Saturday, January 17, 2015
Installing Chines Part 2 Starting the Sheers
After doing the initial bending using the new steaming tool I continued cutting additional notches in the frames for the chine. The notches at the front of the boat (frames 4, 5 and 6) are cut at at a much steeper angle than those that are aft of frame 4. This makes sense when you consider the amount of bend that is necessary to get the chine down to the stem.
But determining that angle requires several trail runs on installation of the chine unless your some kind of a math wiz (Im not!). Additionally, cutting these notches is harder than the others because they are "U shaped notches rather than "L" shaped like the aft notches. Theres insufficient room to get the saw in there to cut the bottom cut. I could have rigged up a routing jig, but this seemed like a lot of work for little payback and with three completely different notches, would have probably required three separate jigs.
What I end up doing and which turned out to be fairly accurate was to mark the extents of the cuts and then saw vertically down to them, making multiple parallel slices about 3/32 inch apart. This includes making a vertical cut at the very ends of the bottom edge.
Then using a chisel and hammer, I broke these smaller sections out. All that remained was to use a file and smooth out the cut. One additional thing I did was to cut the notches shallow (less than needed). This allowed me to judge my cut angles as well as the actual depth needed for the chine. You have to keep in mind that there must be sufficient remaining material on both the chine and the frames for fairing away. Each notch is different so this is more of a matter of trial and error than anything else. As you get closer to the final depth and angle you make smaller cuts.
The chine had to be steamed more to get get it to lay into the notches in frames 5 and 6. If you look closely, you can see the way there is material on the frames that will need to be faired away to match the front curvature of the hull.
Once I had the chine into these notches, I needed to tackle the final bend down to the stem. This was very difficult to accomplish because the remaining piece of lumber was short which provided inadequate leverage for bending. Even with lengthy steaming, it was difficult to force the part down to the stem. I did manage, but I knew that there was going to be a lot of strain on that part.
After making this bend I also realized that I needed to increase the angle on the notch in frame 6. Also required was cutting the end of the chine to match up flat against the stem.I made an initial cut using the stem as a rough guide. The cut needed to be parallel to the stem horizontally and vertically. Because of the clamps I needed to hold the part down, I couldnt make the cut with the chine in its bent position. I had to mark the cuts and do them after releasing the part.
You can see in the previous picture that I didnt get this quite right. Also notice the way I was trying to clamp on the angled chine. This was also not satisfactory and required a small piece of wood screwed into the chine to give the clamps something to hold on to.
Fortunately, I have the Glen L Builders Forum to go to and as is almost always the case, someone had a better idea on clamping. In retrospect, it seems obvious, but I failed to see it until it was pointed out to me. One of my concerns when trying to clamp the chine down is that I didnt accidentally force frame 6 out of position. Its pretty solidly glued in, but I didnt want to take a chance.
The clamping solution was to lay a 2 by 4 board on the back side of the frame so that it was roughly parallel to the chine. The board stretched between the stem and frame 6. Then using two clamps and alternately screwing them down. I was able to clamp the chine up to the stem quite easily.
The previous picture shows the chine angle at the stem already cut correctly, but it wasnt that way initially. The same builder who gave me the advice on clamping also suggested I use a thin piece of would laid up against the stem. It needed to be slightly thicker than the widest part of the gap in the angled cut. Then using the wood as a guide, I sawed down through the chine using my Japanese razor saw. After that the cut looked like it does in the previous photo. (Thanks Skip!)
Of course, cutting away this material at the front meant that the chine had to be shifted forward. The angled cut needs to be the correct distance back from the the forward edge of the stem so that when the stem is faired to an angle, the angle will run directly into the chine. Imagine a line running parallel to the outer edge of the chine out past the forward edge of the stem. If two lines are imagined, one for each chine, they should meet over the center of the stem forward edge.
Fortunately, there is an easier way to determine this. A simply tool cut from a piece of scrap wood can be set on the stem and indicate if its far enough forward or backwards to be in the proper position. The following photo shows this tool and how its used. The small leg on the left lines up with the centerline of the stem when the chine is in the correct position.
