Wooden Boat People

By McKenzieDriftBoat.com

How much rocker?

So I'm about at the point of tracing and installing the floor. Sofar I have built tweaking the lines from my models. I'm wondering how much rocker I really want, and what is typical. Originally I thought 12" at the stem, 10" at the transom. My original models pretty much got me there, but when I dished the chine I lost a little. The transom bottom will have a curve so there isn't much worry of pushing the flat transom bottom edge in the water. Right now I am at about 9.25" at the transom before the curve cut, 11.5" at the stem. The lines look really good so I am hesitant to change too much, but I am wondering if I need a bit more rocker. My current boat does not have much rocker at all, but it plows into waves. I was hoping for a boat that would go up an over. Alot of the fishing boats I see around here don't have tons of rocker either? I have rowed heavily rockered mckenzies and they turn well, but do not track great. Looking for something in the middle. My design is a dished mckenzie 17x54. This boat will be built as a decked whitewater fory. As I said things look pretty good so I am hesitant to mess with much. I really like the bow profile and it looks right to my eye. Will 11.5" inches in the bow be enough? Do I need more rocker in the tail.? I could still dish the end of the panel slightly when I cut the curve in the transom bottom, I could also add a bit more angle to the transom cut similar to my older models. I could also narrow the transom slightly, or increase the flair....or do all three if I need to. I don't think I'm too far off, but wondering if anybody with more knowledge of mckenzie lines can point me in the direction of what's typical.

I'm liking what I have going, but just want to make sure I am no too far off of what has worked successfully in the past. I'm more likely to change the transom end than the bow, but I haven't ruled out wither yet. I need to decide soon though because its goons be time to mix more goo and get into the floor here soon.

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Permalink Reply by Randy Dersham on June 17, 2013 at 7:09am

Chris I think you have it right.

More than 12 inches is a lot, less than ten inches runs the risk of being pushed in Class III or above. Obviously the more flat the water you will be on the less rocker you need.

I think you will like the boat that you have designed a lot. The bottom of my 17x52 is very close to what you are describing. The one thing that you could do is to create a higher bottom of the transom by lifting the last 12-18 inches of the bottom by giving it a reverse dish. This will not affect your tracking because that part of the boat ( or most of that part of that boat) will be above the water line most of the time. The goal is to avoid having the bottom of the transome dip below the water line and allow the river to push the boat. When that happens it is a very uncomfortable feeling of the boat becoming hard to control.

The disadvantage of this approach is that you end up with an S-curve bottom which will add some complexity to attaching installing the chine log and attaching the chine. Don't do too much or you will need to be steam bending.

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Permalink Reply by Jayson Hayes on June 19, 2013 at 6:17am

Chris, I am going to have to agree with Randy, the 17x54 i just built has 14 1/2" at the bow and 11 at the transom and even fully loaded for multi day trips it is plenty (and then some) and if you plan on decking this boat you will be adding weight causing it to draft a little more, its all about water displacement.........ride high and displace as much water as possible

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Permalink Reply by lhedrick on June 22, 2013 at 3:57pm

Too much rocker will raise the floor up front and make it worse in waves not better. A flatter bottom will allow the water to lift the hull. This might seem opposite to what you would think but, it's the water under the front floor which helps lift the hull up to climb the really big wavers. I added a bit too much rocker on my last boat and it noses into the waves a bit too much before the water has a chance to get under the front floor and lift it but, it spins on a dime and is very good in low water when you must move all around rocks.

There is no correct answer to this one as you might like one behavior over another. A longer flatter bottom will track better but be slower to spin, you may like that you may not.

If the Mckenzie does not track as well as you want you could drop the bottom of the stem down 2 or 3 inches. Run a line from the new point back to the center of the side panel. The question will be how much will be the right amount for you.