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Jlagos    23

Nicely finished. So will the plate beneath the strut change the angle of the thrust produced by the propeller. If so, will it then try to lift the back as you were describing to boardjnky4. How about turning at idle?

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volzalum    277

I know the bigger prop will give more lift, and I expect the 1.5 degrees to give a little more as well. When I went from the 15 inch prop to the 14 previously, I had to put 250 pounds of lead forward of the cockpit to compensate for the smaller prop. I expect to be moving most of it back to the rear when the 15.5 goes on. As for idle steering, I do not expect any difference. The angle change does not impact the prop efficiency significantly (about 1.5% more thrust loss compared to before the mod) I will find out this weekend when I run the 14 inch prop after the adjustments. 

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boardjnky4    8

So I was eye'ing up the 15.5x15x.075 as well. That's just a really strange cup for a 15 pitch prop.

What engine is in your boat? A PCM 6.0?

Please let us know what your top speed and rpm end up being.

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boardjnky4    8
18 hours ago, volzalum said:

When you are wakeboarding and surfing, you are weighted enough to probably not have cavitation or slipping. The ½ inch prop size change at most would impact the rpm 50 rpm, so it may be so close that you are not seeing the difference. When empty at WOT (how often do you actually do that?), the rear is probably getting air to the prop. 

Almost never, it's just a data point to benchmark from.

I was led to believe the RPM decrease would be significant. With the speed control constantly changing things, it would be impossible to measure a 50 rpm difference. Heck the difference in chop/wind at any given moment can change the rpm more than that.

I guess I was just expecting too much.

Edited by boardjnky4

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volzalum    277
55 minutes ago, boardjnky4 said:

What engine is in your boat? A PCM 6.0?

I have the XR550 in my boat with the 1.48:1 V-drive.

54 minutes ago, boardjnky4 said:

Almost never, it's just a data point to benchmark from.

I was led to believe the RPM decrease would be significant. With the speed control constantly changing things, it would be impossible to measure a 50 rpm difference. Heck the difference in chop/wind at any given moment can change the rpm more than that.

I guess I was just expecting too much.

ACME said I would lose too much cruise speed if I dropped below the 15 pitch prop. With the original 15x15.75 I was 42 mph at WOT and with the 14x16, I am at 40 MPH WOT. The 14x16 also increased the RPM for holding surf speed. Since my engine will hit the 5400 RPM with either prop, and then go into control I am not sure what the final change is. I saw between 100-150 rpm difference for the 1 inch diameter and .25 degree pitch change. I also tried a 14x17.75 before the 14x16 and it had similar rpms to the 15 but could not hold surf speeds for anything.

I'll update after this weekend and the comparison to the 15.5 inch prop next weekend.

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boardjnky4    8
13 minutes ago, volzalum said:

I have the XR550 in my boat with the 1.48:1 V-drive.

ACME said I would lose too much cruise speed if I dropped below the 15 pitch prop. With the original 15x15.75 I was 42 mph at WOT and with the 14x16, I am at 40 MPH WOT. The 14x16 also increased the RPM for holding surf speed. Since my engine will hit the 5400 RPM with either prop, and then go into control I am not sure what the final change is. I saw between 100-150 rpm difference for the 1 inch diameter and .25 degree pitch change. I also tried a 14x17.75 before the 14x16 and it had similar rpms to the 15 but could not hold surf speeds for anything.

I'll update after this weekend and the comparison to the 15.5 inch prop next weekend.

OK that's a big difference from my 409/1.72:1 setup

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volzalum    277

Yes, I was actually disappointed in the boat when Centurion put the 1.48 in it instead of the 1.72. They essentially defeated the benefit of the more powerful engine by cutting it off at the v-drive ratio.

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Troy    230

Fantastic! Can't wait to hear the outcome of all your hard work. 

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boardjnky4    8

Since I'm stuck with the prop I have, I'm going to have it re-pitched to a 15.5x14x.105 at Nettles.

