How do I understand prop slip and use it?

[Thad]

Re: How do I understand prop slip and use it?

OKEEDOKEE

I ordered the Solas Rubex 4/19p and a new (spare) nut and spacer kit this morning from iboats

I should receive it Sat. or Mon.

I'll get you some #'s as soon as I can.
Next weekend (Aug. 7&8) will not be productive #'s as I will be on Lake Michigan with a LOT of weight on board.
Some might say I'm not real smart
So when I get back home and can run under similar conditions to the previous #'s I'll take some readings.

Thanx again...you have no idea how much I appreciate the help:

 

[hwsiii]

Re: How do I understand prop slip and use it?

I am glad to be able to help you Thad.


H

 

[Thad]

Re: How do I understand prop slip and use it?

If it were'nt for bad luck...

I trashed my new four blade prop Saturday. Taking it to the shop tonight to see if it repairable.

But mainly, if I have to buy a new prop, what do you think a 21p would do.
I bought the Solas Rubex w/ removable hub. I don't really have any numbers to work with except for the boat ran at 4900 rpm's WOT and a speed of 50.6 mph.
I assume that the 21 would lower my rpm's to a "safer" level. The recommended top rpm is 4600-4800. But, would I loose the powerfull hole shot and the ability to get a heavy boat out the water (like when I have a lot of people and gear on board)?

Or should I stay with the 19 and watch my rpm's closely to keep in the range I need. I don't know what difference 100 r's makes but it probably isn't good over the long run. Then again, will a heavier load in turn lower my WOT rpm's?

 

[hwsiii]

Re: How do I understand prop slip and use it?

Thad, I am very sorry to hear about your prop and I hope they can repair it for you.
The WOT RPM is a little high at 4,900 but it is not anything that will hurt your motor at all. First of all you will lose a decent amount of your hole shot if you change to a 21" pitch and your RPM will go down to about 4,450 RPM with the change, which will be loading your motor at all times and RPM as well as you will be at the bottom of your recommended WOT operating range. Second it will encumber your ability to have a great hole shot and great acceleration when you have a lot of people and gear on the boat. And when you have a load on the boat the RPM will be at 4,800 or less RPM.
It is not a good idea to run your boat at WOT on a regular basis, most people run their motor at a cruising speed of between 3,200 and 3,800 RPM on a motor like yours. In some heavier boats they have to run the motor at higher RPM because the motor is too small for the boat and load it is carrying, but as a normal course of events you wouldn't want to cruise higher than about 4,000 RPM.
With all of that being said, if you run your boat at top speed on a regular basis you might be happier with a 21" prop.
Here is my numbers for your new prop with the information I have, it is the last one on the bottom. I hope this helps Thad.


Prop Slip

Prop Change

H