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Permalink Reply by Dave Z on March 9, 2011 at 6:05pm

not necessarily straight on a boat built on a strong back.  dependent on the sheer line on top and amount of rocker + flare, you could very well end up with curved lines.  I think most framed boats are at best an approximation and ease of building end up with straight panels.

 

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Permalink Reply by Eric Loudenslager on March 9, 2011 at 7:01pm

If you can get a copy of Roger Fletcher's book you will see that the Hindman boats had a straight chine. The Briggs Canyon dories and the Rogue dory have a curve (arc) cut into the chine. This will lower the amount of rocker, and permit more flare in the side panel relative to the rocker. However this will give you a "lower" side mid-ships and provide an opportunity for water to come over the sheer.

Check out the montana-riverboats.com forum. There have been extensive discussion and a few pics about reducing rocker by changing the chine.

Finally, in Roger's book he shows that the Rapid Robert had a couple inches cut out of chine at the very end of the boat....increasing the rocker.

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Permalink Reply by Lawrence E. Long on March 9, 2011 at 7:24pm

Jordan:  Follow the plan/directions.  Some boats have curved panels and some are straight cuts.  The planks on the Peapod (5 on a side) taht I am building don't have a straight line and none of them are the same  on the same side of the boat.

Good Luck

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Permalink Reply by Randy Dersham on March 9, 2011 at 7:49pm

Dave, what do you mean that framed boats are an approximation?  I'd like to understand.

 

There is a very complex dynamic between the curve created by the width of the frames and, when rolled out flat, a side that has a straight line along the chine or shear.  Early McKenzie Double Enders had the sides pre-cut from the panel and the straight line was easy to cut and worked well.  Early plywood was 14ft long and the continuous rocker made by the straight line cut was effective and attractive. 

 

As the boat moved to 16ft plywood the straight line built with the same method (with a fair chine line-meaning a smooth transition along the chine) meant that the rocker was increased.  That's not all bad but it was more rocker than was necessary.  Woodie Hindman reduced this rocker by increasing the width of frame 7 and 4.  By widening those two frames three things happened.  The boat had just a little less rocker, a little more displacement, and a slight flat spot with a straighter chine at the boat's center.  This is one of the few times that a design change resulted in win/win.  The compromise to the design change was the lower rocker but the 16ft piece of plywood didn't need all of the rocker it formed when using the straight line cut.  The panel still has a straight line when rolled out flat even though the shape of the chine has more curve on the ends and less curve in the center of the boat. 

 

You can also reduce the rocker of the boat by adding flair. Bob Pritchett's Rogue River Special is the most extreme at using all three techniques. 

 

Jordan, If you have your strong back built so the chine line is curved then go with the curve. You have already established the line for the chine and the shear by building on a strong back.  Now that those lines are established by the frames that are in place, fit the side panel to the frames and let the panel go where it goes.  You aren't in any trouble.  The worst is it might take a little extra plywood if you are outside the dimensions of getting both sides out of one sheet.  You do not HAVE to use extra plywood if you are willing to give up some freeboard and trim down your frames just a little. 

 

As boats got bigger rocker was also reduced by creating a smooth curve to the side panels at the chine and shear.  Take a look in Roger's book of the Colorado Dory.  You'll see a dishing out of the chine line and a convex curve on the shear line.  The dishing out helped tame the rocker and the convex curve on the shear kept the freeboard height at the oarlocks. Without the convex curve at the shear the freeboard would have been reduced as Eric mentions. Obviously the Colorado Dory also has a straight line along the chine hull, so Jerry Briggs was using both techniques for his boat; a little bit of dished out chine shape in the panel and widened frames in front of and behind the center of the boat. 

 

 

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Permalink Reply by Jordan Davis on March 9, 2011 at 8:40pm

This makes a lot of sense Randy.  As far as free board goes...  I can see that by using a straight line on the shear I will loose a few inches off of the rear most frames, losing less and less and I move towards the front of the boat.  Is there a good rule of thumb for free board on a 17'(ish) boat?

