Designing a Cordova, Alaska Bowpicker
Designing a Cordova, Alaska Bowpicker.
As a boat builder, I’m always looking for new markets and potential customers. The market for new bowpickers for fishermen who fish out of Cordova, Alaska appears to offer such an opportunity.
The Copper River flows for approximately 300 miles through the Wrangell and Chugach mountains. Every mid-May, the first salmon of the season return to the Copper River to swim upstream and spawn. The Copper River is a large and swift moving river. As the fish approach spawning season, they decrease their feeding and rely on stores of extra fat and oils to survive the trip upstream. The high fat and oil content is why many people consider the Copper River salmon some of the best-eating salmon in the world.
Approximately 500 fishing boats converge in Cordova every May to fish the 35 mile wide delta of the Copper River. The natural environment the fishermen operate in has influenced the design of the Cordova bowpickers. The fishermen have a 35-50 mile run from the harbor in Cordova to the river delta area. Due to the relatively long run, the fishermen prefer a vessel with a top speed in the 35-40 MPH range. The fishermen are keenly aware of fuel costs and expect operating efficiency. The delta area is referred to as the “flats”, as the water is very shallow. Due to the shallow water conditions, jet drives have evolved to become the propulsion system of choice. The delta is exposed to the Gulf of Alaska and, as a result, the sea conditions can become fairly rough and therefore the fishermen require a seaworthy vessel. Due to strong winds, the fishermen prefer a vessel that has minimal windage.
The design of the Cordova Bowpicker has evolved over the years, as fishermen learned what does and does not work. During the last 25-30 years, the fleet has evolved toward a vessel of approximately 32 feet in length and 11 to 11.5-foot beam. The boats are characterized by a cabin in the aft third of the vessel with twin gas or diesel engines powering twin jet propulsion units sequestered under the cabin. The vessels are typically bowpickers with a bow roller mounted on the bow and a gillnet reel mounted on the deck approximately seven to eight feet aft of the bow roller. Aft of the gillnet reel, there are typically six fish holds that will hold approximately 7,200 pounds of fish. Fishermen place a netted bag, called a brailer bag, in each hold and use the bags to quickly offload their catch to waiting tenders.
The majority of new vessels are constructed of marine grade aluminum, but several builders are offering fiberglass vessels. Most of the shops that build Cordova bowpickers are relatively small and will deliver two to six vessels per year.
There appears to be three different groups with opinions on the size and general configuration of the vessels. One group prefers vessels that are as light as possible. To achieve their goal of reducing weight to the minimum, these builders typically build a smaller vessel with less overall length, less beam, and less fullness in the bow. They also minimize structural framing and interior accommodations that add weight to the finished vessel. These vessels are known for their speed with a given size engine and better fuel efficiency.
Another group prefers a larger, more robust vessel. These vessels tend to be larger than the norm, with greater overall length, beam, and freeboard. While these vessels are less efficient than their lighter competitors, they have an excellent reputation for being able to handle rough water and providing a more secure vessel to fish from.
The third group aims for moderation in size and weight. They build vessels that are approximately 32 feet long and usually about 11 feet in beam. In comparison to the lighter vessels, they sacrifice somewhat in operating efficiency to gain a more robust construction and more comfortable platform to fish from. One of the reasons some of these builders limit their beam to 11 feet is because they build in Anchorage and then truck the vessel to Whittier. To make this delivery, they have to go through a tunnel with a width restriction of 11 feet. Therefore, they design the vessel to the tunnel, not to the mission.
Improving the Breed
As a builder who is attempting to cultivate a share in the market, my two main objectives are to improve the design and construction of the vessels. To help achieve these goals, I asked Steve Pollard, owner of Specmar, Inc., to co-develop the vessel design. Steve has more than 40 years’ experience in building and designing aluminum boats.
