Double Eagle, center console.

Report the performance of your boat, supply as much information as possible (weight, HP, prop, speed, etc.).
Subject: Make the Glen-L design name the subject. If the design already has a posting, add your information to that post.

Moderator: Bill Edmundson

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kens
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Double Eagle, center console.

Post by kens » Mon Nov 26, 2007 7:42 pm

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?
Last edited by kens on Mon Mar 21, 2011 4:56 pm, edited 13 times in total.

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Bill Edmundson
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Post by Bill Edmundson » Mon Nov 26, 2007 8:24 pm

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. :roll:

Beware of free advice! :wink:

Bill
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kens
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Post by kens » Tue Nov 27, 2007 2:50 am

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.

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Bill Edmundson
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Post by Bill Edmundson » Tue Nov 27, 2007 5:47 am

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
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Mr Hot Rod
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Post by Mr Hot Rod » Tue Nov 27, 2007 1:10 pm

Beware of free advice :wink:
Great advice, Bill :lol: 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 :!:
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kens
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Post by kens » Tue Nov 27, 2007 3:29 pm

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.

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kens
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Post by kens » Tue Nov 27, 2007 3:34 pm

"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 :!: "
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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? :D

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Dave Grason
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Post by Dave Grason » Tue Nov 27, 2007 9:49 pm

....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.
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.

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Post by Nova SS » Wed Nov 28, 2007 5:24 am

Dave Grason wrote:....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.
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

Nova SS
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Post by Nova SS » Wed Nov 28, 2007 5:28 am

kens wrote: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? :D
Me too please...can I have a ride 8) 8)

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Jimmy70
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Post by Jimmy70 » Wed Nov 28, 2007 5:28 am

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
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Bill Edmundson
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Post by Bill Edmundson » Wed Nov 28, 2007 11:34 am

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
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Mr Hot Rod
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Post by Mr Hot Rod » Wed Nov 28, 2007 12:47 pm

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).

Code: Select all

RPM = 4400
Ratio = 1.9:1
Shaft RPM = 2316

Pitch Theor   10%      20%   30%   40%   50%
----- ------   --------  -------  ------  ------   ------       
  12  26.32  (23.68)  21.05  18.42  15.79  13.16   
  13  28.51  (25.66)  22.81  19.96  17.11  14.25  
  14  30.70  (27.63)  24.56  21.49  18.42  15.35  
  15  32.89  (29.61)  26.32  23.03  19.74  16.45  
  16  35.09  (31.58)  28.07  24.56  21.05  17.54  
  17  37.28  (33.55)  29.82  26.10  22.37  18.64  
  18  39.47  (35.53)  31.58  27.63  23.68  19.74  

Code: Select all

RPM = 3000
Ratio = 1.9:1
Shaft RPM = 1579

Pitch Theor   10%      20%   30%   40%   50%
----- ------   --------  -------  ------  ------   ------       
  12  17.94  (16.15)  14.35  12.56  10.77   8.97  
  13  19.44  (17.49)  15.55  13.61  11.66   9.72  
  14  20.93  (18.84)  16.75  14.65  12.56  10.47  
  15  22.43  (20.19)  17.94  15.70  13.46  11.21  
  16  23.92  (21.53)  19.14  16.75  14.35  11.96  
  17  25.42  (22.88)  20.33  17.79  15.25  12.71  
  18  26.91  (24.22)  21.53  18.84  16.15  13.46 
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 !
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Last edited by Mr Hot Rod on Thu Jan 26, 2017 5:00 pm, edited 1 time in total.

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kens
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Post by kens » Wed Nov 28, 2007 4:00 pm

Bill Edmundson wrote:Ken,
That 12% slip on the 16X16 kinda surprised me. All I can guess is that there's less turbulance off the flatter prop. :?

Bill, you might be on the mark there. This design does have a forefoot, that raises up when at speed; raises up and makes shaft angle steeper. I just got off the phone with my propshop, he's gonna loan me a 17x14 and see what happens. He says to go largest dia. possible regardless of pitch. I gonna try it. If the 17" prop slip gets down to 10% or less, then it might work. Acme tried to sell me a 17x14, but I dont really see how that can work unless the slip is near zero.

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, are you sure about that? .1mph per 100rpm? It is more like 1mph per 100rpm.
Bill

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kens
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Post by kens » Wed Nov 28, 2007 4:11 pm

Jimmy70 wrote: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
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.

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