Tomcat 255 Gross Weight Don't Make Sense To Me

[plfinch]

The Tomcat manual (http://www.c-dory.com/owners/manuals/tomcat_255_manual.pdf) lists the following:

Hull Weight less motors, batteries, controls: 6,000 pounds
Design Weight (boat, motor, fuel, gear, passengers): 7500 pounds
Maximum Gross Weight: 8,000 pounds

Motors including batteries and controls (2 Honda 150): 1,100 pounds
Full Fuel (150 gal x 6 pounds): 900 pounds
Full Water (30 gal x 8.35 pounds): 250 pounds

So before I even add passengers, or even a paper chart, at full fuel and water, with motors, batteries, and controls, I am at 8,250 pounds - 250 pounds over maximum gross and 750 pounds over design weight.

What am I doing wrong or missing here?

Peter

[plfinch]

I did find this thread http://www.c-brats.com/viewtopic.php?t=10588&postdays=0&postorder=asc&start=30 which basically says the manual weights are all wet (no pun intended) but did not provide any manufacturer validated figures.

[thataway]

You have to understand where the Tom Cat 255 came from. There was first a Tom Cat 24--which is basically the same hulls, but with euro transoms, which had engine mounts on each side, no engine bracket or transom as we know it in the 255. The cockpit and cabin were both smaller and lighter. I suspect that some of the weights came from the boat, and were never upgraded.

We all fill our boats up and go. No issues with the Tom Cats as some other cats have had, like the Glacier Bays, ProKats etc. A couple of Glacier Bay's capsized, some Prokats have had hull to deck problems and sunk. Some of the other cats tend to sneeze bury the bow etc--the Tom Cats are very well behaved. They also have huge cabins in comparison to other 25 foot cats.

The proof is in the performance and handling. We did trials on the boat when we first got it--no added weight--and as I recollect top speed was just under 50 mph. Now, 4 to 5 years later, the boat has more stuff aboard--including the refer/freezer, generator, Air conditioner, extra batteries, dinghy, dinghy motor, folding chairs, and table, sun shade for the beach, full camper canvas--I am sure over 2000 lbs--and the boat still handles well, top speed is somewhere in the mid 40's. (This is with the Suzuki's which swing a larger prop than most of the same size engines).

Ideally I would like to see more tunnel clearance. But a neighbor has a Tom Cat 24 which has been kept light and there is not much difference in the ride--except that boat has twin Yahama 115's, instead of the Suzuki 150's, so it is a little slower, but gets better fuel economy.

So--Peter--buy the boat--put what you want on it and enjoy....

[Alok]

This discussion has been held more than once. The consensus was that the factory figures are a gross underestimate. There are no newer, validated figures available.

As Dr. Bob has noted, the Tomcat underwent a major design change about 6 years ago. The current hull and cabin configuration has been very well behaved.

[Captains Cat]

I figure my TC255 loaded on the trailer goes between 10K and 11K. At least that what it feels like!!

Charlie

[matt_unique]

The consensus on rig weight (boat/trailer) is 10K.

I did not check the thread mentioned above but I was among those that started such a thread - the C25 and TC255 weights when I began researching C-Dory's were all incorrect and low.

Not to be confused with weight, the USCG approved Napoleon as a 7 gross ton vessel.

[billtwymank]

*
As ever, Bob has great input.

The engineered weight/load on each planning surface must not exceed the kgm/sq.cm of the surface area or it will not plane.

This is the reason to keep the load as light as possible as it will stay on a plane at lower engine rpm,
and be more fuel efficient.

Maybe Bob can come up with that gross figure,
but it does not appear that 10,000lbs is near the maximum limit.


The TC255 seems to be a fuel efficient semi-displacement hull that planes around 20knots with our Honda 135's,
all the while treating its passengers gently.
*

[journey on]

The subject of reality comes up once in a while. While I cannot speak for the TC255, I did a weight analysis for the CD-25, which is similar to the TC255. This is shown below and indicates the factory weight is reasonable, but as cruisers we pack a lot on. The dry hull weight from the factory is that, an empty hull. We do add a lot of equipment, such as the refer, the stove, etc. The differences between a TC255 and a CD-25 are (obviously) another motor, a catamaran hull (which has to be heavier,) and more space to store stuff. So, the table herein certainly is a minimum and you can add your own delta. Please note that the total weight below is from a scale, not estimates. The truth is we're towing 8000# with another 200# in the back of the truck. The weight in the water of Journey On is ~7500#, which is quite possible over the factory (which factory?) recommendations, but not untypical. A TC255 certainly is at least 700# over that.



Boris

[thataway]

The Tom Cat 255 is a planing catmaran. There seems like little difference between the planing and non planing boats. But it evolves around the hard chines, and amount of flat surface aft. The Glacier Bay and World Cats are displacement and semi displacement hulls (don't ask about the difference, but it involves the configuration of the aft part of the hull!)...
The semi displacement boats will be more fuel effecient at the speeds from 8 to 16 knots--but with the low planing speed, the Tom Cat may be aa effecient even down in the 14 to 15 knot range.

When the boat is static in the water there some bouyancy provided by both the Armstrong bracket and the wing deck aft--which is resting on the water. At lower speeds this is still wetted. As the boat comes up to a planing speed, the tunnel does open up. The critical weight for a Tom Cat would be where the tunnel does not clear the water on a plane.

People disagree at what speeds the boat planes--and this is understandable due to different weights, engines, props, and the presence of Permatrims. The Permatrim will allow a lower planing speed. Some say as low as 9 knots--I think it is closer to 12 knots. The four blade Suzuki props give more stern lift--combinded with the reverse of the counter rotating engine, which also contributes to stern lift and a lower planing speed.

I don't know what the critical weight is, but people load the boat for a month in Alaska--and still plane. As I recollect one owner was disappointed and he had a dive compressor, up to 6 divers and gear aboard. I sea trialed his boat--and there was a definate difference in handling between it and the boat I pruchased. I attributed that to weight, and engines/props.

[Sam Walker]

Great review and explanation as usual, Dr. Bob. As I remember, the TomCat that you trialed was the first or second one made. Is it also possible that improvements to the design or brackets could account for some of the different handling?

[thataway]

The first Tom Cat I sea trialed did have the 24" bracket (same as currently)--there was no hull modification--except the boat was very heavy, there were counter rotating engines, and the trim tabs were not in a location where it was easy to use them when the boat was under way. (I fiddle with the trim tabs to get the best ride/fuel effeciency). It was #4 boat, and the Amrstong bracket had been moved up--I believe to current height.

[journey on]

Bob, do you recall what happened to the boat with the dive compressor? If I remember correctly, he also had a fly by wire steering on the stern. I guess that boat was way overloaded, in order to make a living.

Boris

[Captains Cat]

[Dreamer]

Boris,

The very heavy TC255 was DiveCat. Les at EQ rigged it and it was at the Jan 2006 Seattle Boat Show. In addition to the dive compressor, it had a large inverter and battery bank and watermaker! There might have been a generator involved too.

As of Jan. 2007, it was for sale at a brokerage and the compressor had been removed. It eventually sold but I'm not sure where it went. BobCat was the owner (formerly Scaly Waterman). He used the boat for sport diving in SoCal. Search the site for DiveCat for more info.