WOT testing

[WanabeBoater]

When testing props for upgrade...Should the boat be ran at WOT with just the driver or should it be able to run WOT at any time...load vs. no load?

 

[Haut Medoc]

Re: WOT testing

How much load?
Driver & Wench with some gear is OK....
Fat mother in law, well.....
You get the picture.....
You, & a full tank of gas on reasonable water should get to WOT with no trouble d......JK

 

[Don S]

Re: WOT testing

Do your WOT testing at NORMAL load.

 

[Mahoney]

Re: WOT testing

If you are like me I like to get the most out of my engine and prop setup as well, which means propping it so that I can get the fastest top end and cruising efficency with only myself and like a half tank of gas. Sure this feels great knowing that you have it maxed out, but taking a couple friends out and topping the tank off is no fun when you have to move people around to get on plane, then the engine is really lugging to get close to your WOT.

I tend to do excactly as Don said and prop it for normal load knowing you will have to back off a bit and watch the rpms under light load, or better yet have 2 props available and the tools to quickly change it "BEFORE you get to the ramp" depending on your days boating needs.

 

[WanabeBoater]

Re: WOT testing

Thanks Guys,

I have a 1994 Starcraft 2010ss with a 5.7 Carb Alpha 1. I am currently running a 14.5 X 19 pitch and with normal load I am running 4150rpm. I am rated to run 4400 - 4600 rpms. I am looking to upgrade from an alum to a SS prop. Any suggestions to the confused?

 

[imported_Old_Machinist]

Re: WOT testing

Thanks Guys,

I have a 1994 Starcraft 2010ss with a 5.7 Carb Alpha 1. I am currently running a 14.5 X 19 pitch and with normal load I am running 4150rpm. I am rated to run 4400 - 4600 rpms. I am looking to upgrade from an alum to a SS prop. Any suggestions to the confused?

 

[imported_Old_Machinist]

Re: WOT testing

Yea I would like to know that also. I run the same engine setup and run 4200 RPM with only wife and 15 year old. Boat planes out well and cruises at 2400 staying on plane. I don't plan on running flat out much as I have discovered (boy what a suprise) you spend a lot of time getting on first name basis with the fuel pump babe! So with that statement would you still prop up for more hole shot and lower RPM cruise on plane.

Thanks,
Grant
aka Old_Machinist
1998 VIP Valiant 5.7 Mercruiser, Alpha 1

 

[Don S]

Re: WOT testing

Thanks Guys,

I have a 1994 Starcraft 2010ss with a 5.7 Carb Alpha 1. I am currently running a 14.5 X 19 pitch and with normal load I am running 4150rpm. I am rated to run 4400 - 4600 rpms. I am looking to upgrade from an alum to a SS prop. Any suggestions to the confused?

That would be better asked in the prop forum.
Heres a link to it.

http://forums.iboats.com/bbBoard.cgi?a=viewforum;fid=40

 

[Boatist]

Re: WOT testing

If you get a simular style prop you could go down to a 17 pitch and should turn ablut 4550 RPMs. This would give you a better hole shot but likely reduce your top end by about 2 miles per hour. Plus use a little more Fuel.

 

[Mahoney]

Re: WOT testing

Do you have tabs on your boat? I don't want to swing this post the wrong way, but a set of Smart Tabs from Nauticus(No I don't work for them, just an extremely satisfied customer) You will definitely have much better response getting on plane, and wont believe how slow you can go staying there.

Best thing is you can put them on yourself in about an hour and they are fully automatic.

 

[John_S]

Re: WOT testing

Wannabe, Old Mach, Do you know what drive ratio you have and can you post what your normal load is? Drive ratio (unless it was changed) is marked on the side of the alpha drive. The numbers posted seem low in comparison to mine. A drive ratio difference could be the reason. My brother has a Starcraft '98 2010. If your year is similiar, it appears as a standard V-hull bow rider. The hull is similiar to my 20' Bayliner.

Boat: '97 Bayliner 2050CL w/5.7L Mercruiser (no engine mods) Alpha II Gen II 1.47 gear ratio, prop: Merc Black Max (alum) 14.5 X 19 X 3, Smart Tabs ST1290

Load: Full gas 28 gal, 2 adults approx 430lbs, two teens approx 270lbs = approx 700lbs people.

Performance: Once on plane, trimmed to running position, tach is very close to speedo reading. ie 3000 rpms is about 30mph, maxes out with that load at 4500 rpms:45 mph. Able to stay on plane, to something under 20 mph.

Anyway, while your issue maybe just a prop, I'd thought you would want "something" to compare to.

Update: I just took a quick look at the numbers in a prop calc. Your ratio would need to be lower than 1.47, which is not likely. I believe there is a 1.32 ratio, but it was only for hi-perf boats. If you have a different ratio, it is probably 1.62. From the calculator, going from 1.47 to 1.62 and keeping rpm, slip, and mph constant, requires a 21" pitch for 1.62 vs 19" pitch for 1.47.

Either your load or boat is significantly heavier (by design or water logged) than mine, or something else (dirty bottom/drive, bad tach reading, engine performance) etc maybe going on. Might not want to be throwing props at it, until further checks could be made.

 

[WanabeBoater]

Re: WOT testing

John,

My Alpha 1 gen 2 gear ratio is a 1.50. My normal load is approx. 700lbs. At 4150rpms I'm running an even 45mph with a 14.5x19x4. But with my 14.5x19x3, I'm running 55mph at 4200rpms. Both props are alum by michigan wheel. I bought the boat this year and have done nothing to the engine, besides a complete tune-up and normal maintenance. If these numbers calculate okay, then I'm wondering if I can squeeze a little more speed out of a SS prop or if I should have the carb tuned for better performance.

 

[Don S]

Re: WOT testing

So far, you are overpropped and need to get a prop that will put your engine rpm up between 4400 and 4600 or your engine isn't going to last very long.
With only 4150 - 4200 rpm, you are overloading the engine...... Not good.

 

[QC]

Re: WOT testing

At 4150rpms I'm running an even 45mph with a 14.5x19x4. But with my 14.5x19x3, I'm running 55mph at 4200rpms.

There's something else wrong here too. 10 MPH between those two props with a 50 RPM difference just aint right . . . ??? I think you need to:

A) Verify the tach is correct (check switch behind tach. If it is on the 6 cylinder instead of 8 it could be reading 25% low which I don't believe. I also don't believe 55mph at 4200 . . . )
B) Verify your speed numbers (GPS?)
C) Get fresh data after A & B and both props under the same exact conditions i.e. 10 minutes apart
D) Start a new thread in the prop section with the new data.

If you're really running 55 MPH with that three blade I wouldn't touch anything . . .

 

[Reel Poor]

Re: WOT testing

hummmm,,,,,,so 50 rpm's will get me 10 mph

 

[QC]

Re: WOT testing

hummmm,,,,,,so 50 rpm's will get me 10 mph

Maybe with a steam engine . . .

 

[John_S]

Re: WOT testing

Wannabe, there has to be something else going on. The 3 blade and 55 mph means you have a negative slip. Just not possible. The 4 blade numbers show about a 10% slip. I think slip of 10-20% is the "normal" range for a V hulled bowrider in this size range. There are a number of prop calcs out there, here is one: http://www.rbbi.com/folders/prop/propcalc.htm

 

[WanabeBoater]

Re: WOT testing

I apologize, the four blader is a 14.5x18 not 14.5x19. And yes that is the difference in speed but not 10 minutes apart. I think I tested the 3 blader with only half the weight load. That is my fault. But I did test the four blader under the same conditions and found to get only 45 mph consistently. I will test both again on the same day with the same load. thank again