boat not square

[1fast68]

I am building an uncle johns jon boat. I have the transom, bow and sides put together. not a bottom yet and no seat braces. I cut the sides at the same time and both are the same length. I measured from the inside bow end in a straight line to the transom and get within a 1/4" measurement. If I measure from opposite corners I get a 3" difference. If I move the long corner in to match, the left side (facing front to back) is bowed more than the right. I have double checked all measurements and can't figure out what's wrong. I put a string down the middle from transom to bow for a center line and put a brace across the side joints on the top (not the bottom. Has anyone else experianced these problems before.

Thanks for any help.
Shane

 

[seedtick]

I don't have an absolute answer to solve your problem but you can look at the "out of square" problem from several different aspects to help understand what's going on.

From what you're describing, the transom and bow are parallel and the sides are parallel. Do your corner to corner measurements match on the top corners as well as the bottom corners? Could be the angle on each side of the transom and the angle on each side of the bow are not the same.

Restring your centerline from middle of bow to middle of transom and with a framing square, check squareness of the string to each end. Flip the boat over and do the same on the other side.

With the center string in place, check the distance out to the sides in several spots. They should match.

In building boats with boards we sometimes run into boards that do not have the same flexibility and do not readily flex to produce matching sides. Occasionally pieces of plywood do not have the same flexibility and one side will bend easier than the other.

In short, measure that thing every which way from Sunday until you figure what is wrong.

 

[JEM]

It sounds like it's twisted like
_
\_\

I'm not familiar with Uncle J's method of creating the bottom. Do you draw that up by plotting offsets or do you trace the shape provided by the sides and transom?

 

[Kayak Jack]

Matt,

You echoed my thoughts. The ends may be parallel to each other, but still not be PERPENDICULAR to the centerline of the boat. A parallelogram.

 

[1fast68]

jem, you trace the shape so I can't really put a bottom on it till I feel like it's right.

The funny (not really) thing is that if I twist it the transom comes off level on my work table. If I push it square one side is bowed more, where one side has a boat shape and the other just a straight line. Is a few inches something to worry about. I want to put at least a 25hp motor on this boat so I want it to track straight. I made it with 23" sides, 60" bottom width at the transom, and 48" bottom width at the bow. I am going to put a front and back deck and double up the transom for the extra weight of the motor. Oh... 16' long (191"). I just have it screwed together and can take it bake apart at this point but I can measure everything how it is right now. I could also post pictures if that would help anyone help me.

Thanks guys,
Shane

 

[JEM]

hmmm....

If it's just stitched together, I cut the stitches lose and switch the hull side panels around. Even if they are butt blocked and you used the wooden patch method, I'd do this just as a check to your mesurements.

If the problem goes away, recut, and reassemble. It just might be a fluke thing. Although it sounds like one panel is bowing more than the other.

 

[1fast68]

I'll try switching sides tonight. I am using sheet rock screws for now. And I used a dovetail jig to cut and connect the sides together. Other than one side looking slightly better than the other I can use either without any problem.

I just want to correct the problem as quickly as possible... the support from the wife is unbearable.

 

[Kayak Jack]

Maybe one side is shorter than the other?

 

[1fast68]

checked the sides and they are the same, plus I had them clamed together when they were cut. It my end up being on my transom. After I switch the sides I'll re-post to let you know where I'm at.

 

[Kayak Jack]

What the heck ever you find - let us know! You may have uncovered one of those spots on Earth where optical illusions abound. Tall guys look short. Fat guys look thin. I appear to be handsome. Chuckie looks smart. Weird stuff like that.

We have a "Mystery Spot" just westerly of the straits, here in Michigan. Island Piper came from there. (Though he lives in Looooosianna now, he used to be honest. He originally lived in the Upper Peninsula of Michigan. We call it the UP, and he's a closet Yooper.) When Keith was there, he looked pretty good. Now that he's escaped? Well ........ He's in circus sideshows and folks throw quarters at him, just to see him scurry.

Location, location location.

 

[JEM]

Might be one of the transoms. Check the diagonal measurements from corner to corner.

Then check measuring from the mid point out to the ends.

Do let us know what you find. It'll be good reference for future builders.

 

[oldsparkey]

You don't have the seats of supports in across the boat ? You might want to try that and see if it squares things up, sometimes when building a boat the side are at the correct measurement but the boards (side) bowed at different angles and it takes the cross members to pull them in and correct it.

You have the bow and the stern connected to the side boards but nothing in the middle to true it up.

Just searching my mind about how I remember the instructions to make one of Uncle Johns Jon Boats. I have not made one , Yet. Was going to but I got sidetracked from that project by making a prototype of the Freedom for Matt.

Chuck.

 

[seedtick]

I think what maybe happening is that you've definitely got the parallelogram that we talked about above. But when you clamp in the long corners, instead of the boat racking to square - one of the sides bends giving you the unsymmetric looks to the boat and likely throws the bow and transom out of their previous parallel state.

You might want to try clamping a board to the more flexible side and try racking the boat square. Clamping the board to the flexible side will make it stiffer and force the other side to bend more. You may have to experiment with different size boards( 1X 1, 1X2, 1X3, etc.) clamped to the flexible side until you can get both sides symmetrical when the boat is square.

I don't think the boat needs to be dead on square but you should get it down to 1/4" or so or at least to where it's not visible.

 

[keith]

jon boat

When I lay out my sides for my jon boat, I mark all my ribs, seats, drybox, decks and have them square and use them for reference when installind my jigs and can rack it if need be to keep it square. Later Keith

 

[nobucks]

Did you switch the sides yet? I like Sparkey's suggestion of trying it with the crossmembers. When framing kayaks I've found that things may pul to one side or the other during construction, plywood may be warped, etc., but, as I add parts, everything pulls into place.

Apples and oranges, obviously, but my experience was similar with the Bateau cheap canoe, and things squared up when everything was tied together.

 

[gpratt]

Maybe the forms/cross braces are not lined up along the centerline of the boat. Measure to get a center mark on them and use a string to make sure all are line up on a centerline.

 

[1fast68]

I put some cross braces on the top of the sides and it did pull it in a bit. I didn't swap sides and didn't put braces on the bottom yet. I am going to cut my inner braces tonight and secure the sides and see where I'm at. It looks like I can pull it within about 1in and still look equal on the bow of the sides. I will keep everyone informed about the progress and will post a picture if I can after I get the braces on the inside. You guys have been a great source of infomation.

 

[1fast68]

Just to add I checked the diag. on the transom and the bow plate and both where within an 1/8".

 

[Kayak Jack]

Good luck and keep at it, 68. A few years ago, a fella in FL didn't get his hull configuration right and ended up with a wooden flower box instead of a nice, light canoe for the BWCA. Take care with your lovely, new boat.

 

[oldsparkey]

Jack

That boat did not turn into a flower box , I soaked in metracal and it shrunk down to 3 feet long. After that I sold it to this lady who is dong crawfish boils and needed a pirogue to put the crawdads in as a serving dish.
A person has to stay with the Cajun theam when eating Crawdads ... ya know.

Here is the picture of it with one of the local (Male ) Models holding it. I don't remember his name but he said he has posed for Play Girl Magazine several times.:roll:

Chuck.
PS. It looks like he has eaten his share of crawdads in the past. :lol: