Should I try a 19?

[Titanium48]

I'm trying to determine if there is something wrong with my setup or if the Turning Point prop selector is giving me wacky numbers. When I input the specifications of my boat, it suggests a 19 or 21 pitch propeller, but I currently have a 13.25 x 17 Hustler, which gives me 5400 RPM and 54 km/h at WOT, which seems about right (I think).

Here's the data:

Boat: 1976 14.5 ft Glasspar (appears identical to Larson "All American 150" of the same year). From Larson website, base weight is 834 lb, length is 14.5 ft, beam is 75.5 in (center) or 68.5 in (transom). I have verified the measurements, but not the weight. Max recommended hp is 75.

Motor: 1976 70 hp Evinrude (according to bracket model number). I think the powerhead was swapped as some point as it's model number corresponds to a 1986, but I believe both had the same 29:12 (2.42:1) gear ratio and 4500 - 5500 recommended WOT RPM range. Generally runs well but stalls occasionally when idling in gear.

Prop: 13.25 x 17 Turning Point Hustler (3 blade aluminum). Some minor damage, but has been filed smooth.

Test conditions: 2 people (420 lb), 60 L of fuel, ~50 lb of other stuff. GPS said 54 km/h (34 MPH), Tachometer read 5400 RPM

Normal Usage: Cruising, watersports. For cruising, 2-3 people (400-600 lb total), up to 80 L of fuel, and up to 200 lb of gear. I have another prop (15 pitch) for watersports.

Anti-ventilation plate height: About 0.5 in above keel at trim setting used for test. See picture. Note that motor has manual trim.

 

[steelespike]

Re: Should I try a 19?

I think you are just about right.The Hustler should allow the motor to be raised higher.A 19 will kill your rpm and it will be sluggish and the motor wouldn't be happy
lugging at possibly under 5,000.
If your not getting any ventilation (cavitation) you should raise it to a point just before you get venting. Also fiddle with the trim.Be sure the motor is well tuned and the throttle plates in the carb are opening all the way.Bottom clean.But your just about there.

 

[Titanium48]

Re: Should I try a 19?

Thanks. At what point might I consider a 19 if I see significant improvements from tuning, trim adjustments or raising the motor?

 

[180shabah]

Re: Should I try a 19?

Thanks. At what point might I consider a 19 if I see significant improvements from tuning, trim adjustments or raising the motor?

When WOT gets ABOVE 55-5600

 

[Titanium48]

Re: Should I try a 19?

Well, it looks like a trip to the prop shop might be in order. I raised the motor one hole and gained 300 rpm (now 5700), although I forgot the GPS at home so I don't know if the top speed increased proportionally. No problems with ventilation and the anti-ventilation plate is now visible on top of the water while on plane, just like in hwsiii's picture.

Unfortunately I now get spray coming into the motor well while on plane. Not sure exactly where it's coming from, but there is a lot more than there was before I raised the motor. Any ideas?

Thanks.

 

[Titanium48]

Re: Should I try a 19?

More on the unwanted spray - it seems to be originating from somewhere near the leading edge of the lower unit and rising near vertically. It seems to be distributed over about a 90? arc on each side. Should I try to get some pictures of it?

 

[steelespike]

Re: Should I try a 19?

If your not getting any ventilation you might try one more hole up.
Or perhaps move a little weight forward.It would seem the surface of the water is right at a critical portion of the motor.