Prop selection question

[kenny26]

I'm looking for a spare prop, the current prop has really nice acceleration and holeshot for when i'm pulling the kids on the tube. I'm getting 31 MPH, with 2 people in the boat, WOT, on light chop. I'd like the spare prop to give me more top end, willing to let holeshot suffer for spare prop to be used for cruising. Would a 13p or 14p help the top end or am i at the limit? What about a stainless?

Also the boat doesn't seem like trimming helps it much. I start trimmed in all the way and once on plane try to trim out, but it seems to only gain about a 1 mph and then starts porpoising.

1) Performance issue you are trying to correct.
Acceleration and hole shot is excellent, would like a bit more top end speed.
2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
Mercury, p16702a40p12, aluminum
3) Current prop diameter and pitch (required).
Pitch is 12, diameter is ~10 1/2 I think..
4) Wide open throttle RPM and speed with an average load (very helpful)
Turning 5600-5700 RPM at WOT with 2 people in the boat, could possibly carry a third but i'm looking for a spare prop to cruise with for the wife and I.
5) Engine/drive make, model, year, and HP
2007 Mercury 50 HP ELPTO 2 stroke
6) Boat make model, year, length and weight
1990 Bayliner Capri 1700 CV BR 17' runabout (fully restored so no water in the hull)

 

[usskydvr]

Re: Prop selection question

You are running right at/over the WOT limit (5000-5500)for your engine per the manual. You prop appears to be a 10 3/4 x 12 unit. I would go to a 14 pitch which should drop your WOT by 300-400. (you actually may get away with a 16, but I would want to try one first before buying)

 

[steelespike]

Re: Prop selection question

I think your doing really well; dry weight is over 1,000lbs.
If you go to a 13 or 14 you'll probably just lose rpm and make the motor work harder.If you did gain any speed probably be less than a mph.
If your looking at cruising at partial throttle with the most speed possible
a 4 blade prop may be what you want it will plane quicker stay on plane with less power and diddling. I belive will cruise faster on less throttle.Your top speed may be reduced.

 

[kenny26]

Re: Prop selection question

I think your doing really well; dry weight is over 1,000lbs.
If you go to a 13 or 14 you'll probably just lose rpm and make the motor work harder.If you did gain any speed probably be less than a mph.
If your looking at cruising at partial throttle with the most speed possible
a 4 blade prop may be what you want it will plane quicker stay on plane with less power and diddling. I belive will cruise faster on less throttle.Your top speed may be reduced.

if i were to go with the 4 blade, what pitch should i get?

 

[RicMic]

Re: Prop selection question

I'm keeping an eye on this thread. I have the identical engine, even the year model and a similar boat, although it may be just a tad lighter. I recently bought the boat and want to get it set up just the way I want it, before I put it in the water and the original owner NEVER started the motor. I has the 10 3/8", 14P, three blade prop that the dealer put on. I hate going out without a spare though. From the prop selector charts, imperfect may they be, going by weight rather than rpms, they seem very consistant on 13 or 14pitch, three or four blade.

 

[usskydvr]

Re: Prop selection question

4 blade 14pitch. 3 to 4 in same pitch generally costs you 100RPM.
Prop selectors using weight are good for a starting point, but WOT RPM is way better to be used in your consideration along with your choice of Top Speed/Best Cruise/Acceleration/Pulling power.

 

[kenny26]

Re: Prop selection question

RicMic, my motor is brand spankin' new too. I found it as old stock at basspro shops for cheap. I've got < 10 hours on it. I'll let you know how it goes. I'm getting the itch to pull the trigger and will likely be buying a new 4 blade 14p prop real soon.

 

[trendsetter240]

Re: Prop selection question

My personal choice for that setup would be the 4 blade solas amita 13p. You should also look at raising your motor with the new prop. The anti-ventilation plate should be about 1" above the bottom of the hull for best top speed.