How is USCG capacity rating determined?

[Wdeertz]

The boat I purchased came with a 2008 11.5’ Bullfrog tender (http://www.bullfrogboats.com/utility-yacht-tender-11_5.html). I really like this tender as it’s a tank and almost indestructible/unsinkable. Other than some cosmetic scratches in the polymer collars and slight blemishes in the stainless rails the boats in really good shape for being 15 years old. I challenge any inflatable to provide such longevity.

I’m thinking of replacing the tender with a new model purely to have something more “aesthetically pretty” and also an outboard with EFI. My current tender has a USCG capacity tag of 4 persons/630 lbs with max 30HP. While looking at the website for the current model it list capacity at 3 person/391 lbs. I reached out to the manufacturer and they confirmed the current model is 100% the same as my 2008 model. He said they recently went through a USCG certification and these were the figures provided. He couldn’t explain the different ratings between my 2008 model and the current model.

Does anyone have any insights as to how these capacity ratings are determined? Has there been a significant change in the standards from 2008 that would explain the difference?

I’ve had 4 adults in my current tender and was probably about 700lbs and the tender handled fine. I’ve seen similar sized inflatables with a rated capacity of 6 people/1400lbs.

 

[psneeld]

I believe I have seen capacity plates that list the motor separate from the cargo/people and others where it is combined.

How much does a 30hp motor plus fuel weigh?....near the difference?

Don't try and compare RIBs and solid hull boats, I believe the average inflatable is much higher.

 

[Wdeertz]

I believe I have seen capacity plates that list the motor separate from the cargo/people and others where it is combined.

How much does a 30hp motor plus fuel weigh?....near the difference?

Don't try and compare RIBs and solid hull boats, I believe the average inflatable is much higher.

30HP Honda outboard is about 160lbs. The faceplate gives a total weight of 800lbs with motor/gear. My hardsided tender has more freeboard than a comparable length inflatable with 17” tubes. The interior of my tender is about 44” while most inflatables about the same size are 36”. So I guess the tubes provide more buoyancy. But that doesn’t explain why the rated capacity dropped about 240lbs.

 

[RT Firefly]

Greetings,
America is getting fatter?

 

[Wdeertz]

Greetings,
America is getting fatter?

That would make sense if it was 3 person and 630lbs?

 

[ABfish]

I had a 21 ft. flat bottomed skiff with a listed capacity of 14 persons. Never did figure out that one.

 

[jgwinks]

Greetings,
America is getting fatter?

Actually that is one cause, at least for commercial passenger vessels. The capacities were originally computed using 150# per adult, and a few years ago they changed it to 175#. IMO that's still light. A lot of pax vessels had to either accept the lower capacity or go through remeasurement which is complicated and expensive.
That may have been one reason for changing capacities on small pleasure craft but I doubt it would halve the numbers.

 

[twistedtree]

I looked into this some time ago for reasons that escape me, but I recall there is a formula for the capacity ratings. A little google work should turn it up.


As for the change, maybe the rules/formula changed, or maybe the original rating was incorrect and fixed along the way. That's all I can think of.

 

[Comodave]

Found this, although it isn’t as specific as I would like.

The USCG, ABYC, Canada and ISO all rate capacity for boats under 20 feet (6m)
the same way. It is not based on a specific weight of a person such as 150 or 160 pounds. Capacity on small boats is based on displacement weight. This is the amount of weight it would take to sink the boat. First the displacement weight is determined either by calculation or a test. Then the maximum weight capacity is determined by dividing the displacement weight by five or seven depending on the type of boat. The weight for persons is then determined based on the maximum weight capacity. Then the number of persons is calculated using the formula, persons weight + 32 /141. The important figure is persons weight, not number of persons.

 

[psneeld]

Not sure but in the persons category they may consider "live weight" now.

Can't explain why the manufacturer claimed no change though.

 

[smitty477]

I had a 21 ft. flat bottomed skiff with a listed capacity of 14 persons. Never did figure out that one.

We had a 24' RIB rated for 300hp and 24 people.

 

[Delta Riverat]

My Newport Baja weighs 160 pounds, rated for 20 HP (I'm running 15) rated for 6 people and 1500 pounds.