Wooden Boat Plans explained

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Looking at small a wooden boat, it's hard to see how it could all be so difficult!

This is what I thought back in 2001. "Find a plan and cut out some wood"...what a disaster! I'll explain why all the fuss. 

All wooden boat plans until now have been about 2 or 3 sheets only. One sheet showing top and side view and the other a table of offsets. This has been done this way since at least the turn of the century.

The views show specific lines such as sheer, chine, buttocks, water lines and sometimes deck crown. To interpret the table of offsets you need to know where these lines are on any boat, and what the designer means by "half breadths" and "WL6" etc. It is daunting to say the least. Each designer has his own quirks and shortcuts for information. All of the measurements given refer to the outside of the vessel.

A well educated guess tells me that the final plans for all wooden boats is only ever done after the first boat is finished, hence the outer dimensions.

The Problems:

Going on the offsets provided by the original designer of any great boat plan, you would assume they were correct. Very wrong! Out of the hundreds of plans I have personally lofted to full size I can perhaps quote 2 or 3 that were correct. This is either a careless mistake, a wrong refernce line use or something just as silly. The problem now is you have cut and formed your frames or cut out notches for the sheer etc and there is no way to know which frame is out! Is it this one or the one after, or was it the last one? Why would the chine or sheer or deck crown suddenly curve in or out contrary to the next or previous frame?

Serious trouble now, which frame or frames is wrong? All you have are the offsets and thats it! There are ways aroung these disasters but I'll go into that in another guide..

Real Plans for everybody:

In my mind the only way past this was full size plans and 1 part etc per page. Obviously CAD systems were not around when these plans were put together so there was no way of proving offsets unless someone built a boat from them and MADE THE CORRECTIONS. This was not the case somehow and the same plans and offsets are still about.

Until a frame or station is drawn up and placed in a 3D assay (in CAD) it still looks fine and fair. The problem arises when the spacings quoted are used to insert the framesand you have boat lines that look like they've had too much sun. Generally it's the same problem, one or more frames cannot possible be the size quoted within the offsets. The deck crown is low, the sheer is wide or the chine is high, one two or even 3 frames flawed, only visible when they are aligned according to the plan. The builder cannot see this until he starts aligning his frames according the sheer heights from a base line, by then it's a little late for corrections.

This is whrere CAD plans can show the problem and correct it using 3 dimensional curves that run through sheer points and chines showing every problem clearly. Any dubius points are left out allowning the curve to run through the true points only, the offending frame is then rectified, one point at a time until it also runs through the curve. This saves everyone the pain and hearache not to mention timber and money.

Other than wrong offsets, lofting these old plans in 3D first also gives an insight into the safety aspect of the vessel. Will gussets be required at chine points etc? Will the specified stringers still be ample for todays high horsepowered engines?


Other wooden boat plans:

You can still buy the old style plans from various sellers. You can spot these easily as they are generally 2 or 3 sheets of information only. This is reflected in the low selling price. Whilst these may be accurate, you must loft the plans yourself and know how to decipher any offsets provided. I have tried this and would never do it again. There is too much room for error, there is no way to check any finished part and the designs generally don't belong to the seller so you're on you're own.

If your seroius about building a wooden boat, get serious boat plans.


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