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Old 27-04-2012, 04:12   #1
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How many kilo's can you carry?

Looking to buy a catamaran and I am not sure how to estimate how much each boat can carry. I understand it is all about the weight of the boat and the displacement. Just recently I was looking at a boat 50ft long with a 26ft beam with an L/B=10.6. The designer told me the max load would be around 1000 kilo's. I asked if the boat was overbuilt and heavy and he assured me it was not overbuilt.
To my way of thinking that boat should be able to carry more like 2500 kilo's.
What part of this do I not understand?
Joe
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Old 27-04-2012, 04:23   #2
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Re: How many kilo's can you carry?

Kilos of WHAT ?????

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Old 27-04-2012, 04:28   #3
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Re: How many kilo's can you carry?

I suppose the Designer knows his boat- I know some Cats in the 35- 40 ft size hold more than 2500 kilos -
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Old 27-04-2012, 05:21   #4
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Re: How many kilo's can you carry?

You can compare different boats' load-carrying capacity by using pounds per inch immersion (PPI), which is the amount of weight it takes to sink the boat one inch deeper on its lines.

According to Ted Brewer ➥ Ted Brewer Yacht Design
http : /www . tedbrewer.com/yachtdesign.html

POUNDS PER INCH IMMERSION (PPI):
The weight required to sink the yacht one inch is calculated by multiplying the LWL* area by 5.333 for sea water or 5.2 for fresh.

* WATERLINE AREA: The area of the LWL, usually expressed in square feet.
It is not always easily obtained but can be calculated roughly for a sailboat by the formula : .67 x LWL x Beam.
It is more accurate if you have the Beam WL rather than the Beam(Max), of course.
LWL x 2 for Catamarans

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.

To approximate PPI, multiply the hull waterline beam times its waterline length times .6 times two (for both hulls) and divide by 64.
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Old 27-04-2012, 06:53   #5
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Re: How many kilo's can you carry?

Payload or whatever the proper word be depends on the design. Look up boat's specs or else ask her designer. The only rule is that too much is bad, multi or mono.

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Old 27-04-2012, 13:41   #6
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Re: How many kilo's can you carry?

Quote:
Originally Posted by GordMay View Post
You can compare different boats' load-carrying capacity by using pounds per inch immersion (PPI), which is the amount of weight it takes to sink the boat one inch deeper on its lines.

According to Ted Brewer ➥ Ted Brewer Yacht Design
http : /www . tedbrewer.com/yachtdesign.html

POUNDS PER INCH IMMERSION (PPI):
The weight required to sink the yacht one inch is calculated by multiplying the LWL* area by 5.333 for sea water or 5.2 for fresh.

* WATERLINE AREA: The area of the LWL, usually expressed in square feet.
It is not always easily obtained but can be calculated roughly for a sailboat by the formula : .67 x LWL x Beam.
It is more accurate if you have the Beam WL rather than the Beam(Max), of course.
LWL x 2 for Catamarans

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.

To approximate PPI, multiply the hull waterline beam times its waterline length times .6 times two (for both hulls) and divide by 64.


Thanks for the reply. You lost me once I couldn't count on my fingers any more. With a waterline length of 49 ft and a WLB ratio of 10.6. 49ft divided by 10.6=4.62ft beam.Beam 4.62times waterline length49=226.38 square feet.2 hulls 452.76 square feet. A one inch high square foot of water weighs 5.34 pounds times 452.76=2418.49 pounds to drop the boat one inch. Ok that can't be right.Well that is what not paying attention in high school gets anyway.Joe
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Old 27-04-2012, 14:15   #7
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Re: How many kilo's can you carry?

All cats are not created equal. A Lagoon 500 (50') has a payload of 6.5 tonnes. What boat are you looking at?
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Old 27-04-2012, 14:27   #8
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Re: How many kilo's can you carry?

