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Rocker/Trim

beekeeper

Well-Known Member
Mar 4, 2009
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Lots of discussion about moving the load to trim a boat and compensate for the boat's rocker on Piper's "A New Marsh Pirogue". I don't want to hijack his post so I will add my 2 cents here.
Changing the trim is changing the amount of rocker in the water, correct? Two boats with different rocker, trimmed so the same amount of floor is submerged will still show the differences in rocker, correct ?
When I changed the trim in my skiffs the tracking improved, but the changes didn't eliminate the effects of the rockered bottom.
Moving gear around has its limitations. I can move my ice chest or tackle box, but I don't want to. I need (like) it where they are (within reach). It is better to have a boat with an amount of rocker that fits your needs.
Changing the rocker changes the water line of the boat. Seems to me little changes here have noticeable effects.
Boat evolution indicates trim is not the total answer to changeing a boats handeling.
I don't know a formula or magic number for figuring the best rocker. I do know Piper is going to like his new marsh pirogue and I bet it fits his needs very well.

beekeeper
 

oldsparkey

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Aug 25, 2003
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Central , Florida
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beekeeper said:
Lots of discussion about moving the load to trim a boat and compensate for the boat's rocker on Piper's "A New Marsh Pirogue". I don't want to hijack his post so I will add my 2 cents here.
Pipers boat building post has been hijacked to the oomph degree so a little more would not hurt anything. :wink:

Changing the trim is changing the amount of rocker in the water, correct? Two boats with different rocker, trimmed so the same amount of floor is submerged will still show the differences in rocker, correct ?
When I changed the trim in my skiffs the tracking improved, but the changes didn't eliminate the effects of the rockered bottom.
Changing the trim of the boat does nothing more then change that , the amount of rocker is still there. Only difference is one end would be higher then the other or the reverse of it. Trimed out the rocker is still there , it will not go away.

Changing the rocker changes the water line of the boat. Seems to me little changes here have noticeable effects.
If you are saying a flat bottom ( No Rocker ) acts differently then one with rocker in it , that is true , there is a lot of handling difference between the two.
If you are having problems paddling the one with the rocker in it then you might be a lot happier with one without any rocker in it. The rocker helps a boat turn to avoid obstacles ( More maneuverable ) then one without any. In plain language ... something with less contact to a surface ( a bow or pivot point in it ) will spin a lot easier then something flat.
 

Kayak Jack

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Aug 26, 2003
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oldsparkey said:
<SNIP>... something with less contact to a surface ( a bow or pivot point in it ) will spin a lot easier then something flat.
That summation pretty well ends discussion of effects of rocker, because anything else that can be said will merely expand on that.

Rocker affects the "underwater line" of a boat, as does cross sectional configuration (flat, vee, rounded, etc.). Trim will affect the built-in handling some, but not outside of the already built-in parameters already there.

A canoe, trimmed nose high a bit, tracks and steers easier under most conditions. An exception to that is going into a headwind that grabs the bow and steers it away from intended course. Then, a nose down trim is a bit easier to control. Paddling either up or down stream, most canoeists prefer a nose high trim - not a lot, just a little, say an inch or two difference. That lets the boat pivot more around the tail end. A canoe trimmed nose down, going down stream, will be difficult to enter a turn, and once in, it will tend to keep on turning.

When I said that trim can affect asymmetrical rocker, let me explain that some more. Take two boats, identical except rocker. One has 1" of rocker at each end, the other has "no rocker at the bow, and 2" at the stern". Set these two, empty boats in the water, and put a carpenter's level in the bottom of each. The carpenter's level will give the same reading in both boats - dead level. Because the boat is following the water level, it can't help but to be level.

All the asymmetrical rocker did was change the height of the sides of the boats. the bottom of the boat still floats level in the water. Trimming by moving weight will only shove one end deeper, changing the natural level of the boat's bottom.
 

tx river rat

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Feb 23, 2007
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I guess it is the yankee water being different than southern water but all these boats sit nose high just like the rocker was set to do.

