Weight Capacity?? - New Boat User

Discussion in 'Boat Design' started by abmayfield, Aug 3, 2011.

  1. abmayfield
    Joined: Aug 2011
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    abmayfield New Member

    Hi! I've got a question for you. I'm new to dealing with boats and have no idea what I'm doing.

    I'm looking to purchase a boat for my disabled husband. I've had a rough
    time this weekend - we purchased 2 boats and both of them ended up being too small once we got them on the water. He and I are both above 300lbs and the first boat (14' fiberglass fishing boat) sat too low in the water making it terrifying and the second one (15' fishing boat with an outboard motor) ended up actually taking on water because of the weight in the back of the boat and water splashing up into it.

    I'm looking at a 17' Deep V-Hull boat right now, and I'm worried that I will get myself stuck with something else that is worthless to me. Do you have an idea as to the weight limit of this type of boat? Here are photos...

  2. lewisboats
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    lewisboats Obsessed Member

    Most boats have a number on the side by the transom...this is the capacity of the boat. There should also be a capacity label somewhere back there too. If the manufacturer went by CG rules then 1 person is rated at 145 lbs...so you need a boat that is rated for at least 5 persons capacity but preferably 6 to keep from being right at the edge of capacity. That 17 footer looks to have been built for 6 passengers so you should be OK...but check the capacity label anyway. It should read 6 passengers or somewhere over 800 lbs capacity.

    edit to correct a number.
  3. Stumble
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    Stumble Senior Member

    Because of the weight, I would ignore the passenger capacity as suggested by Lewis. But I would also point out that the weight limit on a boats plate is the total amount of weight you can add in people and equipment. So your weight plus ice chest, drinks, fishing gear, food, ect. Most small Jon boats are going to be very close to overloaded, and you might think about going to something marginally bigger like a small bass boat.
  4. daiquiri
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    daiquiri Engineering and Design

  5. Ike
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    Ike Senior Member

    Daiquiri, thanks for linking my site.

    The important persons figure on a boats capacity label is not the number of persons, it is the persons weight. It will read like this, 5 Persons or 600 pounds. The pounds figure is the important one.

    Also look at the Maximum Weight Capacity on the label. It will read like; 1000 pounds persons motor and gear for an outboard boat or 1000 pounds persons gear for an inboard or sterndrive. See http://newboatbuilders.com/pages/labels.html

    As Stumble said, the higher the maximum weight capacity the better for you because that means more people capacity plus all your stuff. But you should not exceed the maximum persons capacity. ( 1. it isn't safe, 2. in some states it can get you a ticket)
  6. lewisboats
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    lewisboats Obsessed Member

    So...in essence...nothing I said is incorrect...correct?
  7. Ike
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    Ike Senior Member

    Correct except the USCG doesn't use 145 lbs per person. They use a formula, maximum persons weight plus 32 divided by 141. I could go into the history behind it but it would put you to sleep. LOL
  8. Submarine Tom

    Submarine Tom Previous Member

    A rigid inflatable boat (RIB) may be one you want to consider. Even a soft bottom inflatable would do you well if you're not wanting to go fast (plane). These vessels have considerable reserve buoyancy far exceeding their rated load capacity usually by two or three times which makes them virtually unsinkable as they remain positively buoyant under most uses. (Unless you're into transporting large quantities of lead, gold or even steel.)

    Another small boat that may suit your needs is the 12' Nucanoe.

  9. DCockey
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    DCockey Senior Member

    Interesting that the average weight per passenger was increased for commercial vessel ratings, but not for under 20' recreational vessels.

    I'd like to hear the story about why the slightly obtuse formula is used, but then I'm sometimes interested in the understanding why regulations are the way they are. My guess is it's somehow related to industry desires.
  10. Ike
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    Ike Senior Member

    First you are talking apples and oranges. The persons capacity for commercial vessels and recreational boats are based on two different ways of rating boats.

