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bamaspiveys
01-29-2008, 10:31 PM
Looking advice on getting a fer more top end speed

Why :?:

I barefoot and my fat butt needs to go faster, or lose weight. The weight loss isn't working so I need to speed the boat up. :?

I have a 2007 Outback with about 100 hours on it. When I took it in for the 100 hour oil change and service I asked the dealer about a prop to get more top end speed, but they could not decide what I needed.

One guy said go up in pitch the other said down, they were still discussing it and I just walked off. :x


opinions?

zegm
01-29-2008, 11:15 PM
Not sure what you pitch is now? But to gain more distance per revolution you must increase your pitch. If a prop says 13 x 13 that is the diameter and the pitch with the pitch being the amount of forward travel in inches per revolution. So a 13" pitch goes 13" per revolution and a 14" goes 14". Inboards are around 13/14 Outboard props are 15, 17, 19, 21 and 23 but remember an outboard goes thru a gear box and is NOT a one to one drive.

Buttafewcoe
01-30-2008, 02:09 AM
You want to go up in pitch to a 17 or a 19. It'd be best if you could find someone who'd let you try b4 you buy.
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The 19 may be pushing it, though.
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Hope this helps
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B

BensonWdby
01-30-2008, 05:24 AM
How much speed are you looking for? I have seen comments, either here or on Skifly, that these hulls are designed for max of about 46-48. Take that with a grain of salt....

If I understood it correctly, as the boat tries to go faster the hull actually starts to come down and thus increases drag, thus limiting speed.

I did not even know you could get a 19 for an inboard?

Maybe stainless might be a choice?

Are you long line or on a boom?

bobwells
01-30-2008, 06:06 AM
more pitch = more top end until you run out of horsepower... :cry: I'm with butta try b-4 you buy. If you are running a 13 pitch now try to jump to 15 and work from there. how much mph do you feel you need?

Buttafewcoe
01-30-2008, 11:17 AM
Word of caution.....more pitch will also pull engine rpm's down some, so it'll have to be a balancing act. Good advice on starting with the 15...it may do the job just fine.
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B

Sled491
01-30-2008, 06:25 PM
everthing is a trade. More speed = less hole shot. Try calling the boys at OJ props, they'll talk to you and if they can't firgure this out for you no one can. PS you were right to walk away from a mechanic that thinks less pitch = more speed. More blades won't do it for you either so don't get sucked into that one either. If pitch won't get you there they might have something in the blade or cup design that would work for you

NCSUmoomba
02-04-2008, 07:44 PM
I agree with sled, call OJ and they will tell you exactly what you need, that way, you won't have to make and educated guess.

maxpower220
02-06-2008, 03:25 AM
If we are to believe the folks at Waterski Magazine, they say the prop on the 08 Outback is a 13"x11 prop. You should determine your starting point before moving up in prop size. So perhaps a 13 or 14 pitch prop would do the job, if you are starting with an 11 pitch prop.

Please remember to post your results once you get the new prop.

zegm
02-06-2008, 04:12 PM
Not saying you are wrong but maybe the magazine? Seems like the standard inbooard skiboat (DD) prop for the last 20 years was a 13x13? We are talking about direct drives and old but well proven American V-8 engines, whether it be the Ford Windsor 351 or the Chevy 350, they turn about the same RPMs. You would usually see that the top ends of all these boats was from 45 to 48mph.

maxpower220
02-17-2008, 01:39 AM
After doing some research on newer boats, there is no telling what size or pitch prop the manufacturer is using. The old standard of 13x13 was true when inboards were 19-21' long with a 95" beam and with a 240-285 hp motor. Now, boats are larger, with lots more hp, and more biased to wake speeds (20-22 mph). Boat builders are using different diameter and pitches to aid in wake creation/elimination and to optimize the engines peak hp for given conditions. Take a look online at waterskimag.com. They have the low-down on props for each of the new boats.

Again, you need to know what you current pitch is in order to know where to go.

bamaspiveys
02-17-2008, 09:40 AM
My prop is a 13x13, according to the stamp.

I talked to the a guy at ACME and he suggested a 13x12, however he indicated that after 100 hours if I woulkd swap to all synthetic fluids I would pick up a few HP and a few RPMs and that I might be able to usea 13x12.625 prop they have. I was surprised he suggested a 3blade prop over the 4 blade.

Lastly and this really shocked me, he said if I bought it direct from Acme they had a 30 day money back guaranteee, so if one pitch did not work they would swap it for the another until we got it right. He also indicated they would do cutom cup work for $40.00 per prop if we got close and it needed a little tweaking.

Thankks for all the comments.

zegm
02-17-2008, 04:00 PM
Max you are correct, I ordered an LS and waterski magazine states it has a 13 x 11. I am a little surprised but that might explain the 41mph I see often on the site, whereas the old MC will do about 47 with the 13 x 13.
As far as changin fluids goes I see no reason why you couldn't switch to Mobil One right now. I know there is often a discussion about an engine breaking in before you use the synthetics but Porsches and Corvettes leave the factory with Mobil One in them. I intend to use it!

