2003 Grady White Express 33 with Suzuki 350 duoprop

[LimpetMine]

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!

 

[Kizuna]

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]

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.

 

[Sibs]

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]

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.

 

[DennisG01]

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]

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]

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]

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]

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]

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.

 

[LimpetMine]

Update to engine height, I lowered the engines to the factory recommended height (all the way down) with no holes left. I haven't seen much of an impact in the performance fuel economy wise, still running 4,350rpm getting 32.5-33 mph and around 25gph. Around 100 hours on them now. I noticed an ad with a grady 33 with yamaha 350s running at 4,700 rpms going 36mph burning 38gph so I gave that a try for comparison and fuel consumption rose to 33gph at 36mph. Overall, pretty happy with the performance. Once observation is that in bumpy waters, I have observed at least one of the engines cavitate briefly, then retain traction and the rpms will come back down to the throttle position. Unsure as to why this is happening. The cavitation plates are visible on the port side only (both engines). The wake looks good, the entry point of the boat is ideal, things seem to be just fine now and I can trim to a comfortable point in the water where the 33' will run in a straight line.

 

[DennisG01]

It's still... ventilation, not cavitation. TOTALLY different things - it's important to use proper terms to avoid confusion.

One engine being trimmed higher than other could do it. The boat not running level coudl do it. Also, if there's a thru-hull in front of one of the engines, that could do it under the right conditions. You might just need to keep the trim a little lower in those conditions.

It may just be me, but in that picture, it appears the boat is listing slightly to stbd?

Also, it's not uncommon for dual prop drives to not like as much up trim. Not always, but on average, moreso than single props.

 

[scott furman]

I have a 336 canyon with suzuki 350s with duoprops. I fish the canyons south of long Island. Generally very happy with the first 250 hours. Only issue started at 600 hrs when we noticed metal in the gear oil. Paying close attention, but no gear chatter or noticeable noise. Great economy. 1.2 knots per gallon at 27 knots is the sweet spot.

 

[seasick]

With the motors trimmed straight up and down, go for a run and at different speeds make more and more aggressive turns to both sides. As the turn get more aggressive the hull will lean to one side. When that happens, at some point the engine opposite to the turn may start to ventilate. You should be able to hear the difference and in some cases, the revs on that motor my increase. If that situation occurs ar relatively gentile turns ( as your would normally make) there is a good chance that the engine is mounted too high.
When you had the boat reowered did the installer question your desire to have the motors mounted higher that usual?

 

[DennisG01]

Scott, what do you mean by "metal"? Chunks of metal or just shavings on the magnet? Shavings on the magnet is normal... the rest, well, not so much.

 

[scott furman]

Scott, what do you mean by "metal"? Chunks of metal or just shavings on the magnet? Shavings on the magnet is normal... the rest, well, not so much.

Shavings but some of the shavings are flakes. The largest flake is not large, but noticeably not just a shaving.

 

[scott furman]

Also, noted that the quantity of "shavings" is noticeably more on the port engine than the starboard. Again, no noise and no slipping, but i am paying attention and changing the gear oil every 50 or 60 hours just to see if it increases or decreases. So far, it has been fairly consistent.

 

[DennisG01]

It's tough to get an idea of what it looks like or how much is there from where I'm sitting

But maybe a better way to explain "normal" is to say that the shavings you find on the magnet are more like fine to large dust particles.

Do those engines have mechanical or electronic shifting?

 

[scott furman]

It's tough to get an idea of what it looks like or how much is there from where I'm sitting

But maybe a better way to explain "normal" is to say that the shavings you find on the magnet are more like fine to large dust particles.

Do those engines have mechanical or electronic shifting?

Electronic