Picking a Prop - Effect of Diameter

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

I'd like thoughts on where I am now,

I stopped into my local prop shop Friday to see if he might have the prop I was looking at. No dice but talked to him a bit and he went in the back and brought out a fresh rebuild, 13.75x15 that he said he had decupped a bit and repitched to 13. Since I wanted something to try this weekend I took it.
Boat jumps on plane but w/just me in it but will over rev. Loaded up pulling a tube with the bimini up WOT is 58-6000. I never had a chance to get an actual speed but it feels similar to before.

Now I found the performance awesome and liked the fact that with just me in the boat I could power through a turn by rolling on the throttle and not lose any speed.

So whats your thoughts, stick w/this prop and keep a close eye on the RPM? Switch out for something known and try again?

I will say I think this old tinny throws alot of disturbance as I did notice w/ this prop it sounds like I'm right on the brink of ventilating at WOT. So I'm thinking the height isn't something I want to mess with.

I'll also ask if the new prop should require some trials of other trim settings?

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

I see the potential for this prop on my motor of turning 7000 with just me in the boat and I don't like that idea so I've decided to look for another prop.

Back to looking at the Amitas but after this prop wondering if I really want to go 13 or 15. The rebuilt one I tried this weekend was originally an OMC. Even after his modifications could it of still had more cup? Maybe he depitched it more than he thought?

Any thoughts on any of my ramblings? I'd like to get one ordered so I can have it here to tryout next weekend.

 

[jestor68]

Re: Picking a Prop - Effect of Diameter

My final recommendation is the Solas Rubex 13-4/5 X 13.

It's actually cheaper than the Amita. It costs $8 more, but comes with the hub kit that includes all the hardware to install.

The Amita requires the Solas thrust washer($22 extra).

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Glad you pointed that out Jestor as I didn't know that about the thrust washer.

Do you know if the TW for the 13" and the 15" Amita are the same? I see the part# is but I'd like a conformation. I ask only since I now have that small doubt about going 13" and notice that there isn't a 3 blade 15" listed for the Rubex.

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Crossed my fingers about the thrust washer - 13" Amita ordered. Plus TW of course.

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Received prop today. Looking at thrust washer and I assume that it goes on so that the recess in the flat side of the washer sits in the backside of the prop hub. Is this correct?

 

[Bondo]

Re: Picking a Prop - Effect of Diameter

Received prop today. Looking at thrust washer and I assume that it goes on so that the recess in the flat side of the washer sits in the backside of the prop hub. Is this correct?

Ayuh,... The thrusthub goes on the shaft, matchin' the taper,....

then the prop, spline washer, lockin' tab washer, 'n nut....

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Thanks Bond-o,

Didn't notice the taper on the inside, had to go look again. Makes perfect sense now.

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Swapping prop out today, old thrust washer is stuck on there. Didn't micrometer measure it but the shoulder diameter and depth appear to be the same so I should be ok to just continue to use the old one correct?

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Well a 13" wasn't the answer. Over revs to about 6500. Got 24-25 MPH @ 56-5800.
Could my old 17" just of been so worn and in bad shape too of caused my low RPM?

 

[BonairII]

Re: Picking a Prop - Effect of Diameter

Well a 13" wasn't the answer. Over revs to about 6500. Got 24-25 MPH @ 56-5800.
Could my old 17" just of been so worn and in bad shape too of caused my low RPM?

Something is not adding up here. You were running @ 4800rpm with the 17p prop, but now you get 6500rpm by dropping 4" in prop. That's an increase of 1700rpm.

Normally, you would only gain around 200rpm for every inch in pitch drop. In theory, you should have only gained 800-1000rpm.

Are you sure that your tach is accurate? Was the boat loaded(people/gear) the same for both runs(17p and 13p prop).

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

My testing with this prop was exactly the same as my original posting with the 17.
The tach is only a year old so I'm assuming it's close to right. That's why I'm questioning if my old prop was just so worn if it could of made that big a difference.

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Just a little update of where I'm at,

I took the original rebuilt and reworked 13 3/4x15 (decupped and depitched to 13) back to the local prop shop today and talked to the guy there.

He said my 17p with the bad edge and some damage if anything would add RPM's and that the decupping he did would add RPM. This doesn't explain the results w/ the SA 13p but I went with it. He said wait a few minutes I'll adjust this one(the rebuild I tried at first). He came back out and handed the prop back said he repitched it back closer to the original 15" and give it a try. Said hopefully that should get me right if not come on back and he'd adjust it again, even if its just a fine tuning.

 

[TruckDrivingFool]

Re: Picking a Prop - Effect of Diameter

Should of listened to Steelspike's recommendation for the 15" would of been done messing with this by now. With the adjusted prop that's suppose to be close to an original 13.75X15 with just a bit less cup has me nailed to 6000 @ WOT. Didn't get a speed but has me considering the purchase of the aforementioned Solas to run and keep this one as a spare.