[hawaiifly]

I got a action craft 1620 fly fisher, has a yamaha 115 on it. I think it has the standard prop that comes with the motor. At 5200 rpm I'm going 34.7 knots I think the boat can faster with a better prop, my other concern is that I think the boat burns a lot of fuel for the amount of running I did. Any prop suggestions?

 

[Brett]

I'd keep the prop if it's in good shape. 5200 is in the upper end power band of that outboard.

http://www.outboard-engine.com/enginespecs.php?recordID=238

punched your horsepower and hull weight along with guess-timated load into this calculator
and came up with 34 mph as a result. Matches your real world numbers.

http://hhscott.com/evinrude/docs/BSLAC.htm

An older 2 stroke is never going to get great gas mileage. Basic rules of older 2 stroke tech
say you'll burn about 0.7 lbs of fuel per hour per horsepower at full throttle.
That means a 115 will burn:
115 x 0.7 = 80 lbs of fuel per hour...80 / 6.2 lbs per gallon = 13 gallons per hour

 

[fsae99]

Hawaii Fly,
Are you using ethanol/gas mix or non ethanol fuel? What is the hole shot like? How heavily loaded was the boat to produce 5200 rpm at 34.7Knots?

Using 1:2 gears at 5200 you are either, running about a 17 P with with extremely low slip or about 19P with average slip.
4500 - 5500 is WOT operating range.

 

[hawaiifly]

Im using 87 ethanol mix. The hole shot is ok, those are numbers are with a empty boat and just me in it. I was hoping to get better fuel economy.

 

[Brett]

I was hoping to get better fuel economy.

Keep engine tuned up, run with proper engine trim angle, keep loads light
and slow down....most hulls have a peak intersection of rpms-speed-fuel consumption.
Find that sweet spot and do most of your running at that rpm.

check fuel consumption and rpm at bottom of page

http://www.popularmechanics.com/outdoors/recreation/boating/1276841

Your only other option is to go with a smaller, more efficient outboard.

 

[fsae99]

Well as far as fuel economy is concerned you need to gps the distance against a know amount of fuel. If you do this and get between .6lbs (best to expect) and .7 lbs (worst to expect) per HP/hour you motor is running right. If it is higher then you need to have the motor checked. 1 under performing cylinder could affect up to 25% of the total HP. My GPS lets me set a threshold speed to include in track distance so I set it at 3.5 MPH to eliminate time on the trolling motor (boat moves 4.5MPH at idle speed). On my boat, not an action craft, I get the best distance out of a tank of fuel at WOT (about .3 mile per gallon better than 3/4 throttle). I measure this every time out.

I get an extra 1.2 miles gallon using non ethanol fuel. Also get an extra 1.4MPH.

I think you top speed is about 2-4 knots off where is should be. Unless your prop is beat up, I do not think that is your issue. The pitch should be stamped on the prop see if you can find that and let us know.

I noticed you had tabs, do you run with any bow down in it? This of course reduces speed and fuel economy.

 

[hawaiifly]

Props are so confusing. I e-mailed powertech they suggested the RXB4 stainless prop 13.25X16 I forgot to add the boat has bad handling. making turns I have to slow down a lot. The powertech guys said this prop would be good choice for my boat. I also looked at a Stiletto bay pro 1 in the same size, and Turbo props FX4 prop. Stiletto has the best price. Anyone have any expieriences with any of these props or any other suggestions to help out the handling. I can get the boat to WOT 5400

 

[swaddict]

powertech is one of the better one's, the RXB4 will help with grip