280 Marlin speed and fuel economy with 4 strokes

[Dave56]

I have an 89 280 Marlin. Twin 2005 F250’s. Power tech 4 blades. I’m wonde what any other 280 marlin owners with twin 250 Yamis are getting for speeds and mpg.

 

[Dave56]

No none has a 280 marlin with 4 strikes?

 

[canvasback]

i have a 1990 28 marlin with 250 verado's cruise 4000 rpm about 28-30mph @28gph WOT 42-45mph @ about 52gph 2008 verados 50mph was top speed what are you getting with your yammi's ?

 

[dogdoc]

suzuki 250 4 stroke, 1992 280 marlin. cruise 3850-3900, 30mph, 18 g/hr under ideal situation.

 

[Dave56]

suzuki 250 4 stroke, 1992 280 marlin. cruise 3850-3900, 30mph, 18 g/hr under ideal situation.

What props are you running.

 

[dogdoc]

3x16x21.5. One thing I have noticed is that trimming is not near as critical for optimal efficiency. It does take longer to get on a plane if I forget and have the engines up a couple of chicklets. Once on a plane trimming up or down does not seem to change much. Unlike the 250 OX 66's which were much more critical about trim and efficiency.

 

[Dave56]

i have a 1990 28 marlin with 250 verado's cruise 4000 rpm about 28-30mph @28gph WOT 42-45mph @ about 52gph 2008 verados 50mph was top speed what are you getting with your yammi's ?

I cruise at 25kt, 4500rpm. 21gph. Push her up to 5100rpm it’ll be 31-32kts around 28gph. My wide up is around 38 knots at a ridiculous GPH.

 

[dogdoc]

So after 100 hrs I am thinking that I am just not getting enough rpm at WOT. Seems like no matter what conditions or load the best I can get is 5200 on port and 5150 on starboard and a max top end of 40mph. 280 Marlin with 2022 df250 Suzukis. Currently running 3x16x21.5 props from dealer. I must admit I am pretty ignorant concerning the physics of outboard props and looking for advice.
thanks

 

[Ekea]

sounds like you are over propped. if keeping the other parameters the same, id drop from a 21.5 to either an 17 or 18 inch pitch

 

[seasick]

I am not sure what the WOT limit is for that motor. I think it is 6000 revs. Actually, I read that 5000 to 6000 is the 'operating range'

Your design target WOT revs should be no less that 10% below engine spec so if the spec is 6000, anything 5400 and above is reasonable.
Since you have a 4 blade prop, you have optimized (in theory) you lower end thrust that helps with the hole shot and getting on plane. The downside is that top end performance will be degraded a bit due to the 4 blades decreasing the water flow efficiency of the prop. Prop selection is always a trade off process so the first thing you want to do is specify what performance characteristics you want. Asking what numbers others are getting is not really a great comparison since there can be many variables. It is also important to understand that different brands of motors as well as different models of a manufacturer's line can have different lower unit gear ratios. In that case, you can assume that you will get similar performance figures for a given prop.

 

[dogdoc]

3 blade spec is 55-6100k rpm

 

[Harrysea]

I subscribe to the theory that it’s best to get as close as possible to the high end of your RPM range with a light/normal load with optimum trim.

 

[Legend]

So after 100 hrs I am thinking that I am just not getting enough rpm at WOT. Seems like no matter what conditions or load the best I can get is 5200 on port and 5150 on starboard and a max top end of 40mph. 280 Marlin with 2022 df250 Suzukis. Currently running 3x16x21.5 props from dealer. I must admit I am pretty ignorant concerning the physics of outboard props and looking for advice.
thanks

Im runnung 15 1/2 x 17 and get about 5900. F250 yamaha on 282 Sailfish

 

[seasick]

3 blade spec is 55-6100k rpm

Would it be different with a 4 blade?

 

[SkunkBoat]

ya Dog, you have DF250Ts. They have a 2.3:1 gear ratio. They swing big props and yours are giant. You cannot compare them to Yammies(1.75:1) or Mercs or even the zuke DF250AP (2:1 gears)

You might get 200 rpm per inch so maybe drop pitch to 3x16x20. Or you could drop diameter to 3x15 1/4 x 21. or 4x15 1/4x20
I wish I could say its easy but the best way to get it right is to try different props.

If you go too small you might get 6000 rpm but you won't be able to move the boat out of the hole.

 

[dogdoc]

looks like i am gonna try 3x16x18.5. book says i should get 600rpm and better fuel economy

 

[Ekea]

that should give you some improvement. let us know how it goes

 

[Millartime]

I have a 2007 30 Marlin
with the power techs, fully loaded 4200rpm 30mph, 20gallon per hour.

 

[SkunkBoat]

looks like i am gonna try 3x16x18.5. book says i should get 600rpm and better fuel economy

Your Zuke dealer should let you try those. They seem to be the generic starting point for their motors. They probably have them lying around.
They started with them on my DF200APs (2.5:1 gear). Mind you, different boat and smaller motors..They said they didn't get the rpm they wanted and immediately went to 3x16x20. Those I ran for 20 hours. Did not like them. They got to max 6100 rpm and great fuel eco in the river but they slipped too much on take off and in standing waves in the inlet.
Settled on 4 blade 15 1/4 x 22. They just get to 6000 if you are light and in the river with them raised up.
Point is don't settle til its right. You have a wide heavy boat. Don't get hung up on getting max rpm. There is a RANGE for a reason.
Don't mess with your tabs when you are testing. raise them so they do nothing and test using the motor trim.

 

[dogdoc]

follow up to come asap