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Old 28-05-2018, 01:51   #1
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Reasonable Payload for a 40' Mono

As an example, here's Ted Brewer's Carioca 40:

LOA---39' 6"
LWL---30' 9"
BEAM---11' 10"
DISPLACEMENT---20,500 lbs
DESIGNED TANKAGE---85 gal. diesel, 125 gal. water
POUNDS PER INCH IMMERSION (calculated not listed): ~1925

The payload isn't listed, nor is it clear whether the listed displacement refers to a stripped-out boat, partially-loaded boat, or fully-loaded boat, though I assume it's half-loaded (whatever exactly that means in terms of lbs).

If I filled the ~1640lbs of designed tankage and added 300lbs of crew (at which point the boat would surely still be above its designed WL), how much additional weight do you think I could add without significantly affecting speed or stability? I'd want to add at least another 2500lbs, preferably 3500lbs.




Carioca aside, does anyone have or know where I can find designed payload figures for similarly-sized heavy displacement boats? Also, if you've had a comparable boat, how much did you find you could load it before you noticed a difference in performance?


Thanks in advance
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Old 28-05-2018, 02:31   #2
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Re: Reasonable Payload for a 40' Mono

There should be design information which indicates maximum loading. Note also that it is very important for stability WHERE the load is placed. You would not want a ton of load on the deck of a 10 ton boat with a high freeboard, for example, stating the obvious.

A couple of tons of load not counting tankage should normally be allowed for a 10 ton light ship boat, but ASK THE DESIGNER to be sure. But don't forget that whether it is allowed or not is not the only question -- all weight always degrades sailing performance. An extra ton of load on a 10 ton boat can seriously reduce performance. If that load is poorly distributed (too high or too much in the ends), it can have a negative affect on stability and boat motion, and load in the bows generally hurts pointing ability.

If you plan to carry around that much stuff, you might really consider a bigger boat.
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Old 28-05-2018, 03:23   #3
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Re: Reasonable Payload for a 40' Mono

You can use the Sail Calculator to look up sailboat dimensions in a large database of boats or enter your own boat's dimensions and compare it to the others. In addition, for any boat you can calculate a set of values that will help you measure how it will perform.
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Old 28-05-2018, 04:26   #4
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Re: Reasonable Payload for a 40' Mono

If youíre going to use it as a recreational, even liveaboard boat, and not as a cargo, then my experience has been that you can fill every nook and crany of bilge, locker, lazarette, etc. space without noticeable impact. You can even completely fill a berth with stacked bins.

If youíre going to live aboard thatís exactly what's going to happen anyway, regardless of boat size. It doesnít matter what you calculate. Been there, done that, on a 27, 36, and now 49í boat.

Where you quickly will feel an impact though is when your hull isnít clean. That should be your primary focus if performance is very important to you.

Btw I kinda like a heavier boat in heavier weather. The waves have less stopping power, or more exactly you have more inertia to pound through. But admittedly in light winds you're going to be dead in the water sooner. For anything in between there's no noticeable difference.

You do have to pay attention to trim and where you put the weight on a 40 footer. On my 36í I used to drain the forward water tank first if I expected to go mostly with the wind, or the back tank first if pointing 90 degrees or higher. Weight in the front did help that boat *a lot* to point higher and punch through waves. Every boat is different and it wouldnít take much experimentation to figure out what would make yours happy.
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Old 28-05-2018, 04:41   #5
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Re: Reasonable Payload for a 40' Mono

You should take the factory displacement figure with a grain of salt. Brewer had a displacement target but what comes out of the factory is going to different.

My boat has a design weight of 22k pounds. Without the stick, with mostly empty tanks and the chain and most everything else off the boat she tips the scales at 26k pounds. Full tanks adds about 1800 lbs. I'm a live aboard and I think most of the weight associated with that is tools and my beast sewing machine. I don't have a lot of other heavy gear like a dive compressor and tanks and so forth. That said I'm pretty sure I tip the scale north of 30k lbs with full tanks, stick, and gear. Boat rides pretty much on her factory waterline.

I agree that on a 40' Brewer you're going to be hard pressed to add too much weight just with odds and ends on the boat. Now if you go and add 600 lbs. of chain in the bow that's a different story.

I do try and put heavy stuff down low, like extra chain, my backup anchor, etc. Fortunately I have cavernous cockpit lockers so most of it goes down there.
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Old 28-05-2018, 07:30   #6
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Reasonable Payload for a 40' Mono

Stability is largely a matter of where the load is of course, and just from my observation, you canít add any weight without a performance penalty.
It seems however to be linear, although there may be a point that I have not reached where performance falls off of the cliff, but I doubt it. I think a boat just gets slower, and slower the more weight you add, within logical limits of course, Iím not saying add weight to half sink a boat.

The bigger boat option may not be an option to everyone, at some point you have to decide how much performance penalty is the connivence and comfort worth, for us it trumps performance. Others not so much.

Of course some designs are more tolerant to weight gain than other, the designs that tolerate weight better seem to be those that are not considered performance boats to begin with, which begs the question, do they actually suffer less with weight, or since they werenít performance boats to start with, is the drop less noticeable?

I bought our boat and it had zero equipment, just as a swag I think we have added about 4,000 lbs and a lot of windage. She is as stable or maybe more so than she was when she was light, but the performance hit is significant, I have gone with new sails and gone from a 110 Genoa to a 135 and added a code zero, and still I think we donít perform as well as she did light weight, but we want to have a big powerful RIB, Solar panels, generator, Watermaker, big anchors and all chain rode, a few months food and beer on board etc etc. and it all adds up.
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Old 28-05-2018, 08:57   #7
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Re: Reasonable Payload for a 40' Mono

The main factor is the hull form. Boats with high form stability, so relatively flat bottom and broad stern, rely on lifting the bilge turn to resist heel. Initial stability is high but does not increase dramatically as you heel. A more traditional 'hour glass' form will initially heel more then firm up as the keel weight comes into play. They then hit a very high heel resistance point as the lee side starts to bury.
With a traditional form they can take lots of load with little effect on stability. They will eventually start to 'wallow' when overloaded and obviously slow down with increased whetted surface area.
Boats relying on form factor tend to be faster when lightly loaded but if overloaded rapidly loose stability. You need to pay close attention to loading or you loose the effect of lifting one bilge and they can become very tender. Generally the target is 15deg or less of heal. If you start to notice her healing readily even when not over-pressed or starting to roll more then you may be overloaded. Don't think it is necessarily a capsize risk but it can make the boat yaw and become difficult to control, especially on an autopilot.
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Old 28-05-2018, 09:13   #8
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Re: Reasonable Payload for a 40' Mono

Quote: "does anyone have or know where I can find designed payload figures for similarly-sized heavy displacement boats?"

As others have said, the design displacement is a "close enuff" figure, and that given by the designer is normally for the "bare boat", i.e. for the boat launched and floating on her design lines but before the owner and any of his clobber comes aboard. I do not know of any designer that gives "payload" figures. Boats ain't hairyplanes!

Here is how you calculate you own "payload" figures: For any boat, at all, take the LWL in feet given by the designer, and multiply that by the BWL (Beam on the Water Line) in feet. Multiply the result by .65, and you get the area of the waterline plane of the hull, close enuff, in square feet. Now multiply that number by 64 (the weight in pounds, close enuff, of a cubic foot of sea water), and you get the number of pounds you'd have to put aboard to make the boat "sink into the water" by a foot. Divide that number by 12 and you get the number of pounds taken aboard that will "settle" the boat ONE INCH on her lines.

From there on, it's up to you how many lbs you wish to take aboard, i.e. how many inches YOU, as the responsible skipper, will, in your considered judgement, let her settle. Work up a "stowage plan" to list and total the weight of EVERYTHING you take aboard including people, fuel and vittles. A spreadsheet is the easy way to do that. It's a simplified version of what supercargos do in real life.

Stability is, as others have said, separate consideration, and the effect on stability of the "cargo" depends on where you stow it, i.e. on it's placement within the hull. General rule is "central and low", so, at least conceptually, you start by loading the midships bilge and work "out and up". Obviously the interior design of the boat, and the placement of her furniture "as built", will constrain you - which is why I say "conceptually".

It is possible to calculate the anticipated effect on stability of your "stowage plan", but it gets a tad "scientific", and I doubt that in a heavy displacement Brewer design you will come anywhere near any kind of safety limit taking anything "normal" aboard. You'd have to work at it :-)!

You are also likely to find that "fully laden" she will sail perfectly well. Obviously "settling her" will, in theory, degrade her sailing qualities, but I doubt very much that with a normal "cruising load" you'd be able to discern any difference between her performance when "light" and when "laden". You are not going to be racing her on flat water trying to squeeze the last tenth of a knot, or the last tenth of a point to weather, out of her. So let common sense rule :-)!

Do your homework as explained above, and you will find your anxieties quietened. If they are not, get in touch with Unca Ted and discuss your homework with him. He's retired and a bit housebound, but according to his wife (just last week), he is still happy to answer "reasonable" e-mails and telephone enquiries.

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Old 28-05-2018, 09:14   #9
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Re: Reasonable Payload for a 40' Mono

Three tons
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Old 28-05-2018, 09:40   #10
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Re: Reasonable Payload for a 40' Mono

What are you planning on carrying???

If not a lot of square grouper don’t worry about it :-)
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Old 28-05-2018, 10:05   #11
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Re: Reasonable Payload for a 40' Mono

Go ahead and add the extra 3500 lbs, raise the waterline another 3 inches, and enjoy cruising. The admiral will not want to feel that she is sacrificing to live on the boat, and if the admiral ain't happy, ain't nobody happy.

Yes, you will have a speed penalty, especially if the extra weight is in the ends of the boat. You will still have adequate stability margins for going offshore, and I wouldn't spend a lot of time worrying about stability with that boat.
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Old 28-05-2018, 16:04   #12
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Re: Reasonable Payload for a 40' Mono

Quote:
Originally Posted by akprb View Post
What are you planning on carrying???

If not a lot of square grouper donít worry about it :-)
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Old 28-05-2018, 16:05   #13
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Re: Reasonable Payload for a 40' Mono

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Originally Posted by donradcliffe View Post
Go ahead and add the extra 3500 lbs, raise the waterline another 3 inches, and enjoy cruising. The admiral will not want to feel that she is sacrificing to live on the boat, and if the admiral ain't happy, ain't nobody happy.

Yes, you will have a speed penalty, especially if the extra weight is in the ends of the boat. You will still have adequate stability margins for going offshore, and I wouldn't spend a lot of time worrying about stability with that boat.
^^^^^
This is the reality of cruising! A row around any distant cruising anchorage will reveal plenty of boats that float well below their factory LWL. They all got there...

It's only on the internet that cruising boats sink from overloading!

And yes, there will be a performance loss, and perhaps not so insignificant as some predict. I know that simply filling our tanks (800 L water, 600 L diesel) on a 44 foot LWL knocks nearly a knot off of our motoring speed at our standard cruising RPM. Read into that what you will,but to me that ain't insignificant.

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Old 28-05-2018, 16:08   #14
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Re: Reasonable Payload for a 40' Mono

Look, this is all too technical for me, but I can only say that when the Captain added the extra batteries for solar, the tower, our dinghy, etc, to the ass end of our boat, our waterline sank, especially at the stern. People said we would not sail well. We sail faster now, with less heel, than we ever have. Just sayin'.
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Old 28-05-2018, 16:10   #15
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Re: Reasonable Payload for a 40' Mono

Quote:
My boat has a design weight of 22k pounds. Without the stick, with mostly empty tanks and the chain and most everything else off the boat she tips the scales at 26k pounds. Full tanks adds about 1800 lbs. I'm a live aboard and I think most of the weight associated with that is tools and my beast sewing machine. I don't have a lot of other heavy gear like a dive compressor and tanks and so forth. That said I'm pretty sure I tip the scale north of 30k lbs with full tanks, stick, and gear. Boat rides pretty much on her factory waterline.
I don't see how you can believe that with 8000 lbs over her design weight your boat could possibly float on her design WL. That just ain't possible, or else Archimedes will have to rescind his famous "Eureka"!

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