Quote:
Originally Posted by Joe Burke View Post
Thanks for the reply. You lost me once I couldn't count on my fingers any more. With a waterline length of 49 ft and a WLB ratio of 10.6. 49ft divided by 10.6=4.62ft beam.Beam 4.62times waterline length49=226.38 square feet.2 hulls 452.76 square feet. A one inch high square foot of water weighs 5.34 pounds times 452.76=2418.49 pounds to drop the boat one inch. Ok that can't be right.Well that is what not paying attention in high school gets anyway.Joe
Joe, that would suggest just over 1 tonne will drop a 49ft yacht an inch. Doesn't sound that far out. Can't help you with the measurements, you guys really need to get metricated to do these calculations.

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Old 27-04-2012, 14:55   #9
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Re: How many kilo's can you carry?

I'm building a 49 foot cat with 12:1 Length to beam ratio. I'm told about 700kg (about 1500 lbs) will put her down an inch.

Our payload is 4 metric tonnes. Or about 9000 lbs. (Recently increased from 3 tonnes by the designer due to popular demand, and poor building practices. He just raised the waterline.)
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Old 27-04-2012, 15:00   #10
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Re: How many kilo's can you carry?

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Joe, that would suggest just over 1 tonne will drop a 49ft yacht an inch. Doesn't sound that far out. Can't help you with the measurements, you guys really need to get metricated to do these calculations.

Pete
When those crazy boat builders stop referring to their models in feeticated terms then I will metricate. Outremer 49, Bahia 46, Lagoon 380, Nautitech 475, Discovery 50, Privilege 615, Fusion 40, Leopard 46, Admiral 38, Voyage 450, etc.........
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Old 27-04-2012, 15:12   #11
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Re: How many kilo's can you carry?

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All cats are not created equal. A Lagoon 500 (50') has a payload of 6.5 tonnes. What boat are you looking at?

6.5 tons sounds very good. I guess payload is also determined by what the designer considers safe, and designers may have differing opinions on safe. Does anyone know if their is a standard designers go by?
The boat? It was a custom built boat from the late 90's. I am not buying it but I still don't want to put down someones pride and joy so it shall remain nameless.
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Old 27-04-2012, 15:15   #12
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Re: How many kilo's can you carry?

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Originally Posted by svquintana View Post
I'm building a 49 foot cat with 12:1 Length to beam ratio. I'm told about 700kg (about 1500 lbs) will put her down an inch.

Our payload is 4 metric tonnes. Or about 9000 lbs. (Recently increased from 3 tonnes by the designer due to popular demand, and poor building practices. He just raised the waterline.)
That sounds more like it.Do you know the waterline length.I would like to see if my crazy math can come close to your designers numbers. Joe
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Old 27-04-2012, 15:22   #13
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Re: How many kilo's can you carry?

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Joe, that would suggest just over 1 tonne will drop a 49ft yacht an inch. Doesn't sound that far out. Can't help you with the measurements, you guys really need to get metricated to do these calculations.

Pete

Born in california. Live in New Zealand.I am in a state of mathematical confussion! Joe
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Old 27-04-2012, 15:45   #14
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Re: How many kilo's can you carry?

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Born in california. Live in New Zealand.I am in a state of mathematical confussion! Joe
Wait till you visit Europe, its all Roman X, V and IIIs
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Old 27-04-2012, 17:04   #15
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Re: How many kilo's can you carry?

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Originally Posted by Joe Burke View Post
6.5 tons sounds very good. I guess payload is also determined by what the designer considers safe, and designers may have differing opinions on safe. Does anyone know if their is a standard designers go by?
The boat? It was a custom built boat from the late 90's. I am not buying it but I still don't want to put down someones pride and joy so it shall remain nameless.
The Lagoon 500 has fat hulls and can carry more. It's probably about an 8.5 beam ratio. Yours at 10.6 would theoretically have less payload because the boat would just sink too low. I figure your payload is around 4000 to 6000 LBS. All that cruising crap would be a deduct from that. Get rid of the washing machine and the Harley.
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