does low pitch prop on sterndrive = skiboat

chambers1517

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OK here is a complicated question I keep going round and round with. A friend has a wakeboard boat. It has a 400hp v drive. It pulls hard but pushes alot of water and tops out at around 40. It takes 400hp to push his boat to 40mph. I have a 23' Caravelle interceptor with a 300hp 350mag that tops out at almost 60. It takes 300hp to push my boat to 60. If I propped my boat to top out at 40, would it pull as hard as the v drive? I should also get considerably better mileage at 40 since I would be closer to half throttle. Would a sterndrive severly underpropped hold plane at a much lower speed or be able to push water so it wouldn't matter if it was planed or not.
 

oldjeep

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V-drive wake boats only push a lot of water when you have them ballasted. Un ballasted at speed they put out almost no wake when compared to an I/O. The reason for the speed difference is that they are propped and geared for torque.

If you were to under-prop your boat then you could get a more torque - although not as much as a v-drive for a couple reasons.
1) You are not operating in the powerband - gas engines make most of their HP and torque at the upper RPM ranges
2) due to the much larger physical size of the prop on an inboard/v-drive.

You would have to be really careful not to over rev your motor.

No idea on the fuel consumption question.
 

bruceb58

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Your boat will get better fuel economy at 40 with the prop you have now vs lowering the pitch.

The speed that the hull planes at won't change if you change the pitch of the prop. That is a hull design issue.

A v-drive boat will always be slower than a stern drive boat if the boats are identical and having identical engines. Having the prop aimed downward hurts your top speed.



OK here is a complicated question I keep going round and round with.
And you keep posting on the same subject.You should use your original thread for this topic:
http://forums.iboats.com/forum/gener...s-direct-drive
Maybe the mods can merge them.
 
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roffey

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My bet would be more fuel as there would be more boat in the water and more RPM. Most likely pull anything out of the water I bet. IMO.
 

Chris1956

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I do not agree with some of what was said. Here is my opinion.

You may very well plane your boat at a lower speed with the lower pitch prop, as you will have more power available at lower RPM. Some boats cannot achieve enough power to plane at the lowest speed possible, with a standard pitch prop.

If you lower the prop pitch, it will pull much harder out of the hole, and RPMs will be near max at 40MPH. Your fuel consumption will be about what it is now, with a std prop, at full throttle.

Wake boats are designed to produce a large wake. Some have water ballast, some do not need it to produce a large wake. Usually, the boats that require water ballast are more like professional ski boats, and would produce a flat small wake, without the ballast.

If your friend's boat needs ballast to produce a good wake, and you removed that ballast and increased the pitch of his prop, he could improve his top speed a lot. He probably cannot match the top speed of your boat, with a std prop, because only you can trim your outdrive to carry the bow of your boat and improve it's speed.

JMO.....
 

Bondo

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OK here is a complicated question I keep going round and round with. A friend has a wakeboard boat. It has a 400hp v drive. It pulls hard but pushes alot of water and tops out at around 40. It takes 400hp to push his boat to 40mph. I have a 23' Caravelle interceptor with a 300hp 350mag that tops out at almost 60. It takes 300hp to push my boat to 60. If I propped my boat to top out at 40, would it pull as hard as the v drive? I should also get considerably better mileage at 40 since I would be closer to half throttle. Would a sterndrive severly underpropped hold plane at a much lower speed or be able to push water so it wouldn't matter if it was planed or not.

Ayuh,.... Yer leavin' out the Most Important part of the equation, 'tween those 2 boats,...

The Hulls, in the water, are very, Very different, for very different purposes,....

Just as yer bud's will Never see 60 mph, regardless how much horsepower it's got,...
Yer boat will be hard pressed to supply the tractor like pulin' power of yer bud's hull,....
 

midcarolina

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It's kinda a apples v oranges kinda thing........ a wake boat is a purpose built craft made to do one thing extremely well........ that being said Say for example you have a 21 pitch 3 blade prop and you change to a 18 pitch 4 blade you will have much more usable low end power, the boat will reach planing speed fast.......... and will pull out of the hole much better....... but you will loose big time on the top and will not be able to run WOT with out over revving the engine.

That's why many have multiple props for different needs...... I run one prop for water sports and another for running around at speed.
 

oldjeep

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Ayuh,.... Yer leavin' out the Most Important part of the equation, 'tween those 2 boats,...

The Hulls, in the water, are very, Very different, for very different purposes,....

