Help on performance and prop

**DanielC** · 01-29-2008, 05:13 PM

RE: Help on performance and prop

I use my 1997 Ski Nautique for our show ski team, Portland Water Spectacular. GT-40 motor, the boat has the 1.23 to 1 gear reduction transmission. I use an OJ 4 blade 13x16 prop, and an Acme 12.5x 15.5 4 blade prop.
Using a lower pitch prop will cause your boat to pull harder, but the engine will run faster at all speeds, and use more fuel doing it. You will also easily be able to run your engine past its RPM redline if you use too low of a pitch.
More than about eight skiers, I would rather use a outboard twin rig.
Having your skiers do a dock start will also be easier on the boat, rather than pulling them out of the water.

**TRBenj** · 01-29-2008, 05:27 PM

RE: Help on performance and prop

An '89 should have the 240hp 351w mated to the 1.23 tranny.

The biggest improvement you can make for the boat is to change the prop. Either the Acme 470 or 1442 will improve all around performance- especially the holeshot. Depending on whether you plan to keep the motor stock or not would influence exactly which one I would recommend, but you really cant lose with either. The 470 will turn a few more RPM, which is good if you dont want to touch the engine. It should top out around 4600rpm, which is plenty safe. The 1442 would be what I recommend if you plan to make any engine upgrades at all- its slightly larger in diameter, so if you can spin it, buy it.

If you want to talk engine upgrades, youre only limited by what you want to spend. Give us some more info and we can help you out. There are more technical guys on CCFan, though.

**Kristof** · 01-30-2008, 07:22 AM

RE: Help on performance and prop

TRBenj, thanks. This year, I will not touch the engine (maybe next year), so I think I'll go for the
ACME 470 as you recommend.
When (and if) we will upgrade the engine, I'll come back to you on the subject. As far as the prop goes,
If I do the upgrade on the engine, I wont have any problems reselling the 470 prop, for it is not easy to come by
here in Belgium...

Thanks again,
K

**TRBenj** · 01-30-2008, 08:50 AM

RE: Help on performance and prop

Kristof, I assume that means you confirmed that you have the 1.23 tranny? If, for some strange reason, you have the 1:1, you'll want a different prop. Make sure you check before you buy anything.

**Kristof** · 01-30-2008, 09:21 AM

RE: Help on performance and prop

TR, I'll get back to you on that and confirm saturday, for my boat is in my friends garage
for the winterperiod and he won't be back till friday night.
I'll doublecheck the tranny then.

**Hollywood** · 01-30-2008, 09:46 AM

RE: Help on performance and prop

Is your engine tilted the same angle as the prop shaft? If so you have a rare 1:1, if it sits level with the floor you have a 1.23:1

**Kristof** · 01-30-2008, 02:34 PM

RE: Help on performance and prop

Yet again, in all honesty Hollywood, I haven't payed enough attention to the tilt of the engine
to know if it's levelled or tilted the same angle as the prop shaft...
Untill now I'm just too thrilled about being a Nautique owner after at least ten years of dreaming about it...!!!
So I will give you all the specs this weekend, promise :mrgreen: :mrgreen: :mrgreen:

I'm just new at all of this eh...

**Hollywood** · 01-30-2008, 03:41 PM

RE: Help on performance and prop

Your English better than a lot of people born and raised here in the states, which is making me want to help you even more. Acme props are highly regarded by skiers and boarders, no matter what engine/trans combo you have there is one that will suit your needs.

**Kristof** · 01-30-2008, 03:57 PM

RE: Help on performance and prop

Thanks Hollywood!
And I'm hereby added to the PN MAP...

**Kristof** · 02-02-2008, 11:46 AM

RE: Help on performance and prop

Guys guys guys!!! I brought her to her new home...!!!
Check my gallery!

And to confirm: she has a 1.23:1 tranny. And here's the good news... The prop is actually an ACME 470!!
I must be blessed with good karma!!! Yellow_Flash_Colorz: Yellow_Flash_Colorz: Yellow_Flash_Colorz:

I started tho work on her today. Peeled the stickers of and started on the buffing job.

Man, life is good!

**M3Fan** · 02-02-2008, 12:12 PM

Re: RE: Help on performance and prop

Originally posted by Kristof

Guys guys guys!!! I brought her to her new home...!!!
Check my gallery!

And to confirm: she has a 1.23:1 tranny. And here's the good news... The prop is actually an ACME 470!!
I must be blessed with good karma!!! Yellow_Flash_Colorz: Yellow_Flash_Colorz: Yellow_Flash_Colorz:

I started tho work on her today. Peeled the stickers of and started on the buffing job.

