Trimming a differential rocker canoe

What is “neutral” trim for a boat like an Argosy? With symmetric rocker, you can trim neutral by getting both ends the same depth in the water. The Argosy, however, is taller and more rockered in the bow than in the stern. Should the bow be a bit higher than the stern to match the hull’s profile?

good question
if I had the blue prints I would trim it by the waterline. ei: On a comp cruiser I helped build It had

1/2 inch rear rocker. I would put lines 4 inches up on the bow bow and 3 1/2 on the stern and trim them level initially. Then after seeing how it runs, races and turns I would shift my trim to how the boat wants to run.

I would assume the same would be true of the argosy. put marks to reflect the design and have some one tell you how you look. If it had (for examples sake ) 1 inch front rocker I would put tape 3 inches up from the bottom on the front and 4 inches on the stern. trim to those initially then shift your trim to find the sweet spot for you and the boat.

Have fun, trim is an issue the whole family can argue about and still be friends!

… sure is

If I was in a hull that was dedicated to either sitting or kneeling, I would start out trusting the designers seat location, and I would keep trusting it unless I really lost confidence in it over time. But in a hull like the Argosy that is not dedicated to sitting or kneeling, I guess I would go with what feels right to me, depending on posture and conditions at the time.

Can’t answer the question without also
knowing the shape of the hull. AND it will take some experience on the water.

My Millbrook Edsel is slightly fishform, and has some differential rocker, although it has so much rocker overall that the rocker differential is of less significance. When I got the boat, it seemed at first that the pedestal was too far back, and I moved it forward several inches. This made the boat look less bow light in photos taken by my wife.

But the boat didn’t seem to handle properly. I e-mailed the designer and asked him where he had his pedestal. He had it back where I had placed mine originally. I moved mine back, and the Edsel handled much better. On reflection, a fishform ww boat should look kind of bow up unless you are leaning way forward while paddling.

On a Swedeform boat, regardless of differential rocker, the risk is to place the solo seat too far back. You have to set your paddling position so that, with your normal paddling posture, the bow of the boat is properly engaged.

Maybe CE Wilson will spot the thread and offer comments.

Come back solotripping!
Solo-tripping had lots of great stuff on the ideal seat positioning for kneeling in an Argosy… and on trim, generally: as and when the forums are restored, I trust this most helpful content will still be there.

IIRC, one rule of thumb was that a cupful of water should puddle just infront of the paddler when the hull was at rest… and then slide under the paddler at normal cruising pace. Kinda makes sense… but I’d also be interested to see how that generalisation might need tweaking for different hull shapes.

Yes, a good question
In any boat.

Swift put trim tabs on my Winisk.

As others have suggested, I would start by trusting that the manufacturer has outfitted the boat with gunwales, thwarts and seats such that the empty boat floats, properly trimmed, on the design waterline. Then I would mark trim tabs on the bow and stern at the waterline when the boat is floating empty.

Once the boat is properly trimmed when empty, you can see what happens to the waterline trim tabs when you sit in the boat, kneel in he boat, have two people in the boat, have gear in the boat, etc.

Deja Vu all over again
The subject of trimming came up a while back with regard to trimming sliding seats in an Osprey (an asymmetrical hull). I shared the method I routinely use for setting the trim on my asymmetrical hull. Perhaps there is a better way and perhaps it results in a trim other than that which the designer had in mind, but it works pretty well for me. If there are better ways, I’d like to hear them.

I start by loading the boat up with the stuff needed for the day. Heaviest stuff low and toward the middle. Launch, get a few feet out and into deep enough water to get a decent paddle stroke without hitting bottom. Avoid wind and current as much as you can initially. Kneel if you kneel, sit if you sit. Do a draw stroke or two (a pry would work also if you’re more comfortable with that…)with the paddle coming in to the hull at a comfortable location for you. If the boat moves straight sideways without changing heading, you’re trimmed. If the bow draws more, move weight forward to “pin” the bow a bit. If the stern skids more, move weight back. Now you’re trimmed for weight.

You may want to adjust things a bit from there if you plan on doing a lot ferrys (a bit heavier to the downstream end - bow for back ferrys, stern for upstream ferrys)or are paddling in a wind (downwind end a bit lighter). You’ll have to remember to compensate for that by paddle placement when sideslipping or course correction when going crosswind without retrimming.

I’m not sure this method guarantees the absolute best glide or hull efficiency for any given hull design, but it’s always given me results that are “close enough for jazz.” It gives me a boat trimmed in a way that I can easily and instinctively control. This is something that can perhaps be over-thought. Any well designed hull should have a bit of margin for error built in.

