Another Prop Question

[pair of jacks]

There is no name or brand on the prop so I couldn't tell you. The anti-cav/ventilation plate is right on top of the water on plane like it should be and appears to be just above the bottom of the keel (but difficult to tell exactly as boat is in water). Bow does rise on hole shot takeoff. WOT is 5400 rpm's.

The Evinrude prop I was looking at was a 15 inch 14 pitch version as opposed to the current 14.5 inch and 15 pitch.

[McGillicuddy]

Originally Posted by pair of jacks

There is no name or brand on the prop so I couldn't tell you. The anti-cav/ventilation plate is right on top of the water on plane like it should be and appears to be just above the bottom of the keel (but difficult to tell exactly as boat is in water). Bow does rise on hole shot takeoff. WOT is 5400 rpm's.

The Evinrude prop I was looking at was a 15 inch 14 pitch version as opposed to the current 14.5 inch and 15 pitch.

I'm not so sure you are under-powered. Right now your prop slip at speed is about 15% that's not so hot.

The bow lift suggests a stern-lifting prop is in order. I will also guess that your current prop has too much cup or rake or both based less than desirable rpm. Also might consider getting in the water and assure the the ant-cav plate is about an 1-1/2 inches above the keel with the 2 planes parallel. This is also a source of rpm loss and possibly the most overlooked aspect of dialing in your ride, epecially on a SeaCraft. A 15 pitch should turn easy with your power. Your gear ratio however is 1.85:1 or so so a bigger diameter wheel is probably not the answer.

Bushwacker's recommendations are on the money. The Rogue is BRP's reputed stern-lifter, although most 4 blades offer that attribute. I don't know the Rogue. I do know the classic merc Black Max is a stern lifting champ. I would ask dealer to try a 14-3/4 x 15 Black Max with an etec hub and go from there. It's an easy to turn wheel which is helpful. Seems Bigshrimpin ran a 15p Mirage Plus on a 175 (might have been a Merc) with good results (nearly 40 mph on a 23), too. Good luck.

[sidelock]

If WOT RPM is higher than the manufacturer's listed RPM range for the specific motor, could it cause any damage to the motor if you run it higher than its RPM range ?

[Bushwacker]

Originally Posted by sidelock

If WOT RPM is higher than the manufacturer's listed RPM range for the specific motor, could it cause any damage to the motor if you run it higher than its RPM range ?

That's much less likely to cause damage than lugging the motor! (running BELOW the recommended RPM range at WOT by running a prop with too much pitch/diameter!) Check out that E-Tec link in my earlier post for more info. Most modern motors like the E-Tec have speed limiters built in to the EMM that will keep you from over revving them.

[sidelock]

Originally Posted by Bushwacker

That's much less likely to cause damage than lugging the motor! (running BELOW the recommended RPM range at WOT by running a prop with too much pitch/diameter!) Check out that E-Tec link in my earlier post for more info. Most modern motors like the E-Tec have speed limiters built in to the EMM that will keep you from over revving them.

Bushwacker, I'm running a Yamaha C115 two stroke on an 18' SF. What prop would you recommand I should have ?

[Bushwacker]

I ran a 13 3/4 x 15P OMC SST on a 115 my Seafari for years and it was a perfect match. However that was a 1975 motor rated at the powerhead, so it was probably only about 90-100 hp at the prop, and your boat is lighter so you should be able to turn something like a 13 1/2 X 17p prop. I'm not that familiar with Yamahas and don't know what gear ratio they run, which would affect prop selection. It was 2:1 on my old Evinrude. Snookerd ran a 130 yami 2S on his 18, so could probably give you a better recommendation.

There are at least 3 things you need to do before you start changing props: 1. Make sure your tach is accurate. 2. Make sure motor mounting height is correct (AV plate out of water when on plane). 3. Do all your testing with full fuel and the maximum load you intend to carry. Add some water ballast if necessary.

[sidelock]

How do I check the tach for accuracy ? I quess you can tell by now that I'm a newbie ! & eager to learn.