2003 Grady White Express 33 with Suzuki 350 duoprop

LimpetMine

Member
Joined
Sep 2, 2014
Messages
11
Reaction score
1
Points
3
Good day everyone! I recently repowered my 2003 Grady Express 33 from a pair of DF300s to the new Suzuki 350 duoprop and the performance is great so far. I run them around 4,300 - 4,350 RPM at about 34 MPH burning around 26 GPH (1.3 MPG). A question I have is the boatyard put the engines on near the top of the bolt pattern (high) reasoning that the duoprop would be fine because of the additional bite and the reduced drag would be advantageous. The problem is, if I trim them up, cavitation occurs, so basically you can't trim the motors up to adjust the trim of the boat. I know they need to come down, just wondering if anyone else has installed these on an Express 33. My DF300s were all the way down on the transom and gave lots of trim options. Anyone with this boat knows they can bow steer if not trimmed out properly, which this boat is doing a bit of right now. Generally, love the new engines though...

Thanks!
 

Attachments

  • Love
Reactions: SkunkBoat

Kizuna

Well-Known Member
Joined
Jun 26, 2019
Messages
52
Reaction score
8
Points
8
Location
Hampton Bays, NY
Model
Marlin
The height of the engines should be set so the anti-cavitation plate is level with the bottom of the hull. I don't think the dual props would change the dynamics of that.

I repowered my 05 Marlin with Suzuki 300s, and ended up raising the engines up one bolt from the initial install. This along with toeing in the engines helped with some giggling I felt on plane as well as the bow steer. I run with the trim at 35-40% without any cavitation.

Congrats on the new set-up!
 

DennisG01

GreatGrady Captain
Joined
Sep 1, 2013
Messages
4,395
Reaction score
453
Points
83
Location
Allentown, PA & Friendship, ME
Model
Offshore
Just about any planing-style hull will hull/bow steer when trimmed too far down, so you're not alone there. While it's true that dual-props will give better bite and could allow the engine to be a bit higher, it's not magic. Definitely sounds too high. I've been on this board for a while and don't recall seeing many (if any at all) boats setup like yours. I suspect you're just going to need to do some trial and error - which is a relatively normal thing. I would expect the shop to do this for no charge, as well.

FYI, it's "ventillation" and "anti-ventillation plate", not cavitation. Cavitation is something completely different.
 
  • Like
Reactions: LimpetMine

Sibs

Active Member
Joined
Sep 11, 2019
Messages
43
Reaction score
15
Points
8
Age
54
Location
Falmouth MA
Model
Express 330
On a different note I was thinking of repower on my 33 with zuke dual prop, how do you feel the boat and transom handled the extra weight of these engines? Thanks in advance
 

Kizuna

Well-Known Member
Joined
Jun 26, 2019
Messages
52
Reaction score
8
Points
8
Location
Hampton Bays, NY
Model
Marlin
FYI, it's "ventillation" and "anti-ventillation plate", not cavitation. Cavitation is something completely different.
Interesting I've never heard of it being called an anti-ventilation plate before but after a quick search it seems it's called both. In the Suzuki manual it's called an anti-cavitation plate. Anyhow you learn something new everyday.DP300_Parts.jpeg
 

DennisG01

GreatGrady Captain
Joined
Sep 1, 2013
Messages
4,395
Reaction score
453
Points
83
Location
Allentown, PA & Friendship, ME
Model
Offshore
Looks like Suzuki is wrong, too! :)

Ventilation is the introduction of air into the path of the propeller - which I'm sure is what everyone is actually talking about. The plate prevents air from being drawn in (or loss of water) to the prop when traveling at higher speeds.

Cavitation is actually tiny explosions (actually, I believe it's "implosions" or a "collapse" of the bubble) - and I'm sure google can probably explain it better it than me ;) Cavitation is often caused by rough edges of a propeller and can actually create tiny pock marks in the metal... essentially like little bombs going off on the surface of the prop.
 

Kizuna

Well-Known Member
Joined
Jun 26, 2019
Messages
52
Reaction score
8
Points
8
Location
Hampton Bays, NY
Model
Marlin
I think more brands than Suzuki has it wrong.

It makes sense that ventilation is what is actually happening from over trimming, and cavitation is more related to how fluid the water moves with the prop. It also seems cavitation is mis used extensively. Thanks for the lesson! :)
 

Flot

Well-Known Member
Joined
Dec 1, 2018
Messages
111
Reaction score
13
Points
18
Age
44
Model
Express 330
1.3 Sounds great - I agree, it sounds like it is worth moving the engines down a hole or two to give you more control.

Please keep us posted how it goes. I'd love to repower with these, but definitely want to hear more about handling, weight on transom, mpg and top speed?
 

LimpetMine

Member
Joined
Sep 2, 2014
Messages
11
Reaction score
1
Points
3
On a different note I was thinking of repower on my 33 with zuke dual prop, how do you feel the boat and transom handled the extra weight of these engines? Thanks in advance
So far so good. They don't weigh much more than the 300's, so just a torque issue. I know Grady will say it isn't rated for that much power, but seems fine so far. My Grady wasn't engineered for the 300s either lol.
 

LimpetMine

Member
Joined
Sep 2, 2014
Messages
11
Reaction score
1
Points
3
1.3 Sounds great - I agree, it sounds like it is worth moving the engines down a hole or two to give you more control.

Please keep us posted how it goes. I'd love to repower with these, but definitely want to hear more about handling, weight on transom, mpg and top speed?
Top speed is about 48 MPH. I'm gonna drop them down at least 2 holes. The boat feels great with the 350s, I just can't trim using the motors...
 

Dhirsh

Well-Known Member
Joined
Sep 14, 2020
Messages
61
Reaction score
23
Points
8
Age
53
Model
Canyon 336
Those seem like good numbers. I can hit 1.3 with my 350 yamahas, but only if I run them at under 4000 rpms and at a slower speed than you are getting. . I’ll bet with the proper height and less boat in the water, your numbers will improve some.
 
  • Like
Reactions: LimpetMine