Glen-L.com

OK guys, help me out here. Many of you saw me splash the boat at Guntersville. I was overpropped that day. Now I am on my 4th prop, and still overpropped. Here is what I got.
3.0L gas inboard. 135hp rated @ 4400 rpm.
VelvetDrive 1.91:1 gear.
Boat weight 2480lbs (weighed at truckers CAT scales)
OAL length 24'8"
Beam 8'
Boat design, Double Eagle. stretched 10%
No hooks/rockers in the running bottom.
Engine setting on C.B. per plans.

Prop #1. 16x18 =3950rpm @28mph
#2. 14.6x17.5cup=3975rpm @28mph
#3. 14.6x18 =4100rpm @28mph
#4 16x16 =4175rpm @28.5mph
#5 16x15 =4400rpm @27mph
#6 15x16 =4400rpm @28mph
#7 14.5x17 #2cup =4300rpm@28.7mph
#8 16x14 #3 cup =4150rpm@29mph
#9 17x15 #2cup =3800rpm, 27mph, high fuel consumption
#10 16x13 #4 cup= 4000rpm @ 29.5mph
#11 17x14 DynaQuad 4blade=4500rpm @27mph
#12 16x12 4cup =4550rpm @ 27.5mph
#13 15x15 medium cup=4000rpm @ 27mph
#14 15x14 cupped out to the tips=4000rpm @ 28mph, best cruise prop to date @ 3000rpm
All speed runs were 2 directions to allow for wind/current. All speeds per GPS. Tach previously checked against a calibrated optical tach; as such the tranny has been verified at 1.91:1. Shaft alignment checked.

So, the question is: Why does my RPM not come up? Nor speed go up?
Look at #1 & #4. That is the same prop re-pitched to 16. Took out 2 FULL inches pitch and only gained 225rpm. But, here is the kicker, slip dropped by 5% in removing 2" pitch. No change in speed though.
WHY is my speed not changing, preferrably going up?
Look at #1 & #3. Lost nearly 1 1/2" dia. and only got 150rpm. Say what?

The only cupped prop is #2. All props are MRI scanned to class1.
WHY is there so little change happening here? Is there something wrong with my boat setup?

Ken,

My understanding is that a cupped prop effectively adds 1" to the pitch. So, a 16 cup is the same as 17. If that is right, #1 is about the same as #2.

I've read 1" dia. or 1" pitch is usually about 200 rpm.

My guess is to take prop #3 to 14.6X16, or #4 to 16X14.

Beware of free advice!

Bill

_________________
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

I even talked to my prop shop as well as Michigan Wheel support. They too say 1"=200rpm.
But my boat aint responding to that effect. Not even close.
Taking 4 full inches out of the first prop just dont seem right, even prop shop agrees, it dont seem right.

And the cup thing. Looks like cup only torque loads the engine without adding any speed at all.

Ken,

I guess, that leaves engine tuning or throttle range. Are you getting full movement at the engine with full movement at the helm?

Bill

_________________
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Great advice, Bill Also applies to the following :

I'm not an expert by any stretch, but I'd hazard a guess that the numbers aren't changing because you don't have enough torque 'on tap' at WOT to turn the prop (very little RPM spread). Try re-running your tests at the engine's rated peak torque RPM instead (2400-2800 RPM). At that RPM you'll know that max torque is being produced. The numbers should be more relevant. Regardless, pitch and diameter will have to be reduced until you hit the sweet spot. You could also try a 13x15 to establish a rough baseline and see what it would spin to.

It was a pleasure meeting all of you at the Gathering. Kens, I really enjoyed the ride in your boat. Next year, it will be our turn to splash the boats
__________________
Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod

Yeah, the throttle is going wide-open. Thats the 1st thing I looked at. I even ponied up the money for a new carb. No help.
Why am I only getting 100rpm per inch of prop change?
but, here is another one. At the speed I am getting, it indicates that HP is being produced. It is just getting the RPM up, and getting the sweet spot prop.
Also, on a fuel consumption run, my fuel burn is dreadfully high for this HP. I am burning @ 3000 what I should burn WOT.

"It was a pleasure meeting all of you at the Gathering. Kens, I really enjoyed the ride in your boat. Next year, it will be our turn to splash the boats "
__________________
Paul Kane Chelsea, PQ


I cant wait to see one of the HOT boats. I would love to get a ride in yours. Can I hold the GPS for you next year?

....and splash my boat I will!

Miss Connie has never been one to be able to see what I see in the boat. As a result, I've never felt that she was especially supportive of the entire project although she gets mad at me if I say that out loud. But then she saw Tom Drake's boat and now she's as fired up about having our's ready for next year as I am.

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Isn't it amazing!! The person that never has the fortitude to pursue his own dreams, will be the first to try and discourage you from pursuing yours.

Dave, that is a major step forward. Sometimes the nonbelievers have to see something in person to KNOW that it is possible while the people that believe KNOW its possible without seeing it first hand. Getting your nonbelieving significant other to believe it can be done is, I think, harder then building the boat..lol

Congrats on the major milestone Its all easy sailing from here on out

Me too please...can I have a ride

Kens
I am wondering if you are creating a air pocket under the boat someway and cavatating at that specified speed. From reading your specs it seems that something else is going on in that area as you would surely see some increase in speed with a few extra RPM's even if it was a 1 or 2 mph more.
Jimmy

_________________
Dreams are free, Reality cost money.

Ken,

The slip numbers are very interesting. I didn't understand (and, don't) how that worked. I ran the numbers, and sure enough 5% change!

That 12% slip on the 16X16 kinda surprised me. All I can guess is that there's less turbulance off the flatter prop. I'm going to ask our pump expert.

As far as more speed goes...

200 rpm @ engine = 104.7 rpm @ prop. works out to .10 mph/1"of pitch. - minus slip.

I don't think we can measure that close.

Bill

_________________
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Nice to see everyone motivated for the next Gathering ! It will be a blast . . .

Wow ! I guess I'm not the only gearhead out there. Bill has been doing his homework ! Here's more fuel for the fire :

We tweaked a copy of our Theoretical Speed Table to include bigger pitches and 1.9:1 reduction ratio. The following numbers might help (or hinder) the process. Column 1 = propeller pitch, 2 = theoretical speed, subsequent columns are slippage. Bracketized numbers () are what we're shooting for (10% slippage).


Try re-running your GPS tests at 3000 RPM and compare them to the numbers above. Your prop might be more efficient at the lower RPM (peak torque).Click here to view the complete table.

Hope this helps !
__________________
Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod

No, I dont think so. Nothing strange like that going on. If anything strange, is the wake, as flat as a jon boat.
I have even tried to blow-out the prop in sharp turns. No way. Gone helm hard-over and slam the throttle open, she's hooked up. Gone WOT and put in full helm, prop remains hooked up, to the point of lugging the engine.