Interesting. I’ll add it to the water
puddle method as a tool in the decision.

having a hard time picturing

I don’t see how an empty asymmetrically rockered boat is going to rest empty at the design differential waterline.

It seems to me the bottom would tend to rest horizontal to the water line, and not say stern an inch deeper than the bow. But maybe I’m missing something.

Water puddle

– Last Updated: Jul-13-10 3:23 PM EST –

is a fine method. I completely agree. I note that when paddling also. The more rockered the boat, the better it works. Works great on rainy days.
Packs and kneeling pads can screw it up a little though. And as it gets colder I grow more averse to having water sloshing about my knees. I get more serious about sponging it up right away.

Water doesn't always move freely in the bottom of a loaded canoe and is not as visible under packs as one might wish - or it gets sopped up by a pack or something. Not so much a problem for a day trip, but the more stuff you're carrying the less you can see of the bottom - and the more out-of-trim its possible to get with a sloppy packing job.

bubble level
with the canoe floating empty, i epoxy putty a level vial into the hull just ahead of the seat where i can see it when paddling. Using the putty lets me adjust the vial so it reads level in the empty canoe. Then its a simple matter to look down at the level and adjust trim to put the bubble between the center marks on the vial.


Trust instinct and experience?

– Last Updated: Jul-13-10 4:21 PM EST –

Just a thought... but once you've obtained your preferred hull... and you've got it set up so that the trim is right with no packs in it (through seat positioning)... and you've experimented a bit with your packs to get even weight distribution fore and aft... I'd expect you to have a pretty decent "feel" for (or even instinct for) what's right!

Maybe I'm missing something... but once the seat / thwart is in the right place, my priority with kit is ensuring that the stern will skid nicely and that I can draw the bow to the paddle - and maybe then tweaking the load distribution slightly to make better use of (rather than just fight) any breeze that might be bothering me.

The sort of sliding seat that comes as standard with the Swift Osprey would seem a logical next step for anyone overly concerned with trim... but I'm assuming that instinct and trial and error will result in appropriate trim with even modest experience - pretty much as it has to for sea kayak paddlers who have access to a retractable skeg.

Confused by your confusion
Maybe we’re using words differently.

I think of a canoe as having a waterline shape, a sheerline shape and a rockerline (or keel line) shape.

The waterline is a plan view–the outline shape the hull makes on the water surface if you look at it from directly below. Presumably the designer has distributed the mass and volume of the hull to achieve this designed waterline when the boat rests unloaded, empty.

The rockerline will only affect the waterline shape if the rocker is below the waterline, which it may or may not be in whole or in part.

The depth of the hull at any point is the sheerline minus the rockerline.

The stern of an asymmetrically rockered canoe rests “closer” to the water as a result of how the volume and mass of the boat is distributed in the naturally resting (level) state, which surely is the empty state for most canoes.

I suggest you float an empty differentially rockered boat on flat water. You will see the asymmetry of the rockerline.

Some suggest testing loaded trim against a bubble level near the gunwale or against a water puddle on the bottom. That makes sense, but only if a “base case” is first established for the bubble level or puddle. That is, as a base case, you have to set the bubble level or mark the place of the puddle, initially, when you know the boat is in trim. To me, that initial in-trim status is determined when the boat floats unloaded, unless the designer specifically says otherwise.

It is possible, for example, for a designer to believe a boat boat should be trimmed somewhat bow light from the resting state. There could be two reasons for this. First, the designer masterfully intended throughout the design process that the boat should be paddled with more weight astern. Second, the designer, after the fact, realizes that his creation is a dog when paddled on the resting waterline. In either case, absent such info from the designer, what else should we assume other than that the canoe is “in trim” when floating unloaded (empty)?

As someone has already pointed out, …

– Last Updated: Jul-13-10 5:21 PM EST –

... it might be reasonable to expect an asymmetrical and differentially-rockered canoe to float empty at an orientation that is different than the orientation that occurs when properly balanced with a load. Since the bow has more rocker and the empty canoe "barely touches the water" so overall hull profile is mostly out of the water, you'd expect the empty canoe to sit bow-low compared to when loaded and more of the hull is engaged, and the less-rockered stern sits deeper in the water as designed. I simply wouldn't trust that an empty boat with perhaps 2 inches more rocker up front will actually "sit level" when empty. It's just counter-intuitive to expect that.

