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The plans are not exactly clear about how to finish off the last 6 inches of the keel located between Stations #13 and #14.  While the plans specify the 5+5/8” and 4+5/8”  horizontal offsets for the top and bottom corners of the back edge of the plank, the plans do nothing to locate the corners vertically.  And what are we to make of the magic floating 3” measurement?

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In trying to replicate the drawing around station #13, it is reasonable to assume that the angles between the top and bottom edges of the keel and the reference line near the stern should  be constant.  The top edge of the keel rises 11/16” from Station #11 to #12, and another 11/16” to reach Station #13.  That looks pretty constant to me, and would give the boat a flat run at the stern, which is ideal for hull speed.  It also straightens the last 30” of the top of the keel, which facilitates measuring that 112° between the transom and the keel.  So the top corner of the keel should be (5+5/8”)/(12”)*(11/16”) ~= 5/16” higher than it was at Station #13, or 3+11/16” above the reference line.  For the bottom edge, if we continue the slope from Station #12 through #13 and onward for another 4+5/8”, we end up with the bottom corner (4+5/8”)/(12”)*(1+5/8”) ~= 11/16” higher, or 1-3/16” above the reference line.  Now our drawing would look like this ...

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Clearly something is amiss.  The angle from the top of the keel to the transom is now 115°, which is much larger than the 112° specified elsewhere in the plans, and the deck will not be long enough to fill the gap between the stem and the transom.  The angle of the run (top of the keel) with respect to our horizontal reference line is arctan( (11/16”)/(12”) ) = 3.28°.  If we subtract 3.28° from 112°, our target angle from the reference line to the transom at the rear of the keel becomes 108.72°.

So what could that magic floating 3” be referencing?  How about the vertical distance between the top and bottom corners of the keel?  The horizontal distance between the corners is 5+5/8” – 4+5/8” = 1”.  A vertical rise of 3” with that 1” horizontal run specifies an angle of arctan(3”/1”) = 108.4° , which is very close to our target of 108.7°.  Keeping the 4+5/8” horizontal dimension of the rear corner constant and sliding the corner downwards to 3/16” to achieve that 3” vertical separation, we arrive at this configuration …

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But now we have a rather rude kink in the bottom of the keel.  Looking carefully at the offsets and doing a little math, we discover that the angles at the bottom of the keel from Station #6 rearward are 1.9°, 3.9°, 5.4°, 5.4°, 6°, 6°, 7.7°, and 1.6°.  Clearly the  7.7° angle at Station #13 is too steep.  If we lower that point from  1/2” above the reference line down to 1/8”, the angles become 1.9°, 3.9°, 5.4°, 5.4°, 6°, 6°, 6°, and 6.2°.  Much better.  Also, we can adjust the bottom corner by a 1/16” inch down and forward to get the transom angle closer to a whole degree, which will make the measuring a little easier and more accurate.  So it appears that the plans should have been drawn thusly … 

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But now the plans are a little cluttered.  The two important details are that the top corner be located 5+5/8” rearward of Station #13, and that the transom rise upwards from the reference line at 109°.  So we can delete all of the extraneous information from the plans and redraw them thusly ...

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… and then add the explanation that the batten marking the bottom of the keel should run long to complete the curve of the bottom and locate the corner where it meets the 109° of the transom.

We can summarize these alterations to the plans thusly.

• At Station #13, the bottom edge should be lowered from 1/2” above the reference line to 1/8” above the reference line.
  
• The top rear corner of the keel is located 5+5/8” beyond Station #13, and 3+11/16” above the reference line.
  
• The bottom rear corner of the keel is located about 4+9/16” beyond Station #13, and about 5/8” above the reference line.
  
  
• The rear edge of the keel should be angled 109° from the reference line, should pass directly through the top corner, and pass within a nail’s diameter of the where the bottom corner is marked.
  

Any comments?

Cheers
Tom

This is all a bit academic. If you run a batten through all the known reference points, they should hit in a fair line. This assumes the plans are fair. If some points of reference aren't clear, skip them and move to the next one. If at the end of a line, like this situation, then let the batten run out fair, forming sweet line.

The batten should be the final point of reference for a cut line, not measurements on the plans. Assuming you've measured as correctly as possible, pencil line thickness, slight variations in pencil point placement, etc. will introduce some minor errors in the work (again assuming no error in the drawings or offsets). The batten finds these and sighting down it fixes any irregularities.

