Grady 360 w/Suzuki 300s

[VADMJ]

I recently repurchased my 2007 Grady 360. The boat was recently repowered with triple Suzuki DF300AP engines (16 hrs). The motors were mounted the same as the previous Yamaha 250s (one bolt hole left to lower). I am experiencing a problem with cavitation anytime I push the throttle (coming out of the hole, etc.). Also, during a hard turn, she drops rpms significantly. The prior owner installed four bladed props. I think this may be the problem. I checked with Grady and they only use 3 bladed 15 1/2” x 17” props for Yamaha 250 or 300 hp.
Does anyone have experience running Suzuki 300s, on the Grady 360? What props are you running and what bolt hole are the engines mounted to?
Thanks!
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[seasick]

What are the shaft lengths of the zukes? Do you know the shaft lengths of the old motors?

What you are calling cavitation is probably blowout. I doubt that the switch to 4 blades is the cause if the blowout is as bad as you state. The props may be wrong in general though and I don't know for sure if you can compare props on the yamis to the zukes since I am not sure if the lower unit gear ratio is the same.
If when at rest the anti-ventilation plates arebelow the water line the most likely cause of blowout is undersized props

 

[VADMJ]

What are the shaft lengths of the zukes? Do you know the shaft lengths of the old motors?

What you are calling cavitation is probably blowout. I doubt that the switch to 4 blades is the cause if the blowout is as bad as you state. The props may be wrong in general though and I don't know for sure if you can compare props on the yamis to the zukes since I am not sure if the lower unit gear ratio is the same.
If when at rest the anti-ventilation plates arebelow the water line the most likely cause of blowout is undersized props

The shaft lengths of the Suzukis vs. Yamaha are the same (25” outboard engines, 30” center). Actually, the Yamahas are .3” deeper. Anti-ventilation plates are 3’ below waterline and just below hull. Gear ratio on the Suzukis is 2.08:1, Yamis are 1.75:1.

Thanks for your response.

 

[seasick]

Those numbers seem correct. I think I would talk to a good prop shop for advice. It would help to know the specs of the current props.

 

[VADMJ]

The shaft lengths of the Suzukis vs. Yamaha are the same (25” outboard engines, 30” center). Actually, the Yamahas are .3” deeper. Anti-ventilation plates are 3’ below waterline and just below hull. Gear ratio on the Suzukis is 2.08:1, Yamis are 1.75:1.

Thanks for your response.

Those numbers seem correct. I think I would talk to a good prop shop for advice. It would help to know the specs of the current props.

Thank you. The installer believes the props are 15” x 15”. He stated that those engines should not run 4-bladed props but the owner was insistent. He also said the Zukes should not run less than a 16” diameter prop, that a 16” x 17” prop is the only prop for the Grady. He may be correct. I am just trying to get educated before dropping $2K on non-returnable props.
I appreciate your help!

 

[family affair]

Looks like you owe yourself a call to Propgods. They won't be guessing. They will know what you need. They also offer prop exchange.

 

[VADMJ]

Looks like you owe yourself a call to Propgods. They won't be guessing. They will know what you need. They also offer prop exchange.

I have already sent Ken a couple of emails.
I agree. Thanks!

 

[SkunkBoat]

properly sized 4 blades would have less blowout than properly sized 3 blade props.

There is no "right" answer other than when it is the way you like it that is right.

Suzuki 3 blades are always 16" dia. Going to 4 blades there is a choice between 15.25 and 16" dia. The pitch will need to be less with a 16" dia.
Forget about what Yamahas use. That is meaningless.

15 x15 seems to my mind like it would spin up badly . I base that on my experience with propping my twin Zuke 200s. But I don't have a 360 with triples
My 200s have 4 x15.25 x 21.5. I have heard that 4x16x20 also work well on the 200s. By comparison, the recommended 3 blade was 16 x18.5. I was not happy with them. They spun up when you goosed it in a strong current at the inlet and when I was heavy with fuel and ice. There was a trade off. I lost some top speed and some top rpm but still in the acceptable range.

4 blades are not always the answer but generally they provide more lift and less blowout in turns and in rough seas.
They tend to be used on heavy boats with twins running offshore alot. Having triples may remove the benefit, idk...

 

[brdawg2001]

zukes need larger props for sure...once you get it dialed in you will be pleased...

 

[jip40]

I repowered my 330 with DF250APs (same engine as DF300AP) and got with Marcus at PowerTech he put me on 4x16x15 props - work great BUT I only have 2 engines & boat is lighter - I would still talk with Marcus

 

[Legal Bill]

As to engine height, when you are up on plane, where are the ventilation plates in relation to the water?