mechanics of stem lamination

[Dennis Rioux]

I am getting ready to laminate the outer stem of the Penobscot 14 that I am building. I searched the archives and could not find an answer to what I am sure is a very basic procedure but nevertheless has me befuddled. The outer stem uses the inner stem as a mold. Here is my question: Do you just do this in one fell swoop? That is, make up a sure-to-be-slippery multilayer sandwich and clamp it on? Starting at the point of greatest curvature and working out symmetrically on either side? That ought to be something. I read an older post by Al Meyer in which he steamed and fitted his laminations and left them for a time to develop a shape memory. Perhaps that is the way to go? (Running out of time in my unheated garage, though, and I really wanted to get some planking done before the snow flies.) For what it is worth, I have been playing with the wood and have decided on eight 5/32" laminations of white oak should work for me. Anyway, thank you in advance for any advice you care to share.
Dennis

[rstclair]

I am also building a Penobscot 14. What I did was follow the instructions in the book and video as far as size and such. I was plenty worried, like you, as to what to expect when I tried to clamp those slick pieces to the stem. I dry fit and clamped the laminate pieces to the stem. I left the laminates plenty long and wide. After 2 or 3 days (CRS) I unclamped and the laminates had prety much taken the shape of the stem. This made it relatively easy for a beginner like me to apply epoxy and clamp the laminates to the stem.

I left the pieces longer and wider than necessary. When I had it dry fitted I made whitness marks so I could trim the length and put it back together the same way. I still have to trim the width, but that won't be a problem. My laminates were 3/16" thick.

Hope this helps.
Bob

[DougWilde]

Dry fit your pieces to the outer stem. While clamped in place, at the end where you want to start during the final glue-up, drill a hole through all the layers and into the inner stem to accept a dowel. Now pull the dowel and all the pieces off. Slather on your favorite goo, insert the dowel and install in place. Finish the clamping. Later you can trim whatever sticks proud. If you wish, you can drill for other dowels along the length of the stem. This technique worked well for me when I had to laminate a 15' rubrail. I used glue dowels from my local Lowe's, driven between each frame and a screw at (into) each frame. Final glue-up was as stress-free as it could be.

Doug Wilde

[Kevin L.]

I did the laminations on mine, fresh off the table saw, in one fell swoop. Although it can be fairly messy, it isn't difficult. I'd try a dry run (with all of them at once) to be sure that your laminations will make the bend without excessive force - if not, go a little thinner on each and use more. I think mine was made up of 8-9 laminations of SYP. Be sure to use a lot of plastic wrap to keep from gluing the laminations to the inner stem, wet out each strip with unthickened epoxy before spreading a little thickened epoxy, and scrounge up as many clamps as you can. If using white oak, you might want to take other precautions such as rough sand with 60 grit before glue-up. BTW, I experienced no "spring back" with the unbraced stem which sat for about 6 months before I finally attached it to the boat.

[almeyer]

I made my stem facing from ash, and when I tried to bend the laminates cold, I immediately snapped two strips. Always make some spares! Since this wouldn't work, I soaked all the laminates in the shower for about a half hour and then dry-fit them (no epoxy), clamped up, to get a memory. I think I let mine set for about a week before applying the goop, but this long probably wasn't necessary. A couple of days or even overnight might work. Once you put the epoxy on, I would recommend letting it cure for about a week. As Kevin suggested, make sure you have plenty of plastic around the inner stem so you don't glue the two together. Once the epoxy was cured and I removed the facing from the stem, I screwed some braces from one end of the stem to the other to make sure it held it's shape. If the epoxy is fully cured, that shouldn't be a problem, but it was cheap insurance.
An alternate approach which may work if you're in a real hurry to start planking and you still have the plywood template you used when you made the inner stem. Use that template to make a mold following the outside edge of the inner stem. The mold should be at least as thick as the stem facing laminates, and can be screwed down to the workbench or some other place out of the way. Wrap the mold with plastic, then epoxy the laminates against the mold, leaving you free to work on the boat. I haven't tried this method, but it seems like it ought to work.
Al

[Bob Quick]

Dennis

[Bob Quick]

Dennis
I thought about it for a long time before I did mine. You should be able to find posts by Al and myself with pictures. If you can't let us know.
I started at the upper end (closest to the floor when building up side down) of the inner stem and clamped about every 6 to 8 inches until I had it down. I, by chance, had a milk crate that I rested the ends on for the first clamp and I had help, my daughter, in holding and clamping. We dry fit everything first and then did a fast glue up. The forces in the 10 fir laminations that I used was surprising but it really when pretty easy, just lots of pressure. I did have a little trouble with the ends spreading apart as I reached the far end but a small clamp across the layup fixed that. You'll need lots of clamps, I have a number of 8 in C clamps and used them. I liked Al's scrap lumber clamps as well. Bob St Clair's stem looked really good when I saw it as well.

Getting ready to run to church. I try to post a few pictures if you like when we get home.

Bob

[Dennis Rioux]

Thank you all for sharing your methods and ideas. One big sandwich it is. I think I will do a dry fit when I get the laminations resawn and let it sit for a couple days to get some shape memory in there. I can tent the bow section and heat it if it gets too cold. Meanwhile I can tackle the keel bevel starting at the other end of the boat.

Bob -- I have all the photos you and Al have posted in the past right here on the laptop. A folder for each of you. smile.gif I refer to them to see if I am on the correct trajectory -- for example, I was mighty interested to see how you both dealt with the twist on the lowest stringer as it passses into the transom. That was a puzzler for a while since there was no way mine were going to twist enough to make it square to the planking line-land-facet-whatever-it-is-called thingy (I love boatbuilding -- it is a good excuse to learn a whole bunch of new words). Anyway, thank you for sharing them -- you don't need to go to the bother of reposting. My biggest question was about the all-at-once aspect of the glue up. Thanks again.

Dennis