Pennsylvania Angler & Boater, September-October 2002 www.fish.state.pa.us12

Over the years, I’ve seen outboard jet applications used forfishing saltwater bays and shallow lakes and navigating rock-filled eastern river flats and the raging white water of north-western rivers. Having climbed aboard a number of outboardjet rigs, I’ve learned there may be no limit to where we will findoutboard jet use in the future. However, there are limitationson how they are best used in shallow eastern rivers. A hull thatperforms well in one application may not perform well inothers. Here are seven steps that can help you select a jet boatto traverse Pennsylvania rivers successfully.

The list order is important because each step offersinformation that helps to define the next step. Because of thespecific needs associated with river travel, I place carefulattention on areas that may never even get a second look inother marine applications. Following these seven steps willresolve many limitations common to outboard jetting.

Hull shapeWhen many PA anglers consider a river craft, they turn

first to a flat-bottomed johnboat. When it comes to outboardjets, flat-bottomed hulls tend to cavitate more than any otherhull type. Cavitation occurs when the jet intake pulls moreair than water into the pump housing. Flat-bottomed hullshave a tendency to channel air bubbles and carry them fromthe bow to the stern and into the jet intake.

A slight degree of deadrise in the hull splits off the airbubbles before they reach the intake. This small deadrise alsoimproves handling. Many aluminum boat manufacturersnow offer sled and johnboat hulls with 3 to 6 degrees ofdeadrise from the bow to the stern.

Regardless of which outboard brand name you select, ifthe engine has a jet attached to the lower unit, it wasmanufactured by Outboard Jet, a division of Specialty Manu-

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Selecting an Outboar

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tby Chris Gorsuch

www.fish.state.pa.us Pennsylvania Angler & Boater, September-October 2002 13

facturing. Outboard Jet publishes a guideline for selecting ajet hull. One of the first key elements is the hull’s chine. Thechine is the area where the hull’s side meets the bottom. Foroptimum performance, you must select a hull with a sharpchine. A sharp chine reduces drag and helps the hull get onplane better than a soft, rounded chine.

Bottom widthMost, if not all, jet-powered boats are designed to run in

shallow water while on plane. The key is to select a hull thatdrafts shallow while on a drift. The wider the bottom of thehull, the more displacement the boat offers. The increaseddisplacement produces a shallow draft when the craft drifts.Under power, even though there is increased surface area, thehull tends to jump on plane quicker because of the short rise.Jet drives should not be considered for any craft that does nothave a consistent bottom width equal to or greater than 48inches. Based on several other key elements, you should selecta hull that is 48 to 66 inches wide.

The general rule when it comes to a jet hull length isstraightforward—nothing less than 14 feet. This rule standsto reason, because there aren’t too many sled or johnboat hullsless than 14 feet that offer 48-inch bottoms. The mostpopular hull lengths seem to be in the range of 16 to 18 feet.At this length, the hull size and weight are a good match fora mid-range jet engine.

Another consideration for the length and width selectedis the basic characteristics of the river where you’ll most oftenuse the boat. Tight areas and narrow passes may put limita-tions on the hull size.

Hull constructionAluminum hulls are the best bet for shallow rivers.

Aluminum hulls offer superior durability and are lighter thanother hull materials. Anyone who has ever operated a jet-powered boat knows that hitting shallow ledges is inevitable.To help counter the occasional impact associated with rivertravel, the hull gauge should be no less than .100-inch thick.Anything less will not likely hold up over time. Here again,many hull manufacturers offer hull gauges in .100-inch and.125-inch thicknesses.

