Prop test advice

[Daintreeboy]

I had an opportunity to do some prop testing on the new motor for my boat on the weekend and keen to get some expert advice from the knowledgeable folk on here.
I figured before the trial that the standard 3 blade 14 inch pitch I picked up was going to be the one after some initial tests in the Cairns inlet of three other props.

I took those with me to test as well. The testing was done at altitude and fresh water in Tinaroo dam so the numbers are skewed to what I will normally be doing. The good news is I do have some information from the salt water tests to do a bit of a comparison.

My thoughts are the 3 blade 14 inch is still the pick but keen to see what others think, especially since I didn't achieve the recommended WOT range (5500 to 6000 and I got 5350). Considering the salt water data showed a massive increase of at least 300 rpm in the other props I figured I would be fine going with the 14 X 3 blade as it will come up within range. The fresh water tests were done with a relatively full tank and two adults on board. I would say the load was on the light side with no esky, ice or fish on board. Having said that, WOT testing in the salt with the 13 X 3 showed no decline in WOT RPM between light and heavy loads.

The final prop is to be stainless too and I've heard the rpm might pick up a bit more due to the thinner blades?

Anyway some observations not shown in the pictures are that the 4 blade props do plane the boat faster and allow slower planing but in the fresh, not by much. I figure since my rev range/speed will be around the 4000 to 4500 mark and 20 knots, this was the sweet spot for the 14 X 3 although it was almost the pick all the way through. I also figured that in the salt when it gets another 300 rpm plus it will outperform the others in the higher range as well being able to generate more power?
This boat rides so well and planes easy enough I figured the few times I would need to plane slower would not outweigh the extra speed/economy the 3 blade offers in my cruising range. Hole shot is not an issue.

I still plan to do a final run in the salt to confirm but keen to get peoples thoughts on the attached information and what the stainless version might do in comparison to the alloy.
Props tested were all Alloy, the 4 blades were the spitfires. Boat is a modified Hartley Scamp design around 16 feet long, weight unknown.
Thanks.

[GLXMAN]

Tks for the heads-up,
hope to get there early in the new year, was there back in 2009, loved the place
Turn 70 in the new year so I deserve another trip away from SA cold
Didn't catch any Barra last time but just loved the place, stayed at Downfall creek
Had a 11ft tinny at the time, (3.4m), now 4.95M, should help, got quite rough at times and made the trip back interesting \

I didn't think about the altitude factor!
Hope to also get back to Lucinda, another favorited of mine
.........Gary

[gofishin]

Some pretty thorough testing there DTB, well done!

...The final prop is to be stainless too and I've heard the rpm might pick up a bit more due to the thinner blades?...

Possibly! Never tested any myself in this HP range, however if I were to 'guess' I would say that there might not be as much of a performance gap as in the large HP props. Is there a lot of timber in the dams you fish, and will your salt water boating be in areas where you might do a bit of dredging? Alloy might be the best option regardless.

...and what the stainless version might do in comparison to the alloy...

"might" is important word here. You won't really know until you test one/them, and compare.

Will most of your boating be in the fresh or salt? Doing the same 4 tests on the salt will probably produce slightly different profiles, and change the relationship between them. Note the economy figures for the only two consecutive data figures you got in the salt (3x10.38x13), then see that the corresponding min/max in the fresh are transposed.

My 2c; from the f/water tests I like both 3 blades, and actually like the 13" better. Apart from the one data dip (which looks like a rounding error etc), it has a flatter profile in both economy and speed, and not the steep initial speed profile. This will make the boat easier to drive and easier to maintain a more comfortable ride in the slop. However, if you will always be boating in glass out conditions, the 14" would be the pick.
Cheers
Brendon


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[Daintreeboy]

Here is the latest with the 14 X 3 blade in the salt. Big improvement in the lower rev range plus a slight improvement in the higher range. WOT yielded around 5840 rpm, almost 500 rpm more than the fresh water at altitude test. Very interesting.

[gofishin]

Wow! Wouldn't have thought as much lower end improvement, and that the curve would have flattened out so much! Yes, very interesting.


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[Fed]

I bet the boats really get going on the Dead Sea.

[FNQCairns]

What about trying a 15x10.12 3 blade, possibly useless for Tinaroo but if heading offshore all day and not full of blokes it just might get the boat there a bit faster quieter and cheaper than that 14 3 blade.....a 15x10.0 3 blade of the right design would be better again to test but dunno if they are even attainable.

What I do is have at them with the angle grinder to lower the overall surface area when I need a prop that is in-between anything to be found on the shelf, not advocating just saying.

[chris69]

Thats is very interesting i thought that the fuel injection would have compensated for the different altitude,at lower level dams you just add a inch of pitch to compensate for the fresh with less push.

I was thinking that a 13 3/4 or 13 1/5 inch pitch might get your rpm closer to 6000 in the 3 blade and that would help up at tinaroo.

[Dignity]

Wow! Wouldn't have thought as much lower end improvement, and that the curve would have flattened out so much! Yes, very interesting.


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I also found that going into the wind improved performance against going with the wind, mind you when I did my test it was blowing a solid 15 knots.