Reasonable Payload for a 40' Mono

[HankOnthewater]

Originally Posted by KISS

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.
Thanks in advance

I think your immersion factor of 1 inch for 1995 lbs (approx 1 cm for 400 kg) for a 39 ft boat with a waterline of 31 ft, is a bit optimistic.

I think all previous posters has been correct, even the very succinct short answer of "3 tonnes".
The reality is that most people that spend long periods of time on board, carry too much stuff and then raise the waterline, sometimes more than once. Generally, from what I have seen and done, the waterline is then not raised a single inch, but 2 or 3 ... or even 4.
If you don't want to do that, you have a further 3 options, with option 2 being the raising of waterline:
1. scrub the waterline often
3. move a few tonnes back onto land
4. or buy a bigger boat

And with option 1 and 2, just cop the performance drop of your boat.

[Dockhead]

Originally Posted by CaptsWife

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'.

I am sincerely curious -- what does "just sayin'" mean? Does it mean that you said something, but you don't intend to convey any meaning? I must be the wrong generation to feel what this means.

Extra weight might make a boat faster if the boat was tender to begin with, and if the weight is added to the bottom of the keel, or well below the CG, but otherwise -- hmm. It would be like putting bags of sand in the trunk of your BMW and saying it drives faster now. Except that it's even worse on a boat if you are adding things like towers and dinghies which add windage.

Weight increases immersion which increases friction and increases the amount of power required to go a given speed. Even if you are adding weight to the keel, this same thing happens due to immutable laws of physics. Only lowering the CG by adding weight to the keel allows you to carry disproportionately more sail which means you might in many cases be able to make the boat faster by increasing sail area disproportionately to the weight increase.

But hanging a tower and dinghy off the "ass end" (charming terminology) of the boat, and adding a bunch of batteries, to make it go faster? Mmm, no. Just sayin'.

[KISS]

Originally Posted by HankOnthewater

I think your immersion factor of 1 inch for 1995 lbs (approx 1 cm for 400 kg) for a 39 ft boat with a waterline of 31 ft, is a bit optimistic.

You're right, I miscalculated.

(LWL x B x 0.67) x 5.33 = pounds per inch immersion

I forgot the 0.67.

So it should be 1290lbs, not 1925lbs.

At that rate, 2500lbs should sink it 2 inches: 3500lbs, 3 inches.

Originally Posted by Dockhead

There should be design information which indicates maximum loading.

It might be in the plans available for purchase; I don't have those.

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.

What would be your target weight?

[AKA-None]

Oh and don’t forget that where your water line is depends on what water your in and what time of year it is.

[Jim Cate]

Originally Posted by AKA-None

Oh and don’t forget that where your water line is depends on what water your in and what time of year it is.

Would you care to expand upon this statement just a bit, please?

Jim

[StuM]

Originally Posted by Jim Cate

Would you care to expand upon this statement just a bit, please?

Jim

Possibly a misunderstanding of the purpose of a Load Line?

[TrentePieds]

Not so much a misunderstanding of the principles, I would think, as a mistaken belief that they matter in a practical sense for yachts.

TP

[Suijin]

Originally Posted by Jim Cate

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"!

Jim

I said "factory waterline" not "design waterline". That's my whole point.

I know where that is on my boat after taking down both the bottom and the topsides in recent years. She floats pretty much on it.

I'm a fairly minimalist cruiser so I don't have a lot of added stuff on the boat. Two solar panels on the bimini, an 8hp motor on the pushpit and a dinghy on deck. No generator, AC, water maker, etc. Weight wise, she's not much over what what came out of the factory.

My point was that the designer's spec'ed displacement is not what comes out of the factory, even in a minimally equipped boat, at least for older semi-custom boats. Look up the specs for my boat and it universally says 22k lbs. Valiant 40s were built in two different yards, with a ton of changes throughout their run of @ 150 boats. I'm sure the "design waterline" and the "factory waterline" were two different animals.

Yes I'm sure a Beneteau Oceanis 41.1 coming out the door is pretty close to the spec'ed weight, but not older blue water boats.

[hellosailor]

Stu-
Have you ever seen a full set of load lines like that, on a YACHT? Not a megayacht, just speaking of the typical 28-45' recreational privately owned yacht?

[Jim Cate]

Originally Posted by Suijin

I said "factory waterline" not "design waterline". That's my whole point.

I know where that is on my boat after taking down both the bottom and the topsides in recent years. She floats pretty much on it.

I'm a fairly minimalist cruiser so I don't have a lot of added stuff on the boat. Two solar panels on the bimini, an 8hp motor on the pushpit and a dinghy on deck. No generator, AC, water maker, etc. Weight wise, she's not much over what what came out of the factory.

My point was that the designer's spec'ed displacement is not what comes out of the factory, even in a minimally equipped boat, at least for older semi-custom boats. Look up the specs for my boat and it universally says 22k lbs. Valiant 40s were built in two different yards, with a ton of changes throughout their run of @ 150 boats. I'm sure the "design waterline" and the "factory waterline" were two different animals.