As mentioned, the chine has to be slid forward a small amount to get the chine angle up against the stem. This is why I left the part long at the aft end of the boat. Once I had the chine / stem angle correct, I could go back and trim the aft end of the chine to the final length.
All that remained was to glue the chine into position. I had to do a small amount of final tweaking of notches before doing this. That was quickly accomplished. The chine is held in place with epoxy and 2 inch #10 bronze screws. These screws need to be recessed below the surface so that they dont interfere with fairing later on.
The process of attaching the stem was straightforward. Apply some unthickened epoxy to all mating surfaces, then thickened epoxy, then clamp into position, drill and recess the screw holes, and add the screws. I didnt do all this at once, but rather attached the aft three frames first, then the middle two frames, and then finally the two bow frames. At each step, the chine was left to spring to its natural position except where it was being attached. This made it easier to get the chine into the correct position at these attachments. I also delayed adding the epoxy until just before I needed to attach the chine to a particular frame. I supported the loose end of the chine (at the bow) on a roller stand.
The first chine is now glued into position and will be ready for fairing when I get to that point.
This has considerably stiffened the structure. I am beginning to have a real appreciation for the overall strength of the design. Once all these longitudinal pieces are in place and the skins applied, the hull should be quite strong.
While waiting for the chines to steam, I also started working on the sheer battens. These are the longitudinals that run the length of the boat at the top edge of the frames (closest to the floor right now). The challenge I face with these parts is that they also need a severe bend at the bow end. To get them into the initial bend they need to extend quite a bit out to the side. You can see that in the next photos.
However, there is insufficient room on the opposite side of the boat to perform this bend. So what I will be doing is doing a pre-bend of all the sheer pieces (two per side) on thee same side (where I have more room to work with). Final fitting can then be performed on the opposite side of the boat for those pieces.
Pre-bending was accomplished using steam and some clamps. As with the chine, I had difficulty with clamping he forward end of the sheer to the stem and breasthook. I have a temporary arrangement that works okay for steaming and bending, but I will need a different arrangement for gluing so that the entire gluing surface is clamped into place. I have a plan for this clamping arrangement which I will detail in a future posting.
In order to bend the sheer I first needed to add the sheer notches at each frame. This is not an easy task for me because it requires lying on my back and making the cuts. I have a problem of nausea when lying on my back so the cutting was a slow process. But eventually they were cut. Like the chine notches, those at the bow end are cut at steeper angles to accommodate the bend.
Once the sheer was adequately steamed (about 50 minutes because the parts are much thinner), I quickly bent and clamped it into position. Here are some pictures of the process.
The sheers are made from two laminated pieces of lumber on each side of the boat. So all four pieces will need to be bent. Also, because the lumber is not long enough, I will have to add additional length by using a scarf joint like I used for the chines and keel. I plan to do that after the pre-bending is done. I did it this way so that I wouldnt have to try and accommodate extra lumber length during the bending process.
So far I only have one sheer pre-bent as I have been concentrating on the chines. I still have one more chine to install so that will be accomplished first. When I make the next posting, hopefully I can write about the completion of the chines and more work on the sheers.
Until next time, take care.
Update 9/14/2014:
I have been fairing the hull for nearly four months and one area that has given me a lot of trouble has been the forward bends of the chine. In hindsight, the steaming of the chines allowed the wood to bend in a different manner than would have been best for the boats shape. Ideally, the chines should have been installed at the front first and then bent around to the transom. Using gradual motion and maybe some heat, I could have gotten a better more fair curve in this area forward of frame 4. Lack of space in my garage prevented me from doing that and I had therefore chosen the steam method and worked my way forward.
Because of that, the chines were too low and a bit too flat. This required me to add shims to the exterior of the chines in this area in order to get a more fair curve.
