�� Planing Hull Bottom Types Buyer guide jetcraft.ru Boat Materials

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Planing Hull Bottom Types �� 

There are a number of hull choices for river / shallow water service. Each has their own

merits and shortcomings depending on the conditions the boat is expected to operate in.

Many are completely unacceptable for use in anything but shallow water. However,

Marathon�s Radius works well in both rivers and inland lakes and waterways.

It also works well with a variety of power choices including outboards and sterndrives.

Marathon has built and tested just about every variation of jet boat since 1967. We have

learned that there is no one hull design that answers the exact needs of all operators. As a

result we incorporate the very best of every feature wherever we can. What follows is a

brief summary of what we have experienced with different hull shapes and a brief

description of our Radius Bottom.

Excluding racing hulls, there are generally two types of shallow water planning hulls.

� Constant deadrise V (including modified V hulls)

� Flat bottom hulls

In addition to this there may be two different bow type entries incorporated in the design.

These include:

� Shallow entry

� Sharp entry

Constant deadrise V (including modified V hulls)

As the centerline profile of a V hull generally forms a point the following applies:

Sharper point = deeper deadrise = more hull in the water = softer ride.

Correspondingly:

The more hull in the water = more wetted surface = more drag = higher fuel consumption

Whether at rest or on plane, a deep V constant deadrise hull will sit / plane deeper in the

water. It will also have the tendency to roll at rest. The constant deadrise V certainly has

its place and Marathon builds many V hulls - generally with 12 degree deadrise. We have

found this to be the optimum deadrise for shallow water operation, stability at rest and

rough water handling. However, we have also found that no matter what deadrise is

specified a V hull will lose lift in turns - which translates into slower boat speeds when

cornering and less responsive hull performance overall.

Flat bottom hulls (8 degrees deadrise or less)

This type of hull generates better lift and makes for an awesome shallow water boat. It is

quick to plane and has much less hull in the water to be damaged by underwater

obstacles. As is always the case there is a trade off. Flat bottom hulls are extremely rough

riding in anything but calm or flat water conditions. This type of hull is also best suited

for a seasoned operator that is familiar with its unique handling characteristics. These

boats tend to �slide� when cornering and cavitate in rough or white water conditions.

Many operators swear by this bottom design. While they do have a place where

navigating extremely shallow water, their maneuverability and performance is ill suited

for navigation in white water where stability and split second positive direction changes

are required.

Boats: What to Look For. �� .

Introduction.

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Welded Boats in General:

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Our Bias

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Shop for a Manufacturer First

Look in the used boat ads

Judging the Production Staff

Manufacturer Reputation

Buying a Welded Boat for the First Time

Know the Boat you want

There is no Perfect Boat

Take a test ride.

Acceleration out of the hole

Bottom Width and Engine Size and Type.

Turning ability.

Stability at Speed: Porpoising versus bow down ��.

The Hook.

Spray Line?.

Boat Materials: Aluminum versus Fiberglass .

Cost differences between glass and aluminum . �� .

Types of Aluminum. �� .

Material Thickness

A Word about Welding

Suck marks, caterpillar tracks

Folded, �Origami� Construction

Hull Design

Delta Keel.

Deadrise (Vee)

Planing Hull Bottom Types ��

Constant deadrise V (including modified V hulls)

Flat bottom hulls (8 degrees deadrise or less)

Bow Entry Types. ��

Shallow Entry

Sharp Entry

Radius Bottom �� .

Lift Forces Explained.

Lateral Stability During Planing Turns

Bottom Shape and Jet Intake

Planing Ability

Reverse Chines

Bottom Width: Flair is not everything

No Trim.

Hull Construction Standards

Shallow Water Operation

No Exposed Drive

Safety

Thrust line and Center of Gravity In line

Propeller Torque is Different than Impeller Torque

Propulsion Resistance.

Power Plants

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Derived from Impeller Curves.

RPM Curve Derivation

Conclusion

Hull Resistance.

Boat attitude..

Jet Drives

How jets work .

Impeller

Cut.

Cut, Speed and Load

Wear ring.

Nozzle

Stator.

Hard Anodized.

Cavitation .

Intake

Seals

Mixed flow

Axial flow.

Outboard jet:

Inboard jets:

So, what is the best jet?

Corrosion.....

UHMW...

Jet Diagnosis...

Rattle at Idle (V8 boats)

Speed too low for a Given RPM.

Poor acceleration or �holeshot�, combined with high top end

Definitions.

Porpoising .

Chine walk: 9

Ram effect .

Static thrust:

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Spiridonov S. E.

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JETCRAFT. ��. �� . �� . ��. �� . �� . (Boats: What to Look For . Buyer guide)