The never ending "which prop" question or "how long is a piece of string"

[Woodsyau]

Hi Gents, i know this is one of those "piece of string" questions (do you have that saying in USA?) but........

Here's the story and some questions:

I run a small low (very low) budget ski race team in Australia and am looking for a prop with that extra edge (aren't we all. LOL).
We run a 2013 Mercury 200 Pro XS in 200HP class standard, so no engine mods allowed.
Our current hull is a Force F18 which runs 82mph with no skiers and 76MPH with 2 skiers turning a Mercury Fury 27P prop. Bare hull weight is 280Kg RPM is just clicking off the limiter now and again, engine height is about 15mm bellow the plank which seemed to work best with pretty much all the props we tried so far.

We have tried a number of 3 & 4 blade props in different pitches, ET 4 blade, ET lightning, Chopper, Tempest, but the 27P Fury gives best speed and pull out of the hole with 2 skiers.

I have all the data from our prop tests if that would help.

Any recommendations on what to try next?

Has anyone got experiance with running a diferent brand say OMC etc prop like say a Raker on a Merc?

Any recomendations on who i could buy props from in USA that can do a decent balancing job on them?

Currently paying around $590 delivered no balanceing for a 27P Fury out of USA (we pay $750 here )


TIA

PS pic is @ 80MPH no skiers

[HStream1]

Contact DAH. John and Jeff can get you going in the right direction. They calculate their custom prop work directly around your boat, set up, engine, weight and use.

D.A.H.® Custom Pro-pellers 34111 Washington Ave. Burlington, Wisconsin 53105 USA

John or Jeff Janaky phone (262) 534-4440 fax (262) 534-2738

[simplyorange]

i would try a surfacing prop with more engine height and a drag plate to get it out of the hole. but that would just be me expierimenting

[HStream1]

He's a little over 9/16" (.590 = 15mm) below the plank (pad) as he puts it. I'd guess he doesn't have LWPU lower and even if he does. A surface running prop pulling skiers .

[transomstand]

Bare hull weight is 280Kg RPM is just clicking off the limiter now and again, engine height is about 15mm bellow the plank which seemed to work best with pretty much all the props we tried so far.

Man, we'd probably really like you guys....if we could ever figure out what you're saying

I'll agree with HStream1, I think you're to the point where you need to work with a prop guy to fine tune what you've got. Too much hit and miss with trying more props. I'd also question how much good prop advice you'd get from us, since few of us drag around 400 lbs of humans at 80 mph


Looking at the photo, I'd say you're pretty darn close on you're setup, just need small tweaks from here.

[Lockjaw]

I don't think a raker is going to make you happy unless you can get it tweaked or drop the engine. They are not renowned for their holeshot as much as they are for mid to upper rpm speed. Of all the props I tried on my boat, the fury was the best out of the hole and was the fastest except for one funky merc prop I have, that I have no idea what it is.

My raker 2 breaks loose as the boat comes over on plane, which would totally suck for pulling a skier.

[the ol man]

man let me c if I got this right!? your running 82 mph- with a stock 200 merc and u want 2 go faster? well shut the front door!!! you can bolt all the props in the world on that boat an your never gon-a go any faster , if u do ill bet u neverget over 1 more mph out of er . I don't think u got m any problems with your set up, il almost bet u can tweek and tweek and your not goin-a c much difference

[flabum1017]

man let me c if I got this right!? your running 82 mph-

And pulling two skiers................

[HStream1]

82 with no skiers and 76 with two skiers. While those numbers are very good, if you do the math (say 6500 rpm's and 7000 rpm's) he probably has a little more to gain. And as in any race situation a little more rather than less can mean the checkered flag or not. I'd like him to post what RPM's he is actually turning in both situations.

[Woodsyau]

LOL, sorry guys I’ll talk in imperial from now on.

For a start let me say again the class we race is 200HP standard.

NO motor mods other than nose cone.

No low water pick up’s.
No High RPM rev packs.
NO Drag plates.
No anything other than nose cone and prop changes.

So this means for us, 5750 RPM which is factory standard.
19/32 (15mm) bellow the pad is about as high as I can go without loosing all the water pressure.

Hsteam1 thanks, I’ll contact DAH

[Woodsyau]

Here's the data we have so far

Engine height	Prop	Pitch	Blades	Speed boat only	Speed 1 skier	Speed 2 skiers	RPM	Notes
50	Lazer	23	3	71	69	67	5750	On Rev limiter all time. Only rev to 4000 on take off to avoid prop slip
50	Pro ET	26	4	75	75	wont pull up	5750	On Rev limiter all time. Will not pull 2 up
50	Fury	27	3	80	76		5650	Not quiet on rev limiter. Easy to drive
40	Lazer	26	3		71		5750	Great pull 1 up
40	Chopper	28	3	73			5750	Lab ground
40	Lightning ET	28	3	76	75		5750	Good pull. On rev limiter
15	Fury	27	3	80		74	5750	Just on rev limiter. Good on take off
				Engine height = measurement bellow plank (Pad) to centre of prop shaft

[HStream1]

Well I hate to be the one to burst you guys bubble. But (and I only ran 1 number) 27 Fury at 5750 rpm with 15 mm engine height. And assuming your stock lower is a 1.87 ratio. It's physically impossible to run 80 MPH. And if your lower is lets say a 1.72 then your current prop slip is only 6% and thats nothing to get upset about. But assuming DAH can get it down to say 4% which is possible but might take a couple trips back and forth across the pacific. You can possibly achieve 82 MPH with a 1.72 gear ratio.

So here's the calculations.

Assuming you have a 1.87 gear ratio;

5750 rpm X 27" prop = 155250 = 78.61 MPH @ 0% slip1056 constant x 1.87 ratio = 1816.32

Assuming you have a 1.72 gear ratio

5750 rpm x 27" prop = 155250 = 85.47 MPH @ 0% slip 85.47 - 6% slip = 80.34 mph
1056 constant x 1.72 = 1816.32

I guess the next question is exactly what gear ratio is your gear case?

If by chance you don't want to believe my numbers. PM me or e-mail me (see banner) your e-mail address and I'll send you a electronic prop slip calculator. But the numbers are not going to change.

[Woodsyau]

Thanks Hstream, G box is 1.75:1 I’ll e-mail you for the calc, all readings are from GPS the only thing is I’m trying to remember if the reading was up or down stream as the river could easy be moving at 2mph I guess., I’d better add another column to the spread sheet and do a run each way.

[HStream1]

E-mail returned. just let me know.

!!!

[vnemous]

Your tach could be off also