03-2010, 08:10 AM
I never did a plywood scarf until I built a glued lapstrake canoe. I used a sharp block plane according to Tom Hill's instructions (Ultralight Boat Building) and they came out great. No trouble at all really, and the are nearly invisible, even under varnish.

Learn to scarf. You will be happier in the long run.

Brian

Bill Huson
02-03-2010, 10:40 AM
Anyone ever scarfed plywood with a router by cutting each laminate back say a few inches then stepping to the next laminate? Sort of like a step pattern viewed in section.
Would be dead easy to jig up and would yield a nice finish on the face laminates if done well.
I agree with a butt strap joint though, I've seen those fibreglass joins, they're as ugly raw as they are finished....

Regards, Andrew.

Yes. B&B Yachts has a CNC router gizmo to cut out parts for their kit boats. I visited their shop and watched the CNC gizmo in action. Cool! It cut a scarf in a couple of the parts by stepping back the router bit and jacking it up a mm or sso. Result - a fine and barely noticeable stepped scarf joint, and the very tip was left about a 1/2 mm thick to notch into the stepped edge on the second piece. This reduced the possibility of the thin scarf edge being damaged in shipment, and served as an accurate guide for the builder of the kit to get the panels lined up.

Of course this was a CNC gizmo, so all one does is design the program, put on ear muffs, mash the go button, and stand around sipping coffee while the machine whizzes over the plywood panel. Since I guesstimated the steps are 0.5mm x 4mm I think it would be a bugger-bear to do that by hand.

andrewe
02-03-2010, 02:35 PM
I used scarphs on my Oughtred boat ( length of material was not an issue) max width about 1ft. Very easy, just stacked up the lengths on the bench and planed them down. First with a power planer (carefully!) then with a long hand plane. Matter of minutes. I previously made a router jig, but the B&D 600wt was so weak kneed that it was a wast of time. An 1800wt with a fly cutter would do it, if there were enough joints.
A

Those 'epoxy' scarphs look pretty horrible ( no offence to Dynamite) apart from the cost of the epoxy, they can only be justified if the length of planks is compromised by the overlap.

Candyfloss
02-03-2010, 02:50 PM
Butt blocks are simplest & perfectly adequate. 8/1 slope scarfs are best & easiest with simple hand tools. Anything else, including Payson butts, is way more work than it's worth.