View Full Version : Shellback Stem Goof
After laminating the stem on the Shellback Dinghy I'm building with 14 strips of 1/8" fir, I realize I've made this thing too thick. Apparently, the thickness of some of my strips weren't exactly 1/8", and I've just learned that little errors add up to big mistakes. The stem is 2" wide instead of 1-3/4". I can't see any way of cutting the thing back to it's proper size (sanding or with a sabre saw), and I'm wondering if it is going to matter anyway. It seems I would need to cut the outside of the curve, not the inside (which I could probably do with an electric planer). I could use some advice at this point. Starting over would be a bit demoralizing.
09-21-2000, 08:29 PM
If I'm seeing this properly, and you have a good lamination, I should think cutting a bit off the front of the stem wouldn't do any harm. Are you concerned that the outer layer will no longer be a neat continuous piece? It still remains to shape the stem to it's final shape, yes? I've not had a look at the Shellbacks plans. Is it a two piece, stem and apron arrangement?
From what I'm seeing, don't waste a good lamination because it's too big. All mistakes should be so bad! Almost anything can be fixed with the proper way of looking at it.
Planer or saber saw would work. Lay out a clear mark and cut proud then work down by hand. Careful with the saber saw as I suspect in that thick a lamination it might want to wander down glue lines.
And, reading Norm's post, I agree. Leaving it be, unless it causes some other problem that I can't imagine, would be fine too.
[This message has been edited by ishmael (edited 09-21-2000).]
09-21-2000, 08:32 PM
Demoralizing, indeed. When you say too wide do you mean from side to side. Hmmm. I don't think so since it would be the molded (fore and aft) thickness that would be controled by the thickness of the individual strips. So the boat will be 1/4" longer than expected. Big deal, no?
Surely there will be a response from someone who has built a Shellback but if not, proceed.
Dub, I laminated the stem for my Haven 121/2 and intentionally made the thickness more that what the plans called for, to allow for spring back and fairing. I would suggest that you lay a template of the stem profile on the laminations, mark it and fair it to the line with a sharp plane. It worked for me.
09-22-2000, 08:54 AM
I presume the excess is on the outside of the correct stem curve, since you probably bent it over the outside of a male mold. IMHO, it doesn't make a d*mn bit of difference. You cut the ends of the planks to fit the stem anyway, and 1/4" won't make any significant difference in the bevel angles. The stem will be slightly stronger, and the boat will go faster because of the longer waterline ;) I suppose you could cut it down on a bandsaw, or maybe a belt sander, but why bother?
09-22-2000, 09:22 AM
Yeah, leave it be.
09-22-2000, 10:46 AM
I've read the Shellback building manual, but I don't have the actual plans. As I recall, they give you the actual panel lines to expand, correct? If this is so, and you leave the stem lamination the way it is, the panels will come up a bit short. I would leave an extra 1/2" of material on the forward end of each panel and trim it back after it is in place.
09-22-2000, 11:16 AM
It's so difficult sometimes to see what is going on, but if the stem was laminated over a mold of the inside of the stem then shouldn't it make no difference in the plank length? The stem will just be a bit prouder (1/4 inch) than drawn? Shouldn't make any difference as far as I can see. Draw apex, bearding and rabbet lines using the inside as reference and when you go to shape it you can always take the quarter extra off if it bothers you.
My take, and maybe I aint seeing something.
Cedar Hill Boatworks
09-22-2000, 11:56 AM
Leave it alone, build the boat.
09-22-2000, 11:57 AM
I am building the Pooduck which is the 12' 10" version of the Shellback. Shouldn't make any difference as long as you cut the planks long and trim them off to fit which you should do anyway.
09-22-2000, 12:00 PM
Also, remember it is a 2 piece stem and if you take some off the inside piece the outside piece will most likely not fit very well to it.
09-22-2000, 12:54 PM
Oh good lord, just when I think I've got it soused Don comes along and tells us it's a two part stem.
When you go to shape the stem, cut it to the proper size. Use whatever tools you're comfortable with, and go slow till you get the hang if that's an issue. Making the inner stem the proper size just simplifies everything else. No big deal. Like I said, too much stock is rarely a real problem. Best of luck.
09-22-2000, 05:08 PM
As I recall, the way the instructions say to make the inner and outer pieces of a Shellback stem is to laminate them both at the same time on the same form, with a piece of waxed paper between so you can get 'em apart. Much easier than building two molds.
If this is the way "Dub" did it, they'll fit perfectly, and taking stock off the inner one to fit the plans will just mess things up, like DonB said. The boat will still be 1/4" longer, but somehow I think we can all live with that.
[This message has been edited by Keith Wilson (edited 09-22-2000).]
09-22-2000, 05:37 PM
Okay, that does it, I'm gonna shut my silly yap and let those who know the design figure it out. Best of luck over what I suspect is a problem generating alot of smoke, but not any serious fire.