In round numbers, a Cordova Bowpicker will weigh approximately 13,000 pounds with no fuel, hydraulic fluid, water, crew or gear. This is called “light ship.” When a fisherman prepares to leave the dock to journey to the fishing grounds, he will add approximately 200 gallons of fuel (about 1,400 pounds), 30 to 40 gallons of hydraulic fluid (about 250 pounds), 20 to 40 gallons of fresh water (about 250 pounds), crew (about 200 to 400 pounds), and gear (about 500 pounds). Thus, the vessel weighs approximately 14,500 to 17,000 pounds as it leaves the dock. This is referred to as “performance ship.” Once a vessel starts to fish, the total weigh of the vessel and fish increase to 21,000 to 25,000 pounds. This is called “heavy ship.”
The challenge facing the designer is to create a vessel that will operate efficiently and safely within these weight ranges. There are three basic considerations that must be addressed in the design – deadrise, bottom loading, and dynamic stability.
Deadrise is a measurement of the angle, or V, to the bottom of the vessel. Deadrise measures the angle the bottom of the vessel goes up from the keel to the chine. A jet powered vessel needs sufficient deadrise to help provide directional stability. However, excessive deadrise needs to be avoided because lift, generated by the hull bottom for planing, decreases as deadrise increases. Experience suggests a good compromise for deadrise at the transom is approximately 12 degrees.
Deadrise at the bow is equally important. The entry must have sufficient deadrise to cut the water and prevent pounding. However, excessive deadrise must be avoided because of the tendency for a Bowpicker to trim bow down with a full load of fish and to help prevent the bow from digging into the water when running in a following sea. If the bow digs in (called bow steering), the vessel loses directional stability and may broach. Or, worse case, the bow may bury into a wave and the vessel could pitch pole.
Bottom loading is a measure of how many pounds of weight are being supported by each square foot of the running surface. If the bottom loading is too light, the vessel will have poor handling characteristics and become skittish or even, in some cases, unsafe. If the bottom loading is too heavy, the vessel will fail to plane and lose significant speed capability. Under extreme conditions of overloading, the vessel will become unsafe, exhibiting very poor handling characteristics, and may be subject to flooding and potentially, sinking. The objective of properly bottom loading is to design a vessel that will operate at optimal conditions with the best possible fuel efficiency under “normal” operating conditions.
Dynamic stability is the ability of a vessel to operate safely at speed with the vessel to maintaining its intended course without the helmsperson having to constantly steer to maintain course stability. Dynamic stability is important for two reasons, the safety of the vessel and ease of steering and operation by the helmsperson. Dynamic stability is determined by the design of the running surface of the hull and the lateral center of gravity of the loaded vessel in comparison to the centroid (the center of the hull’s bottom) of the running surface. Fishing vessels are difficult to design, as the loading of fish will significantly alter the center of gravity of the vessel and may negatively impact the dynamic stability of the vessel.
As Steve Pollard and I begin the design process, one of the first variables we consider is deadrise. Based on experience, we judge the optimal deadrise at the transom is approximately 12 degrees. This deadrise angle will help to ensure directional stability, minimize pounding, promote excellent jet power operation, and provide the hull with the ability to carry heavy loads and still remain on step.
In a review of the existing fleet, our conclusion is that most vessels do not have adequate deadrise forward. We conclude an optimal deadrise angle at the cutwater is approximately 45 degrees. This deadrise forward allows the vessel to cut through the water without excessive pounding. Yet, it retains enough fullness and buoyancy in the bow to minimize the tendency for the vessel to bury its bow which leads to broaching, or worst case scenario, pitch poling.
Next, we consider the width of the chines flats. Chines are the intersection of the hull bottom and hull side. Most planing hulls have a flat chine running from the bow to the transom. The chines serve three purposes. First they separate the flow of water from the hull bottom and hull side, resulting in more efficient operation. Second, they knock down spray, making for a dryer boat. And third, they provide a flat running surface that provides hydrodynamic lift, resulting in a faster and more fuel-efficient vessel. Many of the vessels currently in operation or being built have what I consider to be an excessively narrow chine flat.
