1990 Marlin with Suzuki DF250s

[LimpetMine]

I am a new Grady owner and I so far love this boat. I am experiencing some sluggishness however that maybe someone has seen before. The engines are 2005 Suzukis with around 450 hours. Not sure as to the prop pitch, but checking today. At 4,100 RPM this boat is planing, but only cruising at around 21 knots. Allegedly this should be closer to 25 or 26 knots. There is new bottom paint on the boat and the engines were surveyed recently and had compression within factory specifications. It also seems to be burning more than the characteristic 19 or so GPH that other users seem to be getting. Factory specs for this hull w/ 2005 yamahas (according to grady white) is 19.5 GPH at 4100 RPM should cruise at around 26 MPH. Any ideas? The boat comes out of the water just fine, but the cruise speed is slow.... Thanks!

 

[Daman858]

Are your readings in NMPH or MPH. 21 NMPH equals about 24 MPH. Boat trimmed properly? Just asking, not criticizing.
Lots of things go into speed, fuel usage, etc.

 

[GreatWhite23]

I have a 1991 marlin with Ox66 250s it seems to get 1mpg ,older motors less fuel efficient. It is a big heavy boat that rides like a dream so if it is not a hybrid so be it. My trim tabs are not working either. Seas are 2-4 on the eights. Suzukid250s are great motors an extra .5 mpg would make a big difference in the ability to run 100 plus of shore.

 

[onoahimahi]

What is your wide-open-throttle RPM? And the WOT spec for that motor? That should tell you if it is propped right.

My friend's 96 Marlin with 250 two-strokes does 1 MPG.

 

[Mr Honey Do]

How big is your vessel?
I have a 1990 28 Marlin, with twin 250 ox66's
I cruse at 3700 rpm and get 26 kts.
im spinning 4 blade SS 17 deg

Talk to Ken at
KR@Propgods.com

I've learned with my 18.5 Sea Ray and my Grady.... Props are EVERYTHING!!!!

Also make sure your gas is good and have clean fuel filters on them.

It is avery good boat. GL

 

[seasick]

I am a new Grady owner and I so far love this boat. I am experiencing some sluggishness however that maybe someone has seen before. The engines are 2005 Suzukis with around 450 hours. Not sure as to the prop pitch, but checking today. At 4,100 RPM this boat is planing, but only cruising at around 21 knots. Allegedly this should be closer to 25 or 26 knots. There is new bottom paint on the boat and the engines were surveyed recently and had compression within factory specifications. It also seems to be burning more than the characteristic 19 or so GPH that other users seem to be getting. Factory specs for this hull w/ 2005 yamahas (according to grady white) is 19.5 GPH at 4100 RPM should cruise at around 26 MPH. Any ideas? The boat comes out of the water just fine, but the cruise speed is slow.... Thanks!

Need to know number of blades, prop diam and pitch and what the load is, fuel persons etc.

 

[LimpetMine]

Ok I got a full tuneup, that helped, new plugs fuel filters etc. The WOT is now 5,200 and at 4200 rpm I am running about 24KT. The motors sound better at 4200 then at 4100. The props are stainless 16x18. I am thinking I have the wrong props. Sounds like the spec on the boat is a 15.25x19. I ran with full fuel, full water, 2 adults. This is a 28' boat. Thanks!

 

[LimpetMine]

How big is your vessel?
I have a 1990 28 Marlin, with twin 250 ox66's
I cruse at 3700 rpm and get 26 kts.
im spinning 4 blade SS 17 deg

Talk to Ken at
KR@Propgods.com

I've learned with my 18.5 Sea Ray and my Grady.... Props are EVERYTHING!!!!

Also make sure your gas is good and have clean fuel filters on them.

It is avery good boat. GL

Its a 28' boat with 3 blade 16x18 props I am hunting around for some loaner props to try out something else

 

[LimpetMine]

Update on my craft - the owner from 2005 repowered this boat with DF250s (new) but for whatever reason put long shafts on. The engines are pretty low in the water. I have a couple jack plates on order to raise them up about 5". When running the cavitation plate is way under water. The techs seem to think this will make a big difference, and my research would indicate the same. I will update after the modification has been made and I have run it a bit.

Thanks!

 

[SmokyMtnGrady]

I dont know if I can add any value to the discussion but what you found would cause a fair amount of drag and the motors seem to be over propped too. You likely have 2 things going on there. Good luck