How do I properly read these specs?

Assessment of the situation for the recreational skipper is by eye and gut feel, that's almost universally true. But the laws of physics govern, whether we know how to do the math or not, and the inputs are rarely available or terribly accurate.

My point was simply to realize these facts and give them some thought before deciding to forego filling the fuel tanks in favor of inviting another few guests on the fly bridge to watch the fireworks. You're in charge, and you're responsible.

So I'm not sure whether any of us has answered the OP, but I bet we've made him nervous...

However...in some cases leaving consumables and packables ashore to take passengers isn't all bad.

You still have to step back and think...not all have the instinct or experience to do it.... there are operators...and everyone else.

Physics and possibly laws of nature that exist but haven't been discovered yet might govern....but try to pass that on here or even to your most experienced boating friend in person...mot likely much will actually change.

So the best we can do here is pass along some experiences we all have had and say to the OP...take a stab at it...unless you feel really comfy...best to bring along someone that knows the tricks or can do the math ahead of time.

chriscritchett said:

Cappy - all due respect, but no. It's not how it looks to you vs me vs him. It's physics. And please don't advise anyone to bring less fuel and water so they can load up the people and stuff on deck. That backfires quite easily.

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My experience over the last 35 years of both commercial boating and yachting is that boats accumulate tons (literally) of junk on the boat over time. This extra weight is NEVER taken into account as far as Pax load is concerned (until afterwards). Every boat has a weight limit that it was designed to operate at. This is reflected in the 'normal waterline. Getting weight OFF the boat helps return the boat to float at the designed waterline.
The people being unable to understand that 'just because you can physically fit on 10 more pax does not mean you should. Some people just keep adding pax until they have the 'whole guest list' aboard. And, no boat I have ever run has the pax count depending upon FULL fuel tanks. Quite the opposite. Empty is worst case scenario, and that is how pax count is determined.

People operating boats and trying to decide on how many is too many often don't get the whole scheme of things not because they don't want to know, but the answers are very tough to come by unless your vessel has an occupancy plate. (good luck finding that over 20') or unless the vessel has or had a stability letter and documented pax capacity some time in the past.
Here's an interesting read about how many people fit on a 34' silverton.
This seems to be a point of interest for Chicagoan as general information about running a boat.
http://www.boatus.com/seaworthy/magazine/2013/january/capacity-of-large-boats.asp

How is the capacity calculated? Seemingly, the experts assume a hundred-pound (or a bit more) person in their calculations.

Sorta like a pissed off mule - chucks its loot and keeps on a goen!

Britannia said:

Just to be clear - displacement is the same as weight. As Archimedes pointed out, a floating vessel displaces a weight of water equal to its own weight. I see "half load" quoted a number of times. I'm not sure if that means tanks half full? On my boat the combined weight of full tanks of fuel and water total over 13,500 lb.

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Ah...are you sure about that Britt. By my reckoning, (@ 2.2 pounds per kg, your boat would only weight about 6140kg = 6.140 tonne, and my 34ft CHB weights about 8.5 tonne, and your vessel is A Kadey Krogen 54, is she not..? I would say she weighs about 28-30 tonne, i.e. about 60,000 lbs

Sorry, my bad, I see you were just talking about the fuel and water weight - that does feel much more correct...but how close was I in the overall boat weight estimate anyway, just out of interest..?

Peter B said:

Ah...are you sure about that Britt. By my reckoning, (@ 2.2 pounds per kg, your boat would only weight about 6140kg = 6.140 tonne, and my 34ft CHB weights about 8.5 tonne, and your vessel is A Kadey Krogen 54, is she not..? I would say she weighs about 28-30 tonne, i.e. about 60,000 lbs

Sorry, my bad, I see you were just talking about the fuel and water weight - that does feel much more correct...but how close was I in the overall boat weight estimate anyway, just out of interest..?

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Hah! I do recognize with some awe that the weight of my fuel alone is about the same as the weight of my first sailboat - a Catalina 30!

Krogen lists my boat as 67,800 lb displacement. So yes, you were close. Full cruising weight it probably closer to 85,000 lb. I'll make sure I get the weight next time she's hauled.

Richard

Britannia said:

Hah! I do recognize with some awe that the weight of my fuel alone is about the same as the weight of my first sailboat - a Catalina 30!

Krogen lists my boat as 67,800 lb displacement. So yes, you were close. Full cruising weight it probably closer to 85,000 lb. I'll make sure I get the weight next time she's hauled.

Richard

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Geeeezzz - Talk about being weight conscious! - LOL Don't you guys know BIG girls are in these days! Curves... got luv them curves!!