To put this in a more visual perspective, imagine that you have half an inch of rocker in the stern and 2.5 inches in the bow, with the bow rocker occupying the front one-third of the boat's length. Since an empty canoe commonly floats less than one-inch-deep in the water, the empty boat floating "level" would need to have most of the forward one-third of the boat completely out of the water, and that ain't gonna happen, especially since the sides of the hull are higher (more weight) there (these rocker figures are a bit extreme, but more-typical figures would give the same effect, just less pronounced and less easy to "picture" when described in words). I figure that such a boat needs to be loaded properly before it will actually be "level", and when empty it will be bow-low. Overall hull volume will make a difference too, and perhaps a very-narrow rear half of the boat with more flare than the front half (so relative floatation when loaded is the same as when empty) would cancel-out the bow rocker when the boat floats empty, but accounting for that sort of thing (whether the boat is level or not) would take some serious math. Anyway, long story short, I figure the boat needs to be loaded before proper trim can be observed, so I agree with those who say sit or kneel in the boat and see how it rests (which assumes the designer put the seat in the correct place), then load gear so that "degree of level" does not change.

I don’t skid the stern that much. Skids
suggest I have lost control. I lean back and dig the outside back edge of the boat in, and the boat turns fast, in a controlled fashion.

thanks for the detailed explanation

As I suspected, I was missing something.

Regarding setting the bubble on a level …, what I have done is to put a 2’ level in the very center of the canoe and in the bottom. Then I block the canoe so that the bubble shows level. Then with the 2’ level still in place, I mount the level that will be used for trim wherever I want on the gunnel. I use spacers so that it is also showing level (even though the gunnel at that point is not level).

I think this method works pretty well because the level I use in the bottom is only 2’. With a differentially rockered boat, I think the results would be less accurate in replicating waterline “level” with say a 6’ level.

But then again, maybe I’m missing something …

Consider the waterline shape and balance
"what I have done is to put a 2’ level in the very center of the canoe and in the bottom"

Clarion, theoretically, this would work only if the center of mass (the trim balance point) is exactly in the geometric center of the canoe. That would likely be true only in a perfectly symmetrical canoe–symmetrical waterline, symmetrical rockerline and symmetrical sheerline. If there is asymmetry in any of these lines, especially the waterline, the center of mass of the boat is not likely to be at the geometric center of the boat.

Consider the waterline, the “footprint”. Most modern canoes and kayaks don’t have symmetrical waterlines. They either have a “swedeform” waterline, meaning more boat length abow of the center point, or they have a “fishform” waterline, meaning more boat length astern of the center point.

Racing hulls of canoes, kayaks, sailboats and power boats are often radically swedeform or “delta” shaped.

The importance of this to trim is that the balance point of swedeform and fishform hulls probably will not be in the geometric center.

Differential sheerline could also affect the balance point. Most canoes have more sheerline upsweep in the bow to deflect waves, resulting a higher bow than stern. This added hull material in the bow will make the boat heavier in the bow and hence affect the location of the center of mass or balance point.

If the manufacturer hasn’t marked the balance point, you would have to establish it yourself. That’s where you should put your initial bubble level, it seems to me, using your method.

Now, I’ve never cared enough to take all these steps, but I am trying to be correct on theory.

A half measure
if you want to put in a bubble level… Instead of simply floating the boat and sticking a bubble level to that and assuming that’s how it should float loaded (as I have done and never gotten it exactly right - RV levels with the double-sided tape backing are cheap and stick well BTW) try putting a couple of forty pound sand bags on the seat. It won’t be exactly right but it’ll be a lot closer to right than you’d be setting it empty. I can’t imagine how any designer worth his salt wouldn’t consider the paddler’s weight and where its placed in his design. I’d think that would be covered in the prerequisite course to the introduction to the introduction of the first boat design course.

self stick levels
If the hull bottom is flat and the canoe has no rocker, the self-stick levels will work. The thickness of a core bottom or the cloth covering cross-ribs can make the bottom uneven at the point of attachment and without some filler material between the level and the hull, its hard to “level” the level. The canoe always tells me if its happy at the trim i am running. The bubble level gives me a reference point to any changes in trim. On flat water in the 17’ Jensen with really no rocker, the boat is happiest dead level. We can move gear when starting out to achieve trim, but underway the only easy adjustment is with the sliding seats. The bubble tells us how far we moved and the canoe tells us if that is going to work.

In my solos it also seems to work with the bubble set in an empty canoe. Loaded to a dead-on bubble, water in the hull stays near the center of the canoe indicating little change in the trim from empty.

I will take a solo and load the seat in stages to see how much the bubble moves and use the “water-in-the-boat” indicator at the same time. Then replace the ballast with me and see what changes occur. I think my paddling position will put my center of gravity ahead of the seat, due to shoulder and leg weight. How much that will change things is unknown.

This is getting interesting,


Word from Wenonah
Just a quick addendum…

Got a nice response from Wenonah about this question, and their answer confirms that neutral trim would cause a tennis ball or drop of water to come to rest in the center of the hull, fore/aft.