How
to determine the correct outboard shaft length:
First, lets get a better understanding of outboard shaft lengths
and what they mean. Shaft length is simply a "what your boat
requires" matter. In other words, you don't really have a
choice. A long shaft doesn't go any faster or slower than a short
shaft. However, selecting the right shaft length is crucial and
improper selection could result in severe engine damage.
Measure
from the top of your transom to the bottom of your keel. If it
is 15" to 17" you'll need a "short shaft"
outboard. If it is from 20" to 22" you'll need a "long
shaft" outboard. Tohatsu/Nissan outboard shafts are measured
from the bottom of the engine mounting clamp bracket to the cavitation
plate (large fin above propeller) on the lower unit - see diagram
below. Generally most boats need either a short or long shaft
although some boats require a 25" "ultra-long shaft"
outboard. Below is a diagram on how to measure your transom for
proper shaft length. NOTE: ANY
OTHER MEASUREMENT OTHER THAN THE ONE DISPLAYED BELOW WILL BE USELESS
INFORMATION. |
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| For
normal operation your engine's cavitation plate should be even with
the bottom of the hull. A gap of 1-2" in either direction is
acceptable and considered normal. If you are still unsure as to
which shaft length your boat needs contact your hull's manufacturer.
Your outboard owner's manual will also contain more information
on shaft length and proper installation. |
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Related
Frequently Asked Questions: |
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Q:
Can I use a long shaft engine on a short shaft boat? |
A:
We don't advise it but many folks do. Having a long shaft
engine on a short shaft hull can create extra drag and could have
an effect on maneuverability. |
|
Q:
Can I use a short shaft engine on a long shaft boat? |
A:
No. This will not allow the engine to intake adequate cooling
water resulting in overheating and severe engine damage. |
|
Q:
I have an adjustable outboard motor bracket can I use a short
shaft? |
A:
Yes, if the bracket is correctly installed and allows for proper
travel so that the engine is in the proper operating position
in the bracket's down position. |
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Q:
Can you convert a short shaft to long shaft? |
A:
Possibly. Some manufacturers have kits available to complete this
shaft length conversion. Not all makes and models have these kits
available. Tohatsu/Nissan has several kits available for certain
hp's and models. |
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Q:
My motor cavitates and comes out of the water. Do I have the wrong
shaft length? |
A:
Likely so. This can occur if you are in very high seas, especially
if the engine is mounted at the stern. However, if this is occurring
more often you may need to adjust the tilt pin, motor/transom
bracket (if possible), or you likely have the wrong size shaft
length. Engines that cavitate frequently can wear out water pumps
prematurely as well as not allow for adequate engine cooling both
which could lead to severe engine damage. You should take corrective
action immediately. |
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| Below
are examples of 15" short, 20" long, and 25" ultra
long shaft lengths: |
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 |
 |
TOHATSU
15" SHORT SHAFT |
TOHATSU
20" LONG SHAFT |
9.8HP
FOUR-STROKE OUTBOARD |
9.8HP
FOUR-STROKE OUTBOARD |
| |
|
|
TOHATSU
25" ULTRA-LONG SHAFT |
9.8HP
TOHATSU OUTBOARD |