A human eye can see the difference of .003" and can be relied on for batten adjustments in the .010" range. This is as precise as most machine shops folks. Trust the eye. If the eye says it's a sweet, fair line, screw whatever the plans might say.

In other words, if you're hitting most of your reference points, but a few pull the batten out of fair, then discount them and move on.

That's the most sensible advice I've EVER HEARD.

Greetings Paul,

Well, that’s good information to know … NOW … after I struggled with the keel for several hours more than necessary.

Who keeps quoting … “Experience is what you get, right after you need it.” ?

But with regards to the plans, 3/8” is a lot to be unfair, and if the transom-to-keel angle is supposed to be 112°, then it should be marked as 109° from the reference line so that you get the angle correct before the saw bites into the wood. Since the plans do not specify the angle, the angle will be determined by the locations of the corners. Every 1/16” of error here bends the transom by 1.3°.  Every 1.3° changes the stem-to-transom length by 1/2”.

The plans as drawn leave the novice builder guessing, and he is ill-equipped to judge what is correct.

Cheers,
Tom

Which boat are you building Tom?

There's an old saying in boat building, "if it looks correct, it is correct".

Fair is fair, and your eye can find it, which is my only point. I understand the confusion over plans, reading them properly, comprehending what the designer intended, etc., can be frustrating.

With the exception of class racers or exact replicas, which may be required to fit within a very specific set of complicated measurements, pleasure boats generally don't have to.

If you transom is a couple of degrees off, but the lines are fair, seams tight and the wet stuff stays on the outside of the boat come launch day, other then yourself, who's to know or care?

In all my plans, I don't offer full size patterns. I do this partly because I don't have a 5' wide printer, but mostly because lofting up the lines of the boat full size, forces you the learn so much about the way a particular boat is shaped, it eliminates many of these "measurement" issues.

Until computer aided drafting came along, offsets and the lines that they were derived from, were hand picked. I've never seen a set off offsets (for a new design) that didn't have errors in them. In other words if you used each and every reference point, you'd end up with a set of lines that were almost fair, but had spots where clearly something wasn't quite right.

This is why builders use battens. A batten doesn't care how many reference points or measurements you have marked. It will produce whatever you tell it to, fair or humpy. The builder's eye is the ultimate "judge" in where these lines will actually fall and how they'll look.

For you transom to keel angle, draw up the transom angle on a scrap piece of plywood. Draw up the bottom planking, maybe a reference line for the LWL or bulkhead, etc. then "pick up" the correct angle, directly from your drawing. Another way is to just "work from the work". This means use a straight edge on the transom and project the line down onto the keel and cut to that line. It doesn't matter what the actual angle in degrees is, so long as it is a straight line.

If it were me, I'd take a piece of cheap thin plywood and make a quick template. The template would be a tracing of the transom angle, and the top of the keel (or the bottom of the bottom planking). Using this template, you can place it on the keel stock and "tick off" the angle. If you want to measure it to find out what it turned out to be, cool, but if it's 110.5 degrees, it really isn't as important as it looking right and being in "column" with the rake of the transom.

Greetings Craig,

I am building a Weekender as time permits.  The problem is making the time.  There always seems to be some other honey-do project, life event, the weather, work, etc that gets in the way.  Last year I “wasted” a few hundred hours training (rode 4,400 miles) for some bicycle racing I do.  But the season’s campaign was successful, and I have some bling to show for the effort, so I can’t complain too much.

I figure I am about half done.  I have assembled a keel, hull bottom, transom, lazarette, cabin bulkhead, front bulkhead, deck, and mastbox, and the bits, all from okume, mohagany, and some southern yellow pine.  The interior of the forepeak has been painted and I am ready to attach the hull sides … as soon as it warms up enough to start gluing again.

Here is a progress photo from last summer.

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It will be interesting to see which boat gets finished first, my weekender, or the Saralee II.  Are the plans done yet?  Or is your naval architect still trying to fit a beer magazine into the binnacle like a giant PEZ dispensor?



Cheers,
Tom

You should be done first as I will not start II until we get back to Fla.  Yesterday another job popped up so there is still hope.  The beer magazine is a great idea although the tanker version has promise as well.  Be careful withthe plans for your boat Tom.  At this stage they are more guide than exact.  Fair lines and good looks are more importand the the exact angle.  These boats squat so bad the a file optimization of the exit doesn't matter anyway.  Read the drawings for what you are going to do then thak the measurement off you existing structure.  Your eye will tell you whats right.  happy building.  Spring is in the air and moving east.