300 Marlin repower with Suzuki 300s

Kizuna

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I've recently repowered my 300 Marlin with Suzuki 300s replacing the original Yamaha 225s.

Since the repower, I've noticed that the boat doesn't feel as stable as it did before. Now if this was at WOT I would just attribute it to the added power and speed; however I have symptoms even at 17-18 knots. Essentially any speed up on plane.

I first noticed this when I would catch a small boat's wake either from the side or riding through it from behind. The boat would list heavily side to side and the only way to regain control is to back off the throttle and come off plane. This past weekend my sister and wife riding in the back noticed the boat felt like it was moving back and forth similar to the feeling of riding in a tube being pulled by a boat as it jiggles in the boat's wake. This was both in a flat bay as well ocean with 1'-3' seas. The boat is also behaving like this regardless of load.

Essentially, the boat feels like it's riding higher out of the water then it did before, and get's disrupted more easily. Between my father and I, we've had a 20' Overnighter, 25' Sailfish, 268 Islander and now my 300 Marlin. I'm very familiar with how Grady's handle and how smooth and stable the SeaV hulls are.

I'm looking for any information on what could correct the boat's current behavior. The engine's are mounted on the second hole from the top with the anti-cavitation plates level with the hull. On plane they are not above the water, but it looks like water is just skimming over them. Currently using 3/16/8.5 props and have room to gain a few hundred RPM at the top end.

Some things I've thought about but are total guesses at this point are:

1. Raising the engines one notch. I know I'll lose drag and gain RPM, but I don't know if this will affect how the hull planes.
2. Coming down to a 17 pitch prop.
3. Does the toe need to be adjusted?

Thanks in advance for any help.
 

SkunkBoat

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They only thing I've heard about Suzuki setup is regarding the trim. Someone on a forum mentioned that the default min trim was 0 degrees so they did't "tuck in" all the way. There was a setting to allow negative trim.
On a 265, they get up on plane best with full negative trim and no trim tabs.

I don't know if thats your situation. You didn't mention how trim effects your symptom. Also, where are your trim tabs ?

You may have tried this but I would start at Bow Up trim (tabs flat and not doing anything) and leave them there. Then go through the range of motor trim to see how that effects your ride.
Then if you think you found a good running trim, start experimenting with tabs.
 

seasick

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It could be a toe in setting. While at mid speed om plane, take a look aft and estimate how far back the motor wakes meet. The wakes should meet at least 25 feet or so off the transom ( assuming the motors are not on brackets)
Also, the leaning you describe can be caused by excessive trim tab settings. So as mentioned, start with tabs all the way up and go from there
 

Kizuna

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Yes, I've played with the trim tabs. I always run them all the way in (bow up) and then will bow down if necessary based on weight, wind to level the boat. Only time I bow down the tabs is if I'm running straight into the wind for a long distance; however, haven't done that with these motors.

Regarding trim, I always trim down before taking off, and then bring the trim up to 30% as I get on plane, the boat seems to be most efficient here. Why, I'm puzzled is that the boat never felt unstable or squirrelly before regardless of trim or trim tabs.
 

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That's a pretty wierd scenario. I repowered my 99 272 sailfish with zuke 250's previously having ysmaha 225 2 strokes and noticed the exact oppisite effect. My boat now rides heavier in the rear and has lost almost all the bow steer you talk about while crossing a wake. Im not at my boat now but I believe I am also on the 2nd hole from the top and as far as toe goes I am 1/2 inch closer at the bottom than the top. I am running the 17 pitch suzuki props. My boat rides much better now with the heavier morors. Which side is your counter rotating enginge?
 
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Kizuna

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That's a pretty wierd scenario. I repowered my 99 272 sailfish with zuke 250's previously having ysmaha 225 2 strokes and noticed the exact oppisite effect. My boat now rides heavier in the rear and has lost almost all the bow steer you talk about while crossing a wake. Im not at my boat now but I believe I am also on the 2nd hole from the top and as far as toe goes I am 1/2 inch closer at the bottom than the top. I am running the 17 pitch suzuki props. My boat rides much better now with the heavier morors. Which side is your counter rotating enginge?

Yeah, I was expecting the boat to handle better and more efficiently with the new engines. With the added horsepower and torque, larger prop etc, the boat pops right up on plane and can cruise faster with less fuel burn. During the install, my dealer said he was going to play with swapping the counter rotation, but I believe he stayed with the more standard counter on the port. I will confirm.

The boat is getting pulled this week for the 20 hour service and I'm having them check the toe/alignment. Good to know you're at 1/2" in.
 