    Commercial boats use stability as the criteria for the maximum number of people. They perform a stability test to determine what weight of people based (now) on 185 lbs per person will result in a capsize. (that's exactly what happened in the Ethan Allen case) See How Many People Is Too Much? http://newboatbuilders.com/docs/safeloading.pdf

    Recreational boats base the persons capacity on how much weight it will take to sink the boat, or what is called displacement weight. That weight is divided by 5 for outboard boats, and 7 for inboards and sterndrives. Manually Propelled boats use 3/10 of the displacement weight. Then persons capacity in pounds is determined by subtracting the weight of the outboard. (the highest current production weight of all outboards of the rated horsepower, not the weight of the outboard on the boat)

    For inboards or sterndrives Persons Capacity can be up to the same as Maximum Weight Capacity but most manufacturers down rate this number for gear, coolers, etc.

    For boats with less than 550 lbs maximum weight capacity there is a stability test that can be done as an alternative to calculating the weight but they should work out nearly the same. You put weight on one side until water comes in, then divided that weight by 0.60 to get persons weight.

    For manually propelled boats, Persons Capacity is 9/10 of the Maximum Weight Capacity (for a discussion of this see Building A Sailing Pram http://newboatbuilders.com/pages/Dinghy-3.html

    (See http://newboatbuilders.com/pages/load.html)

    Then you find the number of persons.

    History: Actually all of this goes way back to tests done by the British on lifeboats to determine how many passengers to fit in a lifeboat, back in the 20's and 30's. Then in the 50's and 60's the industry and the USCG together did a lot of testing of small boats to determine what was a safe load. After the Federal Boat Safety Act Passed in 1971, the USCG collected a lot of data on existing boats and what capacities they were using, and they conducted a lot of tank tests to see if they were realistic. They then did a statistical regression analysis to determine a correlation between all the data. (you'll have to ask a statistician what all that means.) Out of all the studies and the statistical analysis came that formula.

    Some in the industry have complained about it over the years but it does provide what is a good safety factor for recreational boats, and it provides a level playing field because they all have to use the same formula.

    The other factor here is that the important figure is the maximum persons weight, not the number of people. This is hard to explain to a LEO on the water seeing 10 people in a boat rated for 8, but 6 of those are kids weighing less than 100 pounds. But anyway the number that should not be exceed is the weight. Of course if you have ten and the label says 8 almost every state has a law saying you can't exceed the numbers on the label, so you'll get the ticket anyway and those six kids better have on lifejackets!

    The USCG cannot (not will not, cannot) cite you for exceeding the numbers because under Federal law those are a manufacturer requirement, not an operator requirement. However, if in the judgement of the boarding officer the boat is overloaded (say 10 full grown adults on that boat) then you will get cited for Negligent Operation. But if nothing appears to be a danger they will probably just tell you don't exceed the numbers, and go away.

    And you are right the industry is very involved. The USCG participates with the industry (and any interested party for that matter) in the American Boat And Yacht Council which is the industry standards association for boats. See htpp://www.abycinc.org, with other standards Societies dealing with boats, such as UL, SAE, NFPA, ISO and so on. Many of the regulations are taken directly from industry standards (and Vice versa) But no regulation gets into law without public participation. There always has to be a comment period, and sometimes public hearings before a final rule is written. And of course those fools on the hill get to have their say as well.

    PS: Sorry: Long answer to a short question
    Last edited: Aug 4, 2011

  11. Wynand N
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    Wynand N Retired Steelboatbuilder

    Being retired from boating, I still survey and issue COF's for boats (leisure use under 9 meters) part time to put some jam on the bread.
    I use a simple rule of thumb method for persons allowed on the COF and it goes like this;
    One person per meter of boat. :cool: For example, <4.4m = 4 persons and lets say >4.6 = 5 persons.
    OK, what about the .5 number? If the boat err on the light side of displacement is defaults to the lower number and the bigger hull to higher number.

    If people sat close to transom and engine, any small boat will have flotation problems at the stern. Moreso if it has a big outboard motor...
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