Glacier Boats

Glacier Boats

of Alaska LLC

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Seaworthiness:

First, a bit of background. Stability is the boat's tendency to return to an upright and level condition when something upsets the boat's upright orientation. Waves, wind, loads shifting or being moved within the boat, etcetera are examples of what may do this. Stability can be further broken down into what is known as initial stability and ultimate stability. Initial stability is the boat's tendency to right itself given small changes in heel, say less than 10-15 degrees of heel or so. Ultimate stability is a measure of the boat's ability to resist capsizing when heeled very large amounts. Boats resist capsizing through two means, a) by generating a very high righting moment when heeled to a high degree, and b) by preventing downflooding (water spilling in through openings or over the sheer) to the highest degree of heeling possible. Most boats in this size range can only heel approximately 45-50 degrees before downflooding occurs, yet the Great Alaskan can heel up to around 60 degrees before downflooding occurs.
Boats with high initial stability are less tender ('tippy') but not necessarily more seaworthy. Initial stability relates as much to comfort as it does to safety. Ultimate stability is more important since a high ultimate stability means the boat will withstand capsize more capably. If you look at the righting moment v. degrees of heel curve (see Hydrostatics), notice how the initial 10 degrees of heel or so have a steeper curve.
The total stability of a planing hull comes from the sum of two components, a) Form Stability and b) Weight Stability. Weight stability refers to the relationship between a hull's vertical center of gravity (VCG) and its center of buoyancy (center of submerged volume or CB.) The further the VCG is located below the CB, the more weight stability a boat has. If the VCG is above the CB, then the boat's weight works against stability. In general, the VCG can only be located below the CB in heavy displacement vessels, and nearly never for normal planing hulls. Therefore, responsible designers and builders should work to achieve the lowest possible center of gravity in order to minimize the negative effects of a too-high (top-heavy) VCG. A low VCG is obtained by using heavier materials for lower hull structure and by placing heavy items (fuel, motors, batteries, appliances, etcetera) as low as possible in the hull. Furthermore, a low VCG will create a righting moment if a boat is heeled far enough to lift the VCG above water level while a high VCG may not exhibit much of a righting moment in these conditions at all. The measure of weight stability in a boat is the vertical distance that the VCG is above (or below) the center of buoyancy (CB).
Form Stability is achieved by the boat's underwater shape. Think of a flat styrofoam sheet floating on the water versus a round cylinder of styrofoam. The flat sheet is very difficult to capsize (turn over), while the cylinder will easily spin in place. This is because with the cylinder, the shape of the displaced volume does not change as it is rotate and therefore there is no opportunity for the center of buoyancy to move off center. When the center of buoyancy moves off center relative to the center of gravity, it creates a righting moment. In other words, as one side of a boat is rolled into the water, the center of buoyancy also moves to that side and tries to lift that side of the boat back up ...righting the boat to a level condition. While this is all good, too high of a righting moment can be a problem as well. If a boat is too hard to turn over, the boat tends to 'snap roll' with waves that pass under the boat. This is not only uncomfortable, but it is also hard on the boat structurally. Conversely, if the boat turns over too easily then it is not only at risk of responding too slowly to the sea, it also generates a sickly motion that most passengers find to be uncomfortable. Every type of boat has a 'right' amount of form stability and the best way to determine what it should be for a particular size and type of boat is to compare it to other similar designs that have proven to be successful. The measure of form stability that you can compare different boats with is the Transverse Metacentric Height (GMt). The higher this number is, the stiffer the boat is. Most boats similar to the Great Alaskan weigh approximately twice as much and have GMt's that range from 30" to 42". The Great Alaskan is more similar in weight and style to the Tolman Jumbo, albeit wider and longer. The Jumbo has a GMt of around 50" and has a long solid reputation for being the best compromise between comfort and stability. The GMt of the Great Alaskan it also around 50". (In both cases, the GMt varies with loading, as with all boats.)

The Great Alaskan's form stability is similar to the Calkins Bartender and Tolman Jumbo Alaskan Skiff, both of which have strong reputations for seaworthiness. In addition, the Great Alaskan's offshore sea skiff type of hull form (flared sides, classic sheer, modest deadrise, freeboard) give the boat great reserve buoyancy. Compared to boats with more vertical sides such as you find on most commercial offerings, the Great Alaskan increases in the number of pounds per inch immersion (PPI) that must be overcome very quickly as the boat is pressed down into the water. What this really means is that as water rises up the boat, whether from wind or heel or waves, the boat will bob up and over the water rather than allow it to climb up the sides and risk swamping the boat.

Other factors that are important to achieving offshore seaworthiness are the boat's ability to resist broaching, ability to cut through a chop while still being able to rise into a head sea, and the boat's maneuverability. To resist broaching, the boat needs to a) be as symmetrical fore and aft as it can and b) have a center of lateral resistance (CLR) aft of amidships (but in balance to the craft.) The Great Alaskan has buoyant bow sections that we believe are the best compromise between achieving forward buoyancy while not 'pounding' when driven through a chop. It compares well to other boats in its size range. The Great Alaskan's stern sections are slightly narrower than the amidships sections. This slightly reduces buoyancy aft which further balances the fore aft buoyancy of the boat. The slightly-reduced buoyance aft is OK since the wood-composite structure requires less horsepower, e.g. lighter weight motor(s), than what heavy fiberglass or aluminum boats of similar size would. Note that the Great Alaskan can carry up to 1000 pounds on the transom ...plenty of capacity to allow two mid-sized outboard motors or a single larger outboard motor ...and trolling motor or 'kicker'. The Great Alaskan has side and center strakes on the boat's bottom that allow the boat to be beached (common in Alaska and certain parts of the Pacific Northwest) and also help keep the center of lateral resistance aft of amidships as it should be to balance the boat against broaching.