With the hull material selected, the next decision is howit is fabricated. Aluminum is either riveted or welded. Eventhough many manufacturers have explanations for which oneis best, having owned both types, I’ve drawn my own conclu-sions. In a lake setting with pounding waves, a riveted hull

Engine Weight 235

Battery (2) + 115

Fuel (@ ~8lbs per Gal) + 95

Your Weight + 175

Passenger A + 190

Passenger B + 165

Gear Weight + 50

(A) Weight in Payload 1025

Hull Weight + 550

(B) Total Gross Weight 2,600

(weight in pounds)

Weight Calculation Example Worksheet

Chart AEstimating Overall Weight

Pennsylvania Angler & Boater, September-October 2002 www.fish.state.pa.us14

seems to travel better. How-ever, for river applications Iprefer a welded hull becauseit will just last longer.

Overall weightOverall weight is the

most overlooked area, eventhough jets are known to bemore susceptible than prop-powered hulls. Beyond thehull weight, which can rangefrom 400 to 1,000 pounds,it is important to estimateclosely the total weight yourengine will be pushing. Tobe accurate, include the en-gine, batteries, passengersand any expected payload.The chart on page 13 provides an example and doubles as aworksheet to help you calculate your overall weight.

Estimating the overall weight will help to outline twoneeds. First, use Chart A as a guide to ensure that the hullselected is rated well above this calculated total capacity.Weight will vary between passengers and gear, so it is alwaysbest to guess on the high side. Second, total gross weight(Chart B) should be used in the next step to help select theproper engine size. Each step prepares you for the next.

Engine sizeSelecting the correct engine size for an outboard jet does

not have to be a mysterious process. Here is a safe guidelinefor selecting the right-sized engine: You need a ratio of 1horsepower for every 25 pounds your craft will be pushing.

Use the engine powerheadrating, not the jet rating,when using this calculation.

For example, a 60/40jet engine will effectivelybring 1,500 pounds of grossweight on plane. Additionalweight beyond this numberwill greatly affect perfor-mance.

The chart at left wascreated to be used as a quickreference guide. The blackline on the chart follows the25:1 weight ratio. The folksat Outboard Jet produce achart similar to this one.

Hull layoutSelecting the right hull layout is an essential part of the

process. Homework here can help balance the weight fromstern to bow. Appropriate weight distribution greatly im-proves the time it takes the boat to reach plane and waterdepth that can safely be drifted through. The situation toavoid is a layout that places all the weight in the boat stern.Console placement can greatly assist in balancing the overallweight.

The illustration on page 15 shows the effects of adjustingthe console forward. The goal is to get the craft to sit as levelas possible.

A forward-mounted console offers more than just weightdistribution—it improves the line of sight while runningnarrow channels or shallow flats. To add further to the varietyto hull steering options, several manufacturers offer jet craftsin side-console, center-console and stick-steer models. Each

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Chart BWeight Compared with Horsepower

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Horsepower Rating

www.fish.state.pa.us Pennsylvania Angler & Boater, September-October 2002 15

Console Placement and Balancing Weight

Unacceptable trim

Better trim

Best trimBest trim

has advantages and is well worth consider-ation. I have operated crafts with each setup.They all work well when they are set upproperly.

Multiple seat base positions let passen-gers sit in several locations when the craft isunder power. Seating options become im-portant because the number of passengersmay change from trip to trip.

Customizing the hull layout can be oneof the most rewarding and beneficial steps inoptimizing the boat for how it will most oftenbe used. The only caution is the tendency tochoose too many options. Multiple storagebins, rod lockers and other accessories arenice, but they also add weight. For shalloweastern rivers, it is important to keep theweight down.

Test driveThe best advice I can give anyone is

always ask for a test drive before you buy. Itis the final exam for how well the first six stepswere followed. Marine shops that have a goodproduct will not have any problems taking apotential buyer out on the water first. Takethe helm, drive it, and test how it maneuvers.Get a feel for how well it drifts and how muchyour drafting depth is. This is a sizablepurchase. If you let the performance of thehull do the talking, you’ll ensure that yourmoney is well-spent. If for some reason a testrun cannot be provided and you’re still sold ona particular craft, ask to speak with a customerwho purchased a similar package. Youwouldn’t buy a car without a test drive first, sowhy should it be any different with a boat? Atest drive is the only way to ensure yoursatisfaction.