Spindrift 12 #1275 - side stringers - trim, bevels & tapers

[J. Cote]

My question is about the bevels & tapers on the side stringers (see attached plan page):

1) The top of the page calls for a 12" bevel at the forward end.  But it looks to me like a taper..... 12" long, material taken from the outboard surface of the stringer. If that is correct, how much do I taper to? (i.e. dimension between the red arrows I marked on the page)?

2) The 10 deg graduated to 17 deg bevel going forward makes sense, so the stringer's top surface is horizontal when it butterflies.  (material is taken from the outboard surface of the stringer).

3) The 36" taper at the forward end makes sense so the stringer can flex to fit the boat curve.  This looks like the material is taken from the inboard surface of the stringer.

 

If I am correct above, in what order should I do all this shaping?  I did the 10 deg. Next I was going to do the graduation to 17 deg.  Then the 12" taper (bevel). Then the 36" taper to zero at the front.

Is this OK?

[Alan Stewart]

Good questions. I can see how that is confusing. The top figure in the sheet you attached is intended more for boats built from plans. In this case the boat is folded up before the side stringer is installed and the stringer is glued in after the fact due to the difficulty in drawing the stringers location accurately on the flat panel. We now show a plan sheet with dimensions for the stringer referencing the edges of the side panel but still say to glue it in after folding. In the past it was marked on the inside of the hull with a straight edge laid across the longitudinal bulkheads after they were fitted. In this case the forward bulkhead is already in place so the side stringer is ended at the bulkhead for simplicity and to ease the bending of the stringer that inside forward portion is trimmed off as the figure shows. 

 

Now we have the kit version. For the boat built from the kit, the stringer location is drawn perfectly onto the hull panels so the stringer can be confidently glued to the side panel first which saves it having to be done in situ (a little easier of a job). In this case we bevel the stringer and then glue it down. Then it is tapered down to zero to ease bending the bow part and eliminate the potential of a hard spot. The stringer goes through the fwd bulkhead in this case. 

 

The extra 7 degrees of bevel as the stringer transitions forward is fairly minor and i think it's fine to just glue it down with just the 10 degree bevel and then simply tweak the top surface with a block plane after the boat is folded up. The difference in angle makes for only about 3/32" or so variation with gluing down the seat tops which is very easily filled up with thickened epoxy. 

 

On the smaller Spindrift 9,10 and 11 it's a lot easier to bend the side panels without the stringer in place and then install it afterward but on the 12 it's no problem. The last S11 kit we did a test fold up for a boat show with the stringer pre-glued and the bend was a bit too much for the piece just behind the forward bulkhead and it "kinked' on the inside right where we'd used a drywall screw to hold it while gluing forming an ugly hard spot on the outside of the hull. The screw hole clearly weakened the wood ever so slightly but that particular piece of wood chosen for that stringer wasn't too good either which highlights that the side stringers should have nice straight grain with no runout especially in the forward half of the boat.

[J. Cote]

Thank you Alan, confidence is restored. 

I am tempted to taper the stringer before gluing it down.  In fact, I thought maybe I should taper the outboard surface then glue it down.  When the boat is folded, the stresses would be closer to zero, and my 1/4" round over is preserved till it disappears to the taper ...... am I overthinking this?

[Alan Stewart]

Sure, you could do that if you wanted. Just be careful not to crack the wood with screws. You could also glue the stringer on with the side panels cambered/bowed inward a bit like a pre-bend. I've never tried that but can't see the harm so long as you did both side panels that way equally. Probably just makes gluing them on harder though. You could also just leave the forward ends of the side stringers loose like stop the glue say 4' back from the fwd end of the stringer and then after the boat is folded up, pull the stringer away a bit and squirt glue in there and glue the fwd section in post-folding.

 

Probably all of that is overthinking it because the bend on the S12 just isn't that severe not like the smaller Spindrifts. In the first 6 feet it's only 4 3/4" of camber. 

 

 

[J. Cote]

Excellent warning about the risk of cracking the wood with screws if it's tapered in advance.

I am overthinking it, and enjoying every minute of it.  Thanks Alan.