The statement Jack made just doesnt pan out ,if you have a boat that is designed with no rocker for 12 ft and then the rocker starts there the boat will float nose high. The design of the hull also effects how it floats an asymmetrical hull will react differently than a symmetrical when combined with the same rocker because of more are less displacement in those areas of the boat
Look at the pics.
Rocker is designed into a boat to make it preform up to the task it was designed for, high
in front to take you over obstacles make landing easier, turning ease.
double rocker will let you spin on a top.( these traits also take away from water line length and tracking and speed)
No rocker you cant turn the boat without some leaning or heeling the boat ,but it will track and be fast for the length and width of the boat.
We trim our boats to sit in the water to maximize the design ,trim has nothing to do with the design of the boat,most boats are designed for a single paddler and to sit with the desired rocker,we move the load around to try to trim back out to that point.
After close to 50 years of building buying running and paddling power boats hover craft canoes kayaks I have never seen a single time that triming nose down helped ,it always made the boats hard to handle and took away from performance. Why would you want to get your boat into a trim that makes it hard to handle ,harder to paddle in conditions of wind . In the south wind means waves and rough water ,I want the best out of my boat in these conditions and trimed properly I will get the best handling traits of my craft.
I have a fiend that paddles more in a year than 99 percent of this board combined ( between 4 and 5 thousand miles a year) and to quote him, a nose down trimed boat paddles like a drunk pig, those are my findings also.
Ron
 

Kayak Jack

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Aug 26, 2003
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Interesting. Image# 1 shows a loaded boat, not an empty boat. Image# 2 looks like it's floating about even, but both ends aren't visible. Image# 3 looks about even, but, again, both ends can't be seen. Image# 4 looks like it's grounded. What was it these pictures are supposed to indicate? You lost me here, Ron.
 

tx river rat

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Feb 23, 2007
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Wrong again Jack non of the boats are loaded or grounded ,I am not posting this to argue with you . In my opion you are wrong so I stated mine.
Ron
 

tx river rat

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Feb 23, 2007
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Ok Jack Here we go ,that boat was designed around that cooler ,wich empty might weigh a couple lbs. so the rocker of the boat was set for it. no different than a deck running up that far.
. Sorry but i didnt take a pic of the inside.
I will have to say I will heed your advice and go on believing just what I wrote.
There are a lot of new folks coming and going here ,If I see something posted that I feel like is not true or half true I feel a responsibility to give another view of that subject then they can make up there own minds.
You have beliefs that I total disagree with at times and I respect that but I have the same rights to my beliefs and trying to show why I believe that way.
Now I can get sharp tongued and catty also but I dont do that unless I recieve that type of remarks ,other wise its just two guys expressing there views.
Ron
 

beekeeper

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Mar 4, 2009
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Chuck
I thought my boats with "lots" of rocker could be improved to better suit me, so I did build one with less rocker. For my use it is a much better boat. I am better served by it than a boat that might turn on a dime. For me better tracking trumps ease of turning where I paddle.
If everyone will bring their boats to Piper's for the rendezvous, we can solve this. :roll: :wink: :lol:

beekeeper
 

seedtick

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Jul 22, 2006
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Denham Springs, LA
at 2' wide and an approximate 14' bottom length, the water footprint is something like 14 sq. ft.

so it takes something like 70 pounds to evenly sink it one inch

so climb in with you and your stuff and you add what 250 - 300lb? so the boat sinks 3 or 4 inches more

unless you scoot the weight mostly to the back, that one or two inch clearance above the water that's shown in the empty pics will disappear when loaded, making it nose down

to me nose down is when the bottom of the front stem touches the water - we may all be talking about different definitions of nose down
 

Kayak Jack

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Aug 26, 2003
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seedtick said:
<SNIP> to me nose down is when the bottom of the front stem touches the water - we may all be talking about different definitions of nose down
You may be correct on that, Seedtick. I'm thinking of an "off level" interpretation. Neutral trim, to me, is dead level. Nose up trim is off level, with the nose higher than the stern.

If we had a standard carpenter's level (maybe they ARE standard, I don't know) then we could say 1/2 bubble nose high, one bubble nose high, etc. Measuring in degrees is obviously standard, but I don't have an instrument to measure that finely, and likely others don't either.

