Glacier Bay 2690 vs Tom Cat 255

[thataway]

No I haven't gotten to sea trail a Tom Cat 255 yet, but hope to before too long. I would love to see some price lists and fuel burn numbers on the 255!!
But here is my take on the nearest competitor, the Glacier Bay 2690:

One of the several cats we are considering to replace a 28 foot V hull (weight about 8000 lbs, 18 degrees dead rise, 300 hp, I/O) is the Glacier Bay 2690. We viewed a 2680 which does not have the galley, but does have a slightly shorter hard top, and the same layout foreward--head and shower in the port hull, and large queen berth over the bridge deck and Stb hull. We sea trialed a 2670, which has the short hardtop, a bait well and lounge seat, instead of the galley and dinete, and a lower windshied--front and side curtains instead of full windshield, side glass windows and aft full bulkhead--weight about 600 lbs less than the 2690. We had 500 lbs of crew, 1/2 fuel (holds 180 gal) and otherwise no cruising gear. The boat had twin Yahama 150's counter rotating. Top speed was 38 mph (measured on the Yahama speedo--not gps, but I have a Yahama, on another boat, and the speedo, is almost exactly the same as a GPS at planing speeds.) Top speed was 38 mph, with a fuel burn giving 1.4 mpg. At 30 mph fuel burn was l.7 mpg and at 24 mph fuel burn was 2.2 mpg. These were exactly in line with the factory prediction and would give the 2690 (heavier boat) a range of 270 miles with adequate reserve. This fuel consumption and range is about 30% better than the 28 foot V hull I own currently.

Tracking was excellent--even with chop ahead, or at 45 degrees off the bow, or even astern the boat held its course. There was none of the wondering of a deep V--and steering was at a minimum. We had about a 1 to 2 foot surface chop in the Gulf, and hit some 3 to 4 foot wakes. At cruising speed there was no slamming or pounding, but at slow speed there was some "thumping" The ride was not quite as smooth as I had anticipated, but certainly much better than the V hull. There was a little "sneeze"--which might have been eliminated by trimming up slightly. There was some quickness to the motion which took a little to get used to. Although the boat is touted as a semi displacement hull, they have added running "shoe" which is about 1 1/2" wide under the bows and broadens to about 4 to 5" at the stern. There are strakes at the chine, and asymetrical rounded bilges. I suspect the running shoe gives a bit more lift than the origional boat which was fully round bottom.

We are considering a "trailerable, power cat" which has facilities for staying aboard for several weeks. The requirements are good bunk, enclosed head, with shower, galley and dinette, which can be easily towed by a 3/4 ton truck. The Glacier Bay had a dinette which does convert into a bunk, but it is only 5' 5" long, compared to the Tom Cat 255 which has a dinette 6' 4" long. Also the Tom cat allows the foreward passanger to face foreward, the GB, faces the foreward person facing aft. The galley is considerably smaller in the Glacier Bay, with a one burner alcohol /electric stove and a small sink. The Tom Cat has a much larger diesel two burner stove/heater available. Also the Glacier Bay does not have a foreward opening windshield, so the pilot house area is much hotter than the Tom Cat, where a 2 x 2 foot section of the windshield opens. The lack of ventillation (although the 2690 does have two small opening hatches on the cabin top) is a real negitive for us in the Florida heat.

We would consider putting in larger opening hatches on the pilot house top--or a marinized RV airconditioner on the pilot house top. The same could be done with a Tom Cat 255.

The fiberglass work on the Glacier Bay was very well done, but some one had hit the anchor pulpit and cracked both sides--so that certianly needed to be beefed up. Finish work was good. All systems were accessiable and all tanks could be removed without cutting any of the flooring.

The generator was a Honda EU 2000, in a fiberglass case, with an exhaust port and SS louvers, which sat on the middle swim step. It was difficult to step over. The air conditioning had one duct to the foreward stateroom/head/bunk area, and another to the pilot house--I don't think that 7000 BTU would be adequate to cool the pilot house, except perhaps after dark.

We hope to run a 24 foot Tom Cat in the next week or so--and the Tom Cat 255 in the next few months.

