I have been looking at the Class Weight Table for Multihulls:

http://www.ussailing.org/portsmouth/mhweights01.htm

I have a few questions:

1. What does the column "Maximum Added Weight" mean?

2. Is this table useful for determining how much weight a given cat can handle fairly reasonably gracefully?

I'm not a racer. What I would really like is a table that shows the weights a boat can carry reasonably well for recreational sailing...

Jonathan

Manufacturers of beach cats sold in Europe are required to give the maximum load-carrying capacity. Not so in the United States. The attached photo shows how we determine maximum capacity in this country -- in this case for a Hobie Wave.

Thanks Mary ,-needed a laugh today ,

Also recall a report of a total capasity of 26 on the 16 ft cat ,
that ,-"again reportedly " in a swimming pool ,
It then took an hour to reach the other end of the pool ,-so
given the added fat boy rating allowances multiplied it now recieves a rating number of 4076 .
P rating numbers are based on the time it takes to sail distance compared to another sailing team on various catamaran designs . The average winning time per team is recorded and averaged out then categorized by class .
--Some think an individual handicap system --like golf uses would be more benificial and help encourage new catsailors into the sport.
Then use a design rating or combination rating that would help define and categorize cat design and further encourage categorical classes like A s and Formula classes or same categorical rating groups to race together. -Class racing being the ideal fair form of racing as used in Olympics and most all major forms of racing.

Most cat classes have a min weight requirement ,-The H-18 for example had a 290 min crew weight ,-with a max 50 Lb added ,--which means a 240 crew could add 50 lbs of weight and make the min.290 required class rules for racing .

-In P-rating there is also an added category time advantage factor for heavier crews known as the fatboy rule.
There is a warning [ in very small print } not to use this added multiple crew and fat boy allowance time handicap stategy to win on "handicap time " -this mainly due to not having adequate beverage cooler capasity supply per coastal patrol regulations . Min, 4 beverages per person ,* 26 =104 bev. which req . min 250 gallon cooler capasity .

This is really the main reason why we generally see 2 3 or 4 people on most beach cats ,-the cooler capasity regulatory aspect ,-though most all would win any regatta or race using this multiple crew fat boy allowance multiplier strategy ,
though only one very short race per weekend could be run with these multi-crew race teams racing all day ,-all that night ,-and all day Sun with numerous crew replacements to finish the A -C one half mile course ,-but they do have "fun".
joking -

If any want to roughly calc. hull volume of a specific cat ,
water weighs 62 -to 64 Lb s per cu ft .-fresh water -sea water .-To calc volume of hulls ,-designers generally divide the hulls into 10 equally spaced sections along the length.
By taking measurements of each from an ideal waterline depth on the hull its possible to average the volume per length and multiple it by weight of water it is displacing . Designers also use what is termed a P C {prismatic coeffecient number .
That is a comparison of the section staion with the largest volume expressed as a solid per length in comparison to actual hull volume .-many cat hulls have a P C number around 60 to 65 %.
Once you establish ideal waterlines-- weight-- volume -you can then calc how much per inch from there it takes to submerge the hulls lower and lower until you end up like the Wave photo .-Though many hulls continue to flare out towards the deck line to increase volume ,-particularly at the bows and with wl to length overhang -bow curve or angle .
You can also find typical boat measurement of many catamaran classes on the ISAF website
http://www.sailing.org/
Great site ,-free to register ,-they send e-mails and have great info and articles similar to catsailor .

A real quick method may be to measure your boats widest hull measurement at one ft above the bottom and assume a .50 P C --or half that volume ,-rocker profile ect are very different on different designs but this is a safe assumption .
You may find your cat measurement and specs also under the manufacterers web site ,along with ISAF and other sites.
If your 16s hull is 12 inches wide at 12 inch depth -times a 16 ft length average with a p c .50 then you have half or 8 cu ft at 12 inch depth times 64 per which again roughly is 500 per hull .
Given the number of people in the pic this seems about right . Again subtract boat weight and crew weight ,-plus consider the movement of crew weight to one corner ,-add the downward force of sails which increase as the cube of wind speed increases , then add waves and moment -pitch characteristics . --whew .

