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Author Topic:   Interesting swamped capacity spec
prm1177 posted 08-02-2005 07:34 PM ET (US)   Profile for prm1177   Send Email to prm1177  
I found a curious fact going over BW's brochures for the Conquests. The 255 actually has the greatest swamped capacity. The capacity actually goes down in the larger boats. Here's the run down:

CQ 235 - 4400 lbs
CQ 255 - 6100 lbs
CQ 275 - 5600 lbs
CQ 305 - 2200 lbs

Thoughts. Is it a relationship to interior volume vs hull thickness? I remember a paleontologist friend of mine said there was a practical limit to the size of land based animals as their mass went up as a factor of their volume (cube of dimension) while the bone strength was a function of the bone area which increased at a lower rate (2piR). Is this the same factor. The hulls on the larger boats are not as thick relatively to maintain similar buoyancy ratios?

Chuck Tribolet posted 08-02-2005 07:40 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Bone strength goes up with the cross section, or the square
of the radius: Pi*R*R. So if we multiply a chimp by two in
all four dimensions, we get an ape that's eight times
heavier, but the bones are only four times stronger. That's
way gorillas are stocky and chimps are skinnier.

That also means that if you double the size of a boat in all
dimensions, the price goes up by 8x.


prm1177 posted 08-03-2005 10:43 AM ET (US)     Profile for prm1177  Send Email to prm1177     
Thanks for the correction, Chuck. (And I actually got good scores on my Math SATs :) Who'd have thought it? Aren't boat prices logarithmic instead of exponential?
17 bodega posted 08-03-2005 03:32 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
What about the physics of boat strength. In theory, a smaller boat would be stronger tougher to break in half than a larger boat, right? Like a small walnut would be harder to crack than a larger one? I was also thinking of an interesting scenario for being lost at sea.

Imagine you have 30 or so squall sailboats and you were able to link them together by very strong rope lines. If one were to flip, you could easily right one boat while standing in another. You could not do this with a large boat, therefore the same theory stands where you might be safer lost at sea in 10 linked squalls than a larger craft.

some fun thoughts.


prm1177 posted 08-04-2005 11:59 AM ET (US)     Profile for prm1177  Send Email to prm1177     
One last observation. The Outrage 320 has twice the swamped capacity (4800 lbs) of the Conquest320. I suspect all the cabin goodies to be at fault here as they add weight but not buoyancy.
macfam posted 08-05-2005 10:20 AM ET (US)     Profile for macfam  Send Email to macfam     
I think you're on the right track.
It's the cabin area.
I don't think it's the goodies in the cabin, it's that the cabin can hold a great volume of water.
I envision that when you consider "Swamped capacity", the cabin being the lowest part of the boat, would be filled with water. Lots of heavy water
But the only area to hold water on the Outrage 320 is inside the the center console. Much smaller.
So even if the Conquest 305 has scuppers drain the deck area, the cabin would remain full, lowering the swamped capacity rating.
Sounds reasonable to me.
handn posted 08-05-2005 05:11 PM ET (US)     Profile for handn  Send Email to handn     
The 305 Conquest carries 300 gallons of fuel, a generator and air with the cruising package and over 1200 pounds of Verados. Even though the hull has more boyancy than the smaller Conquests all that stuff reduces the swamped capacity.
Hopefully, if a 305 Conquest owner took green water over the stern he would have his deck hatches and cabin door closed. If water didn't get into the cabin or below the deck, the swamped capacity would be much higher.
Plotman posted 08-05-2005 06:00 PM ET (US)     Profile for Plotman  Send Email to Plotman     
I'd love to know what swamped capacity really means - is that the amount of weight that the boat can float with the gunwales above water, have in it and remain stable, what?

When you consider that the engines and gear are easily going to surpass the "swamped capacity" before you start adding people, you really are getting more into the realm of marketing with these bigger boats than perhaps the practical ability to self-recover from a swamping, even if the boat won't sink.

Not sure where fuel fits into the equation as it actually floats - has ~1lb of bouyancy per gallon.


prm1177 posted 08-07-2005 03:28 PM ET (US)     Profile for prm1177  Send Email to prm1177     
Plotman: Swamped capacity is the amount of weight the hull can carry (including engines, equipment and gear) when filled to the gunnel's with water. The boat will float level in calm water with the power heads above water level. Stability is not guaranteed, as in rough conditions any boat can capsize. On my 98 Conquest 23 the swamped capacity is 4500 lbs. My math says after 2 Opti 135s (900 lbs), fuel (125 gallons @ 6.25lbs/gallon), gear (say 500 lbs) that comes to another 2440 lbs which averages to around 10 beefy fishing buddies. Not bad. And no other boat manufacturer I know of publishes this spec.

That said, I never intend to get my self in a situation where I can test this spec.

RocketMan posted 08-15-2005 07:39 PM ET (US)     Profile for RocketMan  Send Email to RocketMan     
I posted the comment below on another thread earlier today because I understood the 2005 Boston Whaler catalogue to state that swamped capacity is WITHOUT engines. Please correct if that is wrong, the catalogue is at the office.

