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Twin Suzuki DF350s to Yamaha 425s or even quad DF300s?

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Twin Suzuki DF350s to Yamaha 425s or even quad DF300s?

Old 09-09-2020, 10:15 PM
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Default Twin Suzuki DF350s to Yamaha 425s or even quad DF300s?

Ok, twin DF350s on a 34 x 12 (20,500#) catamaran just aren’t getting it done and there are serious questions about the reliability and durability of them. Honestly, the boat shouldn’t have ever been fitted with only 700hp, but that’s a totally different discussion. One blew up at 188 hours and last weekend a prop cracked at 390 hours (no sign of impact on any of the 6 blades on that motor). Piece of mind when running 70 miles offshore may be weaning.

So, options... the boat is equipped with the optimus/sea station package. There is a rear helm too.

Replace with twin Yamaha 425s That means a all new rigging, gauges, and maybe the sea station set up???

What about quad DF300s? Assuming the transom can handle the weight. It’s aluminum, so not overwhelming to reinforce if needed (for sure discuss wi5 the builder). Benefits are we can keep the rigging, gauges, etc. no redoing the dashes. Also, lots more redundancy if we smoke one or lose a prop (3 motors left).

I thought about 250s, as 1,000 hp is plenty. But why bother when 250s are the same weight?

just looking for ideas, just in case. How much room in each motor wheel would twin DF300s take? I’m assuming there’s enough room back there, but I don’t actually know how much space they need to fit. 12’ beam.

let em rip...
Old 09-10-2020, 05:09 AM
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so the yammys weigh nearly 2000 lbs for the pair and four df300s weigh 2500. The power to weight ratio is hugely in favor of the quads. the simplicity of twins is nice but the performance reports I have read surprisingly dont show a substantial improvement over the 350s so thats not a great option. Quad 300 v8 mercs would be within 200 lbs of the 425s but substantially more in cost and not save any room. So yeah 1200 hp and the ability to run home on three should something happen would be a huge upgrade in performance.
Old 09-10-2020, 12:04 PM
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4-300AP'S? keep some of your rigging/$/ & Optimus etc...or have you given up...

Edit - misread, thought you were considering F300's...We run15" wheels on ours

Last edited by MarkV; 09-10-2020 at 12:45 PM.
Old 09-10-2020, 12:19 PM
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The difference between DF300 and DF250 is solely the ECM module which feeds a bit more fuel into the 300 and allows it to spin a couple of hundred rpms faster at WOT. As far as I understand, practically *all* that extra 50Hp is at the very top end, in low- and mid-range rpms DF250 and DF300 perform identically.

I would check carefully if you have enough space for quads in the back. Also, the issue for the transom is not only handling the weight, but the thrust as well. A transom that was designed for 700Hp might not behave well with 1200Hp, even if the weight of the motors is not that different.
Old 09-10-2020, 12:50 PM
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Doubt any 34’ boat that weighs 20,000lbs will ever perform very well. Most in that size range weigh closer to 10,000 than 20,0000
Old 09-10-2020, 12:55 PM
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Have you discussed this with the company who made and rigged the boat?
Old 09-10-2020, 01:27 PM
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The 350s push her 40mph (WOT) in the ocean, a little faster in the Sound. So, the current power seems just barely enough. Would be happy to cruise in the 35-40 mph range and not routinely rely on the higher rpm range.

If the owners lean more toward quads, it’ll be a chat between them and the builder. I’m trying to get outside input/experiences to help inform the boat owners. Build a list of pros and cons.
Old 09-10-2020, 02:48 PM
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You could probably get into quad 300 zukes while keeping your steering and some rigging for less then converting to twin 425 yami's. I think the quad move is the better direction if the boat will handle it.
Old 09-10-2020, 02:51 PM
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If the Suzuki 350s blew under warranty would think there would be good will toward replacement with quads DF300s and come out much cheaper and better all the way around. If the boat can handle them.

To cruise at the speeds you are after, will need at least 1000hp on it and even then hull design will come into play.
Old 09-10-2020, 04:12 PM
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Need to find out if she will hold quads without too much work. If so, go for it. Also, don’t know about up there but the mercs are quite a bit lighter, more powerful, more efficient, and close to the same price here.
Old 09-10-2020, 05:02 PM
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The 425 is a beast though. Lots of displacement, low end power. I’d consider quad Merc v8 300s before quad zuke. Pound for pound they’re great engines. Just went out of Venice on a 39 contender with trip 300s and they were very impressive.

Old 09-11-2020, 04:32 AM
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Quad V8 Mercury 300s would be tough to beat with power:weight, fuel economy and smoothness. The V8 Verados have the larger cushiony motor mounts to keep NVH to an absolute minimum on the aluminum hull.
Old 09-11-2020, 09:22 AM
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Anybody know the minimum width a pair of 300s needs to fit on a transom?
Old 09-11-2020, 09:31 AM
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Take a serious look at the Merc's, I'm very impressed with them, and I don't say that easily as I wasn't a big merc fan. but that's old school mindset which is not good!
Old 09-11-2020, 11:03 AM
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If you got budget and can do it go with the 300 v8 mercs. You have to check the weight requirements. I think the v8 mercs are 40lbs heavier than the 300 yams
Old 09-11-2020, 11:05 AM
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Twin 7 Marine 626 HP should do it just fine...
No need for trips or quads

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