Man, life is good!

Nice boat, and WHAT A TOW VEHICLE!!! AWESOME! You should talk to "Chaboo" over on Themalibucrew.com- he tows with a 740i over in Germany.

Tow vehicle: http://www.planetnautique.com/index....mp;pic_id=1766

**DanielC** · 02-02-2008, 01:26 PM

RE: Re: RE: Help on performance and prop

This will be a slightly different opinion. The picture of your very nice boat shows a three blade prop. Is that the Acme 470?
Pulling multiple skiers (more than five or six adults) causes the boat to operate in a condition of fairly high prop slippage. What is the best prop for pulling a single deep up skier up to speed may not be the best prop for pulling a large act.
I ran a series of tests on my outboard boat several years ago. Above about 25 miles per hour, the props all ran about the same speed and rpm. Below 20 miles per hour, there were major differences. I am not saying that they were all the same above 25 MPH, there were differences, but the differences below 20 MPH were much more pronounced.
Below 20 MPH the prop, and boat is going slow enough that water can move out of the way, without really moving the boat, to a degree. The water yields to the boat. Above 25 MPH, the water does not yield so much, and the boat has to go faster to allow the prop, or engine RPM to go up. Another example, try to barefoot going too slow, and the water is too soft, and you cannot do it, you sink in.
A prop needs a lot of blade area to "grab" as much water as is possible, at slow speeds. The more water the prop can connect to and hold, the more thrust, given the same prop rpm, at slow speeds.
You also have to take into account a prop that "holds" better at low speeds, also holds down the engine rpm. At low rpm, the engine has less torque, and that means less thrust, but the prop that holds better might be able to generate more thrust, with the lower available torque. The opposite could also be true, a prop that slips more will allow the motor to rev higher at slow speeds, the engine will have more torque available, and even though the prop is not as good at converting engine torque to thrust, you could have more thrust to pull many skiers out of the water.
I use an OJ 4 blade 13x16 prop, and an Acme 12.5x 15.5 4 blade prop. The prop I like the best is the OJ prop. For most people the Acme prop is the best of the two to run. The OJ prop does run better after it has been sent to a prop shop once, it is truer.
You might have to test different props to find the best one for you, and it can be hard to get many different props to test.
If you do engine modifications to get more power, you might make the boat worse at low speeds. Most modifications that increase power at max RPM do it by shifting the peak torque RPM of the engine to a higher RPM, and that means you have less torque at low RPM.
I am a National Show Ski "A" driver. I have been using my 1997 Ski Nautique for pulling my show team's skiers since I got the boat, in 1997. I currently have 1967 hours on my boat. I do have a little experience using a Ski Nautique for show ski teams.

**Kristof** · 02-02-2008, 07:18 PM

RE: Re: RE: Help on performance and prop

Thanks a lot Daniel, that is helpful information from a guy with a lot of experience, for I'm still have much to learn before being an "A" driver (yet eager to learn!).
The prop on the pictures is indeed a three blade one, but the ACME came with the boat.
So, in your opinion, the best prop for pulling show teams is in this case the OJ one?
I believe you're right by saying that the best way to know is testing...
As you mentionned, getting props here for ski nautiques is not so easy, we have to order them in the States, and they take time to get over here...

M3Fan, thanks for the comment on my tow vehicle :grin: It's a **** of a fine car, I can assure you!
But in the end, it's all about the boat hehe. My wife says that the smile on my face looks like it's gonna be permanent Yellow_Flash_Colorz:

**TRBenj** · 02-02-2008, 09:45 PM

Re: RE: Re: RE: Help on performance and prop

Originally posted by DanielC

At low rpm, the engine has less torque, and that means less thrust, but the prop that holds better might be able to generate more thrust, with the lower available torque.

If you do engine modifications to get more power, you might make the boat worse at low speeds. Most modifications that increase power at max RPM do it by shifting the peak torque RPM of the engine to a higher RPM, and that means you have less torque at low RPM..

While I agree that trying many props is the best way to find the one that works the best, I disagree with just about everything else.

The torque peak on our Fords is quite low. Id say its on the range of 3k RPM's (rough guess). I get more instant RPM's than that coming out of the hole.

I agree with the blade surface argument- but the Acme's have superior blade surface area to the OJ's. The 3-blade Acmes and 4-blade Acmes are nearly equal as well.

Youre right that an improperly modified motor might push the powerband too high and hurt holeshot. However, that is an extreme case. You can improve breathing quite a bit on these Fords to pick up a LOT of mid range and high end power. This can be done while still improving holeshot, not hurting it.

Help on performance and prop

Help on performance and prop

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment