Show Posts
1
Blog, New Designs Discussion / Re: POLL: Which Great Alaskan version do YOU want?
« on: July 08, 2025, 09:38:54 AM »
High Justin - good questions! The biggest thing to keep in mind when comparing the Great Alaskan to the 'tug' cruisers, is the type of hull and what the trade-offs are. There are 3 types of hull / boat designs in the world:
Displacement Hull - These just push through the water and are limited, hydrodynamically, to "hull speed". Hull speed is the maximum speed the hull can travel through water without having to use exorbitant amounts of power, e.g. realistic powering limits. The hull speed is 1.34 times the square root of the waterline length. Assuming a 29' waterline length on your tug, the hull speed is just 7.2 kts.
Planing Hull - These hulls plane (skip across the top of the water) when travelling above their minimum planing speed. The Great Alaskan series of boats are true planing hulls capable of high speeds.
Semi-Displacement Hull - These hulls are best described as a deep-hull planing hull that is too compromised in it's design to be able to achieve true planing.
So ... given the explanations above, the answer for you is yes, you can use the Great Alaskan as you describe, but there ARE strict limitations on weight placement in the boat, and to a slightly lesser degree, limitations on how much weight you can put in the boat as well. Given a basic, as-designed for typical usage, boat - additional weights added to the boat on either side of the LCG must be balanced out by an equivalent "moment" on the other side of the LCG. A moment is the moment-arm (distance) times the weight of the item. Gobble-dee-gook ... Best described with an example. The Great Alaskan comes with a drawing(s) that show typical placements of motors (and their weights), fuel tanks, appliances, storage etc that show the 'expected' way to fill the boat with what you want in it. The LCG is shown in the drawing (TBD - not added yet). As a realistic example, if I add a 30 lb load, say a refrigerator, at 10 feet forward of the LCG, that creates a bow-down moment of 30 lbs times 10 feet, or about a bow-down moment of 300 lb-ft. To balance the boat, I would need a moment of 300 lb-ft behind (aft of) the LCG. For example, placing a 60 lb weight at 5 feet aft of the LCG would create a balancing bow-up moment of 300 lb-ft (60 lbs times 5 feet) and the LCG would stay in the same exact location. To balance that refrigerator, I could perhaps locate the house battery near the stern of the boat ... or I could use a longer motor bracket or a heavier motor, or add a kicker motor if there were not already one on the boat. Simple, yes? LOL.
The best idea is to try to keep the apple close to the apple tree and use the given layouts as a general guideline, and look at trim versus weight placements from what others have done. You can of course ask me for guidance, and post questions in the Builder's Forums (the BEST idea) at https://www.glacierboats.NET .
Displacement Hull - These just push through the water and are limited, hydrodynamically, to "hull speed". Hull speed is the maximum speed the hull can travel through water without having to use exorbitant amounts of power, e.g. realistic powering limits. The hull speed is 1.34 times the square root of the waterline length. Assuming a 29' waterline length on your tug, the hull speed is just 7.2 kts.
- PROS: Super efficient, large load capacity, maximum cubic footage inside the boat (deep hull)
- CONS: Slow, typically more expensive to build (there is a strong correlation between ship weight and cost to build ... think "dollars per pound to build this boat". Best efficiency is at half hull speed or slower.
Planing Hull - These hulls plane (skip across the top of the water) when travelling above their minimum planing speed. The Great Alaskan series of boats are true planing hulls capable of high speeds.
- PROS: Modest efficiency, lowest cost to build (lightest boat style), and fast! Speeds on plan can range from around 10 kts to over 50 kts, depending on the boat's design, loading, and power. Efficiency while on place is moderately high, higher than semi-displacement hulls but lower than true displacement hulls. Planing hulls have the least cubic feet of interior volume due to more modest deadrise (the 'V' in a V-hull).
- CONS: Least payload or carrying capacity of all, strict requirements on where the longitudinal center of gravity (LCG) must be located in order to plane with no bad habits or characteristics. Very little flexibility in the payload and weight distribution in the boat due to the LCG requirements (LCG must be within 60% to 65% aft of the forward end of the waterline when in use). If you need more volume or weight capacity, then build one of the larger versions of the Great Alaskan.
Semi-Displacement Hull - These hulls are best described as a deep-hull planing hull that is too compromised in it's design to be able to achieve true planing.
- PROS: High efficiency when speeds are limited to those described for displacement hulls (above) - a good work boat where most of the day is spent taking care of slower tasks (lobster boats etc). Able to achieve faster speeds than a displacement hull since the boat can partially rise on plane, e.g. faster getting to/from port and the fishing grounds. High payload capacity, although typically not as high as for true displacement hulls.
- CONS: Only efficient when travelling slowly. When partially on plane, e.g. "semi-displacement mode", this hull is the least efficient of all - the one and only advantage is it's higher speed than a displacement hull.
So ... given the explanations above, the answer for you is yes, you can use the Great Alaskan as you describe, but there ARE strict limitations on weight placement in the boat, and to a slightly lesser degree, limitations on how much weight you can put in the boat as well. Given a basic, as-designed for typical usage, boat - additional weights added to the boat on either side of the LCG must be balanced out by an equivalent "moment" on the other side of the LCG. A moment is the moment-arm (distance) times the weight of the item. Gobble-dee-gook ... Best described with an example. The Great Alaskan comes with a drawing(s) that show typical placements of motors (and their weights), fuel tanks, appliances, storage etc that show the 'expected' way to fill the boat with what you want in it. The LCG is shown in the drawing (TBD - not added yet). As a realistic example, if I add a 30 lb load, say a refrigerator, at 10 feet forward of the LCG, that creates a bow-down moment of 30 lbs times 10 feet, or about a bow-down moment of 300 lb-ft. To balance the boat, I would need a moment of 300 lb-ft behind (aft of) the LCG. For example, placing a 60 lb weight at 5 feet aft of the LCG would create a balancing bow-up moment of 300 lb-ft (60 lbs times 5 feet) and the LCG would stay in the same exact location. To balance that refrigerator, I could perhaps locate the house battery near the stern of the boat ... or I could use a longer motor bracket or a heavier motor, or add a kicker motor if there were not already one on the boat. Simple, yes? LOL.
The best idea is to try to keep the apple close to the apple tree and use the given layouts as a general guideline, and look at trim versus weight placements from what others have done. You can of course ask me for guidance, and post questions in the Builder's Forums (the BEST idea) at https://www.glacierboats.NET .
