Engineering Help Needed

Don S/V ILLusion · Oct 13, 2023

Search “how to calculate lever effort”. There are plug-in calculators on the internet.

capta · Oct 13, 2023

The Polynesian pirogues usually use one "outrigger" made of regular old sticks. I don't think there is much engineering involved, but they work very well and I've always felt safe when traveling in one. Check them out on the web and KISS.

kloudie1 · Oct 14, 2023

Think of it as torque or righting moment; with both pontoons out of the water, everything is balanced. As one pontoon touches the water, the other is out of the water. The 10 pound weight puts 30 ft pounds of torque on center line. The force on the gunwale is 30 pounds at 1 foot from the center line. To that, you’d add the flotation force from the other pontoon. So if it has 4 pounds of flotation force when submerged, it would add another 12 foot pounds of righting moment. That would make 42 pounds at the high side gunwale .
back of envelope calculation.. May translate from Cajunese to Taterese?
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LloydB · Oct 14, 2023

"My knees are just too sensitive these days to put them low as the Scouts taught me"
Be careful that napkin doesn't have any coffee stains on it and takes on center of effort but doesn't necessarily take on center of mass so I think you brought the question to the right place because you might be wanting to think how to add a keel rather than balance on top of a flagpole.

capta · Oct 14, 2023

Tater said:
Capta, I will have a pontoon on each side. My knees are just too sensitive these days to put them low as the Scouts taught me.

It makes no difference in other areas, such as SE Asia. use two. They just use any crooked tree branches of the right size and shape as cross members and the actual outrigger is usually straight except where it may curve upward a bit at the front.
All I'm trying to say, don't get too hung up on a lot of modern stuff when there is an easier and cheaper way, unless you require the aesthetics to be modern rather than "island style".

jssailem · Oct 14, 2023

Check out this idea of "pourable foam". I have seen Total Boat marketing Pourable closed cell foam.

This guy is putting foam as a floatation and strengthening agent for the pontoons he built on his RC race boat. If you are thinking about building sealed pontoons for your boat, the foam could help hold them structurally and support them floating in place.

Ralph Johnstone · Oct 14, 2023

Tater said:
The pontoon is 2 feet from the edge of the beam and displaces 10 pounds. The fulcrum is at centerline of the canoe, 1 foot from the beam.

As @kloudie1 suggested, lets look at a balance of the rotating moments (or torque). The first thing you always want to do is make a drawing of the object which is subject to the applied moments. In this case, we only need to initially look at one half of the pontoon arrangement. Later on, if needed, we can add secondary forces (which produce moments) to fine tune our calculations.

The first thing we see is that the only thing that remains motionless is the point where the the outrigger is attached to the centreline of the canoe. This is the fulcrum point as @Tater originally described.

The clockwise moment are :

- a downward force of 20 lbs. acting at a distance of 1 ft. = a moment of 20 lb.ft.

The counterclockwise moments are:

- an upward force of 10 lbs. acting at a distance of 3 ft. = a moment of 30 lb.ft.

Our CW moment ≠ CCW moment so our drawing is not in equilibrium. Several things could bring it back into equilibrium such as the pontoon pushes up with less force as it rises higher in the water or more weight can be added to the force on the beam.

In this case, lets just say the maximum allowable weight that @Tater could apply to the beam would be :

30 lbs. X 1ft. = a moment 30 lb.ft. in a CW direction and our drawing is now in equilibrium as the pontoon juuuuuuust slips below the water level.

This is the situation described in its most basic form. Other forces which would come into play would be the weight of the pontoons and how they affect each other, where the paddler is standing, how deep the paddler is willing to allow a pontoon sink and anything else you can dream up both large and small.

capta · Oct 15, 2023

Tater said:
studied bass for many years and they just don't swim that fast.

So far, 17 knots is the fastest speed I've hooked up at. Most ended up being lower jaws, but we got the occasional tuna aboard. It was a 65' aloy crew boat and we were directed "at the fastest prudent speed.... ", in other words no, dilly dallying about, fishing.
I haven't found the bass, stripers, in the last 2 seasons I've been here, and I do have one of those 115hp, 24 knot boats. I thought I was a pretty good fisherman, but I guess I'm not. Rats, foiled again....

JamesG161 · Oct 15, 2023

Tater said:
I am using PVC pipe for the frame. I haven't found a good material yet for the pontoons.

You can use PVC Pipe as the pontoons too. Try a 8 Inch Pipe or maybe 2, filled with Foam and end capped.
All components can be connected with PVC Tees, couples etc.

Add Pontoon Buoyancy to your Moment diagram. I like think of a force Moment as a "Tendency" to move in a direction.

Jim...

Apex · Oct 16, 2023

jssailem · Oct 16, 2023

A canoe with training wheels.
What happens when you need beer?

That would be a disaster waiting to happen for Bubba J.

WayneH · Oct 16, 2023

You drink the ones in the blue cooler until it's empty. Then beach the canoe and swap put for a red cooler. Repeat for the other cooler then go back to the store.

kappykaplan · Oct 19, 2023

Tater said:
Project complete: all that remains is strapping it on and testing.