Trim is an individual choice, for situations that confront the paddler.
 

tx river rat

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Feb 23, 2007
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As normal these kind of discussions bring out some good points and make us think about how a hull shape and the things we do to that shape effect the handling of a boat.
So lets design a boat with rocker to do the job we want it to do.
Draw a straight line (bottom of the boat) 16 ft length. That is a perfectly level trim no rocker
Just as a general rule I like 2 inches of rocker in the front and 1 inch in the rear.
lets put in these rockers 4 ft from each end , bottom line is still level.
Now set the boat into the water and look at it ,you have 4 ft of rocker front and back so the 8 ft flat area in the center is going to hold the boat in the same plane as it was to the line.
Basically you have an 8 ft boat both ends out of the water, both ends are balance front is 2 high back is 1 inch high are still close to it with a 40 lb boat
now I sit down in the boat in water my seat at the center of flotation. What happens.
At my 200 lbs the boat is going to sink a couple of inches.
Now is when the rocker starts coming into play . My weight should sink the boat around 2 inches
depending on the hull width. go back to your line and remember the words center of flotation, that means I am sitting where I exert pressure straight down .
so you hold the same level as you do with an empty boat.
Front is just touching the water , the back is one inch deep.center section should be 2 inches deep.
This is what I want in a boat easy turning long water line so it is picking all the efficiency it can from the hull , good tracking, and a smooth entry and exit point for the water around the boat. add some more weight and it should get even better up to a point.Of course as you add weight you need to try to keep this trim
Nose down to me is anytime the nose of the boat is lower than that two inches from the line we drew to start laying the boat out, the original level line.
This seems to be the best all around trim for my kind of paddling.
As far as an acurate level you are on the best one in the world if it is calm.
WATER you have a 16 ft level your sitting in.
Ron
PS you can do the same thing with a boat that has 2 inches in front and no rocker in the rear ,the 12 ft of straight bottom of the boat will hold the nose up to the rocker height
 

oldsparkey

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Aug 25, 2003
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As a wise person told me one time..... " There ain't no perfect tent, wood, boat, hatch, sleeping bag or women ".

I guess the perfect part is up to an individual and there likes or dislikes. Or in other words , One man's wine is another man's poison.

What works for me , you would probably hate and what works for you , I would think it is something to plant flowers in. Different strokes for different folks since we all paddle our boats but in a lot of different environments , water and even the way we use the paddle strokes.
There is no way anyone will ever get 10 people to agree on a certain matter , there will always be a difference of thought and trying to change that is like beating your head against a brick wall. I can guarantee you the wall will not be damaged unless it is a Yankee beating his head against it and then only slightly , but the wall will win. :wink:

Rocker in a boat for me is something I like , it makes the boat scoot , dodge and duck around trees , blow downs , cypress knees , and other seen or unseen obsticals. Plus I can just paddle up to the shore , nose the boat up on the bank , get up and walk out to set up camp with dry feet.
The further I move back in the boat when beaching it the further the bow will go up on the shore. :D

As far as the trim , nose up to a slight degree when on the water so it will go over items and not try to ram them like a destroyer would do to a German submarine in WW 2. I really prefer to slid up on something then to ram it and come to a abrupt halt.

Again it's personal preference and not what the other guy wants or does since it is not for him , it's for me.
 

tx river rat

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Feb 23, 2007
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Beekeeper
The same thing happens if you have the boat loaded for proper trim .I think this is the thing most folks miss,you build and design a boat to float a certain way and you add weight to keep as close to that same trim when it is loaded
Here is a pic of the T-V with around 500 including me in her .she still has the same trim as an empty T-V


.
Chuck I am not pushing any combination of rocker ,or design of boat . Just my take on the effects and the way it works in the water so a builder has an ideal of why and how the rocker effects the boat they are building.
Ron
 

seedtick

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Jul 22, 2006
1,161
7
Denham Springs, LA
i'm not pushing any design combination either,

but i do believe that once the bottom of the front stem is underwater, as shown in Ron's pic with the boat loaded, amount of rocker becomes pretty insignificant
 

beekeeper

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Mar 4, 2009
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Are ya'll saying, two similar boats but with different rocker, trimed the same (level/correctly), with the load of each boat such that the ends are submerged, rocker is insignificant?

beekeeper