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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

more about my 9.9. cavitates a lot???

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77Gypsy
Captain

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USA
356 Posts

Initially Posted - 06/21/2003 : 20:28:06

i have the extended shaft of 25". it seemed the prop was only submurged about 5-6 inches. the mount was on the farthest down position possible. is that ok? when i had one person standing on the bow, the motor was making a horible noise.
questions:
1. could this be affecting the speed?
2. should i replace the mount?
3. should i lower the bracket on the transom a few inches?

Steve
78 C25 SR/FK - Gypsy
<img src="http://www.websdf.com/gypsy_sign.jpg" border=0>

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/21/2003 : 21:22:24

"the motor was making a horible noise"

Yowser... don't run your motor with the lower unit popped out of the water. You'll ruin your water pump in very short order !

... regarding cavitation/motor position...

1. could this be affecting the speed?

Maybe... if it's cavitating all the time. When cavitating, the motor will rev up because it's not doing much work pumping air into the water. As a test, get some extra weight in the stern and see what happens when you know the prop is well buried. Where's your anti-cavitation plate in relation to the water ? It should be buried 4" to 6" or so.

2. should i replace the mount?

Dunno, what mount do you have? Some mounts have more 'throw' than others and depending on your current mount bolt hole situation, replacing the mount may/may not be easier than item #3 below

3. should i lower the bracket on the transom a few inches?

Not a bad idea as long as you can get the motor clear of the water and it's not so deep that the powerhead gets swamped.

Regarding your speed problems in general ?

How do you know you're making 2kts ? GPS or Knotmeter?
Over ground or water speed?

What prop do you have on the Honda ? A speed prop or a power prop?
For a sailboat, you want a power prop.. low pitch, big blades. Even with the speed prop you should still easily make your hull speed.

Why is the prop covered with Barnacles? Are you leaving the motor down in the water? (most folks raise them when not in use).

What kind of shape is your bottom in ? Do you have fresh anti-fouling paint on? If not, you may have so much growth (friction) that you aren't going to go anywhere fast until you clean it.

Currently maintaining two holes in the water...'77 Venture 23 and new to the family,
'78 Catalina 25

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Bill Holcomb
Admiral

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USA
769 Posts

Response Posted - 06/22/2003 : 09:43:01

Hi Steve,

We need more info. What engine do you have and what outboard bracket?

But, running the engine with the lower unit & prop out of the water is NOT a good thing.

Bill Holcomb - C25 Snickerdoodle #4839

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thacket3
Navigator

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USA
101 Posts

Response Posted - 06/23/2003 : 15:10:23

I have a "kind of" related question to this. When my motor braket, holding a 9.9 HP engine is inthe "all the way down" setting, I noticed that the thrust of the engine pushes the bracket inward. (the springs that lift the engine) this does not happen when the mount is inthe middle position. But I like having the motor as deep as possible to prevent cavitation. Is this "spring" ok? or is it time to replace the mount itself? I would hate to be motoring and loose the motor.

Anyone have any thoughts?

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OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 06/23/2003 : 15:40:15

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
. . . when my motor braket, holding a 9.9 HP engine is inthe "all the way down" setting, I noticed that the thrust of the engine pushes the bracket inward . . .
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

Maybe this falls into the high thrust category?

What motor and what bracket do you have?

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77Gypsy
Captain

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USA
356 Posts

Response Posted - 07/03/2003 : 22:46:50

not sure of the motor bracket. it came with the boat. it doesn't look stock though.

i have the fancy honda 9.9 4 stroke with a 25" shaft.

the cavitation plate sits about 1 inch under the waterline. when i have a bit of chop the motor comes out of the water.

Steve
78 C25 SR/FK - Gypsy
<img src="http://www.websdf.com/logo.jpg" border=0>

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deastburn
Captain

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USA
334 Posts

Response Posted - 07/04/2003 : 00:12:28

I have the Honda 9.9 with a 28" shaft, which is what is recommended for sailboats. All O/B brackets are not created equal, and the difference between a nine inch travel and a fifteen inch travel, coupled with the shorter shaft, could easily have your motor popping out of the water when someone spits. I should add, if only for consolation, that my 28" 9.9 Honda on an OMC bracket cavitates in any kind of a chop, particularly on the way into and out of harbor channels, where the tide often runs against the wind. Outboard sailboats work best on small lakes. Given that, occasional cavitation, as in a severe chop or swell, will not destroy your motor. Prolonged cavitation will. So, give us more information...

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77Gypsy
Captain

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USA
356 Posts

Response Posted - 07/07/2003 : 04:31:52

i guess it only really happens when i hit some wake. other than that, i'm pretty much ok. i may lower or replace the bracket next year, possibly to get the prop about another 4 inches under water. it's on my many "to do's" list.

Steve
78 C25 SR/FK - Gypsy
<img src="http://www.websdf.com/logo.jpg" border=0>

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.