TomCat 255 Weight Question

[Mike...]

In anticipation of finalizing the deal on the TomCat, I was pondering various accessories, which got me thinking about weight.

I checked the manual, and it says the max gross weight of the boat is 8000 lbs. But, when you add up the dry weight, two Honda 150s, and a full load of fuel and water -- you are at 8150 lbs. before the bodies, gear, and that canvas top for the cockpit.

Is that right? Or is my math off?

TC255 = ~6000 lbs.
2 x Honda 150 + Batteries = ~1000 lbs.
150 Gal. Fuel = ~900 lbs.
30 Gal. Water = ~250 lbs.

I'll be needing to go on a diet, I think.

Thanks...
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mike

[eNORMous]

So, think of it this way. The weight is with regards to the "physical entiry" not the actual "net tonnage" carrying capacity of the vessel.

Examples: These numbers are NOT exact, but a very good approximation.

My Ford F-250 weighs ~6600 lbs but it can carry substantially more than the "physcial entity" itself (e.g. the truck). I don't recall the amount I can carry on the 8' bed (let's just say it's 2000 lbs for simplicity). Well, the design characteristics of the vehicle when it was manufactured were specified to contain leaf springs, rotors, brakes, nuts, bolts, axles, tires, rims, etc not to exceed let's say ~6600 lbs. The near same logic holds true for a boat, but is fashioned more with respect to the ability to displace water based upon physical characteristics of the vessel itself (since all buoyant vessels must displace water to remain afloat).

My C-Dory 25' Cruiser has a max gross weight of (as I recall) ~4500 lbs but it can carry substantially more than the "physical entity" itself (e.g. the boat).

The C-Dory 25' Cruiser has a minimum net tonnage capacity of 5.3 tons (based upon the physcial design characteristics of the vessel - the most important of which is the ability to displace water and remain afloat). Albeit, if I do NOT exceed a max gross weight of 4500 lbs (the physical entity itself), and I do NOT change the physical attributes of the vessel itself (lower the gunwales, reduce the size of the transom, lengthen/shorten the hull, widen the bow, etc - I can maintain a net tonnage capacity between 9540 lbs (short tons) & 10,600 lbs (long tons).

The manufacturer is required to state the max gross weight of the vessel since the "physical entity" itself - those objects, items, articles, pieces of equipment which are physically attached to the vessel and comprise the normal physical properties of the vessel which are required to maintain its position in a normal running condition (in a buoyant state) - in this case a vessel capable of displacing water - were designed of materials whose compositions cannot exceed max gross 4500 lbs (based upon the physical attributes of the vessel).

If an owner elects to widen the hull, lengthen the hull, raise the transom, redesign the transom and make it of solid stainless steel and then EXCEEDS the max gross weight of the vessel - well, obviously the vessel was not physically designed to "maintain" as a portion of its physical integral attributes the additional weight of a stainless steel transom. I think you get the point.

So, if you elect to physically change the attributes of the vessel by changing composition of materials (as an example) and the vessel comes in over 4500 lbs, well C-Dory didn't design the vessel to exceed 4500 lbs gross weight - but that is NOT its net tonnage or ability to carry weight.

If the boat leaves the factory and you then decide to remove and replace the decking with stainless steel, remove the entire cabin of fiberglass and change it out for teak, or replace the transom with a stainless steel transom - even "if" you maintain the same physical "design" of the boat, you will have exceeded the max gross weight (based upon composition of materials for the design of the vessel).

Hope that makes some sense

[eNORMous]

I just looked at the 25' Cruiser Owner's Manual; and, I would have to say I am not in full agreement with the manufacturer based upon the statements made in the manual. That is merely my opinion.

If you add the hull weight (less motor) 3602 lbs, fuel (100 gals @ 6 lbs/gal = 642 lbs), water (24 gals @ 8.3 lbs/gal) you arrive at 4443.20 lbs. That leaves no weight for an engine - I guess we need to use oars.

Then they state on page 12 of the Owner's Manual the Normal Running weight is 3800 lbs can these folks use a fricking calculator or what? They've designed a boat to use no water, no fuel and run on a trolling motor?

