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Old 10-05-2021, 08:31   #1
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Actual Weight Database

The displacement of all reputable multihulls (and monohulls) is published information, but actual empty weight is virtually impossible to find. This very important lack of information seems to be of little concern ... due to ignorance??.... within the multihull community.


Any multihuller who doesn't log their boat weight when hauled out... assuming the lift can weigh it, is making a big mistake. This weight should be logged every time along with a description of what is onboard for future reference.


We have an excellent drag device database that is endlessly interesting to read, and contains potentially life saving information, but we have no online database of multihull weights. I would like to see the numbers listed:


Manufacturer's displacement figures
Manufacturer's estimated empty weight .... (usually a deep dark secret)
Owner's actual weight measurements, and what is included in those weights


At the risk of insulting some people's intelligence, it would be foolish indeed to buy a multihull not knowing at least two of these numbers and what they mean.




H.W.
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Old 10-05-2021, 09:02   #2
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Re: Actual Weight Database

My experience with haul out cranes is that the scales are not calibrated or accurate. They are basically used to identify when the boat is fully lifted clear- according to two operators.

For trailerable boats, we take those to certified scales and weigh on the trailer, and then return with empty trailer and weigh it. Boat weight is the difference.

For a large cat, I don't know how you can get an accurate weight. Even what the manufacturers state varies widely for the same model and different years.
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Old 10-05-2021, 10:34   #3
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Re: Actual Weight Database

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Originally Posted by sailjumanji View Post
My experience with haul out cranes is that the scales are not calibrated or accurate. They are basically used to identify when the boat is fully lifted clear- according to two operators.

For trailerable boats, we take those to certified scales and weigh on the trailer, and then return with empty trailer and weigh it. Boat weight is the difference.

For a large cat, I don't know how you can get an accurate weight. Even what the manufacturers state varies widely for the same model and different years.

Of course those numbers are not "accurate" in the sense of a certified scale, but on most large multihulls it's the best you are going to get, and is useful if one keeps that in mind. It should be accurate within a few hundred pounds.


Precision isn't the concern as much as being in the ballpark. It's about bridge deck clearance primarily. A specific loaded waterline in inches of freeboard would be useful in that respect, as would a displacement chart for each inch above or below that mark. It's pretty clear that once the boat is out the door, it's your problem. I doubt that the painted on waterline from the factory is at all meaningful.



This is information that is important to any owner of a multihull..... or should be, yet it is largely ignored because it's "inconvenient".



Multihull Dynamics has a good database, but lists only loaded displacements.... it seems that I'm about the only one who really gives these things any significant thought.



I know for example that the displacement of the FP Maldives 32 is 67200, but I do not know what the boat weighs in any form, delivered, or as a buyer offers it for sale. That figure leaves very little for boat weight, which may be fairly light for it's size due to the foam sandwich construction, but I would still estimate it at about 4500 lbs.... but that is give or take 500 lbs. So my effective payload with that boat might be anywhere from a mere 1500 lbs up to 2500 lbs.......... The weight from a travel lift scale would be a useful ballpark, and something I would insist on having if I were doing a pre-purchase survey on any cat.



Only on owner built boats are design empty and loaded displacements listed, but what do they mean? What is included? Does it include mast, sails, and rigging? Does it include some engine weight? Probably not the the ground tackle, batteries, etc. How about winches, how about stanchions and lifelines? What about the head and tankage for potable water, gray and black water, and fuel?..... and the list goes on and on.


A database of REAL WORLD travel lift weights with a rough description of what's included would not be perfect, but it would be useful.


H.W.
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Old 10-05-2021, 10:46   #4
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Re: Actual Weight Database

The problem with Travelift weights is the beam of the multihulls. The smallest Travelift on which our cat has been hauled is a 150-ton unit. We're getting hauled next month on a 300-ton.

