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Old 16-09-2019, 09:03   #1
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Cargo Capacity of Sailboat

I have recently pondered making a run over to the Abacos to deliver some post Hurricane Dorian Relief supplies. My boat has a published light ship displacement of 26,500 lbs., with a more representative cruising weight of 32,000 lbs. or so.

When considering a cargo weight (I also have to be full tanks and provisions for autonomous operation since replenishment is not likely at current times) I figured that 500 lbs would be easily accomplished. But, why not 1,000 lbs? Or perhaps even more? Is a ton within reason?

I realize that boat speed/handling will suffer until supplies are off loaded, but how would one make a determination as to maximum capacity, especially as sailboats do not typically have manufacturer's capacity data plates?

Any thoughts?
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Old 16-09-2019, 09:17   #2
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Re: Cargo Capacity of Sailboat

Every boat is going to be different, and loads will vary according to what you’re carrying and how it can be stowed. Lashing heavy stuff on deck could make a boat topheavy - not a good idea. Loose jerrycans of water or fuel below might not be smart either. Loading supplies until the waterline is as far underwater as you think is safe may be the best way to gauge the load you can carry. We set out Transatlantic on a 38’ sloop with the waterline about 4” under because of all the food and supplies we were carrying.
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Old 16-09-2019, 09:28   #3
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Re: Cargo Capacity of Sailboat

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Originally Posted by redsky49 View Post
I have recently pondered making a run over to the Abacos to deliver some post Hurricane Dorian Relief supplies. My boat has a published light ship displacement of 26,500 lbs., with a more representative cruising weight of 32,000 lbs. or so.

When considering a cargo weight (I also have to be full tanks and provisions for autonomous operation since replenishment is not likely at current times) I figured that 500 lbs would be easily accomplished. But, why not 1,000 lbs? Or perhaps even more? Is a ton within reason?

I realize that boat speed/handling will suffer until supplies are off loaded, but how would one make a determination as to maximum capacity, especially as sailboats do not typically have manufacturer's capacity data plates?

Any thoughts?
Where you place the cargo is important as mentioned. Also, you would have to check your boat specs to determine the "pounds per inch of immersion" - this is calculated by the designer and it will indicate how much below the designed water line the boat will float. Some heavy cruising boats has 1"/1000 pounds.
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Old 16-09-2019, 09:31   #4
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Re: Cargo Capacity of Sailboat

For argument's sake, let's assume that the weight is relatively low in the boat, and somewhat centered.
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Old 16-09-2019, 09:37   #5
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Re: Cargo Capacity of Sailboat

The PPI:

"The formula is POUNDS PER INCH IMMERSION (PPI): The weight required to sink the yacht one inch. It is calculated by multiplying the LWL area by 5.333 for sea water or 5.2 for fresh. The PPI usually increases as the hull sinks into the water as the LWL area is also increasing due to the shape of the hull above water."


from https://www.tedbrewer.com/yachtdesig...he%20yacht%20o
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Old 16-09-2019, 09:53   #6
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Re: Cargo Capacity of Sailboat

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For argument's sake, let's assume that the weight is relatively low in the boat, and somewhat centered.
Ant that it will not shift around.
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Old 16-09-2019, 16:21   #7
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Re: Cargo Capacity of Sailboat

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The PPI:

"The formula is POUNDS PER INCH IMMERSION (PPI): The weight required to sink the yacht one inch. It is calculated by multiplying the LWL area by 5.333 for sea water or 5.2 for fresh. The PPI usually increases as the hull sinks into the water as the LWL area is also increasing due to the shape of the hull above water."


from https://www.tedbrewer.com/yachtdesig...he%20yacht%20o

And how to calculate the LWL area?
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Old 16-09-2019, 16:33   #8
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Re: Cargo Capacity of Sailboat

Open the link... The formula is there. Fairly easy and also usefull to calculate how much paint is required.
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And how to calculate the LWL area?
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Old 16-09-2019, 16:37   #9
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Re: Cargo Capacity of Sailboat

A Bristol 41.1 can carry 1535 Pounds per Inch of Immersion.
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Old 16-09-2019, 22:57   #10
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Re: Cargo Capacity of Sailboat

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A Bristol 41.1 can carry 1535 Pounds per Inch of Immersion.
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Thank you Gord. Once again to the rescue. So, with full tanks, but only moderate provisions, I should readily handle 1000 lbs., and even a full ton (2000 lbs. on this side of the Atlantic) could be possible.