Efficiency:

What makes a boat efficient to operate depends highly on what type of boat it is. Displacement hulls such as sail boats will always be the most efficient, but that doesn't mean a planing hull can't be efficient also. A planing boat's efficiency, in terms of the power requirements and how much fuel is burned, is a function of the boat's ability to plane in the first place and the resistence generated while it is doing so. Boats with deep-V's are the least efficient, and if heavy, are even worse. If a boat can be designed with a modest deadrise (angle of the hull's bottom relative to a level line), light weight, yet still be seaworthy and sturdy, then you'd have a real winner. This is exactly what we tried to do with the Great Alaskan. The wood/composite structure is one of the lightest construction methods there is. Consider that aluminum weighs 165 pounds per cubic foot while wood/composite only weighs 40 pounds per cubic foot. A wood/composite boat naturally requires a lot less horsepower just by virtue of this fact alone. We feel that this is a more than fair trade-off versus an aluminum boat's ability to be abused. A properly built wood/composite boat requires lower maintenance than a commercially produced fiberglass boat yet is not as abuse resistent as an aluminum boat. The Great Alaskan utilizes a modest deadrise (aft) of only 13 degrees. Compare that to most deep-V boats which use 17 to 25 degree deadrise angles. In addition, the Great Alaskan has a nearly prismatic hull form. The amidships deadrise is only 14.25 degrees. This enables the boat to plane more easily and more efficiently. It is one of the key factors that make the Calkins Bartender and Tolman Alaskan Skiff plane as easily as they do as well, although the Great Alaskan hull form is closer to being a prismatic monohedron than either of these. In addition to the seaworthiness designed into the Great Alaskan, the light weight, modest deadrise, and near-prismatic hull form give it great efficiency. Note that most commercial boats in this size range will obtain 1.0 to 2.0 miles per gallon while the Great Alaskan will obtain 3.0 to 5.5 miles per gallon (depending on weather and water conditions.) The Great Alaskan will have a range of 300 to 600 miles, depending on motor and fuel tank selection (100+ gallons typical). These numbers are based on real performance measured on the two similar boats that I've been comparing too all along.

Ease and Cost of Building:

As mentioned in the discussion on our home page, the Great Alaskan is not a plywood-on-frame constructed boat nor does it utilize any other time-consuming or difficult building methods. Ply-on-frame results in a heavier less efficient boat, is difficult to clean and maintain (since frames impede water flow inside the boat), and very time consuming to build. Each frame must be individually fit to the shape of the boat and the entire structure must be build on a accurate strongback. The Great Alaskan uses nearly all 90 degree cuts that are easy to do with virtually any jig saw, is a semi-monocoque structure requiring a minimum of bulkheads, and only about 40% the parts count of boats using more traditional methods of construction. The lower parts count results in low cost of building, although I must admit that wood and paint is lower cost than epoxy. We believe that the lowered parts count, savings in labor, and highly reduced maintenance more than makes up for any savings associated with not using epoxy. Compared with aluminum, currently averaging $7 per pound (!), the Great Alaskan is far more economical to build. We estimate, in September 2005 prices, that the entire hull and superstructure can be assembled for less than $6000. Remaining costs are those associated with fuel tanks, windows and equipment such as hatches, trailer, motor(s), and electronics. A typical ready-for-water project cost for this boat will be from $15,000 to $30,000, depending on personal decisions on the list of items other than the basic hull and superstructure. Compare that price to any used or new commercially produced boat with equivalent capability and let me know if you find a better deal! The construction method and procedure is completely suitable for pay-as-you-go project financing. Time to build ranges from 7 to 9 months for those who can use nights and weekends to do the build up to 2 years for those that must build on a time-available basis (family, work, etcetera). We've seen similar boats built in as little as 4 months (but are not suggesting such a hard-pressed schedule ourselves ...life should be more enjoyable than that!)

As mentioned on our home page, the construction method and procedure is designed so that virtually anybody can build this boat even if they only own basic hand tools and don't have boat building experience. A required tool selection includes: jig saw, circular saw, sanders, carbide scraper, rulers, tape measure, low-angle block plane, and screw drivers. Optional tools include: table saw and portable thickness planer. Optional means optional. The optional tools are not required. To build this boat to 26', we recommend having a shop sized 28' in length by 12' wide and a door that can open to 8' high or higher as a minimum. You will need 2 helpers when you turn over the bottom panel assembly, and approximately 10 to 14 helpers when you turn over the hull, but no special equipment such as chain lifts or tripod slings ...just a few friends, some old tires and blankets, and your favorite food and refreshments to say 'Thanks for helping turn over the boat!'

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