Prop performance calculator?

[keninaz]

Is there a calculator that will estimate performance out there that takes boat size/weight and motor size/prop pitch into consideration?

 

[steelespike]

There are a number of what I call prop selectors. Just do a search
I use a site that simply evaluates prop performance based on the information given.
I'm pretty sure there is a Mercury prop selector site.use a number of specific details.
There are lots of folks on iboats prop forum that can help evaluate your setup and suggest
a prop.Problem going directly to a selector is some times the condition of the motor or the hull skews the results.
Often the tachs and onboard speedos are suspect. so a gps speed is best.

 

[keninaz]

The Mercury prop selector does not do comparisons. It did recommend a 6.5 pitch for my application however that I have on order.
I don't have speedo or tach in the boat. This is tiller operated and I use an inductive Tiny Tach and my GPS for RPM and Speed as stated before.
The motor is new.
Just for kicks I tested without a load and the motor will hit WOT tach specs quite easily so the motor is not malfunctioning. I however now think that this motor has yet to break in properly as regardless of throttle position on the tiller the RPM range was not being met.
Now just waiting for the 6.5" prop to see how that works out. 8-10 MPH at elevation would be nice.

 

[steelespike]

The Mercury prop selector does not do comparisons. It did recommend a 6.5 pitch for my application however that I have on order.
I don't have speedo or tach in the boat. This is tiller operated and I use an inductive Tiny Tach and my GPS for RPM and Speed as stated before.
The motor is new.
Just for kicks I tested without a load and the motor will hit WOT tach specs quite easily so the motor is not malfunctioning. I however now think that this motor has yet to break in properly as regardless of throttle position on the tiller the RPM range was not being met.
Now just waiting for the 6.5" prop to see how that works out. 8-10 MPH at elevation would be nice.

If your testing on muffs any motor will rev freely even one one cylinder or suspect fuel delivery.
It's pretty common for a motor to run" right" on muffs and run very poorly in the water if at all.
Hopefully your new motor will be better with the 6.5" prop.
I forget if we did a cylinder drop test.?

 

[keninaz]

No, I did not remove a spark plug wire as it runs so smooth and well. I am honestly wondering now if the timing is failing to advance under load. Could be I suppose. The dealer is going to supply a prop to me and I should have it by mid week and I will try it all out again but honestly I cannot see how a 2.25" change in pitch is going to get this motor up to RPM where it could finish breaking in and run right. I may have to turn this motor in for testing but it's new and under warranty. Never had so many problems with a motor in my life trying to compensate to elevation but this is my first attempt with an outboard motor.

 

[keninaz]

OK, I just went out and put the muffs on and warmed the motor up and then pulled one wire at a time from each cylinder to make sure they were both firing. They were OK and responded the same when given throttle without the other running. So that test is OK.

 

[steelespike]

2.25 doesn't seem like much but it is about a 25% change.
There are 8 sizes listed.6.5 is 5 changes from 9" and there is only one size left.
you are close to going from the biggest to the smallest.

 

[keninaz]

As of today I am almost certain that I have my problem solved.
Today our granddaughter is staying with us and wife wanted to take her for a ride in the boat has at 6 years old this is her 1st time ever in a boat.
So I added well over 300 pounds back to the boat with the extra passengers and gear and while boating I had the passengers sit in the very front of the boat.
So now the Lowe V1467 WT that weighs some 262# and is 13' 11" long is back where I would normally use it fishing and such.
Much to my surprise versus the results I had as suggested with the latest boat possible and only obtaining 3900 RPM the boat was able to reach nearly 4200 RPM and the boat actually planed and maintained that plane quite easily. I did not have the GPS with me to monitor speed but I would estimate that I obtained somewhere between 8-8 1/2 mph
The Dealer also called me and told me that my prop for correction at altitude is in stock and that is an 8.9 X6 .5 which when installed should raise the rpm's perhaps another 300 to 400 RPM.
I noticed yesterday that my plugs were pretty dirty and fouling due to the low RPM range I have been in so perhaps with better balance and load and the new prop I will get enough RPMs that they will burn clean. I could always go to a hotter burning plug to correct this problem however.
I have a few posts going so I will post this in all of them as it may help someone else along the line. I never figured that adding so much weight to this boat would increase the speed. Lessons learned.

 

[keninaz]

Today, with a full load in the boat, all but the trolling motor itself, and the new 8.9x6.5 prop that Mercury Marine said to use at 5000' I took the boat out and it hit 5400 RPM max and over 12 MPH max. Steady speeds against the wind and all was 10-11 MPH easily.
Problem finally solved after doing a few experiments.
The only other thing that I did was at idle it was loading up a bit so I drilled the plug they had installed over the fuel screw for idle and adjusted it. It now starts better and idles better and does not load up at extending idling.

 

[steelespike]

That's nice! 12 mph must be just about planed out.I figured a light boat if you could make 6000 you would get about 16 mph.
I think 12 is very respectable.

 

[keninaz]

It actually planed around 8-9 MPH the other day before the new prop. You are never going to get 6000 RPM out of the new Mercury 4 strokes as most I am informed are pre programmed to start reducing spark at 5850. Specs for my motor at 5700-5800 but with the elevation and all I am quite happy overall now.

The boat is rated for 20 HP and even with the 800# load that I am carrying that 20 HP must cook right along if my 10 can achieve what I am getting. And is this thing stingy on fuel!

 

[fishrdan]

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