Include boat -crew -and most importantly beverage weight also in the calc .
The great folks who volunteer for coastal patrol and rescue have been known to give out heafty fines for not having enough beverages on board per requirements
particularly if you do not offer them one ,

hope that helps
Carl

Jonathan,
I just found something on this subject from boating channel.com.
It's supposed to be a rule of thumb way to roughly determine the maximum number of adults that can be carried by a boat less than 20 feet long: Multiply the boat’s overall LOA in feet by the beam, and then divide that result by 15.
(The way I figure it, that means a Hobie 18 can carry 10 adults.)

Hey Mary -

Maybe that formula is intended for single-hull displacement?? You'd have to be pretty good friends with the 9 other folks on that 18!

With two people onboard my TheMightyHobie18 last year, we caught two other H18s that each had 7 people onboard in Charleston, SC. The boats were handling it but waves were constantly coming overtop of the hulls. Before we could transfer some to my boat, a storm came up and since they were very near their launch spot (and I was not) we turned around for home. That would have been a great party! (16 people between three Hobie 18s).

Jonathan,
I'm sorry nobody has yet seriously answered your questions. I was just throwing in some humor because I didn't know the answers. But somebody must know. Have you called any of the manufacturers to ask if they know what a reasonable upper weight limit is for safe sailing with reasonable performance?

Jonathon-
Not sure about the table, but as Mary asserted in her first post boats sold in Europe and Australia generally DO designate a "maximum capacity" which includes people, coolers, gear, etc. So you might try some of the European or Australian manufacturer websites (or E-mail them) to get this information since many of the boats are also sold over here. I know the Taipan site lists this info. for instance. Make SURE it IS the same boat (ie many of the Aus NACRA's are lighter than the same US ones so stands to reason they might have different capacities).

Just a thought-

Kirt

Jonathan,

I think the max added weight in that table is the most weight you will need to add if you are underweight according to your class rules...i.e. if the max added weight is 65lbs, you're minimum class weight is specified at 325lb (the weight of both crew), and you're actual combined weight is 250lbs, the most weight you would need to add to meet the rules is 65lbs (in this case it would only get you to 315lbs). I don't image that max weight is used very often.

What kind of boat do you have? I'm sure we could give you a good idea of what to expect with a certain number of people on board.

Kirt and Mary gave me a helpful way forward - I called Peformance Cats, and they told me there is something called the CE Weight, which is the maximum weight the boat is designed to carry safely with reasonable recreational performance. The guy from Performance Cat said he would look these CE weights up for me and get back with me. I also sent an email to Hobie.

Now if they get back with me, I will post the results...

Jonathan

Jake wrote:

What kind of boat do you have? I'm sure we
could give you a good idea of what to expect
with a certain number of people on board.

We have a Prindle 16. We are currently sailing with two people, weight a total of 360 pounds. I am not sure how to tell when the boat is sitting too deep in the water, but it doesn't seem to be bogging down too much for our undemanding recreational status, but I have nothing to compare to, since this is the only cat we have experience with.

So what would happen if I added another person - say, a 45 pound 5 year old or a 150+ pound teen?

Jonathan

Jonathan-
Just noted you are from Durham- I used to live in Chapel Hill. The local Hobie Fleet used to be very welcoming of non-Hobies (I haven't lived there in ~6 years) and would be a good group to hook up with. You will be fine with the either of the "kids" onboard your P 16 (IMO)- I used to have one and have had up to four adults on it. Space gets a little cramped and weight distribution on the boat is something that's a little harder to control but is really only an issue in higher winds. If you are looking for a boat to handle, say, all these "persons" (2 adults, teenager and 5 year old- your family perhaps??) I would recommend an 18-20 foot boat. If you like the simplicity of the P 16 then a P 18 or Nacra 5.7 or G-cat 5.7 would be good (even a Nacra 5.0 if you want to stay 16 or the Hobie Getaway) if you are willing to deal with daggerboards then a P 18-2, P 19, Nacra 5.2, 5.5, or 5.8 or Hobie 18 (especially the Magnum since it has the "wings" that provide more spaces to "sit") or 20 could be considered.

Hope that helps some-

Kirt

Thanks for the info!

Now if I can figure out how to do a perfect roll-tack with four adults on board....

Jonathan

with all that weight on board, the boat will just coast through the tack! You should find that it tacks very easily. That is, unless you completely overload it with 6 to eight people and keep yourself from being able to build up any speed.