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Old 11-26-2014, 04:17 PM   #1
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How much cargo can I carry?

Can't seem to find any topics that address this, so here goes:

We have started flying some supplies from FL to the Bahamas for a group called Bahamas Habitat. Problem is, the plane (Cessna 182) will carry only about 475# of stuff, with my wife and me and enough fuel for there and back.

Our boat, on the other hand (a 43' Gulfstar Trawler) could carry a lot more. I mean, a LOT MORE! Question is, how much? (I think at least a couple thousand lbs, but it might be many thousand pounds - hence the post.) If we can take 100 boxes of dried prepared meals, that's 3,600 lbs and 28,800 meals. Could we take 100? 150? 200?

How does one determine the cargo capacity (weight - I can figure out the volume) of a boat like ours?

Thanks so much,

Brian
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Old 11-26-2014, 04:47 PM   #2
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If we guess at a waterplane of roughly 40' by 13', it will take 2000 pounds to sink her one inch in salt water.

Obviously load the freight as low as possible. Probably the exhaust system will be the limiting factor. You don't want the engine swallowing a gulp of salt water. Also turn off all through-hulls just above the light ship waterline.
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Old 11-26-2014, 05:05 PM   #3
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The specs for our KK42 are 2,000 lbs/in of immersion. That's with 39"2" water line by 15' beam as listed by the builder.
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Old 11-26-2014, 05:27 PM   #4
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If we guess at a waterplane of roughly 40' by 13', it will take 2000 pounds to sink her one inch in salt water.

Obviously load the freight as low as possible. Probably the exhaust system will be the limiting factor. You don't want the engine swallowing a gulp of salt water. Also turn off all through-hulls just above the light ship waterline.
Of course there's a formula for this - doh! (Big boat newbie, obviously.)

RE: your comment about the exhaust system. Yes, our exhaust pipes are just above the waterline, so with enough added weight, they'd be partially submerged. However, once inside the engine room, they go up at least 18" (maybe 24" - I'm not near the boat now so can't measure) before they connect to the actual engine exhaust manifolds. So why would it matter if some water (a couple inches, say) got into those exhaust pipes? Right now, with a following sea and some choppy waves, it seems like some water is getting into them anyway.

Thanks - I really appreciate your input! (You too, Larry M.)
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Old 11-26-2014, 05:49 PM   #5
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Look at all the through hull fittings above the water line, especially bilge pump discharges. See how much rise there is, as on some boats it does not take much for one to siphon or otherwise flow back. Also evaluate the main and gennie exhaust as they can cause trouble.

Just got off a boat last week that was flowing water backward through a bilge pump!!

Otherwise, you should be able to carry a few thousand pounds easy. Put more dense things lower, and make sure that if you start taking rolls, cargo is braced so it can't move around.

Shifting cargo has sunk many a craft!!

You may run out of room before you take on too much weight.

Don't block access to bilges, engine room or anywhere else you might need to go.
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Old 11-26-2014, 06:18 PM   #6
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Look at all the through hull fittings above the water line, especially bilge pump discharges. See how much rise there is, as on some boats it does not take much for one to siphon or otherwise flow back. Also evaluate the main and gennie exhaust as they can cause trouble.
What do you mean about evaluating the exhausts?

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You may run out of room before you take on too much weight.
That's what I'm hoping - I'd love to take at least 100 boxes (3,600 lbs)!

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Don't block access to bilges, engine room or anywhere else you might need to go.
I was thinking about that, too - the trip will take just a day, so I can load up both staterooms, which are low, as well as most of the down galley, without blocking access to anything important.
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Old 11-26-2014, 06:24 PM   #7
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Of course there's a formula for this - doh! (Big boat newbie, obviously.)

RE: your comment about the exhaust system. Yes, our exhaust pipes are just above the waterline, so with enough added weight, they'd be partially submerged. However, once inside the engine room, they go up at least 18" (maybe 24" - I'm not near the boat now so can't measure) before they connect to the actual engine exhaust manifolds. So why would it matter if some water (a couple inches, say) got into those exhaust pipes? Right now, with a following sea and some choppy waves, it seems like some water is getting into them anyway.

Thanks - I really appreciate your input! (You too, Larry M.)
It's just something to be aware of....if the exhaust runs generally uphill with a high riser at the engine you should be fine. Loading can change the trim and if you get bow down significantly water could find it's way forward.....
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Old 11-26-2014, 07:25 PM   #8
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If your 182 can carry 475 lb of cargo doing 120 knots and burning 12 gph, that's 0.42 gallons per nautical mile per ton.

If your boat can carry 3600 lb of cargo doing 8 knots and burning 2 gph, that's 0.14 gal/nm/ton.