Sled491
02-17-2008, 09:07 PM
A four blade prop is never faster than a 3 blade. 4 blades give you hole shot and maybe fuel economy but never speed

kaneboats
02-24-2008, 12:38 AM
OK, I understand why the hole shot is better with the 4 blade- it's pure physics. But fuel economy? Is it just b/c the 4 blade is more efficient.

I have a 2000 Outback LS that I have not even been out on yet other than a test drive. It's got a 4 blade on it now but the original 3 blade is in a box ( I think it's a 13x13). I'm coming off a 115 hp outboard that me (215 lb.) and my two brothers (210 and 235 lb- yea, we enjoy BBQ) ski and learned to wakeboard behind.

I was wondering if we should be running the 4 blade or go back to the 3 blade. We wakeboard now about 60% of the time and ski about 10%. The other 30% is split between pulling toys like tubes and bananas for kids and running 35-40 MPH to get up the river to our ski zone.

In my estimation, coming off the outboard the hole shot is going to seem awesome to us no matter which prop we use and whether we are skiing or wakeboarding. We got great mileage with the outboard so I know our fuel cost is going to go up. So I was thinking about running the 3 blade. But, if overall fuel economy is going to be better with the 4 blade then maybe we just stick with it b/c top speed is really not a big concern. Thoughts anyone? (Thanks for all the input and assistance- you guys are the best and reaffirm every day that I made the right choice to join the Moomba family!)

maxpower220
02-24-2008, 02:50 AM
The efficiency that you will see (or not see) between 3 and 4 blades in fuel will be difficult to detect. On order of less than 1/2 mpg, if you choose to look at it that way. I suggest that you use the boat the way it is for a while and get use to it. Especially look at your table size and shape. Then change out the prop and note the differences.
I like the 4 blades props that I have had on my last 2 boats. I still don't understand why props aren't made skewed and shrouded.

zegm
02-24-2008, 02:14 PM
I don't understand why they haven't come up with a variable pitch prop yet! You could change it on the fly like our subs do! OH! Cost! Ok!

Sled491
02-24-2008, 05:56 PM
You know, back in the day we ran some pretty fast OB's in around the 95 - 100 mph range (and that was almost 20yrs ago). There was one guy running a variable pitch prop on his big Yammy. It was manual but variable none the less. Seemed to work fine, just wasn't available in a lot of configurations.

Kaneboats the 4 blade is what I think will fill your needs the best, especially with the split on watersports you list.

Now if some one can just help me with our clutching problem at the track I'd be golden :lol:

zegm
02-24-2008, 08:08 PM
Sled,
Now I am going to have to get on the internet and look that up, that sounds great, I wonder why they stop producing it. In order to do that now we would need a hollow driveshaft and a hollow crankshaft to be able to run the mechanicals down to the prop. This is not unreasonble as there were several WWII fighters that had guns firing through the propeller hubs! I will start on this tomorrow at work!

Sled491
02-24-2008, 09:11 PM
Say Z, this isn't going to cost anything is it :lol:

zegm
02-24-2008, 10:27 PM
Ah don't worry about it, remember I am contracted out to the US Navy. I am sure I can find a way to charge it to them for the projects I am working on now. Just got to relate it to the work I am doing with the helios! Or maybe I just go on the library on base and see what I can find!

sar
02-25-2008, 01:12 AM
Careful Zegm, we're going to get into some real engineering here.

IO boats sometimes have cheaper composite props that are variable pitch for one size fits all technology. The bright side is that if you break a blade a new one screws right back in. I only wonder if the blade breaks away, does the hub unlock still and save the other blades?

If you were looking for remote control pitch control and you used a small hollow driveshaft/strut you could use hydraulics to control the pitch, either with exhaust air or a liquid system. Most variable valve controls on cars function based on the pressure from either the air pump or the exhaust. If you ran an exhaust line to the prop pressure would increase as rpm and throttle increase. A lot of trick would be involved in the return mechanism.

Additional exhaust out of the prop potentially adds thrust power, dilutes the exhaust, captures heavier than air particles in the water - potentially reducing chances of co and co2 exposure. The downside is that the wake and thrust become aerated like an outboard's.

In my experience with our io, moving up even one pitch size will create a noticeable difference in top end and low end throttle. Upgrading materials also results in the harder faster pull (al to ss)

zegm
02-25-2008, 02:32 PM
Ok now I am looking at the Variable cam timing on my BMW and this has the mind going. We could put a hydraulic slip ring over the driveshaft somewhere after the transmission but before it leaves the hull. The driveshaft will be hollow to send this force down to the prop mechanism. Using the engine oil pressure (like the BMW) we now have the force to activate the mechanism to change the pitch (I will start thinking about this next). The next thing we need is some programming that takes into account the RPM,s the engine load, the speed and maybe a couple other variables. The computer will control the electronically activated hydraulic solenoid to change the pitch as the need arises! Using a computer we will have a variable rate pitch prop that will work for all conditions.

Sled491
02-25-2008, 03:14 PM
slow down Z. We need to see if we can sell this idea before some one takes it for free like they did with cold fusion :lol:

zegm
02-25-2008, 03:50 PM
Upppppps, giving away too much information huh?
The more I think about this.................well, email me at my home address!