20' SeaCraft - better w/ or w/o a bracket ???

[Fr. Frank]

Transom angle on all the 20' SeaCrafts is 14 degrees.

[Bigshrimpin]

This is on the take off . . . if I punch it with the motor trimmed down. The boat rockets up on a plane and the bow will stay down. The sternlift from the mirage plus helps quite a bit.

[76Red18]

Does that prop hold well enough to trim the motor up and lift the boat for max speed also. Thats supposed the be about the best prop for these boats. I run a Michigan Apollo which picks up the stern but really doesn' t give a whole lot of bow lift when necessary.

[Bigshrimpin]

It holds the water like a screw moving through wood on the take off. I need to raise the motor on my boat up a hole or two, but I love mirage plus for these boats.

[gofastsandman]

Hey Big Shrimpin and Fr Frank,

Thanks for the previous advice.
I was up in Stuart Fri at the 50% off sale and got a very nice 17p mirage plus at a nice price. Can`t wait to try it. Anyone want a michigan wheel? 14 1/2 x 17p
GFS

[76Red18]

Good to know. That Michigan prop breaks loose and makes the boat porpoise at about 30% trim.

[Fr. Frank]

Ben, those numbers seem a bit low. I have a 20' Seafari, with a remanufactured Merc 150, probably putting out about 190-200 hp. I also have SlicKote bottom paint. With a new, stock lower unit, I can run about 42 mph on the GPS at WOT, loaded with 4 adults, full fuel, and the Bimini up. With the top down, just myself, and full fuel I can run about 47-48.

With my old lower unit, Bob's nose-cone w/ low water pick-up I could touch 53 mph under the right weather conditions: cold air, high humidity, 10-15 knot winds, light to moderate wind chop and running downwind. At 50+ mph, a Seafari positively dances across the chop like a ballerina It feels like it's almost airborne, just touching the tops of the waves; very light and nimble, like it could chine-walk, but simply has too much class and manners to behave in such an unseemly fashion.

It's truly exhilarating. Just one of the reasons I love the Seafari.

[CaptLloyd]

Ben,

I'm running a Power Tech Prop, 3 blade SS, and if I remember correctly, it's 15X16 (I'm not near my boat right now, so I can't confirm). Anyway, I know I'm alittle under proped, but I wanted to get good low end performance out of the 4-stroke (running Sebastian inlet, low end punch is a must) At 4500rpm I cruise 23kts(26mph), and WOT, 6100rpm and 36kts(41mph). These numbers are running light, with 30 gal livewell, a few more guys, and the rest of the stuff, I lose 2-3kts. I know I'm not setting any speed records, but the hole shot is descent for a 4-stroke. The first prop I tried was a 20 pitch, my boat would do almost 50mph @ 5500rpm, but the hole shot was terrible. Then I tried a 18 pitch, light load conditions it was fine, but with the livewell full and 3 guys, it was a bit slow out of the hole. So I went with the 16, and gave up some top end speed. I would like to try the mirage plus and see how it works.

I hope this info helps. Good Luck

Lloyd

[Fr. Frank]

BTW, I also run a PowerTech prop, although mine's a custom 15X16.5 pitch, behind a 1.64 gear ratio.

Calculated slip ratio, properly trimmed, is about 11% with this prop, an excellent, very low slip ratio. My experience is that most props, even high-performance props show effective or "apparent" slip ratios between 15% and 20%, depending on the application.

The weight of the load, depth of the prop, angle of attack, all obviously make a huge difference, as well. Having a prop with excessive pitch that will not turn up into the powerband of the motor can give you slip ratios approaching 30%

For instance, a very well set up high-performance bass boat might show an apparent slip of only 8% to 9%. A 23' SeaCraft will be doing very well indeed to get below 18%

At any rate, my max RPM behind the new lower unit gearcase now is about 5900. (Old case w/ nosecone was 6100, with slip of 10.5%) I also went with the lower pitch prop for loaded holeshot and acceleration under adverse sea conditions. The motor also doesn't strain as hard at cruise rpm of 3900 - 4000, about 32-33 mph.

[CaptLloyd]

Fr. Frank,

Thanks for the great info, I like the numbers you're getting. My gear ratio is 2.59:1 on my Suzuki 140 4-stroke, and I know we're comparing apples and oranges with your boat/motor setup and my boat/motor setup, but my question is do you think I may gain some overall performance with a 4 blade prop? I know we'll getting into "mystery science" with all the variables involved, but I'm curious about any experience with 3 blade vs. 4 blade.

Thanks again!

Lloyd