# estimated weight caps

Discussion in 'Boat Design' started by tdd4, Aug 6, 2011.

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### tdd4tdd4

Ok I need some one to follow my math...... am I close?......My boat, a handy punt type. It is 12' long x3'wide x2' tall gunwales x 62.4 is the volume of a brick this size, divided by 7 after subtracting the weight of the boat 150lbs ( conservative est.)and and 120 lbs est.for shape ....... ok so far.... I have an boat that will support 550 lbs total including 2 people in a reasonable safe fashion....correct

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### PoidaSenior Member

What's the brick got to do with it and why are you dividing by 7?

Multiply the L X W X H Length Width height in feet = Cubic Feet
Multiply that by 62.4 the weight of water.

This gives you the total weight the boat will support just before it sinks.
So, divide it by two and that will give you ther weight the boat can handle with the water half way up the side.

This includes the weight of the boat, people, fuel everything.

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### DCockeySenior Member

Ike's page with summary of the USCG rules for small boat capacity: http://newboatbuilders.com/pages/load.html
USCG Boatbuilders Handbook which has more detail: http://www.uscgboating.org/regulations/boat_builders_handbook_and_regulations.aspx

USCG standards for small boat capacity are considerably less than half the displacement just before the boat floods.

Unless the boat is a box with flat surfaces and no sheer, the volume will be less than L X W X H.

A punt which is 12' x 3' x 2' may be less stable than desirable with 550 lbs on board.

4. ### Submarine TomPrevious Member

Roughly, 10 X 2 X 2 = 40 (It's not a brick shape, right?)

40 X 62 = ~2500 pounds buoyancy, or less.

So, working load ~800 pounds less boat, engine, dock lines, beer, fuel, people, dog, fishing gear, etc.

-Tom

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### tdd4tdd4

What's the brick got to do with it and why are you dividing by 7

welllllllllllllllllllll............. I got the 7 from another site that told me to divide by seven
I guess it reduces the the load tto save freeboard but what do I know I'm a truck driver
I'm going with 42 inch beam then

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### tdd4tdd4

Maximum Weight Capacity = (Maximum Displacement - boat weight)/7 = W
is the formula I got from http://newboatbuilders.com/pages/load.html
is this a good formula

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### PoidaSenior Member

I divided by 2 not suggestion that was the regulation, but to indicate you divide by a number to provide the amount of freeboard you required.

If 7 is the safety factor required then divide by 7.

However the formula you quoted is for an empty boat. Unfortunately with small craft they can be more easily overloaded than a larger vessel, however you would probably be better checking your local laws.

I am not a boat designer and only meant to give you the principles of floatation.

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### tdd4tdd4

I with you and did find the answer to my question..thanks one and all
I use the formula off the suggested site and I see where this question is asked and answered a lot .thanks again

I do have one more question... How wide can a vessel be and still be comfortable to paddle?

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### PoidaSenior Member

That depends whether you want to paddle it as a kayak or a canoe.
Either way go to you kayak/canoe shop and measure them.

Somehow, and I don't know how, canoe paddlers can paddle on one side of the canoe and keep it straight. They do that in the olympics.

If you want a wider vessel use oars and if you want to face forward when you row there is a thread on forward facing rowing systems.

I kayak a fair bit, not as much as time will allow but when you paddle your paddle can be on 2 angles. A low angle for touring and a steeper angle for power. So the width can depend on the type of paddling you are doing.

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### BATAANSenior Member

Do you mean paddle or row?

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### tdd4tdd4

Well,I paddled the boundary waters in Canada when I was a younger man and found that I could pause at the end of each stroke and make small rudder type adjustments that would keep the canoe straight (paddling on one side).This would not work when power was needed; it was good for leisurely paddling in flat calm water and that's what I was wanting to be able to do in my punt, but rowing may have to suffice. Also I am not planning on more than a trolling motor for power so I am staying in protected water.
I'm thinking in that situation and rear deck may support a paddler if the boat is 36 inches wide but may not if its wider. Sorry rambling a bit.
At any rate construction starts tomorrow. hip hip her ray

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### tdd4tdd4

Paddle Double or single but single is preferred.

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### BATAANSenior Member

I've never had much luck paddling my pram, as when heeled, the shape makes it steer strongly, unlike a canoe. I wind up rowing, and often use the BC method, sitting on a plank on the gunwales, facing forward and pushing. This is to avoid rocks in our cluttered waters.

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