Homemade OC1, Stability Issues

[road_warrior64]

I built my first composite OC1 with mixed results. It was my own design and several improvements could be made.

Mistake #1: Although the chines are rounded, the sides are completely vertical.

Mistake #2: No tumblehome. Even at 28", the paddle reach is awkward and cross stroke are almost impossible.

Mistake #3: Completely flat bottom, 24" wide before the rounded chines begin.

With my factory made boats (Mohawk Solo 13, Old Town Penobscot), they feel predictably stable and will teeter without tipping. As I lean, the hulls seem to provide progressive resistance. It's like the red zone on a tachometer warning you not to go any further. If my Solo 13 had higher sides and airbags, I'd feel comfortable up to Class III. With my homemade boat, the stability is all or nothing. It resist leaning up to a point and then is ready to flip There is no transitional stage (secondary stability?) What can I do on future designs to improve this? Thanks!

John

[Sir Adam]

The hull should be more rounded, and not flat on bottom. This will give you that sense of transition vs. an all or nothing.

You may want to add more width as well - 24" at the waterline isn't going to feel very stable (says the person who built a C1 at 22.5"...). 26" seems to feel OK for most folks, wider than that starts to feel really stable (this is the C1 vs OC1 world). Rounding it out more and keeping your 28" width may solve this (or you may want wider still).


Either way congratulations on building what you did, and I hope paddling a craft you designed and built puts a smile on your face:)

[Bob P]

It depends on how much rocker is built in, but you might just pull in the gunwales a couple of inches in the center of the boat. That will narrow the boat (especially at the top) and round the hull a bit. That's what I did with my Spark, and it's still an easy boat to paddle.

[Bob P]

P.S.

It looks like you've cored the bottom. It might be too stiff when you pull in the gunwales. If it is, I would cut through the core longitudinally, maybe 2 cuts about 6" apart. That will allow the hull to round a bit when you pull in at the top. You can lay up additional material on top of the core after the hull is re-shaped.

[Roy]

As Adam writes: welcome to the boat-building world.

As far as stability is concerned, I ask, how much have you paddled it? Many paddlers have ended up with a too-tender canoe right out of the box...but, eventually figured the boat out.

As far as tumblehome...Bob is right, some canoes can be yanked in with shorter thwarts. But, also consider, anyone who can build a boat can figure out how to cut down the shear line, make molded-tumblehome sides, and attach them. Some can do such cut-paste jobs and make them look great; others of us are fine with 50' Craftsmanship (that is, looks fine from 50' away).

Roy

[Paddle Power]

goggle john winters, the canoe designer
you'll find some boat building theory

[kaz]

The very first OC1 I designed, looked a lot like your boat. I strongly recommend making it wider in the waterline.

[Bob P]

The very first OC1 I designed, looked a lot like your boat. I strongly recommend making it wider in the waterline.

I guess the Reaktor isn't what you're talking about. Interestingly enough, despite its lack of initial stability, I found the Reaktor (24" wide, relatively round hull) one of the easiest boats I've paddled in "weird" water.

[Roy]

I think he is saying his wetted width is 28". The 24" is the flat part of the total width.

If that is true, I still think more time in the boat might solve the stability problem. Of course, some boats need to be sold for 25 bucks to someone who wants to make a planter out of it (Yes, I know that for a FACT).

I moved from a OC1 built from a Hartung C2 hull mold to one built from a Max II hull mold. The Max II was like an ice cube on a hot griddle for the first week.

Roy

[JimW]

OK, what you have is typical of many barges, and even catamarans. The completely flat hull sits nice and flat on flat water and it takes considerable effort (heeling moment) to make it heel, up to a certain point. In a catamaran the point is when one of the hulls lifts off the water, with a flat/barge hull it is less obvious when it will happen, but your righting lever curve will plummet rapidly when you get to that point. Typically for barges (AKA pontoons in some of the standards) we don't apply the same stability criteria as to ships - they easily manage to get the righting energy and righting energy ratios that a ship requires, but the problem is that stability vanishes at a much lower angle, so often the righting energy stuff is thrown away and we look for the maximum righting lever to occur after 20 degrees, or in some cases after 15 degrees if another requirement can be satisfied - this is becuase once the righting lever reaches maximum, it drops almost directly to zero, so another degree of heel = capsize. So for a flat bottomed vessel we might expect that if it goes past about 20 degrees, it will go right over, whilst a conventional ship shape might go to 60 degrees or more and still be able to come back upright (obviously a self righting lifeboat is designed to go to 180 and still return upright and that takes some doing!).

Adding a shallow arch or shallow V to the bottom will make some difference right away - a lot of people find a V hull flip flops side to side settling at the V angle either way (i.e when one side of the bottom is flat on the water), so it can feel primarily unstable, but suddenly firms up.

The next thing to thing about is flaring the sides - not in the middle perhaps as you will be at the full width you want, but as you go forward and aft from the middle have the sides flare out from where the bottom transitions to side until I guess 2/3 of the depth or more. From there, certainly in the centre and forward part you will need some tumblehome up to the gunwale to enable you to get the paddle in.

Do you want a symmetric boat that has same shape in bow and stern, or do you want asymmetric? If you want assymmetric you can have some fun experimenting with narrowing the forward section sooner (to get paddle strokes in) and aft section later, and adding perhaps more flare aft for that secondary stability. You need to test paddle some prototypes to make sure it feels balanced OK and not like it tips over and forward at the same time (i.e. the bow trims down as you heel because you cut too much flare/volume out of the front).

I'm sure you will pick up other things as you go along.

Have fun!