"Back of a napkin gymnastics using 2005 Boston Whaler and Mercury catalogue spec data: Swamped capacity for an open 36' LOA hull extrapolates into the 3000 - 3500 category. One 200 - 275 HP Verado specs out at about 650 lbs, 3x that would be 2000 lbs. dry. Now you have just 1000-1500 lbs. for rigging, fluids, passengers, gear, etc. While a sharper pencil is required, 36' appears to represent quite a challenge and perhaps an outer bound for BW unsinkability using current design and manufacturing technology. Enough now, back to rocket science."

RocketMan posted 08-16-2005 09:26 AM ET (US)     Profile for RocketMan  Send Email to RocketMan     
Last mumble. From the 2005 Boston Whaler catalogue: " Swamped (5) Total weight (persons, motor and gear) boat will support if filled with water." Which means the number listed is for a barehull. Out.
Captain Billy posted 08-17-2005 11:52 AM ET (US)     Profile for Captain Billy  Send Email to Captain Billy     
Can someone tell me why the swamped capacity has dropped in the last decade? My 1992 27WA which also has a cabin is listed as 10,000 lb swamped capacity. Are they using a different method of figuring it now?
prm1177 posted 08-17-2005 01:35 PM ET (US)     Profile for prm1177  Send Email to prm1177     
My guess is that the weight of the boats themselves is increasing. A 2006 17 foot whaler is heavier than its 1995 counterpart. Swamped capacity will be affected by the gross weight of the boat itself.
Captain Billy posted 08-18-2005 09:22 AM ET (US)     Profile for Captain Billy  Send Email to Captain Billy     
According to the specs, the 2006 285 Conquest is 60 lbs heaver than a 1992 27WA.
But the swamped capacity is 7,000 lbs less.
(also the max HP dropped from 600 to 450)
I don’t get it.
prm1177 posted 08-18-2005 03:14 PM ET (US)     Profile for prm1177  Send Email to prm1177     
Hmmm. Sounds like they are either using a different methodology or liability concerns are forcing a much more conservative definition. My 98 CQ 23 has a swamped capacity of 4800 lbs (weight is 2900 lbs) and the 2006 CQ23 has a swamped capacity of 4400 lbs but a dry weight of 3730. New boat is 800 lbs heavier with 400 lbs less swamped capacity. Probably both measurement technique and legal considerations at work here.
Buckda posted 08-18-2005 03:38 PM ET (US)     Profile for Buckda  Send Email to Buckda     
The comment above about how much water the boat will hold has to be part of this equation.

For instance - the newer hulls (outrage series) have much higher gunwales than the classics....

prj posted 08-18-2005 05:17 PM ET (US)     Profile for prj  Send Email to prj     
And the lowest spot on the transom,
the overflow, if you will,
is really the determining factor on water holding capacity.
RocketMan posted 08-18-2005 08:01 PM ET (US)     Profile for RocketMan  Send Email to RocketMan     
Where in the methodology does the variation come from?

The Boston Whaler catalogue lists SPECIFICATIONS, which should be FACTS. No legal interpretation or opinion needed. And swamped capacity is no more complex than archimedes principle. The 2005 catalogue states that swamped capacity is the amount of weight that the boat will float when filled with water. Pretty straightforward so far.

We need a design trade number, so using the back of a local napkin we calculate a trade factor for swamped capacity. We'll use a 25 ft. length by 8 ft. beam one inch deep as rough numbers. To get the weight, just multiply out the dimensions 25(12) x 8(12) x 1 = 28800 cubic inches of water, which is 124 gallons, which is about 1000 pounds. Bottom line: Every inch of additional float is 1000 pounds for a 25 ft. boat, roughly.

I could see all swamped 25 foot boats of a particular model falling within a two inch band, which would be 2000 lbs. But to get to 7000 lbs, that would be a 7 inch band and that seems excessive. As far as design, I would look for differences in gunnel height as a primary driver.

In terms of 'conservatively reporting facts', we could say this. Perhaps swamped capacity was some nominal or even some maximum value and that today in the name of statistics it is reported as a minus-3-sigma or minimum value. That could account for an inch or two and therefore 1000-2000 pounds.

Also, how significant is the effect of extra weight on floatation if the boat is primarily made of fiberglass/resin? Isn't that at least mildly bouyant? The lions share of floatation appears to come from the foam construction holding air and displacing water. Or, in other words, swamped capacity is primarily driven by the volume of foam in the boat, not the overall weight.

Gotta go, baby on the way....

Rocket out.