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volzalum    277

So my new prop (15.5x15x0.075) came in and is installed. I dinged my 14 inch (14x16x0.105) on Sunday, so when I send it off for Repair I will get it pitched to a 14x14. I can say the prop angle change was noticeable on the 14 inch prop. It was barely able to get to surf speed going upstream (though there was a 2.5 mph current), and I lost 1 mph on the WOT (dropped from 40.5 to 39.5). At my empty cruise speed of 24 mph, the rpm changed just under 100 rpm. I will get results with the 15.5 inch one this weekend. Pictures attached. 

65C361EB-B6A1-4573-A7CC-189427E871BE.jpeg

68EA0760-6CC7-49A7-8E0B-702A4F0B5C3F.jpeg

50F088A7-95F8-43A7-8FF6-773941A6D0DE.jpeg

DFA1B5AC-EFA4-4ECA-9BC0-974363D1E896.jpeg

12AF1AF0-7A88-46AA-B636-7B9D6214AE03.jpeg

F4287BA7-43D2-405B-BFF1-A223C391C51C.jpeg

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volzalum    277

So I am very happy with the mod. With the 15.5 inch prop, I gained 2 mph at top end. Dropped 400 rpm at surf speed and 24 mph cruise speed. Does 28 at old 24 mph rpms. Holds all ballast with no issues now for surfing. I was able to accelerate to 15 mph (upstream) with all ballast full with testing quicksurf (with the 14 inch prop I could not get above 9). At normal lean I was at 3100 rpm for surfing setup.

So if you have enough adjustments in your engine mounts (room to go up in front and down in back) and enough clearance in the through hull, then this mod is 100% worth doing. I am very happy.

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Troy    230

That is awesome news!!! Wave back to normal?

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volzalum    277
1 hour ago, Troy said:

That is awesome news!!! Wave back to normal?

Yes. There was no impact on the wave. It was fun seeing its limits. In goofy surf configuration, a gps speed of 11.9 (upstream in 2.5 mph current) was the fastest I could get it with the 14 inch prop. There was a 4.5 mph current on Saturday and I took it up to 15 mph upstream (so 19.5 mph water speed). But at my rider profile settings, the wave was still clean and similar size.

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Troy    230

When I changed the pitch of my prop last year, I noticed a change in the push of the wave for the better. Wave looked the same but i could feel the difference. 

Awesome to hear the changes to your boat made that kind of difference.  I love the FS series and with this info it wouldn't hold me back from getting one with which ever engine. But I'll be keeping my Avy for the foreseeable future.

Great job for thinking outside the box!!!

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volzalum    277

Well I finally had enough people in the boat to do some surfing this weekend. The wave was great, and the surf RPM was 2900-3000 RPMs from 11.3 to 11.6 MPH with minimal current. There is more lift in the rear of the boat now, so I am going to move 100 pounds of lead from the front of the boat to the back and see how that works out. Not sure if I will get to test it before My Lake Powell trip at the end of the month or not.

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InfinitySurf    306

Awesome! 

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volzalum    277

Since I’ve been getting a few private questions, I will post this to help someone if they decide to attempt on their boat.

The important things:

1) The biggest thing to make sure of is that your front motor mounts have room to adjust the front up and that the rear ones have room to adjust the rear down. You will need more clearance total between front and back than the thickness of the wedge. For mine I adjusted the about an inch total up and down.

2) The next important item is the through hull. Mine was near the bottom of the opening before the wedge and near the center afterwards.

3) The other import items are how much space you have on the prop shaft between the prop and the strut. The prop will be ¼ to ⅜ inch closer after adjusting.

And finally, the dimensions for your wedge. I changed mine 1.5 degrees with my wedge. You have to calculate where the wedge is to determine the wedge thickness for each end of it. If I’d gone any larger I would not have been able to get my engine aligned.

Here is my wedge dimensions, which may be significantly different for other boats.

CA1FE469-7838-48AB-9E3D-524E5CF47952.jpeg

Edited by volzalum

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