Yes I'm sure a Beneteau Oceanis 41.1 coming out the door is pretty close to the spec'ed weight, but not older blue water boats.

OK, point taken. Query: how did you determine where the "factory" WL was? And if there is so much variation between examples of semi-custom boats, how would the factory itself determine where that line was?

And finally, while I can understand some variation in build weights, 8000 lbs increment in a nominal 22000 lb (a 36% increase) is very hard to rationalize. It would have a HUGE impact on performance and on AVS curves. I wonder if Bob Perry would comment on that if he were still here on CF?

Jim

[barnakiel]

If you start adding the load low down, you limit is how much freeboard you wish to carry.

However, few modern cruising boats are built this way. You add weight HIGH and then plenty of things change.

BTW a classic (deep) hull with plenty of load added becomes a pig too, so I think the idea is to add as little as one can.

Cheers,
b.

[TrentePieds]

The OP re-did his numbers and, on revision, came to a plausible PPI, viz 1,290 lbs. I get something like 1,120, using .65 rather than .67 for the CWP, so we are close enuff. Again, using "close enuff", a half ton of cargo will settle a ten-tonner 1". I've no idea where the 8K lbs came from, but, as it happens, that weight is basically equal to a ten-tonner's ballast.

I smiled a bit at the pat "three tons" answer Boatman gave. Tongue in cheek, I'm sure, and prolly rolling his eyes as well ;-)

Three tons would settle a ten-tonner 6 inches. Carioca, which is the particular boat under discussion, has a freeboard, it appears from the plans on HolyMotherNet, of about 40”. That means inter alia that she floats quite high, and that cargo must therefore of necessity be stowed quite high. Settling her 6” with all of the cargo stowed high would not be too swift of an idea, I wouldn't think, let alone the 8” the 8K lbs implies.

The OP might like to make mental note that almost any 10-tonner, or put another way, almost any 40 footer, will settle an inch for every half ton taken aboard. I recommend developing a continuous awareness of total weight of cargo aboard at any given time. No need for serious accuracy. A hundredweight more of less doesn't really matter, but a reasonable notion is nice to have.

Don't think I ever told you this: As you know, we got TP for cheap because the PO was pretty clueless and had made “improvements”. First time we had 'er on the hard, I was squinting at the boot-top thinking “that can't be right”. But that's how she floated. Well, when I came to inspect the ground tackle I found at the bottom of the chain locker three lead ingots at about 45 or 50 lbs each whose raison d'etre apparently was to hold down the drainage grating to which the bitter end was held by a MILD steel shackle! In a five tonner, that 150 lbs right forward matters!

TP

[AKA-None]

Originally Posted by TrentePieds

Not so much a misunderstanding of the principles, I would think, as a mistaken belief that they matter in a practical sense for yachts.

TP

Well if you’re punting on calculating the water line based on hypothetical Hull shapes then you might as well consider the buoyancy of the water.

[2big2small]

Originally Posted by Jim Cate

Query: how did you determine where the "factory" WL was? And if there is so much variation between examples of semi-custom boats, how would the factory itself determine where that line was?

Hallberg-Rassy has a nice way to determine the, wat I would call “cosmetic,” waterline.

They build the boat and add the options such as generator etc, then they put it in the water and just mark the waterline, which will be different for every combination of options. These marks determine where they stick the striping and maybe other cosmetic details. As a consequence this also determines up to where the antifouling will reach.

[Suijin]

Originally Posted by Jim Cate

OK, point taken. Query: how did you determine where the "factory" WL was? And if there is so much variation between examples of semi-custom boats, how would the factory itself determine where that line was?

And finally, while I can understand some variation in build weights, 8000 lbs increment in a nominal 22000 lb (a 36% increase) is very hard to rationalize. It would have a HUGE impact on performance and on AVS curves. I wonder if Bob Perry would comment on that if he were still here on CF?

Jim

Valiants came out of the factory painted. My boat had never been repainted. Taking down the existing paint confirmed that. I repainted her along the same line. She does ride slightly low from a practical perspective, with the bootstripe about 3" above flat water. Wish it was higher just so it stayed cleaner.

I'm not saying that the actual factory weight was 8000 lbs. over the design weight...4000 lbs of that is fuel, water, and gear. Let's say there was 1000 lbs. of fluid just for arguments sake in the tanks when she was weighed. So that would put her at 25k lbs. That would put her about 13% over her design weight.

As for how the factory would track this, and what Bob Perry would say about it, I have no idea. Maybe I'll ask him over at SA. But the fact of the matter is that boats came out of the factory with a significant difference in gear and displacement. I rafted up with a V42 a few years ago which had everything but the kitchen sink on it (generator, water maker, dive compressor, 300' of 3/8" chain, and redundant systems throughout), installed at the factory and I stepped down onto the boat quite a few inches.

My point was simple. Don't assume when looking at an old Brewer that her displacement matches up closely to her specified design weight.