Speaking of props....
 

I had a discussion with a friend this afternoon about props and he was
trying to parse the difference between a 14 1/2 x 23 three blade and a
13 1/2 four blade for the same outboard. Apparently, he was told he
will get much better trim response on a 20 ft CC with a four blade,
but the size difference is to prevent the prop spinning on the hub.

As I'm not much of a prop guy, I really couldn't answer that question
although we batted around some ideas.

Anybody say which would be better for, say, a 225 Johnson?

Later,

Tom

I assume the pitch is the same on both (23) and I assume the material is the
same (I hope SS for this application).
The smaller diameter is to compensate for the extra blade surface of the 4
blades vs 3. This will allow you to maintain the correct rpms on top
end/wot.
Otherwise you would see a drop in rpms and speed or you would have to go to
a lower pitch which would still mean a drop in speed.

The 4 blade will be a better prop for this application assuming my
assumption above is correct.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Short Wave Sportfishing" wrote in message
...
I had a discussion with a friend this afternoon about props and he was
trying to parse the difference between a 14 1/2 x 23 three blade and a
13 1/2 four blade for the same outboard. Apparently, he was told he
will get much better trim response on a 20 ft CC with a four blade,
but the size difference is to prevent the prop spinning on the hub.

As I'm not much of a prop guy, I really couldn't answer that question
although we batted around some ideas.

Anybody say which would be better for, say, a 225 Johnson?

Later,

Tom

On Sun, 29 Aug 2004 00:55:42 GMT, "Tony Thomas"
wrote:

I assume the pitch is the same on both (23) and I assume the material is the
same (I hope SS for this application).

Exactly.

The smaller diameter is to compensate for the extra blade surface of the 4
blades vs 3. This will allow you to maintain the correct rpms on top
end/wot.

That's what I figured.

Otherwise you would see a drop in rpms and speed or you would have to go to
a lower pitch which would still mean a drop in speed.

The 4 blade will be a better prop for this application assuming my
assumption above is correct.

I was guessing, but that was my thinking on the subject - the main
problem with this boat is that the COG has changed somewhat with the
addition of a T-top. The result is that the boat has a problem at
speed in a heavy chop - the current prop, the 14 1/2 x 23, doesn't
push the boat through the chop properly at any trim angle and it tends
to pound and in certain wave conditions, the prop will cavitate.

The idea, in this case, was to add some extra punch to the prop by
changing diameter and adding a blade to give some extra grab via the
extra blade.

I'm also thinking that dropping the engine another notch or so to keep
the cavitation plate in the water would be a good idea.

Thanks for your thoughts.

Later,

Tom

Don't drop the engine too far. The cavitation plate should be at water
level or above. Definetly not below.

You might consider a whale tail after trying the prop. They really do help
if the prop does not completely do it.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Short Wave Sportfishing" wrote in message
...
On Sun, 29 Aug 2004 00:55:42 GMT, "Tony Thomas"
wrote:

I assume the pitch is the same on both (23) and I assume the material is
the
same (I hope SS for this application).

Exactly.

The smaller diameter is to compensate for the extra blade surface of the
4
blades vs 3. This will allow you to maintain the correct rpms on top
end/wot.

That's what I figured.

Otherwise you would see a drop in rpms and speed or you would have to go
to
a lower pitch which would still mean a drop in speed.

The 4 blade will be a better prop for this application assuming my
assumption above is correct.

I was guessing, but that was my thinking on the subject - the main
problem with this boat is that the COG has changed somewhat with the
addition of a T-top. The result is that the boat has a problem at
speed in a heavy chop - the current prop, the 14 1/2 x 23, doesn't
push the boat through the chop properly at any trim angle and it tends
to pound and in certain wave conditions, the prop will cavitate.

The idea, in this case, was to add some extra punch to the prop by
changing diameter and adding a blade to give some extra grab via the
extra blade.

I'm also thinking that dropping the engine another notch or so to keep
the cavitation plate in the water would be a good idea.

Thanks for your thoughts.

Later,

Tom

On Sun, 29 Aug 2004 02:32:15 GMT, "Tony Thomas"
wrote:

Don't drop the engine too far. The cavitation plate should be at water
level or above. Definetly not below.

You might consider a whale tail after trying the prop. They really do help
if the prop does not completely do it.

That's Part III. :)

Thanks.

Later,

Tom