Just as yer bud's will Never see 60 mph, regardless how much horsepower it's got,...
Yer boat will be hard pressed to supply the tractor like pulin' power of yer bud's hull,....

You could prop one to go 60, but it would be scary as hell at that speed. Mine only goes around 45 as it is currently propped, but my FIL's Malibu Response was originally propped for 52mph - damn scary at that speed on that hull.
 

Brian 26

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I can't answer any of your questions directly but here are my thoughts on the questions raised (great thread discussion).

Are you using GPS to measure speed in both boats (60 sounds high for your boat)?
The HP rating the manufacturer gives are measured at the crank, a V drive has less parasitic loss of power than a IO does.
I don't think it will help your gas mileage, it takes a specific amount of energy to move your boat at a specific speed, while the engine will work not work as hard with a lower gear ratio it will have to work faster. Also as mentioned it will depend on how much of the hull is out of the water when on plane.
 

chambers1517

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My boat on GPS actually did 55.4 mph before the rev limiter kicks in. I can run 55 with some throttle left. I have a 21p vengence prop and think I could do a little better with a better prop in a 22p. Maybe. My friends boat does 41. No doubt I get much better mpg. I would think if I was propped to top out at 40 I would be at the rev limit but it would require a lot less than full throttle so I should get better mpg than him. I was wondering if the power comes from low pitch prop at the cost of fuel and top speed which could be duplicated in a sterndrive yet still have the advantage of a faster more efficient hull.
 
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thumpar

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What sterndrive do you have? If you want to pop out of the water a Bravo 3 or DuoProp would be the best to get up on the water fast. Next would be a lower pitch 5 blade prop on a single prop drive.

The guy I bought our boat from had a Supra also. It had more HP than the Crownline an took more fuel and was slower because he added concrete to the hull for wakeboarding.
 

bruceb58

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I would think if I was propped to top out at 40 I would be at the rev limit but it would require a lot less than full throttle so I should get better mpg than him.
Not sure why you are comparing to him. As has been mentioned 10 times or so, you have 2 totally different configurations. With your current prop at 40 MPH, you will be using a lot less fuel than 40MPH with a lower pitch prop.

If the purpose of this thread was to ask if should get a lower pitch prop...you shouldn't.
 
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chambers1517

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Sorry for the confusion. I was just debating with him. I was saying I could have similar pulling power with a low pitch prop but I don't think he could match my speed and efficiency. Sterndrive vs V drive debate.
 

rallyart

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At 30 mph I'd bet he, with his 400 hp v-drive, has better fuel economy than you do at 30, with your 300 hp sterndrive. He'll also accelerate to that speed faster than you regardless of your prop due to hull design. Above 35 his economy will plummet as the inboard keeps too much water in touch with the hull. Another significant benefit, as a ski boat, to the inboard is the stability it would have with side pull from the rider. The two boats are just designed for different purposes.
A sterndrive can make a great wake for boarding and can give you that great top speed, but it does not do the job the same way as an inboard.
For me (with my family use), there is no way I'd go back to a sterndrive after my inboard. But I liked the sterndrive when I had it.
 

thumpar

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I am able to throw up a better wake than some of the wakeboard boats on our lake. Our Crownline has a 8'6" beam and is pretty heavy. A few weeks ago we were on the lake and some jet skis were playing in the wake of a 20' or so wakeboard v-drive boat. I joined in and kept my trim up while off plane and matched speeds. The jet skis ended up playing in my wake over his. I have a fat sack if I need more wake than that.
 

oldjeep

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Unless you are amusing jet ski drivers, it is not the size of the wake it is the shape and the ability to control it. If all wake boarders wanted was huge wakes the would just buy a tug boat ;)
 

thumpar

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Unless you are amusing jet ski drivers, it is not the size of the wake it is the shape and the ability to control it. If all wake boarders wanted was huge wakes the would just buy a tug boat ;)
I agree but the previous owner of my boat has a supra also and used the crownline for wakeboarding.
 

midcarolina

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Unless you are amusing jet ski drivers, it is not the size of the wake it is the shape and the ability to control it. If all wake boarders wanted was huge wakes the would just buy a tug boat ;)

Years ago we were flounder gigging at night in a 14 foot jon boat........ running down the river and just about the same time I saw the submarine we hit the submarines wake...:eek: It was like we sailed off a ramp! scared the crap outta me........think my heart skipped 2 beats.
 
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