Prop recommendation please

[simplystressed]

Hello, I'm looking to replace my existing prop as it has a bit of wear on it, and am hoping to get some more MPH out of my setup.

Boat: 16.5ft aluminum
Weight: 1500 loaded with two people
Motor: 50hp
Current Prop:
Material: Aluminum
Diameter: 10 - 3/8?
Pitch: 14?
Blades: 3
Rotation: Standard (Clockwise)
Gear Ratio: 1.83:1
Max RPM: 6000
Current RPM @ WOT: 5450-5500
Current Speed @ WOT: 29.5-31MPH

Quite happy with existing holeshot and mid range power. I'd like to see if I could squeeze a few more MPH's out of it and get closer to 6000RPM @ WOT. Let me know what you think would work.

Thanks!

 

[steelespike]

Re: Prop recommendation please

What year motor? 4 stroke?
Start by being sure the motor is in excellent tune and the throttle opens all the way at the carbs.Raise the motor on the treansom to a point just before venting becomes a problem.
If there is room to gain a couple of inches you could gain a couple mph just by raising the motor.It is possible a 12" stainless prop might get the rpm up enogh to gain a little speed.

 

[simplystressed]

Re: Prop recommendation please

What year motor? 4 stroke?
Start by being sure the motor is in excellent tune and the throttle opens all the way at the carbs.Raise the motor on the treansom to a point just before venting becomes a problem.
If there is room to gain a couple of inches you could gain a couple mph just by raising the motor.It is possible a 12" stainless prop might get the rpm up enogh to gain a little speed.

Hey thanks for the reply. Its a 98 merc 4 stroke. Motor is running very well. Raising motor isn't really possible as its bolted on but I had it trimmed just to the point of venting when I got those numbers.

The merc calculator is telling me a 13'' 4 blade might work Spitfire prop: AL 4blade 10.3dia 13.0pit RH

What do you think? Maybe a solas 1313-105-13?

 

[CRay45DB]

Re: Prop recommendation please

Missing a couple of pieces of the puzzle.

1. WOT is 6,000. Is there a range given in the book, like 5000 to 6000? Gas boats have more leeway in propping than Diesel. What you want to achieve is 6,000 RPM's WOT with full fuel and gear. Seen too many boats over propped which kills your engine. The prop is the most important piece that most people are to cheap to do correctly. I have a rapto on my cobalt Nd a Solas on my tender. What they have in common is after I put them on, tested it, is that they both got sent to a prop shot to customize to the boat. When the prop shop is dome with them, there are no longer a Solas or raptor. These companies are making props for the masses. So I buy what is close, record your findings, RPM Wot, are you cavitating, meaning it's like you have no traction vs. Too much traction. If you hit these numbers your a lucky guy. But if you want to do it right, send it out to a shop, giving them your data, what you are at regarding WOT rpm vs specs. From there they will make it perfect, or close to it. It sucked the first time I put a Solas on my boat and it wasn't great. But after the prop shop did their work, it's like a new boat.

Good luck!

 

[SparkieBoat]

Re: Prop recommendation please

you already have about the right prop..30 MPH with a 50 HP motor on a 17' alum boat is about right, if you want to go faster get a 2 stroke 70 and put on there. and about raising the motor it is possible to UNBOLT bolts. so I am not sure why you say it is not possible, It is actually done every day. raising the motor could make a huge difference, if you can raise it without ventilating the prop, some guys even get jack plates.