Then they state on page 12 of the Owner's Manual the Maximum Gross Weight (which they spelled incorrectly in 2005 and haven't changed in over three years) is 4500 lbs e.g. you can place a 56.8 lb trolling motor on the back of the transom, send it off into the deep blue via remote control but you can't board the vessel itself because you're plainly over the max gross weight limit.

I'm not sure they did their math right on this. Hopefully the new Fluid Marine owners of C-Dory will UPDATE the Owner's Manual (if nothing else review it for the spelling errors).

And, I don't recall where I read this within our own forum, but there was an error in some logic regarding volume and water displacement. An object is buoyant no matter what material the object is submersed into (be it a solid into a solid, a solid into a gas, a gas into a solid, a liquid into a solid, a liquid into a liquid, etc - e.g. regardless of the phase state) based upon one of three properties: positively buoyant, neutral buoyancy, or negatively buoyant. If the weight (mass) of an object is less than the weight (mass) of the solute (in our case water) it displaces, such as in the case of a boat, the object will float - it is positively buoyant. The ability or inability to remain buoyant resides solely with the masses of the two objects (unless Archimedes was wrong or I am).

That object (whether positively, neutrally or negatively buoyant) will continue to displace a mass or volume (the relationship is proportional as I recall but someone please correct me on this) based upon whichever comes first - the mass or the volume of the solute (material) displaced.

Therefore, the volume of solute (material; in our case water) displaced by an object (in our case a boat) is proportinal to either the mass or the volume (whichever comes first).

If my 25' C-Dory displaces 1149 gallons of water, that is the equivalent of displacing roughly 5.3 short-tons of water (measured at 8.3 lbs/gal). If I were to load up the empty volume inside my boat to the point of maintaining less than 1149 lbs, I should (theoretically) remain positively buoyant. I damn well hope I do - if nothing else, I'll hope for neutral buoyancy for a couple of days. I am of the opinion that no where is there a requirement to ADD the weight of the vessel itself (e.g. 4500 lbs). Since, as designed (the physically designed characteristics of the boat) it will displace 1149 gallons of water (or 5.3 net ton capacity). When the NVDC documents the vessels based upon the manufacturer's stated design characteristics, they arrive at net tonnage - the ability to accomodate (consume) mass into the empty volume of space of the vessel - regardless of the vessel's physical weight (mass). I believe this was and is still regarded (as Bob pointed out at one point), the unlikely probability (today at least) of the military or merchant maritime provinces to employ a federally registered (documented) vessel for maritime use. However, it does have very specific meaning with regards to commercial navigation.

Someone check me on my reasoning - I'm not above making false or incorrect statements.

[matt_unique]

The weight ratings in the documentation are wrong for the C-25 and Tomcat and probably all the others.

The Tomcat has an 1800 lb capacity in addition to engines, fuel, batteries, water, etc.

[JamesTXSD]

I don't have a TomCat, although we have cruised plenty with our friends on Discovery. I also have no idea what the manual says for capacity on the TomCat, but Brent and Dixie have had no problem bringing anything they want along.

"Brent, do you have an anvil I can use to mount a snap?" No problem.

"What do you want to do for supper tonight?" Dixie pulls a side of beef out of their freezer.

Go into their boat, and it looks neat as a pin... one of those "sixth dimension" sorta things, I guess, but that boat swallows up a lot of stuff. Don't worry, Mike/wannaboat, that TomCat will carry plenty.

Now, having said that, we also don't travel light with Wild Blue, Keep in mind that excess weight will affect performance (speed and mpg), though. I have no idea who at the factory is responsible for these weight figures, but I was also told that our CD-25 would weigh 6500 pounds "all up" on the trailer, Only missed that by about a ton. I'm guessing that TomCat, loaded on the trailer is going to be between 9,000-10,000 pounds.

Perhaps not the exact number you were wanting, but rest assured that you will have plenty of carrying capacity and space for all the stuff you want to bring along.

It still amazes me that we can go to the store, come back with 10 bags of groceries, and when Joan is done putting it all away in the boat, there is nothing sitting in the aisle. We fill the fuel and water tanks; carry extra fuel and water in jerry cans; a generator; inflatable dinghy and motor; clothes and supplies for extended time out; a cat and all that goes with her (litter, food, etc); and still have room for a travel guitar, TV, computer, folding chairs for the cockpit, etc, etc. (Insert Bill's "less is more" opposing opinion here )

I used to be a pilot and always did weight and balance calculations. I'm not sure I understood most of what Norm wrote there , just know that you have the capacity to haul plenty of stuff.

