Express 305 prop advice-all 300 Marlin and 305 Express owner

[bea5454]

Think I am a bit over-propped and have reviewed previous threads, but appreciate the input of any Marlin or 305 owners - most especially anyone powered with F300's.

2011 Express 305, F300 4.2L, 15 1/4 x 19 SWS II props, bottom paint (good to exc condition), curtains in-place.

Sea trial - Very light load (3-4 people, 50 gallons gas, no gear) 5350-5400 max rpm 44.4 mph. Best cruise around 4200 rpm, 32 mph, 1.1 mpg in FAC.

Loaded w fuel 290 gal, 3 people, several hundred pounds of gear, but no ice or meaningful water aboard. Cruise at 4200-4300 in modest seas, 30-ish mpg, 1 mpg +/-. With 400 miles under our belt, we never touched greater than 1.2 mpg (statute mile) and that only in FAC and very light load. Heavy seas we were down as low as 0.8 at times and the representative was 1.0 mpg.

Have convinced myself right prop is drop the 2" to the 15 1/4 x 17 for which there is a Performance Bulletin. Really hope to see improved efficiency 1.3 mpg? and 30-32 mph cruise at 4000-4200 rpm - realistic?

I figure Marlin is 600 pounds lighter so I should be slightly adverse to that. Any real world experiences to report or other advice?

Very much appreciate the help to-date and any further thoughts. Really love the boat so far, though the gas burn to-date has me a bit concerned.

 

[bea5454]

Re: Express 305 prop advice-all 300 Marlin and 305 Express o

Any Marlin or 305 owners with input?

 

[Polapea]

Re: Express 305 prop advice-all 300 Marlin and 305 Express o

If you're only getting 5400 rpms max you're over-propped. Our Marlin is turning 5900 max and hitting 50mph @ .8 mpg. Around 5500 we are getting 1.0 or so.

GW site lists std props as 15-1/2 x 17

 

[lyncha00]

Re: Express 305 prop advice-all 300 Marlin and 305 Express o

If you drop pitch you will automatically be slower at 4200-4300 and with the same blade shape, probably won't see any improvement in mpg unless at higher rpm. You need more diameter and a different blade shape to see a difference.

Agree you are also overpropped, might try a 17" enertia eco. I would call ken at prop gods.

 

[bea5454]

Re: Express 305 prop advice-all 300 Marlin and 305 Express o

If you drop pitch you will automatically be slower at 4200-4300 and with the same blade shape, probably won't see any improvement in mpg unless at higher rpm. You need more diameter and a different blade shape to see a difference.

Agree you are also overpropped, might try a 17" enertia eco. I would call ken at prop gods.

Thank you. My shop had a pair of 15-1/2 x 17 swsII's used for a couple sea trials. As suggested, lost about .5 mph at 4200 and 1 mph top-end, but calculated slip much less and fuel efficiency up 8-10 percent through much of the range.

 

[lyncha00]

Re: Express 305 prop advice-all 300 Marlin and 305 Express o

Sounds like a good improvement, how much more rpm did you pick up at wot?

 

[bea5454]

Re: Express 305 prop advice-all 300 Marlin and 305 Express o

Sounds like a good improvement, how much more rpm did you pick up at wot?

Surprisingly (at least to me) only up to 5600 with 90 pct fuel/water and one person, but boat had been sitting a while so possible it picked-up some minor growth. All-in-all happy with the improvement.