On the last 150-ton haul the operator told me our boat was "really light", his gauge showed 5 tons total weight, and yet I know our loaded displacement is 2x that value. But that is still well down in the < 10% full scale of the lift weight cells and in the area where errors are likely to be large. So, at least in my experience, the weight value I can get from the Travelift is useless.
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Old 10-05-2021, 15:56   #5
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Re: Actual Weight Database

Quote:
Originally Posted by owly View Post
The displacement of all reputable multihulls (and monohulls) is published information, but actual empty weight is virtually impossible to find. This very important lack of information seems to be of little concern ... due to ignorance??.... within the multihull community.
...
Manufacturer's displacement figures
Manufacturer's estimated empty weight .... (usually a deep dark secret)

From the Belize Owner's Manual (deosn't seem too secret to me )
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Old 10-05-2021, 16:37   #6
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Re: Actual Weight Database

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Originally Posted by Dsanduril View Post
The problem with Travelift weights is the beam of the multihulls. The smallest Travelift on which our cat has been hauled is a 150-ton unit. We're getting hauled next month on a 300-ton.
<snip>
So, at least in my experience, the weight value I can get from the Travelift is useless.

Our boat doesn't budge the meter on the 300 ton lift in Port Townsend where we're currently hauled.



We do have the plans for the boat and it's displacement at design water line. By keeping the boat on it's lines, we have a pretty good idea of what it weighs. We also have the weight per inch of immersion so we can judge how much extra we might have on board not that we ever do


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Old 11-05-2021, 02:53   #7
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Re: Actual Weight Database

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Originally Posted by owly View Post
. it seems that I'm about the only one who really gives these things any significant thought.










H.W.
And yet the rest of us seem to get by ok....
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Old 11-05-2021, 06:08   #8
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Re: Actual Weight Database

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Originally Posted by jdazey View Post
Our boat doesn't budge the meter on the 300 ton lift in Port Townsend where we're currently hauled.



We do have the plans for the boat and it's displacement at design water line. By keeping the boat on it's lines, we have a pretty good idea of what it weighs. We also have the weight per inch of immersion so we can judge how much extra we might have on board not that we ever do


Cheers,

You are correct most wide beam cats won't even tickle the needle on a big travel lift.



About the heaviest easily adjustable items on a boat are fresh water and fuel. Ideally starting with empty tanks and reference marks on the waterline fore and aft, port and starboard you could estimate the weight per inch of immersion but unless the tanks sit evenly you will still end up approximating the final value. Of course this figure will only be relevant very close to where you start unless your hulls are barge shaped.


The OP is frustrated by the lack of data but as can be seen there are so many variables it is very difficult and even if it was made a requirement of sale the PR departments would manipulate the numbers in one way or another. VW went to the trouble of writing software to fiddle fuel consumption. Even customs builds where every ounce of resin and sq ft of reinforcement is measured will never yield meaningful results because of the variation of fixtures and fittings. At least in a custom build the designer should know the waterline displacement. Perhaps this is the figure manufacturers should be persuaded to publish.



I have just ordered some new hatches the specs say 7.3kg the box says net weight 10.5 and they actually weigh 8.3. Depending on the size of "your" cut out you may need half a tube (150gms) or two tubes (600gms) of sealant. A variation 7.45 - 11.1 of close to 50%.
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Old 11-05-2021, 06:37   #9
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Re: Actual Weight Database

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Originally Posted by owly View Post
Of course those numbers are not "accurate" in the sense of a certified scale, but on most large multihulls it's the best you are going to get, and is useful if one keeps that in mind. It should be accurate within a few hundred pounds.
Dude, you are so "misinformed" I will say nicely. Listen, I am on a PHRF rating committee, and have been on various ones for multihulls for more than 20 years. Have experimented with several performance prediction models, even modified one that seems to work for us, and guess what - they all have weight as an input. For us, its super important to get weight right, to get performance prediction right. For anyone else, I don't know why they'd care.

But regarding your statement of a "few hundred pounds" accuracy, let me give you some real world examples. We have a Condor 30 in the fleet. Has been pulled at two yards. He's a racer, and doesnt carry anything extra. Same empty boat except there might have been a difference in fuel in the 3 gal tank. One scale said 5000 lbs, one said 7000 lbs. In my math, that is a 2000 lb difference - or 40%. And both could actually be right. But there is your relatively-light boat example.

For even lighter example, where your few hundred pounds example might be accurate. Back in 2003, at Corsair Nationals, the factory showed up with calibrated scales. The F31 Class had decided they were going to weigh their boats and assign handicap based on weight. (Boats had different interiors and decks, but mast and sails identical.) Boats in the fleet ranged from 3300-4000 lbs. Three boats (hulls 221, 220, 162) were weighed in both 2003 and 2004 at the Nationals. Each boat weighed 210 pounds less in 2004. No one knows why, and the very expensive scale had been factory recalibrated weeks before. So that is how ludicrous your statement of only off a few hundred pounds it. This was a controlled weight procedure, with very expensive certified scales.