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Sounds like you run it the same way I run my 265.
The only time I get that squirrelly feeling is with near empty fuel tanks, especially if the sea is flat. Then boat really gets high out of the water and feels very strange, even scary if you open it up over 40mph+.
Once I emptied the forward tank first(not paying attention) and it felt strange with all the weight aft.
Maybe the increased transom weight of the 300's combined with added power is making things feel different.

I can't imagine that you would need to go down to a 17 prop. Thats the minimum for a DF300. Zukes are geared for higher pitch props.
If anything maybe give 20 a try. Of course , staying in your max/min WOT revs is important.
I could see the engine height having an effect but I have no experience with that.
 

Blempa47

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... i have a 97 marlin and had 300 zukes put on last summer... we generally run a pretty heavy boat with offshore gear and mostly full fuel... i have the same props you are using and the same 2nd hole mount... we run anywhere between 3800 and 4500 depending on conditions... we can get them up to 5800... but only for like a 1/2 mile coming in the inlet... i feel that the boat rides much better than it did with the 250 ox66's... we just power through small wakes and chop... now i dont really use the trim tabs a whole lot unless we have bigger sleeping guys on one side when running... i think you can control the boat with the engine trims just fine... and i also start out all the way down and will trim up to 40-50% to cruise ...depending on the sea conditions...i do think that it rides a little further back on the keel which reduces the bow steer in a following sea... which i like....

... you may want to make sure that the steering lines were bled and filled all the way... we had a bad seal in the steering pump at the helm and that would let the boat get a tad loose at the end of last year... took it out and replaced the seal bled the lines and its nice and tight again...
 

Kizuna

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Sounds like you run it the same way I run my 265.
The only time I get that squirrelly feeling is with near empty fuel tanks, especially if the sea is flat. Then boat really gets high out of the water and feels very strange, even scary if you open it up over 40mph+.
Once I emptied the forward tank first(not paying attention) and it felt strange with all the weight aft.
Maybe the increased transom weight of the 300's combined with added power is making things feel different.

I can't imagine that you would need to go down to a 17 prop. Thats the minimum for a DF300. Zukes are geared for higher pitch props.
If anything maybe give 20 a try. Of course , staying in your max/min WOT revs is important.
I could see the engine height having an effect but I have no experience with that.
To my understanding, I've only gained 112 lbs with the engines. Currently my main tank is less then half and the auxilary is nearly empty. However, I've felt this with the main tank full and full load of people (my paint line was sitting about an inch under water and typically sits about an inch above).

I know what you mean with the auxilary full and main empty, I've made the same mistake. Anyhow, the boat feels like it is running lighter, higher in the water, and I hope I can find and adjustment or two that will get it back to feeling more like a Grady.
 

Kizuna

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... i have a 97 marlin and had 300 zukes put on last summer... we generally run a pretty heavy boat with offshore gear and mostly full fuel... i have the same props you are using and the same 2nd hole mount... we run anywhere between 3800 and 4500 depending on conditions... we can get them up to 5800... but only for like a 1/2 mile coming in the inlet... i feel that the boat rides much better than it did with the 250 ox66's... we just power through small wakes and chop... now i dont really use the trim tabs a whole lot unless we have bigger sleeping guys on one side when running... i think you can control the boat with the engine trims just fine... and i also start out all the way down and will trim up to 40-50% to cruise ...depending on the sea conditions...i do think that it rides a little further back on the keel which reduces the bow steer in a following sea... which i like....

... you may want to make sure that the steering lines were bled and filled all the way... we had a bad seal in the steering pump at the helm and that would let the boat get a tad loose at the end of last year... took it out and replaced the seal bled the lines and its nice and tight again...
Thanks, I typically cruise between 3800-4200 and sometimes bump up to 4500. WOT is close to 5700 with a light load. Every Grady I've had after the 20' Overnighter powered through small wake and chop including this one. The 20' even did an amazing job for its size.

I haven't cruised with the trim up as high as you, and will definitely try that this coming weekend. And I'll have them inspect the steering lines during her service this week.
 
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I repowered my Grady trophy pro with zukes and had problems at first.
Then I went to a 3x16x20 prop. And I have 3x16x21.5 props. Boat handles amazing , great fuel economy, etc.....

If anything I would go up in prop pitch not down! You will. Prob see a big difference
 

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I'm having the flop over problem with my new zukes. Need different props.Will get them at 20 hour service. Have 3x16x20. Tilewave got the same motors so they put 4x15.25x22. Took a ride with him...much better!