What determines boat capacity?

salmonee

Chief Petty Officer
Joined
Jun 26, 2008
Messages
408
I saw two boat similar in size but very different in capacity. Boat #1: 18'6", 7'6" beam, capacity 1250#. Boat #2: 18', 8' beam, capacity 850#. Both boats spec are very similar to one another yet boat #1 has 50% more capacity. Why?
 

Whoopbass

Senior Chief Petty Officer
Joined
Jun 29, 2006
Messages
653
Re: What determines boat capacity?

A dartboard and dart.
None of it makes any sense. Some boats i've seen would have trouble handling the rated capacity and others could probably handle double the rated capacity.
I don't pay any attention to those stickers.
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
Joined
May 19, 2001
Messages
26,053
Re: What determines boat capacity?

http://www.uscgboating.org/

Some manufacturers will not risk anything. The lawyers, the safety people. the USCG all work together to keep things safe in the event of an insurance claim.

The beam and length of a boat can be identical but one may have lower profile and designed for a lake and the other the ocean. I consider the depth to the water's surface, length of a motor shaft too. A 15" transom will not be as safe as a boat with a 20-25" deep one in certain conditions.
 

salmonee

Chief Petty Officer
Joined
Jun 26, 2008
Messages
408
Re: What determines boat capacity?

These two boats are very very similar. The second one is a higher end builder. My reason for asking this question is not to get ticketed for having too many people on a boat that is fully capable? This is my first boat so am not sure of the rules and reg.
 

CaptNCamille

Petty Officer 2nd Class
Joined
Apr 23, 2009
Messages
107
Re: What determines boat capacity?

See the USCG website above. It 's a complicated formula base on size, wieght, bouyancy etc.
 

RotaryRacer

Lieutenant
Joined
Jul 18, 2004
Messages
1,361
Re: What determines boat capacity?

Are you looking at the same capacity on each boat?

There is the number of passengers (and passenger weight) a boat is rated for and then there is the total load capacity. On a typical USCG decal the # of passengers is in big bold letters and under it in smaller writting it states the total cacpacity with people, motor and gear.

Example:

P8190698Medium.jpg
 

H20Rat

Vice Admiral
Joined
Mar 8, 2009
Messages
5,204
Re: What determines boat capacity?

**deleted**
 
Last edited:

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: What determines boat capacity?

There are a lot of myths about this. A lot of uninformed cynicism, too.

Most important difference? What will this hull keep afloat when fully swamped?
 

Expidia

Commander
Joined
Aug 26, 2006
Messages
2,368
Re: What determines boat capacity?

Also keep in mind most of those capacity rating plates on the older boats were calculated with the weight of 2 stroke O/B's.

You would think they would force people to replace the old capacity plate with a new one that the manufacturer could send to the new owner. Not much of an issue with the newer boats, but what year did the manufacturers start calculating the much heavy 4 strokes into their their boat capacity plates?

My opinion is that those plates should be updated when someone re-registers it for the weight of 4 strokes.

Take the plate that a poster took a pic of above. Says 850 in total.
So 4 people at an average of 180 lbs equals 720 lbs.
Next throw on a 35 hp 4 stroke and add on another probably 180 lbs and you are over 900 lbs without any gas or gear.

Who even knows what formula they have now come up with to calculate the new boats? They certainly are not doing anyone any favors for safe operation by allowing all those old capacity plates to be left on all of the older used boats.

I'd like to see it mandatory to have a dealer rivet on a new plate when ever someone upgrades their O/B on a used rig.
 

Tommy in FLL

Seaman Apprentice
Joined
Apr 10, 2009
Messages
44
Re: What determines boat capacity?

I think the various posters on this thread are correct when they posit that the boat manufacturer wants to avoid liability lawsuits.

[Sorry, but I have to say that we need SERIOUS tort-reform legislation in this country!!!!]

I wonder if boat manufacturers limit loading based upon model. Perhaps a fishing boat or bow-rider will have a much-limited max loading, while a ski-boat, since it presumably is less-likely to carry a bunch of friends...might be allowed to carry what it's hull is really capable of.

-Boeing pulls the same thing, though for a financial reason, with their airplanes.

I fly jets for Fedex, and one of my previous airline jobs was flying 747's for Kalitta Air, an all cargo airline out of Ypsilanti, Michigan. We had 15 airplanes, and each one of them was different. What amazed me was the fact that N704CK had a max takeoff weight of 802,000 pounds, while N714CK had a max takeoff weight of 833,000 pounds. 704 had engines that developed 55,000 pounds of thrust each, while 714 had weaker engines- they only made 52,000 pounds each. I was curious about this, asked around the company during recurrent training, and I was told that 704 could EASILY take the greater weight- there was no problem with structural strength. 704 and 714 were exactly the same. The difference was that the airlines that originally bought these planes also bought PERFORMANCE DATA from Boeing. If you paid a bit more....suddenly you could load another 29,000 pounds of freight or human meat. Connie Kalitta, the drag racer who owns the company, refused to pay Boeing the exorbitant sum they demanded. It doesn't matter- on a regular basis, I took off from Hong Kong, used every INCH of the 11,000 foot runway, pulled the plane off the pavement at the last possible moment...and then just barely climbed. Thankfully, we were usually headed west, towards Macau and a large expanse of water, so only the fishermen were scared when the 231 foot long airplane passed about 8 feet above their heads at 250 mph.