Anyone contemplating this build or a similar boat should allow themselves the room to accomplish the chine installation as it is outlined in "Boatbuilding With Plywood" by Glenn Witt in order to avoid the problems I ran into. In the end, I was able to correct the mistakes and the boat will be okay.
But determining that angle requires several trail runs on installation of the chine unless your some kind of a math wiz (Im not!). Additionally, cutting these notches is harder than the others because they are "U shaped notches rather than "L" shaped like the aft notches. Theres insufficient room to get the saw in there to cut the bottom cut. I could have rigged up a routing jig, but this seemed like a lot of work for little payback and with three completely different notches, would have probably required three separate jigs.
What I end up doing and which turned out to be fairly accurate was to mark the extents of the cuts and then saw vertically down to them, making multiple parallel slices about 3/32 inch apart. This includes making a vertical cut at the very ends of the bottom edge.
Then using a chisel and hammer, I broke these smaller sections out. All that remained was to use a file and smooth out the cut. One additional thing I did was to cut the notches shallow (less than needed). This allowed me to judge my cut angles as well as the actual depth needed for the chine. You have to keep in mind that there must be sufficient remaining material on both the chine and the frames for fairing away. Each notch is different so this is more of a matter of trial and error than anything else. As you get closer to the final depth and angle you make smaller cuts.
The chine had to be steamed more to get get it to lay into the notches in frames 5 and 6. If you look closely, you can see the way there is material on the frames that will need to be faired away to match the front curvature of the hull.
Once I had the chine into these notches, I needed to tackle the final bend down to the stem. This was very difficult to accomplish because the remaining piece of lumber was short which provided inadequate leverage for bending. Even with lengthy steaming, it was difficult to force the part down to the stem. I did manage, but I knew that there was going to be a lot of strain on that part.
After making this bend I also realized that I needed to increase the angle on the notch in frame 6. Also required was cutting the end of the chine to match up flat against the stem.I made an initial cut using the stem as a rough guide. The cut needed to be parallel to the stem horizontally and vertically. Because of the clamps I needed to hold the part down, I couldnt make the cut with the chine in its bent position. I had to mark the cuts and do them after releasing the part.
You can see in the previous picture that I didnt get this quite right. Also notice the way I was trying to clamp on the angled chine. This was also not satisfactory and required a small piece of wood screwed into the chine to give the clamps something to hold on to.
Fortunately, I have the Glen L Builders Forum to go to and as is almost always the case, someone had a better idea on clamping. In retrospect, it seems obvious, but I failed to see it until it was pointed out to me. One of my concerns when trying to clamp the chine down is that I didnt accidentally force frame 6 out of position. Its pretty solidly glued in, but I didnt want to take a chance.
The clamping solution was to lay a 2 by 4 board on the back side of the frame so that it was roughly parallel to the chine. The board stretched between the stem and frame 6. Then using two clamps and alternately screwing them down. I was able to clamp the chine up to the stem quite easily.
The previous picture shows the chine angle at the stem already cut correctly, but it wasnt that way initially. The same builder who gave me the advice on clamping also suggested I use a thin piece of would laid up against the stem. It needed to be slightly thicker than the widest part of the gap in the angled cut. Then using the wood as a guide, I sawed down through the chine using my Japanese razor saw. After that the cut looked like it does in the previous photo. (Thanks Skip!)
Of course, cutting away this material at the front meant that the chine had to be shifted forward. The angled cut needs to be the correct distance back from the the forward edge of the stem so that when the stem is faired to an angle, the angle will run directly into the chine. Imagine a line running parallel to the outer edge of the chine out past the forward edge of the stem. If two lines are imagined, one for each chine, they should meet over the center of the stem forward edge.
Fortunately, there is an easier way to determine this. A simply tool cut from a piece of scrap wood can be set on the stem and indicate if its far enough forward or backwards to be in the proper position. The following photo shows this tool and how its used. The small leg on the left lines up with the centerline of the stem when the chine is in the correct position.
