Johnson 25 3-cyl, 4 or 3-blade?

[Grumman59]

I have a '98 Johnson 25 3-cylinder on a 14'-6" Princecraft side console aluminum fishing boat.

I'd like to get a spare prop. The OEM prop is a 4-blade 10-1/2x12" which gives me about 25 mph at about 5500-5600 RPM. I'm quite happy with the current performance and I can buy a spare Solas replacement right here for a reasonable price.

Two questions really, since I can buy a 3 or 4-blade for practically the same price. Would a 3-blade of similar spec be a suitable replacement, or how might it change the performance? It might be a good idea to try a different prop anyway.

And why would this outfit come with a 4-blade prop instead of the normal 3-blade? (The boat was supplied with this motor by the factory back when OMC owned Princecraft.)

 

[steelespike]

Re: Johnson 25 3-cyl, 4 or 3-blade?

It appears your doing pretty well allready.
I would be surprised to find a 4 blade stock but maybe they did their homework and felt it needed it. Basically a 4 blade gives better low to midrange performance,stays on plane better at reduced throttle, handles better at the dock and at speed.Will resist ventilation allowing a higher motor installation.Usually the top speed will be reduced slightly.Basically a 3 blade will give good overall performance with a little better top end.
If you want to experiment an 11" or 12" Turning Point Rascal ,a 3 blade, that could both surprise or dissapoint.I don't see a Rascal here at iboats so maybe a 12" Solas 3blade for a change of pace.

 

[Grumman59]

Re: Johnson 25 3-cyl, 4 or 3-blade?

Thanks, steelespike. Actually, I just need a spare prop because we are plagued with tree-stumps and rocks in the rivers and lakes here on the Nature Coast (Fl.)

I'm quite satisfied with the performance as it is. Top end is OK, it gets up nicely and stays on the plane at reasonably low revs and since iboats have 30% off right now on the Solas 4-blade, I just bought one of those, same specs as the OEM. Can't refuse a deal like that. http://forums.iboats.com/images/smilies/smile.gif

It's interesting what you say about the motor being able to be mounted higher with a 4-blade because the brackets are bolted about 1" above the transom and I believe this boat was factory rigged. So like you say, looks like they did their homework.

 

[steelespike]

Re: Johnson 25 3-cyl, 4 or 3-blade?

Yes raising the motor reduces drag and puts the prop a tiny bit farther from the bottom.