Another thing I am considering is that the extended duration of such extreme winds will have obliterated any aids to navigation (such as there are in the Bahamas), but also that any channels may likely be shifted or eliminated. Having sailed most of my life on the Chesapeake I am no stranger to running aground, but there are some hard spots in the Bahamas I would like to avoid. Also there is likely still some debris in the water. And recently weather conditions have been rather breezy up until today - strong winds out of the north (Humberto), which complicates crossing the Stream. And where do you check into Customs now?

So, I am still thinking this over. Thanks to all who contributed!
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Old 17-09-2019, 08:31   #11
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Re: Cargo Capacity of Sailboat

I don’t think that you could overload a “traditional” ballasted sailboat to the point that you’d risk capsizing and/or dramatic decrease in performance. You’ll run out of volume first with any cargo that comes to mind. I had a fifty foot single engine trawler which transported the materials to build a house on Long Island (Bahamas): rebar, bags of cement, concrete blocks etc. that actually did affect performance: from eight knot cruise to about six, but no stability issues. Back in the day, a forty-two-ish foot boat like yours may have transported three to four thousand pounds of Colombias’ finest alternative smoking product. The poor crew would be sleeping on top with maybe sitting headroom to the overhead, but the boat sailed just fine.
Good luck in your relief efforts: remember that Bahamian customs may enforce the existing tax on imported stuff. Your good deed may not go unpunished.
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Old 17-09-2019, 08:39   #12
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Re: Cargo Capacity of Sailboat

Expect a communication from Border Control........
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Old 17-09-2019, 08:40   #13
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Re: Cargo Capacity of Sailboat

As mentioned above you need to find the area of the water plane. As a rough gide you can take the wll x beam x 0.6 (typical block coeficient for a sailboat).
The second and probably more important factor is the hull shape. A traditional 'winglass' hull shape can load up until you are worried about freeboard and will still handle OK if slowly. A modern lightweight canoe boady shape relies in part on the hull form so if heavely loaded will quickly become very tender an may roll dangerously. You heed to make an estimate of where your boat lies on that spectrum.

Some modern boat have a plate stating max load, its compulsary for European boats and on th CE plate. Don't know if they do that for US boats. If you can find a sister ship made for Europe you might get a good idea from that.
To give an idea of the difference my boat is a 32ft traditional shape and faily heavy displacement and she will haapily take an extra couple of tons. I have seen moder charter style boat the same size where the CE plate load limit is less than the weight of my ground takle!!! So be careful.
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Old 17-09-2019, 08:52   #14
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Re: Cargo Capacity of Sailboat

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Expect a communication from Border Control........
Thanks to people willing to help.

We ran into the most trouble with local customs entering with supplies. (Eastern Caribbean) They wanted duty and expected a cut of the supplies. Your good intentions could wind up as black market fodder. You may be limited in what will be allowed in. I highly recommend you work through a proper aid agency to avoid expensive and disappointing surprises.
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Old 17-09-2019, 09:00   #15
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Cargo Capacity of Sailboat

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I don’t think that you could overload a “traditional” ballasted sailboat to the point that you’d risk capsizing and/or dramatic decrease in performance. You’ll run out of volume first with any cargo that comes to mind. I had a fifty foot single engine trawler which transported the materials to build a house on Long Island (Bahamas): rebar, bags of cement, concrete blocks etc. that actually did affect performance: from eight knot cruise to about six, but no stability issues. Back in the day, a forty-two-ish foot boat like yours may have transported three to four thousand pounds of Colombias’ finest alternative smoking product. The poor crew would be sleeping on top with maybe sitting headroom to the overhead, but the boat sailed just fine.

Good luck in your relief efforts: remember that Bahamian customs may enforce the existing tax on imported stuff. Your good deed may not go unpunished.


I personally think this is the most correct answer, sure overloaded it’s going to sail like a slug, but the trip isn’t far and you can almost guarantee good weather for the crossing if you watch forecasts.
Just keep the heaviest items low if possible.
Also watch your engine exhaust, it’s entirely possible to load a boat so that with a following sea you hydrolock the engine. If it’s running its not going to hydrolock, I’d plan on running the motor when it’s overloaded and motorsailing or plain motoring. Or at least plug the exhaust if your determined to not motor.
However I think it may be prudent if possible to have a planned route with a planned place to clear and call first to ensure you can bring in relief supplies duty free.
Just of course do not sell anything, even if your not making a profit, doing that may have you end up under the jail, maybe.
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