The 26 foot Glacier Bays have made some very impressive trips--to New York to Bermuda, Seattle to Alaska (Kenai) , and Hawaii to Midway, with only one refuel stop! These are very much outfitted as sport fishing boats, with livewells, and fish boxes. I suspect that the Tomcat will be a little better with the cruising amenities. I did like the idea of a fiberglass enclosure for the Honda EU 2000. I also really liked the fuel capacity of 180 gallons.

[B~C]

Bob you seem to be studied up on power cats, could you school me on cat hull types. I read where the G.B. handles different than other cats because it has displacement hulls. I always equated displacement hulls with 8kts, so me thinks they're not referring to a true displacement hull. What type of hulls does the TC have and how do you suppose the ride and handling would compare to the GB? Would it be more comparable to the World Cat?

I hope curiosity doesn't kill my cat dreams

[stevej]

Ken I just received a brochure I ordered from Glacier Bay and they are a true displacement cat. This is why they have such narrow sharp entry hulls and max hp rating of 300 hp. You start digging a hole on the water if you attempt to push the boat beyond around 40 mph so more hp does little but burn additional gas with only a small increase in speed.
Have the same question about the CD but expect that it is a planing hull, maybe Jeff from CD can jump in and answer the question.

stevej

[Captains Cat]

A true displacement hull will NOT plane. The speed/HP curve goes vertical (almost infinite HP will not result in a speed increase). The "displacement speed" (in knots) of a hull is ~1.33 times the square root of the waterline length. Therefore, if you have a 25' hull (at the waterline), 1.33 times sqrt of the wl Length is 1.33 times 5 or about 6.65 kts. This is primarily due to the bow wave coming back together at the stern and creating a "suction" that the boat cannot overcome unless it gets out of the water (planes).

That's not to say that the GB Cat doesn't have a displacement type hull, it's just light enough to come up out of the water and plane. It's not in the displacement mode when it does that.

End of lecture! At last got to put my sailboat and Naval Arch experience to a practical use!

Charlie

[thataway]

The first part of Captain's choice is correct--that most displacment monohulls are limited to 1.34 x sq root Length waterline. His explaination about climbing over the bow wave is correct. However there are some exceptions. With enough power, semi displacment hulls can plane. The other exception is that a narrow beam water line can exceed the theoretical 1.34 x sq root LWL. Most all cats have very narrow hulls. Most all of the early sailing cats were narrow hulls of displacment or semi displacement type. Many of these--including the early Hobbie cats could reach speeds of 15 to 20 knots. So also important in the speed equation is the ratio of the beam water line to the length waterline. The long narrow boat can exceed the theoretical equation--and the narrow hull of a cat or tri is the extreme of this.

The semidisplacment hulls with narrow beams will reach high speeds--similar to planing hulls. The Glacier Bay is a bit of a hybrid. I understand that the hull form was changed about 2000, and that this running strake or shoe was added--which does give more lift, and allows the use of larger motors--more flotation aft.

What is said about lightness has some merit--a lighter cat will run faster, and be more fuel effecient. However the Glacier bay is not fast because it is light--in fact is quite a heavy boat. It weighs about as much as a 28 foot deep V I also own--which planes, but not as effeciently as a flat bottom boat. Both the deep V--and the very narrow hulls of the cats "cut the water//and waves" to decrease the pounding, which is characteristic of flat bottom boats (our C Dories are fairly flat bottom boats--but with some V foreward).

Malcom Tennant is an Australian designer of catamarrans, who has been building cats for many years and is well respicted in the field. At:
http://www.pedigreecats.com/faq.htm#disp There is a graph of displacment cats vs planing cats. The point he makes is that the planing boat has to "get over a hump"--that is it takes a lot of horsepower to get on a plane--and the narrow displacement hulls have almost a linear power to speed ratio. I think that this is a bit blurred--and perhaps Jeff or Scott will address this. However looking at the Tom Cat 255's RPM vs speed I don't see much of a hump (the classic C dory does not have as much of a hump as a deep V). The RPM vs speed seemed fairly close on both the Tom Cat--as published, and the Glacier Bay. Although the Tom Cat 255 has a hard chine,--flatter bottom, and the Glacier Bay 26 has a rounded chine (and smaller flat surface)--the hulls appear to be acting relitively similarly. I suspect we will know more when fuel consumption numbers are available for the TC 255. Generally planing cats will be more fuel effecient at higher speeds--and the displacement hulls will be more fuel effecient at medium speeds.

