newbie prop question

[kwt2000]

Hi all, I have a 1981 Ski Supreme, for the most part i am happy with the boat it handles well plus looks neat setting in the water.

i have a 13x13 LH prop on it now and at 4600 RPM i hit 42mph max both gauges read the same and verified with GPS, and i would like to run faster not alot but 50ish would be nice as we use it more for family cruising and pulling the kids on a tube(s) than anything else.

can i go to a bigger diameter prop at all and what pitch could you recommend, and from what i can find it is either a 1" shaft or 1 1/8" shaft but if it is a tapered fit where can i take the measurement to be sure?

 

[QC]

Re: newbie prop question

Welcome aboard kwt!!! Well . . . it kinda goes like this. Tournament waterski boats don't go any faster Even with added horesepower. They just don't. Save yourself some money and save some aggravation. Go to "Boattest.com" and compare with some new examples. Look for straight inboards, tournament boats. Ignore v-drives, but even they are slow. Very rare one over 45, and some have a bunch of horsepower, nearing 400 in some cases. I am betting yours is around 230 - 260.

No on diameter unless it is wrong now. 13 x 13 is pretty common stuff for an older inboard like yours. Probably a 1 inch shaft, but you should measure.

Edit: Oh, all that horsepower goes to flattening the wake. Kills speed

 

[QC]

Re: newbie prop question

Here's a Mastercraft: MasterCraft*X-30 (2006-)* Reviews,performance,compare,price,warranty, specs,Reports,Specifications Layout, video | BoatTEST.com 42 MPH 350 hp

Here's Tige with 340hp: Tig?*20V (2005-2009)*2009* Reviews,performance,compare,price,warranty, specs,Reports,Specifications Layout, video | BoatTEST.com 46 MPH 340 hp

Both are 60 MPH boats if they were an I/O and typical hull and around 22 ft. I couldn't find any straight inboards at first glance and they might be slower. You're doing good at 42, but VERY typical. This is one reason I never recommend them unless you are very serious watersports guy. That and poor ride quality. Handling and quality are usually very high, the rest favors an I/O or even and OB. Not bagging on your boat at all, but she is just a specialist.

 

[steelespike]

Re: newbie prop question

What he said^^.
Its amazing how similar some of these straight drive props are.
I had a 18 ft. 53 Chriscraft runabout with a 105 Chris craft 6. I think it had something like a 12 X 12 prop.
My max rpm rating was something like 3600. Thats about 3600 ft a minute disregarding slip.That works out to
about 40 mph but you can cut that by at least 10% for slip makes it about 36 mph.
But keep in mind it was intended to go as fast as possible not lay down flat and smooth out the water.
By the way they were great ski boats and able to pop a skier up with little effort even a 95 hp 18 footer.
And very steady with the toughest slalom skier.

 

[Bondo]

Re: newbie prop question

Welcome aboard kwt!!! Well . . . it kinda goes like this. Tournament waterski boats don't go any faster Even with added horesepower. They just don't. Save yourself some money and save some aggravation. Go to "Boattest.com" and compare with some new examples. Look for straight inboards, tournament boats. Ignore v-drives, but even they are slow. Very rare one over 45, and some have a bunch of horsepower, nearing 400 in some cases. I am betting yours is around 230 - 260.

No on diameter unless it is wrong now. 13 x 13 is pretty common stuff for an older inboard like yours. Probably a 1 inch shaft, but you should measure.

Edit: Oh, all that horsepower goes to flattening the wake. Kills speed

Ayuh,.... What QC says,... Think of a Tournament waterski boat, as the Tractor of boats,...

Lotsa pullin' power, but it ain't gonna run Fast....

Beside that, yer Outa horsepower,... More prop will drop the rpms, 'n horsepower with 'em...

 

[kwt2000]

Re: newbie prop question

thanks for the replys everyone, i was hoping to beable to run with my sisters tigr 22' but she has alot more engine than i do so i will just have my prop repaired and keep it for a little longer and then upgrade to a different boat,

like i said i am happy with it for the most part

 

[QC]

Re: newbie prop question

Tige 22? Which model? The fastest 22 Tige I can find is 46 MPH and that's with any engine.

 

[Silvertip]

Re: newbie prop question

Props are the transmission for your boat and you have just one gear. You shift up or down by increasing or decreasing pitch. Your wide open throttle rpm is at or near the recommended (4600 in your case). To go faster with the same prop you must make the engine spin faster. Since WOT is 4600 that's not possible since increasing pitch will lug the engine and make matters worse. If the engine was capable spinning a 14 inch prop or say a 13 inch with 14 or 15P, the engine would be over rev'ing with the 13. Is this making sense so far? Ok then, lets brings the revs up by DECREASING pitch. There is roughly a 200 RPM increase in engine rpm per inch of pitch change down. So if you dropped pitch to 11 for example, you would likely increase engine revs by 400 which now puts wide open throttle at 5000 rpm so you must then be able to fly -- right???? Wrong!!!!! Since you decreased pitch, the prop is taking less bite on the water with each rev moving the boat forward only 11 inches per rev rather 13 with the current prop. So you see, you increased revs but the boat now requires 5000 rpm to do the same speed it did before.. It would pull the dock off the shoreline or skiers arms from their sockets, but it reduces top end speed and increases over rev significantly.