Based upon experience, I judge bowpickers will benefit from a wider chine. Many vessels have a chine width of four to six inches at the transom. I have elected to increase our chine width to nine inches. I believe wider chines will provide more lift, resulting in a slightly faster and more fuel efficient vessel. I have limited the chine width to nine inches, as a wider chine would adversely affect the deadrise angle. Everything in boat design is a compromise!
Bottom Loading and Size
I conducted an extensive analysis of bottom loading to help determine the optimal size vessel considering the anticipated weights for an operational vessel. I consider three weights, first “light ship” with no fuel, hydraulic fluid, water, crew, or gear; second, “performance ship” with fuel, hydraulic fluid, water, crew, and gear; and third, “heavy ship” with a load of 8,000 to 10,000 pounds of fish.
For purposes of analysis I estimated light ship at 13,000 to 14,000 pounds, performance ship at 16,000 to 17,000 pounds, and heavy ship at 20,000 to 24,000 pounds. To determine bottom size, I assumed the length of the vessel from the transom to the chine/stem intersection and the chine beam. I used the Blount Dynamic Stability program as developed by Donald Blount and Lou Codega, two very highly regarded naval architects who specialize in high speed planning hull designs.
My analysis of bottom size ranges from a transom to chine/stem intersection length of 28 feet to 31 feet and chine beam of 10 feet to 11 feet. For the purpose of bottom loading analysis, I have constructed three tables. The first table reflects bottom-loading capacity for 10-foot chine beam vessels ranging in length from 28 to 31 feet. The second table reflects bottom-loading capacity for 10.5-foot chine beam vessels ranging in length from 28 to 31 feet. The third table reflects bottom-loading capacity for 11-foot chine beam vessels ranging in length from 28 to 31 feet.
If I assume the average weight of a vessel as it leaves the dock to be 16,500 pounds and our objective is to achieve maximum fuel efficiency at this weight, my analysis suggests I consider a 31-foot by 10-foot, 30-foot by 10.5-foot, or a 28-foot or 29-foot by 11-foot vessel.
Keeping in mind the design of a vessel represents intelligent compromise; I want to avoid excessive length, as that increases construction costs. I want to avoid excessive beam, as that makes it more difficult to efficiently operate the vessel due to greater drag. And, I want to avoid too narrow of a vessel, as that reduces stability and limits room for the fishermen. Based on the above considerations, I consider a 29.5-foot long by 10.5-foot chine beam vessel as the “ideal” compromise:
I estimate lightship at 13,500 pounds and the above noted vessel size is best suited to a lightship of 14,300 pounds. But, the reality is a fisherman will never operate the vessel at lightship weight, as he needs fuel, gear, and crew at a minimum. I estimate performance ship weight when leaving the dock at 16,500 pounds, plus or minus 500 pounds. If the fisherman burns 35 gallons of fuel, then his weight will reduce to 16,250 pounds. The above noted vessel size delivers optimal performance at approximately 16,250 pounds. We are spot on for optimal performance and fuel efficiency. I estimate heavy ship weight at 20-24,000 depending upon the weight of the catch. This above noted vessel should continue to plane with a fish load of approximately 7,200 pounds, which is equal to six 1,200 pound brailer bags. If the vessel is loaded heavier than 7,200 pounds, it will most likely continue to plane in shallow water, as these vessels tend to have an ability to carry heavier loads in two to three feet of water.
Based on the above analysis, I conclude the “ideal” Cordova bowpicker should have a transom to chine/stem intersection length of 29.5 feet and a chine beam of 10.5 feet. This is slightly larger than the moderate size vessels that are currently popular with many fishermen. I anticipate our size vessel will provide more efficient fuel economy and better fish carrying capacity than the moderate size vessels.
