Scarfing Question

[Joe Dupere]

The Shellback Dinghy plans use 3 4x8 sheets of
1/4" plywood for the planks, to be scarfed into 2 sheets of 4x12. I've scarfed molding around the house, and read about scarfing plywood about a jillion times so I know I can do it.

Here's my question. Lofting the lines onto the scarfed plywood will put all of the scarfs in the same section of the hull. Is this a problem? I've
read in planking a hull you need to alternate the location of the scarfs. The Shellback is lapstrake so my guess is that it's okay. I just wanted to ask around before I started cutting planks.

Joe

[cs]

Joe I would try to alternate the scarf locations. Maybe lay one plank out from one side and the next one out from the other side.

Chad

[Dutch.Rub]

...... if you do your scarf joints correctly they will be just as strong if not more so than the surrounding plywood- if you dont believe me do a small test piece and load it to failure- see what busts first........

[NormMessinger]

I believe what Dutch says is correct and try to do as Chad does. Stagger the scarfs if you can but don't obsess about it.

[whb]

In some plans they suggest that you do a rough layup and cutout and then scarf then final cutout. The reason being that you can reduce the amount of waste.

It would also allow you to vary the locations.

Howard

[Bruce Hooke]

Hmmm...it seems like I'm missing something here.

Lofting usually means drawing the lines and construction details of the boat full size. The actual plank shapes are usually picked up off the actually boat in progress. So, I don't see how the way you loft the boat would impact the way you cut the planks out of the scrafed plywood.

Or, do the Shellback plans include patterns for each plank and when you talk about "lofting" are you talking about transfering these patterns to the plywood? If this is the case, why can't you simply, say, alternate the orientation of the planks as you cut them out of the plywood so that the scarfs alternate between being closer to the bow and closer to the stern?

[Dan McCosh]

The issue with the scarfs is not the strength, but the possiblity that they will generate a visible hard point. Keeping them in line could be a way of minimizing the effect on this design. Just a thought.

[Joe Dupere]

Originally posted by Bruce Hooke:
Lofting usually means drawing the lines and construction details of the boat full size...
Lofting was probably the wrong term.


Or, do the Shellback plans include patterns for each plank and when you talk about "lofting" are you talking about transfering these patterns to the plywood? Yes, what I meant was transferring the patterns.


If this is the case, why can't you simply, say, alternate the orientation of the planks as you cut them out of the plywood so that the scarfs alternate between being closer to the bow and closer to the stern?The way Joel White has his plans drawn, if you transfer the pattern to the plywood according to the plans, you get the most efficient use of your scarfed plywood. I had thought about alternating as you suggested, but I don't know what that'll do to the rest of the layout.

But it doesn't sound like it'll be a problem structurally so I won't sweat it.

Thanks for all the help everyone.
Joe

[gary porter]

Joe, pretty much everyone above is correct. Since the scarf on the Shellback is four feet in there is no hard bend and such and if you do a half decent job on the scarf it will be strong and not noticeable. Bruce , you guessed it, Joel White provided the layout of the planks and there are only three so not a problem. They are trimed down to fit as you put them on. One consideration is if you plan to leave the inside bright. If so, pay attention to the grain pattern on the ply so it flows nicely or as close as you can get it. If your going to paint inside and out then there is really no consideration, it will all work just fine and for this boat don't worry about the location of the scarfs.
Gary

[Jack Heinlen]

HI Joe, nice to hear from you.

I'd only add that when you go to glue the scarfs don't overweight/clamp them. Epoxy likes to stay in the joint, not be pressed out. Just enough pressure to bring the pieces firmly together is what is called for. Starved joints from over clamping is the most common cause of joint failure with epoxy.

With a scarf in ply sheets this usually isn't as much a problem as when you have screw clamps in play, but...

As to staggering joints, I'd do whatever White lays out.

P.S. You've probably read this already, but Tom Hill's Ultralight Boatbuilding is a good source.

[ 01-08-2004, 05:12 PM: Message edited by: Jack Heinlen ]

[JimConlin]

If you're going to scarph up two 4x12 panels, will you be sandwiching them together and cutting pairs of planks at the same time? If so, just end-for-end one of the panels first. That way, the pairs of planks you cut will have their scarphs in different places. Makes staggering them on the boat easier.

Jim

[Bruce Hooke]

If nothing else, I think the shortest answer is:

If Joel White says to do it a certain way then I think you can safely do it that way! :D :D

[kng]

Hi I have built the shellback and did it like Joe is saying, nothing has happen to the scarfs, and I have to confess that I have put some epoxy to make the "bad scarf" be flat, remember it was my first project, and the scarfs make a little zagg, but I think they finally look good and work better.
an other thing I don´t understand or may be I remember bad is that the bottom scarf is in the way of mast step..... I did it that way an everything is ok.... wonderful boat !! good luck
if you want to see mine here is the link:
shellback (http://www25.brinkster.com/kng/shellback.htm)

mirror site (http://fire.prohosting.com/kng2/shellback.htm)

sorry for the banners, the page doesn´t have them and suddenly they decide to put them... I will try to fix the problem...

saludos !!
cheers !
Emiliano

[Joe Dupere]

Originally posted by JimConlin:
If you're going to scarph up two 4x12 panels, will you be sandwiching them together and cutting pairs of planks at the same time? If so, just end-for-end one of the panels first. That way, the pairs of planks you cut will have their scarphs in different places. Makes staggering them on the boat easier.

JimIn the words of the great Homer Simpson, "DOH!!"
I hadn't considered that as an option, but it makes sense for ease of cutting out the planks. Based on all of this, I'm not going to worry about it.

Thanks, again.