View Full Version : Shellback building problems
07-29-2001, 01:25 PM
I am currently building a shellback dinghy. I've assembled the building jig (from scratch)and cut out the bottom. When I dry fitted the bottom, my reference marks did not line up at station #1 and #1/2. I checked all my measurement and they appear to be correct. I even rebuilt the ladder with new lumber and it is still off by the same 1/2 inch. Has anyone else experienced the same problem? Are the plans correct? Can I move the stations up so they match the reference marks or will this throw everything else off with the remainder of the project?
07-29-2001, 07:32 PM
I've built the Pooduck skiff (very similar to Shellback, a bit larger); I had minor alignment problems as well. One was putting a mold on the wrong side of the line. The others I ignored. As long as you don't have a problem which will result in an unfail line, or in scanting material some place, I suggest you don't agonize. You're not building a piano; few boats are built with complete and utter perfection - you might as well get used to it now.
You've checked everything over; check it again, and, if you're using a level, make sure it is accurate. If all this seems to pan out, then trust your eye and go for it.
07-29-2001, 08:23 PM
Are the molds on the correct side of the station lines? 1/2 inch sounds like that sort of error if the molds are 12" thick.
07-29-2001, 09:43 PM
I was so fustrated, I even had my wife check it. The only reason I ask versus forging ahead is that I have seen dimension discrepencies between the book and the plans. I think I will have my dog look it over in the morning. she's really smart.
07-29-2001, 11:10 PM
Not having seen the plans for the shellback dingy, I can only offer the following observations/suggestions:
1. Unless the table of offsets is labeled as being "corrected" you should assume that minor corrections will be required (that is on the order of mabey 1/4 inch). To one degree or another, this is true of most offsets.
2. If you LOFTED the design correctly (you did loft it didn't you?) then you have no worries. Just forge ahead and finish the boat. Like Ross said, you are building a boat, not a piano. The worst that can happen is that the boat might require some minor tweaking . . . . and you would be far from the first to have to tweak!
3. Whatever you do, remember that fair is fair!!!!! In addition to checking the fairness of the plan lines during lofting, you should be checking for fairness of the molds during setup. Ultimately, this is what really counts. If it isn't fair then it needs fixing regardless of what the plans say. Remember, you are the builder not the guy who drew the plans.
4. Frequently a person gets too close to the problem and can stare right at a mistake and not see it. Only cure for this is to take a break and come back fresh (or have your better half look at it).
5. Remember that a properly setup shop has a groaning chair . . . . . (actually I have several).
[This message has been edited by PugetSound (edited 07-29-2001).]
07-29-2001, 11:32 PM
Originally posted by JodyAdamonis:
I think I will have my dog look it over in the morning. she's really smart.
My neighbor had a pet cockatoo, which keeled over in the cage. He took it to the vet, the vet took a brief look at the bird and said, "It's dead."
The neighbor said he'd like a second opinion, so the vet called in his pet siamese. The cat took a look, pawed the bird once and said, "Yep. Bird's dead, allright."
The neighbor said "I just can't accept the opinion of a stupid feline," so the vet calle his labrador retriever. The dog walked over, sniffed around the bird carefully, licked it's wings and tailfeathers, sat down and said "That, sirs, is one dead bird."
The neighbor finally gave up and asked for the bill. The vet handed him an invoice for $328.00. The neighbor screamed in surprise and asked why the bill was so high. Vet said, "$8.00 for my opinion, $320.00 for the cat scan and lab report."
Your dog should be able to pinpoint the problem fairly readily. Good luck!
07-30-2001, 09:28 AM
Is the transom on the mold yet? If so, check the alignment and the placement of the cleat. A small error in the cleat placement can translate to big problems later on. On the other hand, 1/2" off on the stations is standard operating procedure.
07-30-2001, 01:49 PM
This is one of those problems that fifteen guys can kibbitz over and still not be helpful because we can't really see what is going on. All of the above is good advice. Let me add one more perhaps obvious observation. Are your measurements accurate? Sounds like a Homer Simpson kind of thing, but most problems are.
First, loft the boat carefully making sure your lines are fair. Keep working with it until they are. It is always cheaper and easier to erase pencil lines than to cut wood. Once the lofting is satisfactory, THROW AWAY YOUR TAPE MEASURE! Take your measurements off the lofting with "tick sticks" and make patterns wherever it seems useful.
Odd as it seems, you CAN easily be off using a tape measure. (Carpenters work to the nearest 1/4", cabinetmakers work to the nearest 1/16" and boatbuilders work to the nearest boat!) Say you have only six stations. To end up with a 1/2" error, you only have to have an error of something like 3/32" or so. That's pretty easy to do. If you keep repeating the error a station at a time, you end up 1/2" off. If, on the other hand, you take your measurements from the whole tape or, preferably, from your lofting, you will minimize the repetitive error. Sneaky thing, repetitive measurement errors, but they sure do add up quickly. Hope that may help a bit.
07-31-2001, 10:48 AM
Yah, repetitive measurements can bite you. We were placing rafter trusses on a garage and the guy measuring had measured each two feet separately from the previous one instead of from the gable end wall plate. Ended up having to move a bunch of trusses http://media5.hypernet.com/~dick/ubb/frown.gif
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