Surface shipping for the win! 3 times better than air freight, not even considering that 100LL costs more than diesel.
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Old 11-26-2014, 08:04 PM   #9
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Borrow some capacity. Now before you laugh too much, think of what weight you can reduce. I don't know if your boat has a capacity plate or not. But let's say the boat capacity is 10 people. Make the trip with only two and you've gained 1200 lbs. Let's say your water capacity is 130 gallons. Make the trip with 30. Another 800 pounds. Let's say your fuel capacity is 300 gallons but 200 gives you more than enough plus a reserve. That's another 700 pounds. Let's say the normal capacity for gear and equipment impacting the level 1" was 2000 pounds. Now suddenly you have a capacity of 4700 pounds. i'd allow for some margin but perhaps in that case would feel quite comfortable with 4000 pounds. Now, my numbers are just as an example and may be far different than your boat. Just suggesting you consider all the other weight factors in addition to the potential cargo.
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Old 11-26-2014, 10:09 PM   #10
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Looks like there is scope for some enterprising person calculating and marking the Plimsoll line on pleasure boats.
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Old 11-27-2014, 12:47 AM   #11
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Looks like there is scope for some enterprising person calculating and marking the Plimsoll line on pleasure boats.
I've certainly seen some that looked like they could have used it. The waterline was clearly not as it originally was designed.
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Old 11-27-2014, 09:17 AM   #12
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If your 182 can carry 475 lb of cargo doing 120 knots and burning 12 gph, that's 0.42 gallons per nautical mile per ton.

If your boat can carry 3600 lb of cargo doing 8 knots and burning 2 gph, that's 0.14 gal/nm/ton.

Surface shipping for the win! 3 times better than air freight, not even considering that 100LL costs more than diesel.
AND... when we fly over, it's an over-and-back trip, with maybe one overnight. Taking the boat - we'll stay for a week! Shipping is the clear winner, for sure. (Although flying in the Bahamas is pretty cool, too!)
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Old 11-27-2014, 09:20 AM   #13
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Borrow some capacity. Now before you laugh too much, think of what weight you can reduce. I don't know if your boat has a capacity plate or not. But let's say the boat capacity is 10 people. Make the trip with only two and you've gained 1200 lbs. Let's say your water capacity is 130 gallons. Make the trip with 30. Another 800 pounds. Let's say your fuel capacity is 300 gallons but 200 gives you more than enough plus a reserve. That's another 700 pounds. Let's say the normal capacity for gear and equipment impacting the level 1" was 2000 pounds. Now suddenly you have a capacity of 4700 pounds. i'd allow for some margin but perhaps in that case would feel quite comfortable with 4000 pounds. Now, my numbers are just as an example and may be far different than your boat. Just suggesting you consider all the other weight factors in addition to the potential cargo.
Not laughing at all - in fact, we already thought about some of those things (especially the liquids). We could probably leave 400 - 500 lbs of spares at home (we really don't need TWO spare props and TWO spare shafts, and a spare heat exchanger, and a box full of every electrical connector known to man, and on and on and on...).
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Old 11-27-2014, 11:37 AM   #14
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Not laughing at all - in fact, we already thought about some of those things (especially the liquids). We could probably leave 400 - 500 lbs of spares at home (we really don't need TWO spare props and TWO spare shafts, and a spare heat exchanger, and a box full of every electrical connector known to man, and on and on and on...).
Your biggest issue is finding a way to secure all the cargo. The one thing you must absolutely avoid is shifting of load as that could be extremely dangerous. Think Korean ferry. It only takes one or two boxes to shift and cause others to as well. And while you're replacing pounds of liquids with pounds of cargo, they are not in the same locations so your stability could be impacted.
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Old 11-27-2014, 12:32 PM   #15
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Your biggest issue is finding a way to secure all the cargo. The one thing you must absolutely avoid is shifting of load as that could be extremely dangerous. Think Korean ferry. It only takes one or two boxes to shift and cause others to as well. And while you're replacing pounds of liquids with pounds of cargo, they are not in the same locations so your stability could be impacted.
We'll be sure to load it all as low as possible, and to make sure it can't shift around. And, we'll pick the calmest day we can for the crossing. Fortunately, we'll be on the open ocean for only about 9 - 10 hours, so with a decent forecast, our exposure will be limited.
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Old 11-27-2014, 01:30 PM   #16
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We'll be sure to load it all as low as possible, and to make sure it can't shift around. And, we'll pick the calmest day we can for the crossing. Fortunately, we'll be on the open ocean for only about 9 - 10 hours, so with a decent forecast, our exposure will be limited.
You'll do fine. Just don't use these guys as an example. This is an interisland supply boat we saw a few years ago fully loaded.
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Old 11-27-2014, 01:44 PM   #17
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When you are stowing the cargo remember it can't fall off the floor.
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Old 11-27-2014, 02:40 PM   #18
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You'll do fine. Just don't use these guys as an example. This is an interisland supply boat we saw a few years ago fully loaded.

Larry, pictures like those and literally hundreds others just like them make me realize just how much we overthink crap around here
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Old 11-27-2014, 06:19 PM   #19
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Larry, pictures like those and literally hundreds others just like them make me realize just how much we overthink crap around here
Something about, "We who fear the ocean only get drowned now and then."
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Old 11-27-2014, 06:33 PM   #20
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You will run out of space before you overload the boat I'm will to bet. Between fuel, water, stuff, and people I can change the weight of my 42 ft buy 6000# with out much change. The boat is a displacement hull.
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