As mentioned, the chine has to be slid forward a small amount to get the chine angle up against the stem. This is why I left the part long at the aft end of the boat. Once I had the chine / stem angle correct, I could go back and trim the aft end of the chine to the final length.
All that remained was to glue the chine into position. I had to do a small amount of final tweaking of notches before doing this. That was quickly accomplished. The chine is held in place with epoxy and 2 inch #10 bronze screws. These screws need to be recessed below the surface so that they dont interfere with fairing later on.
The process of attaching the stem was straightforward. Apply some unthickened epoxy to all mating surfaces, then thickened epoxy, then clamp into position, drill and recess the screw holes, and add the screws. I didnt do all this at once, but rather attached the aft three frames first, then the middle two frames, and then finally the two bow frames. At each step, the chine was left to spring to its natural position except where it was being attached. This made it easier to get the chine into the correct position at these attachments. I also delayed adding the epoxy until just before I needed to attach the chine to a particular frame. I supported the loose end of the chine (at the bow) on a roller stand.
The first chine is now glued into position and will be ready for fairing when I get to that point.
This has considerably stiffened the structure. I am beginning to have a real appreciation for the overall strength of the design. Once all these longitudinal pieces are in place and the skins applied, the hull should be quite strong.
While waiting for the chines to steam, I also started working on the sheer battens. These are the longitudinals that run the length of the boat at the top edge of the frames (closest to the floor right now). The challenge I face with these parts is that they also need a severe bend at the bow end. To get them into the initial bend they need to extend quite a bit out to the side. You can see that in the next photos.
However, there is insufficient room on the opposite side of the boat to perform this bend. So what I will be doing is doing a pre-bend of all the sheer pieces (two per side) on thee same side (where I have more room to work with). Final fitting can then be performed on the opposite side of the boat for those pieces.
Pre-bending was accomplished using steam and some clamps. As with the chine, I had difficulty with clamping he forward end of the sheer to the stem and breasthook. I have a temporary arrangement that works okay for steaming and bending, but I will need a different arrangement for gluing so that the entire gluing surface is clamped into place. I have a plan for this clamping arrangement which I will detail in a future posting.
In order to bend the sheer I first needed to add the sheer notches at each frame. This is not an easy task for me because it requires lying on my back and making the cuts. I have a problem of nausea when lying on my back so the cutting was a slow process. But eventually they were cut. Like the chine notches, those at the bow end are cut at steeper angles to accommodate the bend.
Once the sheer was adequately steamed (about 50 minutes because the parts are much thinner), I quickly bent and clamped it into position. Here are some pictures of the process.
The sheers are made from two laminated pieces of lumber on each side of the boat. So all four pieces will need to be bent. Also, because the lumber is not long enough, I will have to add additional length by using a scarf joint like I used for the chines and keel. I plan to do that after the pre-bending is done. I did it this way so that I wouldnt have to try and accommodate extra lumber length during the bending process.
So far I only have one sheer pre-bent as I have been concentrating on the chines. I still have one more chine to install so that will be accomplished first. When I make the next posting, hopefully I can write about the completion of the chines and more work on the sheers.
Until next time, take care.
Update 9/14/2014:
I have been fairing the hull for nearly four months and one area that has given me a lot of trouble has been the forward bends of the chine. In hindsight, the steaming of the chines allowed the wood to bend in a different manner than would have been best for the boats shape. Ideally, the chines should have been installed at the front first and then bent around to the transom. Using gradual motion and maybe some heat, I could have gotten a better more fair curve in this area forward of frame 4. Lack of space in my garage prevented me from doing that and I had therefore chosen the steam method and worked my way forward.
Because of that, the chines were too low and a bit too flat. This required me to add shims to the exterior of the chines in this area in order to get a more fair curve.
Anyone contemplating this build or a similar boat should allow themselves the room to accomplish the chine installation as it is outlined in "Boatbuilding With Plywood" by Glenn Witt in order to avoid the problems I ran into. In the end, I was able to correct the mistakes and the boat will be okay.
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