With a reasonable rake to the bow, our “ideal” bowpicker will be approximately 33 feet long on the deck. This is about one foot longer than the current moderate size vessel. This additional length will add slightly to the weight and cost of the vessel, but should make for a more fuel-efficient vessel and a better sea boat that is less sensitive to sink and trim as fish are loaded.
Dynamic stability is determined by the hull shape and the center of gravity of the loaded vessel in relation to the centroid of the bottom. As previously mentioned, we will have a transom deadrise of approximately 12 degrees and a cutwater deadrise of approximately 45 degrees. This hull design should prove to have excellent dynamic stability. If we assume the centroid of the bottom is approximately 40 percent forward of the transom, or 11.8 feet, then we need to maintain the center of gravity of the loaded vessel aft of the centroid for dynamic stability. Our dynamic stability program recommends a center of gravity for a performance vessel of 10 feet forward of the transom and a center of gravity for a heavily loaded vessel of 10.43 feet forward of the transom. Considering that Cordova bowpickers are naturally stern heavy due to engine and cabin placement, these center of gravity guidelines are very reasonable and easily achieved. Our design should be very dynamically stable and therefore safe in adverse sea conditions.
One advantage to the extra foot of hull length is that the cabin can be increased in size from the standard 10-foot length to 11 feet. Due to a 6-inch wider beam than normal, the cabin width is increased from 9.5 feet to 10 feet. This results in a 15.8 percent increase in interior room, making the vessel more comfortable and easier to live on.
Computer Aided Design and Router Cut
The final step we have taken to improve the breed is to utilize computer aided design and router cutting of the material. Many boat builders design their vessels on the proverbial back of an envelope. They are reluctant to invest the time and money required to have professional design. Computer design enables the designer to conduct hydrostatic calculation, calculate performance estimates, and design an efficient hull structure that provides needed strength with minimal weight. By utilizing computer aided design, the designer always knows exactly what he is dealing with and he can make changes to the vessel to optimize performance, seaworthiness, and strength. Computer design has the additional advantage that aluminum used to build the vessel can be router cut. Router cutting makes for an accuracy measured in the thousandths of an inch compared to hand lofting and material cutting with a Skill Saw that will produce accuracy typically within plus or minus a quarter-inch. Router cutting is more expensive, due to the need to have computer design and to pay for the cutting costs (which average about $.85 per pound for the fabricated hull). However, increased costs are quickly recovered by the builder with more efficient fabrication of the vessel and the elimination of time-consuming hand fitting and repeated fitting and cutting to achieve a reasonable material fit.
Presenting the “Ideal” Design
A lines drawing is shown. Note the 45 percent deadrise angle at the cutwater for a better entrance. Note also the deadrise aft and the wider than normal chines for optimal performance. And note the straight buttock lines on the aft section of the hull bottom. Buttock lines are the longitudinal sections of a vessel’s hull parallel to the keel. Straight buttock lines make for a better performing planing hull.
A profile and plan drawing is shown. Note the internal framing for this vessel. We will utilize a well-proven concept – aircraft style box construction with transverse frames and longitudinal girders. Box construction makes for a light but incredibly strong vessel.
A cabin drawing is also shown. The larger than normal cabin provides a roomy and comfortable retreat while fishing or overnighting on the vessel. Note the large head, which can be equipped with a shower and also used for hanging wet clothing to dry. There is a large galley (4.5 feet long) and two extra-large bunks, each measuring 6 feet, 9 inches long and 36 inches wide. Standard is a forward facing dinette for one man. An optional dinette with two seats may be specified. And there is a large recessed area just forward of the head for a propane or diesel cabin heater.
The goal of our design process was to create a superior vessel for the Cordova-based fishermen. By utilizing computer-aided design, we have a high level of confidence in the performance of the vessel. We know a router cut vessel will be easier, faster, and more accurate to fabricate than a hand lofted and cut vessel. We will have the ability to offer engine choices and many choices regarding equipment and accessories.
Should you have comments or questions regarding this design or the design process, please feel free to call Jim Bower at 425.301.6016.