Re: big cat displacement, look at how many different numbers are published for a model, even just by the manufacturer. Which one is right? You will find sailing mag interviews with one number, online manufacturer lists another, brochure another.

Finally, if you can get in the factory and talked to someone there, many weigh their boats. But you have to dig deeper and find out what stage of the process/completion. For instance, one large cat builder lists a light displacement that if you check into it is before the outboard motors, mast, boom, sails, and some of the rigging is finalized. In their build process, it happens to be the last time they lift the hull, and is their best chance to weigh. This is not unusual, as I've found several that list light displacement that is not for a complete boat. Or worse yet, some are just for a hull with bulkheads and after all of the glass work is done, but before rigging, electrical, batteries, etc. And their normal displacement number reported is even more of a cloud, as typically this is a calculated number with unlisted amount of fuel, water, etc., assumed. Yeah, and you want to trust displacement numbers?

Getting to these weight numbers is important to us, only because we are trying to PHRF rate boats that typically don't have much race data to rely on. But otherwise, I wouldn't bother trying to know, and if I was just a cruiser, I wouldn't care. Keep your boat as light as possible, which will make it sail better/faster, and just don't worry about what your boat weighs. If you want some clue as to what displacement is for a particular boat, look at construction method, and how much interior furnishings there are. Look at how much wood they use, how many systems, how wide and tall are their hulls, etc. No one makes a light cat that looks like a behemoth with 4 berths and 4 heads. Regardless of what displacement number they may publish.
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Old 11-05-2021, 06:43   #10
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Re: Actual Weight Database

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Originally Posted by jdazey View Post
We do have the plans for the boat and it's displacement at design water line. By keeping the boat on it's lines, we have a pretty good idea of what it weighs. We also have the weight per inch of immersion so we can judge how much extra we might have on board not that we ever do


Cheers,
Yep, and I have seen a few of these displacement vs waterline diagrams. Super helpful for us to know what real displacement is for a particular boat. They are very hard to get from manufacturer. In my experience.
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Old 11-05-2021, 19:53   #11
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Re: Actual Weight Database

As noted by Stum most of the french and south african manufacturers owners manuals state the Lightship weight per the CE definition, then add to that the number of persons at 75kg each balance of fuel and water + all the other "stuff" cruisers put on plus margin and you end up at the maximum weight which is often printed on the CE plate attached to the hull.


See attached extract from Lagoon 500 manual - shows the break up in a fair amount of detail.
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Old 12-05-2021, 06:37   #12
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Re: Actual Weight Database

The Lagoon chart is exactly what should be readily available on line for potential buyers of used boats. On newer boats, at least the owner's manual is probably with the boat. With that gone, all you have is the "displacement", which is loaded design displacement. Potential buyers of used craft are "flying blind". Weight is critically important on multihulls, and almost irrelevant on monohulls (within reason). Any pre-purchase survey is incomplete without weight data that gives the potential buyer an idea how much margin he has for loading. A number of older cats have a terrible reputation for pounding, and or a reputation for beam cracks and such, but if and when you do find the numbers... which I have in one case, the difference between the "light ship displacement" as it was termed, and the loaded displacement is so small that it is obvious that with the number of people it was designed to accommodate, and the barest of necessities / supplies for that crew, it would be grossly overloaded. (This was the Iroquois).......... Not a boat that ever interested me, just wondering what kind of payload boats of that era had, it was the only one I could find the info on.



This is not a trivial concern. A recent post stated that the owner had weighed his boat loaded and ready to go, and found that it was 2000 lbs over design displacement, implying that they thought design displacement was the baseline, and the 2000 lbs payload they were rated for was above this, when in fact their 2000 payload should have put them at the design displacement, and they were in fact 2000 lbs over. When we are talking about boats as light as catamarans that often have design displacements that may range from 6k to double that for the smaller cats, 2000 lbs is a huge overload.... It could be overloaded as much as 30% of the weight of the boat.



There is no excuse for travel lifts not having at least somewhat accurate scales. Load cell technology is well developed, and reliable. I have an ordinary (home built) shop engine lift "floor crane" that uses a hydraulic cylinder and electric pump, and have been able to calibrate things that at a specific boom angle and extension, I can work out the weight from hydraulic pressure to within about 10 pounds within it's 2500 lb lift capacity. (yes it's a big one). I would not expect travel lifts to be "certified" scales, but it's not unreasonable to expect that they should be within a few hundred pounds.