17 bodega posted 08-18-2005 08:45 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Hey! Congradulations Dad!
aquaman posted 08-19-2005 12:56 AM ET (US)     Profile for aquaman  Send Email to aquaman     
Don't know if I'm hangin with you guys on this one... If the stated theory is higher gunwales equals higher swamped capacity, then explain my 1994 24' Outrage with 8,500# of swamped capacity and no transom door. There is maybe 12 inches from the waterline to the top of the transom, not much freeboard at the transom. Many other whalers this size have less swamped capacity and much more freeboard. I know if must have something to do with hull weight and overall dimensions. My 24' is fairly light in weight (3,300#) compared to overall size. Any other ideas on swamped capacity??? I haven't clue...
Tom W Clark posted 08-19-2005 01:07 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Swamped capacity has NOTHING to do with gunwale height and freeboard. It has to do with hull VOLUME minus hull WEIGHT.

It's really very simple. Swamped capacity is how much weight (motors included) the hull will hold if water is free to enter the interior spaces, i.e. it's "swamped".

RocketMan posted 08-22-2005 12:48 PM ET (US)     Profile for RocketMan  Send Email to RocketMan     
Back now. Thanks, had a 9-1/2 lb'er and am now vividly re-experiencing those 'round the clock feedings.

I think the gunnel height or the freeboard does play a role in swamped capacity if the gunnel thickness is small. For a given hull bottom a shorter gunnel would tend to reduce the volume of water the hull is trying to float when swamped, which would result in a greater swamped capacity.

The question no one's been able to answer is why has Capt. Billy's swamped capacity changed by 7000 lb? and has BW changed its swamped capacity spec methodology ? I wonder why there are seemingly no Boston Whaler 'officials' that participate in the forum.

revsrobson posted 01-05-2006 10:57 PM ET (US)     Profile for revsrobson  Send Email to revsrobson     
I can't even get any Boston Whaler "officials" to correct the mistakes on the Boston Whaler Website, let alone explain why Captain Billy's 27 Whaler Drive has a 7,000 pound higher swamped capacity than a 2006 model 285????? Also, why can't I put on twin 250's on a 2006 Boston Whaler 285 when Billy's boat will take 600 horsepower and even a 265 Edgewater is rated for 500 Horsepower. I DON'T GET IT!!!!!!!!!!
thomasfxlt posted 01-06-2006 09:26 PM ET (US)     Profile for thomasfxlt  Send Email to thomasfxlt     
I own a 305 and I don't think you want this or any 30 + footer to fill with water. I seriously doubt that the 305 will really float much with full gear and fuel. You might get a seriously unstable neutral buoyancy of sorts, but "unsinkable" applies to the Dauntless class.

I will say this, I trust this boat and I wouldn't want anything else in it's class. It's a great craft. Very well built.

deepwater posted 01-07-2006 12:18 PM ET (US)     Profile for deepwater  Send Email to deepwater     
has anyone asked them to join?? if they should join are they leagely bound by wat they respond to ?? how much time would We pull from one of them,,this would be a fulltime job for 5 ppl at bw ,,5 ppl that would not be productive company wise,,if anyone of them joined it would be as we are just another bw owner with better answers
kingfish posted 01-07-2006 12:49 PM ET (US)     Profile for kingfish  Send Email to kingfish     
...Agh, you lost me, deepwater...
Backlash posted 01-07-2006 06:54 PM ET (US)     Profile for Backlash  Send Email to Backlash     
Dave and RocketMan are on the right track about the newer models having higher gunwales (thus holding more water) which must be factored into the equation. IMO, gunwale height has EVERYTHING to do with the swamped capacity, and is the main reason the newer, deeper, higher freeboard hulls have (in most cases) a lower swamped capacity than the classics.

Swamped Capacity: Total weight (persons, motor, and gear) boat will support {b}if filled with water[/b].

We (on this forum) don't know how much water any particular model will hold, but it doesn't take a rocket scientist (no pun intended RocketMan) to figure out that a boat with higher gunwales will hold more water than one with lower gunwales. The weight of this water must be subtracted to arrive at the swamped capacity.

Tom W Clark posted 01-07-2006 07:13 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

This is one instance where I am going to completely disagree with you. As I said above, Swamped Capacity has NOTHING to do with gunwale height and freeboard.

Think about it. At what point does the hull no longer support the weight? It's the point where the hull sinks. The height if the gunwale at this point is irrelevant.

I will say it again, a hull will support as much weight as it the water it displaces when fully immersed minus the weight of the hull itself.

swist posted 01-07-2006 07:58 PM ET (US)     Profile for swist  Send Email to swist     
I agree with Tom. It's basic physics - has nothing to do with the gunwale height.
prm1177 posted 01-13-2006 05:01 PM ET (US)     Profile for prm1177  Send Email to prm1177     
I think Gunwale height does have a small bearing in Whalers as the sides of the boat contain foam. I suspect the equation depends on the displacement of the boat vs the volume of the floatation chambers (in this case the foam sandwich). If the volume of water displaced by the boat and its load is less than the volume of the floatation chambers, the boat will have a positive buoyancy when swamped. As boats get larger, it becomes less economical and practical to increase the size of the floatation chambers. Hulls would get geometrically thicker.

I remember my geometry teacher in high school telling us that animals do not scale in nature since their weight increases with the cube of their dimensions and their support structure (bone diameter) scales only with the square of their dimensions. Something like this is probably operating here.

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