09-22-2000, 10:16 PM
Yup. As my ole pappy used to say, "Son," he'd say, "Son, if ya cut it to short ya can always splice it but if you cut it to long there ain't nothin' ya can do about it."
Tough luck Dub.
Yes, I did laminate the inner and outer stem together, and my great fear was that if I trimmed down the inner stem, the outer stem wouldn't fit. Well, I can assure you that if *I* trimmed down the inner stem, the outer stem definitely wouldn't fit.
I was hoping someone would tell me I could cut the grove the stem sits in of mold 1/2 or that 2x4 fork a little deeper and have the 1/4" excess *inside* the boat, but no one suggested that. Would that work?
Well, I sure you all know this is going to drive me nuts. And what will I say to the chief measurer when it comes time to race this thing?
09-24-2000, 11:03 AM
Okay, here goes:
Yes of course you can put the extra 1/4" inside the stem. No problem.
In the end, er when all is built, you won't know the difference. Seems like I recall using the stem for the 15' MacGregor sailing canoe by Iain Oughtred when I built the 17' version. Didn't realize it til I reviewed the layout prior to starting the second canoe. This aint rocket science. Dont let the quest for perfection paralyze you.
Can the chief measurer really measure within plus or minus a quarter of an inch?
[This message has been edited by NormMessinger (edited 09-24-2000).]
01-21-2002, 09:22 AM
On the topic of Shellback stems and frames, in the book and the plans, it uses the phrase "finished siding to be 7/8"." The stem is to be built up in strips 1/8" x 1-3/4".
I'm confused as to what this term means.
[This message has been edited by MikeH (edited 01-21-2002).]
Siding is the dimension along the side of the boat; if you hold the edge of your ruler along the joint between lapstrake planks,pointing along the run of the plank at the ends, you're measuring the siding dimension.
Molding is the dimension perpendicular to siding; it's the dimension into the boat, if you hold the end of your ruler at the plank and point the other end at the center of the boat, that's the molding.
At the stem and stern, molding is still pointing into the boat, and siding is still pointing along the planks, although both have "swung" 90 degrees.
I don't know of a boaty term for the third direction of dimension, although I'll wager that there is one; in some ways "girth" does this.
01-22-2002, 07:15 AM
Ok. That helps. Thanks.
But, it leads to another question that's specific to the plans/book for the Shellback. On the Shellback, the midship frame and stem are built up from 1/8" strips. For the stem, it says 1/8 x 1-3/4 - finished siding to be 7/8" (that's what the book says, the plans say finished siding to be 1-3/8"(?)). For the frame, it uses 1/8 x 1-1/8 - finished siding to be 7/8".
Besides the obvious discrepancy in the finished siding value for the stem between the book and the plans, I'm curious why they call out material sizes that don't match the finished sizes. My suspicion is that the lamination is to be planed to a uniform width or siding to take care of differences introduced by the lamination process. Sound reasonable or does anyone know, for sure?
If that's the case, how have those of you who have gone through this before gotten the laminations down to their specified siding dimensions?
01-22-2002, 08:15 AM
Your assumption is correct, as you have already experienced the laminations do tend to slide side ways during glue up. The easiest way to get the laminations down to finished dimensions is to joint them and then run them through planer, not having those tools available, if you can get one side flat and straight, you can cut the laminations on a table saw with great care. Otherwise, it will need to be done with a hand plane or electric plane. The stem size can be fixed by making a pattern off the plans and plane it to size.
Its a great little boat, enjoy the process.
01-22-2002, 11:44 AM
More good info. Thanks. I'm really glad I ran into this resource. If you can't have a more experienced person looking over your shoulder, this seems like the next best thing.
As I had mentioned before, I'm in the early stages of building a Shellback and am confused about the outer stem. I've scoured the plans and Eric Dow's book and can't find the details I think I need.
It looks like the inner stem is to be 1-3/4" thick (molding?). No problem. But, how thick is the outer stem that's formed over it in step 12 of the book?
[This message has been edited by MikeH (edited 01-22-2002).]
01-22-2002, 02:06 PM
The outer stem is 1/2" x 1 3/4", temporarily screw the outer stem to the stem while you are working it to its final thickness. The outer stem is applied after the boat has been planked. It will then be faired from a scribed line on the front of the outer stem back to planking, the scribed line is determined by the width of the flat you will need for the brass strip. I think 1/2" should do it. But that is down the road at this point.
01-23-2002, 12:13 PM
Dub, You should not have a problem with your stem being too thick. When you laminate the thing thats what you want. Take your pattern from the drawings on the page with all the forms etc. and cut it down to match that. You can use a bandsaw if you have it or sabersaw or a rasp or anything. Plane the thickness down to the 7/8" first then transfer your pattern. The outer stem will fit because you will bend it into place to fit. No problem. When you cut down the stem to match your pattern , line the inside edge of the stem with the inside edge of the pattern and cut the outside edge to match. It will all work out.......gary
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