Re-powering my seacraft

[RUSTYNTABATHA]

WOW !!!
i have 3 questions.
1 Why did you go with the 150 ? ( max hp on the boat is 175. the 150 and 175 weigh the same on that motor )
2 Are you mounted on the transome or bracket
3 do you have a noticable difference in noise level at the console ?

[infanterene]

Originally Posted by RUSTYNTABATHA

WOW !!!
i have 3 questions.
1 Why did you go with the 150 ? ( max hp on the boat is 175. the 150 and 175 weigh the same on that motor )
2 Are you mounted on the transome or bracket
3 do you have a noticable difference in noise level at the console ?

1. My 18' is max rated for 150hp. The dealer told me that there is very little difference between the 150 and the 175, maybe 10-15 hp.

2. I am transom mounted

3. the etec is much quieter than my old Yamaha at idle, cruise and somewhat quieter at WOT.

As is, the boat cruises real nice at 35-37mph burning 7-8 gph or 4.5-5.2 mpg. I was hoping to hit 50mph but was probably being too optimistic.

[infanterene]

Originally Posted by Bushwacker

Wow, you're over-propped by at least 700 rpm! Surprised that a full tank of gas and extra person made that much difference, but that's why Fr. Frank always says to test props with the max load you intend to carry. You definitely need less pitch; maybe a 3B might be better for you if you want a high speed cruise, but I still think you need some stern lift with a relatively heavy motor on a small boat. Maybe try a 15" pitch 3B Rebel prop, which has a lot of blade area, hangs on plane well and has good stern lift. Too bad we don't live closer . . . you could try my 15x15 4B prop. I can only turn it to 5450, but the optimum rpm for my 2007 motor is 5400-5500. You could probably turn it faster on a lighter boat.

Did you get a look at the AV plate to see if it's dry on plane? If motor is mounted too low, that might get you another 100 rpm or so. Also what was your min-planing speed with that prop? Suggest you send a PM to forum member Keys Cruz, who is also running a 150 E-Tec on an 18 to see what prop he's running. He lives close to you when he's not living on his trawler in the Keys.

Unfortunately I think my motor is a little too low. Im at the last hole, so no room for adjustment.

Your 4B 15x15 would probably be a lot better than my 17. The dealer offered a 3B. Is your prop a BRP prop?

[RUSTYNTABATHA]

sorry forgot yours was a 18. the 20 is rated for 175. if you got to 47... 50 is possible fresh wax on bottom, trim, motor height, etc.. the trade off for top end is not always worth it. I thought the motors were rated at the prop in real world HP. 150 =150 at the prop shaft 175=175 at the prop shaft.. if and when i can swing the new motor i will be extatic with 4 + mpg @ 35 mph..

[Bushwacker]

Originally Posted by infanterene

Unfortunately I think my motor is a little too low. Im at the last hole, so no room for adjustment.

Your 4B 15x15 would probably be a lot better than my 17. The dealer offered a 3B. Is your prop a BRP prop?

You're way down in RPM, so I suspect you could easily hit 50 mph with the right prop. That motor develops max HP at 5350, so it's not putting out it's max HP with your current prop. I think Keys Cruz' rig will do over 50. You should be able to have the mount holes redrilled higher to pick up some more speed AND MPG!

My 15" prop is a PowerTech ELE4. My dealer didn't carry any BRP props and only had used props for trials. He said the 2.7L V-6 typically can't turn a Rebel fast enough on a boat like mine and that it's normally used by the guys with the 3.3/3.4L big block V-6, but it will fit your motor so I'd try a 15P version if they'll let you.

I have an aluminum Michigan Vortex 4B 14x20 that I had repitched to 14x18 which turns about 5500 and I use it for a spare. I also have a 14.125x20 4B Michigan Apollo that I once hit almost 50 mph with; it gives a little better mileage than the 15x15, but it only turns about 4600 with a very heavy load and 5200 with a light load and is much slower to get on plane. I also tried the same model PowerTech in 15x17P size, but it's down about 200 rpm compared to the 15P version. The 15x15 jumps on plane at only 40-45% throttle, will stay there down to about 12 mph, and turns the same max rpm regardless of load. I can basically run any speed I want with that prop, so I've been running it for about 6 years. Still not sure it's the best, but I think it's close!

[Bushwacker]

Originally Posted by RUSTYNTABATHA

. . . I thought the motors were rated at the prop in real world HP. 150 =150 at the prop shaft 175=175 at the prop shaft.. if and when i can swing the new motor i will be extatic with 4 + mpg @ 35 mph..

NAEBM rules only require that the actual HP be within +-10% of the advertised HP! BRP appears to be sandbagging by the full 10% on the ratings of their more mildly tuned motors, because they've published HP curves showing that the "150" E-TEC is actually 165 hp at the prop, so it's a very strong "150"! They also build the "175" and "200" hp motors on the same 158 cu. in. block, but I suspect the actual hp of the "175" is about 180-185, while the "200" maybe somewhere around 190-200. The 3.3L"200" HP big block V-6 is reportedly a very strong motor at about 220 hp, but it's also over 100 lbs heavier than the small block V-6.

If you look at HP/cu. in., that'll give you a clue as to how strong the motor really is, especially in the mid range where you want maximum torque for getting on plane. The more conservatively rated motors tend to have more mid-range torque than motors that are tuned for maximum top end HP. One of the most knowledgeable techs on the E-TEC Owners Forum claims that the 105 cu in. V-4 115 is actually has noticeably more mid-range torque than the 130 HP version of the same powerhead! HP and Torque are two different things, and both 2 and 4-stroke motors can be tuned to optimize one at the expense of the other!

[76Red18]

I'm still testing a new prop I purchaced for my 18. It's a Stiletto Bay Pro 3, 4 blade 14 1/4 x 15. I raised the motor all the way up (2" or so above the keel) but need to lower it a bit due to over heating at full throttle full trim. I hit 44 @ about 5500 rpm briefly before i had to back down on the throttle. Cruise was 32 @ 4000 rpm. The old Johnson 150 loves 4000 rpm. The boat was fully loaded. More testing this weekend.

[infanterene]

I tried a 3 blade 16P. I was able to hit 5500 +/- fully loaded but only went 45mph. My cruise dropped to 30-32mph and fuel consumption went up. It wouldnt plane as slow either.

Its weird but the 4B over propped setup felt better.

[McGillicuddy]

Originally Posted by infanterene

I tried a 3 blade 17P. I was able to hit 5500 +/- fully loaded but only went 45mph. My cruise dropped to 30-32mph and fuel consumption went up. It wouldnt plane as slow either.

Its weird but the 4B over propped setup felt better.

What 3 blade 17p prop did you try?

[Bushwacker]

4 Blades will always produce more stern lift than a 3B, so that's why you could stay on plane longer with the 4B. I think they generally have less slippage so they're more efficient at cruise, although the drag of the extra blade may cost you a few mph on top end.

Sounds like you just need to get your motor height corrected and then find the right combo of pitch/diameter 4B. You might try Ken at Prop Gods or try the PowerTech web site, where they have a data sheet you fill out with boat weight and the performance numbers you're getting with current prop. They will then advise what prop would best suit your application. If being able to hang on plane at low speed is a priority (which I think is important for a 20 that you run offshore), be sure to mention that.