H.W.





Quote:
Originally Posted by Tin Tin View Post
As noted by Stum most of the french and south african manufacturers owners manuals state the Lightship weight per the CE definition, then add to that the number of persons at 75kg each balance of fuel and water + all the other "stuff" cruisers put on plus margin and you end up at the maximum weight which is often printed on the CE plate attached to the hull.


See attached extract from Lagoon 500 manual - shows the break up in a fair amount of detail.
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Old 12-05-2021, 07:14   #13
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Re: Actual Weight Database

Using your own example amplified to a 150-ton Travelift 300000*10/2500=1200 pounds. Is that close enough? On a 300-ton lift the error would be twice that.

Looking at it another way, your 10 lb accuracy is 5-10% error when weighing 100-200 pounds, which is where many cats fall on the scale range of the lifts that haul them. Is that close enough?

More importantly, why would a Travelift operator care? Their only real use is to prevent overload. The only reason they would care is if it made a marketable difference that allowed them to either charge more or get more business. And judging by the market, there doesn’t seem to be much monetary interest. So why would a Travelift owner go to the extra expense of installing and maintaining a high accuracy weighing device?

It seems that to tilt at this windmill it would be more reasonable to drive rules that require the boat manufacturer to set permanent, non-removable marks at the full load waterline. This would be far, far simpler for a potential buyer to evaluate - is she floating at, above, or below the design waterline?
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Old 12-05-2021, 09:45   #14
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Re: Actual Weight Database

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Originally Posted by Dsanduril View Post
Using your own example amplified to a 150-ton Travelift 300000*10/2500=1200 pounds. Is that close enough? On a 300-ton lift the error would be twice that.

Looking at it another way, your 10 lb accuracy is 5-10% error when weighing 100-200 pounds, which is where many cats fall on the scale range of the lifts that haul them. Is that close enough?

More importantly, why would a Travelift operator care? Their only real use is to prevent overload. The only reason they would care is if it made a marketable difference that allowed them to either charge more or get more business. And judging by the market, there doesn’t seem to be much monetary interest. So why would a Travelift owner go to the extra expense of installing and maintaining a high accuracy weighing device?

It seems that to tilt at this windmill it would be more reasonable to drive rules that require the boat manufacturer to set permanent, non-removable marks at the full load waterline. This would be far, far simpler for a potential buyer to evaluate - is she floating at, above, or below the design waterline?

I've never been around the really big travel lifts... that's a lot of weight!


I agree that markings on the boat are the answer.....but "permanent" markings do not seem realistic. For them to be permanent, they would have to a physical shape change... a chine or something. What IS realistic and very doable is a permanent plaque with dimensions from the sheer line in specified locations so you could reproduce an accurate loaded waterline, or estimate it with a tape measure. Any engineer's drawings are going to show the displacement at various depths of immersion, so you can calculate from the actual waterline what boat weight is..... of course fore and aft weight distribution complicates that, but interpolation / extrapolation is not difficult.


Of course how often do we have calm enough water to get a meaningful measurement? With today's technology, you could simply have a sensor that measured the distance to the water under the bridge deck and generated the average clearance, and from that a weight. It would be accurate enough over time for our purposes.



The typical boat owner packs more and more stuff aboard.... a wise multihull owner looks for things to get rid of. The basic information is important.


Once the boat is out the door, it's anybody's guess what it weighs....




H.W.
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Old 12-05-2021, 14:48   #15
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Re: Actual Weight Database

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Originally Posted by Tin Tin View Post
As noted by Stum most of the french and south african manufacturers owners manuals state the Lightship weight per the CE definition, then add to that the number of persons at 75kg each balance of fuel and water + all the other "stuff" cruisers put on plus margin and you end up at the maximum weight which is often printed on the CE plate attached to the hull.


See attached extract from Lagoon 500 manual - shows the break up in a fair amount of detail.
Lagoon is quite honest about weight. Looks like others are not. Our boat can easily match performance of typical 45 feet cat. we have roughly 20% less sail area and on paper all these boats are still couple T lighter. Yeah right ! If you believe that then I have news for you : I was born yesterday.
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