Buy the boat. Load the boat. Go have fun with the boat.

Best wishes,
Jim B.

[Wefings]

What about the Oxy Acetylene Torch/Plasma Cutter combo they seem to carry for minor repairs........?
Marc

[drjohn71a]

Wannabe,

I am a bit embarrassed by the incongruity of C-Dory's figures about weight and capacities over the years. I do not know why this exists, but maybe some insurance or other legal requirement makes it more expeditious to understate the weight and capacity.

In the real world, very heavily loaded, on the trailer, mine has come in from 10,300 to almost 11,500 pounds (including the trailer) as told to me by the guys who take it to the mechanics shop. I have not weighed it myself.

In any case, the TomCat seems under complete control and not overloaded in actual use to me and my very experienced passengers over the last several years.

I could not explain to the local lake safety inspectors exactly why C-Dory does not include a manufacturer's personage and weight capacity sticker.

I guess they are exempt due to the hull length. At any rate, the boat has shown to be seaworthy over time by the many owners in the many differing locations.

I guess you could take it to a scale and weigh it.

Good luck,

John

[matt_unique]

I explored this with the factory when I bought mine. Tom Broschart (one of the engineers) replied with the data:

>>From: Tom Broschart

......
The capacity numbers on the sticker are:

3800lb - means the total weight of persons, engines and gear.
12 persons or 1800 lbs – means the weight for persons and gear.
.......

Thomas<<

I have not weighed mine but from others on this site I believe it weighs 10,500 on an aluminum trailer.

[eNORMous]

With regard to:

[journey on]

OK, here's a weight table for a C-25, giving a total cruising weight of 7392 #. The weight is high, because we cruise the boat, but it's not abnormal. Also it agrees with scale weights for the boat and trailer. What it shows is that the gross weight is twice that of the hull weight (number at bottom of chart.} Just as on a F-250 gross weight is the truck and load; all the weight on the tyres. Or in the case of a boat, all the weight inside the hull surface.

Now a C-25 is a monohull, and I wouldn't try to load a catamaran to a gross weight of twice the hull weight, but on Journey On, it works quite well.



Boris

[Mike...]

I wasn't clear in my initial post, but I am interested in the max gross weight on the water. Not the max gross trailering weight.

[eNORMous]

I'd probably say you're "within" the numbers. Notice the numbers you're quoting are from a C-Dory 25' Cruiser (which are the numbers provided to you by Boris which you're employing in your logic).

I think you're buying a Tomcat 255 - which is not a monohull and therefore (empirically) those numbers are not going to align. However, I believe others (in similar threads - including Bob [Thataway]) have obtained National Vessel Documentation Center documenation for Tomcat 255 and it meets the net 5 tons minimum requirement. That being the minimum you should be able to safely accomodate (consume) between 9540 lbs (short tons) & 10,600 lbs (long tons). The only discrepancy I see in my logic here is not having taken into account the conversion of GRT (Gross Registered Tonnage) into Net Tonnage. Net Tonnage, is quite different than how I have been explaining (evidently a not so simplified view).

GRT was replaced by NT in 1982 for international standards. Here is a link on the math:

http://en.wikipedia.org/wiki/Net_tonnage

HTH
Norm

[matt_unique]

I think the most practical data point is 1800 lb capacity. The rest is essentially fixed.

The amount of space on the Tomcat is great. I can comfortably carry 4 divers with gear. I try to limit the number of guests to 4 so everyone has a seat inside if the weather does not cooperate.

[thataway]

Documentation weight has no basis in reality of the carrying capacity of the boat. It is a volumetric determination for documentation purposes only.

The C Dory can easily carry 1800 lbs. What will happen is that the top speed will drop and there will be less tunnel clearance both at rest, low speeds and on a plane. There will be little difference in handling. I suspect that we carry more than 1800 lbs when cruising. At least one boat has a second fresh water tank, and we have a second tank, yet to be installed.

I agree that on the trailer the Tom Cat 255 will come in over 10,000 lbs. scale weight.

[Mike...]

For those of you that mentioned your loaded trailer weight above, do you know how much your trailers weigh empty?

Thanks...
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mike