Yes we were overloaded on a regular basis. Overloading anything is a BAD idea...trust me!

T
 

This_lil_fishy

Master Chief Petty Officer
Joined
Jul 23, 2008
Messages
841
Re: What determines boat capacity?

This is all very interesting. My boat clearly states 9 passengers, I'd be damned if I'd dare load 9 adults into it and head out on the lake. Also the tags are woefully misleading, seriously, 4 people or 475pounds? That's 118.75 pounds each...um...the only person I know that weighs near that is my wife. Other then that I am 170, my friend is about 225, so the two of us would max your boat with a cooler of..um...water and ice...yeah that's it...water..in case we get thirsty.


Ian
 

sickwilly

Lieutenant Junior Grade
Joined
Jul 9, 2007
Messages
1,089
Re: What determines boat capacity?

I called out Department of Wildlife Management in Tennessee about capacity and was told that, at least in TN, you can get a ticket with many less "adults" than specified, as well as not get a ticket with more than specified. The officers in this state supposedly make a determination based on how they are seeing the boat run and sit in the water. Add this to the confusion about the capacity plate!

What scares me are some of these newer wake board boats. They have weight large capacities, like 12 adults. Then they throw in several ballast tanks. I have seen a couple that I think are one good wave away from submerging when not planning.
 

superjay

Cadet
Joined
Apr 7, 2008
Messages
28
Re: What determines boat capacity?

I have a 14 foot aluminum boat with a 20hp motor, the capacity says something like 4 persons max 800lbs, 1050lbs with motor,gas, gear etc....

I wouldn't dare put 4 people in my boat or come near to that 1050lbs, even with 3 people coming in around 600lbs the boat doesn't feel to good even with a little bit of chop.
 

salmonee

Chief Petty Officer
Joined
Jun 26, 2008
Messages
408
Re: What determines boat capacity?

Both boats are relatively new. Boat #2 is '07 and boat #1 is '03. The capacity plate numbers I'm referring to are the big bold black letters so yes I'm comparing apples to apples. Both hull are self bailing as well.
 

fgough

Recruit
Joined
Sep 17, 2005
Messages
4
Re: What determines boat capacity?

Most manufacturers post limits of no more than 75% of max. Here's the USCG formula for maximum legal HP. Max legal persons or weight capacity is different.

The formula for vessels to 26' is this:
(LxWx2)-90 rounded to the next higher 5hp increment

L= Length = LOA rounded to the next higher foot measurement. LOA also includes any permanently attached accessories such as swim platform, transom bracket, etcetera, and also includes outdrive on sterndrive boats.
W = Width = Beam at the transom rounded to the next higher foot measurement

So for my 1972 SeaCraft Seafari, 19'8" hull length, plus 17" swim platform, plus 12" anchor pulpit = 21'15" = 22' LOA for max capacity HP calculations
Beam at transom is 7'5" = 8' width for those calculations

SO then, (22x8x2)-90=262, rounded up to 265 hp maximum capacity for my boat. And sure enough, the most powerful option for my boat was a 260hp sterndrive. My hull is an outboard and the original decal gave a max OB power of 240hp. Later years of this hull were placarded at a max OB hp rating of 175.
 

H20Rat

Vice Admiral
Joined
Mar 8, 2009
Messages
5,204
Re: What determines boat capacity?

Most manufacturers post limits of no more than 75% of max. Here's the USCG formula for maximum legal HP. Max legal persons or weight capacity is different.

The formula for vessels to 26' is this:
(LxWx2)-90 rounded to the next higher 5hp increment


and to add to the confusion, that formula is vastly wrong even in some cases. My boat is 17 feet LOA, 6.5 wide. it comes with engine options of 175, 210, and 240 hp. (all rated for 6 people) Given the formula above, 130 would be the max.

Of course, this is in a jetboat that is 100% capable of being completely swamped and continue running like nothing happened. (nothing like cruising along at 40 mph and tossing it into reverse. The front end submerges instantly.
 

Lion hunter

Lieutenant Commander
Joined
Apr 9, 2005
Messages
1,529
Re: What determines boat capacity?

It may depend on a manufacturers testing. I think they are allowed to go up to the max based on the CG formula. 1 maker may test their boats and know it can handle the max and tag it as such. To cut costs another maker may not test, just use the formula and rate the boat at a lesser amount to err on the side of safety. Also it may depend on the build of the interior components. I beleive that the rating are based on the hulls only, not what the manufacturer puts inside. They may start out with a hull that is rated for a certain capacity but by the time they add the interior which may be made from materials that add significantly more weight they figure they should derate the boat to compensate for that.
I'm just shooting in the dark here, I don't know if anyone but the maker actually knows. It would be nice if one of them would show up and tell us.
 
Top