The Glacier Bays were first run with lower HP and did fine--but it was found that the boats rode better at higher speeds. I suspect that this same characteristic will be found with the Tom Cat 255. From what I saw in the numbers on the first TC 255, I would order one with the 150 hp engines to get the most out of the hull.

The salesman wanted to demonistate to me the stability of the GB in a full lock over wheel turn at 30 mph. The boat was stable. However I had to tell him, that I had ridden in a formula one racing boat and made a full lock turn at 130 mph--a force of 3 G--so the 30 mph was tame!

There are many factors in hull design--and it is not a simple subject.

[gljjr]

Hey Capn,

Woudln't you have to multiply that times 2 for each hull since this is a cat? Just curious!

[Captains Cat]

[Captains Cat]

Well, after my last post, I did some research...

From another source:

Quote

Power catamarans are becoming an increasingly prominent part of the boating scene. Just like monohulled vessels there are numerous sorts of power catamaran. Which one is used depends on the purpose for which it was designed. And, just like monohulls, you need to have the right boat for the job. However unlike the monohulled vessel there is a much greater overlap in performance and behavior between the two basic types of catamaran; the planning craft and the displacement vessel. This is largely because a displacement catamaran can, unlike its monohulled cousin, often go just as fast as a planning one, and in some conditions faster. However there are many more variables than just the hull form. There are two basic types; the planing hull and the displacement hull.


Planing catamaran is usually similar in shape to that of a planing monohull. It is generally a relatively low dead rise hard chine hull with no rocker. Just like a monohull it may have planing strakes and the currently very fashionable steps. There are planing catamaran hulls in which the deadrise angle is constant for at least the last half of the hull and others where it will vary along the length. Others may be similar in section to the deep vee monohull. There are also a number of variations on the single chine/multiple chine/longitudinal and transverse steps theme. Displacement cats also lean outward in a turn but because the angle of heel in their case is around half a degree it is usually not even noticed. Extra wrinkle can be thrown into the mix by fitting foils to boats that are intended to exceed 28 knots. Foils allow the boats to plane sooner and also carry heavier loads when on the plane. The fitting of foils is an approach that is difficult to use on a monohull but the catamaran configuration is perfectly suited to them as the main load carrying foil is generally fitted between the hulls. Foils, par-ticularly the active systems, are also sometimes fitted to the larger displacement hull forms, such as those found on high speed ferries, to improve the ride quality.


Generally the planing cat is designed for relatively flat water but it will still handle rougher conditions better than a monohull provided there is sufficient wing deck clearance. Essentially, if you want to go fast in a “short” catamaran you use a planning hull form. Displacement catamaran designs capable of more than 30 knots with quite minimal horsepower and the more extreme high speed catamaran ferries are achiev-ing 60 knots from very long thin displacement hulls. The distribution of the buoyancy has changed and the entry has been fined up even further including the “wave piercing” designs of Craig Loomes. Most of the hulls low resistance may be attributable to the basic shape and reduced appendage drag from 12 to 15%.


However weight issue does raise another point of differentiation between the planning and displacement cat. The power cat is very well “punching” straight into a seaway. Although some extra weight does not have much effect on the performance of the displacement hull form. In a similar way the “wave piercing” displacement cat designs of Craig Loomes use the larger central “hull” to prevent burying the low freeboard hulls and minimize slamming of the wing deck. All displacement hull power catamarans are in reality “wave piercers”. They all slice through the waves. The “perceived” size of the vessel would put off some pleasure boaters who have a tendency to want to use all of the available space, including the space between the bows.

Unquote

I think that explains the difference!

Charlie