What Prop is Right for My Boat?

[greg82255]

Hello,

Just bought a new boat, a 1986 Formula 206 LS Spyder (open bow). It has the original 350 merc/alpha one package. The guy I bought it from was running what he says was the original propeller (a 14.25x21" cleaver) and the boat did about 47 (I did a water test), but I forgot to look at the RPMs @ this speed. I am hoping to get close to 50 out of it by changing the prop. I have a 14.75x21 Mirage prop, and I was planning on using that, but I hear the Mirage has too much area to use with a small block because the motor doesn't provide enough torque, and that a laser II or Ballistic would be a better choice. Any suggestions for which prop would work the best? Thanks

 

[alldodge]

Re: What Prop is Right for My Boat?

Hello,

Just bought a new boat, a 1986 Formula 206 LS Spyder (open bow). It has the original 350 merc/alpha one package. The guy I bought it from was running what he says was the original propeller (a 14.25x21" cleaver) and the boat did about 47 (I did a water test), but I forgot to look at the RPMs @ this speed. I am hoping to get close to 50 out of it by changing the prop. I have a 14.75x21 Mirage prop, and I was planning on using that, but I hear the Mirage has too much area to use with a small block because the motor doesn't provide enough torque, and that a laser II or Ballistic would be a better choice. Any suggestions for which prop would work the best? Thanks

In order to obtain max speed you need to know your max RPM first. The 350 should turn between 4800-5200 RPM at WOT (wide open throttle). If your allready turning 5000 and doing 47 MPH you don't stand a chance of getting the extra by replacing the prop no matter what type. Need to go and determine your numbers.

 

[QC]

Re: What Prop is Right for My Boat?

Forget torque, whoever said that doesn't completely understand this topic . . . there is some truth in it, but nothing you should consider for prop selection at this point.

AllDodge is close, but there are 350s that are rated between 4200 and 4600 as well and no 350s spun 5200 in the 80s . . . Need your specs and your results. Need them dead nuts accurate for them to be usuable. Tach must be right and speed by GPS. This assumes that this is the original package and with a boat that age that is a huge assumption.

My guess is that you have a "260" which at the time was hp at the flywheel. Only equal to a rating of 230 - 235 today as we now rate at the propshaft. High 40s may be all she's got in her . . . The 260 was indeed 4200 - 4600 stock out of the box. There is a 350 "Mag" that delivers 10 more hp, but I am not clear on the WOT range for that iteration. Gear Ratio would be 1.5 for both.

 

[Tail_Gunner]

Re: What Prop is Right for My Boat?

Hello,

Just bought a new boat, a 1986 Formula 206 LS Spyder (open bow). It has the original 350 merc/alpha one package. The guy I bought it from was running what he says was the original propeller (a 14.25x21" cleaver) and the boat did about 47 (I did a water test), but I forgot to look at the RPMs @ this speed. I am hoping to get close to 50 out of it by changing the prop. I have a 14.75x21 Mirage prop, and I was planning on using that, but I hear the Mirage has too much area to use with a small block because the motor doesn't provide enough torque, and that a laser II or Ballistic would be a better choice. Any suggestions for which prop would work the best? Thanks

Put the Mirage on and make a run...The mirage does not have to much blade area and is one of the better props on the market. I suspect you have to much prop there 21p prop on a 21' boat with 1.5 gearing gets 58 mph @ 10% slip.

If that engine does turn that prop to 4800.. Your golden..But id suspect your going to end up in the 18-19 area.

 

[greg82255]

Re: What Prop is Right for My Boat?

It was my mistake for not looking at the tach when I test drove it.. I guess I will have to wait until the spring to try it out. However, I did get the 47 mph using my GPS. I'm pretty sure the Merc 260 is the original package. After 700 hours of use I'm not sure how much HP it actually puts out, but it was able to get on plane fairly easily with the 21" cleaver that was on there when I drove it. I suspect the Mirage will perform slightly better, but I also suspect that you are right that I should be around 19" pitch. Is there a general rule for how many RPM's you will gain/lose by going up/down an inch of pitch?

 

[QC]

Re: What Prop is Right for My Boat?

200