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Diameter of prop________________ D
diameter of prop_____ D
Prop
to rudder__________________ A
Prop to rudder_______ A
Top
of prop to hull_______________ C
top of prop to hull____ C
Bottom
of Prop to fairing: __________C
Back
of propProp to cutlass bearing___E
Using
your existing propeller measure C, D, then add C to ½ of d. this is the distance from the shaft centerline to the hull.
This
chart shows the clearance % for a propeller diameter and can be used to determine the diameter of standard propeller that will fit on your on your boat with the given clearence. E.G. A 12 inch diameter propeller
with 2 1/2 inches of clearence is a 8 1/2 inch dimension. which will allow 21% clearance for a 12 inch prop or a 15% clearance
on a 13 inch propeller.
Prop dia
|
1/2D +C |
11 |
12 |
13 |
14 |
15 |
16 |
|
|
|
|
|
|
|
|
|
|
|
7 |
14% |
|
|
|
|
|
|
|
7 1/4 |
16% |
|
|
|
|
|
|
|
7 1/2 |
18% |
|
|
|
|
|
|
|
7 3/4 |
20% |
15% |
|
|
|
|
|
|
8 |
|
17% |
|
|
|
|
|
|
8 1/4 |
|
19% |
|
|
|
|
|
|
8 1/2 |
|
21% |
15% |
|
|
|
|
|
8 3/4 |
|
|
17% |
|
|
|
|
|
9 |
|
|
25% |
|
|
|
|
|
9 1/4 |
|
|
21% |
15% |
|
|
|
|
9 1/2 |
|
|
|
17% |
|
|
|
|
9 3/4 |
|
|
|
19% |
14% |
|
|
|
10 |
|
|
|
21% |
16% |
|
|
|
10 1/4 |
|
|
|
|
18% |
13% |
|
|
10 1/2 |
|
|
|
|
19% |
15% |
12% |
|
10 3/4 |
|
|
|
|
21% |
16% |
13% |
|
11 |
|
|
|
|
|
18% |
15% |
This is the largest size of a standard propeller that would fit on your boat with the needed minimum clearence. Smaller
sizes can be used but larger sizes will cause additional noise and be harder to control.
Sometimes the best propeller for a motor is larger than will fit on
the boat with proper clearance.
| 15 inch extendo replacing a 12 inch bronze. |
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If your prop is in open water, Performance Propellers has
available special hub Extendo Propellers that mount on the existing shaft but position the propeller 6 inches aft. This change in position of the propeller,
due to the angle of the propeller shaft to the hull, can permit a 2 to 3 inch larger propeller.
Angle hull to shaft
10 12 14
16 18
20 22
24 26
Prop Dia chg
2.12 2.55
2.99 3.44
3.90 4.37
4.85 5.34 5.85
extendo clearence adder 1.06 1.28 1.50 1.72 1.95 2.18 2.42 2.67 2.93
For example a 12 inch propeller
on a boat that has a 16 degree angle propeller shaft to hull can be replaced by a 15 inch extended propeller.
A more accurate size
and clearence can be determined by adding 1/2 the diameter of the existing prop(D) , the propeller clearence (C) and the
extendo clearence adder and checking propeller clearence again. for example the 12 inch propeller with 2 1/2
inches of clearence on a 18 degree angle has a max size dimension of 6+2 1/2 + 1.95 =10 .450 or about 10 1/2 inches.
acording to the chart that will allow 19% clearence on a 15 inch propeller or 15% on a 16 inch propeller.
| aperature |
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We can help with your propeller choices
If your propeller is in and aperture,
then the propeller must be calculated using a maximum diameter and altering pitch to find an acceptable propeller. Propellers
that substitute pitch for diameter as in this instance are less efficient but will still deliver more horse power to the water.
A three blade propeller can some times can help put extra power into the water in the aperature but the three blade prop
will have additional drag while sailing.
Fill out our Size Questionnaire and give us a call we can help find a 2 blade propeller for you and give you an opinion if a three blade is necessary.
More information about propeller design and selection
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