Jon Richer Posted February 1, 2014 Report Share Posted February 1, 2014 Hello out there- I'm building a Ravenswood with some students in my school. All was/is going fine... today we lashed the bow and I notice when I stand back of the stern that there seems to be a slight crook in the bow direction. I can't overstate how many times I checked frame location and double-checked when the kids left... all's good. Any suggestions? Thanks- Jon Quote Link to comment Share on other sites More sharing options...
Kudzu Posted February 1, 2014 Report Share Posted February 1, 2014 Define slight. That is sort of like saying a boat is stable or a boat is fast. It depends on your perspective. Here are some thoughts: If your slight and my slight are the same I wouldn't worry too much. No boat is ever perfect but some are close. If it is under the water then it could affect the handling. If it is up in the air, then it is just cosmetic. Sterns act as rudders and you want that as straight as possible! My initial reaction is fix it. You will not get a second chance and it is a good lesson for the kids about not cutting corners. But it all comes down to what you define as slight. Quote Link to comment Share on other sites More sharing options...
Jon Richer Posted February 1, 2014 Author Report Share Posted February 1, 2014 I'm a little bit at a loss as to how I might approach the fix. Any suggestions, such as where to check for out of alignment, or how to pull the bow assembly together without it pulling one way or the other, would be appreciated. I'll snap some good shots on Monday for more advice. Thanks Jeff- this is, by far, the most meaningful project I've ever undertaken with students... so many lessons (for teacher as well). Jon Quote Link to comment Share on other sites More sharing options...
GaryMinor Posted February 1, 2014 Report Share Posted February 1, 2014 Jon, I would try to shift the position where the stringers attach to the bow assembly. That is, the frame and bow piece. You will have to undo the lashings that hold the stringers to the assembly. Straighten the stringers on one side, and add curve to stringers on the other side. This will shift the stringers, fore and aft, along the edge of the frame and the surface of the bow piece. Then lash them securely in place. To illustrate this, hold your arms extended straight in front of you, with palms together. As you move both arms together from left to right, the palms will shift from front to back. Disclaimer----- I am more of an engineer than I am a boat builder. This "seems to me" to be a workable idea. I lack the experience that the professionals like Jeff have to offer. Gary in Wake Forest Quote Link to comment Share on other sites More sharing options...
Jon Richer Posted February 1, 2014 Author Report Share Posted February 1, 2014 Thanks Gary, excellent explanation- I'll give it a shot. Jon Quote Link to comment Share on other sites More sharing options...
labrat Posted February 2, 2014 Report Share Posted February 2, 2014 One problem I had with my Curlew was that as soon as I took it off the strongback it corkscrewed slightly. Dimensions were OK but I think the cause was that the sheer stringers were not straight when cut and scarfed and I did not align them to counteract this. Hence one had a natural slight curve upward and the other went slightly downward. I decided to try a "brute force and ignorance" method of fixing it before going back to square 1. This involved forcing it into a position where it was twisted about 10 or 15 degrees past the straight position back the other way. It was left like this for several days and when released was very close to straight. Of course this may not be your particular problem but if the stringers are not matched in curvature before bending them to fit the frames then there could well be residual stresses that create an overal bend or twist. Quote Link to comment Share on other sites More sharing options...
Hirilonde Posted February 2, 2014 Report Share Posted February 2, 2014 I think Gary gave a good explanation of a straightening process. The only thing I will add is that if the stringers on opposite sides do not land exactly opposite each other now, (after straightening) you may want to rasp or sand the longer ones to match the shorter before relashing. The exact landing location on the bow and stern pieces of the stringers is less important than being symmetrical and straight. Quote Link to comment Share on other sites More sharing options...
northernMike Posted February 3, 2014 Report Share Posted February 3, 2014 Perhaps the stringers / keel / deckridge were not dry enough when cut, or have changed in moisture content since? The wrong kind of grain combined with hygrometric changes can make straight wood "aircraft grade" (propeller shaped) quickly, in my small experience. Quote Link to comment Share on other sites More sharing options...
Hirilonde Posted February 4, 2014 Report Share Posted February 4, 2014 I don't think moisture had much if anything to do with it. Drying wood shrinks in width and thickness, not length. And because the opposing stringers are bent in pairs of opposite forces they rarely change shape once lashed. I would bet that the bend in the hull occurred by forces on the frames and/or bow pieces and possible slipping of the frames on the brackets during lashing. In other words; human error. Quote Link to comment Share on other sites More sharing options...
Jon Richer Posted February 4, 2014 Author Report Share Posted February 4, 2014 Thanks for the thoughtful comments. Here's a JPEG of the bow assembly. Perhaps after a few days of not paying attention to it, it's not as severe as I thought. If anything, I'm considering detaching the gunwales, sanding/rasping down the one that's 2-3 cm longer than the other and reassembling. Quote Link to comment Share on other sites More sharing options...
Kudzu Posted February 4, 2014 Report Share Posted February 4, 2014 That does look very slight and FROM HERE, like it is not a problem. The area to be concerned with is down low. Make sure the keel and the ends all are in a straight line. I had one slip and the stern was cocked sideways when I skinned it (Fixed that design problem BTW) and the boat wanted to turn left all the time. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.