C-Dory Johnson 70 prop selection

[Lowranger]

22' C-Dory Cruiser about 3500# powered by '89 Johnson 70 w/VRO2. Currently running OMC 14x13 cupped aluminum 3 blade. Top speed is about 24 mph @ 5600 rpm. The experienced techs in the J/E forum REALLY like to see my engine propped to max out @ 6000 rpm so I don't lug my motor. Is jumping down to a 14x11 3 blade aluminum going too far(over 6000 rpm)? Any guesses about speed/rpms? I see that I-Boats has a great deal on a Michigan Match 14x12 4 blade aluminum. This prop would drop my pitch by just one inch. However, is the additional blade going to have enough extra drag to keep my rpms from rising to where I want them(6000)? Is this a big enough jump to get my rpms up to 6000? Also, any thoughts on 4 blade-vs-3 blade for my application? Btw, I typically cruise her at about 4500-5000 rpm and 14-19 mph. Very very rarely do I exceed 5200 rpm with my current setup(the hull will pound). Any help selecting the right prop will be appreciated.

 

[walleyehed]

Re: C-Dory Johnson 70 prop selection

I would look here;<br />http://www.iboats.com/mall/propfinder/?**********=39649401&*******=856800924&pitch=11.00&prop_chart_relation_id=6208&search=Product&manufacturer=Johnson&rotation=Standard&horsepowe r=70&year=1989&url_mode=standard&chart=15<br />The 11P is going to bring the R's up, but the SS prop will be a bit more efficient, speed-wise.<br />A 12P 4-bld will not increase your RPM..infact, it would be about the same as the 13 in 3-blade.

 

[Lowranger]

Re: C-Dory Johnson 70 prop selection

Hi Kenny, Thank you for your quick reply.

A 12P 4-bld will not increase your RPM..infact, it would be about the same as the 13 in 3-blade.<br /><br />

Yes, that is what I suspected. I guess if I'm serious about picking up those 400 rpms I'll need to go with an 11.

 

[walleyehed]

Re: C-Dory Johnson 70 prop selection

Can you raise the engine some yet???

 

[Lowranger]

Re: C-Dory Johnson 70 prop selection

No, I can't do that. In a frothy chop she occasionally ventilates with the height I'm running now.

A 12P 4-bld will not increase your RPM..infact, it would be about the same as the 13 in 3-blade

How about a 4 blade 14x10? $71.99 during the I-Boats prop sale.

 

[walleyehed]

Re: C-Dory Johnson 70 prop selection

For that price, I would give it a try...It's the only way to know for sure.

 

[Lowranger]

Re: C-Dory Johnson 70 prop selection

For that price, I would give it a try

I agree with you Kenny. The prices in this sale are outstanding. I'll give it a try and however it turns out I'll report back with the results. Maybe it'll be helpful to others.