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Permalink Reply by Roger Fletcher on March 9, 2011 at 8:40pm

I’ll come at your question a little differently. Straight  top lines and chine lines are fairly customary for McKenzies. The straight-lined side panel configuration has as much to do with the efficient use of material as anything else. In a standard 16’ drift boat (as measured around the sheer or gunwale) with a 48-inch bottom two side panels can be extracted from one 4 x 16’ sheet of ¼” plywood. These features have, in part, given rise to what I call free form construction. This construction eliminated the need for a strong-back; the frames are built and fitted to the station lines of the boat, which serves to give the boat its shapes and rocker. Any one of these boats may be built using a strongback but ( and this is a big BUT) the frames must be canted or angled (generally off vertical) in the strongback  in order to conform to the station lines on the side panel. If they are not canted then the side panel will not conform to the frames. This is not a big deal so long as the side panel hasn't been pre-cut and station lines marked. You appear to have set the frames and then outlines the side panel. Right on! The only problem I see is you may not be able to extract two side panels from one 4 x sheet -- if that was your plan.

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Permalink Reply by Jordan Davis on March 9, 2011 at 9:27pm

Okay!  Thank you all for your help.  The biggest worry I had was the chine line being curved.  Because I traced the chine line VERY close to the edge of the ply I have decided not to cut that line and trim it to the chine log after the side has been applied.  That way the curvature of the line wont be in question.

 

This brings me to the next issue though.  The gentleman who designed this boat is a great engineer but I think not completely familiar with McKenzies.  Some of the frame heights do not work (they get longer then shorter then longer again!!!).  If you were to follow the sheer line created by the frame tops you would have an ugly wavy line.  I have seen this in other pictures of his boats finished from novice builders to master carpenters, the wavy sheer line is a design flaw.

I had planned on trimming the frames to the sheer line anyways, so snapping a chalk line from transom to stem should work.  My question then becomes, how much free board is necessary at say, frame 2, 5, and 8?  If I use a straight line for the sheer line when cutting out the panel I will lose 3 1/2" on frame 2.  2 1/8 inches on frame 5 and 1 1/2 inches at frame 8.  Essentially I will have 26 3/4" of free board at frame 2, 31" at frame 5, and 34 3/4" at frame 8.  Will this be sufficient?

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Permalink Reply by Dave Z on March 10, 2011 at 5:32am

Randy-  What i said was a lazy response about "approximation."  I think you and Roger stated what I was thinking.  Ease of construction, effective panel use and balance of rocker and flare.  As I designed my flyfisher skiff, I wanted a flat spot in th emiddle bottom, but doing so would have creatted a curved cut on the side.  Didn't want that so I got close enough or "approximately."  What I wanted with an easy to cut side panel.  haha.  call me lazy!

 

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Permalink Reply by Don Wakefield on March 10, 2011 at 6:21pm

Hi Jordan --  When I built my frames, I made a line on the side frames at exactly where I wanted the top cuts to be made, according to the plans, which I generated.  I noticed that some of boat plans in Rogers book (if not all) the sides in fact were straight when the plywood was layed out flat.  Neither the chine nor sheer line on mine ended up straight at all.  I built my rocker amount into the strong back. 

Then came the problem of how to lay out the sides, and cut them so they would adequately make a fair curve and not be too short at the chine or sheer.  I went and bought some fairly heavy butcher paper and wrapped the frames.  I marked the chines and sheer points on the paper.  This gave me an idea of how big to lay out and cut the plywood. I did the same thing for the bottom panels.  Then I just wrapped, the 3/8"  oversize side panels onto the frames.  Like so: Then made the same marks on to the plywood for a rough cut.  When I made the top cut on the sides, I made sure they were cut on the original line as per plan.  Hope that helps. Shoot the arrow, then draw the target.  I found that when I was trying to force the plywood to go somewhere, I'd lose my fairness, and it would stress the plywood at the same time.  

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